Learning Forum

[jordimarce]

I want to solve a modal analysis of a geometry that it is embedded in a fluid, but I want to avoid an FSI model.
I read that viscous damping could be the type of damping representing "a system immersed in a fluid" so, it would be useful if you can provide me some help/advise in how to do it.
I am testing two options to do this, but I am not sure if it is possible or I am doing something wrong. The idea Is to convert the fluid to some spring-dashpot model

1. For the stiffness part (spring) I create an elastic boundary condition defined by the Elastic Foundation Stiffness and I am wondering if it is possible via APDL to include some damping properties in the elastic support

2. I am trying to define the Rayleigh parameters in the menu of the modal analysis (Analysis settings - Solver controls - damped yes and then define them in damping controls. But when I am defining some random values for alpha and beta, I got always an erroneous solution of the modal analysis where I have some modes, but they are all in 0 Hz. (Not only the six degree of freedom, all)

I hope if you can help me in how to define the fluid in a modal analysis and, moreover, if you have some values that could be good for fluids. I don't find any information about it.

Thanks in advance for your help
jordi

[sk_cheah]

Hi Jordi,

Acoustic Fluid elements may be what you're looking for. An example here is for a modal analysis of a ring submerged in water. You could try adding viscous properties in fluid elements for some damping though be careful of how it is applied. 

 

Kind regards,
Jason

[jordimarce]

Hi! Thank you for your answer but I work in Workbench. Is there any example available in Workbench?

I would appreciate it! Thanks!

(*sorry, when I wrote via APDL I meant including code in workbench like this example:  https://www.simutechgroup.com/tips-and-tricks/fea-articles/143-a-normal-and-tangential-elastic-foundation-in-workbench-mechanical)

[jj77]

THis post should/might help

 

https://forum.ansys.com/forums/topic/plate-simulation-with-harmonic-acoustics-in-water-domain/

 

[jordimarce]

Thanks for the information of the acoustics ACT. I am not familiar with it and I need time to understand what is doing and what I can do. Meanwhile, my first idea was more simple than a FSI. Is it possible to do it with viscous damping defining Rayleigh parameters? I tried to use them in the modal and the results are really weird.  I got always an erroneous solution of the modal analysis where I have some modes, but they are all in 0 Hz. (Not only the six degree of freedom, all)