Project - 2 - Meshing on the suspension Assembly

VOLUME MESH GENERATION AND DEPLOYING CONNECTIONS FOR CAR REAR SUSPENSION

OBJECTIVE:

• Importing rear car suspension geometry into ANSA.
• Clean up the geometry until no topological error is found.
• Generate mid surface for required parts.
• Generate volume mesh for hollow parts.
• Improve the mesh flow and solve off elements according to given quality criteria.
• Give connections for rear suspension for NVH analysis.

ABSRTACT:

In this Project-2, ANSA pre-processor is used to generate mid surface, volume mesh. The quality criteria for some parts are different. Therefore, 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 automobiles. The rear suspension of a vehicle performs the same general function as front suspension, but the specific construction is typically quite different. The ideal suspension for a vehicle depends a lot on the vehicle's body style and performance requirements. The most basic purposes of a suspension system are to prevent the body of a vehicle from hitting the ground and to keep the tires in contact with the road.

Cadillac suspension suspension parts

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 leaf-spring rear suspension, which consists 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 USED:

PROCEDURE:

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

Step 2: Clean the geometry using checks manager. Enable unchecked faces, collapsed cons, triple cons, needle faces, overlapped faces, cracks, single cons. Clear all these issues until no error is found. One can use fix option in ANSA 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.

Geometry clean-up done for rim, tyre, subframe, link stabilizer

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 sometimes 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 in the model browser and assign the mid surface to that new part. Then open the 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.

Surface mesh generated for tyre using quality criteria

Surface mesh generated for rim using quality criteria

Generated batch mesh for various components

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. Therefore, we must manually update our model to closed volume.
• To convert our model to closed volume one must define volume.
• ANSA might crash if you generate volume mesh for the whole geometry. So, define individual closed volumes for different PID’s.
• Defined volumes can be checked under list option under volume dialog box.
• One can give either Tetra Rapid or Tetra FEM under unstructured mesh dialog box for closed volume.

Step 4:

Mid Surface Generation for sub frame and macpherson strut outer surface

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

Mid generated by casting

Step 5:

Surface mesh generation and volume mesh generation for remaining parts

• For Remaining all parts, I have generated batch mesh by isolating each part individually.
• 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.

surface and volume mesh for steering knuckle surface and volume mesh for control bar

surface and volume mesh for coil spring surface and volume mesh for macpherson strut

Step 6:

Connections for rear suspension

• 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.
• Bolt 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 à COG is basically a 3D point, convert this 3D point to bolt à Now open connections manager and select the bolt symbol which has created in earlier step à Then assign P1,P2,P3 à Select FE type as Bolt and give the required values and constraints à apply and then realize the connection.
• I have simply given bolt connections by connecting two cluster RB2’s with two node RB2 as shown in the below figure.

Bolt connection deployed

Connections deployed for whole rear suspension

Step 7:

Transform

• After completing surface mesh, volume mesh, mid surfacing and connections we have to use transform 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.

Selecting entities to transform

• Now, use symmetry à 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.

Project 2 Outcome:

Learning Outcomes:

• Able to do topological clean-up with no errors.
• Assigned separate PIDs for different surfaces and volumes.
• Able to generate mid surface and volume mesh.
• Aware of all the quality criterias and mesh parameters during mesh generation.Learned how to improve mesh flow and remove trias to achieve better mesh flow.
• Understood concets regarding connections. Deployed different types of connections.
• 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 surfaces and volume mesh using different options available in ANSA. Did topological clean up. Able to achieve better mesh flow using smooth,reconstruct,swap,paste,move options. Eliminated kinks and raised edges. Successfully applied different quality criterias and mesh parameters for different parts and cleared off elements during mesh generation. Successfully deployed connections for the rear suspension. Overall I have done pre processing for rear suspension using ANSA.

model link:-https://drive.google.com/file/d/1yICzS1zycSepXh4Doof1yUX30SgngQN-/view?usp=sharing