In the paper, we present the application of IDA-PBC (Interconnection and Damping Assignment Passivity-Based Control) method to a marine riser control. In reentry operations, it is required to move the riser's lower end to a seabed manifold smoothly as soon as possible. In the motion control system design, the performance is expected to be better with a nonlinear control method because the dynamics of a riser is strongly influenced by the nonlinear effect such as hydrodynamic forces. In the paper, a nonlinear controller for a simplified riser model is designed using passivity-based control method, and the advantage of the control method is shown through numerical simulations.
Marine risers are widely used for the offshore oil drilling and production. It is also expected to play important roles in the other ocean activities such as scientific investigations. In the case of extremely bad weather, such as typhoon, the vessel holding a marine riser must detach its lower end from a seabed manifold, leave for a safer sea, and return to the original position when whether serves. Then, reentry operation is necessary to connect the lower end of a riser to a seabed manifold. Although a riser is made of rigid material and its diameter is tens of centimeters, it has characteristics as a flexible structure due to the long length up to thousands meters. Moreover hydrodynamic forces work on a marine riser, so its dynamics becomes very complex and the prediction of motion is difficult. Human operation of reentry might spend half a day because of the difficulty of predicting the behavior. Therefore it is strongly desired to develop a control system to support such a reentry operation. Pioneering works in Japan on the reentry control based in LQG control theory were done by Suzuki, H. et al (1993,1995,1997).