AM-Intro 13.0 L02 Meshing Methods

Customer Training Material

L t Lecture 2 Meshing g Methods

Introduction to ANSYS Meshing ANSYS, Inc. Proprietary © 2011 ANSYS, Inc. All rights reserved.

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Release 13.0 February 2011

Introduction to ANSYS Meshing

Meshing Methods


What you will learn from this presentation ¾ Automatic Meshing ¾ Algorithms for Tetrahedral Meshing ¾ Different methods for Hex Meshing ¾ CutCell meshing g for 2D and shell analysis y ¾ Meshing ¾ New Features: • Direct Meshing • Parameterization P t i ti in i ANSYS M Meshing hi • Extended Meshing

ANSYS, Inc. Proprietary © 2011 ANSYS, Inc. All rights reserved.

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Preprocessing Workflow Geometry Creation OR Geometry Import

Sketches and a es Planes 3D Operations Extrude, Revolve, Sweep etc Sweep,

Geometry Import Options Direct CAD/BiDirectional CAD


Geometry Operations

Meshing

Solver

Meshing Methods

3D Operations

Hybrid Mesh: Tet, Prisms, Pyramids

Boolean, Body Operations, Split, etc

Hexa Dominant, Sweep meshing

Geometry Cleanup and Repair

CutCell meshing

Automatic Cleanup

Global Mesh Settings

Merge, Connect, Projection, Flow Volume Extraction, etc

Local Mesh Settings Sizing, g Body/Sphere of Influence, Match Control, etc


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Meshing Process in ANSYS Meshing


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Meshing Methods


• Meshing Methods available for 3D bodies – Automatic – Tetrahedrons • Patch Conforming • Patch Independent

– MultiZone • Mainly hexahedral elements

– Hex dominant – Sweep – CutCell

• Meshing Methods available for 2D bodies – – – –

Automatic A t ti Method M th d (Q (Quad dD Dominant) i t) Triangles Uniform Quad/Tri U if Uniform Q Quad d


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Triangle (Tri)

Quadrilateral (Quad)


Introduction to ANSYS Meshing Customer Training Material

Automatic Meshing g Method


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Automatic Meshing 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 Patch Conforming Mesh

S ept Meshing Swept


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Tetrahedron/hybrid y Meshing g


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Meshing Methods: Tetrahedron


• Generates tetrahedral elements • Two algorithms are available: – Patch Conforming g ((TGrid)) – Patch Independent (ICEM CFD)

Patch Conforming Mesh


Patch Independent Mesh

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Tetrahedron Meshing Algorithms


• Patch Conforming: – Bottom up approach : Meshing process starts from edge, face and then body – All faces and their boundaries are respected and meshed – Good for clean CAD geometries

• Patch Independent: – Top p down approach pp : The volume mesh is g generated first,, and this is p projected j on to faces and edges to create the surface mesh – The faces and their boundaries (edges and vertices) are not necessarily respected if they fall under a specified tolerance, unless, there is a named selection, l ti lload, d b boundary d condition diti or other th object bj t scoped d tto th them – Good for gross de-featuring of dirty CAD geometries

• Both tetrahedron meshing algorithms can be applied to the parts, bodies and d multibody ltib d parts t New N iin AM 13.0! 13 0! • Both tetrahedron meshing algorithms can be inflated for boundary layer resolution often required for CFD


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Tetrahedron Meshing: Patch Conforming Method • Right click on Mesh and insert a Method • Select the body(s) to which the method is to be applied • Set the Method to Tetrahedrons and the Algorithm to Patch Conforming • Different p parts and bodies can have different methods New in AM 13.0! • Surface mesh is generated first which by default respects p the boundaries of all faces and edges g in the geometry and the volume mesh is created from the surface mesh • Mesh does not depend p on any y loads,, boundaryy conditions, Named Selections or results scoped to the bodies


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Faces in close proximity



Tetrahedron Meshing: Patch Conforming Method


Example:

Faces, edges and proximities are respected and resolved


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Tetrahedron Meshing: Patch Independent Method


• Handy for dirty CAD with sliver faces, short edges, poor surface parameterization, etc. • With the Method to Tetrahedrons, set the Algorithm to Patch Independent • The boundaries of faces and edges will not be respected unless there is a ‘Named Selection’, load, boundary condition or other object scoped to them • Note that there are additional settings for mesh defeaturing and also refinement settings based on curvature and proximity • Possible to set different curvature and proximity settings for different bodies • Additional Smooth Transition option New in AM 13.0! • Possible to control the growth rate and the feature angle g locally y New in AM 13.0! • Ability to write ICEM CFD files New in AM 13.0! ANSYS, Inc. Proprietary © 2011 ANSYS, Inc. All rights reserved.

