• Journal of Korean Society of Coastal and Ocean Engineers
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• v.14 no.3
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• pp.240-246
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• 2002

Hydraulic model experiments were conducted fur a series of regular and uni-directional irregular waves propagating over a submerged elliptic shoal. Two different sets of experiments have been studied； one considers regular wave transformation with no breaking, and the other considers uni-directional irregular wave with partial breaking on top of the shoal. The numerical experiments are also performed using a numerical model based on the parabolic approximation equation. The result of the numerical experiments are compared with that of hydraulic experiments.

• Ocean Systems Engineering
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• v.2 no.2
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• pp.147-158
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• 2012

A time-domain simulation of a land-based Oscillating Water Column (OWC) with various irregular waves as a form of PM spectrum is performed by using a two-dimensional fully nonlinear numerical wave tank (NWT) based on the potential theory, mixed Eulerian-Lagrangian (MEL) approach, and boundary element method. The nonlinear free-surface condition inside the OWC chamber was specially devised to describe both the pneumatic effect of the time-varying pressure and the viscous energy loss due to water column motions. The quadratic models for pneumatic pressure and viscous loss are applied to the air and free surface inside the chamber, and their numerical results are compared with those with equivalent linear ones. Various wave spectra are applied to the OWC system to predict the efficiency of wave-energy take-off for various wave conditions. The cases of regular and irregular waves are also compared.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.2
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• pp.158-168
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• 2001

A numerical model based on the wide-angle parabolic approximation equation is developed for the accurate simulation of the directional spreading and partial breaking of irregular waves. This model disintegrates the irregular waves into a series of monochromatic wave components, and the simultaneous calculations are made for each wave component. Then, the computed wave components are superposed to get the wave height of irregular waves. To consider the partial breaking of irregular waves in the computation the amount of energy dissipation due to breaking is estimated using the superposed wave height. The accuracy of the developed model is tested by comparing the numerical results with the experimental measurements reported earlier. In the case of non-breaking waves a considerable accuracy of the model is observed for both regular and irregular waves. On the contrary it is found that the accuracy is significantly degenerated for the case of breaking waves. Some analyses for the accuracy degeneration are presented.

• Journal of the Society of Naval Architects of Korea
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• v.60 no.4
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• pp.266-277
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• 2023

In this study, fundamental research is conducted for the generation technique and analysis of multi-directional irregular waves in the Deep Ocean Engineering Basin (DOEB). A three-dimensional boundary element method-based numerical tank is implemented to perform wave generation simulations, and directional spectrum estimation is carried out using the results of simulations. The wave generation technique of the Snake type wave maker, generating multi-directional irregular waves, is implemented using the Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform (IFFT) algorithms. The wave generation technique is validated by comparing the wave spectrum from simulations and experiments. A Maximum Likelihood Method (MLM) based estimation code is developed for estimating the directional wave spectra. The multi-directional irregular waves are tested in the DOEB and the numerical tank, and directional wave spectra obtained from two methodologies are estimated and compared. A correction procedure for the directional distribution of multi-directional waves is established, and the possibility of correcting the directional spreading function using the numerical tank is validated.

• Journal of Ocean Engineering and Technology
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• v.21 no.6
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• pp.34-41
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• 2007

The present study investigates numerically damping characteristics of irregular waves passing over a permeable seabeds. At first, the numerical model, which is able to consider the flow through a porous medium with inertial, laminar and turbulent resistance terms and determine the eddy viscosity with LES turbulent model, is validated by comparing with existing experimental data. And then, the numerical test on irregular wave damping over a permeable seabeds is performed in case that wave and flume conditions are changed. It is revealed from the numerical results that the more porosity and mean grain are increased, the more wave damping is increased. Also, the effect of wave period on damping of irregular waves over a permeable seabed is discussed.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.186-195
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• 2001

