Meshing of BMW and creating wind tunnel using ANSA

Objective- To Mesh the BMW M6 Model and create a wind tunnel for the same using given dimensions

Procedure-

First of all we imported the CAD file of the model provided to us in ANSA. Then we enabled the edges and shadow mode from wire frame mode and we went ahead for geometrical checks and as expected it had a lot errors.to define the geometry in a detailed manner we used operators like Permetrs in the mesh modeule and gave an input of length as 1 unit instead of 20(earlier value)

Note- we didn’t mesh,we just gave the parameter as 1 and the geometry was defined in more detailed manner.

Fig 1 errors in cad file

We started with working on TOPO errors, more precisely we started with the right handle.

we used various set of operations with various operators like cut project delet and apart from these we used not and inot operators several times to reduce the complexicity our model while working.

After getting done with this we moved to rectify the logo.there also we performed similar operations using the same operators.we deleted the BMW

part of the logo too because it was creating unnecessary volumes and of-course it can be neglected as the model we are working on is very massive in comparison of this logo and it won’t affect our main results of CFD.

After we were done with the right handle of our model we moved to grills.We started with the one at right bottom,beneath the lights(front).As we can see in the diagram given below the component has an seperate volume other than the grills ,which we don’t want and they do have triple cons which are non-desirable .so in order to avoids errors in meshing which is our primary objective we will have rectify the same. We did the same with central grill and the engine inlet grill. Though the set of operations performed were different but the almost the operators used were same and objective was also same e creating single volume from separate ones and eliminate the non-desirable surfaces.

We again did the same we used a set of operators like-

1. Coons – to create new surface
2. Delete – to delete extra surfaces
3. Cut – to separate surfaces
4. Project – to get projections of desired coons on desired surfaces
5. Fitted – to create new surface with different orientation
6. Hot pints - to create hot points at desired locations
7. Paste – to paste two single cons and make them a double con

fig 2(a) errros in grills (before)

fig 2(b) after

After getting done with this part we looked for syymetry in our model and we found that our model was symetric (we hide the tires beacause they might not be si milar).

fig 3 top view showing syymetry

So in order to be more efficient and conserve our tine and efforts we will be deleting the left half of the model and work on the right half and once we are done with the one half we will copy it the other side using transform operator.

fig 4 deleted half

After deleting one half of the body we started again rectifying the topo errors present in the body. We rectified the grills using the similar technique we had applied the grill rectified earlier.

After grills were done we went for assigning different parts through model browser. When we opened it ,we found that it had only one file named as BMW M6 and all the parts were inside it only and it was creating a bit hassle in accessing those files so we diveided the the whole file among different parts by using new part or file option from the model browser and we used not and inot operator too to make the desirable parts visible.

fig 5(a) before assigning varous parts to various files in model browser

fig 5(b) after assigning varous parts to various files in model browser

After this we went ahead for rectifying the topo errors of the silencer part of the body.there also a separate volume was created due to designing .so used operators like cut,coons,project,extent,intersect,glide,delete

To get the desirable results.

fig 6(a) before

fig 6(b) after

After this we went to clear the geometry of the bottom surface of the body which was complex and consisted of several unwanted surfaces.We used the similar operators that we had used earlier in this operation also.Almost in every operation we performed for geometry clean-up we used similar operators like cut,delete,project,coons,paste,release etc with different combinations to obtain the desired results.

And afterwards we found half of our car to free from TOPO errors.

Afterwards we went ahead to symmetrically cut our logo which wasn’t symmetrically divided earlier and we divided that too in a manner which we can be used afterwards to mirror the body to get the full body of the vehicle.

After it we ran a geometry check on half body and we found errors in the form single cons which running along the edge of the body due to symmetrical cut we had performed on the body of the car.we don’t need to worry about that because once we are done with the meshing we will mirroring it obtain the other half and later can be joined using the paste option.

After this operation we went ahead to assign the PIDs so that our job can be easier and smoother.

fig 7 assigning pids

After all these operations we performed one last time geometry checks to look for any errors and we found no errors other than the single cons running on the partion edge of the half body.

Now the only geometrical errors we were left with was tires.

Now upon examining the tires closely we found that almost every tire has no errors apart from triple cons.

