Tgrid tg

TGrid Tutorial Guide

ANSYS, Inc. Release 13.0
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Release 13.0 c ANSYS, Inc. 2010

Release 13.0 c ANSYS, Inc. 2010

Using This Manual

What’s In This Manual
The TGrid Tutorial Guide contains a few tutorials that teach you how to use TGrid for
different types of problems. Each tutorial contains instructions for performing tasks
related to the features demonstrated in the tutorial.

• Tutorial 1 is a detailed tutorial designed to introduce the beginner to TGrid. This
tutorial provides explicit instructions for all steps in the tutorial.
The remaining tutorials assume that you have read or solved Tutorial 1, and that
you are already familiar with TGrid and its interface. In these tutorials, some steps
will not be shown explicitly.

• Tutorial 2 demonstrates the mesh generation procedure for a problem that has
multiple regions. It also describes the procedure to generate a volume mesh using
the automatic refinement feature of TGrid.

• Tutorial 3 demonstrates the mesh generation procedure for a hybrid mesh, starting
from a hexahedral volume mesh and a triangular boundary mesh.

• Tutorial 4 demonstrates the mesh generation procedure for a viscous hybrid mesh,
starting from a triangular boundary mesh for a sedan car body.

• Tutorial 5 explains an application from the automotive industry, thus demonstrat-
ing how the hexcore mesh can significantly reduce the cell count compared with a
fully tetrahedral mesh.

• Tutorial 6 demonstrates the creation of a hexcore mesh upto the domain boundaries
for a sedan car.

• Tutorial 7 demonstrates the use of the boundary wrapper to repair an existing
geometry. It also describes the procedure to improve the wrapper surface quality.

• Tutorial 8 demonstrates the procedure for generating a CutCell mesh.

• Tutorial 9 demonstrates the procedure for replacing an object in the existing mesh
with another by creating a cavity and remeshing it.

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Using This Manual

Where to Find the Files Used in the Tutorials
Each of the tutorials uses an existing mesh file. You can download this file from the
ANSYS Download Center which is accessible from the ANSYS Customer Portal
(http://www1.ansys.com/customer). Navigate through the Download Wizard and select
the ANSYS Meshing Tutorial Input Files download listed in the ANSYS Documentation and
Examples section.
The Preparation step of each tutorial will indicate the necessary files.

Typographical Conventions Used In This Manual
Several typographical conventions are used in the text of the tutorials to facilitate your
learning process.

• An informational icon ( i ) marks an important note.

• A warning icon ( ! ) marks an important note or warning.
• Different type styles are used to indicate graphical user interface menu items and
text interface menu items (e.g., Display Grid panel, display/grid command).

• The text interface type style is also used when illustrating exactly what appears on
the screen or exactly what you need to type in the text field in a panel.

• Instructions for performing each step in a tutorial will appear in standard type.
Additional information about a step in a tutorial appears in italicized type.

• A mini flow chart is used to indicate the menu selections that lead you to a specific
panel. For example,
Display −→Grid...
indicates that the Grid... menu item can be selected from the Display pull-down
menu.
The words surrounded by boxes invoke menus (or submenus) and the arrows point
from a specific menu toward the item you should select from that menu.

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Contents

1 Repairing a Boundary Mesh 1-1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
Prerequisites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2
Step 1: Reading and Displaying the Boundary Mesh . . . . . . . . . . . . 1-2
Step 2: Check for Free and Unused Nodes . . . . . . . . . . . . . . . . . 1-4
Step 3: Repair the Boundary Mesh . . . . . . . . . . . . . . . . . . . . . 1-5
Step 4: Use the Rezoning Feature . . . . . . . . . . . . . . . . . . . . . . 1-7
Step 5: Improve the Boundary Mesh . . . . . . . . . . . . . . . . . . . . 1-9
Step 6: Check the Skewness Distribution of the Boundary Mesh . . . . . 1-10
Step 7: Repairing the Boundary Mesh Further . . . . . . . . . . . . . . . 1-11
Step 8: Generate a Multiple Region Volume Mesh . . . . . . . . . . . . . 1-21
Step 9: Check the Volume Mesh . . . . . . . . . . . . . . . . . . . . . . . 1-23
Step 10: Check and Save the Volume Mesh . . . . . . . . . . . . . . . . . 1-23
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-24

2 Tetrahedral Mesh Generation 2-1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
Prerequisites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
Step 1: Read and Display the Boundary Mesh . . . . . . . . . . . . . . . 2-2
Step 2: Generate the Mesh using the Skewness-Based Reﬁnement Method 2-5
Step 3: Generate the Mesh using the Skewness-Based Reﬁnement Method and
a Size Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10

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Step 4: Generate the Mesh using the Advancing Front Refinement Method
and a Size Function . . . . . . . . . . . . . . . . . . . . . . . . . 2-12
Step 5: Examine the Effect of the Growth Factor . . . . . . . . . . . . . 2-14
Step 6: Generate a Local Refinement in the Wake of the Car . . . . . . . 2-17
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21

3 Zonal Hybrid Mesh Generation 3-1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
Prerequisites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
Step 1: Read and Display the Mesh . . . . . . . . . . . . . . . . . . . . . 3-2
Step 2: Merge the Free Nodes on the Tri/Quad Border . . . . . . . . . . 3-4
Step 3: Check the Skewness Distribution of the Boundary Mesh . . . . . 3-6
Step 4: Generate the Tetrahedral Mesh Using Pyramids to Transition Between
the Hexahedral and Tetrahedral Mesh . . . . . . . . . . . . . . . 3-7
Step 5: Extend the Mesh Using Prisms . . . . . . . . . . . . . . . . . . . 3-12
Step 7: Generate the Tetrahedral Mesh Using a Non-Conformal Transition
Between the Hexahedral and Tetrahedral Mesh . . . . . . . . . . 3-20
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-24

4 Viscous Hybrid Mesh Generation 4-1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1
Prerequisites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1
Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2
Step 2: Check for Free and Unused Nodes . . . . . . . . . . . . . . . . . 4-4
Step 3: Check the Quality of the Surface Mesh . . . . . . . . . . . . . . . 4-5
Step 4: Set Parameters for Prism Layer Shrinkage and Manual Tetrahedral
Meshing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

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CONTENTS

Step 5: Set Parameters for Ignoring Prism Layers and Automatic Meshing 4-18
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-23

5 Hexcore Mesh Generation 5-1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
Prerequisites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
Step 2: Check the Skewness of the Surface Mesh . . . . . . . . . . . . . . 5-3
Step 3: Repair the Boundary Mesh . . . . . . . . . . . . . . . . . . . . . 5-5
Step 4: Generate the Hexcore Mesh . . . . . . . . . . . . . . . . . . . . . 5-7
Step 5: Examine the Effect of the Buffer Layers on the Hexcore Mesh . . 5-9
Step 6: Automatically Generate the Hexcore Mesh with Prism Layers and a
Local Refinement Region . . . . . . . . . . . . . . . . . . . . . . 5-12
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-18

6 Generating the Hexcore Mesh to Domain Boundaries 6-1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
Prerequisites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
Step 2: Delete the Outer Box Boundaries . . . . . . . . . . . . . . . . . . 6-4
Step 3: Set the Hexcore Meshing Parameters . . . . . . . . . . . . . . . . 6-4
Step 4: Automatically Generate the Hexcore Mesh to the Boundaries with
Prism Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8
Step 5: Generate the Hexcore Mesh to the Boundaries with Prism Layers
Using TUI Commands . . . . . . . . . . . . . . . . . . . . . . . . 6-19
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-20

7 Using the Boundary Wrapper 7-1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

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CONTENTS

Prerequisites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2
Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2
Step 2: Perform Pre-Wrapping Operations to Close Holes in the Geometry 7-4
Step 3: Initialize the Surface Wrapper . . . . . . . . . . . . . . . . . . . . 7-12
Step 4: Check the Region to be Wrapped . . . . . . . . . . . . . . . . . . 7-13
Step 5: Reﬁne the Main Region . . . . . . . . . . . . . . . . . . . . . . . 7-19
Step 6: Close Small Holes Automatically . . . . . . . . . . . . . . . . . . 7-20
Step 7: Wrap the Main Region . . . . . . . . . . . . . . . . . . . . . . . . 7-23
Step 8: Capture Features . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-24
Step 9: Post Wrapping Operations . . . . . . . . . . . . . . . . . . . . . 7-27
Step 11: Create the Tunnel . . . . . . . . . . . . . . . . . . . . . . . . . 7-36
Step 12: Generate the Volume Mesh . . . . . . . . . . . . . . . . . . . . 7-37
Step 13: Improve the Volume Mesh . . . . . . . . . . . . . . . . . . . . . 7-39
Step 14: Separate the Tunnel Inlet and Outlet . . . . . . . . . . . . . . . 7-40
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-41

8 CutCell Mesh Generation 8-1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1
Prerequisites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1
Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1
Step 2: Improve the Connectivity of the Geometry . . . . . . . . . . . . . 8-4
Step 3: Generate the CutCell Mesh . . . . . . . . . . . . . . . . . . . . . 8-6
Step 4: Post CutCell Meshing Cleanup Operations . . . . . . . . . . . . . 8-13
Step 5: Generating Prisms for the CutCell Mesh . . . . . . . . . . . . . . 8-14
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-19

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CONTENTS

9 Cavity Remeshing 9-1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1
Prerequisites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1
Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1
Case A. For a Tetrahedral Mesh . . . . . . . . . . . . . . . . . . . . . . . 9-2
Case B. For a Hybrid Mesh (Tetrahedra and Prisms) Having a Single Fluid
Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10
Case C. For a Hybrid Mesh (Tetrahedra and Prisms) Having Multiple Fluid
Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-20
Case D. For a Hexcore Mesh . . . . . . . . . . . . . . . . . . . . . . . . . 9-24
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-27

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CONTENTS

vi Release 13.0 c ANSYS, Inc. 2010

Tutorial 1. Repairing a Boundary Mesh

Introduction
TGrid offers several tools for mesh repair. While there is no right or wrong way to repair
a mesh, the goal is to improve the quality of the mesh with each mesh repair operation.
This tutorial demonstrates the use of some mesh repair tools in TGrid to find and fix
known deficiencies in an existing boundary mesh (a simple 3D geometry).
This tutorial demonstrates how to do the following:

1. Read the mesh file and display the boundary mesh.

2. Check for free and unused nodes.

3. Repair the boundary mesh by recreating missing faces.

4. Use the rezoning feature.

5. Improve the boundary mesh.

6. Check the skewness of the boundary faces.

7. Further repair the boundary mesh.

8. Generate a multiple region volume mesh.

9. Check the quality of the entire volume mesh.

10. Check and save the volume mesh.

Prerequisites
This tutorial assumes that you have little experience with TGrid, but are familiar with
the graphical user interface.

Release 13.0 c ANSYS, Inc. 2010 1-1

Repairing a Boundary Mesh

Preparation
1. Copy mesh-repair.zip to your working directory.
You can download this file from the ANSYS Download Center which is accessible
from the ANSYS Customer Portal (http://www1.ansys.com/customer). Navigate
through the Download Wizard and select the ANSYS Meshing Tutorial Input Files
download listed in the ANSYS Documentation and Examples section.
2. Unzip mesh-repair.zip.
The file, problem-surf.msh can be found in the mesh-repair folder created on
unzipping the file.
3. Start TGrid.

Step 1: Reading and Displaying the Boundary Mesh
1. Read in the boundary mesh file (problem-surf.msh).
File −→ Read −→Boundary Mesh...

(a) Select problem-surf.msh in the Files list.
(b) Click OK.

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2. Display the boundary mesh.

(a) Select boundary in the Face Zone Groups selection list.
(b) Click Display (Figure 1.1).

Figure 1.1: Boundary Mesh

(c) Close the Display Grid panel.

3. Display the boundary mesh with the hidden lines removed.
Display −→Options...
(a) Enable Hidden Line Removal.



(b) Click Apply and close the Display Options panel.
The display will be updated as shown in Figure 1.2.

Figure 1.2: Boundary Mesh With Hidden Lines Removed

Step 2: Check for Free and Unused Nodes
After reading the boundary mesh, check it for topological problems such as free and
multiply-connected nodes and faces.
Boundary −→Merge Nodes...



1. Click Count Free Nodes.
TGrid will report the number of free nodes in the Message box.
Here, the free nodes are due to seven missing faces in the surface mesh. In Step
3, you will use TGrid mesh repair tools to recreate the missing faces.

2. Click Count Unused Nodes.
TGrid will report the number of unused nodes in the Message box. If there are unused
nodes, click Delete Unused Nodes to remove them.

3. Close the Merge Boundary Nodes panel.

Step 3: Repair the Boundary Mesh
In this step, you will recreate the missing faces to repair the boundary mesh.

1. Zoom in to one of the missing faces (Figure 1.3).
The faces surrounding the missing face can be highlighted to enable easy identiﬁca-
tion of the missing face. Enable Free in the Options group box in the Display Grid
panel to highlight the faces surrounding the missing face.

2. Recreate the missing face.
Boundary −→Modify...

(a) Select node in the Filter list.



Figure 1.3: Recreating the Missing Face

(b) Select the three nodes surrounding the missing face using the right mouse
button (see Figure 1.3).
If you select the wrong node, click on it again with the right mouse button to
remove it from the Selections list.
(c) Click Create in the Operation group box when the correct nodes are selected.
TGrid will recreate the missing face.

3. Check if the new face is in the correct boundary zone.

(a) Select zone in the Filter list.
(b) Select the face just created using the right mouse button.
TGrid will display the zone name in the graphics window (Figure 1.4).



Figure 1.4: Verifying the Zone of the New Face

TGrid places the face in the same zone as the majority of the nodes that com-
prise the face. If two out of the three selected nodes are in the symmetry zone,
then the face created is placed in the symmetry zone. In this example, the three
nodes selected are in the wall2 zone, hence the face created is also placed in the
wall2 zone.
(c) If the face is in the wrong zone, use the Rezone option in the Operation group
box to move the face to the appropriate zone (see Step 4).

4. Similarly, recreate the other missing faces.

5. Save an intermediate mesh ﬁle (temp.msh).
File −→ Write −→Mesh...

It is not always possible to undo an operation. Hence, it is recommended
! that you save the mesh periodically when modifying the boundary mesh.

Step 4: Use the Rezoning Feature
This step illustrates the use of the Rezone option to move a face from one zone to another.
First, you will move the face from the wall2 boundary to the symmetry boundary. When
this step is complete, you will move the selected face back to the wall2 zone.

1. Select face in the Filter list.

2. Select the face to be rezoned using the right mouse button (Figure 1.5).



Figure 1.5: Face Selected to be Rezoned

3. Select zone in the Filter list.

4. Select the zone where you want to move the face using the right mouse button
(symmetry).
After selecting the symmetry zone the Selections list in the Modify Boundary panel
will show the face identiﬁcation number and the zone to which you want to move
it.



5. Click Rezone in the Operation group box.
TGrid will move the selected face to the symmetry zone (Figure 1.6).

Figure 1.6: Face Rezoned to Symmetry Boundary

This step was included only to demonstrate the use of the Rezone option.
! Move the selected face back to the wall2 zone using Rezone.
6. Close the Modify Boundary panel.

Step 5: Improve the Boundary Mesh
Boundary −→ Mesh −→Improve...

1. Select all the zones in the Tri Boundary Zones selection list.

2. Select Swap in the Options drop-down list.

3. Click Skew to check if the maximum face skewness is below 0.9.
TGrid will report that the maximum face skewness is approximately 0.992.



4. Click Check to check for Delaunay violations in the boundary mesh.
TGrid will report the violations in the console.

5. Retain the default values of 10 and 0.9 for Max Angle and Max Skew, respectively.

6. Click Apply until TGrid reports zero modiﬁcations made.

7. Click Skew to verify that the maximum face skewness is below 0.9.

8. Close the Boundary Improve panel.

Step 6: Check the Skewness Distribution of the Boundary Mesh
Display −→ Plot −→Face Distribution...

1. Select all the zones in the Boundary Zones selection list.

2. Enter 10 for Partitions.

3. Click Plot (Figure 1.7).

4. Click Print.
TGrid will print the histogram information by decades in the console. There are zero
faces with a skewness greater than 0.9, four faces with a skewness greater than 0.8,
two faces with a skewness greater than 0.7, and 11 faces with a skewness greater
than 0.6.

5. Close the Face Distribution panel.



Figure 1.7: Histogram Plot of Face Skewness

Extra: This tutorial also aims at reducing the maximum face skewness below 0.6. This
tutorial exposes you to some of the mesh repair tools. Then, it is up to you to try
and get the maximum face skewness below 0.6.

Step 7: Repairing the Boundary Mesh Further
In this step, you will repair the mesh by merging and smoothing nodes, swapping and
splitting edges, and splitting faces.

1. Modify the mesh by merging nodes.



(a) Retain the selection of Quality Limit and click First.
TGrid will zoom in on the face having the greatest skewness (Figure 1.8). You
will merge the highlighted node with the corner node to repair the skewed face.

Figure 1.8: Face with the Greatest Skewness

When merging nodes, the first node selected is the one that remains after
merging. Clear the Selections list and select the nodes in the correct order (i.e.,
first select the corner node, and then select the neighboring node). Merge the
two nodes. The corner node will be retained after merging the nodes, since it
was selected first. The procedure is described in the following steps.
(b) Click Clear in the Operation group box.
(c) Select node in the Filter list.
(d) Select the corner node where the symmetry zone meets with the inlet zone and
the wall2 zone and the neighboring node (highlighted before the Selections list
was cleared). See Figure 1.9.

Figure 1.9: Nodes to be Merged



(e) Click Merge in the Operation group box (Figure 1.10).

Figure 1.10: Surface Mesh After Merging Nodes

2. Repair the next highly skewed face.
(a) Click Next in the Modify Boundary panel.
TGrid will zoom in on the face with the next highest skewness (Figure 1.11).
The face highlighted is the face on the opposite corner of the inlet boundary.

Figure 1.11: Face with the Next Greatest Skewness

(b) Clear the Selections list.
(c) Select node in the Filter list.
(d) Select the nodes as shown in Figure 1.12.
(e) Click Merge.
The modiﬁed mesh after merging the nodes is shown in Figure 1.13.



Figure 1.12: Nodes to be Merged

Figure 1.13: Surface Mesh After Merging Nodes



Note: The next two faces that are selected on clicking Next can also be mod-
ified using the node merging operation. Complete these operations as de-
scribed in Steps 7.1 and 2.

3. Modify the mesh by smoothing nodes.
(a) Click Next.
TGrid highlights a face located in the middle of one of the internal walls (Fig-
ure 1.14).
(b) Select node in the Filter list.
(c) Select several nodes surrounding the face highlighted by TGrid (as shown in
Figure 1.14).

