In this paper, the authors propose a new automatic technique, learning Tracking Controller (LTC), to install structures whose flexibility can not be ignored any more in unknown current. This method also control elastic response of the equipment to be installed and applicable much larger structures. The proposed LTC can install underwater structures not only in excellent accuracy in any water depth but also control the elastic responses of structures simultaneously.
The presented LTC, which consists of both feedback controller and feedforward controller, can be operated without any information about current which is difficult and costly to be collected before operation. By learning unknown disturbances translated from the errors between the realized trajectory and objective trajectory, LTC improves its feedforward control force and makes the structure track the objective trajectory accurately in the final stage. The convergence condition and robustness of LTC is shown.
Two types of experimental models, a plane flexible structure and a cubic rigid structure, are designed for basin tests which are carried out under unknown current, in order to confirm the capability and effectiveness of LTC. Both of two models were successfully made track the given trajectory and docked to their targets, by their own LTC respectively in the experiments. To obtain docking accuracy of ± 5 mm the models tracked the trajectory six to seven times for learning. The maximum speed of unknown steady current is 0. 07 m/s. No elastic responses of the flexible model were stimulated.