• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2000
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• pp.348-355
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• 2000

The characteristics on non linear behavior and the failure mechanism of RC space frame structure serving railway under seismic action have been investigated by numerical analysis in time domain. The structure concerned is modeled in 3 dimensional extent and RC frame elements with fibers are employed. Fibers are characterized as RC one and PL one to distinguish different energy release after cracking. Due to deviation of mass center and stiffness center of entire structure the complex behavior under seismic action is shown. The excessive shear force is concentrated on the pier beside flexible one relatively, which leads to failure of bridge concerned.

• Journal of Power Electronics
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• 제15권4호
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• pp.1047-1053
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• 2015

A time-domain simulation tool to predict the dynamic power output of wind turbines in an offshore wind farm was developed in this study. A wind turbine model consisting of first or second order transfer functions of various wind turbine elements was combined with the Ainslie's eddy viscosity wake model to construct the simulation tool. The wind turbine model also includes an aerodynamic model that is a look up table of power and thrust coefficients with respect to the tip speed ratio and pitch angle of the wind turbine obtained by a commercial multi-body dynamics simulation tool. The wake model includes algorithms of superposition of multiple wakes and propagation based on Taylor's frozen turbulence assumption. Torque and pitch control algorithms were implemented in the simulation tool to perform max-Cp and power regulation control of the wind turbines. The simulation tool calculates wind speeds in the two-dimensional domain of the wind farm at the hub height of the wind turbines and yields power outputs from individual wind turbines. The NREL 5MW reference wind turbine was targeted as a wind turbine to obtain parameters for the simulation. To validate the simulation tool, a Danish offshore wind farm with 80 wind turbines was modelled and used to predict the power from the wind farm. A comparison of the prediction with the measured values available in literature showed that the results from the simulation program were fairly close to the measured results in literature except when the wind turbines are congruent with the wind direction.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.1
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• pp.47-52
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• 2006

Recent warnings indicate that there is a potential risk of massive earthquake in Japan within 30 years. These earthquakes could produce large-scale tsunamis. Tsunamis are very powerful and can be traveled thousands of miles and caused damage in many countries. Consideration of the effect of tsunami to the moored ship is very important because it brings the loss of life and vast property damage. In this paper, the numerical simulation procedure to analyze the motions of a moored ship due to the observed waves of tsunami, Tokachi-off earthquake tsunami profile in northern Pacific coasts of Japan on September 26 in 2003. And the effects on the motions and mooring loads are investigated by numerical simulation. Numerical simulations consist of hydrodynamic analyses in a frequency domain and ship motion analyses in a time domain as the motions of moored ships are examined. As the process begins, the hydrodynamic and waveexciting forces for moored ships must be calculated. Ship motions and mooring forces can then be calculated by solving the equations of motion. In order to investigate the safety evaluation on the motions of moored ship by tsunami attack, we applied a numerical simulation procedure to a 135,000m3 LNG carrier moored at an offshore sea berth.

• 대한조선학회논문집
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• 제39권4호
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• pp.1-10
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• 2002

초기쇄파의 수치모사에는 지금까지 경계적분법이 주로 쓰여왔고, 이 방법은 과도한 계산시간의 문제를 제외하고는 어느 정도 성공적이라고 할 수 있다. 본 논문에서는 쇄파실험을 수치모사하기 위한 새로운 수치기법을 보였다. 이 수치기법은 고차 스펙트럴/경계요소법과 경계적분법을 순차적으로 사용하며, 계산시간을 현저히 줄여준다. 조파 및 파 에너지 집중과정은 고차 스펙트럴/경계요소법에 의해 효율적으로 수치모사되고, 파의 전복과정만이 경계적분법에 의해 계산된다. 계산예에서 높은 입자속도와 가속도 등 쇄파의 두드러진 특성이 보여졌다.

• 대한조선학회논문집
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• 제47권3호
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• pp.291-305
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• 2010

A three-dimensional time-domain calculation method is of crucial importance in prediction of the motions and wave loads of a ship advancing in a severe irregular sea. The exact solution of the free surface wave-ship interaction problem is very complicated because of the essentially nonlinear boundary conditions. In this paper, an approximate body nonlinear approach based on the three-dimensional time-domain forward-speed free-surface Green function has been presented. The Froude-Krylov force and the hydrostatic restoring force are calculated over the instantaneous wetted surface of the ship while the forces due to the radiation and scattering potentials over the mean wetted surface. The time-domain radiation and scattering potentials have been obtained from a time invariant kernel of integral equations for the potentials which are discretized according to the second-order boundary element method (Hong and Hong 2008). The diffraction impulse-response functions of the Wigley seakeeping model advancing in transient head waves at various Froude numbers have been presented. A simulation of coupled heave-pitch motion of a long rectangular barge advancing in regular head waves of large amplitude has been carried out. Comparisons between the linear and the approximate body nonlinear numerical results of motions and wave loads of the barge at a nonzero Froude number have been made.

