Project - 2 - Meshing on the suspension Assembly

Project – 2 – Meshing on the suspension Assembly

Objective –

• Importing rear car suspension geometry into ANSA
• Geometry clean-up
• Generate mid surface for uniform parts with thickness less than 5 mm.
• Generate volume mesh for hollow parts or non-uniform parts.
• Improve the mesh flow and solve off elements according to given quality criteria
• Give connections for suspension assembly

Abstract –

In this Project -2 , ANSA pre=processor is used to generate mid surface, volume mesh. The quality criteria for some parts are different. Therefor, one should carefully apply them while meshing. Clear all off elements on surface mesh and then proceed to volume mesh. Understand about various connections used in rear suspension and deploy them accordingly.

Introduction –

Suspension has been an essential component of automobile. The ideal suspension for a vehicle depends a lot on the vehicle’s body style and performance requirements. The most basic purpose of a suspension system is to prevent the body of a vehicle from hitting the ground and to keep the tires in contact with the road.

Suspension systems are generally classified into dependent and independent systems. The wheels in a dependent system are perpendicular to the axle and parallel with each other. The most common suspension of this type is Macpherson Struts, which consist of multiple metal bars, or leaves, bound together. It is an older design but is still most common on trucks and other heavy vehicles.

Quality criteria –

For tyre and rims (volume mesh – Tria Elements)

S. No.	Quality criteria	Value
1	Target/Average length	6.5
2	Minimum length	5
3	Maximum length	10
4	Skewness	45
5	Tet-Collapse	0.2

For other components with non-uniform thickness (Volume mesh – Tria Elements)

S. No.	Quality criteria	Value
1	Target/Average length	4
2	Minimum length	2
3	Maximum length	6
4	Skewness	45
5	Tet-Collapse	0.2

For generation of mid surface with uniform thickness of less than 5 mm.

S. No.	Quality criteria	Value
1	Target/Average length	4
2	Minimum length	2
3	Maximum length	6
4	Aspect	3
5	Warpage	15
6	Skewness	45
7	Jacobian	0.2
8	Max Quad Angle	45
9	Min Quad Angle	135
10	Min Tria Angle	30
11	Max Tria Angle	120
12	Tria Percentage	15

Procedure –

Step -1 Import the geometry into ANSA and do topo to stitch the surfaces. Isolate each part and set PID’s for the suspension assembly.

Step -2 Clean D geometry using cheques manager. Enable uncheckd faces, collapsed cons, triple cons, needle faces, overlap faces, cracks, and single cones. Clear all these issues until no error is found. One can fix option in answer to clear all the errors automatically. However, sometimes manual intervention is required for fixing some errors. Manually we can use options like cut, release and delete for topo clean-up.

Step -3 Surface mesh generation for tyre and rim

• One can do mesh generation for tyre and rim either by meshing them manually using spot mesh or by batch mesh.
• The advantage of batch mesh is that ANSA will do topological clean up automatically which is a time saving process. Even though sometime we must clear some errors manually after batch meshing also.
• Mesh generation using Batch mesh option. The 1^st step is to create a new part of the model browser and assign the mid surface to that new part. Then open batch mesh and create a new meshing scenario.
• Update the content i.e. the mid surface and the required mesh parameters and quality criteria. Then click on RUN to generate batch mesh.

Volume Mesh Generation for Tyre and Rim

• After clearing all the off elements on the surface mesh one can proceed further to volume mesh generation.
• Volume mesh can be created in ANSA only if it recognizes the geometry as a closed volume. Therefor, we must manually define the volume.
• To convert our model to closed volume one must define volume.
• ANSA might crash if you generate volume mesh for the whole geometry at once. So, define individual closed volumes for different PID’s
• Define volumes can be checked under list option under volume deck.
• One can give either Tetra Rapid or Tetra FEM under unstructured mesh dialog box.

Step-4

Mid surface Generation for sub frame and MacPherson strut outer surface.

• Casting option is used for generating mid surface for sub frame and MacPherson strut outer surface.
• The advantage of using casting option is that ANSA generates mesh along with mid surfaces. Don’t forget to assign the quality criteria for mid surface.

Step -5 Surface mesh generation and volume mesh generation for remaining parts

• For remaining all parts, batch mesh is used by isolating each component.
• After generating batch mesh clear off elements manually.
• Trias or ortho trias are used as surface mesh for volume generated parts.
• After surface meshing, define closed volume individually for each part in Nastran deck.
• Now, a list of volumes will be shown in the list dialog box. Generate volume mesh either by tetra rapid or tetra FEM.

Step- 6 Connection for suspension assembly

• After completion of mid surface and volume mesh we must connect them by using connections like Bolt connection, spot weld connection, seam weld connection etc.
• Bold connection can be generated using RB2 option in the Nastran deck.
• Cluster or Spider RB2 – This connection is used when a manual bolt connection must be deployed between two or more surfaces.
• For automatic Bolt connection, one must follow these steps. Create COG for the hole – 3D point, convert this 3D point to a bolt, now open connection manager and select the bolt symbol which has created in earlier step. Then assign P1, P2 P3, select FE type as bolt and give the required values and constrains. Apply and then realise the connection.

Spot Weld -

• Spot Weld is generally a solid connection deployed between two surfaces.
• For generating spot Weld connection, first create a COG point on the FE.
• Now convert this 3D COG point into spot Weld using convert option.
• Then select the generated spot Weld point using connections manager. In the connections manager assigned P1 and P2 for two mid surfaces which are to be connected using spot Weld.
• Convert COG to sot welding point. Use connections manager to generate RBE3-HEXA-RBE3.

Step -7

• Transform – After completing Surface mesh volume mesh mid surfacing and connections we have to use transformation option in order to create exact mirror of the model on the other side. Use transform and select all the entities including connections to generate exact replica of the model. On the other side.
• Now use symmetry mirror 3 points plane option and select 3 points on the edge. These 3 points represent all the 3 coordinates X, Y, Z. This helps all the entities to transform on the other side.

Learning Outcomes –

• Able to do topological cleanup with no errors.
• Assign separate PIDs for different surfaces and volumes. Able to generate mid, surface and volume mesh
• Aware of all the quality criteria and mesh parameters during mesh generation. Learned how to improve mesh.
• Understood all the concepts regarding mid surface generation. Volume mesh generation, meshing, connections used for NVH analysis in ANSA.

Conclusion –

In this project, I have generated mid surface and volume mesh suing different options available in ANSA. Challenge has been completed as per quality criteria.

https://drive.google.com/file/d/1uZi23XDlCjIwLj-fPoxO68CZtxekRG6Q/view?usp=sharing