Figure 1.14: Face to be Modified with Node Smoothing

(d) Click Smooth in the Operation group box.
TGrid performs node smoothing to make the surrounding cells as uniform in
size as possible (see Figure 1.15).
From this point onward, the tutorial attempts to demonstrate some of the additional
face modification tools that are available in TGrid using the cluster of cells shown
in Figure 1.15.

4. Modify the mesh by edge swapping.
(a) Select edge in the Filter list.
(b) Select the edges to be swapped (Figure 1.16).
(c) Click Swap in the Operation group box.
TGrid will swap the selected edges and retriangulate the mesh (Figure 1.17).
This operation did little to produce a better quality mesh. You can use node
smoothing to fix this problem.



Figure 1.15: Surface Mesh After Node Smoothing

Figure 1.16: Edges Selected for Swapping

Figure 1.17: Surface Mesh After Edge Swapping



(d) Select node in the Filter list.
(e) Select the nodes in the vicinity of the swapped edge (Figure 1.18).

Figure 1.18: Nodes Selected for Smoothing

(f) Click Smooth in the Operation group box (Figure 1.19).




5. Modify the mesh by splitting edges.
(a) Select edge in the Filter list.
(b) Select the edge to be split (Figure 1.20).

Figure 1.20: Edge Selected for Splitting

(c) Click Split in the Operation group box (Figure 1.21).

Figure 1.21: Surface Mesh After Edge Splitting

(d) Perform node smoothing by selecting several nodes around the split edge and
clicking Smooth (Figure 1.22).




6. Modify the mesh by splitting faces.
(a) Select face in the Filter list.
(b) Select the face to be split (Figure 1.23).

Figure 1.23: Face Selected for Splitting

(c) Click Split in the Operation group box to split the face (Figure 1.24).
(d) Swap the edges of the split face (Figure 1.25).
(e) Smooth the nodes in the vicinity of the split face (Figure 1.26).



Figure 1.24: Surface Mesh After Splitting the Face

Figure 1.25: Surface Mesh After Edge Swapping




7. Check the maximum face skewness.
Report −→Face Limits...

(a) Select Quality in the Options list.
(b) Select all the zones in the Face Zones selection list.
(c) Click Compute.
TGrid will report the Minimum, Maximum, and Average face skewness.
(d) Close the Report Face Limits panel.
The maximum face skewness at this point in the tutorial is less than 0.65.
There are nine faces with a skewness greater than 0.6 (this information was
obtained from the Face Distribution panel). You can try and reduce the max-
imum face skewness to a value less than 0.6 using the face modification tools
described in the previous steps.

Step 8: Generate a Multiple Region Volume Mesh
There are multiple regions in this mesh (four to be exact). To mesh the whole domain,
you need to change the non-fluid type declaration to fluid in the Initialization tab of the
Tet panel and then generate the volume mesh.

1. Change the Non-Fluid Type from dead to fluid.
Mesh −→Tet...



(a) Select fluid in the Non-Fluid Type drop-down list in the Tet Zones group box.
(b) Click Apply and close the Tri/Tet panel.
By default, TGrid automatically makes the cell zone with the largest volume
the active fluid zone. TGrid treats the remaining cell zones (non-fluid zones)
as dead zones and does not refine them. Hence, if you want to mesh multiple
zones, change the Non-Fluid Type to solid or fluid depending on the problem.
When Non-Fluid Type is set to a type other than dead, TGrid treats all the
zones as active zones and automatically refines these zones.
If the mesh has only one zone, this step is not necessary.
2. Generate the volume mesh.
Mesh −→Auto Mesh...



(a) Retain the default settings and click Mesh.
(b) Close the Auto Mesh panel.

Step 9: Check the Volume Mesh
Report −→Cell Limits...

1. Select all the zones in the Cell Zones selection list.

2. Click Compute to report the Maximum, Minimum, and Average cell skewness values.

3. Close the Report Cell Limits panel.

Step 10: Check and Save the Volume Mesh
1. Check the mesh.
Check the mesh to ensure it has no negative cell volumes or left-handed faces before
saving the mesh ﬁle.
Mesh −→Check
The printed results of the check show no problems, hence the mesh is valid for use
in the solver.

2. Save the mesh.



3. Exit TGrid.
File −→Exit

Summary
This tutorial demonstrated the use of some mesh repair tools available in TGrid to ﬁx
known deﬁciencies in an existing boundary mesh.


Tutorial 2. Tetrahedral Mesh Generation

Introduction
The mesh generation process is highly automated in TGrid. In most cases, you can use the
Auto Mesh feature to create the volume mesh from the surface mesh. However, in some
cases, the boundary mesh may contain irregularities or highly skewed boundary faces
that can lead to an unacceptable volume mesh or cause TGrid to fail while generating the
initial mesh. As a rule of thumb, you need to check the boundary mesh before attempting
to generate the volume mesh. This tutorial demonstrates how to do the following:

• Create a user-defined group for easier selection of boundary sufaces.

• Generate the tetrahedral volume mesh using the various refinement options avail-
able in TGrid.

• Compare the mesh generated using the skewness-based and advancing front refine-
ment methods.

• Examine the effect of the size function.

• Examine the effect of the growth factor.

• Create a local refinement region.

Prerequisites
This tutorial assumes that you have little experience with TGrid, but that you are familiar
with the graphical user interface.

Preparation
1. Copy tet-mesh.zip to your working directory.


Tetrahedral Mesh Generation

2. Unzip tet-mesh.zip.
The ﬁle, sedan.msh.gz can be found in the tet-mesh folder created on unzipping
the ﬁle.

3. Start TGrid.

Step 1: Read and Display the Boundary Mesh
1. Read the boundary mesh.

(a) Select sedan.msh.gz in the Files list.
(b) Click OK.



2. Create a user-defined group for easier selection of the surfaces defining the sedan.
Boundary −→ Zone −→Group...

(a) Select car, mirror, wheel-arch-front, wheel-arch-rear, wheel-front, and wheel-rear
from the Face Zones selection list.
(b) Click Create.
The Group Name dialog box will open, prompting you to specify the group name.

(c) Enter sedan for Name and click OK to close the Group Name dialog box.
The sedan group will now be available in the Face Groups list in the User
Defined Groups panel.
The use of the underscore ( ) in the group name allows the group to be listed
at the top of the Face Zone Groups list in the respective panels.
(d) Close the User Defined Groups panel.

3. Display the boundary mesh (Figure 2.1).
(a) Select sedan in the Face Zone Groups selection list to select all the boundary
zones defining the car in the Face Zones selection list.



(b) Click the Attributes tab.
(c) Click the Colors... button to open the Grid Colors panel.
i. Select Color by ID in the Options list.
ii. Close the Grid Colors panel.
(d) Enable Hidden Line Removal in the Display Options panel.
Display −→Options...
(e) Click Display.

Figure 2.1: Grid Display

(f) Close the Display Grid panel.



Step 2: Generate the Mesh using the Skewness-Based Refinement Method
1. Specify the meshing parameters.
Mesh −→Tet...

(a) Retain the default settings in the Initialization tab.
(b) Click the Refinement tab.

i. Select skewness in the Refine Method drop-down list.
ii. Select none in the Cell Size Function drop-down list.
iii. Retain the default value (2.57e-4) for Max Cell Volume.
The default value for maximum cell volume is calculated as the volume of
an ideal equilateral tetrahedron with edge length equal to the length of the
longest edge in the domain.



You can use the following commands to verify the value:
A. /report/edge-size-limits to obtain the minimum, maximum, and
average edge length.
B. /mesh/tet/local-regions/ideal-vol to calculate the volume of an
√
2
ideal equilateral tetrahedron (side × side × side × ) with side equal
12
to the maximum edge length.
The longest edge may be connected to shorter edges and not characteristic
of the facet or maximum volume value. Hence, you may want to measure
the length of some of the edges on the outer boundary and then calculate
the ideal volume. Select two nodes on the edge and use the hot-key Ctrl +
D to obtain the edge length.
In this case, an edge length of 0.1 would seem appropriate (giving a volume
of 1.18e-4), but the mesh would be larger and slower to generate. Hence,
you will use the default value for the maximum cell volume.
(c) Click Apply and Init&Reﬁne.
(d) Close the Tet panel.

2. Examine the mesh.
(a) Display the mesh on a slide through the mirror and the car (Figure 2.2).

i. Click the Bounds tab and enable Limit by X.
ii. Enter -0.37 for Minimum and Maximum in the X Range group box.
iii. Click the Cells tab and select the ﬂuid zone in the Cell Zones selection list.



iv. Enable All in the Options group box and click Display.
v. Display the left view.
Display −→Views...

A. Select left in the Views list and click Apply.
B. Click Auto Scale.
C. Close the Views panel.



Figure 2.2: Slide of Cells at X = -0.37

(b) Display the mesh on a slide through the wheels (Figure 2.3).
i. Click Reset in the Bounds tab of the Display Grid panel.
ii. Enable Limit by Z and enter 0.38 for Minimum and Maximum in the Z
Range group box.
iii. Click Display and display the front view.
iv. Zoom in to sedan to examine the cell growth.

Figure 2.3: Slide of Cells at Z = 0.38

You can see that the cells inside the domain are not larger than those on



the outer boundary.
v. Close the Display Grid panel.
(c) Check the number of cells.
Report −→Mesh Size...

i. Click Update.
The number of cells is 896718. The exact number may differ on different
platforms.
ii. Close the Report Mesh Size panel.
(d) Check the maximum skewness.

i. Select the fluid zone in the Cell Zones selection list.



ii. Click Compute.
The maximum skewness is 0.904, which is acceptable. The average skew-
ness is 0.298.
iii. Close the Report Cell Limits panel.

Step 3: Generate the Mesh using the Skewness-Based Refinement Method and a
Size Function
1. Delete the previous volume mesh.
Mesh −→Clear
Mesh −→Tet...
(a) Retain the settings in the Initialization tab.
i. Retain the selection of skewness in the Refine Method drop-down list.
ii. Select geometric in the Cell Size Function drop-down list and enter 1.3 for
Growth Rate.
iv. Click Apply and Init&Refine.
v. Close the Tet panel.
(c) Examine the mesh.
i. Display the mesh on a slide through the mirror and the car (x = -0.37).
See Figure 2.4.
ii. Display the mesh on a slide through the wheels (z = 0.38). See Figure 2.5.
(d) Check the number of cells.
platforms.
(e) Check the maximum skewness.
The maximum skewness is 0.904, which is acceptable. The average skewness
is 0.249.
You can see that the transition between small and large cells is smoother than that
for the previous mesh. The transition is smoother when the specified growth rate is
closer to 1.



Step 4: Generate the Mesh using the Advancing Front Refinement Method and a
Size Function
1. Delete the previous volume mesh.
Mesh −→Clear

Mesh −→Tet...
i. Select adv-front in the Refine Method drop-down list.
ii. Retain the selection of geometric in the Cell Size Function drop-down list
and retain 1.3 for Growth Rate.
iv. Click Apply and Init&Refine.
v. Close the Tet panel.
(c) Examine the mesh.
i. Display the mesh on a slide through the mirror and the car (x = -0.37).
See Figure 2.6.


ii. Display the mesh on a slide through the wheels (z = 0.38). See Figure 2.7.




platforms.
The maximum skewness is 0.904, which is acceptable. The average skewness
is 0.264.
Notes:
• The quality is very similar to that obtained with the skewness-based reﬁnement
algorithm.
• As far as the number of cells is concerned, for a strict volume criterion, the
advancing front method will generate more cells, but for a relaxed maximum
volume criterion, the skewness method will generate more cells.
• For a mesh of size similar to that considered in this tutorial, tet reﬁnement for
the advancing front method is approximately 1.8 times faster when compared
with the skewness method. The speedup will increase for bigger size meshes.



Step 5: Examine the Effect of the Growth Factor
1. Clear the mesh.

Mesh −→Tet...
(a) Retain the selection of adv-front in the Reﬁne Method drop-down list and the
Growth Rate of 1.3, respectively.
(b) Enter 2e-2 for Max Cell Volume in the Reﬁnement tab of the Tet panel.

(a) Display the mesh on a slide through the mirror and the car (x = -0.37). See
Figure 2.8.


(b) Display the mesh on a slide through the wheels (z = 0.38). See Figure 2.9.




platforms.
Report −→Cell Limits....
The maximum skewness is 0.904, while the average skewness is 0.266.

4. Clear the mesh.

5. Modify the meshing parameters.
Mesh −→Tet...
(a) Retain the selection of adv-front in the Reﬁne Method drop-down list and the
Max Cell Volume of 2e-2, respectively.
(b) Enter 1.25 for Growth Rate in the Reﬁnement tab of the Tet panel.

(a) Display the mesh on a slide through the mirror and the car (x = -0.37).
(b) Display the mesh on a slide through the wheels (z = 0.38). See Figure 2.11.



platforms.
For the mesh generated, the mesh transition is smoother (see Figure 2.12),
however the number of cells generated is significantly more.

Figure 2.12: Comparison of Meshes Based on Growth Factor

Step 6: Generate a Local Refinement in the Wake of the Car
In TGrid, you can define the local size regions to be meshed at the same time as the global
mesh initialization and refinement. Multiple regions, each with different maximum cell
volume can be defined and activated during the automatic mesh generation process. In
this step, you will generate a local refinement region in the wake of the car.

1. Clear the mesh.
2. Display the car.
(a) Click Reset in the Bounds tab.
(b) Retain the selection of sedan in the Face Zone Groups selection list in the
Faces tab and click Display.




(a) Retain the previous settings in the Initialization tab of the Tet panel.
Mesh −→Tet...
(b) Click the Local Regions... button in the Refinement tab to open the Tet Re-
finement Region panel.

i. Enter wake for Name.
ii. Enter (1, 0.5, 0.2) for Center and (1, 0.5, 0.5) for Length.
iii. Retain the default orientation of (0, 0, 0).
iv. Enter 6e-6 for Max Cell Volume.
v. Retain the value of 1 for Outside Range and enter 1.15 for Growth Rate.
vi. Click Draw to see the extents of the region and the maximum cell volume
specified.
vii. Click Define to define the wake region.
viii. Click Activate for the region to be taken into account during refinement.
ix. Close the Tet Refinement Region panel.
TGrid will report (in the Message field) that there is one active tet refinement
region.
(c) Retain the selection of adv-front in the Refine Method drop-down list and the
Max Cell Volume of 2e-2, respectively.
(d) Enter 1.3 for Growth Rate.
(e) Click Apply and Init&Refine.



(f) Close the Tet panel.

(a) Display the mesh on a slide through the mirror and the car (x = -0.37). See
Figure 2.13.


(b) Display the mesh on a slide through the wheels (z = 0.38).
(c) Display the refinement region along with the cells (Figure 2.14).
i. Click the Local Regions... button in the Tet panel to open the Tet Refine-
ment Region panel.
Mesh −→Tet...
ii. Make sure wake is selected in the Regions selection list and click Draw.
iii. Close the Tet Refinement Region panel.



Figure 2.14: Slide of Cells at Z = 0.38 with the Refinement Region

platforms.
For the mesh generated, the local growth rate defined results in a smooth tran-
sition between the small cells in the wake region and the larger cells in the rest
of the domain (see Figure 2.15). Further manual operations to obtain better
quality are not required in this case.

Figure 2.15: Transition Between Cells in Locally Refined Region and the Rest of the
Domain



1. Check the mesh.
Mesh −→Check
TGrid will perform various checks on the mesh and report the progress in the console.
Make sure the minimum volume reported is a positive number.

2. Save the mesh.
(a) Enter sedan-vol.msh.gz for Mesh File.
(b) Click OK to save the volume mesh.

3. Exit TGrid.
File −→Exit

Summary
This tutorial demonstrated the tetrahedral mesh generation process using both the re-
finement methods available in TGrid. It also examined the effect of the size function and
the growth factor on the generated mesh. The quality of the mesh generated is similar
for both the refinement methods available. However, for most cases, the advancing front
method will be faster due to a greater number of cells generated per second. The use of
local refinement regions was also demonstrated.


Tutorial 3. Zonal Hybrid Mesh Generation

Introduction
There are many cases in which you may use hexahedral cells to mesh one part of your
geometry, but complexities in another part of the geometry require that it be meshed
with tetrahedral cells. In such cases, you can use the usual preprocessor to create the
mixed triangular surface mesh and the hexahedral volume mesh, and then use TGrid to
complete the hybrid mesh generation.
This tutorial demonstrates the mesh generation procedure for a hybrid mesh, starting
from a hexahedral volume mesh and a triangular boundary mesh. This tutorial demon-
strates how to do the following:

1. Read the mesh ﬁles and display the boundary mesh.

2. Merge the free nodes on the two pieces of the mesh (hexahedral volume mesh and
triangular boundary mesh).

3. Create pyramids as a transition between the hexahedral and tetrahedral mesh using
the Auto Mesh procedure.

4. Build prisms from the bottom of the tetrahedral region.

5. Check the quality of the entire volume mesh.

6. Merge the multiple cell zones into a single cell zone.

7. Create a non-conformal interface as a transition between the hexahedral and tetra-
hedral mesh using the Auto Mesh procedure.

Prerequisites
This tutorial assumes that you have little experience with TGrid, but that you are familiar


Zonal Hybrid Mesh Generation

Preparation
1. Copy zonal-hybrid.zip to your working directory.
2. Unzip zonal-hybrid.zip.
The files, hex-vol.msh and tri-srf.msh can be found in the zonal-hybrid folder
created on unzipping the file.
3. Start TGrid.

Step 1: Read and Display the Mesh
1. Read the two mesh files.
File −→ Read −→Mesh...

(a) Select hex-vol.msh in the Files list.
The file will be added to the list of Mesh File(s) in the Select File dialog box.



(b) Select tri-srf.msh in the Files list.
This ﬁle will also be added to the Mesh File(s) list.
(c) Click OK.
TGrid will read both ﬁles and append them, but you will need to merge the shared
nodes (i.e., the boundary nodes located along the circle where the triangular surface
mesh and the quadrilateral surface mesh meet) so that the two meshes can be treated
as a single unit.


(a) Select boundary in the Face Zone Groups selection list to select all the boundary
zones in the Face Zones selection list.
(b) Make sure Free is enabled (in addition to the default, All) in the Options group
box.
This option allows you to see the nodes shared by the triangular and quadrilat-
eral surface meshes. The nodes are free because, though both surface meshes
have nodes at the same location, the two sets of nodes are not aware of one
another. You will merge these nodes so that the two meshes can be treated as
a unit.
(c) Click the Attributes tab and disable Filled in the Options group box.
(d) Click Display.



Figure 3.1: Boundary Mesh for the Valve Port

(e) Zoom in to focus on the free nodes (Figure 3.2).

