• Journal of Korean Port Research
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• v.13 no.1
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• pp.147-154
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• 1999

A Numerical model is developed in order to predict cross-shore beach profile change. In this model it is assumed that sediment transport is generated by waves(bed load transport suspended load transport) and undertow which is defined as offshore directional steady flow in the surf zone. In addition wave tank experiments which reproduce storm-surge were performed. By comparing resulting profile of calculation with experiments, the applicability of this method is verified.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.3
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• pp.193-206
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• 1993

An analytical model of undertow is presented in the surf zone. Each term of the derived governing equation is evaluated by the ordering methods. Then the turbulent normal stresses and the streaming velocity terms are neglected. The driving force of undertow is derived from the wave profile which is approximated by the 4th order Chebyshev polynomials. The three types of vertical distribution of eddy viscosity are assumed and the coefficient of eddy viscosity is decided from the new boundary condition. So the input parameters for the calculation of undertow become very simple. The theoretical solutions of the present model are compared with the various experimental results. This model shows a good agreement with the experimental results in the case of mild slope and linear type eddy viscosity.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.2
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• pp.182-191
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• 2011

In the present study, the dynamically coupled POM-WAM of Chun et al.(2009) was applied to the numerical simulation of undertow, one of the nearshore currents. To improve the accuracy of the numerical model results in surf zone, the transport equation of the surface roller was solved, and its effects were incorporated into the present numerical model. The numerical model has been applied to two hydraulic experiments of Okayasu and Katayama(1992) and Cox and Kobayashi(1997). The numerical results were compared with the hydraulic experimental results to give a good concurrence. It is concluded that the present numerical model can be applied to the shallow water region including surf zone.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.5 no.4
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• pp.357-368
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• 1993

With the assumption of the diffusion dominated flow, a numerical model has been developed for undertow and turbulence structure under the breaking wave by using the $textsc{k}$-$\varepsilon$ turbulence model. Undertow is a strong mean current which moves seqwards below the level of wave trough in the surf zone. The turbulence, generated by wave breaking in the roller, spreads and dissipates downwards. The governing equations are composed of the equation of motion with the period-averaged shear stress due to waves; $textsc{k}$- and $\varepsilon$-equations with the turbulence energy Production due to wave breaking. They are discretised by the three-level fully implicit scheme, which can be solved by using Thomas algorithm. The model gives good agreements with measurements except for the station that is closest to the breaking point.

• Journal of Ocean Engineering and Technology
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• v.30 no.4
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• pp.320-326
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• 2016

Rip current forecasts, based on intensity, are marked in four levels—notice, watch, warning, and danger. However, numerical results are represented by current vectors, whose magnitudes are then converted into predictive levels. In the present study, the rose diagram is adapted as a determinative forecasting index and examined for the case of an ideal rip channel consisting of surface, bottom, and averaged currents. Further, it is employed in the sensitivity analysis of wave-induced currents generated by wave conditions at the Haeundae Beach. The simulation of surface onshore and bottom undertow currents is accomplished by including a mass flux term in the wave-averaged continuity equation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.2
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• pp.333-342
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• 2017

In order to understand the mechanism of the cross-shore evolution of storm (barred) and normal (nonbarred) profiles of a sandy beach, the vertically two-dimensional laboratory experiment was performed with a movable bed. The beach profiles and free surface motion were measured under monochromatic wave conditions evolving the storm and normal beach profiles. The observation was conducted in the surf zone during the alternation of the two wave conditions to reach its quasi-equilibrium state. The sandbar-crest and trough and the steep berm were evolved due to the plunging breakers in the storm case, and the bar-trough was decayed due to the spilling breakers in the normal case. From the measurements, it was found that the storm wave case was in an erosion state and the normal wave case was in an accretion state. The strong undertow, which is a dominant factor of the offshore migration mechanism, was developed in the storm wave case, and the weak undertow was developed in the normal wave case. The skewness and the asymmetry of the nonlinear wave motion, which is a dominant factor of the onshore migration mechanism, was measured similarly in both cases.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1993.07a
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• pp.152-155
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• 1993

쇄파대 내외에서 흐름양의 연직구조는 소유사 및 부유사의 이동과 지형변동 등의 표사이동문제에 있어서 중요하다 특히 지면 근방에서 유속분포예측은 노면마찰력의 평가와 관련하여 매우 중요하다. 일반적으로 해안에서 표사이동과 지형변화의 계산에 있어서는 수심평균된 흐름속도를 이용하는 것으로 충분하지만, 사주 또는 사연의 형성문제에 있어서는 3차원적인 유동구조의 파악이 필요하다. (중략)

• Journal of Ocean Engineering and Technology
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• v.35 no.1
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• pp.75-81
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• 2021

