Structural And Volumetric analysis for BMW M6

Objective- To clear Topological errors and mesh and mesh the BMW model 6. Also create wind tunnel

Mesh parameters are as follows

Body = 3mm Element = tria

Lights = 4mm

Grills = 1mm

Tires and rims = 2mm

Optical rear view mirror(Orvm)= 2mm

Windows = 2 mm

Silencer = 3mm

Logo = 1mm

Wind Tunnel parameters

4 times to the front of car ,6 times to the rear of the car, 3 times to the top, at the bottom in close proximity with tires.

Procedure- Open the BMW M6 Model in the ANSA software,

-Change entity mode to PID mode, enable shadow mode and cross hatches.

-Click on quality criteria on the top tool bar and select presentation parameters. In visualization box (in front of Draw cons in PID, MID mode) should be ticked. This is done to check if cons are single double.

-We can see that the car is not that well defined and surfaces of the car are not sharp, this is because if we check the mesh length of the surface its 30 mm. The mesh is not fine enough to define the surface. So we change the length to 1mm using Length in Parameters in mesh module. We see a very clear logo of BMW.

- If we look at the model of the car we see that there are lines running alone the couture of the car. To see these lines clearly disable the Macros option which is at the bottom of screen besides single cons and double cons option.

-We see the lines clearly. These are the styling lines used to design the car, but we do not require these lines during mesh so by using Delete option at the top of tool bar we delete these lines.

-Click on checks on the main tool bar and on geometry in extension. In order to check if there is continuity in the surface and if there are single cons, cracks etc window select the complete model. After executing we can evaluate errors. We observe lot of Topological errors and discontinuities.

-Firstly we will clear out the errors on the body of the car. Using INOT option and (PID region) select the crosshatch on the body of the car and click scroll twice. On the first click the body is hidden and on the second click the body is seen and other parts are hidden.

-Now we see the first error on the body below the right mirror. We see the two surfaces are not connected together.

-we need to fill the gap or delete the entire surface and create another one. To delete the surface we can create a partition using Cut option.

- Delete the surface and generate another one using New option in faces and select coons. Generate a new surface now we see the single con is converted in double con.

Error 2

-If we see closely the surface is missing which is below the new surface we created.

-We select all option near INOT to see the all components. We see the part which is not selected in Inot option. Select the part on both sides of car and hide other components using Inot. Here we see lot of single cons.

-These surfaces look like they are intersecting with each other but they are not and hence the single cons are created.

- Using project option we project cons on to the surfaces to create triple cons.

-Also we use Extend option to extend the con on to the surface. This also creates triple cons. On the inside surface also we see a lot of surfaces intersecting and still there are single cons. Create triple cons and then delete unwanted surfaces to clear out the geometry.

-After deleting the unwanted surfaces we see minimum triple cons no single cons.

-Error 3

We see that the windows and wind shield both are having triple cons where the join with car body. Isolate the windows and front and back wind shield using Inot we see that the windows have a volume element. Same is for optical rear view mirror and the wind shield.

Delete the volume element and we see there are only double cons.

-Error 4

The BMW logo has a triple con. Now the logo has a very minuscule drag resistance compared to scale of the model. So we delete the logo and just cover it with surface.

We project the outer ring of the logo on the hood and delete the surface inside the ring.

At the bottom side we see there are two single cons, these are basically two single cons at same point. So we use paste option in cons and paste the two cons to create the double con.

We see that the car is symmetric through the centre plan of the car. So we can deleting half of the car. We do not delete the wheels as they are not symmetric.

Error 5 Grills

Isolate the grills.

We see a glitch on the surface of grill. This is because the are two faces. The fins of the grill also has a volume element.

The side and air intake grill has a volume element to it so while surface meshing we don’t need a volume element so we delete the volumes. Now enclose the grill and also eliminating single and triple cons. Patching the grills is done by new and coons.

Delete unwanted surface.

After completing the side and intake grill when you bring back the body of car there are single cons on the boundary of grill and car body. There are two single cons so Paste these cons.

Now for the face of the grill at the bottom we do same thing.