The purpose of this study is to develop the time-dependent, one-dimensional numerical model on the interaction between irregular waves and two-layer permeable coastal structures, by extending and modifying the numerical model PBREAK(Wurjanto and Kobayashi, 1992) which is applicable only to one-layer permeable coastal structures. The two-layer permeable coastal structure consists of two permeable underlayers with different permeable media resting on an impermeable slope and an armor layer covering the permeable underlayer. The numerical model of this study simulates the wave over rough permeable underlayer of arbitrary geometry as well as the waves inside two-permeable underlayers of arbitrary thickness for specified normally-incident irregular waves. The utility of the numerical model is founded from comparing with PBREAK and the four hydraulic model tests under irregular waves. The sensitivities of computed results according to typical parameters(porosity, stone diameter, horizontal width of the permeable underlayer) and major factors(friction factor of primary armor layer etc.) discussed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.6
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• pp.356-367
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• 2019

This study evaluates the variation characteristics of irregular wave fields for two-dimensional Low-Crested Structure (LCS) by olaFlow model based on the two-phases flow by numerical analysis. The numerical results of olaFlow model are verified by comparing irregular wave profile of target wave spectrum and measured one, and their spectra. In addition, spacial variation of irregular wave spectrum, wave transmission ratio, root-mean square wave height, time-averaged velocity and time-averaged turbulent kinetic energy by two-dimensional LCS are discussed numerically. The time-averaged velocity, one of the most important numerical results is formed counterclockwise circulating cell and clockwise nearshore current on the front of LCS, and strong uni-directional flow directing onshore side around still water level.

• Ocean Systems Engineering
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• v.12 no.1
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• pp.23-38
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• 2022

In this paper, a pitch-type wave energy converter (WEC-rotor) is investigated in irregular wave conditions for the real sea testing at the west coast of Jeju Island, South Korea. The present research builds on and extends our previous work on regular waves to irregular waves. The hydrodynamic characteristics of the WEC-rotor are assessed by establishing a quasi-two-dimensional numerical wave tank using computational fluid dynamics by solving the Reynolds-averaged Navier-Stokes equation. The numerical solution is validated with physical experiments, and the comparison shows good agreement. Furthermore, the hydrodynamic performance of the WEC-rotor is explored by investigating the effect of the power take-off (PTO) loading torque by one-way and two-way systems, the wave height, the wave period, operational and high sea wave conditions. Irrespective of the sea wave conditions, the absorbed power is quadratic in nature with the one-way and two-way PTO loading systems. The power absorption increases with the wave height, and the increment is rapid and mild in the two-way and one-way PTO loading torques, respectively. The pitch response amplitude operator increases as the wave period increases until the maximum value and then decreases. For a fixed PTO loading, the power and efficiency are higher in the two-way PTO loading system than in the one-way PTO loading system at different wave periods.

• Journal of Navigation and Port Research
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• v.29 no.3 s.99
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• pp.257-262
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• 2005

Environmental problems and safety problems in coastal area is one of the most important factors for designing coastal structures and maintaining facilities in coastal zone. And thus study on Wave transformation around coastal area is very important to develope a new port or on industrial area. Delft 3D-WAVE is applied to Ulsan new port area and the culculated results are analysed and compared with measured data Delft 3D-wave module is based on SWAN model which considers wave shoaling and refraction for irregular wave. This module also covers wind effect, bottom friction. white-capping and wave breaking effect. The results of this study show a good agreement with measured data and thus Delft 3D-WAVE module can be applied to simulate irregular wave transformation in coastal area.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.373-376
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• 2006

In general, a method for generating irregular wave by combination of component waves obtained from linear wave theory is widely used. In these method, however, mean water surface elevation is rising from time to time because of nonlinear effect of wave. In this study, for the rising problem of mean water surface elevation and stabilization of calculation from time to time, mass transport velocity for horizontal velocity at wave source position is considered. The rising problem of mean water surface elevation is checked by comparing calculated wave profile from numerical technique proposed in this study with target wave profile at wave source position in numerical wave tank by using CADMAS-SURF code. And, by generating irregular wave, the validity of wave overtopping rate estimated from this numerical analysis is discussed by comparing computed results with measured results in hydraulic model experiments for vertical seawall located on a sloping sea bottom. As a results, the computations are validated against the previously experimental results by hydraulic model test and numerical results of this study and a good agreement is observed. Therefore, numerical technique of this study is a powerful tool for estimating wave overtopping rate over the crest of coastal structure.