Motion inside overset mesh
 

Hi guys,
is it possible to use sliding mesh(not superposed motion) inside overset mesh?

Probably. What's the application?

Actually i am simulating an airship in which there are two propellers attached to its body through two suporting rods. now to provide thrust vectoring these two rods can be swiveled around and change the angle of thrust of the propeller. so to model this i was thinking of using overset mesh, but for the rotation motion of the rods and propellers, i need to use sliding mesh. so is it possible? also i am thinking of using dfbi motion to find out its trajectory.

Yes, you can do that, but it will probably be very expensive.

hey me3840, after runnign the simulation for .11 sec i am getting this error "Some acceptorsCells are outside of Main cylinder_O.
This might be due to an overlapping of overset regions or due to invalid mesh configuration!"

here main cylinder is the region with overset grids.

what might be its cause?

Hello Rocky

If you are having Main Cylinder_O as your background mesh, then you have to make sure that the overset boundary has atleast 4-5 layers of overlapping cells for proper intersection of cells during hole cutting process and this configuration has to be maintiained wherever your overset region moves within the background mesh.

Probably you could do with some local refinement in the background mesh along the motion path of overset body

thanks gajendra. actually main cylinder is my overset region but i have already given the local refienments considering the facts you mentioned earlier. i even made sure that the no of cells for proper intersection remains nearly 10 at any course in its path just to be cautious, but even that seems to be not working. can it be because of the sliding mesh i am using?

I missed the fact you are using sliding mesh. You should not be using sliding mesh in any region where overset mesh is intersecting with the background mesh, because sliding mesh needs conformal mesh interface whereas this is not the case with overst mesh.

Overset region will cut hole with the background region and consequently no volume mesh will remain in that portion of background mesh, and as a result, the region with sliding mesh has no interfacial boundary shared with the background mesh. I am not sure though that this will give an error, but it's apparent that the physics will not be captured.

Hello Rocky

I gave your problem some thought.

I realize that you might be creating an overset interface b/w overset and background region. But what about the region having sliding mesh within the overset region? The fact that there's no interface b/w sliding and overst region might be giving that error. Also You cannot create an overset interface as well as sliding interface with the same region.

If you are using version 9.04 , you can try the 'Dynamic Overset' feature.

Thanks gajendra, after some positive response which i got in this thread i thought that i could use sliding mesh inside overset mesh. also i want to ask that if i want to simulate a ship with a propeller using overset mesh and dfbi, is it possible by giving superposed rotation to propeller? if yes then how come we cannot apply the same technique here to simulate other case which involves use of sliding mesh inside overset mesh.

again thanks for your help , i will surely look into the dynamic overset feature.

I don't really see why sliding mesh is necessary at all. Overset can rotate in more than one direction, why not just do that?

i need sliding mesh to facilitate the rotation of propeller and the rotation of the rod whch results in swiveling of the propellers. are you suggesting me to use another overset mesh for the rotation of proellers @me3840 ? i have attached some fotos of airship, showing the propeller and rod region, to explain things a little better.

Attachment 32582

Attachment 32583

The rotation of the rod really doesn't affect the aerodynamics. Just make the problem simpler by ignoring it. Just have the propeller rotate by itself.

yeah but while rotating it i have to swivel it anyway, that means the propeller should rotate about its central axis as well as an axis parellel to the diameter. so even with or without the rod i have to make that region for rod for swiveling. i tried to do it by combination of rotation and superposing rotation but i couldnt align it with the main body. also while using sliding mesh inside overset mesh, it runs for some time and then shows an error "Some acceptorsCells are outside of Main cylinder_O.
This might be due to an overlapping of overset regions or due to invalid mesh configuration!", where main cylinder is my overset region.