Rear View Mirror Mesh using ANSA

Aim:

To check the geometrical errors and mesh of the given Rear View Mirror with Quality criteria and using tetra elements to model the component and there should not and kinks and dips on the surface of the component.

Methodology:

­The methodology of the given Rear View Mirror Element is as follows.

1. Opening the File
2. Checking the Topological Check-up
3. Creating Geometric Clean- up
4. Giving the Quality Criteria and Mesh Parameters
5. Initiating the Mesh Process
6. Setting Up the Volumetric Mesh
7. Checking the Volume

Given Model:

The given Model is the Rear View Mirror Model with the following Parameters.

S. No.	Quality Criteria	Value
1	Target / Average Length	1
2	Minimum Length	0.5
3	Maximum Length	2
4	Tet- Collapse	0.2

Theory:

1. ANSA:

ANSA is a computer-aided engineering tool for Finite Element Analysis and CFD Analysis widely used in the automotive industry. It is developed by BETA CAE Systems.

ANSA maintains the association between CAD geometry and the Finite Element (FE) mesh. This means that the FE meshes are better representations of their geometric parents. Also, it is easy to maintain and update any changes in the geometry by simply reworking the updated area instead of recreating the FE from scratch. It carries several proprietary algorithms for meshing suitable for both CFD and structural models.

The software takes a shell material to the solid geometry and converts it into the finite elements so that the model can get accurate simulation results in a shorter time.

2. Rear View Mirror:

A rear-view mirror (or rearview 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.

The rear-view mirror is augmented by one or more side-view mirrors, which serve as the only rear-vision mirrors on trucks, motorcycles, and bicycles.

Working:

A prismatic rear-view mirror sometimes called a "day/night mirror" can be tilted to reduce the brightness and glare of lights, mostly for high-beam headlights of vehicles behind which would otherwise be reflected directly into the driver's eyes at night. This type of mirror is made of a piece of glass that is wedge-shaped in cross-section—its front and rear surfaces are not parallel.

On manual tilt versions, a tab is used to adjust the mirror between "day" and "night" positions. In the day view position, the front surface is tilted and the reflective back side gives a strong reflection. When the mirror is moved to the night view position, its reflecting rear surface is tilted out of line with the driver's view. This view is a reflection of the low-reflection front surface; only a much-reduced amount of light is reflected in the driver's eyes.

Procedure:

1. Opening the File:

The file is downloaded initially. To open the file, follow the steps.

• Open ANSA >> Give Command Arguments >> OK >> Click Ctrl +O (for opening the file) >> Select the File>> Click Ok.

• On the Whole to describe the Opening of a file, click on the ANSA app, and wait for the launcher dialog box to appear.

• Once it appears, the dialog box contains the information called Additional ANSA command arguments are seen there will be an input box just below it.

• The argument has to be changed to “-performance_mode 3” (This means the performance of the app and it has Slower drawing and yet better quality.) then click ok to continue.
• The ANSA is now opened and then you can either open the file by using file option and open or Ctrl + O

2. Creating the Topological Clean-Up:

• This process is just used to check the topology of the model.

• In order to check the Topology follow the process as Tools>> Checks >> Geometry>> Execute.

• Once executed, it might show a green bar stating there are no errors in the geometry or it may show the dialog box showing the errors present in it.

• These errors can be fixed either by going on with them individually or once Right-clicked on the mouse an additional list pops- up.
• Fix option will be present in that pop-up when it is clicked the errors which can be fixed are executed and it might contain only a few errors which should be fixed manually and if no errors are present then it will show the green bar stating executed.
• The process is called geometric clean- up. It can be done either completely or part-wise of the parent geometry.

3. Generating the Geometrical clean-up:

• Geometric clean-up is done to make the model more suitable for the Quality Criteria.

• Compromises are to be done as the model had the intricate structure which doesn’t meet the Quality Criteria. To make the quality criteria a success, some minor changes in the design should be made.
• Additional lines that are not meeting the criteria are removed by using the cut option. Click Cut (in Faces Buttons tab)>> right click on the mouse to delete the line.

4. Setting up the PID:

• The PID is used to create a property of the particular model parts or the total model. To create a new PID or to check the existing PID’s.
• Click Lists >> Properties.
• You can see the Properties which are created before.
• To create a new PID, right-click on the dialog box, the drop-down appears. Click New >> PSHELL>> PSHELL.
• Then a New PID is created.
• To assign a part to the PID. Select the element needed to be assigned and do the middle click on the mouse to confirm.

5. Producing the Mesh for the Rear View Mirror:

• To create a mesh for any model, in modules select mesh.
• Click Modules >> Mesh.
• Once the mesh module buttons are opened and seen.
• Initially for mesh can be created by using tools like Hot Points, Perimeters, Mesh Generation, Shell Mesh, Elements.
• Firstly when the mid surface is opened in mesh mode, click Length in The procedure is as follows Length >> Perimeters, Macros. Select the entire mesh and confirm it, once it is done a dialog box appears stating the length as 1 in both perimeters and macros simultaneously.
• In mesh generation, Select Spot Mesh and select the element to mesh and confirm it.

