複数の関節を有するタワー状海洋構造物の応答制御

抄録

Active control of a tower-like offshore structure with plural hinges is discussed experimentally. This tower consists of several components which are connected mutually by hinges. Each component is a light weight structure, equipped with thruster. The natural frequency of the first mode of the tower is lower than the frequency of the waves. This kind of tower is suitable for the stationary base of activities in deep waters. Advantages of this light weight structure are the possibility of reduction of construction cost and weight of the tower. Although there is possibility of resonance with waves in the higher mode of motion or vibration and furthermore large drift can be caused in current by comparatively small rigidity, active control system is used to reduce these undesired response.
The models of the tower used in the experiments were consisted of three pipe elements connected by hinges and comparatively small. High accuracy was required for the displacement sensor. Ultrasonic sensors which employed high frequency of 1 MHz were originally designed for experiment. The motion of the each pipe was calculated from the measured distance between the transducer on the each pipe and the receiver on the monitoring post. Collected data were processed by a microcomputer and control force was calculated. Control force was generated by thruster which was built in the the body of the pipe and this thruster was also designed for this experiment.
In the first place, optimal control was applied to the unstable model fully submerged in the test tank. This situation corresponding to survival condition was successively stabilized by feedback control. In this case increased feed back gain cuased vibration of small amplitude on the models. Then drift in the currents was controlled by feedback control and then feedforward control was combined. This feedforward combined control was effective and showed good performance in respect of stability. Configuration of the models were changed from upright to zigzag configuration and upright to inclined one. In the latter case the model was successfully controlled by changing the system matrix from upright one to inclined one. Lastly correspondences between the experiments and the actual system were discussed.