6-1 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Chapter 6 Sweep Meshing ANSYS Meshing Application Introduction

Sweep Meshing 6-2 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Overview 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 6-3 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Sweep Methods for Hexahedral Meshing There are 3 hex meshing or sweeping approaches in Workbench ANSYS 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 6-4 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Sweeping Terminology In evaluation of which method to use there are some important terms to consider/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 6-5 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Sweeping 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 several bodies each with a single source and target face

Sweep Meshing 6-6 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Challenges 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 6-7 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Challenges with Sweeping The Thin Sweep and MultiZone methods were introduced to help resolve some 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 6-8 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Comparing 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 6-9 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Sweep 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 6-10 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Sweepable 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 6-11 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Inflation 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 6-12 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Sweep 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 6-13 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Sweeping 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 6-14 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Sweep 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 6-15 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual When 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 6-16 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Thin 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 6-17 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Thin Solid Sweep Treatment Multiple source Multiple target Multiple sources captured Multiple targets ignored

6-18 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Sweep Meshing for a Multibody Part Workshop 6.1

Sweep Meshing 6-19 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Goals This workshop demonstrates the use of a sweep method for a multibody part and shows how edge sizings can be used to specify the mesh gradation in the sweep direction. It also demonstrates inflation for a swept mesh.

Sweep Meshing 6-20 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Importing 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 6-21 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # 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 6-22 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Edge 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 6-23 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Sweep 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 6-24 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Initial Mesh 11.Generate the Mesh. Note the effect of the Edge Sizing and the Max Skewness

Sweep Meshing 6-25 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Inflating 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 6-26 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Inflated Mesh 13.Generate the Mesh. Observe the nature of the mesh and the Max Skewness.

6-27 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Thin Model Sweep Workshop 6.2

Sweep Meshing 6-28 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Goals 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 model to a form suitable for a normal sweep which allows bias in the sweep direction and inflation

Sweep Meshing 6-29 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Importing 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 6-30 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # 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 6-31 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Mesh 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 6-32 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Mesh and Mesh Quality 15.Generate the Mesh. Note the Mesh count and Skewness metric

Sweep Meshing 6-33 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Inserting 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 6-34 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Modifying 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 6-35 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Inflating 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 6-36 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved. April 28, 2009 Inventory # Training Manual Inflated Mesh 24.Generate the mesh. Note the inflation from the outer edges and the bias in the sweep direction.