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.

FIG 1:Cadillac suspension

FIG 2: 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.

FIG 3: SUSPENSION PARTS

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.

FIG 4: 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 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.

FIG 5:Surface mesh generated for tyre using quality criteria

FIG 6:Surface mesh generated for rim using quality criteria

FIG 7: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.
  

FIG 8:volume mesh generated for tyre

FIG 9:volume mesh generated for rim

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.
  

FIG 10:Selecting surfaces for casting

FIG 11: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.

FIG 12:surface and volume mesh for steering knuckle surface

FIG 13: volume mesh for control bar

FIG 14:surface and volume mesh for coil spring surface

FIG 15: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.

FIG 16:Bolt connection deployed

FIG 17:2 node RB2 and Cluster RB2 connections
Spot Weld

• Spot weld is generally a solid connection deployed between 2 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 connection’s manager assign P1 and P2 for 2
  mid surfaces which are to be connected using spot weld.
  
• Create COG à Convert COG to spot welding point à Use connections manager to generate RBE3-HEXA-RBE3.
  

FIG 18 :Spot weld connection realized

FIG 19 :RBE3-HEXA-RBE3

FIG 20 :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.
  
  

FIG 20 :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.
  

FIG 21 :Selecting 3 points

FIG 22 :Transform implemented successfully

Project 2 Outcome:

FIG 22 : Project Outcome of rear suspension

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.

LINK FOR THE MODEL https://drive.google.com/file/d/18nldY-bzHf_7NRNAEODV1-o1TDEIglSB/view?usp=sharing