An Experimental Study of Wave Forces on a Structure Supported by Vertical Cylinders.

Abstract

Recently, jumbo marine structures such as floating airports, offshore cities, etc., supported by a large number of identical floating elements, have aroused general interest. In these structures, interaction effects between floating elements have great influence upon wave forces and drift forces both on the whole structure and on each of the elements, and upon wave heights between elements as well as those before and behind the structures. It is, therefore, not sufficient to apply methods for a single floating body and simple superposition techniques to the prediction of wave forces, etc. on these compound structures ; it is necessary to develop a method which properly takes into account the interaction effects. On this subject, there is a basic study by Ohkusu, followed by Masumoto's and Takai's studies. We believe, however, that the experiments and calculations of these studies are not systematic enough to reveal the essential characteristics of the interaction effects. In order to make clear the phenomenon more thoroughly, we carried out extensive experiments and investigated the influences of a number of parameters on the interaction effects, and then compared the results with theoretical calculations. From the study, it is found that the intervals of columns, P, that is, the spacing of cylinders in the direction of wave propagation, decides the patterns of interaction effects to the wave length, where as the intervals of rows, B, and the number of columns, N, have influence principally on the intensity of interaction effects, and that there is a fairly wide frequency range abut P/λ=0.5 where incident waves are almost perfectly reflected.