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Huang Z.-C.,National Central University | Hwang K.-S.,Tainan Hydraulics Laboratory | Hwang K.-S.,National Cheng Kung University
Coastal Engineering | Year: 2015

The surface temperature fields of large-scale solitary breaking waves are measured using infrared imaging techniques in a laboratory surf and swash zone. The surface velocity fields obtained by cross-correlating the images are decomposed into wave and turbulent motions using two filtering methods in the spatial and temporal domains. The techniques presented here provide new quantitative descriptions for the evolution of the surface thermal structures, kinematics, and turbulence that are induced by unsteady and highly foamy turbulent coastal flows. Novel organized streaks of thermal structures, which exhibit a finger-like shape, are found on the water surface of the crest roller behind the head of the rebounding jet. These thermal streaks evolve with time and become isotropic when returning to the surrounding bulk water temperature. The Froude-scaled maximum flow speed, accelerations, and vorticity are O(1), and the scaled turbulent kinetic energy (TKE) is O(-. 1); these results are similar to previous findings from numerical results and periodic surf-zone breakers. Significant and concentrated structures of these quantities occur in the moving wave crest during the uprush phase; however, these structures only develop during the late stages of the backwash phase. The TKE increases shoreward from the surf to the swash zones. The ratio of the averaged variance of the turbulent velocity in the wave breaking zone does not agree with the canonical prediction for plane-wake turbulence; however, the ratio is similar to that of boundary-layer turbulence and decreases in the bore region and the swash zone, indicating an increase in the turbulence anisotropy shoreward from the surf to the shallower swash flow. © 2014 Elsevier B.V.

Huang Z.-C.,National Central University | Hwang K.-S.,Tainan Hydraulics Laboratory | Lenain L.,University of California at San Diego | Melville W.K.,University of California at San Diego | Hwung H.-H.,National Cheng Kung University
Proceedings of the Coastal Engineering Conference | Year: 2012

High intensity air bubbles generated in the surf zone and the thinning of swash flow make velocity measurements particularly challenging in coastal areas. These facts have led the need for a new measurement technique to quantify the surf and swash flow dynamics. Here, we tested infrared image techniques to measure the surface temperature and then to derive the velocity fields using cross-correlation algorithm for large-scale solitary waves breaking in the surf and swash zones. From the comparison with unspiked electromagnetic current meter (EMCM) data and previous validation, it is suggested that the infrared image velocimetry (IRIV) is satisfactory to quantify the surface turbulent flow in the surf and swash zones. The data obtained in the experiment provides a new description of surface thermal structure and kinematics for solitary breaking waves. Two-dimensional organized streaks of temperature structures are evident on the water surface behind the head of rebounding jet. Wavenumber spectrum analysis shows that the directionality of these thermal signatures evolves with time. Evolution of vorticity on the water surface during the run-up and run-down process of the solitary broken wave is discussed.

Lee J.-F.,National Cheng Kung University | Tu L.-F.,National Cheng Kung University | Liu C.-C.,Tainan Hydraulics Laboratory
Journal of Marine Science and Technology (Taiwan) | Year: 2014

In this study, an analytic approach for the complete second- order solution proposed by Sulisz and Hudspeth [13] was applied to solve a problem of waves propagating over a rectangular submerged structure. In addition, nonlinear wave evolutions above the submerged structure were studied. The nonlinear problem was expressed up to the second-order boundary value problems by using a Taylor series expansion and the perturbation method. In solving the problem, the nonhomogeneous problem was divided into Stokes wave and free wave counterparts. The solutions of neighboring regions were combined and solved by applying kinematic and dynamic matching conditions. Convergence of the presented theory is examined. The experimental results with and without evanescent modes were compared with previous solutions and effects of evanescent modes can be identified. Further comparisons of the presented theory with previous experimental results also indicated favorable consistency. Using the presented theory, the second-order effects of structural submergence, relative water depth, and wave steepness on wave evolutions were investigated. Parametric studies have indicated that shallow water depths above the structure and shallow relative water depth induce high-shoaling second-order waves. In addition, the second-order wave evolution above the structure increased with the wave steepness.

