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Active control applied to offshore structures: positioning and attenuation of vortex induced vibrations

Abstract : The petroleum exploration in deep water induces many challenges. Some of these problems are due to the extremely long structure that links the platform to the wellhead (risers). The depth increase makes the structure more slender, and consequently much more flexible, and its dynamical behavior may be described by an infinite dimensional system. Two associated problems are studied in this report: the positioning of the bottom structure, to connect it to the wellhead (reentry operation), and the vortex induced vibrations of these slender structures. The first part of this thesis is dedicated to the control of the reentry operation. Two different strategies of motion planning are proposed. The first one is based on a finite dimensional model obtained by a modal approach. The other one considers that the behavior of the structure is close to the behavior of the Bernoulli's historical cable equation, completed with a damping factor. The proposed approximate solutions of this PDE are directly used in the control design. Two different closed loop controls are proposed: one using a Lyapunov function, and another tracking system that uses the system inversion to calculate the tracking feedback. The second part is dedicated to the study of the structure's undergoing vortex induced vibrations (VIV) and to their control. It presents a first control strategy to reduce the VIV. This control strategy is based on a modal analysis of the system equations. The control system generates a displacement in phase opposition to the VIV, attenuating the VIV because of an anti-resonance effect. The simulation results are confirmed by experiments done on a reduced scale setup.
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Submitted on : Tuesday, April 20, 2010 - 8:00:00 AM
Last modification on : Thursday, September 24, 2020 - 5:04:18 PM
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  • HAL Id : pastel-00006011, version 1

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Eugênio Fortaleza. Active control applied to offshore structures: positioning and attenuation of vortex induced vibrations. Mathematics [math]. École Nationale Supérieure des Mines de Paris, 2009. English. ⟨pastel-00006011⟩

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