Motion inside overset mesh

rockydongre · July 10, 2014, 13:44

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

me3840 · July 10, 2014, 21:10

Probably. What's the application?

rockydongre · July 11, 2014, 07:37

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.

me3840 · July 14, 2014, 01:57

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

rockydongre · July 16, 2014, 03:12

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?

ggulgulia · July 23, 2014, 07:03

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

rockydongre · July 23, 2014, 08:08

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?

ggulgulia · July 25, 2014, 06:20

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.

ggulgulia · July 25, 2014, 06:43

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.

rockydongre · July 25, 2014, 07:49

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.

me3840 · July 25, 2014, 18:34

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?

rockydongre · July 26, 2014, 07:12

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.

region sliding meshes.png

prop region.jpg

me3840 · July 26, 2014, 10:25

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.

rockydongre · July 26, 2014, 13:36

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.

July 10, 2014, 13:44	Motion inside overset mesh	#1
rockydongre New Member CFDguy Join Date: May 2014 Posts: 20 Rep Power: 12	Hi guys, is it possible to use sliding mesh(not superposed motion) inside overset mesh?

July 16, 2014, 03:12		#5
rockydongre New Member CFDguy Join Date: May 2014 Posts: 20 Rep Power: 12	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? Last edited by rockydongre; July 16, 2014 at 14:21.

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July 10, 2014, 21:10		#2
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 25	Probably. What's the application?

July 11, 2014, 07:37		#3
rockydongre New Member CFDguy Join Date: May 2014 Posts: 20 Rep Power: 12	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.

July 14, 2014, 01:57		#4
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 25	Yes, you can do that, but it will probably be very expensive.

July 23, 2014, 07:03		#6
ggulgulia Senior Member Gajendra Gulgulia Join Date: Apr 2013 Location: Munich Posts: 144 Rep Power: 13	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

July 23, 2014, 08:08		#7
rockydongre New Member CFDguy Join Date: May 2014 Posts: 20 Rep Power: 12	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?

July 25, 2014, 06:20		#8
ggulgulia Senior Member Gajendra Gulgulia Join Date: Apr 2013 Location: Munich Posts: 144 Rep Power: 13	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.

July 25, 2014, 06:43		#9
ggulgulia Senior Member Gajendra Gulgulia Join Date: Apr 2013 Location: Munich Posts: 144 Rep Power: 13	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.

July 25, 2014, 07:49		#10
rockydongre New Member CFDguy Join Date: May 2014 Posts: 20 Rep Power: 12	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.

July 25, 2014, 18:34		#11
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 25	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?

July 26, 2014, 07:12		#12
rockydongre New Member CFDguy Join Date: May 2014 Posts: 20 Rep Power: 12	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. region sliding meshes.png prop region.jpg

July 26, 2014, 10:25		#13
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 25	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.

July 26, 2014, 13:36		#14
rockydongre New Member CFDguy Join Date: May 2014 Posts: 20 Rep Power: 12	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.