Side-Wall Effects on Radiation and Diffraction Forces on a Ship Advancing in Waves

Abstract

A new theory is developed for predicting the side-wall effects upon the radiation and diffraction forces acting on a ship in waves, by applying the unified slender-ship theory devised by Newman to the case where vertical and parallel side walls are present. In the present theory, only a solution of the radiation problem suffices for the calculation of the wave-exciting force and thus of the ship motions in waves. Needless to say, both zero- and forward-speed problems can be handled with the same calculation scheme.
Numerical results are compared for the zero-speed case with independent results by a 3-D integral-equation method, and compared for the forward-speed case with corresponding experiments which have been obtained by the authors with a floating spheroid of beam-length ratio 1/5 and a Lewis-form ship model of beam-length ratio 1/6, both running at a Froude number 0.1. In all cases excellent agreement exists, and thus it can be concluded that the usefulness of the theory has been confirmed.
As an application of the present work, a number of computations based on the present theory have been performed over a practical range of Froude number, oscillation frequency, and tank width. Then diagrams are newly prepared for predicting not only whether the tank-wall effect is expected or not, but also the region in which the effect is less than 10 percent of the open-sea value.