We see that there are lot of single cons, we project the cons on the surface and the delete the unwanted surface. In this we use command, Hot points Intersect and extend point on con. This projects a hot point on a con which is perpendicular to other con. Delete and patch so as to create double cons.

Error 6

We see that there is unwanted surface which intersects with the wheel. So intersecting the surfaces with the body of the car and then deleting the unwanted surface.

Similarly clearing the single cons at the bottom face of the car.

At The rear of the car the silencer intersects with body. We create space to house the silencer. In order to create a curved surface we use Guide under surfaces, in this command we select the con on surface which needs to be created and the con in the direction in which it needs to be guided.

Near the property icon on top tool bar we also have part icon. On clicking it we see a folder. Opening the folder we see all the parts of the car.

But we need all the parts differently. So using new in the window we name different part such as body, tires and wheels ,lights, grills, silencer etc.

Also naming the PIDs for different parts.

Error wheels

In parts just say show only for wheels, one of the wheel has lot of errors and it cannot be repared So in this case we delete the wheel. And later we can mirror the other wheel.

For the other three wheels we see triple con. To clear this error we project the cons and delete the surface which is hidden in between tyres.

After deleting we see a hollow tyre. complete this process for all three wheels.

Go to geometry checks and execute. We see a lot of single cons errors and others are needle face.

Clearing all the errors other than single cons as these errors are from deleting half of car.

After deleting all the errors we have only single cons for the deleting half of body. We can mesh. So switch to mesh mode.

MESHING

Mesh parameters are as follows

Body = 3mm Element = tria

Lights = 4mm

Grills = 1mm

Tires and rims = 2mm

Optical rear view mirror(Orvm)= 2mm

Windows = 2 mm

Silencer = 3mm

Logo = 1mm

Change the length of all the parts of car model as per the given parameters and then use free mesh to generate the mesh on the surface of model.

After generation of mesh click on checks manager and select surface mesh checks.

Enable the duplicarte check and execute We see that there are errors. Errors in sharp edges intersections and proximity.

Eleminating errors one by one. For sharp edges we use split under elements and cut under micros to clear the sharp edges.

CUT basically creates the con similar to in topo mode. Also in the option box select parametric cut and remesh micros.

Split just splits the element into more elements.

For both the options we use left click to select and scroll to execute the operation. And to reverse the cut we can use right click and execute with scroll.

For Intersection and proximity we remove with going to topo mode and deleting the unwanted surfaces.

Now go to quality criteria and enable only skewness, min length, max length. Values for min length is 0.9 and for max length is 5. This is because our length size varies from 1 to 4mm.

And also disable all other parameters using edit quality criteria.

In mesh parameters change to general and insert 0.9 and 5.

Enable Hidden mode.

We see that quality criteria has been applied and there are certain number of elements off.

If we right click on skewness and click on show only. We see the parts which has skewness and we can also see worst of skewness.

Similarly if we click on min length and say show only. We see the number of elements with min length off.

Using following options to clear all the off elements.

Reconstruct - This options reconstructs the mesh with in the parameters given in option box.

With the help of this most of the off elements are taken care of. We just select the mesh and press scroll to execute.

Also at the front of the grill we see the mininum length is 3.9 mm. This error cannot be eleminated. So we change the min length to less then 3.9 mm.

Swap under elements swaps the skewed element.

MV su and MV free - This can move the hot point along a con in order to eleminate error.

After clearing all the mesh quality criteria error, We can mirror the car along the center also mirror one of the wheels. This is done using transform and copy option on the top tool bar.

We use Symmetry option and 3 point plane. Select three point on the centre and execute.

We see mesh is already generated.

Now to create wind tunnel. We go back to topo mode. The length of the car is 1300 mm, we create the a point at 4 times length of car from front similarly 6 times length of car from rear end and 3 times from top surface. We also create point at 100 mm at the bottom.

Join the point with curves.

We Mirror the point twice in the same plane for each side.

Now to create surface we go plane option in surfaces. Select three point and drag for what length the plane should be.

Create planes for all sides and then intersect it. Delete the excess surface. Thus wind tunnel is created.