I'm running an FEA on a vessel that has a "splashing water" effect with vibrations. The problem I'm really coming up against is what kind of Young's Modulus and Poisson's ratio to use for the fluids? - air and water. I have been successful in using the bulk Modulus, and treat it as uncompressible - i.e. Poisson's ratio of 0.5, but I never used it for vibrational analysis, just static analysis. Are these still good assumptions in a dynamic analysis?

  • $\begingroup$ Interesting. I look forward to seeing the answer to this one. $\endgroup$ – grfrazee Jul 23 '15 at 14:28
  • $\begingroup$ Out of curiousity, what program are you using that can model splashing water in FEA? $\endgroup$ – grfrazee Jul 23 '15 at 16:45
  • $\begingroup$ LISA - it's good and cheap and gets the job done. $\endgroup$ – Mark Jul 23 '15 at 16:52

This may be only a partial answer since I don't have any idea what to do for the Young's modulus of the fluid.

Consider the paper Dynamic Pressures on Accelerated Fluid Containers by G. W. Housner. This is referenced by ASCE 4-98 Seismic Analysis of Safety-Related Nuclear Structures, Commentary Section C3.1, for analysis of hydrodynamic loads on tanks. In the paper, Housner states that:

enter image description here

You can read the rest of the paper at the link above, if interested. It seems that your assumption of incompressibility of the fluid (and correlating Poisson's ratio of 0.5) is reasonable.

You might try doing some searching for computational fluid dynamics (CFD) modeling in regards to the Young's modulus question. Other than that, I have no good suggestion where to find that information.

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  • $\begingroup$ The link gave a lot of useful information. I'll answer the question with information you gave me from the link. And post pictures for @Chris_Mueller $\endgroup$ – Mark Jul 23 '15 at 17:05
  • $\begingroup$ Apparently LISA is hating this tank model - so no nice pictures. But the book gave me all the answers I need to figure out if this is a continuous problem or not - so good job. $\endgroup$ – Mark Jul 24 '15 at 13:55
  • $\begingroup$ Good to hear. Nice to know my shot from the hip actually panned out. $\endgroup$ – grfrazee Jul 24 '15 at 13:56

Section 2.1.14 of the Abaqus Example Problems Manual is 'Water sloshing in a baffled tank', which might be useful (even if you don't use Abaqus at your own institution, the manuals are hosted by many institutions that allow public access). The Abaqus water model uses an equation of state (EOS). If you download the input file from the manual, you can cut and paste the material section or convert it to suit the code that you're using.

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