Ballard, E.J., Du, S.X. and Hudson, D.A.
Motions of mono/multi-hulled vessels in regular waves
In Proceedings of the Sixth International Conference on Fast Sea Transportation (FAST 2001).
The Royal Institution of Naval Architects., .
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The use of a time domain simulation technique for modelling ship motions allows for the evaluation of responses to arbitraryand/or transient excitation. Such a method also accounts for fluid memory effects, exemplified by the generation of motioninduced surface waves, introducing a dependence of the forces and moments on the past motion/excitation. The method usedin this paper uses convolution integrals to describe both the radiation and diffraction contributions. The evaluation of thenon-linear incident wave ((Froude-Krylov)) excitation is carried out at each step of the simulation by integrating thecorresponding pressure over the instantaneous wetted surface. The corresponding, instantaneous hydrostatic restoring forcesand moments are also accounted for by considering weight contributions at the instantaneous attitude of the hull.The effects of forward speed on a fast hull form ((NPL5b)) travelling at Froude number 0.5 in regular head waves areinvestigated. Both monohull and catamaran configurations are examined, the latter with two hull separations, allowing forinteraction effects to be studied. Hydrodynamic data is calculated using frequency domain singularity distribution methods.Two frequency domain methods are used, one employing a pulsating source distribution with forward speed correction, theother using a translating, pulsating source distribution. The data from the frequency domain methods, referenced to a bodyfixed axis system, is transformed into impulse response functions using Fourier transformations. The impulse responsefunctions are used as part of a convolution integral formulation to perform time domain simulations of motions in headwaves. Initially calculations are carried out in regular waves commensurate with the concept of linearity. Subsequently theeffects of non-linearities are investigated by increasing the wave amplitude.
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