Time-Frequency Analysis of Ocean Waves with Reference to Small Fishing Boats

摘要

When a spectrum is estimated using Fourier transform, information regarding time is lost owing to movement from the time domain to the frequency domain. As is evident from the definition of Fourier transform, information in the entire time domain is theoretically required. Time-frequency analysis has been developed to address these issues. In this study, we first explain the uabor transform, which is a short-time Fourier transform; subsequently, we perform time-frequency analysis of time-series dataon ocean waves in Tokyo Bay, measured using wavelet transform, which was improved by Morlet et al, and present the newly obtained findings. Very few studies have analyzed the time and frequency of wind waves with a significant wave height of approximately 1[m], which have a considerable impact on small fishing boats. Ueno et al reported that that rolling occurs in a 19 GT small fishing boat, with both amplitudes exceeding 30°，even when the significant wave height is less than 1[m]. In this case, capsizing does not occur, but it is highly possible that workers on the deck will fall into the sea, and tailing into the sea in cold water can directly lead to death.