Meshing and Deploying Connections for an Automobile Rear Suspension Assembly using ANSA

Aim:

1) To check for the geometrical errors and clean the geometry for the given assembly.

2) To perform surface and volume mesh(Tetra Mesh) throughout the assemby with the given element Quality criteria below.

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:

3) To assign thickness for the mid surfaced components after meshing.

4) To finally provide connections wherever required throughout the assembly.

Theory:

The assembly given to us is an automobile rear suspension assembly. Suspension is the system of tires, tire air, springs, shock absorbers and linkages that connects a vehicle to its wheels and allows relative motion between the two. Suspension systems must support both road holding/handling and ride quality, which are at odds with each other. Any four wheel vehicle needs suspension for both the front wheels and the rear wheels, but in two wheel drive vehicles there can be a very different configuration. For front-wheel drive cars, rear suspension has few constraints and a variety of beam axles and independent suspensions are used. For rear-wheel drive cars, rear suspension has many constraints and the development of the superior but more expensive independent suspension layout has been difficult. Four-wheel drive often has suspensions that are similar for both the front and rear wheels.

Procedure:

1. Importing the CAD Model:

1) First, we import the CAD model of the Rear Suspension Assembly into the ANSA database using the Open option present in the File tab.

2) Then, we go to the Mesh module and click on Length option under the Perimeters tab to give the perimeters and macros length, initially it is given as 1 for better visualization of the CAD model as shown in the images given below.

3) We then perform the Topo operation on the whole model which is present under Faces in the Topo module and proceed to clean the geometry because there are errors like the unchecked faces present in the CAD Geometry as shown in the image given below.

2. Geometry Cleanup:

1) Under the geometry cleanup, we go to the Check Geometry option under the Tools Tab.

2) We run the geometry check and after that we find there so many errors present in the geometry such as triple cons, single cons, cracked faces, unchecked faces, needle faces etc. The check geometry manager results are shown in the image given below.

3) We, then clear all the errors manually going region by region and we use various operation present in the TOPO module to get a clean geometry as shown in the image given below.

4) We finally store a lock view of the parent geometry to access wherever in need of it.

3. Mid-Surfacing:

1) We, first measure the components that are required for creating the mid surface using the Measure option present under the Utilities tab.

2) Then, we start taking mid surface for following components bracket, circular disc, base plate assembly and the conical component.

3) We use the Offset option under the Faces tab of the TOPO module to take the mid surface of the above mentioned components as shown in the images given below.

4) We create Different PID's for all the mid surfaced components as shown in the image given below.

5) We store a lock view of the mid surfaced components so it could accessed easily in the future.

4. Meshing:

1. 2-D Meshing:

1) In the 2-D meshing we will be considering only the above mid surfaced parts and we will be meshing it with mixed elements that include both quad and tria elements according the quality criteria given in the aim. There are some important quality parameters required for the meshing the component namely:

1) Warp angle:

It is defined as the angle between the normal of the two planes by splitting the quad element along the diagonal. So, the maximum angle allowed between the two possiblities is called the warp angle. Warp is not applicable in the triangular element. The ideal value is 0 degree but less than 10 degree is acceptable for good practices.

2) Aspect Ratio:

It is defined as the ratio of max element edge length to the minimum element edge length. the ideal value is 1 but less than 5 is acceptable.

3) Skewness:

If the quad element is not square and has deformation then the skewness defined for as the 90 minus the minimum angle between the two lines joining the opposite mid sides of the element and similarly for the triangular element it is 90 minus the between the line from each node to the opposing mid-side. The ideal value is 0 but less than 45 degree is acceptable.

4) Jacobian:

It is the scale factor used in the transformation of the co-ordinated system.(global to a local coordinate system). This is used for a faster analysis point of view. The ideal value is 1 but greater than 0.6 is acceptable.

5)Minimum element length:

It is very important to check for crash analysis(time step calculation). it is also done to avoid the presence of any zero length element.

6) Target element length:

It is the size of the element by which we can get the most nearer approximate value of the result compared to the experimental result.

2) We use the Best option under the Mesh Generation tab of the Mesh module for generating the mesh over the mid surfaced components.

3) We clear all the quality issues in the mesh to get a good error free mesh over mid surface of the component using the Reconstruct option under the Shell Mesh tab and Split , Swap options under the Elements tab of the Mesh module.

4) We, finally get to see the completely meshed model of the mid surfaced components as shown in the images given below.

