free-surface condition for moving fluid in potentialFreeSurfaceFoam
 

Hi,

I tried to use potentialFreeSurfaceFoam on a ship resistance test case. The case setup is quite similar to the WigleyHull Tutotial, thus a rectangular blockMesh including a static hull shape (trim&sinkage neglected) and some refinements (surface and around the hull) made by snappyHexMesh. The hull remains static while velocity is applied to the Fluid. Different to the WigleyHull, i used a symmetryPlane in y=0 to simulate one half only.

unfortunately, the waves generated do not behave as expected- it seems the waveSurfacePressure Boundary doesn't consider fluid motion, i.e. the waves don't drift downstream, as they should, but rather disperse radially as if the fluid was static. (while on a real ship, the fastest wave is dispersing as fast as the ship speed, thus can not "overtake" the hull).


Initial/boundary conditions are
U:
internal: fixedValue uniform (shipSpeed 0 0)
inlet: fixedValue uniform (shipSpeed 0 0)
walls: fixedValue uniform (shipSpeed 0 0)
hull: fixedValue uniform (0 0 0)
freeSurface: inletOutletParSlipVelocity (as in "oscillatingbox" tut)
outlet: zeroGradient
centerplane: symmetryPlane

p_gh:
internal: uniform 0
freeSurface: waveSurfacePressure (as in "oscillatingBox" tut)
centerplane: symmetryPlane
all others: zeroGradient

p:
"calculated" for all (except of centerplane which is still symmetryPlane)

i have tried out some other similar boundaries (esp for walls and outlet), but could not eliminate the problem, so now i suspect the waveSurfacePressure boundary to be the reason (but there is no other one for use with potentialFreeSurfaceFoam.?).

I tried to modify this Boundary to do the job- without success yet. At least, i could coarsely cope with the syntax and got a modified version ("waveFreeSurfacePressure" ;)) compiled and running, but not working (i guess i'm lacking the necessary cfd backgrounds :o:().

Can anyone help me how to modify waveSurfacePressure to cope with fluid motion (like U∞ in publications)? maybe mapping the waveheight changes to a position which is located dt*U∞ downstream, or using a phi field which is relative to fluid motion or similar?

Has anyone else used potentialFreeSurfaceFoam for ship resistance before, or at least in a case with a moving fluid?

Ideas if anything else could be wrong to cause this phenomena?

Thanks,
simon

Hi Simon,

i has been a long time, but could you solve the problem? I also set up a case and am facing the same problem, the waves are generated at the hull and then move in forward direction as if there was no moving fluid.

Hi Bizzy,

I'm not sure if it is possible with this Foam at all- i finally gave up and solved my problem with interFoam (static hull) and interDyMFoam, respectively (considering trim&sinkage).

What i guess is that pfsf is not capable of simulating a moving fluid. I would prefer it to interfoam as it could save so much computation time, but i was not successful with it- sorry :confused:

best regards

Hi Simon,

thanks for your answer. I will let you know, if I ever find a way to do this, though.

Greets

Hi Bizzy and simon,

Is there any progress about the above mentioned probleem.

If so, please could you also share with me.

Thank you.

B

Hello,

See this post for what I learned about potentialFreeSurfaceFoam: https://www.cfd-online.com/Forums/op...tml#post788284

Cheers