CHARACTERISTIC OF DIRECTIONAL WAVE SPECTRUM AND WAVE TRANSFER FUNCTION IN CONSIDERATION OF SPECTRAL PEAK FREQUENCY

Abstract

Directional wave spectra and spreading parameter are measured to investigate properties of wind waves observed in the Sea of Japan. Goda and Suzuki have shown that the peak value of spreading parameter s decreases as the deepwater wave steepness increases based on the observation by Mitsuyasu et al. and Wilson's formula. The values of directional spreading parameter s observed at Oyashirazu Coast faced the Sea of Japan do not decrease in accordance with the relationship proposed by them. It is found that the value of s decrease as the wave height larger than 4m increases.Transfer function from water surface displacemento wave pressure fluctuation are also evaluated with the field observation data to study the effect of nonlinearity of waves on them and estimate water surface elevation from the wave pressure fluctuation. The values of transfer function in the range of frequency larger then twice the peak frequency decrease rapidly compared to the linear theory. The transfer function measured are formulated and used for estimation of representative wave heights from the wave pressure fluctuation.