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Volume :28 Issue : 2 2001
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A nonlinear controller for offshore structures under wave excitations
Auther : MOHAMAD J. TERRO*, MAGDI S. MAHMOUD** AND MOHAMED ABDEL-RAHMAN*
*Department of Civil Engineering, Kuwait University, P0 Box 5969, Safat-13060, Kuwait, e-mail: terro@kuc01.kuniv.edu.kw, marohman@civil.kuniv.edu.kw
**Modern Sciences & Arts University, Amer Street, Mesaha Square, Dokki, Egypt, e-mail: magdim@yahoo.com
ABSTRACT
In this paper, a new feedback-control design is developed and applied to an offshore structure under wave excitation. The nonlinear Morison equation is employed to estimate the wave forces. The feedback-control design proceeds in two consecutive stages: a nominal stage based on linear quadratic theory for regulating a linear part of the system dynamics, and an adjustment stage in the form of a nonlinear controller with a tuning gain factor for accommodating the nonlinearities while maintaining the overall stability. A SIMULINK model is designed to simulate the response of a three-floor steel jacket platform example. Results of the simulation of this structure with and without feedback-control are discussed to demonstrate the effectiveness of this control method.
Keywords: Feedback control design; Morison equation; nonlinear controllers; offshore structures; wave excitations.