The Theory of Ship Motions

Abstract

Publisher Summary This chapter highlights that the oceangoing ships are designed to operate in a wave environment that is frequently uncomfortable and sometimes hostile. Unsteady motions and structural loading of the ship hull are two of the principal engineering problems that result. Ships generally move with a mean forward velocity and their oscillatory motions in waves are superposed upon a steady flow field. The solution of the steady-state problem is itself of interest, particularly with regard to the calculation of wave resistance in calm water. The problem of ship motions in waves can be regarded as a superposition of these two special cases, but interactions between the steady and oscillatory flow fields complicate the more general problem. The chapter also discusses the dynamics of ship motions that are governed by the equations of motion that balance the external forces and moments acting upon the ship, with the internal force and moment because of gravity and inertia. Assuming the ship to be in stable equilibrium in calm water, its weight is balanced by the force of hydrostatic pressure. Similarly, the steady drag and propulsive force are balanced. These steady forces may be neglected and attention is focused on the unsteady perturbations.