LONGITUDINAL CHANGE OF GRAVEL BEACH UNDER STORM WAVE CONDITION AND BEACH PROFILE PREVENTING WAVE OVERTOPPING

In treating coastal proceses, sediment transport is usually divided into along-shore and on-offshore components. It is believed that the on-offshore component has a prominant connection with short-term profile changes, observed during storm wave climates. Obviously its shift of sand plays a very vital role in shoreline migration. In other words, the beach profile has great bearing on coastal phenomena related to on-offshore sediment transport. As we know, there have been many studies on this kind of sediment transport rate, and considerable amount of knowledge on this problem has been accumulated so far. Yet it seems that we are still far from a reliable formulus to estimate the beach profile changes. The reason why is due to the complexity of mechanics of sediment transport. Therefore, the aim of this study is to examine experimentally the mechanism between onoffshore sediment transport and the deformation processes of twodimensional beach profile. Then , a predictive model of the temporal and spatial distribution of net on-offshore sediment transport based on two-dimensional beach profiles and an equation of continuity of sediment transport is proposed. Various parameters of net on-offshore sediment transport in this model are discussed also.

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APPLICATION OF XBEACH TO MODEL STORM RESPONSE ON A MACROTIDAL GRAVEL BARRIER

Coastal Engineering Proceedings ◽

10.9753/icce.v32.sediment.39 ◽

2011 ◽

Vol 1 (32) ◽

pp. 39 ◽

Cited By ~ 4

Author(s):

Amaia Ruiz de Alegria-Arzaburu ◽

Jon J Williams ◽

Gerhard Masselink

Keyword(s):

Sediment Transport ◽

Hydraulic Conductivity ◽

Numerical Model ◽

Morphological Changes ◽

Coastal Engineering ◽

Beach Profile ◽

Morphological Response ◽

Total Drag ◽

Storm Response ◽

Gravel Beach

The process-based XBeach numerical model has been used to simulate storm-induced morphological response on a macrotidal gravel barrier located in southwest UK. Using well-established parameterisation to define all relevant hydrodynamic, groundwater and sediment processes, the model was applied in 1D mode to simulate observed storm-induced beach profile responses. Investigations showed that the morphological response of the beach was best modelled using a total drag coefficient, CD, of 0.007, and a hydraulic conductivity, K, of 0.05ms-1. Results obtained from simulations with and without beach groundwater highlighted the need to account for groundwater effects when modelling morphological changes on gravel beaches. The model has been found unable of reproducing the formation of a berm, thus, beach recovery conditions cannot be modelled. This is mainly attributed to the fact that XBeach models long waves rather than individual waves, and thus it cannot simulate individual swash events that contribute to onshore sediment transport and berm accretion. However, the model is shown to provide good estimates of post-storm gravel beach/barrier profiles, and to define the threshold for overwash occurrence. Both attributes have utility in a range of practical coastal engineering and management applications.

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A Simple Nozzle-Diffuser Duct Used as a Kuroshio Energy Harvester

Processes ◽

10.3390/pr9091552 ◽

2021 ◽

Vol 9 (9) ◽

pp. 1552

Author(s):

Po-Hung Yeh ◽

Shang-Yu Tsai ◽

Wei-Ren Chen ◽

Shing-Nan Wu ◽

Meng-Chang Hsieh ◽

...

Keyword(s):

Energy Demand ◽

Energy Harvester ◽

Normal Wave ◽

Sea Surface ◽

Ocean Current ◽

Ansys Fluent ◽

Wave Condition ◽

Storm Wave ◽

Wave Conditions ◽

The Kuroshio

In response to the increasing energy demand in Taiwan and the global trend of renewable energy development, Kuroshio energy is a potential energy source. How to extract this invaluable natural resource has then become an intriguing and important question in engineering practices. This study reported the results of a feasibility study for a nozzle-diffuser duct (NDD) as the Kuroshio currents energy harvester. The computational fluid dynamics (CFD) software ANSYS Fluent was employed to calculate the drag and added mass coefficients of the duct anchored to the seabed. Those coefficients were further imported into Orcaflex to simulate the motion of the duct under normal and storm wave conditions. Results showed that the duct was stable 25 m below the sea surface under normal wave conditions. When the wave condition changed to storm waves, the duct needed to dive into at least 90 m below the sea surface to regain its stability and obtain high power take-off (PTO). An optimal design nozzle-diffuser-duct was reported, and a PTO peak of 15 kW was expectable in the Kuroshio currents. Once a suitable offshore platform can be developed with sixty-six NDDs, a Megawatt Kuroshio ocean current power generation system is feasible in the near future.

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Beach Profile Evolution towards Equilibrium from Varying Initial Morphologies

Journal of Marine Science and Engineering ◽

10.3390/jmse7110406 ◽

2019 ◽

Vol 7 (11) ◽

pp. 406 ◽

Cited By ~ 3

Author(s):

Sonja Eichentopf ◽

Joep van der Zanden ◽

Iván Cáceres ◽

José M. Alsina

Keyword(s):

Sediment Transport ◽

Large Scale ◽

Intermediate Energy ◽

Swash Zone ◽

Energy Profile ◽

Beach Profile ◽

Wave Condition ◽

Wave Energy Dissipation ◽

Transport Patterns ◽

In The Beginning

The evolution of different initial beach profiles towards the same final beach configuration is investigated based on large-scale experimental data. The same wave condition was performed three times, each time starting from a different initial profile morphology. The three different initial profiles are an intermediate energy profile with an offshore bar and a small swash berm, a plane profile and a low energy profile with a large berm. The three cases evolve towards the same final (equilibrium) profile determined by the same wave condition. This implies that the same wave condition generates different sediment transport patterns. Largest beach changes and differences in hydrodynamics occur in the beginning of the experimental cases, highlighting the coupling between morphology and hydrodynamics for beach evolution towards the same profile. The coupling between morphology and hydrodynamics that leads to the same final beach profile is associated with differences in sediment transport in the surf and swash zone, and is explained by the presence of bar and berm features. A large breaker bar and concave profile promote wave energy dissipation and reduce the magnitudes of the mean near-bed flow velocity close to the shoreline limiting shoreline erosion. In contrast, a beach profile with reflective features, such as a large berm and a small or no bar, increases negative velocity magnitudes at the berm toe promoting shoreline retreat. The findings are summarised in a conceptual model that describes how the beach changes towards equilibrium from two different initial morphologies.

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