THE DYNAMICS OF A SUBMERGED MOORED SPHERE IN OSCILLATORY WAVES

Abstract

The results of an analytical and experimental investigation into the dynamics of a buoyant sphere moored by a single line in shallow water waves are presented. The sphere motion and the mooring line forces are related to the sphere diameter, weight, submergence and the wave frequency, height and water depth. Analytically, the phenomenon is approached as a forced vibration problem. The sphere and its mooring line acts as a spring-mass system driven by the oscillating wave force. The relevant dimensionless parameters are the ratio between the natural frequency of the moored sphere and the wave frequency and the ratio between the dynamic mooring force due to a given wave and the force on the sphere held stationary in the same wave. Experimental values of the frequency and force ratios obtained from tests made at the Massachusetts Institute of Technology Hydrodynamics Laboratory over a range of sphere and wave characteristics are in essential agreement with the analytically determined values. The investigation was supported by the Humble Oil and Refining Company of Houston, Texas.