[gav]

Hi everyone,

I was hoping someone could give me a bit of advice for meshing a model of a tyre so that it can later be set to a rotating wall bc in CFX. The tyre is just a simple cylindrical shape and tangentially contacts the floor of the rectangular box I've set up as a simulated wind tunnel.

I want to get the surfaces of the box to mesh with nice regular rectangular elements, and similar with the tyre. I can get this to happen when I only run a surface mesh but as soon as I do the volume mesh it re-meshes the surfaces and they look really bad. This seems like a very basic problem I'm having so hopefully someone could help me out a bit.

The other main problem is at the contact point. The meshes always seem to join up for the floor and tyre surface meshes, leaving a hole and incorrect geometry as shown below. Can anyone tell me how to set up the mesh properties to fix this?

Contact_problem_mesh.jpg Contact_problem.jpg

I would really appreciate some help with this as I'm a bit pressed for time and have been struggling with these problems for a few weeks. Even if someone could point me towards some papers of books on this sort of stuff it would be great.

Thanks in advance,

Ciaran

[sarangdalne]

I think that the road surface and you tire surfaces are intersecting and that is the reason why you are seeing bad mesh around contact region.
Following are the things that you should do:
Clean your geometries.
a. Go back to DesignModeler. Make sure you have proper distinction between the two bodies.
b. slice the tire body vertically in to two parts.er doing this even you generate mesh with default settings you will get a pretty descent mesh. You may then play with face sizing to get appropriate quality.
I have tried a similar example and it very fine if you try above options.
See the attached images:
tire1.jpg

tire2.JPG

tire3.JPG

[gav]

Thanks sarangdalne that's good advice about intersecting surfaces but I'm still having issues. What mesh type did you use for your model? And did yours have a volume mesh as well? And when you say split the tyre down the middle do you mean in my geometry software (SolidWorks) or in ICEM? Thanks again.

[dst]

Hi,

working in ICEM clean geometry. Delete all curves and points you have now.

Get curves on the sharp edges only (can't see if there are such on the tire, but one edge - the road-tire intersection). Get the curves using intersections of the surfaces or the surfaces edges (do it manually and not with automatic curve/point definition).

The only curves you need are the curves in the sharp edges. Because only sharp edges should be described by the edges of tetras (let's say, along the line you will have 10 tetras - and all 10 tetras should have their edges attached to the curve directly - that is why you need curves there).

As an example, tetra:

set the global size for tetra in domain and then set sizes for surfaces. For this case you should maybe split the wheel in ICEM in radial direction to have separated surface near to the contact point. The same concerning the road - separate surface to get a special part near to the contact.
This parts you need to set there a small tetra size.
To see the size turn on "tetra size" in surface options.

When ready with setups, generate the solid mesh directly (without any surface mesh before).

For moving wall simulation, make some prism layers on the wheel.

Best regards,
DST

[gav]

Ok so I've tried to clean up the geometry a bit, the only edges are now the boundary box edges and the contact point between the tyre and the road. I've also got a fairing in front of the tyre (I know I shouldn't be making things more complicated until I've figured out how to mesh the tyre first but I couldn't load the other geometry). The fairing has some very sharp edges so it has some curves too. When I run the mesh it looks way better now (thanks for the tips guys) but it doesn't have any volume elements so I can't export to CFX. Here's a screenshot can anyone think of a reason why I'm not getting volume meshed? In 'Global Mesh Setup' I've set the volume mesh parameter to hexa-dominant and ticked the box 'remesh centre'. Then I changed some of the sizing options for individual parts and computed the mesh without first doing a surface only mesh...

fairing.jpg

[PSYMN]

Gav wants a CFD mesh around the tire... Sarangdalne is showing an FEA mesh of the tire and ground plane... Very different.

As usual, DST has given good advice.

Gav, in your final image, I don't see the intersection curve between the wheel and the ground plane. Without this intersection curve you will not get a sharp intersection.

Also, don't use Hexa Dominant. That method requires a quad surface mesh and generates a mesh that is much more suited to FEA solvers.

If you are starting with a quad surface mesh, I recommend the delaunay tetra mesh method. If you are starting with out mesh, I recommend the Octree Tetra mesh method since it creates its own surface mesh...

Either way, you could add density lines or other settings (such as width on the tire) to help refine the mesh locally.

[sarangdalne]

Simon,
I used CFD solver preference with CFX as target solver in the ANSYS meshing application to get the mesh as shown in my previous reply.
However, I was able to mesh the same geometry successfully in ICEM too.

Gav,
As already suggested by Simon, don't use Hex meshing for the tire. I got good results with tetra in combination with some surface sizing.
Hope you get this resolved.

Cheers,
Sarang

[PSYMN]

To be clear, I am not saying don't use Hexa... You could use hexa or Tetra... But don't use the Hexa Dominant Method, and if you use Hexa blocking, you should block around the tire, not the solid portions of the tire and ground plane...

For a new user, tetra is probably easier than interactive hexa blocking.

[gav]

Got it to work. Thanks for the help everyone. What Simon said about tetra being easier for beginners is definitley correct. Here's the a post picture if anyone's interested:
FINAL_TYRE_ISO_STREAMS.jpg

[Dothan]

Hi Gav,
did you simulate the rotation of the wheel?
if so, how did you resolve the contact region and the rotating reference frame?
tnx

[PSYMN]

The wheel looks smooth, so the surface of the wheel probably just has a boundary condition that is rotating (instead of a fixed wall or wall with Cartesian velocity)... It doesn't need a rotating zone or anything that complicated. The mesh doesn't need to move relative to anything, this is just a boco.

[gav]

Dothan,
I did end up getting it to run. The contact point I changed to a depressed section on the tyre so the contact is a defined area rather than a line (with the tangential contact I had before there would need to be infinitesimally small volume elements to mesh it properly). At least that's my understanding of it. Getting the depressed section isn't too difficult it depends on how you're making your geometry model, I used SolidWorks to do it. And the resulting model was a more accurate one as real tyres will obviously be compressed at contact with the road. You'll also need to do a bit of experimenting with different mesh sizing options to get a good result, good luck.

Oh and what Simon said is right, it was just a normal mesh and the tread part was set to a rotating wall to match the cartesian speed of the road surface.

[hkhchiu]

My apologies for digging up an old thread, but I too am having trouble modelling a rotating wheel.

I have tried both a tangential and depressed tyre, but both solutions prove to no avail. Could you possibly describe the steps you took to get your model to work?

My mesh is getting ridiculously fine, but the error message still remains. I have a proE model, which I save to STEP and mesh using ICEM. Thank you for any reply.