Volume Meshing (Tetra Meshing) of an Automobile Rearview Mirror using ANSA

Aim:

1) To clean up the given CAD geometry.

2) To perform 2-D meshing over the given CAD geometry and eliminate errors over meshing if any using given Quality Criteria.

3) To perform volume meshing or tetra meshing through out the given CAD geometry.

4) To eliminate errors if any in after completion of volume meshing.

Theory:

The CAD Geometry given to us is a rear view mirror of an automobile. The covering of the rear view mirror is made up of ABS plastic material. The rear view mirror is used to get a full view of other vehicles passing by from the rear side of the vehicles and can be tilted for better viewing angle of vehicle passing by the rear side.

Procedure:

1. Importing the CAD Model:

1) First, we open ANSA software and import the CAD geometry to ANSA database.

2) On opening the CAD geometry into the ANSA database, we provide perimeter length to the whole component for visualization of the curves & edges and also refine the CAD geometry. For this, we go to the Mesh Module and go to the length option present in perimeters section and provide the perimeters length and macros length as 1 as shown in the image given below.

3) After that, we perform TOPO using the topo option present in the Faces section of the TOPO Module.

2. Geometry Cleanup:

1) We, then check for geometrical errors in the CAD geometry using the check geometry tab present in the Tools toolbar as shown in the image given below.

2) We then fix all the geometric issues and then execute the check once again we obtain zero errors and 100% clean geometry as shown in the image given below.

3) As we are going to do volume meshing we don't need to take the mid surface of the component. We lock the view of the parent geometry.

3. Meshing:

1) We go to the mesh module and before we start meshing the component we have to set the quality criteria and meshing parameters using quality criteria and mesh parameters tab present in the utilities toolbar.

2) In mesh parameters, we set the min, max and target element length of the mesh and we provide the mesh type as tria mesh as shown in the image given below.

3) In the quality criteria, we set the min and max element length of the mesh as shown in the image given below.

4) 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 are important quality parameters required for the meshing the component namely:

1)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.

2) 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.

3) 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,

5) We can now mesh the component using tria elements for flat surfaces and ortho tria elements for curved surfaces using the spot mesh option present in the mesh generation section of the mesh module as shown in the image given below.

6) We need to eliminate all the quality errors caused during by using reconstruct option present in the shell mesh section of the mesh module.

7) We obtain the fully meshed model with zero quality errors as shown in the image given below.

8) After that, we have to define a volume before we proceed for volumetric meshing of the component. We define the volume for the component using the define option present in the volumes section of volume mesh module. We have to define all parts as there 4 parts present in property ID toolbar. We define all the parts and double on the property ID to confirm the volume as shown in the images given below.

9) Then, we have to provide material to the volume by defining the material ID as shown in the image given below.

10) After, that we provide the quality criteria for the tetra mesh as shown in the image given below.

11) We then have to go for tetra meshing by using the Tetra FEM option present in the Unstructured mesh section in the volume mesh module. After finishing the meshing part we remove all the errors like kinks and dips on the surface of the volume using the MV Free option present in the grids section of mesh module as shown in image given below.

12) We finally obtain a mesh volume that occupies the whole geometry which can be visualised by switching off the geometry and FE options present in the visibility tab as shown in the image given below.

Conclusion:

We have initially cleaned up the CAD geometry and performed 2D meshing over the whole component using tria and ortho tria elements. After that, we have defined the volume and then we have created the volume or tetra mesh contained no errors like kinks or dips or collapse elements. The below image shows the final meshed model.

Learning Outcomes:

1) Meshing the given component using only tria and ortho tria elements.

2) Defining a volume and applying volume mesh or tetra mesh over selected volume and clearing errors such as kink, dip and collapse elements.

Model Link:

https://drive.google.com/drive/folders/1O2axC400TvyCrWm_bFzmFdMnshk0guT8?usp=sharing