To improve the safety and reliability of offshore structures subject to wave loading, the active vibration control problem is always one of significant issues in the field of ocean engineering. This paper deals with the near–optimal control problem of offshore structures with a nonlinear energy sink (NES) mechanism. By taking the dominant vibration mode of the offshore structure with the NES into account, a nonlinear dynamic model of the steel–jacket structure subject to wave loading is presented first. Then, using the parameter perturbation approach to solve a nonlinear two–point boundary value problem, an NES–based optimal controller with the form of infinite series sum is presented to suppress the vibration of the offshore structure. Third, an iteration algorithm is provided to obtain the near–optimal controller. Simulation results demonstrate that the NES–based near–optimal controller can mitigate the oscillation amplitude of offshore structures significantly. Moreover, the NES–based optimal controller outperforms the one based on active tuned mass damper.
In deepwater-drilling engineering, it is necessary to disconnect the bottom equipment of the lower marine-riser package from the blowout preventer when encountering multi-hazard environmental factors. In order to reduce the impact of recoil on the drilling platform after the sudden disconnection of the riser, in this paper, an optimal guaranteed cost H∞ recoil control problem is considered for the drilling riser. First, a three-element mass-damper-spring deepwater-drilling riser model subject to fluid discharge and heave motion of offshore platform is given. Then, an optimal guaranteed cost H∞ controller (OGCHC) is designed to suppress the recoil response of the drilling riser, and the sufficient conditions for the asymptotic stability of the closed-loop system are derived. Third, it is found through simulation results that the designed OGCHC can reduce the recoil response effectively. In order to further analyze the advantages of the OGCHC, the performance indices of the riser without active-recoil control and with optimal control (OC) and OGCHC are compared. It is shown that the average response amplitudes of three mass blocks of the riser are almost the same, while the control cost by the OGCHC is less than that by the OC. Further, under the designed recoil control, no riser compression occurs, thereby ensuring the safety of the riser system.
This paper proposes a hybrid control scheme combining adaptive control (APC) and linear active disturbance rejection control (LADRC) to solve the high-speed train (HST) speed tracking control problem. First, in order to meet the actual operation of HST, a multi-mass point dynamic model with time-varying coefficients is established. Second, LADRC is proposed to control the speed of the train, and the anti-disturbance ability of the system is improved by estimating and compensating the total disturbance suffered by the carriage. Third, in order to compensate for the observation error caused by the bandwidth of the linear extended state observer, APC is introduced. The adaptive laws are set for LADRC and train time-varying coefficients, which can effectively eliminate the adverse effects of time-varying coefficients on train operation and improve the control performance of the controller. Meanwhile, the Lyapunov theory is used to prove the stability of the system. Finally, the simulation results show that the hybrid control is more effective in solving the problem of HST speed tracking.
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