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2-1ANSYS, Inc. Proprietary© 2009 ANSYS, Inc. All rights reserved.
April 28, 2009Inventory #002645
Chapter 2
Introduction to theANSYS Meshing Application
ANSYS MeshingApplication Introduction
Introduction to the ANSYS Meshing Application
2-2ANSYS, Inc. Proprietary© 2009 ANSYS, Inc. All rights reserved.
April 28, 2009Inventory #002645
Training ManualOverview
• Introduction to the ANSYS Meshing Application• Meshing Requirements for Different Physics• ANSYS Meshing Workflow• Meshing Methods for 3D and 2D geometries• Workshop 2.1– Automatic Meshing for a Multibody Part– Program Controlled Inflation– Transferring Mesh to CFX or FLUENT
Introduction to the ANSYS Meshing Application
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Training ManualWorkbench Guiding Principles
• Parametric: Parameters drive system• Persistent: Model updates passed through system• Highly-automated: Baseline simulation w/limited input• Flexible: Able to add controls to influence resulting mesh
(complete control over model/simulation)• Physics aware: Key off physics to automate modeling
and simulation throughout system• Adaptive architecture: Open system that can be
adapted to a customer’s process– CAD neutral, meshing neutral, solver neutral, etc.
Introduction to the ANSYS Meshing Application
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Training ManualWhat is the “ANSYS Meshing Application”?
• ANSYS has been working to integrate “best in class” technologies from several sources:– ICEM CFD – TGrid– GAMBIT– CFX– ANSYS Prep/Post– Etc.
Introduction to the ANSYS Meshing Application
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Training ManualANSYS Meshing Application Overview
• The objective of the ANSYS Meshing Application in Workbench is to provide access to common ANSYS Inc. meshing tools in a single location, for use by any analysis type:
–FEA Simulations• Mechanical Dynamics Simulation• Explicit Dynamics Simulation
– AUTODYN– ANSYS LS DYNA
• Electromagnetic Simulation–CFD Simulation
• ANSYS CFX• ANSYS FLUENT
Introduction to the ANSYS Meshing Application
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Training ManualMesh Specification
Purpose– For both CFD (fluid) and FEA (solid) modelling, the software performs
the computations at a range of discrete locations within the domain.
– The purpose of meshing is to decompose the solution domain into an appropriate number of locations for an accurate result.
– The basic building-blocks for a 3D mesh are:
Manifold Example: Outer casting and internal flow region are meshed for coupled thermal/stress gas flow simulation
Tetrahedrons(unstructured)
Hexahedrons(usually structured)
Prisms (formed when a tet mesh is extruded)
Pyramids (where tet. and hex. cells meet)
Introduction to the ANSYS Meshing Application
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Training ManualMesh Specification
Considerations
• Detail: – How much geometric detail is
relevant to the simulation physics.– Including unnecessary detail can
greatly increase the effort required for the simulation.
• Refinement– Where in the domain are the most
complex stress/flow gradients? These areas will require higher densities of mesh elements.
Is it necessary to resolve this
recess?
Extra mesh applied across fluid
boundary layer
Refined mesh around bolt-hole
Introduction to the ANSYS Meshing Application
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Training ManualMesh Specification
• Efficiency– Greater numbers of elements require more compute resource (memory /
processing time). Balance the fidelity of the simulation with available resources.
Introduction to the ANSYS Meshing Application
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Training ManualMesh Specification
• Quality– In areas of high geometric complexity mesh elements can become distorted. Poor
quality elements can lead to poor quality results or, in some cases, no results at all!
– There are a number of methods for measuring mesh element quality (mesh metrics*). For example, one important metric is the element ‘Skewness’. Skewness is a measure of the relative distortion of an element compared to its ideal shape and is scaled from 0 (Excellent) to 1 (Unacceptable).
*Further information on mesh metrics is available in the documentation and training lecture appendices
Introduction to the ANSYS Meshing Application
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Training ManualMesh Specification
This example illustrates an unconverged thermal field in a manifold solid casting. On closer inspection it is clear that the simulation is unable to resolve a sensible data field in the region of poor quality elements.
