Publications

Ribeiro and Silva, S., Santos, T.A. and Guedes Soares, C. (2005), “Parametrically Excited Roll in Regular and Irregular Head Seas”, International Shipbuilding Progress, Vol. 52, Issue 1, pp. 29-56

In this study dynamic stability problems in head seas are investigated with the use of a time-domain, non-linear numerical model of ship's motions in 5 degrees-of-freedom (sway, heave, roll, pitch, and yaw). The results presented in this paper have shown that the ship can be subjected to the wave-induced parametric resonance not only in regular but also in irregular waves. A quasi-static approach is adopted for heave, roll, and pitch motions in waves, in which calculations of significant variations on restoring coefficients are made using a pressure integration technique over the instantaneous submerged hull. Dynamic and hydrodynamic effects in waves for a given encounter frequency are included in the 5 degrees-of-freedom responses calculations, which are based on the potential flow strip theory and with close-fit sections representation of the vessel's up-right position. Comparisons between computed values and applicable experimental results demonstrated the usefulness and reliability of the technique proposed. These results represent a further improvement into the existing uncoupled (linearised and non-linear) theories of stability of vessels in regular waves. Finally, in the stochastic excitation a certain treshold value is assumed for parametric roll response and then the probabilities of exceedence are calculated as a function of the prevailing weather and ship’s operational conditions.

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