Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering)
Online ISSN : 1883-8944
Print ISSN : 1884-2399
ISSN-L : 1883-8944
Current issue
Displaying 1-3 of 3 articles from this issue
Paper (In Japanese)
  • Yoshihiko IDE, Masaru YAMASHIRO, Noriaki HASHIMOTO, Mitsuyoshi KODAMA
    2022 Volume 78 Issue 1 Pages 1-16
    Published: 2022
    Released on J-STAGE: January 20, 2022

     The Guide to Storm Surge Inundation Area Mapping provided by the Japanese government requires the determination of the typhoon path which causes the largest storm surge deviation in the target area (worst typhoon path). In order to find the worst typhoon path, the grid search method is generally used, which is an exhaustive search by gradually translating and rotating a reference path. However, it is unlikely that the “true” worst typhoon path is contained in these paths. Therefore, it is possible to get closer to the worst typhoon path by increasing the degree of freedom of the path representation. However, in the grid search method, it is impossible to find the path with a higher degree of freedom due to the computational cost. In this study, we proposed a new method for finding the worst typhoon path using Bayesian optimization against paths with high degrees of freedom, and developed the search procedure and method. As a result, it is possible to find the path closer to the true worst typhoon path with lower computational costs.

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  • Syunya TOKUMARU, Mutsumi WATANABE, Ryota MIZUSAKO, Shinya FUKUMOTO, Ma ...
    2022 Volume 78 Issue 1 Pages 17-28
    Published: 2022
    Released on J-STAGE: February 20, 2022

     Drone technology is expected to play an important role in various fields, including topographic survey, wave and current monitoring, lifesaving, etc. in the ocean. In the present paper, we propose a new method for bathymetry, with the combination of an unmanned aerial vehicle (UAV) and an unmanned surface vehicle (USV). First, the motion of the USV is evaluated using images obtained by the UAV. Second, the pixel shift values of the seabed are calculated through underwater images by the USV. Finally, according to these results, the water depth is acquired by applying a trigonometry. The experimental results obtained using a wave basin have shown the maximum estimation error of 1.1cm, indicating the effectiveness of the proposed method.

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    2022 Volume 78 Issue 1 Pages 29-41
    Published: 2022
    Released on J-STAGE: February 20, 2022

     The beach topography is subject to seasonal variations, especially in the swash zone, where sediment movement is pronounced and the beach face slope and sediment grain size are constantly changing, resulting in a state of dynamic equilibrium. In this study, the constructal law, which states that the flow system in nature behaves in an efficient manner, was applied to the sediment transport in the swash zone. The dynamic relationship between sediment grain size and beach face slope in the dissipative and reflective beaches was analyzed using the energy model and the Shields number model. There was no difference among the models, and the beach face slope became slower as the wave height increased, similar to the characteristics of the field beaches. The relationships between sediment particle size and beach face slope in the inner bay, open sea and coral reef beaches were explained.

     As an application of the analytical solution, the changes in sediment grain size and beach face slope with the change of waves on an artificial beach are clarified, which is useful for the maintenance and management of the beach. The applicability of the solution to the evaluation method of shoreline retreat due to sea level rise by Bruun’s rule is also discussed.

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