Week 5

Aim :- Rear view mirror geometrical error check and its mesh generation using tetra elements

Objective :- For the given component, check for the geometrical errors and mesh with the given element Quality criteria. Use tetra elements to model the component and there should not and kinks and dips on the surface of the component.

S.No	Quality Criteria	Value
1	Target/Average length	1
2	Minimum Length	0.5
3	Maximum Length	2
4	Tetcolapse	0.2

Introduction :- A rear-view mirror is a flat mirror in automobiles and other vehicles, designed to allow the driver to see rearward through the vehicle's rear window (rear windshield).In cars, the rear-view mirror is usually affixed to the top of the windshield on a double-swivel mount allowing it to be adjusted to suit the height and viewing angle of any driver and to swing harmlessly out of the way if impacted by a vehicle occupant in a collision.

Methodology :-

• Importing the model into ANSA and checking for geometrical errors .
• Dividing the components into small parts and setting different PID
• Giving the quality criteria and mesh parameters
• Performing mesh using in 2D
• Giving the volumetric mesh and checking, solving the errors.

Procedure :-

1. Importing the model into ANSA and checking for geometrical errors

First the CAD based model of the rearview mirror is imported into ANSA.

we will now change the resolution of the model to check quality of the model if there any abrupt surfaces.

Here changing the LENGTH to 1 to make it more fined model

Checking for geometrical errors :-

It is important to check the model to see if there are no single cons and overlapped surfaces due to triple cons. This is done to avoid any errors in the volumetric mesh .

Here the errors we have encountered are

Triple cons

Needle faces

Triple cons can be released to see if there is any additional faces created, then that can be eliminated

Using all the available tools these kind of error can be eliminated at first .

2. Dividing the components into small parts and setting different PID

The rear view mirror cannot be directly meshed because there are small inside surfaces connected using joint. So here the whole component is divided to small parts as

• Frame holder
• Ball or spherical cup joint
• Mirror frame
• Mirror

Using the !NOT, AND, NOT functions the component is separated. Below picture shows the PID window of the component

3. Giving the quality criteria and mesh parameters :-

Before proceeding for the mesh quality criteria given as per the requirement has to be followed. Here quality criteria are

• Minimum and maximum length

Minimum as 0.5

Maximum as 2

This to define the distance between to nodes over the surfaces. Any two nodes having distance less than 0.5 and greater that 2 will fail in element size

• Average length as 1
• Tet collapse

Tet collapse is an important criteria will dealing with the volumetric mesh also it is only applicable to the tetra elements only. As we know that tetra element is 4 noded element having 4 side and 4 nodes.

Tet collapse or TET element is the minimum of (h/sqaure root of A)÷1.24

Where h is the perpendicular distance from node to the opposite face of the TET and

A is the area of the opposite face

Then if the height of the any tetra element falls below the desired height, it will eventually fail for the Tet collapse

There are 2 methods to solve the TET collapse as studied in the article

Article :- skill-lync.freshdesk.com/support/solutions/articles/43000568757-how-to-solve-tet-collapse-in-tetra-unstructured-mesh-

• MV free
• Fix quality

4. Performing mesh using in 2D and volume mesh :-

The components here are first meshed in 2D then those elements are given the volume mesh.

• Meshing of the mirror frame

The above picture shows the mesh of holder with no errors , passing the quality criteria. Here ortho tria was used for the the curved surfaces and tria for the flat surfaces

The above picture shows that the part is not meshed from inside i.e in volume. the part has to be given volumetric mesh otherwise it will be not fit for simulation process. The volumetric process is followed by defining the part as solid in volume mesh. Then we can for either

• Terta FEM
• Terta RAPID

Here we are using the TETRA RAPID method for the volume mesh .

The above picture show that

Total tria = 8550

Total tetra = 40415

the above picture shows the unstructured volume mesh if the frame holder

• Meshing of the cup joint :-

The total tetra element no. as 1918 with no TET collapse and kinks

The picture shows the unstructured volume mesh of the cup joint .

• Meshing of the mirror frame :-

The picture shows mirror frame 2D mesh with no off elements with trias no. 58852

The above picture shows the volume mesh of the mirror frame with no TET collapse and kinks with tetra no. 389252

The picture shows the unstructured volume mesh of frame.

• Meshing of the mirror :-

The above picture shows the 2D mesh of mirror with no off elements with tria no. 52998.

The above picture shows the volume mesh of the mirror with no TET collapse and kinks with tetra no as 156456.

The picture shows the unstructured volume mesh of the mirror .

The above picture show the surface mesh of the whole component in section view.

The above picture shows the volume mesh of the whole component in section view

• Final meshing of the rear view mirror

Results :-

Component	No. of tria elemnt	No. of tetra elements
Frame holder	8550	40415
Fame mirror	58852	389252
Cup joint	1346	1918
Mirror	52998	156456
Total	121746	588033

Conclusion :-

The 2D mesh followed by the volume mesh of rear view mirror is carried out successfully. The volume mesh much quicker than the 2D maybe due not many quality criteria. There can be TET collapse in volume mesh but here we did not encountered any of those. Also comparing with the 2D mesh, 3D mesh are unstructured pattern .

https://drive.google.com/drive/folders/1VXegyvu5cq-LI_GYDLa71vF0YU0P0ToM?usp=sharing