Abstract
The irregular wave disturbance attenuation problem for jacket-type offshore platforms involving the nonlinear characteristics is studied. The main contribution is that a digital-control-based approximation of optimal wave disturbances attenuation controller (AOWDAC) is proposed based on iteration control theory, which consists of a feedback item of offshore state, a feedforward item of wave force and a nonlinear compensated component with iterative sequences. More specifically, by discussing the discrete model of nonlinear offshore platform subject to wave forces generated from the Joint North Sea Wave Project (JONSWAP) wave spectrum and linearized wave theory, the original wave disturbances attenuation problem is formulated as the nonlinear two-point-boundary-value (TPBV) problem. By introducing two vector sequences of system states and nonlinear compensated item, the solution of introduced nonlinear TPBV problem is obtained. Then, a numerical algorithm is designed to realize the feasibility of AOWDAC based on the deviation of performance index between the adjacent iteration processes. Finally, applied the proposed AOWDAC to a jacket-type offshore platform in Bohai Bay, the vibration amplitudes of the displacement and the velocity, and the required energy consumption can be reduced significantly.
Highlights
The offshore platforms provide the basic support for marine operation, such as the oil exploration, drilling operations and transportation
Taking the jacket-type offshore platform located in Bohai Bay into consideration, the parameters of installed active mass damper (AMD) and offshore structure are listed in Table 1 [28]
A digital-control-based approximation of optimal wave disturbances attenuation controller (AOWDAC) was developed for a nonlinear jacket-type offshore platform under external irregular wave disturbances, which consists of feedback items of offshore platform state, feedfoward item for attenuating the external wave disturbance, and compensation sequences for responding to the nonlinear dynamic of offshore platforms
Summary
The offshore platforms provide the basic support for marine operation, such as the oil exploration, drilling operations and transportation. A considerable amount of theoretical and experimental research effort has been aimed at improving the control performance of offshore platforms, including passive and active control [1,2]. Passive control is the classic technology to enhance the safety by using excessive construction materials to guarantee the stability of the offshore structures. Active control technologies have great potential to meet the optimal performance requirements with low consumption requirement [3]. Various kinds of active schemes have been derived and employed for offshore platforms, e.g., using the concepts of non-fragile control [4], sliding mode theory [5] and H∞ control [6]
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