Meshing and Deploying Connections for an Automobile Cross Car Beam (CCB) Assembly using ANSA

Aim:

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

2) To perform 2-D mesh throughout the assemby with the given element Quality criteria below.

S.No	Quality Criteria	Value
1	Target/Average length	5
2	Minimum Length	3
3	Maximum Length	7
4	Aspect	3
5	Warpage	15
6	Skewness	45
7	Jacobian	0.7
8	Minimum Quad Angle	45
9	Maximum Quad Angle	135
10	Minimum Tria Angle	30
11	Maximum Tria Angle	120
10	Tria Percentage	15

3) To assign thickness for all the components after meshing.

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

Theory:

The model given to us is the CCB(Cross Car Beams) assembly. Cross car beams are complex parts, which make a decisive contribution to the stability and safety of every vehicle in which they are used. As a single cross strut in the vehicle interior they ensure that, in the event of a side impact, the passenger compartment is not compressed. Cross car beams also hold the steering wheel, the airbags, and the entire dashboard. Depending on the model, we can manufacture this crucial part in steel or aluminum.

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.

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.

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.

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) We use the Offset and Mid Surface-Skin options under the Faces tab of the TOPO module to take the mid surface of the component one by one.

3) We create property ID's for the mid surfaced components using the Set PID option under the Faces tab of the TOPO module. We also assign materials for the mid surfaced components. PID's and MID's are shown in the images given below.

4) We obtain the Mid Surface for the whole CCB assembly as shown in the image given below.

4. Meshing:

1) In the meshing we will be considering the above mid surfaced component 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 component as shown in the image given below.

5) We also assign thickness to the meshed component. Then, finally we are done meshing all the components.

5. Connections:

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

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 as shown in the image given below.

2) Bolt Connections:

In this type of connections, we provide connections to wherever the bolts are going to be fitted in the component. We first create a 3D point near the holes of the bolt connection using the On COG option present in the Points tab of TOPO module. Then we convert the 3D points into bolt washer point using Convert option present in the Assembly tab. After that, we go to the Connection Manager option present in the Assembly tab and select on the all washer points and then we press middle mouse button to get the connection manager tab. We have 3 tabs in the connection manager menu namely connectivity list, connection list and FE representation settings. We go to the connection list and we proceed to give connection for which all parts we want using F1 tab we go to the model and we select each and every part and press enter to confirm since this model has a single PID we don't need to go every time and select the parts, after confirming the connectivity list tab is also updated based on the connections given. Finally, we go to the FE representation tab and under it we provide the FE representation type as Bolt and then we provide the zones to be attached as In/Out so that all the zones inside the bolt connections get rigidly fixed. We apply all the settings and click on Realize option. We, finally obtain the bolt connection in which all the nodes nearing to the boundry of the bolt connections are connected using RBE2 and there vertical connection between these connections as shown in the image given below.

3) Seam Weld Connections:

In this type of connections, we provide connections to wherever the welding operation is going to performed in the component. In this model, we create seamweld connections only. We first create a curve near the welding area using the Feat Curve option present under the Perimeters of the Mesh module. We then, use the Convert option present in the Assembly tab to convert the curve to a Seamline. After that, we go to the Connection Manager option present in the Assembly tab and select on two parts which are to be welded to each other and then we press middle mouse button to get the connection manager tab. We have 3 tabs in the connection manager menu namely connectivity list, connection list and FE representation settings. We go to the connection list and we proceed to give connection for which all parts we want using F1 tab we go to the model and we select each and every part and press enter to confirm. Finally, we go to the FE representation tab and under it we provide the FE representation type as Y joint shell or Overlap shell according to our requirement. We provide the Search Distance and we provide the Base Sheet as P1, then we provide the width of the weld and Representation type as Double Row, Primary Row or Offset Row and then we create a new Weld PID which could be used for all the seam welds. Finally, we press on Apply and we press on Realize. We see that we obtain a seamweld connection between two parts 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 2-D mesh throughout the assemby with the given element Quality criteria.

3) We have assigned thickness for all the components after meshing.

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

Learning Outcomes:

1) Ability to mesh complex assembly like Cross Car Beam.

2) Ability to give connections to the meshed component.

Model Link:

https://drive.google.com/drive/folders/1OIKtGqpza1LzIPT8QLL8kWfe9FOtCDg3?usp=sharing