On a Free Floating Ship in Waves

摘要

The oscillatory forces on a free floating ship of spherical or ellipsoidal hull at zero forward speed in a head sea are evaluated for the modes of surge, heave, and pitch. The potential boundary-value problem consists of (a) the determination of the radiation potential which is due to the forced oscillation of a floating ship in a calm sea, and (b) the determination of the diffraction potential which is due to the scattering of oncoming waves on a ship fixed in the equilibrium position. Upon knowing the values of the radiation potential over the immersed surface of the ship, the hydrodynamic forces arising from the impingement of oncoming waves are evaluated using the Haskind relation. Thus, the dependencies of added mass, added moment of inertia, and damping coefficients on the frequency of the forced oscillation as well as on the frequency of the oncoming wave are shown. Finally, the equation of motion governing the oscillation of the freely floating ship is obtained through the synthesis of hydrodynamic forces in the radiation and diffraction problems. The frequency dependence of the two pertinent parameters occurring in the equation of motion, the amplitude ratio and the phase lag between the ship motion and the wave motion, is also established. (Author)