Sampled-data straight-line path following control for underactuated ships

For sampled-data underactuated three degree-of-freedom ships, the design of discrete-time surge and yaw state feedback laws that make a ship track a desired straight-line path while maintaining a desired nonzero constant forward speed is considered. First a line-of-sight guidance algorithm is introduced and by using the Euler approximate model of tracking error dynamics, discrete-time surge and yaw state feedback laws are designed. Then by applying the nonlinear sampled-data control theory, the designed surge and yaw state feedback laws achieve sampled-data straight-line path following control. Experimental results are also given to show the efficiency of the design method.