On unstable ship motions resulting from strong non-linear coupling |
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| Authors: | Marcelo AS Neves Claudio A Rodríguez |
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| Institution: | aDepartment of Naval Architecture and Ocean Engineering, LabOceano/COPPE, Federal University of Rio de Janeiro, C.P. 68.508, Rio de Janeiro, 21.945-970, Brazil |
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| Abstract: | In this paper, the modelling of strong parametric resonance in head seas is investigated. Non-linear equations of ship motions in waves describing the couplings between heave, roll and pitch are contemplated. A third-order mathematical model is introduced, aimed at describing strong parametric excitation associated with cyclic changes of the ship restoring characteristics. A derivative model is employed to describe the coupled restoring actions up to third order. Non-linear coupling coefficients are analytically derived in terms of hull form characteristics.The main theoretical aspects of the new model are discussed. Numerical simulations obtained from the derived third-order non-linear mathematical model are compared to experimental results, corresponding to excessive motions of the model of a transom stern fishing vessel in head seas. It is shown that this enhanced model gives very realistic results and a much better comparison with the experiments than a second-order model. |
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| Keywords: | Ship stability Parametric resonance Non-linear equations Ship motions Roll motion Hill equation |
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