Ocean wave spectrum estimation using measured vessel motions from an in-service container ship

Ulrik D. Nielsen, Jesper Dietz

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

This article is about the use of measured wave-induced vessel motions for estimation of ocean wave spectra by application of the wave buoy analogy. In the study, data from a larger, in-service container ship is considered. The estimation of wave spectra, equivalently sea state parameters, is based on measurements from, respectively, a gyro and two accelerometers leading to the simultaneous use of the pitching motion together with the horizontal and vertical accelerations in a position close to the forward perpendicular. The study of in-service data leads to contemplations about the vessel’s advance speed, as the possible existence of sea current means that speed-over-ground (SOG) and speed-through-water (STW) will be dfferent. The article discusses aspects related to advance speed in the context of the wave buoy analogy, and a smaller sensitivity study is conducted. Preceding to the sensitivity study, a comparison is made between sea state estimates by the wave buoy analogy and estimates obtained from a hindcast study. The article shows an acceptable agreement between the two sets of estimates. Following, the main conclusion from the sensitivity study on advance speed is that errors and uncertainties in the speed log have an effect on the estimates of the wave buoy analogy. In fact, the effect can be severe if reliable STW measurements are not available. In the final part, the article includes a few discussions about (non)stationary conditions in the context of the wave buoy analogy, and, although the effect on results is not necessarily detrimental, care must be shown when the wave buoy analogy is applied during in-service conditions.
Original languageEnglish
Article number102682
JournalMarine Structures
Volume69
Number of pages13
ISSN0951-8339
DOIs
Publication statusPublished - 2020

Keywords

  • Wave spectrum estimation
  • Ship motions
  • Directional wave spectrum
  • In-service data
  • Container ship
  • Speed-through-water

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