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Evolution of Velocity Field and Vortex Structure during Run-Down of Solitary Wave over Very Steep Beach

1
Department of Civil Engineering, National Chung Hsing University, Taichung City 40227, Taiwan
2
International Wave Dynamics Research Center, National Cheng Kung University, Tainan City 701, Taiwan
3
Department of Water Resources and Environmental Engineering, Tamkang University, New Taipei City 25137, Taiwan
4
Department of Civil Engineering, KLE Dr. M. S. Sheshgiri College of Engineering and Technology, Angol Main Road, Udyambag, Belgaum, Karnataka 590008, India
*
Author to whom correspondence should be addressed.
Water 2018, 10(12), 1713; https://doi.org/10.3390/w10121713
Received: 6 September 2018 / Revised: 17 November 2018 / Accepted: 19 November 2018 / Published: 23 November 2018
(This article belongs to the Section Hydraulics)
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Abstract

An experimental results on the spatio-temporal variation of velocity field and vortex structure, generated from the separated boundary layers on the offshore side of the still-water shoreline, during the run-down process of non-breaking solitary waves over a 1:3 sloping beach are presented. Three waves having the incident wave-height to water-depth ratios (H0/h0) of 0.363, 0.263, and 0.171 were generated in a wave flume. Two flow visualization techniques and high-speed particle image velocimetry were employed. The primary topics and new findings are: (1) Mechanism of the incipient flow separation, accompanied by formation of the separated shear layer from the beach surface, is elucidated under the adverse pressure gradient, using the fine data of velocity measurements very close to the sloping boundary. (2) Occurrence of hydraulic jump subsequently followed by development of the tongue-shaped free surface and projecting jet is demonstrated through spatio-temporal variation in the Froude number. It is confirmed by a change in the Froude number from supercritical to subcritical range as the free surface rapidly rises from the onshore to offshore side. (3) A complete evolution of the primary vortex structure (including the core position, vortex size, and velocity distribution passing through the vortex core) is first introduced systematically, together with the illustration of temporal variation in the topological structure. The non-dimensional shoreward distance of the vortex core section decreases with the increase in the non-dimensional time. However, the non-dimensional size height of the primary vortex increases with increasing non-dimensional time. (4) Two universal similarity profiles for both the wall jet flow and the shear layer flow demonstrate independency of the two similarity profiles of the wave-height to water-depth ratio and the beach slope. The similarity profiles indicate the promising collapse of the data from three previous studies for 1:20, 1:10, and 1:5 sloping beaches. View Full-Text
Keywords: solitary wave; run-down process; high-speed particle image velocimetry (HSPIV); flow separation; shear layer; hydraulic jump; vortex structure; size height; similarity profile solitary wave; run-down process; high-speed particle image velocimetry (HSPIV); flow separation; shear layer; hydraulic jump; vortex structure; size height; similarity profile
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Lin, C.; Wong, W.-Y.; Kao, M.-J.; Tsai, C.-P.; Hwung, H.-H.; Wu, Y.-T.; Raikar, R.V. Evolution of Velocity Field and Vortex Structure during Run-Down of Solitary Wave over Very Steep Beach. Water 2018, 10, 1713.

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