• Ocean Systems Engineering
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• 제7권1호
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• pp.53-74
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• 2017

Ship shaped FPSO (Floating Production, Storage and Offloading) units are the most commonly used floating production units to extract hydrocarbons from reservoirs under the seabed. These structures are usually much larger than general cargo ships and have their natural frequency outside the wave frequency range. This results in the response to first order wave forces acting on the hull to be negligible. However, second order difference frequency forces start to significantly impact the motions of the structure. When the difference frequency between wave components matches the roll natural frequency, the structure experiences a significant roll motion which is also termed as second order roll. This paper describes the theory and numerical implementation behind the calculation of second order forces and motions of any general floating structure subjected to waves. The numerical implementation is validated in zero speed case against the commercial code OrcaFlex. The paper also describes in detail the popular approximations used to simplify the computation of second order forces and provides a discussion on the limitations of each approximation.

• 한국해안·해양공학회논문집
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• 제20권5호
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• pp.439-451
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• 2008

단일 계단지형에 대한 반사파와 투과파의 해를 이용하여 다중 계단지형에서의 파랑변형을 계산할 수 있는 새로운 산란체법의 모형을 구성하였다. 산란체법의 근사해를 보다 정밀한 Kirby and Dalrymple(1983)이 제시한 EFEM의 해와 비교검증하였다. 진행파만의 근사에서는 산란체법과 EFEM의 해는 동일하다. 계산된 반사율과 투과율에 대한 위상의 경우 억류파를 포함한 산란체법의 해는 진행파만의 근사해보다 훨씬 우수하다. 억류파의 영향이 감소할수록 산란체법의 해는 EFEM의 해로 접근한다.

• 한국항해항만학회지
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• 제41권5호
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• pp.345-352
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• 2017

Recently, a new port reserves deep water depth for safe navigation and mooring, following the trend of larger ship building. Larger port facilities include long and huge breakwaters, and mainly adopt vertical type considering low construction cost. A vertical breakwater creates stem waves combining inclined incident waves and reflected waves, and this causes maneuvering difficulty to the passing vessels, and erosion of shoreline with additional damages to berthing facilities. Thus, in this study, the researchers have investigated the response of stem waves at the vertical breakwater near the entrance channel and applied numerical models, which are commonly used for the analysis of wave response at the harbor design. The basic equation composing models here adopted both the linear parabolic approximation adding the nonlinear dispersion relationship and nonlinear parabolic approximation adding a linear dispersion relationship. To analyze the applicability of both models, the research compared the numerical results with the existing hydraulic model results. The gap of serial breakwaters and aligned angles caused more complicated stem wave generation and secondary stem wave was found through the breakwater gap. Those analyzed results should be applied to ship handling simulation studies at the approaching channels, along with the mooring test.

• 한국해양공학회지
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• 제21권1호
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• pp.31-39
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• 2007

Recently, the nonlinear dynamic responses among waves, submarine pipeline and seabed have become a target of analyses for marine geotechnical and coastal engineers. Specifically, the velocity field around the submarine pipeline and the wave-induced responses of soil, such as stress and strain inside seabed, have been recognized as dominant factors in discussing the stability of submarine pipeline. The aim of this paper is to investigate nonlinear dynamic responses of soil in seabed, around submarine pipeline, under wave loading. In order to examine wave-induced soil responses, first, the calculation is conducted in the whole domain, including wave field and the seabed, using the VOF-FDM method. Then, velocities and pressures, which are obtained on the boundary between the wave field and the seabed, are used as the boundary condition to compute the wave-induced stress and strain inside seabed, using the poro-elastic FEM model, which is based on the approximation of the Biot's equations. Based on the numerical results, the characteristics of wave-induced soil responses around submarine pipeline are investigated, in detail, inrelation to relative separate distance of the submarine pipeline from seabed. Also, the velocity field around the submarine pipeline is discussed.

• 한국해양공학회지
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• 제33권1호
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• pp.76-84
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• 2019

For decades, solitary waves have commonly been used to simulate tsunami conditions in numerical studies. However, the main component of a tsunami waveform acts at completely different spatial and temporal distributions than a solitary waveform. Thus, this study applied a 2-D numerical wave tank that included a non-reflected tsunami generation system based on Navier-Stokes equations (LES-WASS-2D) to directly simulate the run-up of a tsunami-like solitary wave on a slope. First, the waveform and velocity due to the virtual depth factor were applied to the numerical wave tank to generate a tsunami, which made it possible to generate the wide waveform of a tsunami, which was not reproduced with the existing solitary wave approximation theory. Then, to validate the applied numerical model, the validity and effectiveness of the numerical wave tank were verified by comparing the results with the results of a laboratory experiment on a tsunami run-up on a smooth impermeable 1:19.85 slope. Using the numerical results, the run-up characteristics due to a tsunami-like solitary wave on an impermeable slope were also discussed in relation to the volume ratio. The maximum run-up heights increased with the ratio of the tsunami waveform. Therefore, the tsunami run-up is highly likely to be underestimated compared to a real tsunami if the solitary wave of the approximation theory is applied in a tsunami simulation in a coastal region.

