Development of Automatic Construction Technique of Underwater Structures in Unknown Disturbances by Learning Control

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A new automatic technique for installation of underwater structures in unknown environmental disturbances was proposed. Central part of the research is development of Learning Tracking controller (LTC). Elastic response of the equipment and the structure can be controlled. This method is applicable to installation of much larger structures whose flexibility can not be ignored in unknown current. 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 generally 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 was shown. Two types of experimental models, a plane flexible structure and a cubic rigid structure, were designed for basin tests. The tests were carried out in 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. To obtain docking accuracy of *5 mm, the models tracked the trajectory six to seven times to learn the disturbance. The maximum speed of unknown steady current was 0.07 m/s. Elastic responses were well controlled and no elastic responses of the flexible model were stimulated.