Performance of an offshore platform with MR dampers subjected to wave

The vibration suppression of semi-actively controlled jacket-type offshore platforms using Magnetorheological (MR) dampers is studied. The main goal of using MR damper system is to reduce vibration caused by wave hydrodynamic forces. A fixed jacket-type offshore platform affected by wave-induced hydrodynamic forces and controlled by MR dampers is modelled as a semi-active controlled system with 30 DOFs. In comparison with earlier studies, an improvement in problem modelling is made. Based on the wave theory and Morison equation, an exosystem is designed to simulate regular wave forces. The necessary input voltage to MR dampers to generate desired damping force is derived by clipped optimal control algorithm. Desired optimal forces are derived using linear quadratic Gaussian algorithm. For the semi-active control of MR dampers, the Kalman filter is used to estimate the system states of the platform structure based on measurement of node deformations. The results of simulation show that the wave-induced vibrations can be effectively suppressed by installation of MR dampers on offshore structure.