Project 2

AIM

* To check the geometrical errors and generate 2D & Volume mesh according to the thickness of various parts in the Car suspension model. 

* 2D and Volume mesh are applied with the following Quality criteria:

Quality Criteria for Tria Elements (Tyre and Rim): 

Quality criteria for Mixed elements (For Midsurface only):

Quality criteria for Tria (For other components):

Common Quality Criteria for Tetra elements are:

 THEORY                                           

                                                          MacPherson suspension

The system was invented in 1955 and used on the first Ford Consul. The MacPherson suspension is a technology for front and rear suspension. It is an independent suspension type, including a single suspension arm (spring and damper), an anti-roll bar and a lower arm. The junction between sprang and unsprang masses is carried by a ball joint on the wheel side and a side frame axis. The system spring – damper is attached to the hub carrier. This arm is also used as steering axis. The damper has two missions, dampen relative movement between the wheel and the body and participate in the kinematics of the wheel plane via the anti-roll bar and the lower arm. The damper rod has a larger diameter (25mm) than a damper (14mm) used in other suspension types.

ADVANTAGES:

1. Easy assembly
2. Ratio cost / performance
3. Mass
4. Lateral dimension
5. Spring and damper motion ratio equal to 1 (damper displacement/spring displacement = 1)

DISADVANTAGES:

1. Vertical dimension
2. Friction
3. King pin offset
4. Limited possible settings
5. Low camber gain
6. Precision

METHODOLOGY

    I. Geometry Cleanup

 Open the given CAD model in ANSA.Intial step is to set the length of element of whole model to 1mm. After inputing the model, the surface is not regular in view. For that in the Perimeters module button use length option. Then use TOPO for whole model. 

Check geomtrical errors as next step, use CHECKS in tool option. After checking the errors some geomtrical errors will be showing it needs to be resolved. In this case all parts are overlapped each other, so triple cones issues will be coming on giving TOPO for whole model. So in order to avoid the geometrical issues all parts are seperated and saved in different PIDS and resolved the geometrical issues.

  II. 2D mesh generation

In this model its a combination of Uniform thickness and not uniform thickness. Here all the models whose thickness is less than 5mm comes under the section of taking Mid surface and perform 2D mesh.

(The above figure indicates the parts whose thickness is less than 5mm and mid surface is taken)

To extract the mid surface of this model Manual Offset feature method is used, because the mesh that will be getting is better and Features that are present in the model can be captured perfectely.To perform 2D Meshing operation, first lines in the model need to be reconstructed. Then go for MESH in module option. Before start with mesh, Quality criteria need to be input to ANSA Software. Then only Quality mesh will be getting according to the given quality criteria. Assign mesh paramters for setting up the Min and Max length for the mesh.After assigning this values mesh operation can start for each surface. In the given model BATCH command is used for generating mesh for each surface. BATCH mesh generation gives organised mesh and feature capturing will be perfect. During meshing Trias, rotating quads are generated this need to be removed for proper mesh flow. For that various commands are used such as Split command, Paste command, Reconstruction command, Smooth command. In this commands SMOOTH option will try smooth within the range but the RECONSTRUCTION will try change the mesh.

 III. Solid mesh generation

Solid mesh consist of TETRA mesh and HEXA mesh. TETRA mesh means the Unstructured mesh and HEXA mesh is the Structure mesh or Mapped mesh. For HEXA modeling it requires a lot of time to mesh the solid models. Tetra modeling is a TRIA model whose surface mesh then generated unto a VOLUME.

In here we will generate unstructured mesh means TETRA Mesh. Here it consist of ORTHO TRIA & TRIA elements. Ortho Tria are the ones that is should be used first and it should be used on curved faces. It capture features more accurately than normal trias. For flat surface both Tria and Ortho mesh are better. Before generating the TETRA Mesh input the MESH PARAMETRES and QUALITY CRITERIA VALUES. For performing mesh the most used commands in these model are BEST command, BATCH command and SPOT MESH command. 

Here all the parts are divided into Sub parts and stored in PIDS. So each part is seperately taken and Tetra mesh is applied on the surface of the parts.

(Property ID’s assigned to different parts)

  IV. Create Volume inside CAD body

Volume is created on the areas in which TETRA mesh is applied.To create volume inside the CAD body, volume need to be defined. For that use DEFINE Command in Volume module. After defining the volume, drawing screen shows that Unmeshed as 1. It means the volume is defined. Then generate the unstructured mesh inside the CAD model. 

There are 2 unstructured mesh on the Tab that is TETRA RAPID & TETRA FEM.These 2are algorithm for creating volume inside the model. The only difference between these 2 commands is the GROWTH RATE of the element inside the volume. In comparison with this 2 commands, TETRA FEM is having low GROWTH RATE ratio of elements. TETRA FEM is mainly useed for Structural applications.

After genertating the volume look for any kinks and dips on the outer body, if there try to resolve the issue. Use BOUNCE command to identify Kinks & Dips. COLLAPSE is the quality criteria that is checked on any Tetra model. TETRA mesh is called as UNSTRUCTURAL mesh that it does not follow any pattern or any line or any geometry. It just rushes on the volume and generates a prismatic element as per the growth ratio specified by the algorithm. In which some of the elements might fail for quality. Most addred quality at TETRA meshing is TET COLLAPSE.

VOLUME CREATED INSIDE THE CAD MODEL:

 V. Deploy Rigid connection on different areas

a) Cluster RBE2 Connection

Here we don't demonstrate Bolt stem modelling, we just represent the function of rigid bolt. 

Whenever we identify a hole that it will be connected to any other component, we will have to deploy the Cluster RBE2 connection in which all the nodes from 2 surface will comes to join a Master node

 b) Seam Weld Connection

Main welds that are used in automobile industries are SPOT WELD & SEAM WELD connection. SPOT WELD are seen in cars body structural components ie, BIW structure. SEAM WELD are used in load carrying areas.

SEAM WELD that are commonly used are OVERLAP SHELL & Y-JOINT SHELL. Overlap shell is a type of FE representation which always used when the 2 parts are to be welded are PARALLEL to each other, whereas in case of Y-Joint shell are used when 2 parts are perpendicular or inclined to any angle each other.

In this model OVERLAP SHELL is used on the STRUT Assembly.

c) 2 Nodes RBE2 Connection

In this connection setup all the cluster RBE2 connections are joined with 2 node RBE2 connection, in order to represent it as Rigid connection. In most cases Stem connection is used to represent the Bolt stem connection, as in the given model CAD data of bolt is not available. So with an assumption i have represent this connection to be Bolt Stem connection.

 d) C BEAM Connection in Coil Spring

Spring can be converted as 1-D element. If it is converted to be a solid and Hexa mesh to be done on the solid, this will create issues during analysis. As during analysis solving time will be more. So norder to avoid this issue the Spring is converted into 1D element.

In this case a middle curve is created and convert the curve into C BEAM on NASTRAN Deck. On processing element length need to be specified and Area of cross section need to be specified on the Property of Coil Spring

LEARNING OUTCOMES

1. How to create a 2D and Solid mesh in a single model
2. How to deploy connection on Volume areas

CONCLUSION

2D and Volume with proper Rigid connection is generated inside the Rear suspension of car model.