Fluid Solid Interface in Ansys 11

[BCDeemer]

I'm using CFX and the multiphysics/LS-Dyna license in Ansys 11. I would like to create a simulation that allows a deformable body to move freely within a fluid region. The motion of the fluid would control the motion of the deformable body and cause any deformation. The deformable body should also be able to collide with any wall containing the fluid and deform accordingly. I've been unsuccessful in settting this up using the fluid solid interface (FSI). The error messages the solver reports seem to indicate that the deformable body is unconstrained. I set up the simulation based loosely on tutorial 21 which deals with bi-directional FSI, but the deformable object in the tutorial is anchored to a wall, I need my deformable object to be free.

Any thoughts or suggestions would be appreciated. Thanks

 

[cbrn]

Hi,
I'm absolutely not an expert of FSI (never used CFX) but it doesn't surprize me that the body immersed in the fluid causes the error. Structurally speaking, its global matrix is singular, meaning that its determinant is zero because there are stiffness terms which are zero, causing the inversion impossible. It's POSSIBLE, though not guaranteed, that you can avoid this problem by:
- specifying CONTACT / TARGET pairs between the surfaces of that body and the surfaces of the containing wall with whom it could collide
- specify the analysis as full-transient, with inertia effects ON
- use inertia relief in some way (never used it, but I seem to remember that it serves right for the cases in which the force field is "balanced" by an acceleration / motion field)

Re-thinking on it, I think the turnkey is in the third point above... Somebody else could possibly confirm...

Regards