• Journal of Korean Society of Coastal and Ocean Engineers
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• v.8 no.3
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• pp.246-255
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• 1996

A mild slope equation of parabolic type is derived with the revision of the 2nd order differential term and a new approach for the application to large area is presented. The replacement with long waves can overcome the numerical difficulty due to small waves over the system of large grid sizes. No matter how long the replaced wave length is, the refraction and shoaling are maintained by toeing its own wave speed and group velocity, respectively. However, the diffraction effect is modified by means of Eikonal equation. The developed numerical model was applied to the shoal of Ito and Tanimoto (1972) to yield the satisfactory results.

• Journal of Ocean Engineering and Technology
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• v.24 no.1
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• pp.39-46
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• 2010

The calmness inside a harbor plays an important role in the appropriate disposition of harbor structures. However, it is not easy to acquire accurate computational results because these are affected by many factors concerned with wave transformation. Recently, numerical model tests, which are quicker and more economical than hydraulic model experiments, were carried out for the purpose of analyzing wave height distributions in harbors. This paper presents a numerical model that is able to calculate wave heights inside a harbor. It is based on a time-dependent mild slope involving wave refraction, diffraction, shoaling effect, and reflection. In particular, arbitrary reflectivity is used at the boundary in order to simulate the real harbor reflection condition. The proposed numerical model is applied to Samcheon new-harbor in order to investigate harbor calmness.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.51 no.5
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• pp.579-589
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• 2018

Data from the two bottom moorings of ADCP (acoustic doppler current profiler), coastal weather station and CTC (conductivity temperature depth) observations for 2001 were analyzed to describe the physical processes associated with upwelling off the southeast coast of Korea. Winds were favorable for upwelling during summer, but were not correlated with currents. Shoaling of isotherms toward the coast due to the baroclinic tilting of the strong East Korean Warm Current (EKWC) provided a favorable background for immediate upwelling-response of surface temperature to southerly winds. This baroclinic effect was supported by a significant inverse coherence between the upper-layer current and bottom temperature near the coast. This upwelling is similar to the Guinea Current upwelling, which is driven by remote forcing (Houghton, 1989). Persistent southward flow was observed below approximately $10^{\circ}C$ isotherm throughout the observation period.

• Journal of Korean Port Research
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• v.12 no.2
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• pp.281-290
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• 1998

The propagation of water waves over irregular bottom bathymetry and around islands involves many process-shoaling, refraction, energy dissipation and diffraction. Numerical model in this study is developed with the mild slope equation to investigate wave transformation in water of varying depth and combined waves and a current. The method used is splitting method and minimax approximation. The numerical method used in this study is Crank-Nicolson scheme in the FDM. This model is applied to Vincent shoal and compared with laboratory experimental data. The results agreed well with laboratory data. Current effect is considered in this study. This model can be used for the estimation of rip current in the slowly varying topography.

• Journal of Ocean Engineering and Technology
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• v.35 no.2
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• pp.113-120
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• 2021

In order to perform a precise wave tank experiment, it is necessary to maintain the incident wave generated by the wavemaker in a steady state and to effectively remove the reflected waves. In this paper, a combined sloping-wall-type punching plate wave absorber was proposed to attenuate reflected waves effectively in a two-dimensional mini wave tank. Using the four-point reflection separation method, the reflected waves were measured to determine the reflection coefficients. Experiments were conducted under various punching plate porosities, sloping plate angles, and incident wave conditions to evaluate the performance of the combined punching plate wave absorber. The most effective wave absorbing performance was achieved when the porosity was 10% and the inclination angle of the punching plate was 18.6° under the present condition. It was also found that the installation of the sloping plate could improve the wave attenuation performance by generating the shoaling effect of the incident wave.

