Asymmetric Surging of Ships in Following Seas and its Repercussions for Safety |
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Authors: | K J Spyrou |
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Affiliation: | (1) School of Naval Architecture and Marine Engineering, National Technical University of Athens, 9 Iroon Polytechneiou, Zographou, Athens, 157 73, Greece |
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Abstract: | A comprehensive investigation of an asymmetric longitudinal motion of ships displayed in long and steep following waves is
presented. The focus is on the strongly nonlinear response, on the verge of the so called surf-riding condition, where a ship
could be performing large-amplitude longitudinal oscillations around a mean forward speed. Expressions, in closed form, describing
transient surge motion on the phase-plane are derived. For steady-state in particular, is shown that it is possible to determine
an explicit analytical solution in the time-domain. Simple prediction formulae for the higher limit of asymmetric surging
(threshold of global surf-riding) are derived on the basis of two alternative methods. Also, we investigate the effect of
asymmetric surging on a ship's tendency for capsize in the neighborhood of wave crests where restoring capability is often
reduced. The paper includes, as an Appendix, a review of types of ship instability and a summary of the historical roots of
the field.
For a better introduction to the subject we include, as Appendix A, a historical note on the evolution of the theory ship
stability together with a summary of known types of ship instability distinguished on the basis of the angle of encounter
between ship and waves. |
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Keywords: | asymmetric surging broaching nonlinear dynamics ship stability surf-riding |
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