Session: 06-07-01 Metocean, Measurement and Data Interpretation

Submission Number: 153501

Long-Term Prediction of Container Ship Responses Based on Wave Forecasts 

Since the frequency of cargo handling is high in short voyages of one to several days, efficient cargo handling is needed in short voyages. Especially, major container ports are concentrated in the Asian region from the East China Sea to the South China Sea, and in the northern coast of Europe and short voyages of container ships are very active there.

To improve the cargo handling efficiency of the container ship which repeats short voyages, it is desirable to utilize wave forecasts for container stowage planning. It is necessary to evaluate the uncertainty of wave forecasts to conduct long-term prediction of the roll angle, pitch angle, and pitch angle acceleration, which are the dominant load parameters of container lashing devices on container ships.

Regarding the uncertainty of wave forecasts of significant wave heights, the forecasts of JMA GWM were compared with the wave hindcast ERA5 of ECMWF and the wave forecasts of ECMWF HRES-WAM were compared with the nowcasts of JMA GWM for each BMT-GWS region. In evaluating the error of forecasts relative to the hindcast/nowcast values, this study introduced a minor modification to the method of Natskår et al. (2015) to correct the bias of forecasts and to express the error of the logarithm of significant wave height more precisely by the generalized normal distribution. It was found that the wave height obtained offshore Norway in Natskår et al. (2015) with a 0.3 m margin was evaluated conservatively to envelop the uncertainty of wave forecasts in various global sea areas. The conditional probability distribution for significant wave height of wave period was obtained by aggregating significant wave height and wave period of ERA5 in the sea area corresponding to September along the Intra-Asia route.

Using simplified RAO formula of roll angle and pitch angle, long-term prediction of roll angle, pitch angle, and pitch angle acceleration are conducted from the probability distribution of significant wave height and wave period obtained above. The expected response in 25-years return period is expressed as a ratio between the wave forecast and the value based on the North Atlantic wave scatter diagram. This ratio is approximated and enveloped by a linear function of significant wave height, and the result of roll angle is similar to the formula in DNVGL-RU-SHIP-Pt6Ch4.

The significance of this study is that the method of Natskår et al. (2015) was applied to many regions of the world in order to conservatively the uncertainty of wave forecast globally. In addition, this study proposed simplified equations of roll, pitch angle, and pitch angular acceleration, and clarified their technical background as described above.

Presenting Author: Wataru Fujimoto ClassNK

Presenting Author Biography: Wataru Fujimoto is a researcher of ClassNK Research Institute. He earned Ph.D. degree in University of Tokyo for thesis on nonlinear aspects of freak waves and data assimilation. In 2018, he joined MS&AD InterRisk Research Institute and worked as a risk analyst on natural disasters. In 2020, he moved to current position and studies advanced utilization of metocean information for maritime safety.