Practical Prediction Methods of Irregular Disturbances to Automatic Steering System of Ships

Gyoung-woo Lee, California Institute of Technology

The presence of disturbances is one of the main reasons for using control. Without disturbances there is no need for feedback control. The character of the disturbances imposes fundamental limitations on the performance of a control system. When disturbances can be neither eliminated at the source nor measured, it is necessary to resort to prediction. To do so, it is necessary to have models of disturbances that lead to a reasonable formulation of a prediction problem. In the present study, the practical method of imposing irregular disturbances to ship dynamics is proposed, where irregular disturbances implying irregular wave and fluctuating component of wind. Prediction method based on the principle of linear superposition is introduced for expression of irregular disturbance. In order to obtain results of realistic open seas, calculations carried out two kinds of wave conditions, long crested waves and short crested waves.