Simulation of Ringing in Offshore Systems under Viscous Loads

Abstract

In recent years, significant interest has been shown in identifying the nonlinear mechanisms that induce ringing in complex offshore structural systems. This high-frequency transient-type response has been observed in offshore systems, particularly in tension leg platforms (TLPs). Given the implications of this behavior on the fatigue life of TLP tendons, it is essential that ringing be considered in the overall response evaluation. This study uses a simplified structural model exposed to viscous-type loading to demonstrate several of the salient features observed in higher-order potential–type wave–induced loads. Ringing response in pitching mode caused by viscous-type loading is simulated on a cylinder piercing the water surface, and significant mechanisms reponsible for inducing ringing are delineated. Results clearly indicate that, under certain conditions, ringing-type response characteristics are captured under viscous-type loading. The cylinder characteristics are varied to ameliorate the system performance by altering the conditions conducive to ringing.