The example with good quality elements demonstrates no problems in the solution field.
The ANSYS Meshing Application provides many tools to help maximise mesh quality
Example showing difference between good and poor meshes:
Introduction to the ANSYS Meshing Application
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Training ManualFEA Meshing Issues
• Structural FEA– Refine mesh to capture gradients of
concern• E.g. temperature, strain energy, stress
energy, displacement, etc.
– tet mesh dominated, but hex elements still preferred
– some explicit FEA solvers require a hex mesh
– tet meshes for FEA are usually second order (include mid-side nodes on element edges)
Introduction to the ANSYS Meshing Application
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Training ManualCFD Meshing Issues
• CFD– Refine mesh to capture gradients of concern
• E.g. Velocity, pressure, temperature, etc.
– Mesh quality and smoothness critical for accurate results
• This leads to larger mesh sizes, often millions of elements
– tet mesh dominated, but hex elements still preferred
– tet meshes for CFD are usually first order (no mid-side nodes on element edges)
Introduction to the ANSYS Meshing Application
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Training ManualMesh Types
• Tet Mesh and Tet/Prism hybrid
Introduction to the ANSYS Meshing Application
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Training ManualMesh Types
• Hex Mesh
Introduction to the ANSYS Meshing Application
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Training ManualMesh Types
• Tet Mesh1) Can be generated quickly, automatically, and for
complicated geometry
Mesh can be generated in 2 steps:
Step 1: Define element sizing
Step 2: Generate Mesh
Introduction to the ANSYS Meshing Application
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Training ManualMesh Types
• Tet Mesh2) Isotropic refinement – in order to capture gradients in one direction, mesh
is refined in all three directions – cell counts rise rapidly
Perforated plate resulting in pressure drop in x direction
x
Introduction to the ANSYS Meshing Application
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Training ManualMesh Types
• Tet Mesh3) Inflation layer helps with refinement normal to the wall, but still isotropic in
2-D (surface mesh)
Introduction to the ANSYS Meshing Application
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Training ManualMesh Types
• Hex Mesh– Fewer elements required to resolve physics for most CFD
applications
• This hexahedral mesh, which provides the same resolution of flow physics, has LESS than half the amount of nodes as the tet-mesh)
TET HEX
Introduction to the ANSYS Meshing Application
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Training ManualMesh Types
• Hex Mesh– Fewer elements required to resolve physics for most CFD
applications. • Anisotropic elements can be aligned with anisotropic physics
(boundary layers, areas of tight curvature like wing leading and trailing edges)
Introduction to the ANSYS Meshing Application
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Training ManualMesh Types
• Hex Mesh– For arbitrary geometries, hex meshing may require a multi-step
process which can yield a high quality/high efficiency mesh
– For many simpler geometries, sweep techniques can be a simplerway to generate hex meshes
• Sweep• MultiZone
Introduction to the ANSYS Meshing Application
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Training ManualANSYS Meshing Application Workflow
• The ANSYS Meshing Application uses a ‘divide & conquer’ approach
• A different ‘Meshing Method’ can be applied to each part in the geometry–Meshes between bodies in different parts will be non-matching or
non-conformal–Matched or conformal meshes will be generated for bodies in a
single part
• All meshes are written back to a common central database• A number of different methods are available for 3D and
2D geometry
Introduction to the ANSYS Meshing Application
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Training ManualMeshing Methods for 3D Geometry
• There are six different meshing methods in the ANSYS Meshing Application for 3D Geometry:
–Automatic –Tetrahedrons
• Patch Conforming• Patch Independent– (ICEM CFD Tetra algorithm)
– Swept Meshing– MultiZone– Hex Dominant– CFX-Mesh
Introduction to the ANSYS Meshing Application
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Training ManualMeshing Methods for 2D Geometry
• There are four different meshing methods in the ANSYS Meshing Platform for 2D Geometry which can be applied to Surface Bodies or Shells: – Automatic Method
(Quadrilateral Dominant)– All Triangles– Uniform Quad/Tri– Uniform Quad
Introduction to the ANSYS Meshing Application
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Training ManualPatch Conforming Tetrahedrons
• Tetrahedrons Method with Patch Conforming Algorithm– Faces and their boundaries (edges and vertices) are respected – Includes the Expansion Factor setting, which controls the internal growth rate
of tetrahedrons with respect to boundary size– Includes inflation or boundary layer resolution for CFD– Can be mixed with Sweep methods for bodies in a single part – conformal
meshes will be generated
Tetrahedral Mesh
