Boundary Control Of Riser For FDPSO-TLD Under Parametric Excitation

As an emerging type of marine exploitation equipment, the Floating, Drilling, Production, Storage and Offloading system (FDPSO) has attracted more and more attention in offshore oil and gas industry over the years. This concept, which is to add a drilling system on the FPSO with dry tree and top tension risers, combines the function of exploitation, drilling, production, storage and transmission. The inevitable heave motion of the hull by the random wave will cause a longitudinal time-varying parametric excitation in the risers. When the values of amplitude and frequency reach at some interval, the parametric resonance will be excited in transverse direction, which can cause fatigue damage and even failure to the risers.In this paper, the FDPSO-TLD riser system is simplified as a nonlinear Euler-Bernoulli beam since the riser is slender. According to the Hamilton's principle and Morison equation, the equation of motion of the riser is established under parametric excitation and wave excitation. In order to reduce the vibration of riser, two actuators are developed at the top of riser in transverse and longitudinal directions, which are designed by the boundary control theory and Lyapunov's direct method. The numerical simulation is selected by finite element method and time-domain analysis method with MATLAB in this paper. With the results of simulation, the comparison of a 1500m-long riser under different kinds of control conditions is presented, which indicates that the proposed controller can significantly reduce the dynamic response and stress of riser.