am 12 chapter 6
TRANSCRIPT
6-1ANSYS, Inc. Proprietary© 2009 ANSYS, Inc. All rights reserved.
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Chapter 6
Sweep Meshing
ANSYS MeshingApplication Introduction
Sweep Meshing
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Training ManualOverview
• Sweep Approaches for Hexahedral Meshing• Sweeping Terminology• Challenges with Sweeping• Comparing Workbench Sweep Methods• Sweep Meshing Approach• Sweepable Bodies• Inflation for a Swept Mesh• Sweep Method Mesh Controls• Sweep or Thin Sweep?• Thin Model Sweeps• Workshop 6.1 Swept Mesh for a Multibody Part• Workshop 6.2 Thin Model Sweep
Sweep Meshing
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Training ManualSweep Methods for Hexahedral Meshing
There are 3 hex meshing or sweeping approaches in WorkbenchANSYS Meshing:
1. Sweep Method• Traditional sweep method
• Improved at R12
2. Thin Sweep Method• New at R11
• Improved at R12
3. Multizone• New at R12
Sweep Meshing
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Training ManualSweeping Terminology
In evaluation of which method to use there are some important terms toconsider/understand.
• When creating a hex mesh, a source face is meshed and then extruded
to the target face• Other faces are called side face(s)• The sweeping direction or path is defined by the side face(s)• The layers of elements between the source and target faces are
created through interpolation schemes and projected to the side face(s).
Source face
Target face
Side face
Sweep Path
Sweep Meshing
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Training ManualSweeping Terminology
• To mesh a complete solid/fluid, several sweep operations may be required
• Geometry decomposition (splitting/etc) is done:– to control the mesh (get layered mesh in a gap)– or to create sweepable bodies.
• To mesh the sweepable bodies conformally the bodies should be grouped into a multibody part.
• Here the geometry has been split into severalbodies each with a singlesource and target face
Sweep Meshing
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Training ManualChallenges with Sweeping
• Sweeping will only work for geometries that are sweepable. The following are some limitations that pose challenges for sweep mesh methods:
– Multiple source or target faces – Multiple sides along sweep direction (although multiple sides may
pose quality issues due to additional constraints they impose)– Geometry decomposition into sweepable regions– How geometry is constructed, VTs, etc.– Unclear source/target/side definitions– Handling of Multibody parts:
• Unclear sweep direction through multibody parts• Conformal meshing (both for parts where all/most bodies are swept, and those
where some bodies are being meshed with free methods i.e. tetrahedral)
Sweep Meshing
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Training ManualChallenges with Sweeping
The Thin Sweep and MultiZone methods were introduced to help resolvesome of the difficulties with the general sweep approach.
Thin Sweep Method:• Good at handling multiple sources and targets for thin parts
MultiZone Method• Provides free decomposition approach: attempts to slice up the model
without having to do this manually to the geometry• Supports multi-source and multi-target approach
Sweep Meshing
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Training ManualComparing Workbench Sweep Methods
Sweep Method: • Sweeps a single source/face to a single target/face. • Does a good job of handling multiple side faces along sweep• Geometry needs to be decomposed so that each sweep path is represented by 1 body.
Thin Sweep Method: • Sweeps multiple sources to paired multiple targets• Good substitute for midsurfacing shell models to get a pure hex mesh
MultiZone Method: • Free decomposition approach• Multiple sources to multiple targets
Sweep Meshing
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Training ManualSweep Meshing Approach
• Sweepable bodies can be meshed efficiently with hexahedral and wedge elements using this technique
• Sweep Meshing Approach– Source and target faces that are topologically
on the opposite sides of the body are either manually or automatically chosen.