Swept Mesh
Prism
Tet
Pyramid
Element Shapes
Introduction to the ANSYS Meshing Application
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Training ManualPatch Independent Tetrahedrons
• Tetrahedrons Method with Patch Independent (ICEM CFD Tetra) Algorithm– Faces and their boundaries (edges and vertices) are not necessarily respected unless
there is a load, boundary condition, or other object scoped to them– Useful for gross defeaturing or to produce a more uniformly sized mesh – Simplified version of Tetra tightly integrated into the ANSYS Meshing Application– Honors standard ANSYS Meshing Application mesh sizing controls– Tetra parts can also have inflation applied
Coarse mesh ‘walks over’ detail in surface model
Inflation layer
applied for CFD
Prism
Tet
Pyramid
Element Shapes
Introduction to the ANSYS Meshing Application
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Training ManualSweep Method
• Produces Hexes and/or Prisms
• Body must be Sweepable
• Single Source, Single Target
• Inflation can yield pure hex or prisms
Extrusion removed to allow for swept meshing
Body split into 2 parts to allow for swept meshing
Allows for inflation layer (boundary layer resolution) for CFD
Prism
Hex
Element Shapes
Introduction to the ANSYS Meshing Application
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Training ManualThin Solid Sweep Meshing
• Multiple source/target faces
• Works at body level with other methods
• Multiple elements through thickness possible for single body parts
Introduction to the ANSYS Meshing Application
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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)
Introduction to the ANSYS Meshing Application
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Training ManualInflation
• Inflation is accomplished by extruding faces normal to a boundary to increase the boundary mesh resolution, typically for CFD
• Smooth Transition from inflated layer to interior mesh• Collision avoidance: – Stair-stepping – Layer compression
• Preview Inflation• Pre vs. Post inflation• All methods can be inflated except
for Hex-Dominant and Thin Sweep• Sweeping:– Pure hex or wedge
Introduction to the ANSYS Meshing Application
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Training ManualMultiZone Sweep Meshing
• New feature for 12.0• 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!
Introduction to the ANSYS Meshing Application
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Training Manual
• The hex-dominant meshing algorithm creates a quad-dominant surface mesh first, then hexahedral, pyramid and tetrahedral elements are filled in as needed.– Recommended when a hex mesh is desired for a body that cannot be swept– Useful for bodies with large amounts of interior volume– Not useful for thin complicated bodies where the ratio of volume to surface area is low– No boundary layer resolution for CFD
• Mainly used for FEA analysis
Prism
HexTet
Pyramid
Element Shapes
Hex-dominant mesh shown above:19,615 Hex (60%)5,108 Tet (16%)211 Prisms (1%)
7,671 pyramids (24%)
Hex-Dominant Method
Introduction to the ANSYS Meshing Application
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Training ManualCFX-Mesh Method
• CFX-Mesh uses a ‘loose’ integration.– No Meshing Application
sizings are respected or transferred to CFX-Mesh
– Selecting Right Mouse ‘Edit…’ on the Method launches the CFX-Mesh GUI.– Define mesh
settings/controls/inflation
– Preview & generate volume mesh
– Commit the current mesh model
– Return to ANSYS Meshing
– Possible to ‘Generate Mesh’ on a CFX-Mesh method without opening the application
• Uses current or default settings
Generate Volume Mesh
Inflation layer
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Pipe Tee Mesh
Workshop 2.1
Introduction to the ANSYS Meshing Application
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Training ManualGoals
• This workshop will illustrate the use of the Automatic Meshing Method for a single body part
• The transfer of the mesh toFLUENT and CFX is also demonstrated
Introduction to the ANSYS Meshing Application
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Training ManualSpecifying Geometry
1. Copy the pt.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 in the Toolbox
3. Right-click on Geometry in the Mesh
entry in the Project Schematic and
select Import Geometry/Browse
4. Browse to the pt.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
Introduction to the ANSYS Meshing Application
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Training ManualInitial Mesh
6. Double-click the Mesh entry in the
schematic or right-click and select Edit. This will
open the Meshing Application
7. In the Meshing Options panel set the Physics
Preference to CFD, the Mesh Method to
Automatic and press OK
8. Right click on Mesh and select Generate Mesh
9. Use the view manipulation tools and the axis
triad to inspect the meshBased upon choice of physics (CFD), the Meshing Application has produced a mesh accommodating curvature, a reasonable sizing strategy and automatic selection of optimal mesh methods with minimal user input. There are many ways in which the Meshing Application can control and improve the mesh. Some further mesh controls will now be demonstrated.