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Tetrahedron Meshing: Patch Independent Method Example: 1


Without Named selections, faces and edges are not respected

Face and edges under th named the d selection l ti for this method are respected Define Named Selections before grid generation process

Faces and edges under named selections are respected


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Example: 2 Set Mesh Based Defeaturing to On and enter a value for the Defeaturing g Tolerance

Geometry


No Defeaturing

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Defeaturing Tolerance of 0.1





Example: 3 Effect of Curvature and Proximity Refinement

C Curvature t and dP Proximity i it R Refinement fi tY Yes (d (default) f lt)


C Curvature t and dP Proximity i it R Refinement fi tN No

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Example: 4 Effect of Smooth Transition New in AM 13.0! Smooth transition uses advanced front meshing technique S Smooth th T Transition iti Off (default) (d f lt)


S Smooth th T Transition iti O On

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Tetrahedron Meshing with Inflation


• Can be referred to as Prism Layers. Generally needed to : – Resolve high gradients of flow variables and physics complexities in close vicinity of walls for CFD analysis – Resolve thin air gaps in Electromagnetic analysis – Resolve regions of high stress concentrations in Mechanical analysis

• Inflation layers can be generated from Tri and Quad surface mesh • Inflation can be grown both with Patch Conforming as well as Patch Independent tetrahedron meshing methods • Inflation can be applied pp using g ‘global’ g mesh settings g as well as using g ‘Local’ mesh settings

Inflation preview ANSYS, Inc. Proprietary © 2011 ANSYS, Inc. All rights reserved.

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Tet + Prisms Release 13.0 February 2011


Virtual Topology


When to use? • To merge together a number of small (connected) faces/edges • To simplify small features in the model • To simplify load abstraction for mechanical analysis • To create edge splits for better control of the surface mesh New In AM 13.0!

• Virtual cell modifies the topology – Original CAD model remains unchanged – New faceted geometry is created with virtual topology


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Virtual Topology : Example


Without Virtual cells: g are respected p while Edges creating surface mesh With Virtual cells: Small faces are merged to form a single virtual face and edges of the original set of faces are no longer respected for meshing

Creating virtual topologies • RMB on Model tree and select Insert Virtual Topology • Select Virtual Topology from the Tree Outline g RMB • Pick faces or edges, and Insert Virtual Cell ANSYS, Inc. Proprietary © 2011 ANSYS, Inc. All rights reserved.

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Virtual Topology : Example


Creating edge split New in AM 13.0! • Select Virtual Topology from the Tree Outline • Pick the edge(s) • RMB and select ‘Virtual Split Edge at +’ or ‘Virtual Split Edge’ to split the edge at the location specified by the selection, or to enter the split ratio in the Details window respectively window,

With edge splits: g constrains to improve p the mesh We can add edge Edge splits can be moved interactively. Pick the virtual edge, hold the F4 key and move the red node along the edge with the mouse ANSYS, Inc. Proprietary © 2011 ANSYS, Inc. All rights reserved.

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Hex/Hex Dominant Meshing g


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Introduction


• Hex/Hex Dominant Meshing – Reduced element count • Faster convergence

– Elements aligned in direction of flow • Improved Accuracy

Tet Mesh Elements: 83K

– Reduced numerical error

• Methods Available – Hex Dominant – Sweep – MultiZone Hex Dominant Mesh

• Initial Requirements q – Clean geometry

Elements: 24K

• Interoperability between methods – Can be used along with other hex methods New in AM 13.0! ANSYS, Inc. Proprietary © 2011 ANSYS, Inc. All rights reserved.

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Hex Dominant Meshing


• Generates unstructured hex dominant mesh • The mesh contains a combination of tet and pyramid cells with majority of cell being of hex type • Useful f for f bodies which cannot be swept • Useful for CFD applications not requiring inflation • Useful for CFD in the range of acceptable Skewness or Orthogonal Q lit mesh Quality h quality lit metrics ti • Access – RMB on Mesh – Insert Æ Method – Definition Æ Method Æ Hex Dominant

Hex Dominant Mesh ANSYS, Inc. Proprietary © 2011 ANSYS, Inc. All rights reserved.