Figure 3.2: Free Nodes at the Intersection of the Tri and Quad Boundary Meshes

In Figure 3.2, the triangular faces that use the free nodes on the boundary
between the tri and quad face zones are colored.
(f) Close the Display Grid panel.

Step 2: Merge the Free Nodes on the Tri/Quad Border
In this step, you will merge the free nodes on the border between the triangular and
quadrilateral face zones.



1. Select only inlet-pipe in the Boundary Face Zones selection list in the Compare...
group box.
This is the triangular face zone that connects to the quadrilateral face zone for the
side of the hexahedral region.

2. Disable Only Free Nodes and select only quad-side in the Boundary Face Zones se-
lection list in the With... group box.
This is the external face zone of the hexahedral mesh that connects to the triangular
face zone of the inlet pipe.
Note: Disabling Only Free Nodes allows you to compare the free nodes on inlet-pipe
(the triangular face zone) with all the nodes on quad-side (the quadrilateral
face zone). This is necessary because the nodes in question are not free on
the quadrilateral face zone. They are used by the side of the hexahedral region
(quad-side) as well as the cap on the hexahedral region (quad-outlet). The
nodes on the triangular face zone are free because each is used by only one
face.
After you merge the free nodes, the nodes of the triangular face will be con-
nected to quad-outlet and quad-side.

TGrid will report the number of free nodes in the Message box.

4. Click Merge to merge the free nodes.



When the number of merged nodes is reported, not all of the free nodes were merged.
This implies that some of the nodes differ from their counterparts by a distance
greater than the specified Tolerance. Increase the Tolerance by a factor of 10 and
try the merge operation again.

5. Enter 0.002992057 for Tolerance.

6. Click Merge.
The remaining nodes should now be merged.

7. Click Count Free Nodes again to ensure that all the free nodes have been merged.


9. Save the mesh file.
(a) Enter hex-tri-merged.msh for Mesh File.
(b) Click OK to save the mesh.

Step 3: Check the Skewness Distribution of the Boundary Mesh


2. Click Compute.




Figure 3.3: Boundary Mesh Skewness Distribution

You can change the Minimum and Maximum values to display the number of faces between
two speciﬁc skewness values. It is a good practice to display the upper end of the skewness
range (e.g., between 0.8 and 1.0). As a rule of thumb, the maximum boundary face
skewness should be below 0.75.
For details on methods for improving the face skewness, see Tutorial 2.

Step 4: Generate the Tetrahedral Mesh Using Pyramids to Transition Between
the Hexahedral and Tetrahedral Mesh
In this step, you will use the Auto Mesh procedure in TGrid and use pyramids to transition
between the quadrilateral and triangular boundary mesh.

1. Change the boundary type of quad-outlet.
When the surface mesh and the hexahedral mesh were created in the preprocessor,
quad-outlet was given the type wall because there were cells on only one side of the
surface. When you generate the tetrahedral mesh with pyramids on the other side,
this boundary will simply be an interior boundary between ﬂuid cells.
Boundary −→Manage...
(a) Select quad-outlet in the Face Zones selection list and click List.
The current zone type and other information will be reported in the console.
(b) Retain the selection of Change Type in the Options list and select internal in
the Type drop-down list.



It is recommended that you select internal instead of interior for the bound-
! ary type. If you clear the mesh in TGrid, all interior zones will be removed,
but the internal zones will be retained. When you read the completed
mesh into the solver, the internal zones will automatically be converted to
interior type.
(c) Click Apply and close the Manage Face Zones panel.

2. Set the meshing parameters.



(a) Retain the selection of Pyramids in the Quad Tet Transition list and click the
Set... button to open the Pyramids panel.

i. Select quad-outlet in the Boundary Zones selection list.
ii. Retain the selection of Skewness in the Options list.
iii. Click Apply.
iv. Close the Pyramids panel.
(b) Retain the selection of Tet in the Volume Fill list and click the Set... button
to open the Tet panel.

i. Enable Delete Dead Zones in the Tet Zones group box in the Intialization
tab.



ii. Retain the default settings in the Reﬁnement tab.
iii. Click Apply and close the Tet panel.
(c) Click Apply in the Auto Mesh panel.
(d) Preserve the existing hexahedral mesh.

> /mesh/tet/preserve-cell-zone <Enter>
()
Cell Zones(1) [()] fluid* <Enter>
Cell Zones(2) [()] <Enter>

(e) Click Mesh in the Auto Mesh panel.
The maximum and average skewness values reported at the end of the meshing
are approximately 0.848 and 0.367, respectively.
(f) Close the Auto Mesh panel.

3. Display the pyramid cap.
(a) Select quad-outlet and quad-outlet-pyramid-cap-# in the Face Zones selection
list in the Faces tab.
(b) Disable Free in the Options group box.
(c) Click the Attributes tab and enable Filled and Lights in the Options group box.
(d) Click Display and manipulate the display to obtain the view shown in Fig-
ure 3.4.



Figure 3.4: Pyramid Cap

4. Examine the transition between the hexahedral and tetrahedral mesh.
(a) Deselect all the previous selections in the Face Zones selection list in the Faces
tab.
(b) Click the Cells tab and select all the zones in the Cell Zones selection list.
(c) Enable All in the Options group box.
(d) Click the Attributes tab and enter 0.4 for Shrink Factor.
(e) Click the Colors... button to open the Grid Colors panel.
(f) Click Display and zoom in close to the boundary between the hexahedral and
tetrahedral mesh (Figure 3.5).

Figure 3.5: Pyramid Transition Between the Hexahedral and Tetrahedral Mesh



Step 5: Extend the Mesh Using Prisms
Mesh −→Prisms...

1. Select cyn-out in the Boundary Zones selection list.
This is currently the bottom of the cylinder. You will extend the cylinder by building
prisms from this triangular boundary. You can click Draw to display the zone. Make
sure the Shrink Factor is set to 0 in the Attributes tab and the All option is disabled
in the Cells tab of the Display Grid panel before clicking Draw.

2. Set the parameters controlling prism growth.
(a) Retain the selection of uniform in the Oﬀset Method drop-down list and select
geometric in the Growth Method drop-down list, respectively.
(b) Enter 4 for First Height and 1.25 for Rate, respectively.
This means that the ﬁrst prism layer will have a height of 4, the second a
height of 5 (4 × 1.25), and so on.
(c) Enter 10 for Number of Layers.
The Total Height added by the prisms is slightly more than 133.

3. Check that the face normals are pointing the right way.
The normal direction for the face zone determines which side of the zone the prisms
are built on. To extend the domain down from the current cylinder bottom, you need
to ensure that the normals on the cyn-out zone are pointing down.



(a) Enable the display of normals.

i. Click the Attributes tab and enable Normals in the Options group box.
ii. Enter 5 for Normal Scale.
Larger normals are easier to see in the grid display.
(b) Click the Faces tab and deselect the previous selections in the Face Zones
selection list.
(c) Select only cyn-cap and cyn-out in the Face Zones selection list.
(d) Click Display, zoom out, and rotate the display to see the bottom of the cylin-
der (Figure 3.6).

Figure 3.6: Cylinder Normals in Wrong Direction

In Figure 3.6, the normals are not pointing out from the bottom of the cylinder.
Since they need to point out (i.e., down), you need to ﬂip them.



(e) Flip the normals on the cyn-out zone.
i. Select cyn-out in the Face Zones list.
ii. Select Flip Normals in the Options list.
iii. Click Apply and close the Manage Face Zones panel.
(f) Click Display and close the Display Grid panel.

Figure 3.7: Cylinder with Normals in Correct Direction

In Figure 3.7, the normals are pointing in the correct direction. The prisms
built will extend the cylinder below its current bottom.
4. Specify the growth direction for the prisms.



(a) Select Uniform in the Method list.
The Uniform method is recommended when you are simply extruding to form
a straight-sided prism region. You can use the default Normal method when
growing prisms in more complicated regions.
(b) Click Compute in the Vector group box to update the normal direction vector
for the cyn-out zone.

5. Click Apply to save the prism parameters.

6. Save an intermediate mesh file (temp.msh).
It is a good practice to save the prism settings to a mesh file before generating
prisms. If for any reason you are dissatisfied with the prisms, you can read the
mesh file back in, modify the parameters, and try again.

7. Click Create.
TGrid will create the layers of prisms, and summarize the new zones that have been
created:
Prism Layer Summary:

3920 wedge cells created in new zone prism-cells-#.

9128 quadrilateral interior faces created in new zone interior-#.

392 boundary faces created in new zone prism-cap-#.

560 quadrilateral boundary faces created in new zone prism-side-#.

1521 interior nodes created in new zone node-#.

729 boundary nodes created in new zone boundary-node-#.

where, # denotes the respective zone IDs. The exact number may differ on different
platforms.
The face and cell zones of interest are as follows:
interior-# contains the wedge prism cells.
prism-cap-# is the new bottom of the cylinder (with triangular faces).
prism-side-# contains the quadrilateral boundary faces on the outside of the cylin-
der.

8. Close the Prisms panel.



9. Display the new boundaries of the cylinder (Figure 3.8).
(a) Select cyn-cap, prism-cap-#, and prism-side-# in the Face Zones selection list.
(b) Click Display.
Make sure the Normals option has been disabled in the Attributes tab of the
Display Grid panel.

Figure 3.8: Cylinder Extended Using Prisms

10. Change the zone types for the zone you built the prisms from (cyn-out) and the
new cap face (prism-cap-#).
By default, the caps of the prism cells are wall zones. In this tutorial, the cap
faces represent the outlet of the domain. Also, the zone you built the prisms from,
cyn-out, is currently a wall zone. It should be an interior boundary between ﬂuid
cells.
(a) Change the zone type for cyn-out.
i. Select cyn-out in the Face Zones list and click List.
The current zone type and other information will be reported in the con-
sole.
ii. Select internal in the Type drop-down list.



It is recommended that you select internal instead of interior for the bound-
! ary type. If you clear the mesh in TGrid, all interior zones will be removed,
but the internal zones will be retained. When you read the completed
mesh into the solver, the internal zones will automatically be converted to
interior type.
iii. Click Apply.
(b) Change the zone type for prism-cap-#.
i. Select prism-cap-# in the Face Zones list.
ii. Select pressure-outlet in the Type list.
iii. Click Apply.
If required, you can change the zone names using the Rename option in the
Manage Face Zones panel.
(c) Close the Manage Face Zones panel.

1. Check the skewness of the entire volume mesh.
(a) Plot the cell skewness distribution (Figure 3.9).
Display −→ Plot −→Cell Distribution...

i. Select all the zones in the Cell Zones selection list.
ii. Click Compute.
iii. Click Plot.
iv. Close the Cell Distribution panel.



Figure 3.9: Cell Skewness Distribution

(b) Report the worst cell skewness.

ii. Click Compute.
iii. Close the Report Cell Limits panel.

2. Merge the four cell zones.
In this problem, the hexahedral, pyramid, prism, and tetrahedral cells are all part
of the same ﬂuid region. Hence, there is no need to retain four separate cell zones.
In this step, you will merge the cell zones before saving the ﬁnal volume mesh.
Mesh −→Manage...



(a) Select all the zones in the Cell Zones selection list.
(b) Select Merge in the Options list.
(c) Enable Merge Sub Zones.
When the Merge Sub Zones option is enabled, TGrid will merge the face zones
associated with the cell zones, where appropriate.
(d) Click Apply.
You will see the four Cell Zones merge into a single zone in the Manage Cell
Zones panel. The face zones that were merged together while merging the cell
zones will be reported in the console.
(e) Close the Manage Cell Zones panel.

3. Check the volume mesh.
Before saving the mesh ﬁle, check it to ensure that it has no negative cell volumes
or left-handed faces.
Mesh −→Check
The printed results of the check show no problems, so the mesh can be used in the
solver.

4. Save the mesh.



(a) Enter hybrid-pyramids.msh.gz for Mesh File.
(b) Click OK to save the volume mesh.

Step 7: Generate the Tetrahedral Mesh Using a Non-Conformal Transition
Between the Hexahedral and Tetrahedral Mesh
In this step, you will use the Auto Mesh procedure in TGrid and specify a non-conformal
transition between the quadrilateral and triangular boundary mesh. The retriangulation
methods available are as follows:

• Quad-Split (recommended for low aspect ratio quads)

• Prism (recommended for high aspect ratio quads)

• Remesh (recommended for high aspect ratio quads)

In this case, the quads are of a relatively low aspect ratio, hence, you will use the Quad-
Split option. The use of alternative retriangulation options is demonstrated in Tutorial
4.

Note: The steps in this section are similar to those described in previous sections, and
hence are less explicit.



1. Read the mesh ﬁle saved after merging the free nodes (hex-tri-merged.msh).

2. Change the type of the quad-outlet zone to internal.


(a) Select Non Conformals in the Quad Tet Transition list and click the Set... button
to open the Non Conformals panel.



i. Select quad-outlet in the Boundary Zones selection list.
ii. Select Quad Split in the Retriangulation Method list.
iii. Click Apply and close the Non Conformals panel.
(b) Retain the selection of Tet in the Volume Fill list and click the Set... button
i. Enable Delete Dead Zones in the Tet Zones group box in the Initialization
tab.
ii. Retain the default settings in the Reﬁnement tab and click Apply.
iii. Close the Tet panel.
(c) Click Apply in the Auto Mesh panel.
(d) Preserve the existing hexahedral mesh.

> /mesh/tritet/preserve-cell-zone <Enter>
()
Cell Zones(1) [()] fluid* <Enter>

(e) Click Mesh in the Auto Mesh panel.
The maximum and average skewness values reported at the end of the meshing
are approximately 0.849 and 0.370, respectively.

4. Examine the transition between the hexhedral and tetrahedral mesh.
(a) Make sure that any previous selections in the Face Zones selection list are
deselected and select quad-outlet-intf:#.
(b) Disable Free in the Options group box in the Faces tab.
(c) Click the Cells tab and select all the zones in the Cell Zones selection list.
(d) Enable All in the Options group box.
(e) Click the Attributes tab and enable Filled and Lights in the Options group box.
(f) Enter 0.4 for Shrink Factor.
(g) Click the Colors... button to open the Grid Colors panel.
(h) Click Display and zoom in close to the boundary between the hexahedral and
tetrahedral mesh.



Figure 3.10: Non Conformal Transition Between Hexahedral and Tetrahedral Mesh

Extra: If required, you may extend the mesh using prisms as described in Step 5.
Change the type for the appropriate boundaries, as required.

(a) Plot the cell skewness distribution (Figure 3.11).

Figure 3.11: Cell Skewness Distribution

(b) Report the worst cell skewness.
The worst cell skewness is approximately 0.849.



6. Merge the cell zones.

7. Check the volume mesh.
Mesh −→Check

8. Save the mesh (hybrid-nonconformal.msh.gz).

9. Exit TGrid.
File −→Exit

Summary
This tutorial demonstrated the creation of a hybrid mesh starting from a hexahedral
volume mesh and a triangular boundary mesh. The tutorial described the procedure
to create the tetrahedral mesh with a transition layer of pyramid cells, while preserving
the existing hexahedral mesh. It also described the extending of the mesh by building
layers of prism cells from the bottom of the tetrahedral portion of the mesh. Finally you
merged all the cell zones into a single ﬂuid cell zone for convenience. The tutorial also
described the procedure to create a non-conformal transition between the hexahedral and
tetrahedral mesh.


Tutorial 4. Viscous Hybrid Mesh Generation

Introduction
In cases where you want to resolve the boundary layer, it is often more eﬃcient to use
prismatic cells in the boundary layer rather than tetrahedral cells. The prismatic cells
allow you to resolve the normal gradients associated with boundary layers with fewer
cells. The resulting mesh is referred to as a “viscous” hybrid mesh.
TGrid allows you to create a viscous hybrid mesh by growing prisms from the faces on the
surface mesh. It creates high quality prism elements near the boundary and tetrahedral
elements in the rest of the domain. TGrid also supports automatic proximity detection
and height adjustment while growing prisms in a narrow gap.
This tutorial demonstrates the mesh generation procedure for a viscous hybrid mesh,
starting from a triangular boundary mesh for a sedan car body. This tutorial demon-
strates how to do the following:


2. Check for free and unused nodes.

3. Check the skewness of the boundary faces.

4. Set parameters for growing prism cells allowing shrinkage and manual tetrahedral
meshing.

5. Set parameters for growing prism cells ignoring areas of proximity and automatic
meshing.

6. Examine the prisms in areas of proximity and sharp angles.



Prerequisites
This tutorial assumes that you have some experience with TGrid, and that you are familiar


Viscous Hybrid Mesh Generation

Preparation
1. Copy prisms.zip to your working directory.

2. Unzip prisms.zip.
The file, sedan.msh.gz can be found in the prisms folder created on unzipping the
file.

3. Start TGrid.

1. Read the mesh file.




(b) Click OK.


(a) Select boundary in the Face Zone Groups selection list to select all boundary
(b) Click Display.

Figure 4.1: Boundary Mesh for the Sedan



The mesh contains the boundary mesh of the sedan and the tunnel. Prisms
will be generated on the body, the mirror, the wheels, and the ground. Critical
areas are the wheel/ground intersection, the region of proximity of the wheels
and wheel arches, and the mirror.

Step 2: Check for Free and Unused Nodes

TGrid reports the number of free nodes in the Message box. Click Merge to remove
free nodes, if any.

2. Click Count Unused Nodes.
TGrid reports the number of unused nodes in the Message box. Click Delete Unused
Nodes to remove unused nodes, if any. Free nodes are nodes associated with free
edges. There should not be any free nodes unless there are thin walls in the geometry.
If free nodes are located between a zone you are building prisms from and an adjacent
zone, TGrid will be unable to project to and retriangulate the adjacent zone.




Step 3: Check the Quality of the Surface Mesh

1. Select all the surfaces in the Boundary Zones selection list.

2. Click Compute.
The maximum skewness value reported is 0.543 which is good enough to generate a
hybrid mesh. When generating prisms on a surface mesh, the quality must not be
higher than 0.7 or even 0.6 if many layers are to be extruded.


Figure 4.2: Surface Mesh Quality

4. Close the Face Distribution panel.



Step 4: Set Parameters for Prism Layer Shrinkage and Manual Tetrahedral
Meshing
1. Create a user-deﬁned group for easier selection of the zones on which prisms are to
be generated.
Boundary −→ Zone −→Group...

(a) Select car, ground, mirror, wheel-arch-front, wheel-arch-rear, wheel-front, and
wheel-rear in the Face Zones selection list.
(b) Click Draw and verify that the zones selected are appropriate.
(c) Click Create.
The Group Name dialog will open, prompting you to specify the group name.

(d) Enter prisms for Name and click OK.
The use of the underscore ( ) in the group name allows the group to be listed
at the top of the Face Zone Groups list.
(e) Close the User Deﬁned Groups panel.

