• Journal of Ocean Engineering and Technology
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• v.16 no.3
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• pp.1-7
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• 2002

In this paper, a numerical model to analyze the performance of a vertical slit-type wave absorber is developed under the assumption of inviscid water waves. The formulation combines the linear potential theory with a semi-empirical description of the eddy-shedding at a slit-type wave absorber. We investigated the reflection coefficients over a wide frequency range for a vertical slit-type wave absorber both with and without a solid rear wall. Model test was conducted at KRISO' s two dimensional wave tank to validate the theoretical results. It is found that the agreement between theoretical results and experimental data is surprisingly good. We found that the wave absorbing system using a vertical slit plate has sufficient potentials for breakwaters for ocean development.

• Water for future
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• v.20 no.1
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• pp.49-54
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• 1987

A numerical analysis of the characteristics of wave reflection over rippled beds (sand bars) was carried out By Boundary Element Method(B.E.M) using linear elements. It is assumed that the incident wave is normal and oblique to the rippled beds and the wave may be and the escribed by two-dimensional linear theory. The accuracy of the computational scheme is investigated by comparing the laboratory data, the analytic measured results of the other researchers. The B.E.M results for the normal incident wave is held for the mechanism of the resonant Bragg reflection at the point where the wave length of the bottom undulation is one half the wave length of the surface wave.

• Water for future
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• v.20 no.4
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• pp.249-256
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• 1987

Wave forces on fixed two-dimensional objects submerged in water of finite depth were analysed by Boundary Element Method using linear elements.It is assumed that the wave forces may be described by linear theory and that incident wave direction is normal to the objects of infinite length. In this paper, wave forces on a bottom-seated half cross section pipeline, a circular pipeline, a submerged pipeline and submerged breakwater of arbitrary shape were studied. The accuracy of the computational scheme is investigated by comparing the numerical results with the existing laboratory results and analytical solutions of other researchers.

• Journal of Ocean Engineering and Technology
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• v.23 no.6
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• pp.12-16
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• 2009

In this study, the wave profiles and kinematics of highly nonlinear waves at various water depths were calculated using a 2D fully nonlinear Numerical Wave Tank (NWT). The NWT was developed based on the Boundary Element Method (BEM) with the potential theory and the mixed Eulerian-Lagrangian (MEL) time marching scheme by 4th-order Runge-Kutta time integration. The spatial variation of intermediate-depth waves along the direction of wave propagation was caused by the unintended generation of 2nd-order free waves, which were originally investigated both theoretically and experimentally by Goda (1998). These free waves were induced by the mismatch between the linear motion of wave maker and nonlinear displacement of water particles adjacent to the maker. When the 2nd-order wave maker motion was applied, the spatial modulation of the waves caused by the free waves was not observed. The respective magnitudes of the nonlinear wave components for various water depths were compared. It was found that the high-order wave components greatly increase as the water depth decreases. The wave kinematics at various locations were calculated and compared with the linear and the Stokes 2nd-order theories.

• Journal of Advanced Research in Ocean Engineering
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• v.1 no.3
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• pp.157-167
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• 2015

In order to provide simple and accurate wave theory in design of offshore structure, an analytical approximation is introduced in this paper. The solution is limited to flat bottom having a constant water depth. Water is considered as inviscid, incompressible and irrotational. The solution satisfies the continuity equation, bottom boundary condition and non-linear kinematic free surface boundary condition exactly. Error for dynamic condition is quite small. The solution is suitable in description of breaking waves. The solution is presented with closed form and dispersion relation is also presented with closed form. In the last century, there have been two main approaches to the nonlinear problems. One of these is perturbation method. Stokes wave and Cnoidal wave are based on the method. The other is numerical method. Dean's stream function theory is based on the method. In this paper, power series method was considered. The power series method can be applied to certain nonlinear differential equations (initial value problems). The series coefficients are specified by a nonlinear recurrence inherited from the differential equation. Because the non-linear wave problem is a boundary value problem, the power series method cannot be applied to the problem in general. But finite number of coefficients is necessary to describe the wave profile, truncated power series is enough. Therefore the power series method can be applied to the problem. In this case, the series coefficients are specified by a set of equations instead of recurrence. By using the set of equations, the nonlinear wave problem has been solved in this paper.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.5 no.4
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• pp.263-270
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• 1993

A study on the variation of radiation stress and mean water level is carried out for the shoaling and breaking waves on a plane beach. In general, the radiation stresses computed based on the linear wave theory are overestimated. which results in the discrepancy between the computed results and laboratory data of mean water level in the surf zone. In this paper, by modifying the Svendsen's approach (1984), radiation stress is expressed in terms of water depth. The computed results are compared with the results calculated by a linear wave theory and Sawaragi's approach (1984) based on the spectrum of breaking wave components, and published laboratory data. The computed results of the modifed Svendsen's approach are favourably compared with the laboratory data.

• Water for future
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• v.19 no.3
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• pp.259-266
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• 1986

A numerical study of the process of wave deformation, such as reflection and transmission coefficients and wave forms with bottom change was carried out by Boundary Element Method using linear elements. It is assumed that the incident wave is normal and oblique to the bottom and the wave may be described by linear theory The accuracy of the computational scheme is investigated by comparing the results of other researchers in the following several cases. (1) Simple and sloping stepped bottom geometry (2) Submerged breakater type bottom geometry (3) Trench type bottom geometry

• Journal of Korean Port Research
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• v.7 no.1
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• pp.79-88
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• 1993

This study deals with the case of a fixed floating structure(FFS) at the mouth of a rectangular harbor under the action of waves represented by the linear wave theory. Modified forms of the mild-slope equation is applied to the propagation of regular wave over constant water depth. The model is extended to include bottom friction and boundary absorption. A hybrid element approximation is used for calculation of linear wave oscillation in and near coastal harbor. Modification of the model was necessary for the FFS. For the conditions tested, the results of laboratory experiments by Ippen and Goda(1963), and Lee (1969) are compared with the calculated one from this model. The cases of flat cylinderical structures, both fixed and floating, were taken to be in an intermediate water depth.

• Wind and Structures
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• v.29 no.1
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• pp.33-41
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• 2019

The interaction of head waves with an infinite row of identical, equally spaced, rectangular breakwaters is investigated in the presence of uneven bottom topography. Using linear water wave theory and matched eigenfunction expansion method, the boundary value problem is transformed into a system of linear algebraic equations which are numerically solved to know the velocity potentials completely. Utilizing this method, reflected and transmitted wave energy are computed for different physical parameters along with the wave field in the vicinity of breakwaters. It is observed that the wave field becomes more complicated when the incoming wavelength becomes smaller than the channel width. A critical ratio of the gap width to the channel width, corresponding to the inflection point of the transmitted energy variation, is identified for which 1/3 of the total energy is transmitted. Similarly, depending on the incident wavelength, there is a critical breakwater width for which a minimum energy is transmitted. Further, the accuracy of the computed results is verified by using the derived energy relation.

• Journal of Ocean Engineering and Technology
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• v.14 no.1
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• pp.1-5
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• 2000

A numerical analysis for wave motion in the shallow water is presented. The method is based on potential theory. The fully nonlinear free surface boundary condition is assumed in an inner domain and this solution is matched along an assumed common boundary to a linear solution in outer domain. In two-dimensional problem Cauchy's integral theorem is applied to calculate the complex potential and its time derivative along boundary.