Physical and Numerical Modeling of Irregular Wave Transformation over a Fringing Reef

2016 ◽  
Vol 75 (sp1) ◽  
pp. 922-926
Author(s):  
Sungwon Shin ◽  
Young-Taek Kim ◽  
Jong-In Lee
Keyword(s):  
Numerical Modeling ◽  
Wave Transformation ◽  
Fringing Reef ◽  
Irregular Wave

scholarly journals Numerical Simulation of Wave Propagation, Breaking, and Setup on Steep Fringing Reefs

Water ◽  
2018 ◽  
Vol 10 (9) ◽  
pp. 1147 ◽  
Author(s):  
Shanju Zhang ◽  
Liangsheng Zhu ◽  
Jianhua Li
Keyword(s):  
Finite Difference ◽  
Finite Volume ◽  
Boussinesq Equations ◽  
Transformation Process ◽  
Wave Transformation ◽  
Computational Accuracy ◽  
Irregular Wave ◽  
Eddy Viscosity Model ◽  
Fringing Reefs ◽  
Volume Method

The prediction of wave transformation and associated hydrodynamics is essential in the design and construction of reef top structures on fringing reefs. To simulate the transformation process with better accuracy and time efficiency, a shock-capturing numerical model based on the extended Boussinesq equations suitable for rapidly varying topography with respect to wave transformation, breaking and runup, is established. A hybrid finite volume–finite difference scheme is used to discretize conservation form of the extended Boussinesq equations. The finite-volume method with a HLL Riemann solver is applied to the flux terms, while finite-difference discretization is applied to the remaining terms. The fourth-order MUSCL (Monotone Upstream-centered Schemes for Conservation Laws) scheme is employed to create interface variables, with in which the van-Leer limiter is adopted to improve computational accuracy on complex topography. Taking advantage of van-Leer limiter, a nested model is used to take account of both computational run time and accuracy. A modified eddy viscosity model is applied to better accommodate wave breaking on steep reef slopes. The established model is validated with laboratory measurements of regular and irregular wave transformation and breaking on steep fringing reefs. Results show the model can provide satisfactory predictions of wave height, mean water level and the generation of higher harmonics.

Irregular Wave Transformation Affected by Opposing Currents

1987 ◽  
Author(s):  
Shigeki Sakai ◽  
Kouetsu Hiyamizu ◽  
Hiroshi Saeki
Keyword(s):  
Wave Transformation ◽  
Irregular Wave

scholarly journals UNDULAR BORE DEVELOPMENT OVER A LABORATORY FRINGING REEF

2018 ◽  
pp. 53 ◽  
Author(s):  
Marion Tissier ◽  
Jochem Dekkers ◽  
Ad Reniers ◽  
Stuart Pearson ◽  
Ap Van Dongeren
Keyword(s):  
Coral Reefs ◽  
Wave Field ◽  
Reef Flat ◽  
Wave Transformation ◽  
Undular Bore ◽  
Fringing Reef ◽  
Long Wave ◽  
Reef Type ◽  
Run Up ◽  
Infragravity Wave

Several studies have reported the development of undular bores over fringing coral reefs (e.g, Gallagher, 1976; Nwogu and Demirbilek, 2010) but the importance of this phenomenon for reef hydrodynamics has never been studied. Yet, the transformation of a long wave (e.g., swell or infragravity wave) into an undular bore leads to significant modifications of the wave field. The formation of undulations is for example associated to a significant increase of the leading bore height. Moreover, if the undulations have enough time to develop (i.e. if the reef flat is wide enough), the initial long wave will ultimately split into a series of solitons (e.g., Grue et al., 2008). All this is likely to affect wave run-up. As reeffronted coastlines are particularly vulnerable to flooding, a good understanding of long wave transformation over the reef flat, including their possible transformation into undular bores, is crucial. In this study, we investigate undular bore development over reef-type profiles based on a series of laboratory experiments. More specifically, we aim to characterize the conditions under which undular bores develop, and analyse how their development affect the hydrodynamics at the toe of the reef-lined beach and the resulting wave run-up.