2. Verify that the normals are correctly oriented.



(a) Deselect the previous selection of boundary and select prisms in the Face Zone
Groups selection list in the Faces tab.
(b) Click the Attributes tab and enable Normals.

(c) Enter 0.005 for Normal Scale.
(d) Enable Filled and Lights in the Options group box in the Attributes tab of the
Display Grid panel.
(e) Click the Colors... button to open the Grid Colors panel.
(f) Select Color by ID in the Options list and close the Grid Colors panel.
(g) Click Display (Figure 4.3).
The normals on the car, mirror, wheel-arch-front, wheel-arch-rear, wheel-front,
and wheel-rear point outward, while those on the ground point upward.



Figure 4.3: Normals on the Wheel and Wheel Arch Zones

Figure 4.3 shows the normals on the wheels and wheel arches. You will need
to reorient the normals on the wheel-arch-front and wheel-arch-rear zones for
the prisms to be grown in the correct direction.
In TGrid, the normals will always be oriented in the direction of most of the
facets. Hence, if a small region is wrongly oriented, there will not be a problem
with prisms grown.
(h) Close the Display Grid panel.

3. Set the prism meshing parameters.



(a) Select prisms in the Boundary Zone Groups selection list.
(b) Select aspect-ratio in the Oﬀset Method drop-down list and enter 5 for First
Aspect Ratio.
(c) Select geometric in the Growth Method drop-down list and enter 1.2 for Rate.
(d) Set the Number of Layers to 5.
(e) Click Apply (next to Create).
(f) Click the Growth Options... button to open the Prisms Growth Options panel.
i. Make sure Allow Shrinkage is enabled.
The Allow Shrinkage option allows you to enable the prism proximity al-
gorithms in TGrid, which prevent the prism cells colliding with each other
in areas of proximity and sharp angles.

ii. Enter 200 for Max Aspect Ratio and click Apply.
The Max Aspect Ratio limits the shrinkage of the prism layers based on
the local edge length, while the Gap Factor value controls the gap between
the opposing prism layers.
iii. Close the Prisms Growth Options panel.
(g) Click the Direction tab in the Prisms panel.
i. Deselect all the zones selected in the Boundary Zones selection list and
select only wheel-arch-front and wheel-arch-rear.



ii. Click the Orient Normals button to open the Material Point panel.

A. Enter 0, 1, 1 for X, Y, and Z, respectively.
B. Click Apply to orient the normals correctly (Figure 4.4).

Figure 4.4: Normals on Wheels and Wheel Arches After Flipping



C. Close the Material Point panel.
(h) Deselect the zones in the Boundary Zones selection list and select prisms in
the Boundary Zone Groups selection list.
(i) Click Create.
(j) Close the Prisms panel.

4. Examine the prisms generated by displaying a slide of cells at z = 0.38.
(a) Retain the selection of the previously selected zones in the Face Zones selection
list.
(b) Click the Bounds tab and enable Limit by Z.

(c) Enter 0.38 for both Minimum and Maximum in the Z Range group box.
(d) Click the Cells tab and select the prism cells zone (prism-cells-#, where # is
the zone ID) in the Cell Zones selection list.



(e) Enable All in the Options group box and click Display.
Make sure the display of normals is disabled in the Attributes tab.
(f) Zoom in to the region of the wheel/ground intersection and the gap between
the car body and the wheels (Figure 4.5).

Figure 4.5: Prisms Shrunk in Areas of Proximity and Sharp Corners

(g) Close the Display Grid panel.



5. Check the quality of the prism cells generated.

(a) Select the prism cell zone in the Cell Zones selection list and click Compute.
The quality reported is around 0.91.
(b) Improve the prism cell quality.

> /mesh/prism/improve/improve-prism-cells
Cell Zone [] prism-cells* <Enter>
Iterations [5] <Enter>

cell-quality-method [skewness]> skewness <Enter>
Min. skewness (0 1) [0.9] <Enter>
Minimum Improvement [0.001] <Enter>
improved 290 nodes, most improvement 8.514647e-02

The maximum skewness value reported is now below 0.9, which is acceptable.
(c) Close the Cell Distribution panel.

6. Deﬁne the tetrahedral domain.
Mesh −→Domains...



(a) Select inlet, outlet, outlet-side, outlet-top, prism-cap-#, and symmetry in the
Boundary Zones selection list.
(b) Enter tetra for Name and click Create.
The domain tetra will be created and activated.
(c) Verify that all the zones required are included in the defined domain.
i. Click the Bounds tab and click Reset.
ii. Select all the zones in the Face Zones selection list in the Faces tab.
iii. Enable Free in the Options group box.
Enabling the display of free nodes allows you to verify whether the domain
is correctly defined. If any zone is not included in the domain, its adjacent
zones will have free nodes.
iv. Click Display.
v. Close the Display Grid panel.
(d) Close the Domains panel.

7. Set the parameters for tetrahedral meshing.
Mesh −→Tet...
(b) Click the Refinement tab and retain the selection of adv-front in the Refine
Method drop-down list.
(c) Select geometric in the Cell Size Function drop-down list and enter 1.35 for
Growth Rate.



(d) Click Apply and Init&Reﬁne.
(e) Close the Tet panel.

8. Check the quality of the mesh.
The maximum skewness reported is around 0.94.

9. Activate the global domain.
(a) Select global in the Domains list and click Activate.
(b) Close the Domains panel.

10. Examine the mesh by displaying a slide of cells at z = 0.38.
(a) Enable Limit by Z in the Bounds tab and enter 0.38 for both Minimum and
Maximum.
(b) Select the ﬂuid and prism cell zones in the Cell Zones selection list in the Cells
tab.
(c) Enable All in the Options group box and click Display (Figure 4.6).
(d) Examine the areas of proximity (Figure 4.7).



Figure 4.6: Slide of Cells at z = 0.38

Figure 4.7: Prisms Shrunk in Areas of Proximity



11. Merge the cell zones generated.

(a) Select the ﬂuid and prism cell zones in the Cell Zones selection list.
(b) Select Merge in the Options list.
(c) Enable Merge Sub Zones and click Apply.
(d) Close the Manage Cell Zones panel.
12. Check the mesh.
Mesh −→Check
13. Save the mesh (sedan-1.msh.gz).



(a) Enter sedan-1.msh.gz for Mesh File.
(b) Click OK.

Step 5: Set Parameters for Ignoring Prism Layers and Automatic Meshing
The previous sections described the set up and manual meshing procedure for a viscous
mesh with prisms and tetrahedra. This demonstrated how TGrid works with domains.
In this step, you will use the Auto Mesh option to set all the meshing parameters and
automatically generate the viscous mesh in a single step, thereby removing the need for
creating the domain excluding the prism region as an intermediate step.

1. Read the mesh ﬁle (sedan.msh.gz).

2. Display the grid and verify that the normals are correctly oriented.
The normals on the car, mirror, wheel-arch-front, wheel-arch-rear, wheel-front, and
wheel-rear point outward, while those on the ground point upward. You will need to
ﬂip the normals on the wheel-arch-front and wheel-arch-rear zones.




The Prisms option is greyed out as no prism parameters have been set.
(a) Click the Set... button in the Boundary Layer Mesh group box to open the
Prisms panel.
i. Click the Direction tab in the Prisms panel.
A. Select wheel-arch-front and wheel-arch-rear and click Orient Normals to
open the Material Point panel.
B. Enter 0, 1, 1 for X, Y, Z, respectively.
C. Click Apply and close the Material Point panel.
ii. Click the Growth tab and set the prism growth parameters.
A. Select car, ground, mirror, wheel-arch-front, wheel-arch-rear, wheel-front,
and wheel-rear in the Boundary Zones selection list.
B. Select aspect-ratio in the Offset Method drop-down list and enter 5 for
First Aspect Ratio.
C. Select geometric in the Growth Method drop-down list and enter 1.2
for Rate.
D. Set Number of Layers to 5.
E. Click Apply in the Zone Specific Growth group box.

It is necessary to apply the prism growth parameters on specific zones for
! TGrid to retain the growth parameters in memory. The Prisms option in the
Auto Mesh panel will be visible only after applying zone-specific growth.
iii. Click the Growth Options... button to open the Prisms Growth Options
panel.



A. Retain the Allow Shrinkage option and enable Allow Ignore.
B. Enter 0.7 for Gap Factor and 0.2 for Max Shrink Factor, respectively.
C. Click Apply and close the Prisms Growth Options panel.
iv. Click Apply and close the Prisms panel.
(b) Enable Prisms in the Auto Mesh panel.
(c) Select Non Conformals in the Quad Tet Transition group box and click the Set...
button to open the Non Conformals panel.

i. Retain the selection of Prism in the Retriangulation Method list and click
Apply.
When the Quad Split method of retriangulation is selected, each quadri-
lateral face zone will be copied and the quadrilaterals on the copied zone
will then be split to form triangles. This method is recommended when the
quadrilaterals are close to perfect squares (low aspect ratio).
In this case, however, the quadrilaterals are of high aspect ratio, and the
use of the Quad Split method would create highly skewed triangles, and
consequently highly skewed tetrahedra. Of the remaining retriangulation
methods available, the Remesh option will only take into account the nodes
on the edge loop of the quadrilateral zone during retriangulation. The
Prism option will, however, consider the ‘ribs’ (lines joining the base nodes
and the cap nodes along the prism-side) during the retriangulation, thus,
giving a better quality triangular mesh for the curved prism sides.
ii. Close the Non Conformals panel.
(d) Retain the selection of Tet in the Volume Fill group box and click the Set...
button to open the Tet panel.



i. Retain the settings in the Initialization tab.
ii. Click the Reﬁnement tab and retain the selection of adv-front in the Reﬁne
Method drop-down list.
iii. Select geometric in the Cell Size Function drop-down list and enter 1.35
for Growth Rate.
iv. Click Apply and close the Tet panel.

(e) Click Mesh.

4. Examine the mesh by displaying a slide of cells at z = 0.38.
Figure 4.9 shows that prism layer growth was ignored in areas of proximity such as
sharp corners.




Figure 4.9: Prisms Ignored in Areas of Proximity



5. Merge the cell zones.

6. Check the quality of the mesh.

7. Check the mesh.
Mesh −→Check

8. Save the mesh (sedan-2.msh.gz).

Summary
This tutorial demonstrated the creation of a viscous hybrid mesh starting from a tri-
angular mesh. The controls available for creating prisms from multiple zones and the
additional growth options for areas of proximity and sharp corners were demonstrated.
The tutorial also demonstrated the use of the Auto Mesh tool for creating the viscous
hybrid mesh.


Tutorial 5. Hexcore Mesh Generation

Introduction
Hexcore meshing is a hybrid meshing scheme which generates Cartesian cells inside the
core of the domain and tetrahedral cells close to the boundaries. Hanging-node refine-
ments on the Cartesian cells allow efficient cell size transition from the boundary to the
interior of the domain. The hexcore meshing scheme is applicable to all volumes but
is useful for volumes with large internal regions and few internal boundaries. It is fully
automated and compatible with prism (boundary layer) generation.
Hexcore meshes are more useful in applications with large open spaces. One such appli-
cation from the automotive industry is explained here.

1. Read and display the mesh.
2. Check the skewness of the surface mesh.
3. Repair the boundary mesh by merging the nodes and splitting the edges of the
geometry.
4. Generate the hexcore mesh.
5. Examine the effect of buffer layers on the hexcore mesh.
6. Generate the hexcore mesh in conjuction with boundary layer (prism) meshing and
local refinement.

Prerequisites

Preparation
1. Copy hexcore.zip to your working directory.


Hexcore Mesh Generation

2. Unzip hexcore.zip.
The ﬁle, cabin-hvac.msh can be found in the hexcore folder created on unzipping
the ﬁle.

3. Start TGrid.

1. Read the mesh.

(a) Select cabin-hvac.msh in the Files list.
(b) Click OK.

2. Display the mesh (Figure 5.1).



(b) Click Display.



Step 2: Check the Skewness of the Surface Mesh
1. Display the surfaces with higher skewness.
(a) Find the number of faces with a skewness greater than 0.65.



i. Select all the zones in the Boundary Zones selection list.
ii. Enter 0.65 for Minimum.
iii. Click Plot (Figure 5.2).

Figure 5.2: Skewness Distribution Above 0.65

iv. Close the Face Distribution panel.



Step 3: Repair the Boundary Mesh
1. Modify the faces having skewness greater than 0.65.
Boundary −→ Mesh −→Improve...

(a) Select all the zones in the Tri Boundary Zones selection list.
(b) Retain the selection of Skewness in the Quality Measure drop-down list and
enter 0.65 for Quality Limit.
(c) Enter 5 for Angle.
Specifying a lower value for Angle will reduce the modifications made to the
boundary and better maintain the geometry.
(d) Retain the value of 5 for Iterations and click Apply.
TGrid will fix the 6 faces above the specified maximum quality (0.65) and report
that the current maximum quality is approximately 0.649.

2. Convert the quad face zones into tri face zones.
Boundary −→ Mesh −→Triangulate...
(a) Select quad in the Boundary Zone Groups selection list.
The outlet zone will be automatically selected in the Boundary Zones selection
list.



(b) Click Draw (Figure 5.3).

Figure 5.3: Quad Faces in the outlet Zone

(c) Retain the selection of Replace and click Apply.
The quad faces will be split into triangles. TGrid will report that 1200 trian-
gular faces were created in the new zone, outlet:#.
(d) Close the Triangulate Zones panel.
Extra: You can also create a non-conformal interface to allow quad faces during
the hexcore mesh initialization. In this case, TGrid will automatically create



the triangular mesh on all quad faces available in the domain. All the surfaces
having quad elements will be copied and remeshed with triangular cells. The
free nodes of the triangular mesh will be merged with the original surface mesh.

3. Check the quality of the surface mesh.
(a) Select all the zones in the Tri Boundary Zones selection list in the Boundary
Improve panel.
(b) Retain the selection of Skewness in the Quality Measure drop-down list and
0.65 for Quality Limit.
(c) Click Apply.
The maximum skewness reported is still less than 0.65, hence the mesh is
acceptable.
(d) Close the Boundary Improve panel.


Step 4: Generate the Hexcore Mesh
1. Generate the hexcore mesh using the default parameters.
Mesh −→Hexcore...
(a) Enable Delete Dead Zones in the Zones group box.
(b) Retain the default settings for the remaining parameters and click Create.
Note: The maximum skewness reported at the end of the reﬁnement process
is not the ﬁnal value. Some slivers can be removed.
(c) Display the parent face.
i. Click Reset in the Bounds tab.
ii. Click the Faces tab and select parent-face-# in the Face Zones selection
list.
iii. Click Display (Figure 5.4).
(d) Display a slide of cells at y = 50 and y = -525 (Figures 5.5 and 5.6).



Figure 5.4: Parent Face for the Hexcore Mesh

Figure 5.5: Slide of Cells at y = 50 for the Hexcore Mesh With Buﬀer Layers = 1

Figure 5.6: Slide of Cells at y = -525 for the Hexcore Mesh With Buﬀer Layers = 1



2. Check the number of cells generated.
(a) Click Update.
The number of cells is approximately 179817. The exact number may vary
slightly on different platforms.
(b) Close the Report Mesh Size panel.

3. Check the maximum skewness.
(a) Select the fluid zone in the Cell Zones selection list and click Compute.
(b) Close the Report Cell Limits panel.

Step 5: Examine the Effect of the Buffer Layers on the Hexcore Mesh
Buffer Layers specifies the number of extra layers of hex cells of a particular size before
subdivision. Increasing the number of buffer layers will significantly increase the number
of cells.
The default setting for Buffer Layer is 1. You will now examine the effect of different
buffer layer settings on the mesh.

1. Clear the mesh.

2. Generate the hexcore mesh with Buffer Layers set to 0.
(a) Click Compute to determine the value for Max Cell Length based on the current
mesh.
(b) Set Buffer Layers to 0 and click Apply.
A Warning dialog box will appear, warning you that a buffer layer of zero may
result in poor mesh quality.
(c) Click OK in the Warning dialog box.
(d) Click Create.

3. Display the slide of cells at y = 50 and y = -525 (Figures 5.7 and 5.8).

4. Check the maximum skewness and the number of cells.
For buffer layers = 0, the number of cells is 150875 and the maximum skewness is
0.883. The exact values may vary on different platforms.



5. Clear the mesh.

6. Set Buffer Layers to 2 and generate the hexcore mesh.




8. Check the maximum skewness and the number of cells.
For buffer layers = 2, the number of cells is 225364 and the maximum skewness is
0.849. The exact values may vary on different platforms.
Hence, the number of buffer layers has a strong impact on the number of cells.



Step 6: Automatically Generate the Hexcore Mesh with Prism Layers and a Local
Refinement Region
1. Clear the mesh.
2. Verify that the normals on the surfaces you want to create prisms from are pointing
in the right direction.
(a) Click Reset in the Bounds section of the Display Grid panel.
(b) Select ceiling, outlet:#, rearscreen, and windscreen in the Face Zones selection
list.
(c) Click the Attributes tab.
(d) Enable Normals in the Options group box and enter 10 for Normal Scale.
Larger normals are easier to see in the grid display.
(e) Click Display.
If you zoom in, the normals on the selected zones point inward.
3. Define the meshing parameters.
(a) Define the parameters for growing prism layers.
i. Click the Set... button in the Boundary Layer Mesh group box to open the
Prisms panel.



ii. Select ceiling, outlet:#, rearscreen, and windscreen in the Boundary Zones
selection list.
iii. Select aspect-ratio in the Offset Method drop-down list and enter 7 for First
Aspect Ratio.
iv. Select geometric in the Growth Method drop-down list and set the Number
of Layers to 2.
v. Enter 1.15 for Rate.
vi. Click Apply in the Zone Specific Growth group box.

vii. Close the Prisms panel.
viii. Enable Prisms in the Boundary Layer Mesh group box in the Auto Mesh
panel.
(b) Display all the surfaces except right using the Display Grid panel.
Make sure the display of normals is disabled in the Attributes tab.
(c) Define the parameters for hexcore meshing.
i. Select Hexcore in the Volume Fill list in the Auto Mesh panel and click the
Set... button to open the Hexcore panel.
ii. Compute the average length of the faces on the ceiling zone.
A. Zoom in to the ceiling zone in the graphics display.
B. Use the hot-key Ctrl + N to enable the selection of nodes.
C. Select two adjacent nodes using the right mouse button.
D. Use the hot-key Ctrl + D to calculate the distance between the selected
nodes.
The distance between the nodes is computed to be approximately 60.
iii. Enter 120 for Max Cell Length.
This is the maximum length for the hexahedral cells in the volume mesh.
iv. Set Buffer Layers to 1.



v. Enable Delete Dead Zones and Keep Hex Tet Separate in the Zones group
box.
Note: The Keep Hex Tet Separate option is used here primarily for better
visualization of the mesh.
vi. Click the Tet Controls... button to open the Tet panel.
A. Retain the settings in the Tet panel.
B. Close the Tet panel.
vii. Define and visualize the refinement region.
The hex cells will be refined in the local region defined using the Hexcore
Refinement Region panel.
A. Click the Local Regions... button to open the Hexcore Refinement Re-
gion panel.
B. Retain default for Name.
C. Set Level to 3.



