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# The Deformation/Animation inflate and deflate in size

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## The Deformation/Animation inflate and deflate in size

(OP)
Dear all,

I found a problem when apply the torque/twisting moment rigid body. The shape inflate and deflate in size in the animation. The results seem reliable. I did a search, and it looks the reason for these kind of problems are still unknown. Please help me out.

see the similar problem asked by others before.

http://www.xansys.org/forum/viewtopic.php?p=67964&...

Thanks

### RE: The Deformation/Animation inflate and deflate in size

(OP)
It looks like this is a very challenging question. Does anyone know the answer?

### RE: The Deformation/Animation inflate and deflate in size

Hello,

I don't thin this is a problem. Inflating bodies when rotating (regadles of rigidity) is perfectly normal for FE animations.

This effect can be explained: Immagine a rotating cylinder of radius R. Assume the cylinder's symmetry axis is parallel to the global Z axis. Assume cylinder rotates about an angle phi. Take a node on the cylindrical surface and lying on the X axis. The nodal solution for this node is: ux=R*phi, uy=0, uz=0. This is the case, if you assume small displacements (NLGEOM,OFF). So the new position of the node (needed for animation) is a vector [R*phi,0,0]. The length of this vector is R*phi, which is the distance from the center of the cylinder. This is valid for all the nodes on the surface of the cylinder.

Conclusion: the nodes aparently move in tangential and radial direction which causes the inflation.

Regards
Alex

MESHPARTS
Tuning Your Simulation
http://www.meshparts.de

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