• Bulletin of the Korean Chemical Society
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• 제19권5호
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• pp.539-544
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• 1998

A new theoretical method, named the SCF-DWB-IOS approximation, is suggested to investigate the vibrational predissociation of triatomic van der Waals complexes. The meta stable vibrational excited states are described with SCF (self-consistent-field) approximation and the fragmented diatomic continuum states are determined by using IOS (infinite order sudden) approximation. The dissociation process itself is studied by using DWB (distorted wave Born) approximation. As a test case, the predissociation rates, rotational state distributions of products, and the lifetimes of vibrationally excited states of $Ne-I_2$ are all computed which are in reasonable agreements with other theoretical and/or experimental results. The suggested SCF-DWB-IOS approximation scheme is found to be a very simple but efficient theoretical tool to investigate the vibrational predissociation dynamics of small van der Waals complexes.

• 한국해양공학회지
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• 제26권2호
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• pp.8-13
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• 2012

This paper investigates the statistical properties of waves in the sea area of Uljin, which is located in the East Sea area of Korea. The wave data were measured using AWAC (Acoustic Wave and Current Meter), which was installed at a 16-m water depth from November 2010 to March 2011. The wave data acquisition rate, Hmax, monthly mean Hs, Tz, Tp, and wave direction are summarized. The distributions of Hs and Tz were analyzed using the Hs-Tz scatter diagrams. The measurement wave data were analyzed to investigate freak wave characteristics. By comparing the wave spectrum using the measurement wave data with the wave spectrum obtained by varying the JONSWAP wave spectrum, it was possible to approximate the wave spectrum shape at the Uljin Sea area.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 1983년도 제25회 수공학 연구발표회 논문초록집
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• pp.78-79
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• 1983

It is well known that small amplitude wave theory, a first approximation to the complete theoretical description of wave behavior, yields a maximum investment in mathematical endeavor. But, if the wave amplitude is large, the small amplitude considerations are not valid, and finite amplitude wave theory which retains higher-order terms to obtain an accurate representation of the wave motion is numercal theory. The Stream function wave theory, one of the numerical methods, was developed by Dean for use with asymmetric measured wave profiles and with symmetric theoretical wave profiles. Dalrymple later improved the comjputational procedure by adding two Lagrangian constraints so that more efficient convergence of the iterative numerical method to a specified wave heigh and to a zero mean free surface displacement resulted. This paper introduces in details the Dean and Darlymple Stream Function Method in case of the symmetric theoretical wave, because in design purposes, wave height and wave period are given.

• 비파괴검사학회지
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• 제24권6호
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• pp.559-565
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• 2004

원주형 기공(SDH: side-drilled hole)의 초음파 산란장 해석을 두 가지 방법으로 수행하였다. 근사해석법인 Kirchhoff 근사법과 변수분리에 의한 엄밀해법으로 구한 원거리 산란진폭 식을 제시하고 시간영역에서 그 결과를 서로 비교하였다. 수직횡파(SV)의 SDH 입사를 고려하였으며, 원거리 산란 진폭을 주파수와 시간영역에서 각각 구하였다. 엄밀해법은 직접 산란파뿐만 아니라 잠행성 파를 나타내었으며, Kirchhoff 근사법은 잠행성 파를 예측하지 못하는 젓을 제외하고 엄밀해의 결과와 잘 일치하였다. 수침, 펄스-에코 시험법에서 SDH의 수신 신호 응답을 예측할 수 있는 두 가지 측정모델을 소개하였고, 수직 횡파가 45도로 입사할 때 지름 1mm SDH의 수신신호를 계산하고 그 결과를 실험과 비교하였다.

• Ocean Systems Engineering
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• 제3권4호
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• pp.327-348
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• 2013

An Oscillating Water Column (OWC) is a relatively practical and convenient device that converts wave energy to a usable form, which is electricity. The OWC is kept inside a fixed truncated vertical cylinder, which is a hollow structure with one open end submerged in the water and with an air turbine at the top. This research adopts potential theory and Galerkin methods to solve the fluid motion inside the OWC. Using an air-water interaction model, OWC design for energy extraction from regular wave is also explored. The hydrodynamic coefficients of the scattering and radiation potentials are solved for using the Galerkin approximation. The numerical results for the free surface elevation have been verified by a series of experiments conducted in the University of New Orleans towing tank. The effect of varying geometric parameters on the response amplitude operator (RAO) of the OWC is studied and modification of the equation for evaluating the natural frequency of the OWC is made. Using the model of air-water interaction under certain wave parameters and OWC geometric parameters, a computer program is developed to calculate the energy output from the system.