Active control of non-linearly coupled TLP response under wind and wave environments

Abstract

This paper deals with an active control strategy to check the non-linearly coupled response of a tension leg platform (TLP), a deep water semi-submersible type compliant offshore structure moored by vertical taut cables called tendons or tethers. The effects of potential non-linearities together with coupling of various degrees of freedom are studied. Low-frequency viscous drift force has also been taken into account with first-order wave forces. Simulation techniques have been employed to incorporate the random sea and fluctuating wind characteristics. Corrective control force is generated to alleviate the undesirable motion characteristics. The Riccati equation is used to determine the optimal control force. Response time histories and power spectra are generated for long crested random sea along with drift and wind forces. These responses are compared with the same under control. The present study aims at an efficient method of determination of the control force magnitude to design a control strategy for serviceability and survival of tension leg platforms in hostile ocean environments.