Modelling of a Suspension system using ANSA

AIM

To perform shell meshing and also volume meshing along with the necessary connections for the given Suspension system model.

PROCEDURE

We start working on the model by performing a refining operation. This is done to get a better visualisation of the model. To do this, we go to mesh module and set the length of perimeters and macros as 1.

Followed by this, we perform a topo operation on the whole model to stitch the surfaces together and proceed to Geometry cleanup.

Checks-->Geometry

We get 84 errors consisting of triple cons and crack between cons along with unchecked faces. The triple cons are released and topo is performed again after taking appropriate action. Cracks between surfaces can be fixed by performing a topo operation. However, some cases require different approach such as deleting the surface and creating a new one. This is applicable for unchecked faces too.

After the geometry cleanup is done, we proceed to the next phase wherein we assign different PIDs to different parts so that they can be distinguished when worked upon individually.

Followed by this, we move on to mid-surfacing. As this model is a compilation of different parts having different thicknesses, all parts can not be mid-surfaced. Parts with less than 5mm thickness are only midsurfaced. The components for which mid-surface is taken is shown below.

These are the parts for which midsurface is taken as they have uniform thickness and is also less than 5mm. They are mid-surfaced using the manual offset method and their respective thickness' assigned properly.

As it can be observed, the mid-surface has been taken and also meshed according to the given quality criteria. Mixed type is selected for meshing and trias are removed as much as possible. When these shells are drawn as solids, they look like the pictures shown below.

All the other components have thickness more than 5mm and hence they are to be volume meshed. As the given quality criteria are not uniform for the whole model we do it as per the requirements. The tire and rim have different quality criteria and for the rest of the components, it is the same.

Quality Criteria for Tria Elements (Tyre and Rim):

S.No	Quality Criteria	Value
1	Target/Average length	6.5
2	Minimum Length	5
3	Maximum Length	10
4	Skewness	45

Quality criteria for Tria (For other components):

S.No	Quality Criteria	Value
1	Target/Average length	4
2	Minimum Length	2
3	Maximum Length	6
4	Skewness	45

For the 3D elements, the only quality criteria is that of tetra-collapse with a value of 0.2. We start with the components excluding tire and rim. In order to volume meshing, the surface mesh has to be deployed on all the sides and they have to be mapped from one side to another.

We start meshing with ortho-tria elements for the curved regions and use tria elements for the other regions. We use spot mesh for this surface meshing.

These are the parts which are only surface meshed. After meshing all parts which require the surface mesh excluding the tire and the rim, are meshed completely and the focus is shifted towards the tire and the rim. For this, we go the mesh parameters and the quality criteria to reassign the new values given for the tire and rim and proceed with the same steps followed for the other parts.

Once the surface mesh is deployed we can proceed to the volume meshing. For volume meshing, we select components one by one(as assigned by PID) and start the volume meshing. We select a part and proceed to the Vol. mesh module. We start by checking the volumes list which is empty. Now, we define the volume using Volumes-->Define-->Manual and select the whole component. The ID for the volume mesh is created and we give a name and the mesh type to be used. We go with TetraFEM as it is one of the reliable methods available. Now, we right-click on the name and select remesh. This deploys the volume mesh inside the component.

In order to check for the volume mesh, we enable the bounds option present in the lower deck. If the volume mesh is deployed, the bounds option highlights it with a red coloured frame across the mesh.

If the red outline is not visible, we can say that the volume mesh is not deployed. Also, the number of tetra elements and the percentage is displayed on the left side of the screen which also indicates the volume mesh.

This is done for every single part until it is completed fully.

In total, there are 20 components that are volume(Tetra FEM) meshed and this is how it looks fully.

Once the volume mesh is completed, this is how the meshed model looks on a whole. This includes the volume meshed parts and the shell meshed ones.

After this, we proceed to connections which is done as a prerequisite to the solver used for analysis purposes. There are different types of connections deployed across the mesh depending on the requirements. Bolt connection is deployed in the region where two or more components are bolted/attached together. Cluster RBE2 are deployed for rigid required in mechanisms. In 2D mesh, when RBE2 connection for bolt is deployed, zone cut is made to add for the washer element deployed for the spider. For connections, we use the NASTRAN deck present after the volume mesh module.

Seam weld connection is used for attaching two plates/surfaces that are not bolted upon. This weld is primarily used in load-carrying areas. Spot weld is used in other areas that are mere attachments in the car body and have no significant weight carrying ability.

The RBE2 many node is used to connect the holes wherein the edges are considered as slave nodes and the new node created in the center as a connection of all these nodes is called master node. To represent the stem of the bolt, we use 2 node RBE2 which is used to connect two nodes.

A new group called connections is created in the model browser to represent all the connections made in the model.

Here, it can be observed that the bolt connections is made using a spider RBE2 connections on the edges of the holes and the yellow 2-node RBE2 used for representing the stem of the bolt.

In this region, cluster RBE2 is deployed as there is a mechanism involved(the spindle rotates inside the mating part).

Other types of connections include the seam weld connection which is deployed in the strut part which has an attachment to the side.

The two surfaces are parallel to each other and hence we choose overlap shell as both the surfaces are shell meshed. We select the surfaces and also the base plate on which the weld should be deployed. The search distance is mentioned and the weld PID is also created. Upon confirmation and realising, the weld is deployed.

We can observe that the weld is deployed successfully.

The final part of this project is the representation of the spring present in the suspension system. Since springs are usually hexa meshed and we can rather go for 1D representation of the spring using cbar connection in the NASTRAN deck.

We start by taking the curves on the spring using Curves-->Middle option and this creates a 1D curve passing through the centre of the spring. Now, this curve is converted into a cbar connection wherein we give the radius of the spring for it to calculate the area of cross-section.

This is how the spring looks when it is made as a cbar. Now, to visualise this as a 3D component, we go to presetation parameters in the quality criteria and turn on Line Element CrossSection-->as solids. This makes the cbar as a solid which can be seen below.

With this, we have effectively completed the model.

This is how the model looks as it is completed.

LINK TO THE MODEL

https://drive.google.com/file/d/1wyanmZ5r9cxuomQ0r7-pGMd3yNCqg3SZ/view?usp=sharing

LEARNING OUTCOMES

With this model, we have learnt how to effectively model the given component using shell and solid mesh. Also, we've learnt to make connections in the 3D volume mesh as well. This model has given us several learning ideas on how to effectively study and approach a model by achieving minimum work time with maximum accuracy and precision.

CONCLUSION

The modelling of the suspension system is understood and emulated successfully in this project.