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Chapter 3
Meshing Methods for 3D Geometries
ANSYS MeshingApplication Introduction
Meshing Methods for 3D Geometries
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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
Meshing Methods for 3D Geometries
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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)
Meshing Methods for 3D Geometries
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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
Meshing Methods for 3D Geometries
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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
Meshing Methods for 3D Geometries
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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
Meshing Methods for 3D Geometries
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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
Meshing Methods for 3D Geometries
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Training ManualPatch Conforming Tetrahedrons Example
Faces (and edges) are respected
Resolution ofCircular Hole
Meshing Methods for 3D Geometries
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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
Meshing Methods for 3D Geometries
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Training ManualPatch Independent Tetrahedrons
No Named Selections: Faces and Edges are not respected
Meshing Methods for 3D Geometries
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Training ManualPatch Independent Tetrahedrons
Named Selections: Faces and Edges are respected
Meshing Methods for 3D Geometries
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Training ManualInflating the Tetrahedral Method
• Inflation is scoped to bodies and defined for faces
Meshing Methods for 3D Geometries
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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
Meshing Methods for 3D Geometries
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Training ManualSweep Method: Source/Target, Mesh Type
Meshing Methods for 3D Geometries
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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
Meshing Methods for 3D Geometries
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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)
Meshing Methods for 3D Geometries
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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
Meshing Methods for 3D Geometries
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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)
Meshing Methods for 3D Geometries
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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!
Meshing Methods for 3D Geometries
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Training ManualMultiZone for Pipe Intersection
2
1
3
4
Meshing Methods for 3D Geometries
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Training ManualMultiZone for Pipe Intersection
• Free block in center (here meshed with tets)
Meshing Methods for 3D Geometries
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Training ManualAdding Inflation to MultiZone
• As for the tetrahedral meshers, inflation is scoped to bodies anddefined for faces
Meshing Methods for 3D Geometries
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Training ManualMultiZone Mesh with Inflation
Meshing Methods for 3D Geometries
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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
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Static Mixer with Patch Conforming Tetrahedronsand Sweep Methods
Workshop 3.1
Meshing Methods for 3D Geometries
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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
Meshing Methods for 3D Geometries
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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.
Meshing Methods for 3D Geometries
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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
Meshing Methods for 3D Geometries
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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
Meshing Methods for 3D Geometries
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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
Meshing Methods for 3D Geometries
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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
Meshing Methods for 3D Geometries
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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
Meshing Methods for 3D Geometries
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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.
Meshing Methods for 3D Geometries
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Training ManualInterior View of Inflated Mesh