how to use buoyancy pressure boundary condition？
 

Hello， i finished a case "floatingobject"， and there some problems. Firstly， it's choosen buoyancypressure boundary condition for p or p_rgh on tank and floatingobject. I don`t understand why buoyancypressure is choosen, and for a further step, please describe the situation that the bc is used to.

secondly, i change some conditions: water is static, tank' size is infinite and floatingobject is forced to oscillate. For this situation, is it right that buoyancypressure is still applied to tank and floatingbox？

Thanks.