• Journal of Korean Society of Coastal and Ocean Engineers
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• v.17 no.2
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• pp.86-97
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• 2005

Accurate estimation of the wave-induced pore water pressure in the seabed is key factor in studying the stability of the seabed in the vicinity of coastal structure. Most of the existing numerical models for wave structure seabed interaction have been linked through applying hybrid numerical technique which is analysis method separating the wave field and seabed regime. Therefore, it is necessary to develope a numerical model f3r simulating accurately wave$\cdot$structure$\cdot$ seabed interaction under wave loadings by the single domain approach for wave field and seabed regime together. In this study, direct numerical simulation is newly proposed. In this model, modeled fluid drag has been used to detect the hydraulic properties according to the varied geometrical shape inside the porous media by considering the turbulence resistance as well as laminar resistance. Contrary to hybrid numerical technique, direct numerical simulation avoids the explicit formulation of the boundary conditions at the fluid/porous media interface. A good agreement has been obtained by the comparison between existed experimental results by hydraulic model test and direct numerical simulation results far wave $\cdot$structure$\cdot$seabed interaction. Therefore, the newly proposed numerical model is a powerful tool for estimating the nonlinear dynamic responses among a structure, its seabed foundation and water waves.

• Geophysics and Geophysical Exploration
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• v.12 no.1
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• pp.105-113
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• 2009

The interpretation of observed waveform characteristics identified in refraction and wide-angle reflection data increases confidence in the crustal structure model obtained. When calculating traveltimes and raypaths, wavefront methods on a regular grid based on graph theory are robust even with complicated structures, but basically compute only first arrivals. In this paper, we develop new algorithms to compute traveltimes and raypaths not only for first arrivals, but also for fast and later reflection arrivals, later refraction arrivals, and converted waves between P and S, using the modified wavefront method based on slowness network nodes mapped on a multi-layer model. Using the new algorithm, we can interpret reflected arrivals, Pg-later arrivals, strong arrivals appearing behind Pn, triplicated Moho reflected arrivals (PmP) to obtain the shape of the Moho, and phases involving conversion between P and S. Using two models of an ocean-continent transition zone and an oceanic ridge or seamount, we show the usefulness of this algorithm, which is confirmed by synthetic seismograms using the 2D Finite Difference Method (2D-FDM). Characteristics of arrivals and raypaths of the two models differ from each other in that using only first-arrival traveltime data for crustal structure analysis involves risk of erroneous interpretation in the ocean-continent transition zone, or the region around a ridge or seamount.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.11 no.2
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• pp.75-86
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• 1999

호안전면에서의 양빈의 거동이 연구, 조사되며 모래로 이루어진 해변에서의 양빈과 비교하였다. 조건이 서로 다른 6개의 양빈특성이 연구되며 각 조건에 대하여 반복실험이 수행된다. 실험조건에는 모래해변, 호안을 가진 해변, 해안에 직각인 파랑, 그리고 해안에 비스듬한 파랑을 포함한다. 호안을 가진 해안인 경우, 모래입경의 영향이 연구에 포함된다. 또한 호안을 가진 해안에서 모래가 완전히 물에 잠기는 양빈구역의 양단에서 표사이동율을 각각 해변에 직각인 파랑, 해변과 일정한 각도를 이루는 파랑에 대하여 정량화 하였다. 각기 다른 두 개의 표사이동 관계식이 제시되고 검사된다. 비록 약간의 차이가 있더라도 모델에 의한 표사이동율은 실측한 표사이동율과 비교적 잘 일치함을 보여준다.

• Journal of the Korean Society of Marine Environment & Safety
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• v.2 no.1
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• pp.1-10
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• 1996

초음파는 액체 및 고체의 매질 속에서도 그 전달 특성이 우수하여 수중 물체의 감지, 지질 조사 자원탐사뿐만 아니라, 의학 분야에서도 널리 사용되고 있다. 물체유동정보 측정방식에는 연속파를 이용한 도플러식과 펄스 신호를 이용한 도플러는 거리 분해능이 좋으므로 깊이에 따른 속도 정보를 쉽게 얻을 수 있는 장점이 있으나, 수신되는 도플러 신호가 탐촉자의 특성과 매질 속에서의 전파특성 등에 의하여 송신된 신호와 파형이 다르고 복잡한 주파수 특성을 가지므로 연속파에서와 같이 도플러 주파수를 직접 측정하기 곤란하다. 도플러 주파수를 검출하기 위하여 여러 방법이 개발되어 있으나, 측정거리와 측정속도의 제약과 더불어, 실시간(real time) 처리에 의한 분포적 측정이 어려운 실정이다. 본 연구에서는 시간 영역에서 국소 데이터를 이용하여 펄스 신호의 위상을 정의하고 실시간에서 펄스 신호를 위상으로 변환하는 신호 처리법을 제안하였다. 또한 이 신호 처리법을 응용하여 측정 범위의 위상 곡선에서 위상 차를 계산함으로써 평균 가속도와 유동속도정보를 분포적으로 얻을 수 있는 새로운 펄스 도플러 기법을 제안하였으며, 모델 신호를 만들어 제안된 방법의 유용성을 검토하였다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.8 no.3
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• pp.236-245
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• 1996