– Source face meshed with quadrilateral and triangular faces
– Source face mesh copied to the target face.– Hexahedral or wedge elements generated
connecting the two faces and following the exterior topology of the body
• Single source/single target for a body• Can apply single Sweep Method to multiple
bodies in a single part
Sweep Meshing
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Training ManualSweepable Bodies
• A body is sweepable if:– It contains no completely enclosed voids– There is at least one path from a source
surface to a target surface connected by edges or closed surfaces
– There are no hard divisions defined such that there would a different number of divisions on corresponding edges of a source and target face
• Can preview via a right-click on Show Sweepable Bodies– Will not find axis sweepable bodies, but these
can always be set manually
• Source and target faces do not have to be flat or parallel
• Cross-sectional shape does not have to be constant
Sweep Meshing
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Training ManualInflation for Swept Meshes
• For a swept mesh, inflation is applied by selecting the edges from which inflation is desired on the source face
• The Src/Trg Selection on the Mesh method should therefore be set to either Manual Source or Manual Source and Target
•Once a source is defined, you will then be able to define inflation
•Inflation for a swept mesh will use the Pre inflation algorithm
•Only the First Layer or Total Thickness options are available
Sweep Meshing
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Training ManualSweep Method Mesh Controls• Free Face Mesh Type– Quad/Tri (Default)– All Tri– All Quad
• Type– Element Size (Soft Constraint)– Number of Divisions (Hard Constraint)
• Sweep Bias Type– Same as edge biasing (from source to
target) but no graphical feedback
• Constrain Boundary (multibody parts)– Yes prevents the mesher from splitting
the elements at the boundary of a swept mesh region to aid in meshing.
– No allows splitting since the boundary is not constrained (Default)
– Yes prevents tetrahedral and pyramid elements from being introduced into a hexahedral/wedge mesh.
Sweep Meshing
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Training ManualSweeping Around Bends
• When sweeping geometry that contains many twists/bends, the swept mesher can produce twisted elements, causing the mesher to fail– Depends on the underlying topology of the geometry– Geometry created in several steps (e.g. a series of Extrudes and Revolves)
is more likely to cause problems
• One way to avoid this is to create geometry in a single 3D operation– Use a Sweep operation rather than a series of Extrudes/Revolves– In some CAD packages extruding/sweeping along a single spline curve
produces better topology than extruding/sweeping along a segmented curve
Sweep Meshing
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Training ManualSweep or Thin Sweep?
Some models can be meshed with either approach
Sweep Method: • Sweeps a single source/face to a single target/face. • Does a good job of handling multiple side faces along sweep• Geometry needs to be decomposed so that each sweep path is represented by 1 body.
Thin Sweep Method: • Sweeps multiple sources to paired multiple targets• Good substitute for midsurfacing shell models to get a pure hex mesh
Sweep Meshing
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Training ManualWhen to use Sweep vs. Thin Sweep
Use Sweep Method When:
• The side faces are not “thin”*. • You only have 1 source and 1 target• The sweep direction changes along the path
Use Thin Sweep Method When:
• The side faces are “thin”*. • You have multiple sources and targets• Path is linear
* In general, “thin” means that the side faces are small in relation to the source faces (aspect ratio of sides/sources is ~ 1/5th)
Sweep Meshing
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Training ManualThin Model Sweeps
• Thin models with more than one source and face can be swept using the Automatic or Manual Thin Model– Model should be thin and
source(s) and target(s) cannot touch each other.
– The model must have an obvious “side”
– Multibody parts are supported, but only one element through the thickness is allowed
– No inflation or bias in sweep direction
– Multiple sources captured, multiple targets ignored
1
2
3
Sweep Meshing
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Training ManualThin Solid Sweep Treatment
Multiple source Multiple target
Multiple sources captured Multiple targets ignored
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Sweep Meshing for a Multibody Part
Workshop 6.1
Sweep Meshing
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Training ManualGoals
This workshop demonstrates the use of a sweep method for a multibody partand shows how edge sizings can be used to specify the mesh gradationin the sweep direction. It also demonstrates inflation for a swept mesh.
Sweep Meshing
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Training ManualImporting Geometry
1. Copy the multi.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
3. Right-click on Geometry in the
Mesh entry in the Project
Schematic and select Import
Geometry/Browse
4. Browse to the multi.agdb file
you copied and click Open.
Note that the Geometry entry
in the Project Schematic now
has a green check mark.
Sweep Meshing
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Training Manual
5. Double click the Mesh entry in
the Mesh object on the Project
Schematic
6. Close the Meshing Options
Panel at the right without setting
anything.
7. Right-click on Mesh and insert a
Method. Select both bodies and
set the method to Sweep.
