Project - 2 - Meshing on the suspension Assembly

OBJECTIVE:

To perform the appropriate meshing on the given Rear wheel assembly by following the given Quality Criteria.

PROCEDURE:

1) Open the given model in ANSA.

All the suspension parts are found to be defined within a single PID, hence, the different parts are assigned to different PIDs using the ‘Set PID’ tool.

2) Geometry Cleanup

Before proceeding with meshing, it needs to be ensured that the model surface is perfect and free from errors like free edges, cracks, overlap faces, distorted faces, needle faces etc. The geometry check is done using the Checks Manager available under, Tools>Checks>Geometry.

ANSA provides an option to automatically rectify the errors. This is done by, selecting all the errors>rigiht click>Fix. If any errors persist then they can be fixed manually.

3) Measuring thickness

The thicknesses of all the components are measured and the element type is chosen accordingly. For uniform thickness parts with less than 5 mm thickness 2D meshing is carried out and for the non-uniform thickness parts with large thickness, 3D meshing is carried out.

4) 2D Meshing:

• Mid surface extraction

The thickness of the component is measured and it is found to be uniform throughout.

Hence, the mid surface is extracted using manual offset method. Under Faces>Offset, the top or bottom face is selected using the ‘Feature Area’ selection tool. The face is then offset by a distance of 3/2 mm.

New PID is created for the mid surface and the corresponding thickness is assigned.

• Meshing of midsurface

Meshing is performed using the ‘Best’ option under ‘Mesh Generation’. This function automatically meshes Macro Areas using all alternative meshing algorithms and keeps only the mesh of highest quality.

The given quality criteria’s need to be specified using the criteria file editor before meshing the model.

Once the quality criteria’s are set, meshing is performed with a target element size of 4 mm.

The generated mesh is examined properly to ensure that there is a proper mesh flow. Also, the number of trias is kept to a minimum. It’s ensured that there are no rotating quads, back to back trias, opposite trias or trias on feature line.

5) 3D Meshing

• Shell Meshing

For performing tetra meshing, the surfaces of the component have to be initially meshed with Tria elements.

The given quality criteria’s need to be specified using the criteria file editor before meshing the model.

Quality Criteria for Surface Meshing of Tyre and Rim (Element type: Tria): 

Quality criteria for Surface Meshing of Non Uniform thickness components other than Tyre and Rim (Element type: Tria):

Once the quality criteria’s are set, meshing is performed with the target element size. The curved surfaces are meshed using ‘Ortho Tria’ elements and the flat surfaces are meshed using normal ‘Tria’ elements. This is done because Ortho Trias capture the curved surfaces more accurately. But, it is not advisable to mesh the entire model with Ortho Trias as they take more computational time than normal Trias. Hence, only curved surfaces are meshed using Ortho Trias.

• Ensuring quality of elements generated

Check if any elements are failing for any of the given quality criteria’s. If any element is found to be failing the given quality criteria then the required cleanup is done to correct them.

The ‘Reconstruct’ option under ‘Shell Mesh’ can be used to improve the mesh. It examines a given mesh and performs re-meshing to correct problematic areas and optimize the overall quality of the mesh according to the mesh parameters.

• Volume Meshing

After performing 2D meshing on the component with Tria elements, to perform 3D tetra meshing on the components, each of the component has to be defined as an enclosed volume. The volume can be defined using the ‘Define’ option present under Volume Mesh>Volumes.

Quality Criteria for Volume meshing of all Non Uniform thickness components (Element type: Tetra Elements): 

The defined volumes can be viewed under the ‘Volumes>List’ option.

The created volumes can be meshed with tetra elements using either the ‘Tetra Rapid’ or ‘Tetra FEM’ options under Unstructured Mesh.

Volume Mesh>Unstructured Mesh>Tetra Rapid/Tetra FEM

• Ensuring quality of tetra elements generated

Check if any tetra elements are failing for Tet Collapse. If any element is found to be failing for Tet Collapse then it can be corrected automatically using the Fix Quality option under ‘Improve’ or it can be corrected manually by using the ‘MV Free’ option under ‘Grids’. But using the automatic option may lead to kinks or raised edges on the surface of the component, hence, manual correction is preferred. 

6) Modelling of Spring

The suspension spring is modelled using Bar elements. For this first, a curve is created in the middle of the spring using Topo>Curves>Middle.

Then a COG point is defined for this curve.

Using the curve as reference the PBAR element is created from Nastran Deck>Elements>CBAR. A new PID is also created for the CBAR element.

7) Establishing Connections

• RBE2/BOLT Connection:

Rbe2 elements is used to establish a rigid connection at the required locations.

NASTRAN Deck>Elements>RBE2>Two Points/Many Points>Select the points

By selecting ‘Two Points’ the RBE2 element is created between only two nodes whereas by selecting ‘Many Points’ the RBE2 element can be created between many nodes.

Similarly, the connections are established at all the required locations.

FINAL MODEL IMAGE:

LEARNING OUTCOMES:

• Learned how to perform geometry cleanup and extract midsurface for sheet metal components and how to define a volume and perform Solid Meshing on other components by following the given quality criteria’s.
• Gained understanding on how to perform meshing and obtain good quality mesh and proper mesh flow using the various tools available in ANSA pre-processor.
• Gained understanding of the different types of connections available in ANSA and where to deploy them and how to implement connections such as Rbe2(rigid), Bolt, Seam Weld and Spot Weld.

CONCLUSION:

The given components were meshed by choosing the right element type and the mesh quality was also ensured by following the given quality criteria’s. Also, appropriate connections were deployed at the necessary locations on the given model.