# Free surface modelling

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 August 3, 2000, 23:33 Free surface modelling #1 Shane Gillis Guest   Posts: n/a I am trying to model a hull as it passes through the water. What I am interested in is the bow wave that is caused by a bluff object passing through a viscous fluid. I understand how to setup the solution in Fluent, but I do not know how to model a free surface problem (i.e. set the boundary conditions) for Fluent 5.0. I can model my volumes, but how do I define and/or mesh what is air & what is water? I am using Gambit for the modelling. Any help would be appreciated. Thank you.

 August 4, 2000, 04:20 Re: Free surface modelling #2 Rüdiger Schwarze Guest   Posts: n/a You have to use the VOF approach of FLUENT. In order to resolve the air water interface adequatly, You should start with a moderate grid resolution of the flow field and then refine the mesh near the interface using grid adaption.

 August 4, 2000, 08:06 Re: Free surface modelling #3 Shane Gillis Guest   Posts: n/a But how do I define what is water & what is air? Basically, here is my practice setup. I have a large box (my overall volume) and in the center I have a sphere (my bluff body). I want the sphere to be half submerged at a speed/time of zero. How do I tell Gambit/Fluent that all fluid below the sphere equator is water and all fluid above the sphere equator is air?

 August 4, 2000, 08:19 Re: Free surface modelling #4 Rüdiger Schwarze Guest   Posts: n/a Initialize under "SOLVE/Initialize" all cells as "air". Mark all the cells which should contain water using "ADAPT/Region". Then return to "SOLVE/Initialize/Patch" and patch these cells as "water".

 August 4, 2000, 08:27 Re: Free surface modelling #5 Shane Gillis Guest   Posts: n/a Ohhhhhhhhh! So nothing is done in the modeller to specifiy fluid type. Got it, Thank you very much!

 September 26, 2000, 05:50 Re: Free surface modelling #6 Giovanni Guest   Posts: n/a I do not know what results you have obtained since August, but I'm involved in the same problem. I'm trying to model a simple ship hull, using an hybrid mesh (tet, wed, hexa) and steady solver Using only hexa, the results (modelling a cylinder)seem to be good, but using hybrid mesh (and therefore a different setup) the free surface goes down near pressure outlet. There are a lot of problems, if you want we could collaborate. Best regards

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