Reproduction of the Marine Debris Distribution in the Seto Inland Sea Immediately after the July 2018 Heavy Rains in Western Japan Using Multidate Landsat-8 Data

Understanding the spatiotemporal environment of the ocean after a heavy rain disaster is critical for satellite remote sensing research and disaster prevention. We attempted to reproduce changes in marine debris distributions using multidate data of Landsat-8 spectral reflectance acquired immediately after a heavy rain disaster in western Japan in July 2018. Data from cleaning ships were used for screening the marine debris area. As most of the target marine debris consisted of plant fragments, a method based on the corrected floating algae index (cFAI) was applied to Landsat-8 data. Data from cleaning ships clarify that most of the marine debris accumulated in the waters in the northern part of Aki Nada, a part of the Seto Inland Sea. The spectral characteristics of the corresponding marine debris spectral reflectance obtained from the Landsat-8 data were explained by the FAI with band 5 (central wavelength: 865 nm) as the maximum value. Unlike traditional FAI, cFAI eliminated the effect of background water turbidity. The Otsu method was effective for the automatic threshold determination for cFAI. Although Landsat-8 data have limited spatial resolution and observation frequency, these data were useful for understanding marine debris distribution after a heavy rain disaster

沿岸域生態系評価における非線形波動の流体力学的考察

研究期間:平成10-11年度 ; 研究種目:基盤研究B2 ; 課題番号: 10450385原著には既発表論文の別刷を含む

Numerical Study on Unsteady Pressure Distribution on Bulk Carrier in Head Waves with Forward Speed

This study deals with wave-induced unsteady pressure on a ship moving with a constant forward speed in regular head waves. Two different numerical methods are applied to solve wave–ship interaction problems: a Rankine panel method which adopts velocity potential, and a Cartesian-grid method which solves the momentum and mass conservation equations under the assumption of inviscid and incompressible fluids. Before comparing l1ocal pressure distributions, the computational methods are validated for global quantities, such as ship motion responses and added resistance, by comparison with available experimental data. Then, the computational results and experimental data are compared for hydrodynamic pressure, particularly focusing on the magnitude of the first-harmonic component in different sections and vertical locations. Furthermore, the Cartesian-grid method is used to simulate the various wave-amplitude conditions, and the characteristics of the zeroth-, first-, and second-harmonic components of wave-induced pressure are investigated. The nonlinearity of pressure distribution is observed mostly from the pressure near the still-water-level of the ship bow and the normalized first-harmonic component of wave-induced pressure decreases as the wave steepness increases. Lastly, to understand the local characteristics of wave-induced unsteady pressure, the time-averaged added pressure and added local force are analyzed. It is found that the major contribution of the time-averaged added local force that occurs around the ship stem above the design waterline

波浪中を進行する船のまわりの非定常波紋について

向い波中を一定速度で前進する船のdiffraction waveの波紋を理論計算し, 実洞された波紋との比較を行うとともに理論計算された波紋を用いて非定常波形解析法の精度を検柾する.1. まえがき / 2. 周期的吹き出しの速度ポテンシャルと波紋の計算 / 3. 細長船のDiffraction wave / 4. 非定常波形解析法の精度について / 5. まとめ / 参考文

Motion Response Characteristics of a Kyushu-University Semi- Submersible Floating Wind Turbine with Trussed Slender Structures: Experiment vs. Numerical Simulation

Understanding the dynamics of an FWT (Floating Wind Turbine) is essential for its design and operation. Since a truss structure can reduce the wave load/resistance on the floating foundation, it becomes more and more popular in industrial applications. In this regard, knowing the effect of slender members of the truss structure on the motion response characteristics of such an FWT is vital. The present work develops a time-domain method for modeling the dynamics of a floating truss-structure wind turbine with multiple rotors on the deck of the platform. In its hydrodynamic aspect, a hybrid panel-stick model is built up incorporating the potential flow theory to calculate the wave inertia force and a Morison strip method to calculate the wave drag force. A systematic methodology, and the corresponding efficient tool, have been developed to deal with the floating truss-structure consisting of a set of slender cylindrical members in arbitrary lengths, diameters, orientations, and locations. The Morison dynamic solver is incorporated into the time-domain solver for the FWT dynamics. The proposed model is validated against a model experiment of a semi-submersible FWT with a triangular-shaped truss-structured platform, which was carried out in RIAM (Research Institute for Applied Mechanics), Kyushu University. Good agreements between the simulation results and the experimental data confirm the validity of the developed method. Further numerical simulations are performed in a set of wind and wave conditions to investigate the effect of wave drag force on the FWT dynamics. It is found that without the fluid viscosity, resonant responses are excited in the platform motions at frequencies that are close to the natural frequencies of the FWT system. Via a comparison between the parked conditions and operating conditions of the FWT, it is found that in the presence of steady wind, the translational surge or sway motion is significantly excited at its resonance frequency. This may be attributed to the work done by the wind to the FWT, which enhances remarkably the total kinetic energy of the platform and consequently increases the translational surge or sway velocity of the platform at the equilibrium position. Applying a hybrid panel-stick model will be effective in reducing all these non-realistic large resonant responses.Published version is available for viewing only. (See "Related URI")「関連URI」より出版社版の閲覧専用ページへリン