The tire present at the left front was completely distorted and it was very difficult to clean its geometry. So we first checked the alignments of the tires and looked for the orientation that weather it was uniform or not and found that the tires were also symmetric and aligned .So we deleted the two corresponding tires beneath the deleted body and started working on 2 tires left.

In the tires we found one triple cone running at the point of contact which was due to a volume trapped between rims and wheel which we cleared by deleting the extra surface trapped between them.

After this we went ahead to make the logo part half and symmetric so that after meshing we can perform the copy operation using the transform operator.

fig 8 making logo symetric

This is all about finding and rectifying the TOPO errors.

Once we were done with it,we were good to go for meshing.

MESHING

For meshing the model we were given a set of datas because we had to carry out length oriented mesh i.e different parts of the model had different length values.

They are as follows-

1. Body – 3 mm
2. Lights – 4 mm
3. Grilles –1 mm
4. ORVM –2 mm
5. Windows – 2 mm
6. Silencer – 3 mm
7. Logos – 1 mm
8. Tires and rims – 2 mm

Element – tria

So we assigned the different length parameters to the respective parts through highlighting the required one and switching off the visibility for the unnecessary ones through model browser and then we went ahead and meshed the model using the free mesh operator.

fig 9 mesh errors

As you can see in the screenshot above we had several mesh errors when we checked for surface mesh errors using the surface mesh check operator.

It had several off elements too which meant it had surface mesh errors like

Skewness,taperness,warping,angle issues and so on.

This was viewed by using the Hidden Mode present beside the wireframe mode (bottom right side) of the utility menu present beneath.

So we need to fix them in order to complete our objective.

We did the same by using different operators like-

1. Split – to split the elements in to 2 using nodes or edges
2. Mov sur – to move the nodes along a surface
3. Cut (macros) – to get rid of lines which restrict the natural size of elements which further causes surface mesh errors
4. Auto fix – it is a combination of reconstruct,remesh ,reshape which ANSA uses to fix the errors by itself.

By using these operators various times with non-uniform patterns ,we were able to get rid of surface mesh errors.

Note- the surface mesh errors caused are not rectified using a fixed pattern. They are rectified using the operators listed above with different set of combinations.(mostly).

fig 10 no off elements

fig 11 no mesh errors

Note- Although there is a warning message in the mesh-trias on corner segment but that can be ignored as that is a warning only.

After rectifying all the surface mesh errors we were done with meshing part and we then performed the symmetry and replicated the left half by using the transform operator and then our entire model was meshed and had no surface mesh or geometry errors.

Once we were done with meshing we had to create wind tunnel with given parameters now.

The parameters were as follows-

1. 4x front of the car
2. 6x rear of the car
3. 3x top of the car
4. Bottom close proximity with tyres
5. 1x from the centre plane for left and right sides

Where x = length of the car which comes out to be approx. 1300 mm for the given model.

Now in order to create a plane we first had to create 3 points cause only then we can create a plane .

We did the same using the Relative operator present in the pints module in the topo module.

We created respective points with given parameters and for the bottom surface we took a arbitrary distance of 100 mm as we don’t want the tyres to interact with the wind tunnel walls.

After creating the point we created the planes using the plane operator present in the surface module of the topo module.

And we moved to mesh module to mesh the wind tunnel.

Now as the flow will be maximum near the body of the car, we need a finer mesh over there and on the top we don’t need that fine mesh as much we do need for the botton side,so for that we need to assign a varying mesh length parameter i.e 20mm-100mm.

We did the same by using spacing operator present in perimeter module of the mesh module.

fig 12 assigning varrying mesh length

After assigning the variable mesh length perimeter we meshed the same.

And then we assigned separate PIDs for the inlet , outlet and the walls of the wind tunnel.

Conclusion-

1. We learned how to approach for the geometry clean-up for a complex model
2. We learned how to perform symmetry operations and make our work easier and faster i.e smarter.
3. We learned how to rectify surface mesh errors.
4. We learned how to assign variable mesh length parameters.
5. We learned more about the operators of the Mesh module.

Google Drive Link - https://drive.google.com/open?id=1i3JJmnmVj6Su8DxiiWETSbvkianoDibN