Meshing Hood for Structural Analysis using ANSA

Objectives :

• Clean up the given Hood geometry and then mesh the geometry with the Target element size of 5mm.
• Follow the given Quality Criteria and fix the criterian errors.

Topology clean up :

Before stepping into topology clean up of the model, the given model was in '.STP' format which was imported to ANSA. ANSA converted the the '.STP' format file into '.ANSA' file.

Below image shows the imported CAD model into ANSA.

The imported model had several errors including extenstion of parts due to poor CAD modeling, single, double and triple cons. To eliminate these errors we have used plenty of tools in ANSA which are listed down.

Tools used for clean up :

• Fitted - It is used on the selected surface, which are non-planar faces.
• Coons - Creates curves which is used to patch a surface.
• TOPO - Performs topology based on given values.
• Delete - Used to deleted all the cons, surface and any entities which are selected.
• Zone cut - Used to offset selected cons and make a zonal cut.
• Paste - Used to manually or automatically paste nodes.
• Perimeter Length - Used to assign nodal distribution of mesh on node lengths.
• Mesh Generation (BEST) - Generates the mesh for the assigned perimeter length or size.
• Spacing - Used to control nodal spacing on perimeter length.
• Offset - Typically offsets faces.
• RMBDL - Used to check the symmetry.

Procedure followed for Meshing :

1) After the topology clean up, the model was futher checked for any errors present in them using Geometry check.

There were unchecked faces, needle faces, crack between cons and single cons which were then eliminated and fixed completely.

Below figure shows the model after it was completely error free.

The surface was completely error free. The Geometry checks was run again and no error was found.

The Structural Analysis Meshing is done on exact mid plane of the model, so the given model was offset for its half of the thickness.

2) Mid planning or Offset :- Mid planning or Offset is done to make the symmetric geometry so that meshing can be done on one side and then replicated on to the other side thereby, saving computational/meshing time.

The inner pannel of the hood was offset by -0.75/2. The negative value was given to have the offset in the opposite direction of the arrow.

3) To check the Symmetry of the geometry :- It is very essential step as it shows the symmetry of the model that we had offset. This ensures that the model stays the same on both sides of the mid-plane.

This is done using a tool called RMBDL.

The above figure shows the RMBDL tool in action. The similarity factor was set to 100 %. The offset on both the side is shown by blue and green colour. The missing red colour on the hole is not offset as it is not in equal distance from the mid plane. This is very essential to check before meshing the model.

4) Meshing :- Meshing was done using BEST mesh as it uses all the mesh algorithm and then keeps only the mesh of best quality.

A mesh size of 5mm was provided.

Quality Criteria :

Quality Criteria for the Mesh Parameters were checked for Skewness, Minimum length, Maximum length, Maximum and Minimum angle quads and Maximum and Minimum angle trias.

Skewness is the measure of the deviation from the ideal equilateral triangle to the distorted triangle. It can also be defined as the irregularness of the triangle elements.

Maximum Length is the parameter which has a specified value in the quality criteria which should not be exceeded.

Minimum Length is the parameter which has a specified value in the quality criteria which should have a minimum value specified and value cant go below it.

The followed quality criteria is shown below.

After applying the given quality criteria conditions, the model had13472 elements which did not meet the conditions.

Below shown is the minimum length and maximum length errors the model had.

All these errors were manually fixed using move surface, swap, reconstruct and delete options. Then we had a perfect error free surface as shown below.

Conclusion :

• The given Hood model was cleaned for different types of surface errors using set of tools available in ANSA.
• The model was Meshed using the given Perimeter Lengths.
• Given Quality Criteria was followed to have a flawless mesh surface.