Active control for installation of underwater structures |
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Authors: | Keisuke Watanabe Hideyuki Suzuki Koichiro Yoshida |
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Institution: | (1) Department of Marine Design and Engineering, Tokai University, 3-20-1 Orido, Shimizu, 424-8610 Shizuoka, Japan;(2) Department of Environmental and Ocean Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, 113-8656 Tokyo, Japan |
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Abstract: | The trend towards deepwater development requires a new approach to underwater installation of offshore structures. The present
method using crane vessels has some drawbacks in operations at more than 2000 m depth. The natural period of the coupled system
of the rigged structure and the crane vessel becomes longer, so that it is no longer possible to manipulate the cranes to
achieve the desired positioning accuracy. This paper examines the application of an active control technique for underwater
installations as one of the solutions to the present problems. An active control technique also has the advantage that it
can deal with the structural flexibility which allows the structure to be large and light-weight. This structural flexibility
imposes problems of suppressing the elastic responses and securing the stability of the control system. In this paper, anH
∞ controller combined with a low authority control/high authority control (LAC/HAC) feedback controller is designed for cases
where structural flexibility cannot be ignored. A robust model-following controller is examined for cases where the structure
can be treated as rigid. In order to confirm the control algorithm and verify the possibility of the active control installation
method, basin tests are executed using two types of neutrally buoyant flexible models with ultrasound ranging systems and
thrusters. |
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Keywords: | H ∞ control flexible structure underwater docking |
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