• Journal of Ocean Engineering and Technology
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• v.25 no.2
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• pp.29-35
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• 2011

In order to effectively control waves in a coastal zone, Multi-Cylinder Piles have been suggested as economic structures. A numerical analysis was conducted using the Delft-3D: WAVE module based on SWAN, which considered wave shoaling and refraction. Moreover, irregular waves were used to investigate the hydrodynamic characteristics of the wave interaction with the structure. In this paper, a numerical analysis was carried out to research the effect of wave control through a wave height analysis concerning an existing, concrete wave breaker and multi-cylinder piles placed at the same location. As a result, the effect of the wave control is shown using the wave breaker, multi-cylinder piles, and existing data.

• Water for future
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• v.26 no.2
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• pp.39-48
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• 1993

Since major reason of disaster in coastal area is wave action, prediction of wave deformation is one of the most important problems to ocean engineers. Wave deformations are due to physical factors such as shoaling effect, reflection, diffraction, refraction, scattering and radiation etc. Recently, numerical models are widely utilized to calculate wave deformation. In this study, the mild slope equation was used in calculatin gwave deformation which considers diffraction and refraction. In order to slove the governing equation, finite element method is introduced. Even though this method has some difficulties, it is proved to predict the wave deformation accurately even in complicated boundary conditions. To verify the validity of the numerical calculation, experiments were carried out in a model harbour of rectangular shape which has mild slope bottom. The results by F.E.M. are compared with those of both Lee's method and the experiment. The results of these three methods show reasonable agreement.

• Journal of the korean society of oceanography
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• v.38 no.3
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• pp.143-155
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• 2003

Current and sea level were observed in spring 1999 by a bottom mounted ADCP and tide gauge in the central part of the South Sea of Korea. With respect to the front, the distribution of isotherms is prograde in the offshore region whereas that of isohalines is retrograde, especially in the coastal area. The combined effect results in shoaling of isopycnals at the front. This distribution corresponds to a westward coastal flow on the northern side of the front and the eastward Tsushima Warm Current (TWC) to the south, determined by vessel-mounted ADCP observations. The low-frequency current shows either alternating clockwise-counterclockwise rotation or else persistent eastward motion depending on the frontal motion. Fluctuations of wind, sea level and current are coherent at period of 3-4 days and show some characteristics of Ekman-like dynamics.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.1
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• pp.12-23
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• 1995

Currents driven by irregular waves are modelled using numerical model with various empirical relations improved. Kitaigorodskii's equilibrium equation is refined to account for shoaling effect and used for checking the breaking condition. In order to compute the bottom friction realistically. equivalent roughness blights are estimated considering the ripple shape and bed load transport which may be significant the surf zone. Two sets of equations are employed to evaluate the ripple shape: one is suggested by Nielsen and the other by Madsen and Rogengaus. Both equations give similar shape of ripples. but Madsen et al. give lower value of ripple factor than Swart suggesting that the equivalent roughness becomes relatively small. Optimization technique is used to determine the proper values for the empirical parameters of $\kappa$-ι equations, and the longshore current velocity is computed using the values of empirical parameters determined by the optimization technique.

• Journal of Korean Port Research
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• v.12 no.1
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• pp.75-86
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• 1998

To design a coastal structure in the nearshore region, engineers must have means to estimate wave climate. Waves, approaching the surf zone from offshore, experience changes caused by combined effects of bathymetric variations, interference of man-made structure, and nonlinear interactions among wave trains. This paper has attempted to find out the effects of two of the more subtle phenomena involving nonlinear shallow water waves, amplitude dispersion and secondary wave generation. Boussinesq-type equations can be used to model the nonlinear transformation of surface waves in shallow water due to effect of shoaling, refraction, diffraction, and reflection. In this paper, generalized Boussinesq equations under the complex bottom condition is derived using the depth averaged velocity with the series expansion of the velocity potential as a product of powers of the depth of flow. A time stepping finite difference method is used to solve the derived equation. Numerical results are compared to hydraulic model results. The result with the non-linear dispersive wave equation can describe an interesting transformation a sinusoidal wave to one with a cnoidal aspect of a rapid degradation into modulated high frequency waves and transient secondary waves in an intermediate region. The amplitude dispersion of the primary wave crest results in a convex wave front after passing through the shoal and the secondary waves generated by the shoal diffracted in a radial manner into surrounding waters.