## PREPROCESSING BMW M6 MODEL USING ANSA

OBJECTIVE:

To surface mesh the BMW M6 model using different element size for different PIDs using ANSA v17.1.0 and observe the geometric change.

WHAT IS A MESH?

A mesh is a network that is formed of cells and points. It can have almost any shape in any size and is used to solve Partial Differential Equations. Each cell of the mesh represents an individual solution of the equation which, when combined for the whole network, results in a solution for the entire mesh.

PURPOSE OF MESHING?

Solving the entire object without dividing it into smaller pieces can be impossible because of the complexity that is within the object. Holes, corners and angles can make it extremely difficult for solvers to obtain a solution. Hence meshing is preferred.

WHAT IS A SURFACE MESH?

A surface mesh is a discrete representation of the geometry of the individual regions that will be used for the volume mesh generation.It i smade up of faces and vertices.

STEPS TAKEN:

STEP1: IMPORTING THE MODEL

The 1st step is to import the BMW M6 model into ANSA v17.1.0.

STEP2: GEOMETRY CLEANUP

PURPOSE OF GEOMETRY CLEANUP?

With the geometry cleanup process we are making the model geometrically continuous, that is all the gaps in between them are closed and thereby a geometry connectivity is created. Since meshing is a process of dividing the entire geometry into smaller pieces by forming a continuous group of cells over the geometry i.e., like a wire net over an object. Hence, we require geometry cleanups for fine meshing of the component.

Here, from the above image after opening the model and enabling the TOPO module then the SHADOW mode and then making a GEOMETRY CHECK we came to know that our geometry has errorswhich means that there is a gap between surfaces which is highlighted  using a red coloured line known as SINGLE CONS and overlapping of two different surfaces which need to be cleaned up to form a continuous surface.

After switching off the macros icon we see the styling lines of car which is unwanted hence we are deleting it.

Then we are isolating the body of the car using inot command with the pidregion mode switched on to execute geometry cleanup.

In the front right portion of the body of car near the window frame we see a single con that indicates an unattached surface which is corrected by using the command:faces-cut to create a boundary, then command:faces-delete to delete the surface and command:faces-new-coons to create a new surface.

Same in the front right portion of body near the tyre we require a geometry cleanup which is done using the commands

Cons-project to join two surfaces

Faces-extend to merge two surfaces

Faces-intersect to intersect the wanted surfaces

Faces-delete to delete the unwanted surfaces

Faces-new-fitted to create a surface

In the body near the window frame we see triple cons which is due to the volumetric surface of the mirror. But for mesh we do not require the volumetric surface we just need a surface. Hence we are deleting the thickness face and the inner face of the mirror for the mirrors in all the window frames using the command Faces-delete to delete the unwanted surfaces.

The grill on the front side of the bumper has intersection of two surfaces which should be removed and the surfaces between the frames is also removed using the command:delete. Then the frames are aligned using the command: faces-cut, to create a mold like structure which is perfect for mesh.

After completing the geometry cleanup on one half of the BMW M6 model we see that the same errors are occuring on the other half of the model, which means the errors are symmetric. Hence to cleanup the other half of the model is a time consuming process. So we are deleting the other half of the model using the command: delete and continue with the geometry cleanup.

STEP3: ASSIGNING PARTS AND PIDs

Here we are using command:ctrl+R to open the model browser for assigning different parts under a group by creating a new file.

Here by using command: Faces-setPID we are assigning PIDs for different parts created under the model browser and by using the command:compress we are deleting the unwanted PIDs.

STEP4: ASSIGNING LENGTH TO THE PIDs

Body = 3mm
Lights = 4mm
Grills = 1mm
Tires & rims = 2mm
Orvm = 2mm
Windows = 2mm
Silencer = 3mm
Logos = 1mm


To assign node length we should switch from TOPO mode to MESH mode.

As per above mentioned node lengths we are going to assign individual node lengths for each individual PIDs using command: perimeter-length by dragging cursor over individual PIDs

STEP5: SURFACE MESHING

Here, we are setting the mesh parameter values based on the node length for different PIDs.

After setting the mesh parameters, we are meshing the entire model using the command: Mesh generation-Free-Visible. Then we are conducting the surface mesh ckeck.

STEP6: QUALITY CRITERIA VALUES

After selecting the required quality critera we are now switching to the hidden mode which highlights the failed quality criteria over the meshed models to correct them.

STEP7: SYMMETRY OPERATION

After completing all the process we are going to create a symmetrical copy of the model on the other side by selecting a intersection plane.

By clicking on the transform icon, then using copy option and then by dragging over the model we are making a selection of model to be copied. Then by clicking on the symmetry mode and then by selecting the mirror 3 points plane option we are making the symmetric copy of the model selected.

STEP8: CREATING WINDTUNNEL AND MESHING

Once we are done with the above process we have to create a wind tunnel with the given parameters.

The parameters are as follows

1.4x Front of car

2.6x Rear of car

3.3x Top of car

4.Bottom close proximity with tyres

5.1x from the centre plane for left and right sides.

Here x is the length of car 1300mm.

Now to create a plane we should have 3 points which is created using the command:points-relative, followed by the command:curves-new to join the points.

Our next step is to create a plane using the command:surfaces-plane by selecting the created points.

Then we are intersecting the created planes using the command:faces-intersect and delete the unwanted faces using the command:delete.

Then assigning PID and mesh length for the wind tunnel.

Meshing the wind tunnel.

CONCLUSION:

The surface mesh of BMW M6 model using different element size for different PIDs using ANSA v17.1.0 is created successfully.

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