• Journal of Ocean Engineering and Technology
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• v.19 no.4 s.65
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• pp.1-8
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• 2005

A nonlinear time-domain strip theory for vertical wave loads and ship responses is to be investigated. The hydrodynamic memory effect is approximated by a higher order differential equation without convolution. The ship is modeled as a non-uniform Timoshenko beam. Numerical calculations are presented for the S175 Containership translating with the forward speed in regular waves. The approach described in this paper can be used in evaluating ship motions and wave loads in extreme wave conditions and validating nonlinear phenomena in ship design.

• Journal of Korean Society of Transportation
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• v.18 no.4
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• pp.95-105
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• 2000

The Purpose of this study is to present a new Trip Generation Model using Backpropagation Neural Networks. For this purpose, it is compared the performance between existing linear/nonlinear Regression models and a new TriP Generation model using Neural Networks. The study was performed according to the below. First, it is analyzed the limits of conventional Regression models, next Proved the superiority of Neural Networks model in theoretical and empirical aspects, and lastly Presented a new approach of Trip Generation methodology. The results show that Backpropagation Neural Networks model is predominant in estimation and Prediction comparable to Regression analysis. Such results mean the possibility of Neural Networks\` application in Trip Generation modeling. Specially under the circumstances of the chancing transportation situations and unstable transportation on vironments, its application in transportation fields will be extended.

• Proceedings of the KIEE Conference
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• 2001.04a
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• pp.202-204
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• 2001

본 연구에서는 정상상태에서 고조파 전류와 순시전압강하의 보상특성이 우수한 3상 능동형 순시 전압강하 보상기를 제안하고 있다. 제안된 시스템의 보상 알고리즘으로는 구현하기 쉽고 간단한 직접 필터법가 사용되었으며 하이브리드 직렬형 능동전력필터에 적용하였다. 제안된 알고리즘은 전원전압이 순간적으로 왜형과 sag가 발생되더라도 비선형 부하에 인가되는 전압은 일정한 정현파로 제어 가능하며 동시에 전원전류의 고조파와 기본파 무효전류도 보상 가능하다. 정상상태와 과도 상태에서 전력전자전용 시뮬레이터인 PSIM에 의해 제안된 이론의 타당성을 입증하였다.

• Journal of Korea Water Resources Association
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• v.30 no.3
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• pp.195-199
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• 1997

Classical theory of hydrodynamic pressure on dams during earthquakes is revisited and examined with linear transient theory. Because the ground motion during earthquakes is not only transient but also consists of random horizontal and vertical motions, it is proper to treat hydrodynamic pressure on dams with transient theory for random, transient earthquake motions. The present study fines that surface waves are negligible and that the present theory agrees well with the classical theory if the ground motion is horizontal and harmonic with a high frequency.

• Journal of the Korean Society for Marine Environment & Energy
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• v.7 no.4
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• pp.216-223
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• 2004

A nonlinear sloshing problem is numerically simulated. During excessive sloshing the sloshinginduced impact load can cause a critical damage on the tank structure. A three-dimensional free-surface flow in a tank is formulated in the scope of potential flow theory. The exact nonlinear free-surface condition is satisfied numerically. A finite-element method based on Hamiltons principle is employed as a numerical scheme. The problem is treated as an initial-value problem. The computations are made through an iterative method at each time step. The hydrodynamic loading on the pillar in the tank is computed.

• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.1
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• pp.50-56
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• 1999

This paper presents consideration on validity of instantaneous correlation power theory. The proposed power theory is defined and analyzed by time domain approach, thus it is easy to understand and instrument. The power is decomposed into active, fundamental reactive and harmonics components based on the autocorrelation and crosscorrelation signal techniques between voltage and current waveforms. On the compensation property, active power filter deal with three components only. Also, for real time control of active power filter, the power models with difficult concept are not cost effective. To verify the validity of the instantaneous correlation power theory, experimental work for voltage type DSP based active power filter is achieved. The power of thyristor controlled motor drives is decomposed into three orthogonal components by proposed power theory. From compensation results, validity of proposed theory is confirmed. feedback controller needs the information on some motor parameters. New recursive adaptation algorithms for rotor resistance and mutual inductance which can be applied to our nonlinear feedback controller are also presented in this paper. The recursive adaptation algorithms make the estimated values of rotor resistance and mutual inductance track their real values. Some simulation and experimental results show that the adaptation algorithms are robust against the variation of stator resistance and stator inductance.

• Korean Journal of Optics and Photonics
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• v.16 no.1
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• pp.103-108
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• 2005

Second harmonic generation(SHG) by guided phase matching is observed in waveguide structure using the anomalous dispersion of a poled polymer. The second harmonic TM$_{0}$ guided mode could be generated from the fundamental TM$_{0}$ guided mode and then the second harmonic power was higher than any other phase matchable mode because the overlap integral between the fundamental and the second harmonic wave was the largest in the theoretical analysis. Near UV SHG(370 nm) was obtained from the fundamental wavelength of Ti-sapphire laser(740 nm).

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.181-186
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• 2006

In this paper, generation mechanisms of ocean freak waves are briefly introduced in the context of wave-current interaction phenomena. The present model of the fluid motion is based on the Navier-Stokes equations incorporating velocity-pressure formulation because of need to model the nonlinear wave interaction with spatially non-uniform current field. In order to deal with the free surface motion, an Arbitrary Lagrangian-Eulerian (ALE) description is adopted. As an accurate and efficient numerical tool, the spectral element method is presented with general features and specific treatment for the wave-current interaction problem. As an intermediate stage of development, solution procedure and characteristics aspects of the present modeling and numerical method are addressed in detail, and preliminary numerical results prove its accuracy and convergence.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.5 no.3
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• pp.204-211
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• 1993

Boundary element method is applied to simulate nonlinear water waves using Green's identity formula in a numerical wave flume. A system of linear equations is formulated from the governing equation and free surface boundary conditions in order to calculate velocity potential and water surface elevation at each nodal point. The velocity square terms are included in the dynamic free surface boundary condition. The free surface is treated as a moving boundary. the vertical variation of velocity potential being considered in calculating the time derivative of the velocity potential at the free surface. The present method is applied to simulate solitary wave and Stokes 2nd order wave, and shows excellent agreements with their theoretical values.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.1
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• pp.161-167
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• 2022

Ocean waves passing through the underwater bar at a shallow depth experience a shoaling effect caused by decreasing water depth, a nonlinear interaction therein owing to steepening wave slope, and a wave dispersion effect as the water depth increases again. Because this problem includes many complicated phenomena, it is used as a good example of validating a theoretical development or a CFD method for ocean wave applications. Validation is performed mainly for regular waves by comparing the wave elevation patterns in the time domain with the experimental results. In this study, the spectral evolution of wave spectrum is investigated in the frequency domain when a CFD method such as OpenFOAM is applied for this problem. In particular, the effects of initial phase conditions as well as the nonlinear interaction among harmonic waves are studied.