Aim:

To create mid surface for the given hood model, during which PID and thickness assignment has to be done for all the mid surfaces. All the mid surfaces then have to be meshed with the given element quality criteria and mesh parameters.

Procedure:

Importing CAD model and geometrical error check:

1. Import the CAD geometry in ANSA.

Figure 1 - Imported geometry of Hood model

2. Using Tools --> Checks --> Geometry, the geometry of the imported model is checked for errors in geometry

Figure 2 - Checking for errors in geometry

3.Select all the errors, right click and select “Fix” for fixing the errors automatically.

Figure 3 - Automatic Fixing of geometrical errors

Creating Mid surface for the model:

1. At first, Faces --> Mid Surface --> Skin option was used to create mid surface for the given model. But the mid surface obtained from this option was not perfect and hence this will be used as a reference model for the further process

2. Using Faces --> Offset --> Faces and Faces --> Middle --> Single option, the mid surface creation has been done

Figure 4 - Created mid surface for the given bottle cap model

3. After creating mid surface for the given bottle cap model, the surfaces of the model were assigned with a PID in the Properties tab

Figure 5 - Create PID for all the bodies of hood model

Mesh generation:

1. The given quality criteria for meshing the component is assigned in Utilities --> Quality Criteria option

Figure 6 - Quality Criteria

2. Using the Save option, the quality criteria is saved so that next time when the model is loaded, the criteria can be loaded directly and hence reducing the effort of entering the values for every session

Figure 7 - Loading saved quality criteria

3. The mesh parameters are also filled out and saved as .mpar data

Figure 8 - Mesh parameter for the hood model

4. Perimeter Length is assigned to the component using Mesh --> Perimeters --> Length. Length is entered as 1.

5. In the Mesh Generation tab, appropriate option for mesh generation is selected. Mostly Best or Free or Spot Mesh

6. Select the faces to mesh and middle click to complete mesh generation

7. Shell Mesh --> Reconstructis used to rearrange the mesh. This helps in removing tria elements or mesh not generated properly

8. Shell Mesh --> Smooth is used to smoothen the mesh and arrange it equally. This option does not rearrange the mesh. But adjusts only the size of the mesh along the selected area

9. Grids --> Paste, Elements --> Split, Elements --> Swap are used to rearrange the tria elements and hence better mesh flow

10. In some regions, the model may have complex contours or the space between two contour lines maybe so small that the element created would be less than the minimum element size as per the quality criteria.

In such cases, the contour lines of the geometry is altered using Faces --> Cut (in Topo mode) or Macros --> Join (In Mesh mode).

Figure 9 - Modification of contour in Topo mode

Figure 10 - Final mesh of Top Hood

The mesh model still has some OFF elements. Number of OFF elements is 46. These elements were tried to be removed using the mesh flow correction options like Split, .etc.,. But it was not possible. These elements are due to two or more triple CONS. Hence, as mentioned in the challenge statement, these elements were ignored.

Learning Outcomes:

1.Mid surface creation for plastic components

2. Handling of tria elements using Split, Swap and Paste options

3. Modification and creation of geometrical contours using Faces --> Cut option, options in Curves Tab, Cons Tab, .etc., to ensure proper mesh flow

Conclusion:

Midsurface has been created for the given plastic bottle cap model. The geometry was checked for geomterical errors . The mesh has been generated as per the given quality criteria, in which the percentage of tria elements has been maintained at 2.39%, which is lesser than the value given in the criteria