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Sweep Meshing


• Sweeps the surface mesh in the specified direction – Generates hex / wedge elements

•B Body d mustt have h ttopologically l i ll id identical ti l ffaces on two ends, (which act as source and target faces) – Topologically identical faces on two ends are known o as sou source ce a and d ta target get faces aces

• Only one source and one target face is allowed • Thin models can have multiple source and target faces • Access

Sweep Mesh

– RMB on Mesh – Insert Æ Method – Definition Æ Method Æ Sweep


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Sweep Meshing


• Sweepable bodies – ANSYS Meshing can find sweepable bodies in the geometry automatically

Geometry


RMB on Mesh to find sweepable bodies

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Sweepable bodies in green color



Sweep Meshing


• Sweepable bodies – Simple decomposition can give sweepable bodies – Decomposition can be performed in CAD/DM

Geometry with no sweepable body


Decomposed Geometry

Sweepable bodies

(decomposed in CAD/DM)

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Sweep Meshing


• Control: Source/Target Selection – Automatic • ANSYS Meshing automatically finds source and target

– Manual M lS Source & M Manuall S Source and dT Targett • Required in case of defining inflation with sweep method

– Automatic Thin & Manual Thin • Multiple source and target faces Details View of Sweep Method

Sweep Direction ANSYS, Inc. Proprietary © 2011 ANSYS, Inc. All rights reserved.

Source Face L2-28

Target Face Release 13.0 February 2011


Sweep Meshing


• Example: – Src/Trg Selection - Automatic

Automatic Selection

Sweepable Body


Sweep Mesh No inflation

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Sweep Meshing


• Example: – Src/Trg Selection – Manual

Manual Selection

Sweepable Body

Sweep p Mesh with inflation

You cannot perform 3D inflation on bodies scoped with the Sweep method You can perform 2D inflation on the source face of the Sweep, provided that it has been manually selected ANSYS, Inc. Proprietary © 2011 ANSYS, Inc. All rights reserved.

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Sweep Meshing


• Example: – Src/Trg Selection - Rotational sweep for sector like geometry

Target Face

Manual Selection Source Face Sweepable bodies


Sweep Mesh: S M h W Wedge d and Hex elements

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Sweep Meshing


• Example: – Src/Trg Selection – Automatic Thin

Sweepable Body Multiple source faces

Automatic Thin Selection

Thi S Thin Sweep M Mesh h

For multibody parts only one sweep number of divisions is allowed for Automatic or Manual Thin sweep method


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MultiZone Meshing


• Based on blocking approach used in ANSYS ICEM CFD Hexa – Automatically decomposes geometry

• Uses U structured t t d and d unstructured t t d blocks bl k • Can have multiple source and target faces • Depends on settings of Free Mesh Type – St Structured t d blocks bl k are meshed h d with ith Hexa H or Hexa/Prism – If Free Mesh Type is set to other than Not Allowed then unstructured blocks are meshed with Tetra, Hexa Dominant or Hex Core based on the selected method

MultiZone Mesh

• Program Controlled inflation New in AM AM13 13..0! • Access A – RMB on Mesh – Insert Æ Method – Definition Æ Method Æ MultiZone


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MultiZone Meshing


• Control: – Src/Trg Selection - Automatic

Geometry for MultiZone Meshing


Details View of MultiZone Method

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MultiZone Mesh



MultiZone Meshing


• Control: – Src/Trg Selection - Manual

Geometry for MultiZone Meshing


Details View of MultiZone Method

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Cut section of MultiZone Mesh



MultiZone Meshing


• Control: – Free (unstructured) Mesh Type

Type: Tetra

Type: Hexa Dominant

Geometry

Type: Hexa Core ANSYS, Inc. Proprietary © 2011 ANSYS, Inc. All rights reserved.

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MultiZone Meshing


• Control: – Local Defeaturing Tolerance Sliver face in the mesh No Defeaturing

Small face ignored in the mesh

Geometry with a sliver face Using Defeaturing

– C Can b be also l controlled t ll d with ith global l b l defeaturing tolerance New in AM 13.0! ANSYS, Inc. Proprietary © 2011 ANSYS, Inc. All rights reserved.

