A Study on Development of Control System for Long Riser

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Long marine risers are used for many purposes in ocean activities. Their lengths are very long compared with their cross section area, therefore, the stiffness relatively decreases and marine risers show very flexible behavior. These marine risers are always exposed to many external forces such as gravity, fluid forces and reaction force form the floating structure.In this research, in order to develop a scheme of the time series simulation of the VIV of the hanging flexible riser, we carried out some irregular forced oscillating experiments. The top end of the riser model was oscillated irregularly in a horizontal plane (X direction). We think this irregular motion as the surging motion of the floating structure caused by ocean waves. For the wave data of irregular surging motion, we used an International Ship and Offshore Structures Congress (I.S.S.C) wave spectrum, which is defined as having significant wave height (Hw) and mean period (Tw). Experimental conditions were determined as combinations of the Hw and Tw. The resulting three-dimensional motion of the model was measured with CCD cameras, and the results were analyzed using a motion picture analysis method..Finally, by comparing the numerical and experimental results, the accuracy of this numerical scheme was validated.On the basis of above research, we developed a control system of a long riser. A gain scheduling controller is designed using LPV (Linear parameter varying) control method, where its design problem is formulated into a performance optimization problem with LMI (Linear Time Invariant) simultaneously. The performance of this controller is validated by comparing with experimental results.