Hybrid Control of Offshore Jacket Platforms Using Decentralized Sliding Mode Control and Shape Memory Alloy-Rubber Bearing Under Multiple Hazards

Abstract

Abstract The motivation and objective of the present study are to propose a hybrid control system for offshore jacket platforms to mitigate the vibrations induced by multiple hazards, namely, the earthquakes and regular and irregular waves. State-of-the-art indicates that not much work is reported on hybrid control of offshore jacket platforms for multiple hazards using a control algorithm, which is robust against uncertainties. A decentralized sliding mode control algorithm using magneto-rheological (MR) dampers is employed for the semi-active controller because of its robustness against parametric uncertainties and reliability. Passive shape memory alloy rubber bearings (SMARBs) are selected as passive isolators because of their high damping capacities, high fatigue resistance, and super elastic behavior, which are highly desirable for offshore applications. The scope of the present study is to demonstrate the efficiency of the proposed controller and investigate the effects of different influencing parameters. A jacket platform, reported in the literature, is taken as an illustrative example. A significant reduction in the top deck displacement is observed. The position and number of MR dampers affect the performance of the controller significantly. Limitations of the controller imposed due to the greater weightage or penalty imposed on displacements by the semi-active control algorithm as well as due to the magnetic saturation of MR dampers are overcome by the high energy dissipation of the passive SMARBs, thus making the hybrid controller highly efficient. The effectiveness of the controller is more for the earthquakes and random waves than for the regular waves.