coupled acoustic vibration

[mechlau]

hi
im new with using ANSYS and am trying to model an light circular elastic disc backed by an acoustic cavity and solve for natural frequencies and mode shapes.

id like to be able to couple the nodes at the fluid/structural interface so they move the same amount in the z rirection but the fluid nodes are free to slip across in r and theta.

so far ive been specifying a FSI -first meshing appropriate elements (shell63 + fluid30 - with structure flag for those elements at the interface). then using the unsymmetric eigensolver for the solution process.
the natural frequencies returned are not discret + several are very similar - not what i was expecting at all

if anyone had any suggestions or advice about whether i was going about this in the correct way that would be much appreciated.
dave

 

[CESSNA1]

MECHLAU: My suggestion is to take this step by step and do a manual calcualtion for the disc so that you cna obtain the first and/or second mode shape. Then try the FEA model without the fluid and see where you are. Usually for normal mode analysis is customary to include the "apparent mass" of the fluid. It is so long I forget how to do apparent mass, but the people at ANSYS should know (maybe). Then continue to get more and more complex in the modelling.

Regards
Dave

"contrary to what some people will tell you, do not throw out the handbooks when you do FEA. Buy more."