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CutCell Meshing g


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CutCell Meshing


• Cartesian meshing method designed for ANSYS FLUENT solver • Patch independent volume meshing approach with automatic edge defeaturing driven by advanced size functions • Suitable for a wide range of CFD applications • Useful for meshing fluid bodies in single or multibody parts • Inflation support • Access – Set Active to Yes under CutCellMeshing g option from the global control ANSYS, Inc. Proprietary © 2011 ANSYS, Inc. All rights reserved.

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New in AM 13.0! Release 13.0 February 2011


CutCell Meshing

Tetrahedrons


Multizone

Hexa dominant

CutCell

Meshes from default settings. Keeping approximately the same resolution on the inlets ANSYS, Inc. Proprietary © 2011 ANSYS, Inc. All rights reserved.

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CutCell Meshing main controls


• Physics/Solver set to CFD/Fluent • Advanced size function – Edge g p proximity y sources accessible and recommended for better feature capturing

• Use 3D inflation • CutCellMeshing g controls – Feature Capture (default =40) • Smaller angle to capture more features • Angle = 0 to capture all CAD features – Tessellation (faceting) refinement

• Statistics: Orthogonal Quality suitable for CutCell mesh


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CutCell Meshing Workflow


• Set global CutCell meshing and sizing controls. This includes: – – – – –

• • • • •

Set the prerequisites (CFD & Fluent preferences) Activate the CutCell mesh method Set CutCell meshing options (Feature Caption and Tessellation Refinement) Set sizing options Set global inflation controls

Apply scoped sizings Generate the CutCell mesh Apply scoped inflation controls (if inflation is required) Generate the inflation mesh Export the mesh to Fluent – The Th mesh h iis exported t d iin polyhedral l h d l fformatt When CutCell is active some controls and features are inaccessible (see the User’s User s Guide for details)


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CutCell Meshing Workflow Example • Set global CutCell meshing controls and sizing including global inflation, if required


• Set scoped inflation, if required Generate the Mesh

• Generate the inflation

• Set local sizings, g , if required q

Inflation is a post process for CutCell meshing. We can add/delete/modify/suppress local inflation settings, and the meshing process will begin with the initial mesh and inflate from there

• Modify/delete/add y inflation settings • Generate the inflation


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CutCell meshing limitations


• Cannot be used in combination with other Meshing Methods • Only single or multi-body part meshing – Assembly meshing is available as a beta option • Feature recovery limitations – Sharp trailing edges and acute edges will produce a jagged mesh – Recovering some features might lead to bad quality

• Prior to meshing the user has to resolve the geometry features properly in the CAD modeler – Avoid A id unnecessary geometry t d details t il – Min size should be ½ of smallest 3D feature, it needs always to be adjusted

• Neither Body or Surface of Influence are supported • Inflation not supported on baffles or internal walls • Ignored symmetry condition for meshing Failure in the CutCell meshing algorithm is almost always related to faceting issues in relation to the value of Min Size. Make sure that the value of Min Size truly represents the smallest size that you want the curvature and proximity size function to capture ANSYS, Inc. Proprietary © 2011 ANSYS, Inc. All rights reserved.

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CutCell meshing


Example

Min size adjusted to < 0.5 the smallest target feature


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CutCell meshing


Example

Edge proximity Ed i it size i function source used to recover features ANSYS, Inc. Proprietary © 2011 ANSYS, Inc. All rights reserved.

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CutCell meshing


DLR F6 example

Engine cut

Wing cut

Cp

• Meshed with default

Mach

cutcell settings • Converged results regardless the very small min Orthogonal Quality • More refinement needed to get accurate results ANSYS, Inc. Proprietary © 2011 ANSYS, Inc. All rights reserved.

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2D & Shell Meshing g


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Meshes for 2D Analyses


• Both Fluent and the Mechanical Products in the ANSYS Portfolio accept 2D & Shell Meshes for 2D and 3D surface analyses • For 2D analysis in FLUENT generate the mesh in XY plane (z=0). For axisymmetric applications y ≥ 0 and make sure that the domain is axisymmetric about x axis • For 2D analysis in CFX, create a volume mesh (using Sweep) that is 1 element thick in the symmetry direction, i.e., – Thin Block for Planar 2D – Thin Wedge (< 5°) for 2D Axis-symmetric


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Methods for Surface Meshing


• Meshing Methods for Surface Bodies – Automatic Method (Quad Dominant) – Triangles – Uniform Quad/Tri – Uniform Quad

Automatic

Triangles

Uniform Quad


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Surface Meshing with Inflation • Quad mesh with Inflation



Inflation can be applied on the selected edges or named selections New in AM 13.0!