• The Mesh might not be as perfect as it should be and contains many Off elements (Which doesn’t meet the Quality Criteria) to remove the off elements or to reduce them Reconstruct option is used.
• It can be seen in Shell Mesh >> Reconstruct.

• Once the Off elements are fixed or reduced the mesh should be made softer. To make the mesh softer Smooth option is used.
• It can be seen in Shell Mesh >> Smooth.

6. Adding the Quality Criteria and Meshing Parameters:

• Before proceeding with the mesh, the quality criteria and meshing parameters are to be given to meet the requirement.
• The quality criteria are opened by either clicking F11 on the keyboard or by clicking Utilities >> Quality Criteria.

The Quality Criteria which are given are stated below should be entered in the shell icon.

S. No.	Quality Criteria	Value
1	Target / Average Length	1
2	Minimum Length	0.5
3	Maximum Length	2
4	Tet- Collapse	0.2

• After Giving Quality Parameters in the Shell icon, click on apply and then click Presentation Parameters and select element percentage and Detail on Demand effect to all details.
• The Meshing parameters are also added from Utilities >> Meshing Parameters.

7. Constructing the Volumetric Mesh:

• Open Volume Mesh in the modules tab. The new module buttons appear on the right side.
• In Volumes Tab, Select Define >> Select the Element >> Create a PID >> Click on the List icon >> right click on the PID >> Select Re-mesh >> Select Tetra Rapid or Tetra FEM >> Click OK.

• The volume is created for the shell surface.

8. Checking the Volumetric Mesh:

• Checking for Volume Mesh doesn’t require many tools to use.
• It can be seen either by using! Not or Not.

• The above image shows the before and after adding the volume mesh respectively.
• The part which is to be seen is to be kept and the remaining part is selected by using Not.

Terms Used:

1. Topology:

Topology on how the shape and structure of the model are connected. The topology is different from geometry as geometry deals with the shape of the element but the topology tells us how the shape is connected.

2. PID:

The PID is also known as Property ID. The PID generally assigns an ID either to a part of the whole model.

3. Mesh:

A mesh is a network that is formed of cells and points. It can have almost any shape in any size and it is used to solve the partial differential Equations. Each cell of the mesh represents an individual solution of the equation which when combined for the whole network, results in a solution for the entire mesh.

4. Volume Mesh:

Volumetric mesh is a polygonal representation of the interior volume of an object. Unlike polygon meshes, which represent only the surface as polygons, volumetric meshes also discretize the interior structure of the object. It is further divided into structural and unstructured Volume mesh. The structured mesh deals with the mesh network formed structurally or properly. The unstructured mesh deals with the mesh network created by using ortho-tria or tria elements. The volume elements created are as a random element.

Difference between Normal Mesh and Volume Mesh:

Surface Mesh	Volume Mesh
It deals with the creating of the mesh surface of the model.	It deals with creating the mesh for the interior of the model.
Mid-surface has to be created so the parent geometry doesn’t get disturbed.	No mid-surface is created and the mesh is done directly on the parent geometry.
Thickness can be added to the mid surface equal to the parent geometry.	Thickness can’t be added since the mesh is generated on the parent geometry.
It can be used for both shell and solid model creation. (Solid model with uniform and slightly varying thickness models can be dealt with.)	It is used only for the solid model creation. (For varying Thickness models are present, volume mesh is used)
It contains 2D elements like tria and quad.	It contains 3D elements like tetra and Hexa.

Quality Criteria Understanding:

1. Minimum Length:

The minimum length is defined as the least acceptable length for the mesh to get successful.

2. Maximum Length:

The maximum length is defined as the largest acceptable length for the mesh to get successful.

3. Tet- Collapse:

The defect which is generated when the height of the tetrahedron 3D element is less than the target element length is called Tet-collapse. It is defined as the distance of a node from the opposite face divided by the area of the face multiplied by 1.24.

`Tetra Collapse= (Node or height of the Opp.Face)/(sqrt(Area of the face) ×1.24)=h/(sqrt(A)xx 1.24)`

Result:

The Meshing of surface and the volumetric mesh is created without any errors. The mesh which is created is unstructured. The Mesh is shown as below.

The above images show the Cut View and full view of the Rear View Mirror.

Learning Outcomes:

The Basics of ANSA can be learned by practicing in this model. The following outcomes are learned.

• Geometric Clean-up.
• Topological Correcting.
• Creating the Mesh.
• Correction of mesh errors.
• Creating the Volume Mesh.
• Checking the unstructured mesh.

Google Drive Link: Rear View Mirror Meshed File