A disturbance accommodating controller for roll motion of a ship in irregular seaways

An adaptive operation of a disturbance accommodating controller(DAC) depending on the seastate number for roll motion of a ship is suggested. DAC suggested in this paper assumes the shape of the disturbance, i. e. the wave slope excitation as a harmonic signal that consists of two sine waves of different frequencies and the dynamic model of this kind of disturbance is adopted in the controller to estimate the disturbance from the measurement of roll and to generate the control force to counteract exactly the estimated disturbance, Frequencies of the disturbance model used in the controller are selected so that the energy of the roll response in each seastate is to be minimized. Pole placement technique is combined to enhance the performance of DAC. A necessity of an adaptation scheme i. e. tuning the suggested DAC according to the varying sea environment is also shown by the results of the performance assessment of DAC's with different sets of design frequencies optimized for each seastate.