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# Rigid Body Rotation

## Rigid Body Rotation

(OP)
Hello,
First of all i wanted to say that i already searched in the forum for similar problems, because of that i am creating this post.

I wanted to simulate a Rigid Body Rotation.
The point has the coordinates X,Y,Z 0,0,0 and is also the reference point of my analytic rigid body.
On this reference poinit i applied a Rotatary Boundary Condition of UR2: -3.14.
My Problem now is that the Rigid Body changes his scale in local Z-Direction during the Simulation.
I thought a rigid body is rigid and can not change his geometry.
I am using Abaqus Explicit and Dynamic Explicit Steps. I created a sketch in paint that maybe can help you.

Sincerly Rick

### RE: Rigid Body Rotation

Analytic rigid surfaces extend to infinity so I don't think the geometry is changing. The visible/swept length of the surface is specified in Viewer. I think as you rotate the surface you just see more of it. You can control the visible length analytic surfaces in Viewer using View -> ODB Display Options.

This is described in the manual.

### RE: Rigid Body Rotation

(OP)
@Dave442

Thank you very much for your quick answer. I did not know that analytic rigid surfaces extend to infinity. Now Abaqus displays me just my specified depth of extrude. But my Extrusion is in y-Axis Direction but as i said before my rigid part changes size in local z-Direction.
Before that i tried to solve this problem by defining a discret rigid part instead of a analytic rigid part and the result was the same.

Do you know how i can get a 3D rigid part with constant geometry dimensions? I know that i can create a solid 3d discret part and have to " Shell from Solid", but in my Simulations the geometry seems to change either.
Could that be some mass intertia problem? Or do i have to set the reference point in the sketch modul in the coordinate System origin?

Sincerly Rick.

### RE: Rigid Body Rotation

While making rigid make sure you haven't checked the "adjust point to centre of mass at the start of the analysis".

### RE: Rigid Body Rotation

(OP)
@Dave442

Thank you very much it was an ODB Display problem. The extrude depth was auto-computed, so my rigid surface changed his depth in every Frame/step in visuliation.

@SachinSA93

Do i need to define my Rigid Body in the Constraints again as an Analytical Rigid Surface and turn on "adjust point to centre of mass at the start of the analysis" ?
Because i have not assigned any mass or inertia to my rigid body.

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