Forward-Speed Effects on Hydrodynamic Forces Acting on a Submerged Cylinder in Waves

Two-dimensional radiation and diffraction problems are studied of a submerged circular cylinder moving with forward speed while oscillating under the effects of incident waves. After a linear formulation of the boundary-value problem, the numerical solution is obtained by solving the integral equation for the velocity potential on the body surface. With attention focused on the effects of forward speed on hydrodynamic forces, added mass, damping, wave-exciting force, resultant motions, and added resistance are computed. The speed-dependent terms in the body boundary condition, arising from the interactions between steady and oscillatory flow fields, are found to exert a considerable influence on the hydrodynamic forces. The added resistance of a circular cylinder is approximately zero in head waves, whereas in following waves it becomes positive for U/C < 1/2 and negative for 1/2 < U/C <1(where U is the body speed, C the phase velocity of incident wave). It is also shown by numerical computations that there is no added resistance if a circular cylinder is allowed to respond to the first-order hydrodynamic forces. We discussed the method of pressure calculation on the body surface on the premise that the principle of energy conservation must by satisfied in an inviscid fluid.