Artificial Coral Reefs (ACRs) have been introduced to help solve coastal erosion problems, but their feasibility has not been assessed with field data. This study conducted a feasibility analysis of ACRs on their erosion mitigation effects by performing a case study of Cheonjin-Bongpo beach, South Korea. A numerical-physical combined analysis was carried out using a SWAN model simulation and physical model test with a scale of 1/25 based on field observations of Cheonjin-Bongpo beach. Both Dean's parameter and the surf-scaling parameter were applied to comparative analysis between the absence and presence conditions of the ACR. The results for this combined method indicate that ACR attenuates the wave height significantly (59~71%). Furthermore, ACR helps decrease the mass flux (~50%), undertow (~80%), and maximum wave set up (~61%). The decreases in Dean's parameter (~66%) and the surf-scaling parameter suggest that the wave properties changed from the dissipative type to the reflective type even under high wave conditions. Consequently, an ACR can enhance shoreline stability.

• Ocean Systems Engineering
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• v.6 no.1
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• pp.23-60
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• 2016

The major objective of this study was to develop further understanding of 3D nearshore hydrodynamics under a variety of wave and tidal forcing conditions. The main tool used was a comprehensive 3D numerical model - combining the flow module of Delft3D with the WAVE solver of XBeach - of nearshore hydro- and morphodynamics that can simulate flow, sediment transport, and morphological evolution. Surf-swash zone hydrodynamics were modeled using the 3D Navier-Stokes equations, combined with various turbulence models (${\kappa}-{\varepsilon}$, ${\kappa}-L$, ATM and H-LES). Sediment transport and resulting foreshore profile changes were approximated using different sediment transport relations that consider both bed- and suspended-load transport of non-cohesive sediments. The numerical set-up was tested against field data, with good agreement found. Different numerical experiments under a range of bed characteristics and incident wave and tidal conditions were run to test the model's capability to reproduce 3D flow, wave propagation, sediment transport and morphodynamics in the nearshore at the field scale. The results were interpreted according to existing understanding of surf and swash zone processes. Our numerical experiments confirm that the angle between the crest line of the approaching wave and the shoreline defines the direction and strength of the longshore current, while the longshore current velocity varies across the nearshore zone. The model simulates the undertow, hydraulic cell and rip-current patterns generated by radiation stresses and longshore variability in wave heights. Numerical results show that a non-uniform seabed is crucial for generation of rip currents in the nearshore (when bed slope is uniform, rips are not generated). Increasing the wave height increases the peaks of eddy viscosity and TKE (turbulent kinetic energy), while increasing the tidal amplitude reduces these peaks. Wave and tide interaction has most striking effects on the foreshore profile with the formation of the intertidal bar. High values of eddy viscosity, TKE and wave set-up are spread offshore for coarser grain sizes. Beach profile steepness modifies the nearshore circulation pattern, significantly enhancing the vertical component of the flow. The local recirculation within the longshore current in the inshore region causes a transient offshore shift and strengthening of the longshore current. Overall, the analysis shows that, with reasonable hypotheses, it is possible to simulate the nearshore hydrodynamics subjected to oceanic forcing, consistent with existing understanding of this area. Part II of this work presents 3D nearshore morphodynamics induced by the tides and waves.

• Journal of Environmental Science International
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• v.16 no.4
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• pp.523-532
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• 2007

This study utilized the 1/25,000 topographic map of the upper area from the Geum-ho watermark located at the middle of Geum-ho river from the National Geographic Information Institute. For the analysis, first, the influence of the size of critical area to the hydro topographic factors was examined changing grid size to $10m{\times}10m,\;30m{\times}30m\;and\;50m{\times}50m$, and the critical area for the formation of a river to $0.01km^2{\sim}0.50km^2$. It is known from the examination result of watershed morphology according to the grid size that the smaller grid size, the better resolution and accuracy. And it is found, from the analysis result of the degree of the river according to the minimum critical area for each grid size, that the grid size does not affect on the degree of the river, and the number of rivers with 2nd and higher degree does not show remarkable difference while there is big difference in the number of 1st degree rivers. From the results above, it is thought that the critical area of $0.15km^2{\sim}0.20km^2$ is appropriate for formation of a river being irrelevant to the grid size in extraction of hydro topographic parameters that are used in the runoff analysis model using topographic maps. Therefore, the GIUH model applied analysis results by use of the river level difference law proposed in this study for the explanation on the outflow response-changing characters according to the decision of a critical value of a minimum level difference river, showed that, since an ogival occurrence time and an ogival flow volume are very significant in a flood occurrence in case of not undertow facilities, the researcher could obtain a good result for the forecast of river outflow when considering a convenient application of the model and an easy acquisition of data, so it's judged that this model is proper as an algorism for the decision of a critical value of a river basin.