Laboratory studies of gravity waves generated by the movement of a submerged body

Abstract

In order to gain some insight into the phenomenon of gravity waves generated by underwater seismic disturbances, the tsunami, a laboratory study was made of the waves resulting from an idealized two‐dimensional model of the movement of a submerged body. Bodies of several shapes, sizes, and weights were allowed to drop vertically or to slide down inclines of several angles, in water of various depths, from several heights above the bottom, but always below the water surface. The surface time histories were recorded at a point close to the origin of the disturbance, and at a point or points some distance from the origin. In addition, motion pictures were taken of several of the tests. It was found that a crest always formed first, followed by a trough from one to three times the amplitude of the first crest (depending primarily upon the slope of the incline), followed by a crest with about the same amplitude as the trough. Because of the dispersive qualities of the waves, additional crests and troughs continued to form with increasing distance from the origin. The magnitude of the amplitudes depended primarily upon the submerged weight of the body, but also upon the depth of submergence, the water depth, and other characteristics of the generation. Within the limits of experimental conditions, it was found that the time intervals between the first and second crests remained constant regardless of the water depth, the distance of fall, the weight of the body or the time of the fall. It was, however, found to be related to the length of the body, with the period increasing with increasing length, and to the slope of the incline, with the smaller the incline the greater the period.