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Structure vibrating in a fluid, simplified model based on the added mass (preliminary)
Posted Apr 11, 2011, 3:54 a.m. EDT Computational Fluid Dynamics (CFD), Structural Mechanics Version 4.1 1 Reply
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I have seen many threads on modal analysis of structures in a fluid. It's a complex task, but I believe one can do quite nice things with only the "structural module" and by applying some hypothesis to simplify the model, and add the liquid effect as Boundary loads.
In the following example (which is NOT YET VERIFIED NOR VALIDATED, be AWARE!)
I have added the effective mass of the liquid
(Y<H0_liq)*rho_liq*solid.d*(solid.nx*u+solid.ny*v)*solid.iomega^2
acting on a cantilever standing vertical half immersed (up to height "Y0_liq" in a fluid of density "rho_liq".
I assume, as essential simplification hypothesis, that the liquid around is wide, and that we are looking for small motion effects.
I have added a few % structural damping to the beam material to improve the bode plots convergence (without the resonances tend to INF
I would appreciate some feedback and if there are some simple validation examples out there ;)
Reference:
Vol3 Modelling of Mechanical Systems Fluid-Structure Interaction of F.Axisa and J. Antuns from B&H Elsevier ISBN 978-0-750-66847-7 (vol 1 and 2 are as good ;)
Next step would be to add some damping from the viscosity of the liquid
Comments & critics appreciated
--
Have fun COMSOLing
Ivar
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Hello Ivar KJELBERG
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I am working on a very similar problem, so I have been going over your model and I have some questions.
First, what is the difference between your boundary load 1 and your boundary load 2. You seem to have your boundary load 1 disabled, are these loads just alternate methods for apply the pressure associated with the surrounding liquid?
Second, what is your boundary load 3 representing? It is labeled freq sweep and applying a 1 N total force at the fixed constraint, but I am not understanding its purpose or function.
Regarding the studies, what exactly are they telling you? What is the difference between an eigenvalue study and a frequency domain study? Also, I noticed that there is a study called Time dependent modal...what does that study do?
Thanks,
Danielle