Modelling of an Automotive suspension assembly by using ANSA

MESHING AND DEPLOYING CONNECTIONS FOR AN AUTOMOTIVE SUSPENSION ASSEMBLY USING ANSA PRE-PROCESSOR

• Modelling Automotive Suspension Assembly

Automotive suspension assembly separate the wheel/axle assembly from the car body. The primary function of the suspension system is to isolate the vehicle structure from shocks and vibrations due to the irregularities of the road surface.

It is very important to analyze an Automotive suspension Assembly for static and dynamic loads. To perform analysis the first task is to discretize the model into finite number of elements which is called pre-processing or Meshing.

ANSA is used for pre-processing Automotive suspension Assembly and make the model ready for any Analysis.

• AIM

For the given Rear Suspension model, we have to Perform Meshing with give element quality criteria and deploy appropriate connections between parts. steps involved in the process are,

1. Geometry Checks and perform Geometry clean-up
2. Take measurements from various parts of the model and decide which type of element we have to use for Meshing.
3. For parts having uniform thickness and have thickness less than 5 mm we will go for 2D Meshing or shell Meshing with mixed elements. We need to extract mid-surface for shell Meshing
4. For casting parts , parts having non uniform thickness and have thickness greater than 5 mm we do solid Meshing or volume Meshing with Tetra Elements.
5. We have to deploy appropriate connections between different parts inorder to assemble them together
6. Perform symmetry operation to create full Rear suspension assembly.

• Procedure

Step1 : Open the CAD model of rear suspension assembly using File > open

Step 2 : separate the parts of rear suspension assembly by assigning them different PIDs so that it will be easy to work on them

Goto Topo module > Faces > Set PID , select the parts using PID region selection tool . Upon middle click property window opens. Right click on the window > New > PSHELL create a new PID for the part.

Step 3 : Geometry checks and Geometry clean up

We have to checks for geometry errors of each part separately. first, isolate the parts using various focus functions (!Not function )

then check for geometrical errors present in the part, Goto Tools > checks > Geometry

Errors will be displayed on the window, most of the errors can be rectified automatically by ANSA for this select all errors by Cntrl+A then right-click on the selection and apply fix.

The errors that won't fix automatically like triple cons, missing faces etc have to fix manually

The most common case that unwanted triple cons appear is when degenerate faces exist ( such faces have their opposite cons coincide ). This can be solved by deleting the degenerate face, go to Topo module > Faces > delete.

Faces that are associated with the creation of triple cons will appear in the window, we can choose and delete the unwanted face exist.

Tire Rim part after successfully removed geometrical errors

We can delete the unnecessary Hotpoints using Topo Module > Hotpoints > Delete

In the case when there are some missing faces exist in the geometry we have to create a new face using Topo Module > Faces > New > Coons

image below shows there are some missing faces in tire part of the suspension assembly

go to Topo Module > Faces > New > Coons , select the single cons of the missing or deleted face. Preview of the new face will appear, we can check and accept the face by pressing ok.

After geometry cleanup of tire part

similarly, there are missing faces in steering knuckle part

similarly we have to check all parts and perform geometry cleanup.

Step 4 : Defeaturing

Defeaturing has to be done on the geometry in the area where it will fail for minimum length criteria , using

Topo Module > Faces > cut, right click to join the perimeters

In Mesh Module deck we can use Mesh module > Macros > join , select the perimeter we want to join

• Meshing

First we have to measure the thickness of parts and decide which type of meshing we have to use.

For casting parts or non uniform thickness parts and parts having thickness greater than 5 mm we will go for Volumetric Meshing or solid Meshing

Step 5 : Creating Surface Mesh

For tire and rim we have to use volumetric meshing with Tetra element type.

First we have to enter Element quantity criteria and Mesh parameters

In order to create solid Meshing first we need to generate a surface mesh on the geometry using Mesh module > Mesh Generation > spot mesh ,

choose the element type as ortho tria for curved faces and for flat faces we can use normal tria element. Select the face where we want to deploy the mesh and confirm the selection with middle mouse click.

In order to check for element quality we have to switch to hidden mode.

In order to clear the quality of failed elements we can reconstrtuct the mesh using Mesh module > shell mesh > Reconstruct

Also we can use Mesh module > Elements > swap, split option to clear the quality of elements and improve the mesh flow.

Mesh module > shell mesh > smooth option to smoothen the mesh after applying split and swap operation.

Step 6 : Solid Meshing ( Volumetric Meshing )

Now we have to convert the surface mesh created on the geometry into solid Mesh. There are 2 types of solid meshing Tetra Mesh and Hexa Mesh . Here we are using Tetra Meshing

First we have to Define the volume,

go to Volume Mesh module > volumes > Define > Manual , select the entity using left mouse box selection and confirm with middle click.

Property window opens and we can define a new PSOLID property, by right click on the window New > PSOLID

We can check the volume created in Volumes > List menu, We can see the created volume in the list and it is undefined and unmeshed

To generate volume mesh, right click on the volume in the list and select Remesh option select the algorithm as Tetra rapid or Tetra FEM.

Or else go to Volume Mesh module > Unstructed Mesh > choose Tetra rapid or Tetra FEM , select the entire model with left mouse box selection and confirm with middle mouse click.

In order to see the volume created we can switch off the visibility of Geometry and FE and switch on the visibility of volume.

similarly we created volumetric mesh for tire also

Step 7 : Volumetric Meshing of other casting parts

Similarly we have to create solid meshing for other casting or non uniform thickness parts such as steering knuckle, sway bar, control arm bushing, brake disc etc.

