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-   -   Buoy forced oscilation ┐How to avoid wave reflection? (http://www.cfd-online.com/Forums/openfoam-solving/86721-buoy-forced-oscilation-how-avoid-wave-reflection.html)

jordi.muela March 31, 2011 06:23

Buoy forced oscilation ┐How to avoid wave reflection?
 
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Hi!

I'm developing a model with the purpose to obtain the hydrodynamic coefficients of a buoy (added mass and damping).

I have done it in 2D axi-symmetric with a RAS turbulence model (realizableKE), but i'm having principally two problems:

- If i use an 'outlet' BC for the lateral wall (zeroGradient), my level of water increases along the simulation! (first video). On the other hand, if i use a 'wall' BC, like model 'floatingObject' of the tutorials then the problem is the wave reflection. I've already navigated for the forum and saw that more people have this problem too... Does anybody have found a satisfactory solution? Like the advection BC, the 'numerical beach'...

Video 1

Video 2


- For obtaining the coefficients which i'm interested in, i use the libforces.so library and extract the force applied over the buoy. I plotted this force for different meshes and conditions (i multiply the force obtained by 360/5 because my wedge have 5║, and the results match pretty well with a 3D Model that i developed too). Contrary to what I expected, the signal presents greater distorsions for finer meshes, and has a softer look for coarse meshes. Maybe numerical noise? Problem with the integration of the pressure for smaller cell faces? Any idea or opinion will be welcome!

http://dl.dropbox.com/u/23292595/image002.gif

Thank you everyone!

Jordi.


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