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-   -   VOF damping at inlet (http://www.cfd-online.com/Forums/star-ccm/130787-vof-damping-inlet.html)

arun7328 March 4, 2014 10:04

VOF damping at inlet
 
Dear Sir,

I am simulating a case of barge in regular waves and finding the heave and pitch response of the barge. I am comparing this with experimental values. My barge dimensions are ,
L: 2.445 m B: 0.6 m and D : 0.25 m T: 0.12 mt

Set up: The shape of the barge is rectangular with a chine like shape at the fwd. The length of the wave is 6.8 m and its amplitude is 0.025 m( wave period 2.08 secs). I have used first order wave.

Domain: The inlet is 1.5 wavelengths from the barge. Outlet is 2 wavelengths + 2 wavelengths damping zone. Symmetry plane is used to model only half of the domain. The width of the domain is 6m (same as the towing tank). I have used DFBI+morphing to simulate this condition.

Problem: It seems to be working fine for sometime and then the heave starts to fluctuate. I have shown a plot of heave and pitch. The pitch remains steady. When I take the amplitude of heave at the steady condition(3-8 secs) and calculate the RAO, it is very close to the experimental value. I suspected wave reflections so tried to extend the outlet to 8 wavelengths including 2 wavelengths damping zone, and still found the same problem. I have now put another model for running with 4 wavelengths at the inlet. I suspect the problem is because of reflections from inlet. I have also attached the wave elevation plot at 1 wavelength from the barge towards the inlet. It can be seen that there is a spike at about 13-14 secs and also a slight phase shift ( due to the wave radiated from barge?).

I wanted to know if it is possible to give a damping at the inlet to absorb the wave radiated from the barge due to its symmetric motions? I tried to apply a damping field function but found it damps the inlet waves as well. In STAR the damping is not direction dependent right? Can you please suggest a method and help me with this? Please be kind to give some suggestions. I have been working on this for more than a month now.

Thanks
Regards
Arun
Ps: I am using an inviscid model. When i tried to simulate the same using a cylinder in waves, I get a good response.

arun7328 March 4, 2014 10:07

3 Attachment(s)
sorry i forgot the attachments


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