3D Tetrahedral Meshing of Rearview Mirror

3D Tetrahedral Meshing of Rearview Mirror

Aim:

Performing Geometry Clean-up, and 3D Tetrahedral Meshing of the Rearview Mirror using following quality criteria on ANSA.

Sr No.	Quality Criteria	Value
1.	Target / Average length	1
2.	Minimum length	0.5
3.	Maximum length	2
4.	Tetcollapse	0.2

Overview of Solid Meshing:

Solid Meshing also called as 3D Meshing is used in a case where the thickness is above 5 mm. If 2D Meshing is done for part with thickness beyond 5 mm there will be plethora of error, something which is undesirable. In an effort to reduce or eliminate, we go ahead with 3D Mesh. 3D mesh fills the entire volume of the part, which is called as Volumetric Meshing. The pros of solid meshing is, the meshing time comes down against the con that the time required for computation increases.

Solid Meshing is of two type:

1. Structured Solid Meshing
2. Unstructured Solid Meshing

Structured Solid Meshing

Structured mesh are the one having quad elements. Nevertheless any other element shape, including quadrilateral or hexahedral element, is also possible.

Fig: Structured Solid Meshing

Unstructured Solid Meshing

Unstructured mesh are the one having trias elements and is well suited for arbitrary geometries. The use of an unstructured mesh has become more prevalent in CFD applications. The majority of commercial codes nowadays are based on the unstructured-mesh mesh approach. Despite its many advantages, there are disadvantages of employing an unstructured mesh for CFD simulations. It may result in increased computational times in obtaining a solution and may erode the gains in computational efficiency.

Fig: Unstructured Solid Meshing

Procedure:

Rearview Mirror: Rearview mirror is used in every on road as well as off highway automotive.

The given rearview mirror consist of four parts:

• Mirror Base
• Mirror Interior
• Rotating Ball
• Holder

1. Geometry Clean-up

First we will import the CAD geometry in ANSA readable format. Once imported we will perform TOPO over the entire part to join the faces. We will give it a perimeter length of 1mm.

Fig: Imported CAD Fig: After performing TOPO

Before meshing we need to make sure that the given part is free of any topological error. We need to eliminate this to make sure the part is of good quality for meshing.

We will check for number of errors to be addressed by Geometry Check-up. We will address all of the issue one by one and eliminate them until there are no errors left and dialogue box gives green signal on execution.

Fig: Topological error Fig: Error free geometry check

Next, we will set the mesh parameter and quality criteria. In mesh parameter we will set average length as 1 mm. We will also select Ortho Tria and 1^st order.

Fig: Mesh Parameter

We also set the following quality criteria. Minimum length as 0.5 mm, maximum length as 2 mm and collapse to 0.2.

Fig: Quality Criteria

2. Surface Meshing

For the given part, we will use unstructured solid meshing to eke out the best result. We will use normal tria as well as ortho tria for meshing. On curve areas and fillet we will deploy Ortho tria to get smooth mesh and good surface. Normal tria tend to distort the surface, as a result we will deploy it on flat surface or roughly plain surface. We will keep a mix of it to reduce the computational time.

Fig: Ortho Tria on Curve potion and fillet Fig: Normal tria on flat portion

We will carry these with rest of the surface for meshing. Once completed, we will eliminate the off elements. Most of the off elements are reduced by reconstructing the problematic region one at a time. For other areas such as below we can simply use Perimeter Slide option under MOVE command.

Fig: Before Fig: After

Fig: Before Fig: After

In this manner, using series of operation we will reduce the off elements completely. As there are no intricate portion, a complete elimination of off element is possible.

Fig: Surface Meshed Rearview Mirror

3. 3D Tetrahedral Meshing

For 3D meshing, we need to make sure we select each sub part with different PID one at a time and carry out meshing. We will define the volume first, manually. Once done we will carry out Tetra FEM on the subpart.

Fig: Defining Volume

For the following, we define the volume and carry out Tetra FEM. We will check out for any tetcollapse and eliminate each and every one of them using MV Free command. We will also make sure the given part is free of dips and kinks, most of which is seen at edges and fillet areas.

Fig: 3D Tetrahedral Mesh of Rotating Ball

Fig: 3D Tetrahedral Mesh of Mirror Base

Fig: 3D Tetrahedral Mesh of Mirror Interior

Fig: 3D Tetrahedral Mesh of Holder

We can check cross sectional view, from this we can clearly view the mesh inside the volume. The volume are a prismatic structure filing the inside of part.

Fig: Cross sectional view of 3D Tetrahedral Mesh

Result:

Shell

Quad: 0 (0 %)

Trias: 119396 (100 %)

Total: 119396 (100 %)

Volume

Total Tetras: 861129 (100 %)

Conclusion:

The 3D Tetrahedral Meshing of Rearview Mirror after Cleanup of topological error and Surface Meshing is done. The following is the final 3D meshed part.

Link of Solid Meshed Rearview Mirror:

https://drive.google.com/file/d/13oCdvGD_CGhehFAFwnWMLE8LSvvhCbRA/view?usp=sharing