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free-surface condition for moving fluid in potentialFreeSurfaceFoam

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Old   September 30, 2013, 13:01
Default free-surface condition for moving fluid in potentialFreeSurfaceFoam
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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 ).

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
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Old   November 17, 2014, 19:06
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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.
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Old   November 18, 2014, 06:44
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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

best regards
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Old   November 18, 2014, 19:03
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Hi Simon,

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

Greets
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Old   February 25, 2016, 04:55
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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
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free surface flow, potentialfreesurfacefoam, wave making resistance, wave solution; bc

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