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Mass Flux and Vertical Distribution of Currents Caused by Strong Winds in a Wave Tank

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  • 1 Department of Environment and Renewable Systems, Gifu University, Gifu, Japan
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Abstract

The velocity fields of wind-driven currents under strong winds were measured in a wind-wave tank with a double bottom. The tank has the characteristics to satisfy partially the continuity of the mass flux and to reduce return-flow effects on the currents. The lower part of the double-bottom tank functions as a duct to circulate the currents, allowing the measurement of the return-flow velocity. The velocity measurements were made on the currents just below the mean water level by using a high-resolution particle image velocimetry (PIV) system and tracking floats and on the currents inside of the duct by using a normal PIV system. Thus, accurate data of the vertical distribution and mass flux of the currents driven by strong winds were obtained from the PIV data. As a result, it is found that the flux in the surface layer with the thickness of 2 times the significant wave height amounts to about 30% of the total mass flux of the currents driven by strong winds with a reference wind speed of 12.0 m s−1.

Corresponding author address: Dr. Toshinori Ogasawara, Department of Civil and Environmental Engineering, University of Iwate, 4-3-5 Ueda, Morioka Iwate 020-8551, Japan. Email: togasa@iwate-u.ac.jp

Abstract

The velocity fields of wind-driven currents under strong winds were measured in a wind-wave tank with a double bottom. The tank has the characteristics to satisfy partially the continuity of the mass flux and to reduce return-flow effects on the currents. The lower part of the double-bottom tank functions as a duct to circulate the currents, allowing the measurement of the return-flow velocity. The velocity measurements were made on the currents just below the mean water level by using a high-resolution particle image velocimetry (PIV) system and tracking floats and on the currents inside of the duct by using a normal PIV system. Thus, accurate data of the vertical distribution and mass flux of the currents driven by strong winds were obtained from the PIV data. As a result, it is found that the flux in the surface layer with the thickness of 2 times the significant wave height amounts to about 30% of the total mass flux of the currents driven by strong winds with a reference wind speed of 12.0 m s−1.

Corresponding author address: Dr. Toshinori Ogasawara, Department of Civil and Environmental Engineering, University of Iwate, 4-3-5 Ueda, Morioka Iwate 020-8551, Japan. Email: togasa@iwate-u.ac.jp

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