Abaqus: Fluid Cavity - Moving cavity under uniform hydrostatic pressure

[biofriend]

Hi Dear All,

Hope I can have some suggestions to tackle this weird problem.
I have an axisymmetric ball, with CAX8R elements being inflated with hydrostatic fluid elements.
Fluid elements surface is put on the internal surface of the ball (defined by picking the surface of the CAX8R elements).
BC:
Y direction-only allowed for nodes on Y axis.
8 degree of freedom pressurized on the reference node (center of the half circle, cavity reference node), fluid is water.

The internal cavity pressure reaches its expected value at the end of the step. This is very fine and straight forward.
But I see one thing which is rather unrealistic and annoying: The ball moves downward!

My only explanation is that there is something wrong with the normals of the fluid elements, may be not all of them are outward?
But since the surface is automatically defined by abaqus, I don't really know if this is the case and/or how I can tackle it.

Please let me know if I can provide more details.

Thanks a lot!
Amir
P.S: Attached: input file and a jpeg of this simple geometry.
Just change the extension of the pdf file to zip!

 

[Navin A S]

</code>The most likely cause of this phenomenon is due to the fact that the contact between the inner surface of the ball and the fluid element surface is not strong enough. This can happen when the contact surfaces are not properly aligned or when the contact stiffness is inadequate. To fix this, you need to make sure that the contact surfaces are properly aligned and that the contact stiffness is adequate. You can try increasing the contact stiffness or using a different contact algorithm in Abaqus. You can also try using an appropriate mesh size to ensure the contact surfaces are properly aligned. Finally, you can also try adding more contact elements to the model to increase the contact strength.I hope this helps. Good luck!