D. Enter the following parameters:
Center Length Orient
X 650 1400 0
Y 0 2000 12
Z 400 1700 0
E. Click Define.
F. Click Draw to visualize the refinement region (Figure 5.11).

Figure 5.11: Refinement Region

G. Retain the selection of default in the Regions selection list and click
Activate.
H. Close the Hexcore Refinement Region panel.



TGrid will show (in the Active field in the Hexcore panel) that there is one
active hexcore refinement region.
(d) Click Apply and close the Hexcore panel.

4. Click Mesh in the Auto Mesh panel to generate the mesh.
5. Close the Auto Mesh panel.
6. Examine the mesh by zone type.
(a) Select all the zones in the Cell Zones selection list and click List.
You can also draw the cell zones to identify the respective zones. There are
11728 prism cells (prism-cells-#), 191098 tetrahedral cells (fluid-#), and 59962
hexahedral cells (fluid-#:#).
7. Check the cell count and the maximum skewness.
The number of cells is 262788 and the maximum skewness is 0.907. The exact
number may vary on different platforms.
9. Check the size of the largest hex cell.
You should get a value close to 120.



Figure 5.12: Slide of Cells at y = 50

Figure 5.13: Slide of Cells at y = -525




11. Exit TGrid.
File −→Exit

Summary
This tutorial demonstrated the generation of a hexcore mesh using both the manual
and the automatic mesh generation procedure. It also examined the effect of the buffer
layers specified on the generated mesh. The use of local refinement regions was also
demonstrated.


Tutorial 6. Generating the Hexcore Mesh to Domain
Boundaries

Introduction
When generating the hexcore mesh for external flow domains, it may not be necessary
to have a tetrahedral mesh at the domain boundaries. For such cases, you can generate
the hexcore mesh to the domain boundaries, thereby also reducing the cell count. This
tutorial demonstrates the generation of the hexcore mesh to the domain boundaries for
a sedan car.

2. Set parameters for generating the hexcore mesh.
3. Set parameters for creating prism layers and the hexcore mesh using automatic
meshing.

Prerequisites

Preparation
1. Copy hexcore-boundaries.zip to your working directory.
2. Unzip hexcore-boundaries.zip.
The files, sedan.msh.gz, sedan-nonaligned.msh.gz, and sedan hexcore to boundaries.jou
can be found in the hexcore-boundaries folder created on unzipping the file.
3. Start TGrid.


Generating the Hexcore Mesh to Domain Boundaries


(b) Click OK.




(b) Click Display.

Figure 6.1: Boundary Mesh for the Sedan

The mesh contains the boundary mesh of the sedan and the outer box. You
will initally generate the hexcore mesh without using the outer box boundaries
to deﬁne the domain extents.



Step 2: Delete the Outer Box Boundaries

1. Select ground, inlet, outlet, outlet-side, outlet-top, and symmetry in the Face Zones
selection list.

2. Select Delete in the Options list.

3. Retain the Delete Nodes option and click Apply.
A Question dialog box will appear, asking you to conﬁrm if you want to delete the
selected zones.

4. Click Yes in the Question dialog box.

5. Select all the zones in the Face Zones selection list and click Draw.

6. Close the Manage Face Zones panel.

Step 3: Set the Hexcore Meshing Parameters

1. Enter 0.125 for Max Cell Length.

2. Retain the setting of both Buﬀer Layers and Peel Layers to 1.



3. Enable Deﬁne Hexcore Extents.
The Specify... button will be enabled.

4. Click the Specify... button to open the Outer Domain Parameters panel.

(a) Enable Coordinate Extents.



(b) Enter the domain extents as follows:
X Min = -2.5, Y Min = 0, Z Min = 0
X Max = 2.5, Y Max = 2, Z Max = 2
(c) Click Apply in the Coordinate Extents group box.
(d) Enable Draw Outer Box and click Draw.
(e) Click Apply and close the Outer Domain Parameters panel.

5. Enable Delete Dead Zones in the Zones group box.
Enabling Delete Dead Zones ensures that the volume mesh is not generated inside
the sedan body and the wheels, thereby making the meshing process faster.

6. Click Create.

7. Close the Hexcore panel.

8. Examine the mesh generated.
(a) Deselect the previous selections and select boundary in the Face Zone Groups
selection list.
(b) Click the Attributes tab and enable Filled and Lights in the Options group box.
(d) Select Color by ID in the Options list and close the Grid Colors panel.
(e) Display the back view.
i. Select back from the Views list.
ii. Click Apply and close the Views panel.
(f) Click Display in the Display Grid panel (Figure 6.2).
In Figure 6.2, you can see that the hex cells are generated upto the extents
of the domain deﬁned in the Hexcore panel. For easy recognition, the newly
created zones are named wall-x-max, wall-x-min, wall-y-max, etc.
(g) Zoom in to the region shown in Figure 6.3.
In Figure 6.3, you can see that the mesh on the boundaries is made up of hex
cells, except near the sedan.



Figure 6.2: Hexcore Mesh Upto Domain Boundaries

Figure 6.3: Hexcore Mesh Upto Domain Boundaries—Zoomed View



Step 4: Automatically Generate the Hexcore Mesh to the Boundaries with Prism
Layers
In this step, you will set parameters for creating prism layers on the sedan body and
ground, and for generating the hexcore mesh. The outer boundaries must be retained for
the prisms to attach onto them. You will use the automatic mesh generation procedure.

1. Read the mesh file (sedan-nonaligned.msh).
The mesh file contains the boundary mesh of the sedan as well as the outer box.
Note: In order to create the hexcore mesh up to selected boundaries, each boundary
should be separated by an angle of 90 degrees. For example, the auto-align tool
will not work if the tunnel wall and roof are in a single boundary zone. The
outer box in this tutorial constitutes individual zones separated by 90 degrees.
If you have a boundary mesh with the wind tunnel and roof in a single boundary
zone, you will need to separate the zones by an angle of 90 degrees or less using
the Separate Face Zones panel.
Boundary −→ Zone −→Separate...

2. Display the grid.

(a) Set the prism meshing parameters.
i. Click the Set... button in the Boundary Layer Mesh group box to open the
Prisms panel.
ii. Select car, ground, mirror, wheel-arch-front, wheel-arch-rear, wheel-front,
and wheel-rear in the Boundary Zones selection list.
iii. Select aspect-ratio in the Offset Method drop-down list and enter 5 for First
Aspect Ratio.
iv. Select geometric in the Growth Method drop-down list and enter 1.2 for
Rate.



v. Set Number of Layers to 5.
vi. Click Apply in the Zone Speciﬁc Growth group box.

vii. Click the Growth Options... button to open the Prisms Growth Options
panel.

A. Retain the Allow Shrinkage option in the Proximity Options group box.



B. Enter 200 for Max Aspect Ratio.
C. Click Apply and close the Prisms Growth Options panel.
viii. Click Apply and close the Prisms panel.
ix. Enable Prisms in the Boundary Layer Mesh group box in the Auto Mesh
panel.
(b) Set the hexcore meshing parameters.
i. Select Hexcore in the Volume Fill list and click the Set... button to open
the Hexcore panel.

ii. Enter 0.125 for Max Cell Length.
iii. Set Buffer Layers to 2.
Setting the number of buffer layers to 2 ensures smoother size variation.
iv. Set Peel Layers to 0 and click Apply.
The peel layer controls the gap between the hexahedra core and the ge-
ometry. The lower the peel layer specified, the fewer the tetrahedral cells
generated.
v. Enable Define Hexcore Extents.
The Specify... button will be enabled.
vi. Click the Specify... button to open the Outer Domain Parameters panel.



A. Enable Boundary Extents.
The Boundary Extents option is recommended over the Coordinate Ex-
tents option as the boundaries are explicitly deﬁned.
B. Select inlet, outlet, outlet-side, outlet-top, and symmetry in the Bound-
ary Zones selection list.
Note: The ground is not selected as prism layers will be grown from
the ground during the automatic mesh generation process.
C. Click Apply.
D. Enable Draw Outer Box and click Draw (see Figure 6.4).
In Figure 6.4, the outer box snaps to all the selected boundaries, except
the symmetry. This indicates that the symmetry zone is misaligned
with the axis, and the hexcore mesh cannot be grown to this boundary.
You need to align the symmetry zone to be able to grow the hexcore
mesh to the symmetry.
E. Select only symmetry in the Boundary Zones selection list and enable
Auto Align.
F. Click Compute in the Auto Align group box.
G. Retain the computed tolerance and click Apply in the Auto Align group
box.



Figure 6.4: Outer Box for the Hexcore Mesh

An Information dialog box will appear, informing you that the auto
align operation may deform the geometry permanently.
H. Click OK in the Information dialog box.
I. Deselect previous selections in the Boundary Zones list and click Select
to select the zones to which the hexcore mesh is to be generated.
J. Click Apply in the Outer Domain Parameters panel.
K. Make sure Draw Outer Box is enabled and click Draw (see Figure 6.5).
In Figure 6.5, the outer box snaps to the selected boundaries.

Figure 6.5: Outer Box for the Hexcore Mesh After Using Auto Align



L. Enable Delete Old Face Zones and click Apply.
The original outer box zones will be replaced by those created during
the hexcore meshing process.
M. Close the Outer Domain Parameters panel.
vii. Click the Tet Controls... button to open the Tet panel.
A. Retain the default settings in the Initialization tab.
B. Click the Refinement tab and retain the selection of geometric in the
Cell Size Function drop-down list.
C. Enter 1.3 for Growth Rate and click Apply.
D. Close the Tet panel.
viii. Define the local refinement region.
A. Click the Local Regions... button to open the Hexcore Refinement Re-
gion panel.

B. Enter wake for Name.
C. Set Level to 4.
The hexcore mesh is based on a Cartesian grid, hence, the maximum
length inside the local region is defined as a factor of the Max Length
Max Length
defined. The maximum length in the region is equal to .
2(level−1)
0.125
In this case, the Max Length is equal to (4−1) = 0.01562.
2
D. Enter (1, 0.5, 0.2) for Center and (1, 0.5, 0.5) for Length, respec-
tively.
E. Retain the default orientation.



F. Click Draw and check the region extents and maximum length within
the region.
G. Click Define to create the region.
H. Retain the selection of wake in the Regions selection list and click
Activate.
I. Close the Hexcore Refinement Region panel.
TGrid will report (in the Active field in the Hexcore panel) that there is
one active hexcore refinement region.
ix. Enable Delete Dead Zones in the Zones group box.
x. Enable Keep Hex Tet Separate.
Note: The Keep Hex Tet Separate option is used here primarily for better
visualization of the mesh.
xi. Click Apply and close the Hexcore panel.

(c) Click Mesh.
(d) Close the Auto Mesh panel.




(a) Deselect the previous selections and select car, ground, inlet, inlet-#, inlet-
quad:#, mirror, outlet, outlet-#, outlet-quad:#, outlet-side, outlet-side-#, outlet-
side-quad:#, outlet-top, symmetry, symmetry-#, symmetry-quad:#, wheel-arch-
front, wheel-arch-rear, wheel-front, and wheel-rear in the Face Zones selection
list.
Note: The boundaries have been separated by shape due to the separation of
the cell zones into different fluid regions. In order to obtain zone names
similar to those in the input mesh, enable Merge Cell Zones in the Auto
Mesh panel and disable Keep Hex Tet Separate in the Hexcore panel during
the setup.
(b) Click the Attributes tab and enable Filled and Lights in the Options group box.
(d) Select Color by ID in the Options list and close the Grid Colors panel.
(e) Display the back view.
(f) Click Display in the Display Grid panel.
(g) Display the refinement region along with the mesh.
i. Click the Local Regions... button in the Hexcore panel to open the Hexcore
Refinement Region panel.
ii. Make sure wake is selected in the Regions selection list and click Draw.
iii. Close the Hexcore Refinement Region panel.
In Figure 6.6, you can see that the hex cells are generated upto the selected
boundaries. You can also see the refinement region.
(h) Click the Bounds tab in the Display Grid panel and enable Limit by Z.
(i) Enter 0.37 for Minimum and Maximum in the Z Range group box.
(j) Click the Cells tab in the Display Grid panel and select all the zones in the Cell
Zones selection list.
(k) Enable All in the Options group box and click Display (Figure 6.7).
(l) Zoom in to the rear of the sedan (Figure 6.8).
(m) Zoom in to the region of the wheel/ground intersection (Figure 6.9).



Figure 6.6: Hexcore Mesh to Selected Boundaries




Figure 6.8: Hexcore Mesh to Selected Boundaries—Zoomed View

Figure 6.9: Hexcore Mesh to Selected Boundaries—Wheel/Ground Intersection



5. Display the mesh overlaid with a section of cells at x = -0.37 (Figure 6.10).
(a) Click the Bounds tab and click Reset.
(b) Deselect the ﬂuid zones in the Cell Zones selection list in the Cells tab of the
Display Grid panel.
(c) Select car, ground, mirror, symmetry, symmetry-#, symmetry-quad:#, wheel-
arch-front, wheel-arch-rear, wheel-front, and wheel-rear in the Face Zones selec-
tion list.
(d) Click Display.
(e) Enable the overlaying of graphics.
Display −→Scene...
i. Select all the zones in the Names selection list.
ii. Enable Overlays in the Scene Composition group box.
iii. Click Apply and close the Scene Description panel.
(f) Click the Cells tab in the Display Grid panel and make sure All is enabled in
the Options group box.
(g) Select the ﬂuid zones in the Cell Zones selection list.
(h) Enable Limit by X and enter -0.37 for both Minimum and Maximum in the X
Range group box.
(i) Click Display and zoom in as shown in Figure 6.10.

Figure 6.10: Hexcore Mesh to Selected Boundaries—Cells at x = -0.37

6. Check the mesh.
Mesh −→Check




8. Exit TGrid.
File −→Exit

Step 5: Generate the Hexcore Mesh to the Boundaries with Prism Layers Using
TUI Commands
This section demonstrates the use of a jounal ﬁle to generate the hexcore mesh to selected
boundaries. You will set parameters for creating prism layers on the sedan body and
ground, and for generating the hexcore mesh. The outer boundaries must be retained for
the prisms to attach onto them.

1. View the contents of the journal ﬁle (sedan hexcore to boundaries.jou) in a
viewer.
All lines starting with a semi-colon (;) indicate comments.

;Read the mesh file
/file/read-mesh sedan-nonaligned.msh.gz

;Display the grid
/display/boundary-grid * ,

;Specify the prism growth parameters
/mesh/prism/controls/zone-specific-growth/apply-growth car ground mirror
wheel-arch-front wheel-arch-rear wheel-front wheel-rear , aspect-ratio
geometric 5 5 1.2 no
/mesh/prism/controls/proximity/max-aspect-ratio 200

;Specify the hexcore meshing parameters
/mesh/hexcore/controls/maximum-cell-length 0.125
/mesh/hexcore/controls/buffer-layers 2
/mesh/hexcore/controls/peel-layers 0
;Hexcore to selected boundaries
/mesh/hexcore/controls/define-hexcore-extents? yes
/mesh/hexcore/controls/outer-domain-params/specify-boundaries? yes
;;Select the planar boundaries to which hexcore mesh is to be generated
/mesh/hexcore/controls/outer-domain-params/boundaries inlet outlet
outlet-side outlet-top symmetry ,
;;Use auto-align to axis-align the boundaries
/mesh/hexcore/controls/outer-domain-params/auto-align? yes
/mesh/hexcore/controls/outer-domain-params/auto-align-tolerance ,



/mesh/hexcore/controls/outer-domain-params/auto-align-boundaries
;;Make sure delete-old-face-zones is enabled
/mesh/hexcore/controls/outer-domain-params/delete-old-face-zones? yes
;Tet controls
/mesh/tet/controls/cell-size-function geometric 1.3
;Hexcore refinement region
/mesh/hexcore/local-regions/define "wake" 4 1 0.5 0.2 1 0.5 0.5 0 0 0
/mesh/hexcore/local-regions/activate "wake"
;Hexcore zones parameters
/mesh/hexcore/controls/delete-dead-zones? yes

;Generate the mesh
/mesh/auto-mesh yes pyramids hexcore yes no

;Examine the mesh
/display/boundary-grid car ground inlet* mirror outlet* outlet-side*
outlet-top symmetry* wheel-arch-front wheel-arch-rear wheel-front
wheel-rear ,
/display/set/filled-grid? yes
/display/set/lights/lights-on? yes
/display/set/colors/color-by-type? no
/display/set-grid/all-nodes? no
/display/set-grid/z-range 0.37 0.37
/display/set-grid/all-cells? yes
/display/all-grid fluid* ()
/display/view/restore-view back
/display/view/auto-scale

/mesh/check-mesh

2. Start a new TGrid session.

3. Read the journal ﬁle sedan hexcore to boundaries.jou.

Summary
This tutorial demonstrated the generation of a hexcore mesh upto the domain boundaries
for a sedan car. It also demonstrated the creation of prism layers and the use of local
reﬁnement regions in conjunction with the hexcore mesh generation.


Tutorial 7. Using the Boundary Wrapper

Introduction
Geometries imported from various CAD packages often contain gaps and/or overlaps
between surfaces. Repairing such geometries manually is a tedious and time-consuming
process. The boundary wrapper in TGrid can be used to repair such geometries auto-
matically, thereby reducing the time required for preprocessing.
The wrapping procedure is based on the Cartesian grid (or overlay grid) approach. Ini-
tially, a coarse Cartesian grid is overlaid on the input geometry and the intersection
between the Cartesian grid and the geometry is calculated. The intersecting cells are
identiﬁed and a watertight faceted representation is created along the boundary of these
cells. The nodes on the faceted representation are projected onto the input geometry
resulting in a wrapper surface that closely resembles the input geometry.


2. Perform pre-wrapping operations to close holes in the geometry.

3. Initialize the wrapper.

4. Check the region to be wrapped.

5. Reﬁne the Cartesian grid using the local size function.

6. Wrap the surface and imprint necessary features.

7. Check the deviation of the wrapper surface from the original geometry.

8. Perform post-wrapping operations to improve wrapper surface quality.

9. Create a tunnel encompassing the geometry and generate the volume mesh.

10. Improve the volume mesh quality using automatic node movement.

The V-8 engine geometry used in this tutorial is provided by Platinum Pictures Multi-
media Inc., www.3dcafe.com, and Michael Barthels.


