• All the 3D meshing methods require that the geometry consist of solid bodies
Training Manual
• If an imported geometry consists of surface bodies, additional steps would be required to convert it to a 3D solid if a 3D mesh is to be generated in the ANSYS Meshing Application (although surface bodies can be meshed with surface meshing algorithms)
• 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 Manual
• 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)
ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.
3-4
April 28, 2009 Inventory #002645
Meshing Methods for 3D Geometries
Tetrahedral Algorithms
ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.
Training Manual
Faces in Close Proximity
Small Hole
April 28, 2009 Inventory #002645
3-7
Meshing Methods for 3D Geometries
Patch Independent Tetrahedrons
Patch Conforming Tetrahedrons Example
Training Manual
Resolution of Circular Hole Faces (and edges) are respected
ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.
ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.
Faces in Close Proximity
3-9
Small Hole
April 28, 2009 Inventory #002645
Meshing Methods for 3D Geometries
3-8
April 28, 2009 Inventory #002645
Meshing Methods for 3D Geometries
Patch Independent Tetrahedrons
Training Manual
• Useful for CAD with many surface patches, sliver faces, short edges, poor surface parameterization, etc.
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3-5
April 28, 2009 Inventory #002645
Meshing Methods for 3D Geometries
Tetrahedral 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
ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.
3-3
April 28, 2009 Inventory #002645
Meshing Methods for 3D Geometries
Tetrahedral Meshes
Chapter 3
Meshing Methods for 3D Geometries
ANSYS Meshing Application Introduction
ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.
3-1
April 28, 2009 Inventory #002645
• Right click on Mesh, insert a Method and Choose the bodies to which to apply the method. • Set the Method to Tetrahedrons and the Algorithm to Patch Conforming • Different parts can have different methods. 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 can be used in conjunction with Pinch Controls to help remove short edges. It also has built-in mesh defeaturing based on the minimum size
– – – –
Swept Mesh Automatic MultiZone CFX-Mesh
• Workshop 3.1
– Combining Sweep and Tetrahedral Methods for a Multibody Part – Inflating Tetrahedral and Sweep Methods
• Two different algorithms are available for generating tetrahedral meshes in the ANSYS Meshing Platform
Training Manual
– 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 to surfaces 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.
ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.