Studies on fluid-elastic instability and active control of pipes conveying fluid

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This study deals with the fluid-elastic instability and active control of cantilevered pipes conveying fluid. In order to control the response of the cantilevered pipe with a damper, an active control force is derived by the torque produced by a pair of tendons attached to the pipe. The problem is solved by means of the Galerkin method in conjunction with the optimal regulator theory. The combined effect of a damper and a tendon on the critical flow velocity in the uncontrolled system is clarified. Furthermore, the numerical simulation of the response of a pipe conveying fluid is carried out for various conditions, the effect of a damper on the active control of the pipe is also clarified.The main results obtained are summarized as follows :(1)The effect of the positions of a damper and a tendon on the dynamic stability of a pipe conveying fluid in the uncontroled system is complex. In the stabilization of the pipe using a damper, the suitable position of a damper must be decided carefully together with that of a tendon.(2)In the uncontrolled system, a damper is effective to stabilize the pipe conveying fluid only when the most suitable positions of a damper and a tendon are selected. A damper attached to the pipe at the unsuitable position destabilizes the pipe.(3)The active control method using a tendon and a damper is effective to stabilize the pipe when they are set at the suitable position. The settling time of the response of the pipe decreases and a damper reduces the active control energy.(4)The active tendon control method described in this study is effective to stabilize the pipe, even if the pipe is lost its stability by selecting the unsuitable position of a damper. Therefore, the tendon-control pipe system is robust.(5)It is confirmed experimentally that the control system using PID controller is effective to stabilize the pipe conveying fluid.