The Effect of Wind Spectra on the Low-Frequency Motions of a Moored Tanker in Survival Condition

In the design of moored tankers the knowledge of the wave drift forces is of importance. As is known, the low frequency part of the wave drift forces is responsible for the low frequency motions of the vessel. In general the low frequency motions may cause a substantial part of the mooring forces.
Another source of the low frequency excitation can be found from wind spectra. The wind spectra originate from the turbulence in the wind field. Besides the wave drift forces also the fluctuating wind force will induce low frequency oscillations of the tanker.
The purpose of this study is to investigate the effect of a wind spectrum based on an hourly mean wind speed in relation to the 1-minute steady wind gust, both in combination with a co-linearly directed storm wave spectrum on the low frequency motions of a 200 kDWT tanker.
The tanker is moored in 82.5 m deep water. The computations have been applied to a linear type mooring system. To confirm the reliability of the computation procedure model tests have been carried out.

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