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Dynamics of ships and floating platforms

University of British Columbia

Three dimensional angular motions of ships and floating platforms are investigated using Euler's dynamical equations. The solution of Euler's equations predict two new oscillatory motions, namely roll and pitch together with a constant yawing or turning-rate. Unlike classical roll and pitch the new motions have a common period of oscillation which depends on the characteristics of the ship and the magnitude of the turning-rate. The possibility that gyroscopic coupling between rolling and pitching induce yawing is considered for unpowered platforms sitting in oblique regular waves. The rotational kinetic energy shows that for some sea states, there could be a non trivial turning-rate which minimizes the peak energy so that the platform rolls and pitches while turning at a constant-rate. Resonance takes place when the frequency of the wave coincides with the frequency of the coupled motions in still water. For ships maneuvering in regular waves, there are infinite combinations of the turning-rate and the frequency of the wave which could cause resonance. Damping, however small it may be, considerably reduces the amplitude at resonance. Regardless of its orientation with respect to the direction of wave propagation, simple rolling or pitching of an unbalanced body is not possible, instead, there is a combined roll-pitch motion having a common frequency, which does not appear to have been investigated previously.

Text

2010-08-28

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http://hdl.handle.net/2429/27879

Mechanical Engineering

University of British Columbia

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