CAE || Surface Mesh Of BMW M6 using ANSA

OBJECTIVE

The objective of the assignment are;

• Carry out Geometry cleanup of the BMW M6
• Generating the surface mesh of the BMW M6
• To create vitrual wind tunnel for the model

PROCEDURE

1. Cleaning the topological errors
2. Assigning the PID
3. Generating the surface mesh
4. Fixing the mesh errors
5. Creating the virtual wind tunnel
6. Generating the volume 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.

In our case the geometry is symmetric hence only half of the body is taken into consideration then it is mirrored on the later stage. 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.

The below figure shows some of the errors in the given geometry model such as overlapping surface, intersection surface, unwanted surface, etc.

Different operation carried out to solve the topological errors are;

• CONS`->`Project : To project node on cons
• CONS`->`Release : To release the connection between cons
• CONS`->`Paste : To connects two cons
• Delete : To delete unwanted surfaces
• Face`->`Project cut : It is similar to project but here cons selected instead of node
• Face`->`Zone cut : Creates a cut offset to a con
• Face`->`Intersect : Creates a cut on the intersection between two surfaces
• Face`->`Cut : Creates a con between two nodes
• Face`->`New : Creates a new surface
• Face`->`Topo : It connects the surface
• Hotpoints`->`Intersect(with extend) : Creates a node in same line till a intersecting con
• Surface`->`Extrude(Glide) : Create a surface with respect to a guideline

The figures below show some of the topological errors before and after it has been solved;

The above figure represent the half geometry model before and after geometry cleanup and you can see that all the blue cons and red cons has disappered except in the end which is not a problem as it will be solved once the geometry has been mirrored.

ASSIGN PID

Once all the errors has been solved the next step is to assign PID for the geometry so that the components can be distinguished and will be easier to mesh; the below figure show the default PID (left) and assigned PID (right) carried out

MESHING

The mesh size for each component of the geometry(left) and the mesh criteria(right) for the model is as shown below

The mesh size for each component is assigned and genertaed using the following operation;

• Perimeter`->`Length : Select the components and enter the size of elements
• Mesh Generation`->`Free : Generates the mesh based on the size provided

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 below figure shows this explanation pictographically.

Once the intial mesh has been generated only the quality criterian will be visible in the model and there are still other errors that need to be solved, so inorder to find those error run a surface mesh check diagnostics. The below figure show the results of the diagnostics

Different errors involved in the mesh are

• Unmeshed Macros : These are the surface which has not been meshed
• Intersections : These are the elements that are intersecting with each other
• Sharp edges : These are the element which high skewness
• Proximities : These are the elements which are close together (in terms of height)
• Mesh Quality : These are the elements which doesn\'t follow the mesh criterian provided.

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 below figures shows the surface mesh check after eliminating the errors

Once the mesh errors are solved the model is mirrored using the Symmetric operation and Topo is done inorder to connect the surface and the mesh elements. The figure below shows the final mesh after it has been mirrored.

CREATING THE WINDTUNNEL

The dimension of the wind tunnel is as follows

• Front wall - 4 times the length of Car
• Back wall - 6 times the length of Car
• Side wall - 1 times the length of Car
• Top wall - 3 times the length of Car
• Bottom wall - Close proximity to tyres

The wind tunnel is created using the following operation

• Points`->`Relative : Creates a points relative to another point
• Surface`->`Plane : Creates a plane by selecting three points
• Face`->`Intersect : Create CONS on the intersection
• Delete : Deletes the surfaces
• Faces`->`Proj.Cut : Cut a surface upto selected CON

The below figures shows the windtunnel and the mesh carried out.

The volume mesh is not created due to insufficient computational power.

The link to initial Geometry file - https://drive.google.com/open?id=1v4Z9mn9izrxSbQf_YrbeU5AChNNRzZro

The link to final Geoemetry file - https://drive.google.com/open?id=17o8T9LRydD7IrokU9oHnBdihSrdbcaAZ