Minimization of drift force on a floating cylinder by optimizing the flexural rigidity of a concentric annular plate |
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| Institution: | 1. Department of Civil Engineering, Aristotle University of Thessaloniki, Thessaloniki, 54124, Greece;2. Department of Naval Architecture and Ocean Engineering, Osaka University, Suita, Osaka, 5650871, Japan;1. Environmental Process Modelling Centre, NEWRI, Nanyang Technological University, Singapore;2. American Society for Engineering Education, DC, United States;3. U.S. Naval Research Laboratory, Stennis Space Center, MS, United States;4. School of Civil and Environmental Engineering, Nanyang Technological University, Singapore;5. Department of Infrastructure Engineering, University of Melbourne, VIC, Australia;1. University of L’Aquila, Department of Civil, Construction-Architectural and Environmental Engineering (DICEAA), Environmental and Maritime Hydraulic Laboratory (LIam), P.le Pontieri, 1, 67040 Monteluco di Roio, L’Aquila, Italy;2. Technical University of Bari, Department of Civil, Environmental, Building Engineering and Chemistry (DICATECh), Coastal Engineering Laboratory, Area Universitaria di Valenzano S.P. Valenzano Casamassima, Km.3, 70010 Valenzano, Bari, Italy;1. Department of Offshore Oil and Gas Engineering, College of Petroleum Engineering, Xi’an Shiyou University, Xi’an, China;2. Research Institute of Marine Systems Engineering, Department of Naval Architecture and Ocean Engineering, Collage of Engineering, Seoul National University, Seoul, South Korea;3. Institute for Ocean Engineering, China University of Petroleum, Beijing, China;4. Natural Gas Department, Tarim Oilfield Company, PetroChina, Xinjiang, China |
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| Abstract: | The deployment of suitable configurations of mutually interacting floating bodies for efficiently controlling their hydrodynamic interactions towards the reduction of the wave drift forces and, thus, of the mooring lines’ loads, has, nowadays, gained a great scientific interest. In this paper, the hydrodynamic behaviour of a floating cylinder and a concentric annular flexible plate is analysed in the frequency domain aiming at the minimization of the drift forces acting on the cylinder by optimizing the flexural rigidity of the plate. The diffraction/radiation problem is solved using a higher-order boundary element method. The analysis is implemented assuming that both floating bodies oscillate freely in heave, while for the plate, flexible modes are, additionally, considered for describing its structural deformations. The required modes shapes are determined in vacuum (“dry” mode superposition approach) through analytical expressions. The flexural rigidity of the plate, D, is optimized at a specific wave number using a real-coded genetic algorithm. Initially, results are compared with numerical results of other investigators for the case of two rigid concentric floating cylinders. Next, extended results are presented, focusing on the effect of D, including its optimum value, on various physical quantities describing the behaviour of both the cylinder and the plate. Contrary to the isolated cylinder, the presence of the plate introduces sharp peaks in the variation pattern of the drift force of the cylinder, bounded at specific wave numbers, where resonance of the seiche mode of water motion in the annular cavity or of specific flexible modes of the plate occurs. However, by reducing D to its optimum value, the cylinder’s drift force obtains practically zero values at the target wave number, due to an efficient improvement of the wave field in the annular cavity around the cylinder. Moreover, a great reduction of the drift force compared to the isolated cylinder is achieved in the subsequent high frequency range. |
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| Keywords: | Annular flexible plate Modal functions Higher-order boundary element method Wave drift force Hydrodynamic interactions Flexural rigidity |
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