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Mapped Face Meshing: Example


Appropriate definition of vertices and edge grading results in a good structured mesh

E

E E

E

S E

E E

S E

E E

Vertex types are discussed in the chapter on local mesh settings in the mapped face meshing section section.


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Mesh Connections


• For sheet models, connections can be defined as “Mesh connections” • Mesh connections can be used to extend mesh h at mesh h llevell

Gap

– Tolerance Value can be specified to close gaps at mesh level

Connected Mesh

Gap removed at mesh level

• “Mesh connections” will be created at mesh time (rather than as CE in solver)


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Shell Meshing: Example


New in AM 13.0! • Edge colored by the number of connected faces • Automatic A t ti generation ti off mesh h connections ti • Mesh connectivity can be shown also after meshing • Ability to find mappable faces


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New features


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Direct Meshing


• With Direct Meshing from R13.0 the user has greater access to directly mesh bodies of multibody parts • Advantages of Direct Meshing: N New iin AM 13 13.0! 0!

– Bodies can be meshed individually – Mesh seeding from meshed bodies influence neighbors (user has control) – Automated meshing can be used at any time to finish rest of meshing – When controls are added, only affected body meshes go out of date – Selective body updating – Extensive mesh method interoperability Make sure to allow this feature under Meshing Options in ANSYS Meshing


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Direct Meshing


Local meshing • • • •

Bodies can be deleted/meshed/remeshed individually Subsequent bodies will use the attached face mesh The meshing results will depend on the meshing order RMB on the body(ies) and generate the mesh locally Meshing g first the pipe then the block

Automated meshing

Meshing g first the block then the pipe

Hexas

Hexas

Wedges

Meshed with default meshing settings


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Direct Meshing


Local remeshing • Once a multibody part is meshed we can decide later on to put more controls on a set of bodies, such h us: – Local sizings, inflation, BOI, etc

• Put the controls, RMB on the select the body(ies), clean the mesh mesh. and remesh locally Geometry with a BOI inside

Without BOI

BOI

With BOI

Only the affected body is remeshed. The mesh on the adjacent bodies remains unchanged ANSYS, Inc. Proprietary © 2011 ANSYS, Inc. All rights reserved.

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Direct Meshing


Selective body updating

• Only modified body(ies) is remeshed. The mesh on the adjacent bodies remains unchanged g • Significant time savings on model change • The user can have more control by allowing Smart CAD Update and Compare Parts On Update, see User’s Guide for details


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Mesh Method Interoperability


• Now there is method interoperability between all mesh methods

Patch Independent tetrahedrons (Smooth Transition On)

New in AM 13.0! Hexa Dominant

Multizone

Patch Independent tetrahedrons (Smooth Transition Off)

Sweep Patch Conforming tetrahedrons ANSYS, Inc. Proprietary © 2011 ANSYS, Inc. All rights reserved.

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Parameterization in ANSYS Meshing


Meshing controls can now be parameterized – Global controls and local controls – Selection of parameter promotes the parameter to the WB project page – Geometry and Meshing parameters can be related using expressions in the parameter manager

New in AM 13 13.0! 0!


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Parameterization project example


• Number of divisions

8+4=12 2 divisions

on the outlet pipe equal to two times its length • Number of divisons on the inlet pipe equal to its length + 4


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Parameterization project example (Con’t)


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APPENDIX


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Sweep Meshing



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Surface Meshing with Inflation


• Triangular Mesh with ‘Inflation’


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CutCell meshing Blower example


Inlet_duct part

Casting part

Assembly y of p parts meshed with the beta option using default cutcell settings

All beta features are accessible by allowing Beta Options under Tools/Options/Appearance in ANSYS Workbench


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Extended Meshing


• Add-on to ANSYS Meshing to provide Extending Meshing • ANSYS Extended Meshing enables: – Running ICEM CFD or TGrid stand-alone – Running ICEM CFD or TGrid from the ANSYS Meshing application using: • Interactive/Batch scripting options for “Write ICEM CFD Files” • Interactive TGrid as part of CutCell meshing (beta)


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AM-Intro 13.0 L02 Meshing Methods

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