# Wavemaking resistance of a submarine

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 December 11, 2008, 21:15 Wavemaking resistance of a submarine #1 Sam Wilson Guest   Posts: n/a Hi, I am a student trying to investigate the wave making resistance of a submarine traveling just below the surface using CFD. I am very new to CFD and would greatly appreciate any adivce at all on how to go about modeling the problem. Thankyou, Sam

 December 14, 2008, 16:59 Re: Wavemaking resistance of a submarine #2 Chebeba Guest   Posts: n/a Well... What can one say... I have successfully made this calculations for a surface hull. My learning period was about 4 months full time before I could successfully generate a solution, and I now use 20 CPU cores w 20GB RAM to run for about 100hrs to get one solution. It is a difficult problem. So don't fool yourself into thinking you can do it in a week or two... The mesh is the key, as usual. Once you have a good mesh everything is easy. But you need about 10mm vertical resolution at the water surface, more than 5xhull size domain in all dimensions, and very good Y+ values around the hull. I don't think you can do it with unstructured tet's, either you get too little vertical resolution at the surface or your element count will blow through the celing. I use fully structured mesh with 6M elements, 10mm vertical res at surface up to 0.4 m res at domain boundary, Y+ = 20 around the hull, SST turbulence model. There is a very good section of how to set up the free surface model in the CFX manuals.

 December 14, 2008, 17:10 Re: Wavemaking resistance of a submarine #3 Sam Wilson Guest   Posts: n/a Thanks very much, I appreciate the advice its good to get a starting point. Luckily I have all year to work on the project and a few decent clusters at my use. I have read in a few places that VOF modeling is the best way to tackle a free surface do you believe this would be applicable for my model?

 December 15, 2008, 16:49 Re: Wavemaking resistance of a submarine #4 Chebeba Guest   Posts: n/a Yes, certainly. Ansys CFX-Solver Modeling Guide, pages 196-ff

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