Study on Short-term Variability of Ship Responses in Waves

Ulrik Dam Nielsen, Toshio Iseki

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Short-term variability of ship responses is investigated by cross-spectrum analysis. In a steady state condition, it is well known that a certain length of sampled data is required for stable results of the spectral analysis. However, the phase lag between responses, in terms of the phase angle of the cross-spectra, has not been discussed in detail. Using long stationary time series, the transition of amplitudes and relative phase angles of the cross-spectra has been investigated by iterative analyzes with a few seconds of time shifting. In the results, the short-term variability of the relative phase angle was observed. In effect, the variability may compromise the accuracy of the wave buoy analogy.
Original languageEnglish
JournalNihon Kokai Gakkai Ronbunshu / The Journal of Japan Institute of Navigation
Pages (from-to)51-57
Publication statusPublished - 2015


  • Seakeeping
  • Wave buoy analogy
  • Aleatory uncertainty
  • Fourier transform
  • Relative phase


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