Characteristics of Transforming Waves Breaking Over a Fringing Reef

2019 ◽  
Author(s):  
Fuxian Gong ◽  
Manhar R. Dhanak
Keyword(s):  
Energy Flux ◽  
Wave Breaking ◽  
Reef Flat ◽  
Stokes Equations ◽  
Second Harmonic ◽  
Breaking Waves ◽  
Wave Transformation ◽  
Fundamental Wave ◽  
Fringing Reef ◽  
Wave Shoaling

Abstract Direct numerical simulation (DNS), based on solution of the Navier Stokes equations, is used to study the characteristics of the transformation of monochromatic waves over a simplified fringing reef, including wave shoaling, and wave breaking that occurs under certain circumstances. The reef geometry involves a sloped plane beach extended with a simple submerged horizontal reef flat. The characteristics are studied for several case studies involving a selection of submergence depths on the reef flat and for a range of incident wave conditions, corresponding to nonbreaking, a spilling breaker and a plunging breaker, are considered. The results are compared with those of laboratory experiments (Kouvaras and Dhanak, 2018). Consistent with other studies, generation of harmonics of the fundamental wave frequency is found to accompany the wave transformation over the reef and the process of transfer of energy through wave breaking. The energy flux decreases dramatically in the onshore direction when the waves break. The more severe the wave breaking process, the greater the decrease in energy flux, particularly in the wave shoaling process. Most of the wave energy is carried by the first harmonic throughout its passage over the fringing reef. In nonbreaking waves, the energy gradually transfers from the first harmonic to the second harmonic due to bottom effects in terms of flat wave troughs and secondary waves. The further the distance away from the fore edge of the reef, the larger the percentage of the transmission, resulting in a single dominant harmonic frequency at the end of the wave surfing zone. For breaking waves, the energy carried by the first harmonic gradually decreases in the onshore direction. Energy transmission between harmonics is not as efficient as nonbreaking waves, while wave dissipation is significant in the wave breaking process.

Structural Analysis of a Subsurface Cage for Sea Cucumber, Stichopus japonicus, Grow-out Using Numerical Modeling Techniques

2012 ◽  
Vol 46 (5) ◽  
pp. 55-66 ◽  
Author(s):  
Moo-Hwan Oh ◽  
Taeho Kim ◽  
David W. Fredriksson ◽  
Judson DeCew
Keyword(s):  
Numerical Modeling ◽  
Sea Cucumber ◽  
Structural Integrity ◽  
Animal Movement ◽  
Structural Characteristics ◽  
Cage Structure ◽  
Stichopus Japonicus ◽  
Irregular Wave ◽  
Cage System ◽  
Modeling Techniques

AbstractThe structural characteristics of a subsurface cage system for sea cucumber, Stichopus japonicus, grow-out were analyzed by using numerical modeling techniques. The cage system was constructed of polypropylene pipe and netting and weighted to sit on the seafloor bottom. Inside the cage, concrete blocks were used for animal aestivation and weight and a thin-plated device was mounted for animal movement. Environmental loads on the structure, resulting from a prescribed irregular wave field with and without currents, were first determined with a Morison equation-type finite element model. The structural response of beam and truss cage components was then calculated with the software MSC.MARC/Mentat. In addition to the irregular wave and current input forcing parameters of the structure, response was also calculated for possible forces incurred during lifting operations. Reaction loads, bending moments, axial tensions, and von Mises stresses of the sea cucumber cage structure were calculated for evaluation. The results of the study indicate that the combination of numerical model analyses presented can be used to assess structural integrity of these subsurface cage systems. These techniques will become more important as the industry expands and economics of scale promotes the construction of larger sea cucumber containment structures.

scholarly journals HYDRODYNAMIC PERFORMANCE OF A FREE SURFACE SEMICIRCULAR PERFORATED BREAKWATER

2011 ◽  
Vol 1 (32) ◽  
pp. 20 ◽  
Author(s):  
Hee Min Teh ◽  
Vengatesan Venugopal ◽  
Tom Bruce
Keyword(s):  
Free Surface ◽  
Wave Attenuation ◽  
Hydrodynamic Performance ◽  
Wave Transformation ◽  
Hydrodynamic Characteristics ◽  
Wave Forces ◽  
Irregular Wave ◽  
Energy Dissipater ◽  
Horizontal Wave ◽  
Perforated Breakwater

The increasing importance of the sustainability challenge in coastal engineering has led to the development of free surface breakwaters of various configurations. In this study, the hydrodynamic characteristics of a perforated semicircular free surface breakwater (SCB) are investigated for irregular wave conditions. The hydrodynamic performance of the breakwater is evaluated in the form of transmission, reflection and energy dissipation coefficients, which are then presented as a function of the relative submergence depth (D/d) and the relative breakwater width (B/Lp), where D = the depth of immersion, d = the water depth, B = the breakwater width and Lp = the wavelength corresponding to the peak wave period. It is found that the wave attenuation ability of the SCB model improves with the increase of D/d and B/Lp. The SCB performs better as an energy dissipater than as a wave reflector. Based on the analysis of measured data, some empirical equations are proposed to predict the performance of the breakwater under varying submergence depths. The behaviour of wave transformation around and within the breakwater’s chamber is discussed. Also, the measured horizontal wave forces acting on the SCB are reported.

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