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.
This paper investigates the hybrid-driven-based networked control for an offshore steel jacket platform subject to external wave forces. A hybrid driven strategy is introduced to deal with the problem of networked control for offshore platforms. Then, the networked closed-loop system is modeled as a stochastic delay system. Based on this model, a stability criterion is derived using the stochastic control theory and the Lyapunov-Krasovskii functional method. Simulation results show that the hybrid-driven-based networked H ∞ controller is effective to suppress the vibration of the platform and save the limited network resources as well. Moreover, the designed controller is flexible in terms of maintaining a balance between performance requirements of the offshore platform and the utilization of communication network bandwidth. INDEX TERMS Offshore platform, networked control system, H ∞ control, stochastic system, hybrid driven strategy.
We consider the pinning effect for full Ginzburg-Landau functional. The existence of local minimizers with vortices locating in the pinning regions is obtained.
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