AM 12 Chapter 3

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April 28, 2009Inventory #002645

Chapter 3

Meshing Methods for 3D Geometries

ANSYS MeshingApplication Introduction




Training ManualOverview

• Geometry Requirements• Meshing Methods – Tetrahedrons

• Patch Conforming

• Patch Independent (ICEM CFD Tetra)

– Swept Mesh– Automatic– MultiZone– CFX-Mesh

• Workshop 3.1– Combining Sweep and Tetrahedral Methods for a Multibody Part– Inflating Tetrahedral and Sweep Methods




Training ManualGeometry Requirements

• All the 3D meshing methods require that the geometryconsist of solid bodies

• If an imported geometry consists of surface bodies,additional steps would be required to convert it to a3D solid if a 3D mesh is to be generated in the ANSYS Meshing Application (although surface bodies can be meshed with surface meshing algorithms)




Training ManualTetrahedral Meshes

• Advantages– An arbitrary volume can always be filled with tetrahedra– Can be generated quickly, automatically, and for

complicated geometry– Can be easily combined with curvature and proximity

size functions to automatically refine the mesh in critical regions– Can be combined with inflation to refine the mesh near solid walls

(boundary layer resolution)

• Disadvantages– Element and node counts are higher than for a hex mesh with a

similar mesh density– Generally not possible to align the cells with a flow direction– Not well suited for thin solids or annuli due to non-isotropy

of geometry and nature of element




Training ManualTetrahedral Algorithms

• Two different algorithms are available for generating tetrahedral meshes in the ANSYS Meshing Platform

– Patch Conforming: A surface mesh is generated first using a Delaunay or Advancing Front surface mesher which will, by default, respect all faces and edges in the geometry (note: some built-in defeaturing for features below the minimum size limit). The volume mesh is then created from the surface mesh via an algorithm based on TGRID Tetra.

– Patch Independent: Here a volume mesh is generated and projected tosurfaces to yield the surface mesh. Faces and edges will not necessarily be respected unless loads or boundary conditions are scoped to them.This method is more tolerant of poor quality CAD. The patch independent algorithm is based on ICEM CFD Tetra.

• Both tetrahedral algorithms can be inflated for boundary layer resolution often required for CFD




Training ManualTetrahedral Meshing

• Common Parameters–Minimum and Maximum Sizes– Face and Body Sizes– Advanced Size Functions (Curvature and/or Proximity)– Growth Rate (gradual variation for CFD, avoid sudden jumps)– Smoothing (helps achieve a more uniformly sized mesh)– Statistics–Mesh Metrics




Training Manual

• Right click on Mesh, inserta Method and Choose the bodies to which to apply the method.

• Set the Method to Tetrahedrons andthe Algorithm to Patch Conforming

• Different parts can have differentmethods. A single part with multiple bodies can include a mix of patch conforming tetrahedrons and sweep methods and will still produce a conformal mesh (Workshop 3.1)

• The Patch Conforming method canbe used in conjunction with PinchControls to help remove short edges. It also has built-in mesh defeaturing based on the minimum size

Patch Conforming Tetrahedrons

Small HoleFaces inClose Proximity




Training ManualPatch Conforming Tetrahedrons Example

Faces (and edges) are respected

Resolution ofCircular Hole




Training ManualPatch Independent Tetrahedrons

• Useful for CAD with many surface patches, sliver faces, short edges, poor surface parameterization, etc.

• With the Method to Tetrahedrons, setthe Algorithm to Patch Independent

• Faces and edges will not necessarily be respected unless a load or namedselection is scoped to them

• Note that there are additionalsettings concerning defeaturing aswell as settings for curvature and proximity Faces in

Close Proximity

Small Hole





No Named Selections: Faces and Edges are not respected





Named Selections: Faces and Edges are respected




Training ManualInflating the Tetrahedral Method

• Inflation is scoped to bodies and defined for faces




Training ManualSweep Method

• Body must be sweepable• Inflation can yield pure hex or prisms• Manual or automatic source/target• Normally single source to single

target face, automatic thin model can be used for multiple faces with multipleelements through the thickness

• Right-click on Mesh: Show Sweepable Bodies




Training ManualSweep Method: Source/Target, Mesh Type




Training ManualSweep Method: Thin Model

• Useful when there are multiple faces as inthe geometry shown below which has 3source and target faces

1

2

3




Training ManualSweep Example with Bias in Sweep Direction

• Geometry with a single source and target face can be swept with abias in the sweep direction

1

(Faces have been merged either in CAD or with VT)




Training ManualSweep with Inflation

• Inflation is scoped to a face withinflation specified on edges

(Faces have been merged either in CAD or with VT)

1

• Thin Model Sweeps cannot be inflated




Training ManualAutomatic Method

• The Automatic setting toggles between Tetrahedral (Patch Conforming) and Swept Meshing, depending upon whether the body is sweepable. Bodies in the same part will have a conformal mesh.