The quality criteria and mesh parameters are given in the image below

below images show the volumetric mesh created for different parts

The element quality we check for volume mesh is Tet collapse , first switch to hidden mode in order to check the quality of elements

Isolte the failed element using !Not focus functions , right- click with the mouse button in order to define a local co-ordinate

and we can make a node movement to clear the collapsed element using Mesh Module > Grids > MV Free option, select a node of the element in such a way that node movement will not result the formation of any kinks or dips on the surface

thus Tet collapse element quality failure is rectified

Step 8: 2D Meshing (shell Meshing) of Control Arm

For uniform thickness parts or parts having thickness less than 5 mm , we opt for 2D Meshing. Lower Control Arm part of suspension assembly have uniform thickness

First, we have to perform geometry cleanup and make sure there are no geometrical errors.

• Extraction of mid-surface

we have to extract mid-surface of the parts using Topo Module > Faces > Offset option, select top or bottom face of the part using feature angle selection tool and give offset value as half of the thickness. An offset face is created at the middle.

We can assign a new PID to the mid-surface using Topo module > Faces > Set PID and give thickness value.

below image shows final mid-surface of control arm part

• Meshing of the mid-surface

Isolate the mid-surface extracted using !Not focus function and now we can Mesh the mid-surface using

Mesh module > Mesh generation > Spot mesh algorithm. Select the face we want to mesh and confirm with middle mouse click.

In order to check for element quality we have to switch to hidden mode. In order to clear the quality of failed elements we can reconstruct the mesh using Mesh module > shell mesh > Reconstruct

Also we can use Mesh module > Elements > split option and Mesh Module > Grids > paste option to remove opposite tria elements and rotating quads present in the mesh and thereby improve the mesh flow.

Mesh module > shell mesh > smooth option to smoothen the mesh after applying split , swap and paste option

the image below shows meshed mi-surface of control arm part

Step 9 : 1D Element representation of Suspension spring

We can represent the suspension spring as 1D Element and give cross sectional area. Inorder to do that first we have to create a middle curve at the cross section.

Go to Topo Module > Curves > Middle , select cons on the 2 faces of suspension spring.

Thus middle curves are created between the 2 cons selected, we can connect the curves in to a single curve using Curves > Connect > Multi

Now we have to convert the curve into a connection data, using NASTRAN deck > Elements > CBAR/CROD. select the curve and select the orientation by picking any end point of the curve , give element length > ok.

CBAR property window opens, enter area of cross-section and radius > ok. image below shows the 1D elements created

To enable thickness to the 1D element created go to presentation parameters tab under element quality criteria menu and enable line elements cross-section and select draw mode as solids.

image below shows full meshed model of suspension assembly

Step 10: Deploy appropriate connections between different parts

• Representing Bolt connection

Cluster RBE2 Representation

In order to represent bolt connection between 2 mating holes go to NASTRAN deck > Elements > RBE2 > Many nodes Select the slave nodes as nodes on the edge of 2 holes

Click Next , ANSA will automatically create a master node at the COG and upon clicking next, property window opens, enter the Degree of freedom (CM) as 123456

Creating and Realising Bolt connection

In other method create a 3D points on COG of holes using Topo Module > Points > on COG , select the holes of 2 parts to be connected.

Convert the 3D points into bolt connection using, Assembly tab > Convert > 3D points > select the points and middle click to confirm then select the connection type as bolts. Points will be converted to a bolt connection data.

Now we have to Realize the bolt connection created , goto Connection manager, select the bolt connection created and middle click to confirm. Connection Manager window opens, select FE representation type as bolt. Define the parts to be connected as P1, P2 and give search distance > Apply > Realize

• Representation of seam weld

First we need to create a seam weld line, for that we need to create a curve on the edge where the parts are conncted. using Topo Module > Curves > Cons2curve , select the edge.

Now we have to convert the curve in to seam weld line, go to Assembly tab > Convert > Curves select the curve and middle click to confirm then select the connection type as seam line.

Then we have to realize the seam line connection created, go to Connection manager and select the seam line and middle click to confirm.

In connection Manager window , select FE representation type as overlap shell ( if 2 parts to be connected are parallel to each other) or Y- joint shell ( if 2 parts to be connected are perpendicular to each other) then define parts P1 and P2 as parts to be connected , input the search distance > Apply > Realize

Suspension assembly model after meshing and deploying connections

• Perform Symmetry option

In order to create a full automotive suspension assembly we need to perform symmetry operation,

Utility > Transform > Copy > Entities, select the half portion of suspension assembly and confirm with middle mouse click > Go to Symmetry tab > Mirror 3 point plane > select 3 points having different z-values > Apply

• Complete Suspension assembly model

• Learning Outcomes
• Learned how to perform Geometry checks and Geometry clean up of an Automobile Suspension Assembly
• Thickness measurement at various parts and decide which type of element has to use for meshing'
• Learned how to perform surface meshing for casting parts and then how to define volume and perform volumetric mesh
• How to solve Tet collapse for tetra elements in volume mesh
• Extracting mid-surface for sheet metal parts and perform shell meshing with given element quality criteria
• Solving failed elements by various Mesh improvement tools
• How to perform symmetry operation

• Conclusion

performed pre-processing operations ( Meshing and deploying connections ) on an automobile suspension assembly and prepared the model for analysis phase.