8. Set the Src/Trg selection to
Manual Source and select the
two faces shown as the Source
Insert Sweep Mesh
Sweep Meshing
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Training ManualEdge Sizing
9. Define an Edge Sizing for the 2 edges shown with 20 Hard Divisions. Set the
Bias Type to shrink towards the ends and set the Bias Factor to 4
Sweep Meshing
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Training ManualSweep Settings
10. On the Mesh Options, set the Physics Preference to CFD and the Solver
Preference to Fluent. Turn off the Advanced Size Function and set an Element
Size of 0.25 [cm]. Expand the Statistics entry and set the Mesh Metric to
Skewness
Sweep Meshing
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Training ManualInitial Mesh
11. Generate the Mesh. Note the effect of the Edge Sizing and the Max Skewness
Sweep Meshing
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Training ManualInflating the Method
12. Inflate the Sweep Method selecting the 8 edges shown. Set the Inflation Option to
Total Thickness and set 5 layers with a Maximum Thickness of 0.5 [cm].
Sweep Meshing
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Training ManualInflated Mesh
13. Generate the Mesh. Observe the nature of the mesh and the Max Skewness.
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Thin Model Sweep
Workshop 6.2
Sweep Meshing
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Training ManualGoals
This workshop demonstrates the use of the Thin Model Sweep method for a single body with multiple elements through the thickness.It also shows how Virtual Topology can be used to convert the modelto a form suitable for a normal sweep which allows bias in the sweep direction and inflation
Sweep Meshing
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Training ManualImporting Geometry
1. Copy the thinmodel.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
3. Right-click on Geometry in the
Mesh entry in the Project
Schematic and select Import
Geometry/Browse
4. Browse to the thinmodel.agdb
file you copied and click Open.
Note that the Geometry entry
in the Project Schematic now
has a green check mark.
Sweep Meshing
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Training Manual
5. Double click the Mesh entry in
the Mesh object on the Project
Schematic
6. Close the Meshing Options
Panel at the right without setting
anything.
7. Right-click on Mesh and insert a
Method. Select the body and set
the method to Sweep.
8. Set the Src/Trg selection to
Manual Thin and select the three
faces shown as the Source.
9. Set the Sweep Num Divs to 4
Insert Sweep Mesh
Sweep Meshing
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Training ManualMesh Sizing and Metric
10. Click on Mesh in the Outline
11. Change the Physics Preference to
CFD and the Solver Preference to
Fluent
12. Expand the Sizing Entry and note
that the Advanced Size Function is
set to On: Curvature
13. Set the Max Face Size to 0.10 [in].
(Note: if the units are set to some
other system, click on Units in the
Menu Bar and change to U.S.
Customary (in, lbm, …)
14. Expand the Statistics entry and set
the Mesh Metric to Skewness
Sweep Meshing
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Training ManualMesh and Mesh Quality
15. Generate the Mesh. Note the Mesh count and Skewness metric
Sweep Meshing
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Training ManualInserting a Virtual Face
16. If the 3 faces on the source and target faces are combined
into single faces using Virtual Topology, the resulting
model can be swept meshed with a Manual Source which
will allow for inflation and a bias in the sweep direction.
Highlight Model in the Project Outline and then left-click
on the Virtual Topology entry.
17. Set the selection filter to faces and select the 3 faces which
comprise the Sweep source
18. Right click on the Virtual Topology entry which
appeared in the Outline and choose Insert Virtual Cell
Sweep Meshing
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Training ManualModifying the Sweep Method
19. Add a second Virtual Face for the 3
faces on the Target
20. On the Sweep Method, you will need to
change Src/Trg option to Manual Source
and enter the Virtual source face you
created
21. Note that you can now set a bias in the
sweep direction. Set the bias to be finer
on the ends with a Sweep Bias of 2.
Sweep Meshing
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Training ManualInflating the Sweep
22. Right-click on the Sweep Method in the
Outline and choose Inflate This Method
23. Pick the 8 outer edges of the Source
Virtual Face as the Geomety and set the
Inflation Option to Total Thickness with a
value of 0.10 [in].
Sweep Meshing
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Training ManualInflated Mesh
24. Generate the mesh. Note the inflation from the outer edges and the bias in the
sweep direction.