Robust Lateral Control of a Surface Effect Ship using H∞ Mixed Sensitivity Synthesis

This paper presents a systematic procedure to design robust controllers for lateral control of a class of Surface Effect Ship (SES) subjected to the influence of sea waves, currents, and wind loads using robust H∞ techniques. The proposed technique will expand operational weather window for boarding the service personnel to and from offshore wind mills. The vessel under study is equipped with a boarding control system for heave and pitch compensation. The current paper focuses at controlling the sway motion by using the outgoing air flow from the boarding control system to produce lateral control forces. To this end, a mathematical model of the lateral motion is presented and by selecting suitable weighting functions to dictate the desired performance, mixed sensitivity H∞ synthesis method is exploited to design the controller. Model tests has been performed on a scaled model. The performance of the actuators was identified, and is presented in a bode plot. The results of the tests have been used to find a suitable thrust mapping for the controllable forces from the vent valves in sway. Numerical simulations, using this mapping and excitation from realistic external forces from waves and wind, shows satisfactory performance of the control system.