On Linux there is some free software called "blender" that can do really nice 3D simulations, including fluid dynamics.   I don't know of any other free software that is closer to a numerical wave tank for visualizing results.  Does anyone?   For examples see:

http://youtube.com/watch?v=SMxfzil5_qU

http://youtube.com/watch?v=azuNHuj0cjo

      (first I was not sure this was a simulation, but there are no bubbles)

http://youtube.com/watch?v=Rv-ExKhhhZg

     (not just limited to normal laws of fluid dynamics)

http://www.youtube.com/watch?v=ocnLSuuljPo

http://www.youtube.com/watch?v=NJ0Alb5bgE8

http://youtube.com/watch?v=I3O62oyTKDY

http://youtube.com/watch?v=9yEdiIw2VWY

http://youtube.com/watch?v=UJPn3jhbt7s

http://www.youtube.com/watch?v=aRhKs9clRS4

http://www.youtube.com/watch?v=gtvmHutR0bc

http://www.youtube.com/watch?v=I-80sFggoig

http://www.youtube.com/watch?v=-AiLyQWXjIg

http://www.youtube.com/watch?v=bKHKVNoECO8

       Not sure the above is fluid dynamics.  You can just define wave motion in blender without simulating the physics of water.  But the ocean looks cool and it has a boat on it so I am including it anyway.

http://www.youtube.com/watch?v=AbYbv3tSA1s

       This last video has a boat in a wave tank.  I think he had the top of the area the water could go to so low it was hitting the top.  Also, this was 2 years ago and blender has been improving.  This video shows the idea of testing something in a simulated wave tank.  I think it is possible to do much better than this now.

http://www.youtube.com/watch?v=fqKVjKo96Es

    Here is a simulation of boat with a prop pushing in a wave tank.  This in the kind of thing, but with waves. 

http://www.youtube.com/watch?v=g2lsuk4rybY

   This is of a lighthous on a tiny island with a big wave hitting it.  This is very close to the kind of simulations I would like to see for seasteads.  But deep ocean waves not shallow water waves.

At the moment it is not easy to setup a "numerical wave tank" and test some ocean structure.   But it can be done.  If someone setup a simulation  we could all use it.  And judging from the cool 3D pictures people have made, I am sure we have people here who can do this. 

Also, blender is open source.   We have programmers in this group.  It would be possible to make it "wave tank test friendly" where users could enter a few parameters and do some tests.    Would make it much easier/cheaper/faster  than building models and paying for a real wave tank.  So things could move along faster. 

Ideally you could draw something in Google SketchUp and then drop it into a blender simulation to test how it works and make a cool video.   Then post  the video on youtube so  everyone can see the results.  For rigid structures I think this should be possible.  Would need to be able to specify the density of the different parts.  If you have lead ballast and aluminum structure you have to let blender know both of these.  I am not yet worried about testing the strength of the structure, just the stability when interacting with waves.

Seems you can import SketchUp objects into blender:

http://www.blendernation.com/2006/05/11/import-sketchup-and-google-earth...

http://blender-archi.tuxfamily.org/Import_your_model_from_your_Architect...

Seems like a good project for people here to work on.  It is a way to use the computer skills we have in this group to attack the ocean engineering problem.    The resulting system would be good for seastead research and for other people too.    Do people like this idea?   Or do we just want to use real wave tanks?  Are there people here with the time, skills, and inclination to make blender work for us?

If nobody here wants to do it, maybe the Seasteading Institute could fund one of the blender developers to make an easy to use numerical wavetank  so we can just draw something in SketchUp and then simulate it in blender under different wave types?     For someone familiar with blender what we need is probably not that hard to create.  So it probably would not cost too much.