Introduction to the ANSYS Meshing Application
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Training ManualNamed Selections
10.Set the Selection Filter to Faces
and select one of the pipe end
faces as shown. Right-click in the
Model View and choose Create
Named Selection. Enter velocity-
inlet-1 for the Selection Name
11.Repeat for the other two pipe end
faces using the naming as shown
12.The Named Selections just
created are listed in the Outline by
expanding Named Selections.
The names assigned here will be
transferred to the CFD solver so
the appropriate flow conditions
can be applied on these surfaces.
pressure-outlet
velocity-inlet-1velocity-inlet-2
Introduction to the ANSYS Meshing Application
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Training ManualInflation
13.Select Mesh in the Outline and expand Inflation
in Details
14.Set Use Automatic Tet Inflation to Program
Controlled, leave other settings
15.Right click on Mesh and select Generate Mesh.
Note the inflation layers are grown from all
boundaries not assigned a Named Selection.
The thickness of the inflation layers is calculated
as a function of the surface mesh and applied
fully automatically.
Introduction to the ANSYS Meshing Application
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Training ManualSection Planes
16.Orient the model by clicking on
the axis triad (+X Direction)
17.Click on the New Section Plane
icon in the menu bar. Left click,
hold and drag the cursor in the
direction of the arrow as
illustrated to create the Section
Plane
18.Created Section Planes are
listed (bottom left). Planes can
be individually activated using
the checkbox, deleted and
toggled between 3D element
view and 2D slice view. Try this
now (you will need to rotate the
model to see the cross-section)
After the Section Plane has been created the Section Plane cursor tool will still be active. Left clicking in the viewport and dragging will slide the Section Plane along its axis.
Clicking on either side of the Plane tool will cut the mesh on each side respectively. Clicking twice on one side will change the view to a planar slice.
When the position is finalized, select a view manipulation tool
Introduction to the ANSYS Meshing Application
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Training ManualMesh Statistics
19. If you expand the Statistics entry
under Mesh, it will summarize the
number of nodes and elements in
the mesh
20.Under Mesh Metric select
Skewness. Note the reported
mesh quality
Introduction to the ANSYS Meshing Application
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Training ManualTransferring Mesh to CFD
21. After the mesh has been generated, you
can transfer it to a new CFD simulation
22. In the main Workbench Window, right click
on the Mesh entry in the Meshing instance
you created on the Project Schematic and
observe that you can transfer the mesh to
a new FLUENT or CFX simulation
(Transfer Data To New >). Select either
FLUENT or CFX
23. Note that the Mesh entry now has an
Update symbol, right click the Mesh entry
and select Update. This will pass data to
the new FLUENT/CFX instance.
Introduction to the ANSYS Meshing Application
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Training ManualFluent with Workbench Mesh
24. If FLUENT was
selected - Double
click the Setup
entry and accept
the default options
in the FLUENT
Launcher
25. FLUENT will start
with the mesh
loaded
26. Save the project
from the
Workbench File
Menu
Introduction to the ANSYS Meshing Application
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Training ManualCFX with Workbench Mesh
27. If CFX was
selected - Double
click the Setup
entry, CFX Pre will
launch with the
mesh loaded
28. Save the project
from the
Workbench File
Menu