2. 3-D Meshing (Volume Meshing):

5) In the 3-D meshing or Volume Meshing (Tetra Meshing) we will be considering the whole volume of the unmeshed components individually and we will be meshing it with ortho tria and tria elements according the quality criteria given in the aim. There is an important quality parameter required for the meshing the component namely:

1) Tetra Collapse:

Tet Collapse is the most important Quality criteria which is always checked while Tetra mesh is Performed (Tet Collapse is applicable to Tetra Elements only). As we know that Tetra element is a four noded element which has four sides and four nodes. The height of the Tetra element (h) is measured from each of the four nodes to its opposite face, and then divided by the Square root of the opposite face’s area (A). The minimum of four resulting values is then normalized by dividing it by 1.24. Therefore, Tet Collapse can be calculated by,

6) We, first perform 2-D mesh over all components using tria and ortho tria elements according to the quality parameters mentioned in the aim.

7) We use the Spot Mesh option under the Mesh Generation tab in the Mesh module to perform 2-D mesh for all the unmeshed components one by one.

8) Then, we clear all the quality issues in the mesh to get a good error free mesh over mid surface of the component using the Reconstruct option under the Shell Mesh tab and Split , Swap options under the Elements tab of the Mesh module.

9) After that, we define the volume for the components using the Define (Manual) option under the Volumes tab of the Volume Mesh module one by one and also create Different PID's for different components as shown in the image given below.

10) We, then perform volume mesh over all the components one by one using the Tetra FEM option under the Unstructured Mesh tab of the Volume Mesh module. We also check whether there are tetra collapse elements in all the components one by one. We find that there are no tetra collapsed elements, therefore we can say that we have got a good Volume mesh. The image of the volume Meshed components is given below.

11)We define the material for all the 2-D and Volume Meshed components as shown in the image given below.

12) We also assign thickness to the 2-D meshed components. Then, finally we are done meshing all the components. The final meshed assembly of the rear suspension is shown in the image given below.

5. Connections:

After meshing the suspension assembly we proceed to give connections to the model with the following types of connections:

1. RBE2 Connections:

1) RBE2 Single Cluster Connections:

In this type of RBE2, we provide connection to two or more holes on two or more surfaces which nearer to each other and lock their in all axes and all degree of freedom so that they can't move in any direction which makes them as rigid during the noise, vibration and harness simulation in NASTRAN. We should go to NASTRAN module and under elements tab we select the RBE2 option. We provide these type of connections wherever the two or more holes near to each other as shown in the image given below.

2) RBE2 Spider Connections:

In this type of RBE2, we provide connection to one hole which is present on the model to make it rigid in all the axes which avoids movement of it during the noise, vibration and harness simulation in NASTRAN. We should go to NASTRAN module and under elements tab we select the RBE2 option. We provide these types of connections were there are independent holes present as shown in the image given below.

3) RBE2 Two Node Connections:

In this type of RBE2, we provide connection in places like were there are two RBE2 Cluster Connections in this model. We should go to NASTRAN module and under elements tab we select the RBE2 option and under RBE2 we select the Two Node option then we select the two required nodes to create a connection as shown in the image given below.

2. C-Bar Connections:

In C-Bar connection, we provide connection only to the spring in the shock absorber as it translates w.r.t an axis. We try to capture it as a I-D element instead of meshing it. We first, create a curve of the spring using the Middle option in the Curves tab of the TOPO module and then we go to the NASTRAN module and under elements tab, we select the C-Bar option. On selecting it a dailog box opens having options for how the C-Bar has to be represented namely nodes, Curves(seq), Curves(box), node sets and edges. We the Curves(box) option and then we need to create a new PBar Property. On Confirming, we get spring which is captured with I-D elements as shown in the image given below.

6. Providing Symmetry to the Model:

After we finish giving connections, we have to provide symmetry to the model so that the system would look complete. For this, we go to the Transform option in the Utilities tab and we select the entities needed to be given symmetry, on comfirmation we have to select default symmetric plane so as to get the symmetry. Finally, we obtain the complete model as shown in the image given below.

Conclusion:

1) We have checked for the geometrical errors and cleaned the geometry for the given assembly.

2) We have performed surface and volume mesh(Tetra Mesh) throughout the assemby with the given element Quality criteria.

3) We have also assigned thickness for the mid surfaced components after meshing.

4) We have finally also provided connections wherever required throughout the assembly.

Learning Outcomes:

1) Clearing all the geometric errors for complex systems.

2) Performing both 2-D and Volume Meshing for complex systems.

3) Providing Connections to all the necessary areas of the assembly for complex systems

Model Link:

https://drive.google.com/drive/folders/1TuqC1xpFdQBVjHy4Uh-SpmFqf1-CrVCm?usp=sharing