CAE || Meshing Hood for Structural Analysis using ANSA

OBJECTIVE

In this assignment shell meshing of the hood is carried out as per quality criterion and the steps involved are :-

1. Geometry cleanup
2. Generating mid-surface
3. Hemmimg
4. Assigning PID
5. Surface mesh

GEOMETRY CLEANUP

The above figure depicts the initial geometry model [Shadow mode(left) ; Wireframe mode(right)]. The red color indicates the single cons, the yellow color indicates the double cons & the blue color indicates the triple cons. For the perfect model only double cons should be present and in somecase triple cons is also feasible depending on application.

The intial step of the geometry cleanup is to get rid of single cons, then check for intersecting surface, overlapping surface, unwanted surface, etc. Run a geometric check inorder to find out the errors and below figure shows the errors available in the geometry after running the diagnostics. Hence all these errors should be solved before carrying out the mesh procedure.

Different operation carried out to solve the topological errors are;

• Face`->`Topo : It connects the surface
• Face`->`New : Creates a new surface
• CONS`->`Release : To release the connection between cons
• CONS`->`Paste : To connects two cons

The figure below depicts the geometry once it has been cleaned up

In order to verify that there are no topological errors; geometry check diagnostics is run.

Once the signal is green; we jump to next step ie midsurface generation

MIDSURFACE GENERATION

The option used here to generate the midsurface is SKIN option and requirements to carry out this operation are;

1. Clean geoemtry
2. Uniform thickness

From the above requirements the first has been satisfied and inorder to verify whether the geometry has uniform thickness the MEASURE option is used

As shown in fig above the geometry has uniform thickness and since both the requirements are satisfied SKIN option is used by going to Faces`->`Midsurface`->`Skin(make sure the option is selcted as shown below). Once the midsurface has been generated make sure to break the link between the midsurface and actual geometry by going to Faces`->`Convert (Select the midsurfaces).

Do this procedure to all the surfaces like innerpanel,outerpanel,reinforcement. Once the midurface has been generated make sure that those surfaces doesn\'t have any errors. The below figure shows the midsurface generated.

HEMMING

Hemming is the process of joining the inner panel and outer panel together and for creating surface mesh this should be considered and the procedure for that is as follows

1. Project the outer cons of the outer panel to inner panel surface
2. Project the outer cons of the outer panel to outer panel surface
3. Delete the outerpanel surface till the offset
4. Delete the inner panel surface till the projected cons
5. Paste the outer edge of inner panel to outer panel projected cons

Different operation carried out to carry out for hemming are;

• CONS`->`Project : To project cosn on surface
• Delete : To delete unwanted surfaces
• Face`->`Cut : Creates a con between two nodes
• CONS`->`Paste : To connects two cons

The below figure shows the above procedures pictographically

Above figure shows the step 1 & step 2 where the highlighted cons are projected to inner panel and outer panel surface

The figure above represent the step 4 & step 5 where the highlighted surface are deleted

The final step is to paste the cons as shown in the above manner where the maroon colour surface depicts the inner panel and orange colour surface depicts the outer panel.

ASSIGNING PID

The next step is to assign proper PID so that the surface can be differentiated easily which smooths up the meshing process and also defines the thickness as well as material property.

The figure on the left shows the PID assigned and the figure on the right shows the midurface of the inner panel,outer panel & hemming region. The thickness is assigned for the inner panel and outer panel as 0.75 and for the hemming region it is 2.25(2xOuterpanel + Inner panel).

MESHING

This is the final step and surface need to meshed as per the qulaity criterion and it is as follows;

The average size of mesh elements is considered as 5 and different operation carried out to carry out for meshing are;

• Perimeter`->`Length : Select the components and enter the size of elements
• Mesh Generation`->`Best

Once the surface mesh has been generated there will be some errors and some elements doesn\'t follow the criteria provided and those elements need to be solved.The fihure below shows some of the errors

Hence to solve these errors, different operation carried out are;

• Shell Mesh`->`Reconstruct : It remeshes the selected surface based on the max and min length criteria.
• Elements`->`Swap : It swaps the position between the two selected elements
• Elements`->`Split : It splits the elements into two
• Grids`->`Move Surface : It is used to move the node of the element
• Grids`->`Paste : It combine two nodes into one resulting in elimination of one element
• Macros`->`Cut(Left click) : It create a con in surface (to restrict elements)
• Macros`->`Cut(Right click) : It deletes a con in surface ( To unrestirct elememts)

The figure below shows the final mesh which meets the qulaity criterion

The link to initial Geometry file - https://drive.google.com/open?id=1HQtMDkTl94F_kesyLgKuBMSjUV1gbfFd

The link to final Geoemetry file -https://drive.google.com/open?id=1j7rBveHDT8YHX9iDNc4JIw4o58bPFMDi