No inflation Programmed Controlled Inflation

Tetrahedron (Patch Conforming)Swept Tetrahedron (Patch Conforming)




Training ManualMultiZone Sweep Meshing

• Based on ICEM CFD Hexa Blocking• Automatic geometry decomposition– With the swept method, this part would have to be

sliced into 3 bodies to get a pure hex meshWith MultiZone, it can be meshed directly!




Training ManualMultiZone for Pipe Intersection

2

1

3

4




Training ManualMultiZone for Pipe Intersection

• Free block in center (here meshed with tets)




Training ManualAdding Inflation to MultiZone

• As for the tetrahedral meshers, inflation is scoped to bodies anddefined for faces




Training ManualMultiZone Mesh with Inflation




Training ManualCFX-Mesh Method

• Tet/prism mesher or extruded meshes for geometries with a periodic translation or rotation

• CFX-Mesh uses a ‘loose’ integration– Selecting Right Mouse

‘Edit…’ on the Method launches CFX-Mesh as a separate window that isdifferent than the WorkbenchMeshing environment.

– No Meshing Application sizings are respected or transferred to CFX-Mesh



Static Mixer with Patch Conforming Tetrahedronsand Sweep Methods

Workshop 3.1




Training ManualGoals

• This workshop will illustrate combining the Patch Conforming Tetrahedrons and Sweep Methods for a multibody part to yield a conformal mesh with hybrid tet/prism and hex elements

• The use of Inflation is also demonstrated for both the Sweepand Patch Conforming methods




Training ManualSpecifying Geometry

1. Copy the sm.agdb file from the tutorial

files folder to your working directory

2. Start Workbench and double-click the

Mesh entry in the Component

Systems panel at the right

3. Right-click on Geometry in the Mesh

entry in the Project Schematic and

select Import Geometry/Browse

4. Browse to the sm.agdb file you

copied and click Open

5. Note that the Geometry entry in the

Project Schematic now has a green

check mark indicating that geometry

has been specified

The first 9 steps repeatthe process followed forTutorial 2.1.




Training ManualInitial Mesh

7. Double-click the Mesh entry in the

schematic or right-click and select Edit

8. Expand the Geometry entry in the Outline

and note that there is a single part with 4

bodies

9. Left click on the Mesh entry and set the

Physics preference to CFD and select the

FLUENT solver

10.Right click on Mesh and Insert a Mesh

Method. Select the three cylindrical bodies

from the Model View and choose the Sweep

Method

11.Set the Src/Target Selection to Manual

Source and select the three end faces of the

cylindrical bodies

1

2

3




Training ManualPatch Conforming Tetrahedrons

12. Right click on Mesh and Insert a Mesh

Method. Select the central conical bodies

from the Model View and choose the

Tetrahedrons Method with the Patch

Conforming Algorithm




Training ManualInitial Mesh (no Inflation)

13. Expand the Inflation entry in the Mesh

settings and set the Use Automatic tet

Inflation option to None as you will

manually inflate the two different methods

Make sure the mesh settings are as

shown at right

14. Right-click on Mesh and generate the

mesh. Notice that the mesh is conformal




Training ManualInflating the Sweep Method

15. Right-click on the Sweep Method and

choose Inflate this Method. The inflation

will be scoped to the three source faces

16. For the boundary, you will need to select

the three outer circular edges of the faces

(you may need to enable the Select

Edges toggle to simplify this).

17. Set the maximum thickness to 0.2 m,

leaving the other settings at defaults.

Right-click




Training ManualInflating the Tetrahedrons Method

18. Right-click on the Tetrahedrons Method

and choose Inflate this Method. The

inflation will be scoped to the central body.

Select the 2 outer radial faces of the

conical body

19. Set the Inflation Option to Total Thickness

and set the Maximum Thickness to 0.2 m,

leaving the other settings at defaults.

Right-click




Training ManualGenerating the Mesh

20. Generate the mesh. Note that the

swept regions still produce hexes

while the central body produces

prisms and tetrahedrons.

21. Verify that all meshes are conformal

and save your project.




Training ManualInterior View of Inflated Mesh

Documents

AM 12 Chapter 3