• 대한조선학회논문집
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• 제31권2호
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• pp.45-56
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• 1994

2차원 수중익 주위의 비선형 자유표면 유동을 시간영역에서 시뮬레이션할 수 있는 수치해법이 개발되었다. 본 수치해법은 고차 스펙트럴법과 경계요소법을 조합한 스펙트럴/경계요소법(spectral/boundary-element method)이며, 자유표면은 고차 스펙트럴법에 의해 그리고 수중익과 후류 보오텍스는 경계요소법에 의해 다루어 진다. 본 방법은 자유표면과 수중익의 비선형/비정상 상호작용문제에 폭넓게 적용될 수 있으며, 특히 스펙트럴법을 사용하므로 자유표면 유동을 매우 효율적으로 다룰 수 있다. 적용예로 정지상태에서 출발하여 자유표면 근처에서 균속 전진운동 또는 전진 및 동요운동을 하는 경우가 다루어 졌고, 자유표면파와 동유체력에서의 비선형/비정상 효과들이 보여지고 있다. 비정상해의 특수한 경우로 얻어지는 정상상태의 계산결과들이 다른 이론 또는 실험결과들과 비교되었으며, 좋은 일치를 보이고 있다.

• 한국통신학회논문지
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• 제19권10호
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• pp.1849-1860
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• 1994

본 논문은 비정질 회토류 천이 급속 박막내에서의 자벽 역학(Magnetic domain wall dynamics)을 란다우 리프쉬츠 길버트 (Landau Lifshitz Gilbert) 방정식을 이용한 수치적 해석을 수행하여 연구하였다. 박막을 이차원 정방형 격자($30\times30$)로 나누고, 각 격자 셀(Cell)에 쌍극자간 존재한다고 상정하여, 이들 쌍극자간의 상호 교환 작용과 자기 이방성, 외부 인가 자계, 그리고 감자계의 영향이 고려되었다. 단축 자기 이방성이 존재하고 역방향의 자화가 존재한다고 가정된 상태에서 자벽이 형성되는 시간과 자벽의 두께를 알아보았다. 또한 외부 자계의 인가에 따른 자벽 이동을 연구하였다. 시뮬레이션 결과, 감자계를 고려했을 때 자벽 형성 시간이 상당히 빨라졌고, 평균 자벽의 이동도(Mobility)는 약간 증가되었다.

• 한국해양공학회지
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• 제28권6호
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• pp.508-516
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• 2014

A numerical method to investigate the non-linear motion characteristics of a TLP is established. A time domain simulation that includes the memory effect using the convolution integral is used to consider the transient effect of TLP motion. The hydrodynamic coefficients and wave force are calculated using a potential flow model based on the HOBEM(higher order boundary element method). The viscous drag force acting on the platform and tendons is also considered by using Morison’s drag. The results of the present numerical method are compared with experimental data. The focus is the nonlinear effect due to the viscous drag force on the TLP motion. The ringing, springing, and drift motion are due to the drag force based on Morison's formula.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2001년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2001
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• pp.36-43
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• 2001

In Korea, we are absolutely short of earthquake data in good quality from moderate and large earthquakes, which are needed fur the study of strong ground motion characteristics. This means that the best use of the available data is needed far the time being. In this respect, several methods are suggested in this paper, which can be applied in the process of data selection and analysis. First, it is shown that the calibration status of seismic stations can be easily checked by comparing the spectra from accelerometer and velocity sensor both of which are located at the same location. Secondly, it is recommended that S/N ratio in the frequency domain should be checked before discarding the data by only look of the data in time domain. Thirdly, the saturated earthquake data caused by ground motion level exceeding the detection limit of a seismograph are considered to see if such data can be used for spectrum analysis by performing numerical simulation. The result reveals that the saturated data can still be used within the dominant frequency range according to the levels of saturation. Finally, a technique to minimize the window effect that distorts the low frequency spectrum is suggested. This technique involves detrending in displacement domain once the displacement data are obtained by integration of low frequency components of the original data in time domain. Especially, the low frequency component can be separated by using discrete wavelet transform among many alternatives. All of these methods mentioned above may increase the available earthquake data and frequency range.

• 한국해양공학회지
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• 제26권1호
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• pp.17-26
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• 2012

A coupled analysis of a floating crane barge with a crane wire and hanging structure is carried out in thetime domain. The motion analysis of the crane barge is based on the floating multi-body dynamics, and thecrane wire is modeled as a simple spring tension. The hanging structure is assumed to be a rigid body with 3 degree-of-freedom translational motion. In this study, numerical simulations were conducted at three different stages. First, the developed code was validated by comparing the time-domain motion response of a crane barge with the frequency-domain results. Then, a coupled analysis of a crane barge and simple structure hanging by the crane wire was performed using the present scheme. The motion response and wire tension from the present calculations are compared with the results of OrcaFlex. The agreement between the two sets of results isfairly good. Last, lowering simulations in regular and irregular waves were conducted considering buoyancy changes in the hanging structure. The effects of the wave conditions, structure's weight, wire length, and lowering speed on the wire tension are considered.