Evolution of wave properties during propagation in a ship towing tank and an offshore basin

A data set of irregular wave propagation in a ship towing tank is analysed and compared with another wave data set obtained in an offshore basin. It was found that the energy, carrier frequency and spectrum wideness parameter ν decrease along the tank and the decrease depends on the initial steepness. The calculated skewness and kurtosis also appear to depend on the initial steepness. The kurtosis of the series from the wider offshore basin reaches larger values. The probable narrow band three-dimensional modulation characteristic for the series measured in the towing tank influences the kurtosis and leads to smaller values of this quantity. For an initial steepness less than 0.1, after the increase of the kurtosis it remains almost constant for the initial steepness between 0.1 and 0.15. For the steepness greater than 0.15 a tendency is noticed for the kurtosis to decrease. The peak frequency changes faster to lower values for the waves with larger initial steepness. The results for the steepness of the maximum observed waves are compared with other similar experiments. The results show that the steepness of the observed maximum waves systematically decreases with the parameter δS inversely proportional to BFI.

► A data set of a ship towing tank in an offshore basin is studied.
► The energy, carrier frequency and spectrum wideness parameter decrease along the tank.
► The calculated skewness and kurtosis also appear to depend on the initial steepness.
► The kurtosis of the series from the wider offshore basin reaches larger values.
► The peak frequency decreases faster for the waves with larger initial steepness.