AM 12 Chapter 6

6-1ANSYS, Inc. Proprietary© 2009 ANSYS, Inc. All rights reserved.

April 28, 2009Inventory #002645

Chapter 6

Sweep Meshing

ANSYS MeshingApplication Introduction

Sweep Meshing



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



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



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



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



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



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



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



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



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



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



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



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



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



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



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



Training ManualThin Solid Sweep Treatment

Multiple source Multiple target

Multiple sources captured Multiple targets ignored



Sweep Meshing for a Multibody Part

Workshop 6.1

Sweep Meshing



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



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



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



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



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



Training ManualInitial Mesh

11. Generate the Mesh. Note the effect of the Edge Sizing and the Max Skewness

Sweep Meshing



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



Training ManualInflated Mesh

13. Generate the Mesh. Observe the nature of the mesh and the Max Skewness.



Thin Model Sweep

Workshop 6.2

Sweep Meshing



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



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



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



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



Training ManualMesh and Mesh Quality

15. Generate the Mesh. Note the Mesh count and Skewness metric

Sweep Meshing



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



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



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



Training ManualInflated Mesh

24. Generate the mesh. Note the inflation from the outer edges and the bias in the

sweep direction.

AM 12 Chapter 6

Documents

Transcript of AM 12 Chapter 6