Using the Boundary Wrapper

Prerequisites

Preparation
1. Copy wrapper.zip to your working directory.
2. Unzip wrapper.zip.
The files v8-airintake out.msh, v8-block out.msh, v8-cylinder-left out.msh,
v8-cylinder-right out.msh, v8-generator out.msh, v8-manfold out.msh,
v8-top-left out.msh, v8-top-right out.msh, and v8-wheels out.msh can be
found in the v8 folder created on unzipping the file.
3. Start TGrid.

1. Read the mesh files using a filter to select multiple files.



(a) Enter the filter string v8-*.msh in the Filter text box and click Filter.
(b) Click Select All to select the mesh files.
All the respective mesh files will now be added to the Mesh File(s) list.
(c) Click OK.
2. Display the mesh (Figure 7.1).
(a) Select all the zones in the Face Zones selection list.
(b) Click the Attributes tab and enable Filled and Lights in addition to the default,
Edges.
(d) Click the Rendering... button to open the Display Options panel.
i. Select All in the Animation Option drop-down list.
ii. Enable Double Buffering and Hidden Line Removal.
iii. Select Software Z-buffer in the Hidden Surface Method drop-down list.
iv. Click Apply and close the Display Options panel.
(e) Click Display in the Display Grid panel and rotate the geometry about the
x-axis to obtain the view shown in Figure 7.1.


You can save the view using the Views panel and restore the saved view when-
ever necessary.



Step 2: Perform Pre-Wrapping Operations to Close Holes in the Geometry
The geometry contains some large holes (holes signiﬁcantly larger than the mesh size
that will be used) which preferably should be manually closed before proceeding with the
wrapping operations. TGrid provides a variety of options for closing arbitrary openings
between zones, arbitrary openings in the same zone, coplanar openings, etc.
In this step, you will close the holes in the following zones:

• f v8-cylinder-left and f v8-cylinder-right (see Figure 7.2)

• f v8-airintake (see Figure 7.4)

• f v8-top-right (see Figure 7.7)

• f v8-top-left (see Figure 7.10)

1. Close the holes in the f v8-cylinder-left and f v8-cylinder-right zones.
(a) Select the f v8-cylinder-left and f v8-cylinder-right zones in the Display Grid
panel.
(b) Enable Free in the Options group box.
(c) Click Display and rotate the geometry to obtain the view shown in Figure 7.2.

Figure 7.2: Holes to be Closed in the f v8-cylinder-left and f v8-cylinder-right Zones

(d) Select the f v8-cylinder-left and f v8-cylinder-right zones in the display window
using the right-mouse button.
Here, zone is the default selection for Filter.



(e) Use the command /boundary/modify/repair to close the holes (Figure 7.3).
OR
Use the hot-key Ctrl+R to close the holes.
Figure 7.3 shows the holes closed in the f v8-cylinder-left and f v8-cylinder-right
zones.

Figure 7.3: Holes Closed in the f v8-cylinder-left and f v8-cylinder-right Zones

2. Close the holes in the f v8-airintake zone.
(a) Deselect the previously selected zones and select f v8-airintake in the Display
Grid panel.
(b) Disable Free and click Display. Rotate the geometry to obtain the view shown
in Figure 7.4.

Figure 7.4: Holes to be Closed in the f v8-airintake Zone



Four holes are visible in the f v8-airintake zone. You will close only three holes
in this step, the remaining hole will be closed later.

The remaining hole in the f v8-airintake zone will be closed in Step 4 after
! demonstrating the use of the Pan Regions and Trace Path features to detect
and trace a leak in the geometry.
(c) Zoom in to the region shown in Figure 7.5.
(d) Select node in the Filter list in the Modify Boundary panel.
OR
Use the hot-key, Ctrl+N to select node as the Filter.
(e) Select the three nodes surrounding the hole using the right mouse button
(Figure 7.5).
If you select the incorrect node(s), use Esc to deselect the last node selected or
use F2 to deselect all the previously selected nodes.

Figure 7.5: Nodes Selected to Close Hole-1 in f v8-airintake

(f) Click Create in the Operation group box.
OR
Use F5.
TGrid creates a face partially covering the hole, making the hole smaller than
the mesh size used in this tutorial (see Figure 7.6).



Figure 7.6: Closed Hole (Hole-1) in the f v8-airintake Zone

(g) Similarly, close the second and third holes (Hole-2 and Hole-3) in the f v8-
airintake zone.

You will close the remaining hole in Step 4.
!
3. Close the holes in the f v8-top-right zone.
(a) Select all the zones in the Display Grid panel and click Display.
(b) Select zone in the Filter list in the Modify Boundary panel (or use the hot-key,
Ctrl+Z).
(c) Select the f v8-top-right zone and click the Set Ranges button in the Bounds
tab of the Display Grid panel.
(d) Click Display and rotate the geometry to obtain the view shown in Figure 7.7.

Figure 7.7: Coplanar Holes in the f v8-top-right Zone



(e) Clear the Selections list in the Modify Boundary panel and select position in the
Filter list.
OR
Use F2 to clear the Selections list and the hot-key, Ctrl+X to select position as
the Filter.
(f) Select the six positions shown in Figure 7.8 using the right mouse button.
The positions should be selected in either clockwise or anticlockwise order.
(g) Click Create in the Operation group box (or use F5).
TGrid creates six boundary nodes at the selected positions. These nodes are
automatically selected in the Selections list.

Figure 7.8: Nodes Selected to Close Holes in the f v8-top-right Zone

(h) Retain the selection of the newly created nodes in the Selections list.
(i) Select zone in the Filter list and select the f v8-top-right zone (or use the hot-
key, Ctrl+Z).
(j) Select node in the Filter list (hot-key, Ctrl+N) and click Create (or use F5).



Figure 7.9: Holes Closed in the f v8-top-right Zone

4. Close the holes in the f v8-top-left zone by creating a plane surface.
(a) Click Reset in the Bounds tab in the Display Grid panel.
(b) Display the grid.
(c) Select zone in the Filter list in the Modify Boundary panel (or use the hot-key,
Ctrl+Z).
(d) Select the f v8-top-left zone and click the Set Ranges button in the Bounds tab
of the Display Grid panel.
(e) Click Display and rotate the geometry to obtain the view shown in Figure 7.10.

Figure 7.10: Coplanar Holes in the f v8-top-left Zone



(f) Create a plane surface to cover the coplanar holes.
Boundary −→ Create −→Plane Surface...

i. Select Points in the Options list.
ii. Click Select Points... to select the points defining the plane surface.
iii. Select three points to define a plane using the right mouse button (Fig-
ure 7.11).
Select the two points along the longest side first. The coordinates of the
three selected points will be updated in the Planar Points group box.

Figure 7.11: Selection of Points for Creating the Plane Surface

iv. Enter 5 for Edge Length.
v. Click Create.



The Zone Type panel will open, displaying the default entry for Zone Name.

vi. Click OK in the Zone Type panel.
The newly created zone (wall-#, where # is the zone ID) will be added to
the Face Zones selection list.
vii. Close the Plane Surface panel.
(g) Merge the newly created zone (wall-#) with the f v8-top-left zone using the
Larger Area option.
The name of the zone having a larger area will be retained after merging the
zones.
i. Select f v8-top-left and wall-# in the Face Zones selection list.

ii. Select Merge in the Options list.
iii. Select Larger Area in the Merge Options list and click Apply.
The wall-# zone will be merged with the f v8-top-left zone.



iv. Close the Manage Face Zones panel.
(h) Click Display in the Display Grid panel to see the recently closed holes (Fig-
ure 7.12).

Figure 7.12: Holes Closed in the f v8-top-left Zone Using a Plane Surface

5. Save the mesh (engine.msh.gz).

Step 3: Initialize the Surface Wrapper
The accuracy of the wrapper depends on the cell size distribution of the Cartesian grid.
TGrid allows you to specify the cell size of the Cartesian grid according to your require-
ment. Finer cells give better results, but also increase the computational time.
The Min Length is the minimum allowable cell size in the Cartesian grid. In this case,
the targeted Min Length is 5 mm. This is achieved by setting the Default Length to 40
and the Min Length Level to 4.
Boundary −→Wrap...

1. Enter 40 for Default Length and press <Enter>.

2. Enable Proximity and Curvature in the Global Size Function group box.

3. Enable Ignore Self Proximity and increase Buﬀer Layers to 3 in the Options group
box.



4. Click Init.
TGrid will create a Cartesian hanging node grid and reﬁne it based on the deﬁned
size functions. The grid will then be intersected with the geometry, thereby creating
a number of Cartesian closed regions. TGrid will report the regions created.

Step 4: Check the Region to be Wrapped
1. Click Reset in the Bounds tab of the Display Grid panel.

2. Click the Region tab in the Boundary Wrapper panel.



3. Retain the selection of region:1 and click Draw in the Region group box to draw the
largest region.
Figure 7.13 shows the region to be wrapped.

Figure 7.13: Region to be Wrapped



4. Pan the region to examine grid distribution and to search for holes.
(a) Display the entire geometry.
(b) Click the Pan Regions... button in the Region tab of the Boundary Wrapper
panel to open the Pan Regions panel.

i. Enable Overlay Graphics.
ii. Move the slider bar to position the pan plane as shown in Figure 7.14
(Value ≈ 28).
You may need to switch between Positive and Negative to view the geometry
on either side of the pan plane.

Figure 7.14: Pan Plane with the Overlaid Geometry



iii. Zoom in to the region of the leak (Figure 7.15).

Figure 7.15: Region of the Leak

The presence of the main region color on the inside (Figure 7.14) is an
indication of a possible leak. In this case, the remaining hole in the f v8-
airintake zone has caused this leak. You can switch between Positive and
Negative to ﬂip the geometry, if required.
iv. Disable All in the Region group box and set Region to 1 (see Figure 7.16).
(c) Use the Trace Path feature to detect the leakage.
i. Click the Trace Path... button in the Region tab of the Boundary Wrapper
panel to open the Trace Path panel.

ii. Click the Select Points... button and select two points as shown in Fig-
ure 7.16.
iii. Click Trace (Figure 7.17).



Figure 7.16: Detecting the Leakage using the Trace Path Panel

Figure 7.17: Display of Geometry with the Traced Path



The trace path is displayed by coloring all the faces in the path.
You may need to switch between Positive and Negative in the Pan Regions
panel to obtain the display in Figure 7.17.
iv. Zoom in to the hole and select three nodes as shown in Figure 7.18.

Figure 7.18: Nodes Selected to Close the Hole in the f v8-airintake Zone

v. Click Create in the Modify Boundary panel or use the hot-key F5 to close
the hole.

5. Select all the geometry in the Tri Boundary Zones selection list in the Boundary
Wrapper panel.

6. Click Update Regions in the Region tab to update the region based on the newly
added face (see Figure 7.19).

Figure 7.19: Region Updated for the Closed Hole



There are no more big leakages in the geometry. You will however see later that
there are leakages having size smaller than 5 mm but bigger than 2.5 mm.

7. Close the Pan Regions and Trace Path panels.

Step 5: Refine the Main Region
1. Refine the Cartesian grid using the Local Size Function.
(a) Enable Proximity and Curvature in the Local Size Function group box in the
Face Size tab of the Boundary Wrapper panel.
(b) Set Level to 5 in the Local Size Function group box.
(c) Select all the surfaces in the Tri Boundary Zones selection list.
(d) Click Apply in the Local Size Function group box.

(e) Click Refine.
After refining the region, region:1 is now much finer as seen in Figure 7.20.



Figure 7.20: Region After Reﬁning Using Local Size Function

The minimum edge length is now reduced to 2.5 mm, smaller than some leak-
ages. Even though the edge length is now smaller than the leakages, no regions
will be subdivided. The cells at the potential holes will be marked and labeled
as a “hole”.

Step 6: Close Small Holes Automatically
In this step, you will retain and automatically ﬁx all the potential holes for region:1.

1. Set Region to 1 and click Select in the Fix Holes group box in the Region tab of the
Boundary Wrapper panel.
All the potential holes created for region:1 will be selected in the Automatic selection
list.

2. Deselect the previously selected zones in the Face Zones selection list in the Faces
tab of the Display Grid panel.

3. Click Display.
This will allow you to display only the potential holes.



4. Click Draw in the Fix Holes group box in the Region tab of the Boundary Wrapper
panel (Figure 7.21).

Figure 7.21: Potential Holes in region:1

5. Examine the potential holes.
(a) Click First in the Fix Holes group box.



The display will be limited to the vicinity of the first selected hole in the Auto-
matic selection list. The First button will be replaced by Next.
(b) Click Next to view the next selected hole.
(c) Click Next repeatedly to successively display the selected holes.
Figures 7.22 shows examples of holes in the wrapper region.

Figure 7.22: Display of Holes

You will now fix the holes using the automatic hole fixing option.

6. Fix the holes in region:1.
(a) Retain the selection of the holes for region:1 in the Automatic selection list in
the Region tab of the Boundary Wrapper panel.
(b) Click Fix in the Fix Holes group box in the Region tab in the Boundary Wrapper
panel.
(c) Select all the zones in the Face Zones selection list in the Display Grid panel.
(d) Click Display (Figure 7.23).
Figure 7.23 shows the holes closed by the automatic hole fixing operation.
Note: For bigger models having a large number of holes, this step may be omitted
as the time taken may be considerable, as well as some of the “holes” might
not be real holes. In this case, though the initial wrapper surface may have
more cells having higher skewness, the final mesh would have similar quality
as the corresponding mesh with all the holes fixed.



Figure 7.23: Holes Fixed Using the Automatic Hole Fixing Option

Step 7: Wrap the Main Region
1. Select region:1 in the Region list in the Region tab of the Boundary Wrapper panel.

2. Click Wrap.
A Question dialog box will appear, asking if you want to delete all the regions.
Deleting the regions will reduce the peak memory.

3. Click Yes in the Question dialog box.
TGrid will create the wrapper surface for region:1, wrapper-surf-#, which will be
available in the Tri Boundary Zones selection list.

4. Display the wrapper surface (Figure 7.24).

Figure 7.24: Wrapper Surface



You may need to manipulate the display in the graphics window to obtain the view
shown in Figure 7.24.

5. Save the mesh ﬁle (engine00.msh.gz).

Step 8: Capture Features
1. Click the Features tab in the Boundary Wrapper panel.

2. Select all the geometry whose features are to be captured in the Tri Boundary Zones
selection list.
Note: Make sure that the patched holes (zones with the vs preﬁx) and the wrapper
surface are not selected in the Tri Boundary Zones list.

3. Click Extract Features.
The extracted features will now be available in the Edge Zones selection list.

4. Select all the zones in the Edge Zones selection list and click Draw (below the Edge
Zones selection list).
You can reproject the wrapper surface onto the important features extracted. If the
extracted features include details which are not required (e.g., embossed company
logos, etc.), they may be deleted before proceeding with the imprinting.

5. Draw the edge zones individually to determine the important features required for
imprinting.



6. Select the unnecessary edge zones in the Edge Zones selection list in the Boundary
Wrapper panel.

7. Click the Draw button below the Edge Zones selection list (Figure 7.25).

Figure 7.25: Insigniﬁcant Features to be Deleted

8. Click Delete to delete the insigniﬁcant features.

9. Select only the wrapper surface (wrapper-surf-#) in the Tri Boundary Zones selection
list and click Draw.
Zoom in to the region shown in Figure 7.26.

10. Select all the features to be imprinted in the Edge Zones selection list and click
Draw.

11. Click the Reports tab in the Boundary Wrapper panel and click Draw Contours.
In this case, you will use the contours of wrapped surface quality to verify the
imprinting of features.

12. Retain the selection of the wrapper surface and all the features to be imprinted in
the Tri Boundary Zones and Edge Zones selection lists, respectively.



13. Click Imprint.

14. Display the wrapper surface to see the eﬀect of imprinting.

15. Click Draw Contours in the Reports tab of the Boundary Wrapper panel.

16. Retain the selection of the wrapper surface in the Tri Boundary Zones selection list
and the features to be imprinted in the Edge Zones selection list in the Features
tab.

17. Click Imprint again.
Figure 7.26 shows the wrapper surface and contours of distance before and after
imprinting.



Figure 7.26: Wrapper Surface and Contours of Distance During Imprinting

Step 9: Post Wrapping Operations
1. Click the Post Improve tab of the Boundary Wrapper panel.

2. Coarsen the wrapper surface.
(a) Retain the selection of Coarsen in the Options drop-down list.
(b) Retain the value of 2 for Edge Length Change and enter 10 for Max Angle
Change, respectively.



(c) Retain the value of 0 for Min Length and enter 5 for Max Length.
(d) Click Apply.

Figure 7.27: Wrapper Surface (A) Before and (B) After Coarsening

(e) Save the mesh (engine-01.msh.gz).



3. Use the automated post wrapping option to improve the wrapper surface.
(a) Retain the selection of the wrapper surface in the Tri Boundary Zones selection
list.
(b) Select Post Wrap in the Options drop-down list and Auto Post Wrap in the Sub
Options list.

(c) Enter 0.5 for Critical Thickness.
The value speciﬁed is 20% of the minimum size (2.5 mm).
(d) Retain the default settings for the remaining parameters and click Apply.
The Auto Post Wrap option will perform all the remaining post wrapping op-
erations in an optimal order to provide a valid surface mesh of as good quality
as possible, without destroying any features.

4. Save the mesh (engine-02.msh.gz).

5. Extract zones based on the geometry.
(a) Retain the selection of the wrapper surface in the Tri Boundary Zones selection
list.



(b) Select Zone in the Options drop-down list and Recover Zone in the Sub Options
list.
(c) Click Apply (Figure 7.28).

Figure 7.28: Wrapper Surface (A) Before and (B) After Recovering Zones

The wrapper surface will be separated into zones based on the zones in the
original geometry. The extracted wrapper zones will be preﬁxed by wrap-.



(d) Select the extracted wrapper surfaces in the Tri Boundary Zones selection list.

(e) Retain the selection of Zone in the Options drop-down list and select Rezone
in the Sub Options list.
(f) Retain the Reprojection option in the Parameters group box.
(g) Click Apply (Figure 7.29).

Figure 7.29: Wrapper Surface (A) Before and (B) After Rezoning



(h) Save the mesh (engine-03.msh.gz).

6. Merge the small area face zones with the neighboring zones using TUI commands:
> boundary/merge-small-face-zones
Minimum area [0.01] 500

Merged wrap-vs_f_v8-airintake:# with v8-airintake:#
Merged wrap-vs_f_v8-block:# with v8-block:#
Merged 2 zones

7. Plot the face skewness distribution in the range 0.8 to 1.0.

(a) Select wrapper in the Boundary Zone Groups selection list to select all the
wrapper zones in the Boundary Zones selection list.
(b) Enter 0.8 for Minimum.
(c) Click Plot (Figure 7.30).
(d) Close the Face Distribution panel.



