FSI in Ansys

[alphaden]

Hi all,

I'm doing a fluid structure interaction problem using Ansys 9.0. I'm getting a strange error, "The inversion subroutine was supplied with a singular matrix". what does that mean ??? i tried modifying almost everything. in the output window the last message is ... "applying boundary conditions" and immediately after that "The inversion subroutine was supplied with a singular matrix". what is wrong ????
any help would be grateful.
thanks a lot

Alphaden

 

[cbrn]

Hi,
the message means that the solver tried to perform matrix inversion but couldn't do it because the system matrix was "singular", i.e. its Jacobian was zero. This can mean that there is some unconstrained part somewhere, or some zero-mass element somewhere; in other terms, either the stiffness matrix or the mass one has a zero value on the diagonal. Perhaps in the fluid part of the analysis you leaved some part "structurally unconstained" and that didn't produce any error for the fluid solve, whether the structural run is unable to start.
Hope this helps...

Regards

 

[alphaden]

thanks cbrn,

makes sense. I must check all my boundary conditions. the thing is .. if I run the cfd analysis separatey ... it runs well. but in combination with solid .. it doesn't. I'm considering U & V both the BCs for fluid in FSI analysis because thats what is shown in the example in ansys help.
I'll try different BCs and let you know.

thanks again
alphaden