A good way to calculate hydrodynamic coefficients (added mass, radiation damping, excitation forces, hydrostatic stiffness) is to use WAMIT or calculate them with formulas that are available in books but for simple geometries.

so tank for your answer

one of the most popular method for hydrodynamic calculations is boundary element method (BEM) that is used in many other sience applications.

for using BEM i should discrete a 2D section of ship and expanding it to all of the length. but  i cant start BEM for a 2D section that is has tow phase.(ship sections are in tow phase). 

again tanks for your answer.

u can ask D.r reza, i sure he can help u

have good night