Hwung H.-H.,National Cheng Kung University | Huang Z.-C.,National Cheng Kung University | Huang Z.-C.,National Taiwan Normal University | Hwang K.-S.,Tainan Hydraulics Laboratory
Coastal Engineering Journal | Year: 2010

Artificial submerged sand bars have been used as an alternative soft engineering structure for shore protection. To successfully implement the sand bar in an economically beneficial manner, more knowledge is required concerning the evolution of a sand bar under different conditions. A series of experiments is presented to quantify the sediment transport that is induced by artificial submerged sand bars in a wave-driven beach environment. Artificial movable sand bars of various initial geometries were tested on various fixed, inclined bottom slopes by using different incoming regular wave conditions. A new, beneficial parameter, the cumulative transport rate, is defined by integrating the time-dependent cross-shore sediment transport rate from an initial deposition to a quasi-equilibrium state of a sand bar migration. From many tests and analyses, it has been found that the cumulative transport rate of the sand bar is highly dependent on the local Shields number being related to the bed-load transport. Additionally, the Shields-dependent relation is compared to previous field sand bar evolution projects to determine if the sand bar actively migrates onshore or remains stable. An optimal initial bar geometry is suggested to pursue an efficient onshore sediment transport. The effects of the bottom slope on the cumulative transport rate are also discussed. © 2010 World Scientific Publishing Company and Japan Society of Civil Engineers.

Kao R.-C.,Tainan Hydraulics Laboratory | Zavialov P.O.,RAS Shirshov Institute of Oceanology | Ding C.-F.,Tainan Hydraulics Laboratory
Irrigation and Drainage | Year: 2013

Submarine groundwater discharge (SGD) is a potential pathway for nutrients and anthropogenic pollutants that flow from the land into the coastal ocean, and probably influences the aquatic ecosystem in tidal areas. This paper focused on surveying possible groundwater locations around the coastal area. The possible location, pathway and discharge of SGD in the Ping-Tung Shelf of southwestern Taiwan were described by oceanographic measurements. During the field surveys of the study area, onboard surface to bottom CTD (conductivity, temperature, depth) profiling, ADCP (Acoustic Doppler Current Profiler) measurements, and fluorescence profiling were carried out at 25 different stations. The collected hydrographic data were used to identify a suspected SGD site in the central part of the study area, where a local drop of salinity by up to 0.06 psu has been observed in the lowermost 0.2~1.5 m of the water column. Thanks to explicit evidence for a possible pathway and locations, seepage meters were deployed on the sea bed to measure the SGD rate at about 6.0 ml h-1 m-2 in the dry season. Based on the surveyed data, the likely locations of the SGD sources in the study area were specified, all of which were restricted to the inner shelf at a depth less than 8 m. © 2013 John Wiley & Sons, Ltd.

Chiang W.-S.,Tainan Hydraulics Laboratory | Hwung H.-H.,NCKU
Journal of Hydrodynamics | Year: 2010

The long-term evolution of nonlinear wave train in deep water with varied initial wave steepness is investigated experimentally in a super wave flume (300 m long, 5 m wide, 5.2 m deep). The initial wave train is the combination of one carrier wave and a pair of imposed sideband components. Increasing modulation of wave train is observed due to sideband instability until a critical value which either initiates wave breaking or reaches the maximum modulation. The observed maximum local wave steepness increases rapidly with the increase of the initial wave steepness, and levels off at initial wave steepness roughly equal to 0.15 despites that the data exhibits a little scattering. The normalized crest elevation at peak modulation increases rapidly with initial wave steepness and approached a maximum value almost equal to 3.5 which corresponds to initial wave steepness around k ca c =0.15. The results reveal that the large transient wave such as freak wave could be generated during the propagation of nonlinear wave trains in deep water through sideband instability. © 2010 Publishing House for Journal of Hydrodynamics.

Shugan I.,International Wave Dynamic Research Center | Saprykina Y.,Russian Academy of Sciences | Kuznetsov S.,Russian Academy of Sciences | Yang R.-Y.,Tainan Hydraulics Laboratory
Proceedings of the Coastal Engineering Conference | Year: 2014

Physical and numerical modeling of initially monochromatic wave propagation on stepwise opposite current in conditions of deep water was carrying out. The physical experiments demonstrated two steps of downshifting of spectral maximum in the regions of increasing of opposite current. Freak waves arise at the moments of downshifting, when several peaks of spectrum exist, due to superposition of waves, provided by each of spectral peaks. To explain the phenomena of downshifting the dynamical evolution set of equations are constructed. Their solutions perfectly described the main qualitative features of wave transformation during the physical experiments.

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