Figure 7.30: Face Skewness Distribution Between 0.8 and 1.0 (Before Auto Post Improve)

8. Improve the wrapper surfaces using the Auto Post Improve option.

(a) Select Expert in the Options drop-down list and Auto Post Improve in the Sub
Options list.
(b) Enter 0.05 for Min Triangle Area.
Note: All cells having area smaller than the specified value will be removed.
Hence, it is suggested to first find the smallest triangle area before speci-
fying the value.



Report −→Face Limits...

i. Select wrapper in the Face Zone Groups list to select all the wrapper
zones.
ii. Select Size in the Options list.
iii. Click Compute.
iv. Close the Report Face Limits panel.
The value speciﬁed for Min Triangle Area is approximately 10 times the
minimum size reported.
(c) Enter 0.9 for Max Skewness and 10 for Max Size Change, respectively.
(d) Click Apply.
(e) Plot the face skewness distribution in the range 0.8 to 1.0 (Figure 7.31).

Figure 7.31: Face Skewness Distribution Between 0.8 and 1.0 (After First Auto Post
Improve)



In Figure 7.31, you can see that there are no faces above 0.9.
(f) Enter 0.1 for Min Triangle Area and 0.8 for Max Skewness, respectively.
(g) Click Apply.
The worst skewness reported is now below 0.8.
9. Save the mesh (engine-04.msh.gz).
10. Delete the original geometry.
(a) Select the original geometry and patched holes in the Face Zones selection list.
(b) Select Delete in the Options list and click Apply.
A Question dialog box will appear, asking you to conﬁrm if you want to delete
the selected zones.
(c) Click Yes in the Question dialog box.
(d) Close the Manage Face Zones panel.
11. Rename the wrapper surfaces.
(a) Select the wrapper zones in the Tri Boundary Zones selection list in the Bound-
ary Wrapper panel.
(b) Select Zone from the Options drop-down list and Rename in the Sub Options
list.



(c) Enter wrap-f in the From field.
Leave the To field blank so that the prefix will be removed.
(d) Click Apply.

12. Close the Boundary Wrapper panel.

Step 11: Create the Tunnel
Boundary −→ Create −→Bounding Box...

1. Select all the surfaces in the Face Zones selection list and click Compute.

2. Select Relative in the Method list.

3. Enter the values for the extents of the bounding box as shown in the Bounding Box
panel.

4. Click Create.
The Zone Name panel will open.

5. Enter tunnel for Zone Name and click OK.

6. Close the Bounding Box panel.

Disable Filled in the Attributes tab of the Display Grid panel and Hidden Line Removal
in the Display Options panel to obtain the display shown in Figure 7.32.



Figure 7.32: Mesh with the Tunnel

Step 12: Generate the Volume Mesh

1. Retain the selection of Tet in the Volume Fill group box and click the Set... button



(a) Enable Delete Dead Zones in the Tet Zones group box.
(b) Click Apply and close the Tet panel.

2. Click Mesh in the Auto Mesh panel.

3. Close the Auto Mesh panel.

4. Check the quality of the volume mesh (Figure 7.33).

Figure 7.33: Cell Quality Distribution

5. Plot the skewness distribution above 0.95 (Figure 7.34).

Figure 7.34: Cell Quality Distribution Above 0.95



Step 13: Improve the Volume Mesh
In this step, you will attempt to improve the volume mesh such that the maximum skew-
ness is around 0.95.
Mesh −→ Tools −→Auto Node Move...


2. Click Apply in the Auto Correction group box.

3. Check the skewness distribution above 0.95.

4. Enter 0.95 for Quality Limit and 0 for Dihedral Angle, respectively.

5. Disable Restrict Boundary Nodes Along Surface.

6. Click Apply in the Auto Correction group box.
The maximum skewness reported is around 0.95, which is acceptable.

7. Close the Auto Node Move panel.



Step 14: Separate the Tunnel Inlet and Outlet
Boundary −→ Zone −→Separate...

1. Select Seed in the Options list.

2. Enter 20 for Angle.

3. Select the seed face as shown in Figure 7.35.

Figure 7.35: Seed Face for Separating the Tunnel Inlet

4. Click Separate.
TGrid will create the zone tunnel-#, where # is the zone ID.



5. Rename tunnel-# to inlet.
(a) Select tunnel-# in the Face Zones selection list.
(b) Select Rename in the Options list.
(c) Enter inlet for Name and click Apply.

6. Similarly, separate the tunnel outlet and rename it to outlet.

7. Save the mesh (engine-final.msh.gz).

8. Exit TGrid.

Summary
This tutorial demonstrated the wrapping procedure for a V-8 engine mesh. You ini-
tially performed pre-wrapping operations to close large holes in the geometry. You then
initialized the wrapper, examined the region to be wrapped and updated the region to
account for the fixed leakage. The tutorial also demonstrated the use of the automatic
hole fixing functionality to close smaller holes detected when refining the Cartesian grid
using local size functions. After wrapping the main region, and imprinting necessary fea-
tures of the geometry, you performed post-wrapping operations to improve the wrapper
surface quality. You then created a tunnel encompassing the geometry and generated the
volume mesh. The tutorial also described the procedure for using the Auto Node Move
functionality to improve the quality of the volume mesh.


Tutorial 8. CutCell Mesh Generation

Introduction
CutCell meshing is a general purpose meshing technique which is suitable for a large
range of applications. Due to the large fraction of hex cells in the generated mesh, the
CutCell mesh can often produce better results than regular tetrahedral meshes. This
meshing method uses a direct surface and volume approach without needing cleanup or
decomposition, thereby reducing the turn-around time required for meshing. The tutorial
demonstrates the generation of the CutCell mesh for a manifold.


2. Define CutCell objects.

3. Define the sharp features.

4. Define size functions.

5. Create the CutCell mesh.

6. Set parameters and generate prisms for the CutCell mesh.

7. Improve the CutCell mesh quality.

Prerequisites

Preparation
1. Copy cutcell.zip to your working directory.


CutCell Mesh Generation

2. Unzip cutcell.zip.
The file auto manifold-NS.tgf.gz can be found in the cutcell folder created on
unzipping the file.

3. Start TGrid.

1. Read the mesh file auto manifold-NS.tgf.gz.
This file has been created using the TGrid faceted export from ANSYS Meshing.
Named selections have already been created in ANSYS Meshing to indicate the inlets
and outlets.

(a) Select auto manifold-NS.tgf.gz in the Files list.
(b) Click OK.



(a) Select all the zones in the Face Zones selection list and click Display (Fig-
ure 8.1).


(b) Display all the zones containing the string :ﬂuid (Figure 8.2).

Figure 8.2: Grid Display–Fluid Body

(c) Display the grid with free nodes.
i. Select all the zones in the Face Zones selection list.
ii. Enable Free and click Apply.
You will try to improve the connectivity of the geometry using operations like
node merging and faceted stitch in Step 2.



Step 2: Improve the Connectivity of the Geometry
Note: This step may be omitted if the features to be recovered already exist in the initial
mesh ﬁle.

1. Merge the free nodes in the geometry.

(a) Retain the default selections and Tolerance set in the Merge Boundary Nodes
panel.
(b) Click Merge.
(c) Display the grid (Figure 8.3).

Figure 8.3: Grid Display–After Merging Free Nodes



(d) Close the Merge Boundary Nodes panel.

2. Use the faceted stitch operation.
Boundary −→ Mesh −→Faceted Stitch...

(a) Select all the zones in the Tri Boundary Zones selection list.
(b) Enter 0.005 for Tolerance.
(c) Click Stitch.
(d) Display the grid (Figure 8.4).

Figure 8.4: Free Nodes After Using Faceted Stitch



Note: Few free nodes still remain, however, it is not necessary to have a fully
connected model as a prerequisite for generating the CutCell mesh.

Step 3: Generate the CutCell Mesh
Mesh −→CutCell...

1. Deﬁne the volume objects.
(a) Click the Deﬁne Volume Objects... button to open the CutCell Objects panel.



(b) Define the volume object for the solid region.
i. Select gb:1-part:solid and gb:1-part:solid-gb:6103-part:fluid in the Tri Bound-
ary Zones selection list.
ii. Select solid in the Cell Zone Type drop-down list.
iii. Retain the other settings and click Create.
The volume object cutcell-solid-3:1 will be created, and will be available in
the Volume Objects selection list.
(c) Define the volume object for the fluid region.
i. Select all zones except gb:1-part:solid in the Tri Boundary Zones selection
list.
ii. Select fluid in the Cell Zone Type drop-down list.
iii. Set the Priority to 4.
iv. Click Create.
The volume object cutcell-fluid-4:2 will be created, and will also be available
in the Volume Objects selection list.
(d) Close the CutCell Objects panel.

2. Define the features to be captured.
(a) Click the Define Sharp Features... button to open the Feature Modify panel.

The zones appearing in the Edge Zones selection list are the original CAD
features, which in most cases, is a superset of the features that need to be
captured.



(b) Select all the zones in the Edge Zones selection list and click Delete to delete
the original CAD features.

(c) Select gb:1-part:solid and gb:1-part:solid-gb:6103-part:ﬂuid in the Face Zones
selection list.
(d) Retain the selection of Create in the Options list.
(e) Enter 60 for Angle.
Note: The lower the angle specﬁed, the more features captured.
(f) Click Apply to extract the features.
(g) Select all the zones in the Edge Zones list.
(h) Ensure that Draw Edges is enabled and click Draw (Figure 8.5).

Figure 8.5: Features to be Captured



(i) Close the Feature Modify panel.

3. Define the size functions.
(a) Click the Define Size Functions... button to open the Size Functions panel.
(b) Set the global size controls.
i. Enter 3 for Min Size and 12 for Max Size, respectively.
ii. Enter 1.3 for Growth Rate.
iii. Click Apply in the Global Controls group box.

(c) Define the curvature size function.
i. Select gb:1-part:solid and gb:1-part:solid-gb:6103-part:fluid in the Boundary
Zones selection list.
ii. Ensure that curvature is selected in the Size Function Type drop-down list.



iii. Retain the default settings for the curvature size function parameters and
click Add.
(d) Deﬁne the edge proximity size function.
i. Enable Edge Zones in the Specify Zones group box.
ii. Select all the zones in the Edge Zones selection list.

iii. Select proximity in the Size Function Type drop-down list.
iv. Set the Cells Per Gap to 3.
v. Retain the other settings and click Add.
(e) Close the Size Functions panel.



4. Set the parameters for mesh quality improvement.
For a relatively simple model like this, the mesh can be improved beyond the quality
set as default. You will thus modify the improve parameters, specifying a tighter
quality limit for the node movement operation.

> /mesh/cutcell/set/set-post-snap-parameters
Quality limit for Auto Node Move [0.85] 0.75 <Enter>
Iterations for Auto Node Move [1] <Enter>
Iterations per node in Auto Node Move [50] <Enter>
Restrict nodes on surfaces [yes] <Enter>
Dihedral angle for sharp feature angle [120] <Enter>
Quality limit for cavity remeshing [0.9] <Enter>

5. Click Create in the CutCell panel.

(a) Display the surface mesh.
i. Select all the zones preﬁxed by cutcell-boundary and cutcell-contact in the
Face Zones selection list.
ii. Ensure that Free is disabled in the Options group box.
iii. Click Display (Figure 8.6).

Figure 8.6: CutCell Surface Mesh



(b) Display a section through the solid and ﬂuid at Z = -50 overlaid with the
surface mesh.
i. Retain the selected zones and click Compute in the Bounds tab of the
Display Grid panel.
ii. Disable Limit by X and Limit by Y.
iii. Enter -50 for Maximum in the Z Range group box and click Display.
iv. Enable the overlaying of graphics.
A. Select all the zones in the Names selection list.
B. Enable Overlays in the Scene Composition group box.
C. Click Apply and close the Scene Description panel.
v. Click the Cells tab in the Display Grid panel and enable All in the Options
group box.
vi. Select all the cell zones in the Cell Zones selection list.
vii. Enter -50 for Minimum and retain the value of -50 for Maximum in the Z
Range group box in the Bounds tab.
viii. Click Display (Figure 8.7).

Figure 8.7: CutCell Mesh–Section at Z = -50



Step 4: Post CutCell Meshing Cleanup Operations
1. Delete all initial and temporarily created boundary zones and nodes.

> /boundary/delete-unused-faces

removed 33276 boundary faces.

> /boundary/delete-unused-nodes

removed 20185 nodes.

2. Rename the CutCell boundary zones.

(a) Select all the zones prefixed by cutcell-boundary in the Face Zones selection
list.
(b) Select Rename in the Options list.
(c) Enable Change Prefix.
(d) Enter cutcell-boundary- in the From field.
Leave the To field blank so that the prefix will be removed.
(e) Click Apply.



3. Rename the CutCell contact zone.
You will rename the contact zone to prisms as prism layers will be created on this
zone in Step 5.
(a) Select the zone prefixed by cutcell-contact in the Face Zones selection list.
(b) Retain the selection of Rename in the Options list.
(c) Disable Change Prefix.
(d) Enter prisms in the Name field.
(e) Click Apply and close the Manage Face Zones panel.

4. Save the volume mesh.

Step 5: Generating Prisms for the CutCell Mesh
1. Set the environment for post volume mesh prism generation.

> (set-post-mesh-controls!)

This short-cut sets a specific set of defaults which are particularly suited for prism
generation for the CutCell mesh. For details of the relevant commands included,
please refer to Section 13.8: Generating Prisms For the CutCell Mesh in the TGrid
User’s Guide.
Note: For more complex geometries, it is also recommended to include layer by
layer smoothing (using the command /mesh/prism/controls/cell-quality-improve?)
during the prism generation.

2. Set the prism parameters for the prisms zone.
(a) Select prisms in the Boundary Zones selection list.
(b) Select aspect-ratio in the Offset Method drop-down list.
(c) Select geometric in the Growth Method drop-down list.



(d) Enter 5 for First Aspect Ratio.
(e) Set Number of Layers to 5.
(f) Enter 1.2 for Rate.
(g) Click Apply in the Zone Speciﬁc Growth group box.
(h) Click Apply and close the Prisms panel.

3. Create the prism layers using the following command:

> /mesh/cutcell/create-prism
()
Cell Zones(1) [()] cutcell-fluid* <Enter>
Gap Factor [2] 1 <Enter>

Note: You can check the quality of the prism cells (using the Report Cell Limits
panel). If the quality of the prism cells is low, you can use post-prism smooth-
ing to improve the quality.
/mesh/prism/improve/smooth-improve-prism-cells

4. Improve the mesh quality.
Again, the mesh quality can be improved beyond the smoothing quality limits set as
default. You will modify the improve parameters, specifying a tighter quality limit
for the node movement operation.



(a) Set the parameters for mesh quality improvement.

> /mesh/cutcell/set/set-post-morph-parameters
Quality limit for Auto Node Move [0.9] 0.75 <Enter>
Iterations for Auto Node Move [1] <Enter>
Iterations per node in Auto Node Move [50] <Enter>
Restrict nodes on surfaces [yes] no <Enter>
Dihedral angle for sharp feature angle [120] <Enter>
Quality limit for cavity remeshing [0.95] <Enter>

Note: The prism cap in this case is an internal boundary zone, and hence,
you can allow full freedom of node movement to improve quality.
(b) Improve the mesh quality using the following command:

> /mesh/cutcell/modify/post-morph-improve
()
Cell Zones(1) [()] cutcell* <Enter>
()
Face Zones(1) [()] *cap* <Enter>
Face Zones(2) [()] <Enter>

(c) Check the cell distribution above 0.7.
ii. Click the Quality Measure... button and set the quality measure to Or-
thoskew.
iii. Click Plot in the Cell Distribution panel (Figure 8.8).
There are around 27 cells with a quality above 0.7. The worst cell quality
is around 0.75.



Figure 8.8: CutCell Mesh Quality—Cell Distribution Above 0.7

(d) Display a section through the solid and ﬂuid at Z = -50 overlaid with the
surface mesh.
i. Select all the boundary zones in the Face Zones selection list.
ii. Click Compute in the Bounds tab of the Display Grid panel.
iii. Disable Limit by X and Limit by Y.
iv. Enter -50 for Maximum in the Z Range group box and click Display.
v. Enable the overlaying of graphics.
A. Select all the zones in the Names selection list.
B. Enable Overlays in the Scene Composition group box.
C. Click Apply and close the Scene Description panel.
vi. Click the Cells tab in the Display Grid panel and enable All in the Options
group box.
vii. Select all the cell zones in the Cell Zones selection list.
viii. Enter -50 for Minimum and retain the value of -50 for Maximum in the Z
ix. Click Display (Figure 8.7).



Figure 8.9: CutCell Mesh With Prisms

(e) Save the case ﬁle.
File −→ Write −→Case...

i. Enable Write As Polyhedra.
Note: The case will not produce a valid mesh in ANSYS FLUENT without
the Write as Polyhedra option due to hanging node conﬁgurations on



the internal boundary between the solid and the fluid cell zones. This
may be elimianated using a fixed size on this boundary.
ii. Enter auto manifold.cas.gz for Case File and click OK.

5. Exit TGrid.

Summary
This tutorial demonstrated the procedure for generating the CutCell mesh for a manifold.
You defined the CutCell objects, sharp features to be extracted, and size functions for the
CutCell mesh. You then created and examined the CutCell mesh, and performed a few
cleanup operations. Further, you set parameters and generated prisms for the CutCell
mesh. The tutorial also demonstrated the improvement of the CutCell mesh after prism
generation, and finally saving the file for use in ANSYS FLUENT.


Tutorial 9. Cavity Remeshing

Introduction
Cavity remeshing is useful in parametric studies as it allows you to add, remove, or
replace different parts of an existing mesh. This tutorial demonstrates the procedure for
replacing an object in the existing mesh with another by creating a cavity and remeshing
it. This tutorial demonstrates how to do the following:

1. Create and remesh a cavity to replace the mirror in a tetrahedral mesh.

2. Create and remesh a cavity in a hybrid mesh (tetrahedra and prisms) having a
single fluid zone.

3. Create and remesh a cavity in a hybrid mesh (tetrahedra and prisms) having mul-
tiple fluid zones.

4. Create and remesh a cavity in a hexcore mesh.

Prerequisites

Preparation
1. Copy cavity.zip to your working directory.

2. Unzip cavity.zip.
The files, sedan tetra.msh.gz, sedan hyb-1zone.msh.gz, sedan hyb-2zones.msh.gz,
sedan hexcore.msh.gz, mirror.msh.gz, and sedan hyb-2zones-cavity.jou can
be found in the cavity folder created on unzipping the file.

