Fluid Structure interface - Negative Volume
 

Hi I am doing a fluid structure interface simulation on ansys. I have a simple problem where I apply a sinusoidal pressure P=Pmax*sin(2*pi*fr*t) on a solid membrane and in turn the solid membrane will compress the fluid and the fluid pressure will increase. The time step I use is always = 1/20 of the period or 1/f.

I done this simulation with time step ranging from 0.1 to 0.005 and no problem occured, however when I apply smaller time steps the simulation would give me negative volume on the 3rd iteration.

Can someone please explain why does the time step affect the defomration??

Thanks

I am working with a sort of similar situation. This is a tip that I received from Ansys.

There is an rpvar in Fluent which you can use to slow down Fluent convergence- which will also damp out the pressure oscillations. This is:

(rpsetvar 'dynamesh/sc-bc-compressibility-type 1)
(rpsetvar 'dynamesh/sc-bc-compressibility 0.1)

See solution #2022119 for more explanation on usage. Second parameter needs to be decided based on trial and error.

The video in solution 2022119 goes through how to sort it out. Though, I haven't fixed my problem yet...

Thanks for the reply
 

Thanks alot for your reply I applied what you told me and it worked.:):):):):)