A wave prediction model is used to estimate the wave spectrum at Ulsan Bay. The Wave model includes the refraction of wave rays according to water depth changes in transient and shallow waters. The calculation of wave refraction is performed from three wave directions : east, southeast and south. Three target locations are selected and the wave spectrum at each location is computed for several uniform wind speeds and directions. The computation results of wave spectrum are compared with PNJ(Pierson, Newmann and James) nomogram and Bretschneider nomogram as well. The model could be used in selection of proper harbor site and in construction of coastal facilities, providing fundamental data in design.

• 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 the Korean Society of Marine Environment & Safety
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• v.19 no.2
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• pp.200-206
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• 2013

The paper was investigated on the mooring forces(or tension) and motion response characteristics for a 8-point mooring floating dock in regular waves using a commercial code(AQWA). To achieve the aim of the research, a numerical simulation was adapted on an inner port environment condition, which the water depth is 10 meters, significant wave amplitude(1.05 m). wave period(3.85 sec), wind speed(20.21 m/s), wind and current direction ($90^{\circ}$), incident waves(${\chi}=180^{\circ}$, $135^{\circ}$ and $90^{\circ}$). The dimension of the numerical model is length(140 m), breadth(32 m), depth(14.6 m). The maximum length of a mooring line is 120m. We can expected that roll and pitch motions appeared in beam seas better than head sea. the mooring forces also indicated higher in bean seas than in head seas including wind forces.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.17 no.3
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• pp.202-212
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• 2005

In the design of an of offshore structure located near an underwater shoal, the same amount of attention given to the wave height may have to be put to the wave induced current as well since some of the wave energy translates to the current. In the present study, two numerical models each based on the nonlinear Boussinesq equation and the linear mild slope equation are applied to calculate the wave deformation and secondly induced current around a shoal. The underwater shoal in Vincent and briggs' experiment (1989) is used here, and all non-breaking wave conditions of the experiment with various monochromatic and unidirectional or multidirectional spectral wave incidences are concerned. Both numerical models clearly showed wave induced currents symmetrically farmed along the centerline over the shoal. The calculated wave heights along a preset line also generally showed very nice agreements with the experimental values.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.8 no.3
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• pp.274-284
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• 2003

The analysis of wave parametric characteristics in sea regions in the vicinity of Korean Peninsula have been carried out using the third generation wave model, WAVEWATCH-III (Tolman, 1999) and four observed buoy data of Korea Meteorological Administration (KMA). Significant wave height increases about 2-3 hours later after the increase of wind speed. Maximum correlation coefficient between two parameters appears in Donghae buoy data, which is at off-shore region. When land breeze occurs, it can be found that the correlation coefficient decreases. Time differences between wind speeds and wave heights correspond to significant tidal periods at all of the buoy locations except for Donghae buoy. After verifying the WAVEWATCH-III model results by the comparing with observed buoy data, we have carried out numerical experiments near the Kuroshio current and East Sea areas, and then reconfirmed that when there exist an opposite strong current in the propagation direction of the waves or wind direction, wave height and length get higher and shorter, respectively and vice versa. It has been shown that these modulations of wave parameters are considerable when wind speed is week or mean current is relatively strong, and corresponding values have been represented.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3B
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• pp.325-335
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• 2010

The aim of this study is to survey the effects of laying drainage layer in sandy beach on beach stabilization. At first, the numerical model developed by Hur and Lee (2007), which is able to consider the flow through a porous medium with inertia, laminar and turbulent resistance terms, i.e. simulate directly WAve Structure Seabed/Sandy beach interaction and can determine the eddy viscosity with LES turbulent model in 3-D wave field (LES-WASS-3D), is validated by comparing with existing experimental data. And then, numerical simulation is carried out to examine the characteristics of wave-sandy beach interaction for a beach with/without drainage layer. From the numerical results, it is shown that mean ground-water level around a foreshore decreases and offshore-ward flow over a seabed reduces in case of a beach with drainage layer. Moreover, the effects of cross profile of drainage layer and incident wave condition on mean ground-water level around a foreshore are also discussed as well the distribution of wave setup around the foreshore.