Week 5

Objective:

The goal is to clean the surface geometry to avoid errors and carry on the solid meshing (3-D) process and create a mesh that accurately captures the input domain geometry(rear view mirror) with high-quality cells so as to make subsequent calculations intractable.

The above-said goal is achieved by using the most widely used Pre - processing software named ANSA.

What is ANSA?

ANSA is an advanced multidisciplinary CAE pre-processing tool that provides all the necessary functionality for full-model build up, from CAD data to ready-to-run solver input file, in a single integrated environment.

ANSA is the user's preference due to its wide range of features and tools that meet their needs. The list of productive and versatile features is long and the alternative tasks and processes to be completed using them are countless.

Mesh generation:

Mesh generation is the practice of creating a mesh, a subdivision of a continuous geometric space into discrete geometric and topological cells. Often these cells form a simplicial complex. Usually the cells partition the geometric input domain. Mesh cells are used as discrete local approximations of the larger domain.

Purpose of meshing:

Meshes are used for rendering to a computer screen and for physical simulation such as finite element analysis or Computational fluid dynamics.

Finite element calculations cannot be done directly on solid parts. We know to perform those calculations only on points created by the mesh generation process. Thus generating mesh is a must and most important step for any CFD or FEA calculations to be performed.

Steps involved in geometry clean-up by ANSA:

1.The solid part made using any cad modelling software is imported into ANSA. The Procedure is File>Open and select the required solid part.

2.The solid part is initially imported as unconnected surfaces as shown above.This may be due to ANSA's translation issues. TOPO option in faces tab is used to connect the faces of the geometry as shown below.

3.The geometry is checked using the checks button and selecting the geometry checks option as shown

4. The geometry check dialog box displays various errors in the geometry.

5.You can highlight any of the problematic areas by left-clicking on it, or isolate it on the screen by right-clicking on it and selecting “Show only”. Depending on the type of problem ANSA also offers the option to automatically fix it.

6.Close the Checks Manager window. Click “All” from the focus toolbar to make all the faces visible again.

7.De-activate “Shadow” mode and the visibility flag button for “Double” CONS. You will now isolate a region of your part to work on. Activate the “Or” function located in the Focus Toolbar. Make a box selection of the area shown on the left using the left mouse button. The “Or” function leaves visible only the selected Faces. (If you accidentally select wrong Faces, press the All function of the same Group to bring all the entities back to visible).

8. Activate the “Lock” flag button in the Focus Toolbar to lock the currently visible entities. Now when you press the “All” button, only the selected and locked entities will become visible.

9. To view the complete Faces that you have left visible, activate again the “Double” CONS visibility flag. Activate also the “Cross Hatches” visibility flag. This allows the visualization of two green dashed lines along the center isoparametric of the Faces. Apart from visualization purposes, the crosshatches are also used for selecting Faces.

10. After visualizing the surface to be cleaned using various topo corection tools provided in topo mode. Some of the visualized errors are shown below

11. The topo mode provides following menus to perform geometry cleanup

TOPO menu

In this menu, the user can create, modify and clean up the geometry. The menu is divided in groups of functions according to the entities that they refer to.

Hot Points

These functions are used to create or delete Hot Points or Weld Spots.

CONS

Functions that are applied to CONS (Curves ON Surfaces).

Faces

Functions to create or modify Faces.

Surfaces

Functions that create Faces and modify Surfaces.

Curves

Functions to create 3D Curves.

Points

Functions to create 3D Points.

Auxiliaries

Functions to create Working Planes in order to draw in 2D mode.

12. After performing clean up the geometry is again checked for error using geometry checks.

3-D meshing process is explained below:

The quality criteria for the given model

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

The mesh parameters for the given model

• The next step is to mesh the geometry with the tria elements and we can choose either ortho tria or tria. If in case we need to mesh the feature like fillet and curved faces we will go with the ortho tria since it captures the features pretty well and in a proper way and in the flat faces we can go with the tria since the tria and ortho tria gives similar results in the flat faces.
• the model with the surface mesh is shown below

The off elements in the mesh is been corrected by using the reconstruct and smooth options under the Shell mesh option and the MV Free under the Grids options.

• In the volume mesh, we need to define a separate property and to mesh the component with unstructured mesh-like Tetra Rapid or Tetra FEM

• In the Volume module under the list option, we need to right-click on it and to do remesh with Tetra Rapid or Tetra FEM

• The kinks and dips on the surface of the component to be rectified using MV free command under the Grids option

Learning outcomes:

Learned to use Volume mesh and also got the idea of Tetra Rapid vs Tetra FEM.

Studied the structured and unstructured mesh.

Learned to remove the collapse error in the volume mesh.

Conclusion:

The geometry clean up is done properly

Assigned the property, materials, and meshed the component using tria and ortho tria elements.

Initializing the volume and do a Rapid tetra meshing with the provided quality criteria

Link for the Tetra Mesh in Rearview mirror provided below:

https://drive.google.com/file/d/1-yfBZOYmMFdHP65aUIoUwT4y8clEfItc/view?usp=sharing