HI I want to model a ship body. I have decided to make a domain like a tunnel and remove the parts of the ship that is in the water. I want to know that what kind of boundary condition I have to put for the fluid surface to have its dynamic manner? Every clue will be appreciated.

Removing the underwater parts of your ship you lose all the information of the interaction with the fluid (eg: drag). It seems that you are interested in results connected to the interaction air-solid only (air drag or similar). In this case you can impose a no-slip boundary condition in the water surface.

Hi,

It depends on what you are trying to see with the model. If you want to know the ship's trim due to speed or accurate wave drag prediction your only option is to do a multiphase simulation with a free surface. If you are not interested in the wave effects or trim then you can use a no-slip boundary at the water surface as Fusion suggests.

I have also heard a yacht designer doing a simple multiphase model to get the wave pattern then using the water volume only to model the drag effects with the water surface (which now includes waves and troughs) as a no-slip boundary.

Glenn Horrocks