Semi-active Seismic Vibration Control Offshore Jacket Platforms

A semi-active control scheme for the vibration control of offshore steel jacket platforms is developed. Decentralized sliding mode control (SMC) algorithm is adopted for applying the control force to the structure with the help of Magneto-rheological (MR) damper for alleviating the earthquake-induced vibrations. SMC method is used due to its robustness against the parametric variations of the structures. The command voltage to the MR dampers is regulated through the clipped-optimal algorithm. A steel jacket platform, available in the literature, is modelled in MATLAB as an example to investigate the dynamic responses under the environmental loads. The earthquakes ground motions, scaled to 0.3 g PGA, considered in the present study are the El Centro (1940), Northridge (1994), San Fernando (1971) and Chichi (1999). Results indicate that sliding mode controller is able to reduce the responses of the offshore jacket platform significantly, subjected to different earthquake loads. It is observed that the positions and the number of MR dampers affect the performance of the controller to a great extend in the offshore jacket platforms. The control algorithm is stable against the variations and uncertainties in structural parameters.