3. Start TGrid.


Cavity Remeshing

Case A. For a Tetrahedral Mesh
Step 1: Read and Display Mesh
(a) Select sedan tetra.msh.gz in the Files list.
(b) Click OK.

(a) Select car, mirror-old, wheel-arch-front, wheel-arch-rear, wheel-front, and wheel-
rear, in the Face Zones selection list.
(b) Click Display (Figure 9.1).

Figure 9.1: Boundary Mesh

(c) Click the Cells tab and enable All in the Options group box.
(d) Select ﬂuid in the Cell Zone Groups selection list.
(e) Click the Bounds tab and enable Limit by X in the X Range group box.
(f) Enter -0.37 for both Minimum and Maximum in the X Range group box.
(g) Click Display.


Cavity Remeshing

(h) Display the left view.
i. Select left in the Views list.
ii. Click Apply and close the Views panel.
(i) Zoom in and examine the mesh around the mirror (Figure 9.2).
The mesh comprises tetrahedral cells.

Figure 9.2: Tetrahedral Mesh Near the Mirror

Step 2: Import and Connect the New Mirror
In this step, you will replace the mirror (mirror-old) by a modiﬁed geometry. The node
distribution on the boundary on the two mirrors is identical.

1. Read the mesh ﬁle (mirror.msh.gz).
(a) Enable Append File(s).
(b) Select mirror.msh.gz in the Files list and click OK.

2. Verify that the new mirror is appropriately positioned.
(a) Select car, mirror, and mirror-old in the Face Zones selection list in the Faces
tab.


Cavity Remeshing

(b) Enable Free and Multi in the Options group box.
Make sure that the ﬂuid zone is deselected in the Cell Zones selection list in
the Cells tab. Click Reset in the Bounds tab.
(c) Click Display (Figure 9.3).

Figure 9.3: Free Nodes on the Mirror

In Figure 9.3, you can see the free nodes on the boundary of mirror. This
indicates that the mirror is not connected to the car.

3. Connect the mirror to the car.


Cavity Remeshing

(a) Select only car in the Boundary Face Zones selection list in the Compare... group
box and disable Only Free Nodes.
(b) Select only mirror in the Boundary Face Zones selection list in the With... group
box and retain Only Free Nodes.
(c) Enable Percent of shortest connected edge length and enter 10 for Tolerance.
(d) Click Merge.
(e) Click Display in the Display Grid panel.

Figure 9.4: Multiply Connected Nodes on the Mirror

In Figure 9.4, you can see that there is a multiple connection between the
mirrors and the car.
(f) Close the Merge Boundary Nodes panel.

Step 3: Replace the Mirror
In this step, you will replace the existing mirror with a new one, without resetting the
volume mesh. To do this, you will remove a portion of the mesh around the mirror.

1. Replace the mirror.


Cavity Remeshing

Mesh −→ Tools −→Cavity Remesh...

(a) Select mirror-old in the Remove Boundary Zones selection list.
(b) Select mirror in the Add Boundary Zones selection list.
(c) Enter 1 for Scale.
(d) Click Compute.
(e) Click Draw to verify that the cavity defined fits the mirror to be replaced.
(f) Click Create.
TGrid separates the car zone into two—one inside (car:#) and the other outside
the cavity region, creates an interior surface (interior-#:#) at the boundary of
the cavity, and defines and activates a domain for the cavity.
(g) Select car:# and mirror in the Face Zones list in the Display Grid panel.
(h) Click Display and close the Display Grid panel.
(i) Click Draw in the Cavity Remesh panel (Figure 9.5).


Cavity Remeshing

Figure 9.5: Cavity Domain Before Meshing

(j) Close the Cavity Remesh panel.

2. Mesh the cavity with tetrahedral cells.
Mesh −→Tet...
(a) Retain the default settings and click Init&Reﬁne.
(b) Close the Tet panel.

3. Activate the global domain.


Cavity Remeshing

(a) Select global in the Domains list.
(b) Click Activate and close the Domains panel.

(a) Select car, car:#, mirror, wheel-arch-front, wheel-arch-rear, wheel-front, and
wheel-rear in the Face Zones selection list in the Faces tab of the Display Grid
panel.
(b) Disable Free and Multi in the Options group box.
(c) Click Display.
(d) Enable the overlaying of graphics.
i. Select all the zones in the Names selection list.
ii. Enable Overlays in the Scene Composition group box.

iii. Click Apply and close the Scene Description panel.
(e) Click the Cells tab in the Display Grid panel and enable All in the Options group
box.
(f) Select the ﬂuid zones in the Cell Zones selection list.
(g) Click the Bounds tab and enable Limit by X in the X Range group box.
(h) Enter -0.37 for both Minimum and Maximum in the X Range group box.
(i) Click Display.
(j) Click Draw in the Cavity Remesh panel (Figure 9.6).


Cavity Remeshing

Figure 9.6: Cavity Remeshed With Tetrahedral Cells

5. Check the mesh quality.

(a) Select all zones in the Cell Zones selection list.
(b) Click Compute.
The maximum skewness reported is around 0.904. The exact value may vary
slightly on diﬀerent platforms.


Cavity Remeshing

6. Merge the cavity domain with the original mesh.
> /mesh/cavity/merge-cavity
Insert domain name/id [cavity-1] cavity-1 <Enter>
Into domain name/id [global] global <Enter>
Merging cell zone fluid-# (id #) with fluid-#
Merging face zone interior-#:# (id #) with interior-#
Merging face zone car:# (id #) with car

where, # denotes the respective zone IDs.

7. Delete the old mirror.
(a) Select mirror-old in the Face Zones selection list.
(b) Select Delete in the Options list and retain the Delete Nodes option.
(c) Click Apply.
A Question dialog box will appear, asking you to confirm if you want to delete
the selected zone(s).
(d) Click Yes in the Question dialog box.
(e) Close the Manage Face Zones panel.

8. Check the mesh.
Mesh −→Check

9. Save the mesh (sedan-tet-cavity.msh.gz).

Case B. For a Hybrid Mesh (Tetrahedra and Prisms) Having a Single Fluid Zone
1. Read the mesh file (sedan hyb-1zone.msh.gz).
(a) Select sedan hyb-1zone.msh.gz in the Files list.
(b) Click OK.

(a) Click the Cells tab and enable All in the Options group box.
(b) Select fluid in the Cell Zone Groups selection list.


Cavity Remeshing

(c) Click the Bounds tab and enable Limit by X in the X Range group box.
(d) Enter -0.37 for both Minimum and Maximum in the X Range group box.
(e) Click Display.
(f) Display the left view.
(g) Zoom in and examine the mesh around the mirror (Figure 9.7).

Figure 9.7: Hybrid Mesh Near the Mirror

3. Import and connect the mirror.
(a) Read the mesh ﬁle mirror.msh.gz with the Append File(s) option enabled.
i. Enable Append File(s).
ii. Select mirror.msh.gz in the Files list and click OK.
(b) Verify that the mirror is appropriately positioned.
i. Select car, mirror, and mirror-old in the Face Zones selection list in the
Faces tab of the Display Grid panel.
ii. Enable Free and Multi in the Options group box in the Faces tab.
Make sure that the ﬂuid zone is deselected in the Cell Zones selection list
in the Cells tab. Click Reset in the Bounds tab.


Cavity Remeshing

iii. Click Display.
The presence of free nodes indicates that the mirror is not connected to
the car.
(c) Connect the mirror to the car.
i. Select only car in the Boundary Face Zones selection list in the Compare...
group box and disable Only Free Nodes.
ii. Select only mirror in the Boundary Face Zones selection list in the With...
group box and enable Only Free Nodes.
iii. Enable Percent of shortest connected edge length and enter 10 for Tolerance.
iv. Click Merge.
v. Click Display in the Display Grid panel.
Both mirrors are now connected to the car.
vi. Close the Merge Boundary Nodes panel.
4. Replace the mirror.


Cavity Remeshing

(a) Select mirror-old in the Remove Boundary Zones selection list.
(b) Select mirror in the Add Boundary Zones selection list.
(c) Enter 1 for Scale and click Compute.
(d) Click Draw.
The bounding box for the cavity ﬁts the mirror. However, you need to generate
prisms as well as tetrahedral cells in the cavity. Hence, you need to increase
the scale.
(e) Enter 2 for Scale and click Compute.
(f) Click Draw.
(g) Click Create.
TGrid separates the car zone into two—one inside (car:#) and the other outside
the cavity region, creates an interior surface (interior:#:#) at the boundary of
the cavity, and deﬁnes and activates a domain for the cavity.
(h) Select all the zones in the Cavity Remesh panel.
(i) Click Draw to view the domain (Figure 9.8).


Zoom in to the interior zone (as shown in Figure 9.9), to see the quad faces.
When you remesh the cavity, the prisms created during the remeshing will
connect to these quad faces.


Cavity Remeshing

Figure 9.9: Quad Faces in the Interior

(j) Close the Cavity Remesh panel.

5. Specify the meshing parameters for meshing the cavity.

(a) Specify the prism meshing parameters.


Cavity Remeshing

i. Verify that the normals on the mirror are correctly oriented.
A. Select mirror in the Face Zones selection list in the Faces tab.
B. Enable Normals in the Options group box in the Attributes tab and
enter 0.001 for Normal Scale.
C. Click Display.
The normals point outward and hence, are correctly oriented.
D. Disable Normals and close the Display Grid panel.
ii. Click the Set... button in the Boundary Layer Mesh group box in the Auto
Mesh panel to open the Prisms panel.
iii. Select car:# and mirror in the Boundary Zones selection list.
iv. Select aspect-ratio in the Oﬀset Method drop-down list and enter 5 for First
Aspect Ratio.

v. Select geometric in the Growth Method drop-down list and enter 1.2 for
Rate.
vi. Set the Number of Layers to 3.
vii. Click the Growth Options... button to open the Prisms Growth Options
panel.


Cavity Remeshing

A. Make sure that Allow Shrinkage is disabled in the Proximity Options
group box.
B. Click Apply and close the Prisms Growth Options panel.
viii. Click Apply in the Zone Specific Growth group box.

ix. Close the Prisms panel.
x. Enable Prisms in the Auto Mesh panel.
(b) Specify the tetrahedral meshing parameters.
i. Retain the selection of Tet click the Set.... button in the Volume Fill group
box to open the Tet panel.
A. Click the Refinement tab and retain the selection of adv-front in the
Refine Method drop-down list.


Cavity Remeshing

B. Retain the default value for Max Cell Volume.
C. Select geometric in the Cell Size Function drop-down list and enter
1.35 for Growth Rate.
D. Click Apply and close the Tet panel.

(c) Enable Merge Cell Zones.
(d) Click Mesh.
TGrid will generate prism layers around the mirror and the car according to the
defined parameters, automatically create a domain and fill it with tetrahedra,
and finally merge the zones together.


Cavity Remeshing

(e) Close the Auto Mesh panel.
(f) Examine the mesh.
i. Click the Cells tab and enable All in the Options group box.
ii. Select fluid in the Cell Zone Groups selection list.
iii. Click the Bounds tab and enable Limit by X in the X Range group box.
iv. Enter -0.37 for both Minimum and Maximum in the X Range group box.
v. Click Display (Figure 9.10).

Figure 9.10: Remeshed Cavity

In Figure 9.10, you can see the three prism layers generated around the
mirror and car. The rest of the domain is filled with tetrahedra.
vi. Activate the global domain.
A. Select global in the Domains list and click Activate.
B. Close the Domains panel.
vii. Display the original mesh along with the remeshed cavity.
A. Select car, car:#, mirror, wheel-arch-front, wheel-arch-rear, wheel-front,
and wheel-rear in the Face Zones selection list in the Faces tab of the
Display Grid panel.
B. Make sure the fluid zone is deselected in the Cells tab and the display
bounds are reset in the Bounds tab.


Cavity Remeshing

C. Click Display.
D. Enable the overlaying of graphics.
E. Select all the zones in the Names selection list and enable Overlays in
the Scene Compostition group box.
F. Click Apply and close the Scene Description panel.
G. Select the ﬂuid zones in the Cell Zones selection list in the Cells tab of
the Display Grid panel.
H. Enable All in the Options group box.
I. Click the Bounds tab and enable Limit by X in the X Range group box.
J. Enter -0.37 for both Minimum and Maximum in the X Range group
box.
K. Click Display.
L. Click Draw in the Cavity Remesh panel (Figure 9.11).

Figure 9.11: Cavity Remeshed With Hybrid Mesh

In Figure 9.10, you can see that the mesh outside the cavity has not
been modiﬁed. The mesh inside the cavity is connected in a conformal
manner with the original mesh.


Cavity Remeshing

6. Merge the cavity domain with the original mesh.
> /mesh/cavity/merge-cavity
Insert domain name/id [tet] cavity-2 <Enter>
Into domain name/id [cavity-2] global <Enter>
Merging cell zone fluid-# (id #) with fluid-#
Merging face zone interior-#:# (id #) with interior-#
Merging face zone car:# (id #) with car

where, # denotes the respective zone IDs.

7. Delete the old mirror.
(a) Select mirror-old in the Face Zones selection list.
(b) Select Delete in the Options list and retain the Delete Nodes option.
(c) Click Apply.
A Question dialog box will open asking you to confirm if you want to delete the
selected zone(s).
(d) Click Yes to close the Question dialog box.
(e) Close the Manage Face Zones panel.

8. Check the mesh quality.
The maximum skewness reported is around 0.93. The exact value may vary slightly
on different platforms.

9. Check the mesh.
Mesh −→Check

10. Save the mesh (sedan-hyb-1-cavity.msh.gz).

Case C. For a Hybrid Mesh (Tetrahedra and Prisms) Having Multiple Fluid Zones
This section demonstrates the use of a journal file to remesh a cavity in a mesh having
two different fluid zones (prism and tetrahedral cells).

1. View the contents of the journal file (sedan hyb-2zones-cavity.jou) in a viewer.
All lines starting with a semi-colon (;) indicate comments.


Cavity Remeshing

;Read the hybrid mesh and the new mirror
/file/read-multiple-mesh "sedan_hyb-2zones.msh.gz" "mirror.msh.gz"

;Display the cells in the plane x=-0.37
/display/set-grid/x-range -0.37 -0.37
/display/set-grid/all-cells? yes
/display/all-grid * ,

;Set the view
/display/view/camera/target -0.37 0.486 0.48
/display/view/camera/position -1 0.486 0.48
/display/view/camera/field 0.35 0.35
/display/view/camera/up-vector 0 1 0

;Merge the free nodes of the imported mirror with 10% edge tolerance
/boundary/merge-nodes car , mirror , no yes yes 10

;Replace the mirror by creating a cavity with a scale of 2
/mesh/cavity/replace-zones mirror-old , mirror , 2 , , , no

;Specify prism growth parameters
/mesh/prism/controls/zone-specific-growth/apply-growth mirror car:* ,
aspect-ratio geometric 3 5 1.2 no
;Disable shrinkage of prism layers
/mesh/prism/controls/proximity/allow-shrinkage? no

;Mesh the cavity with prisms and tetrahedra
/mesh/tritet/controls/refine-method adv-front
/mesh/tritet/controls/cell-size-function geometric 1.35
/mesh/auto-mesh yes pyramids tritet no

;Activate the global domain
/mesh/domain/activate global

;Merge the fluid zones together
/mesh/manage/merge * , yes

;Display the cells in the plane x = -0.37
/display/all-grid fluid* ,

;Delete the old mirror
/boundary/manage/delete mirror-old , yes


Cavity Remeshing

2. Start a new TGrid session.

3. Read the journal ﬁle sedan hyb-2zones-cavity.jou.
File −→ Read −→Journal...
Figures 9.12—9.14 show the mesh at intermediate stages.

Figure 9.12: Hybrid Mesh Near the Mirror



Cavity Remeshing


Figure 9.15: Cavity Remeshed With Hybrid Mesh


Cavity Remeshing

Case D. For a Hexcore Mesh
The steps in this section are similar to those described in previous sections, and hence
are less explicit.

1. Read the mesh ﬁles sedan hexcore.msh.gz and mirror.msh.gz.

(a) Enable All in the Options group box and select the ﬂuid zone in the Cell Zones
selection list in the Cells tab.
(b) Enable Limit by X and enter -0.37 for both Minimum and Maximum in the X
(c) Click Display.
(d) Display the left view.
(e) Zoom in and examine the mesh around the mirror (Figure 9.16).

Figure 9.16: Hexcore Mesh Near the Mirror

3. Verify that the mirror is appropriately positioned.
Enable the display of free nodes to check whether the mirror is connected to the car.
The presence of free nodes indicates that the mirror is not connected to the car.


Cavity Remeshing

4. Connect the new mirror.
(a) Select only car in the Boundary Face Zones selection list in the Compare... group
box and disable Only Free Nodes.
(b) Select only mirror in the Boundary Face Zones selection list in the With... group
box and retain the Only Free Nodes option.
(c) Enable Percent of shortest connected edge length and enter 10 for Tolerance.
(d) Click Merge.
(e) Close the Merge Boundary Nodes panel.

5. Replace the old mirror with the new one.

(a) Select mirror-old in the Remove Boundary Zones selection list and mirror in the
Add Boundary Zones selection list, respectively.
(b) Enable Hexcore Cavity.
(c) Enter 1.5 for Scale and click Compute.


Cavity Remeshing

(d) Click Create.

6. Click Remesh in the Cavity Remeshing panel.

7. Examine the remeshed cavity by displaying the cells in the plane x = -0.37 (Fig-
ure 9.17).


8. Display the original mesh along with the remeshed cavity (Figure 9.18).
(a) Select car, car:#, mirror, wheel-arch-front, wheel-arch-rear, wheel-front, and
wheel-rear in the Face Zones selection list in the Display Grid panel.
(b) Make sure the ﬂuid zone is deselected in the Cells tab and the display bounds
are reset in the Bounds tab.
(c) Click Display.
(d) Enable the overlaying of graphics in the Scene Description panel.
(e) Select the ﬂuid zone in the Cell Zones selection list and enable All in the Options
group box in the Cells tab of the Display Grid panel.
(f) Enable Limit by X and enter -0.37 for both Minimum and Maximum in the X
(g) Click Display.
(h) Click Draw in the Cavity Remesh panel.


Cavity Remeshing

Figure 9.18: Remeshed Hexcore Cavity

9. Check the mesh.
Mesh −→Check

10. Save the mesh (sedan-hexcore-cavity.msh.gz).

11. Exit TGrid.
File −→Exit

Summary
This tutorial demonstrated the creation of a cavity in an existing mesh to replace an
object, and then remeshing the cavity as appropriate. The procedure for creating and
remeshing the cavity was demonstrated for a tetrahedral mesh (Case A), hybrid mesh
with a single ﬂuid zone (Case B), hybrid mesh with multiple ﬂuid zones (Case C), and a
hexcore mesh (Case D).


Cavity Remeshing


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