• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1996.10a
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• pp.119-123
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• 1996

파랑성분간의 비선형상호작용에 의한 에너지의 교환은 스펙트럼 파랑에너지 보존방정식의 중요한 원천항(source)의 하나이며 이의 정확한 계산에 관한 연구가 파랑모델에서 중요한 문제로서 제기되어 왔다. 그러나 비선형에너지 전달을 엄밀하게 계산하는데는 많은 시간이 소요되기 때문에 현재 현업에서는 스펙트럼파라메타로서 간략화한 식을 사용하고 있다. 비선형상호작용은 파랑이 발달하고 있는 풍역에서 중요하기 때문에 비대칭 스펙트럼에 대한 비선형상호작용의 파라메터화는 풍속이 급변하는 풍장에서 매우 중요하다. (중략)

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.11 no.1
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• pp.7-19
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• 1999

The energy transfer between sea-wave components by way of nonlinear wave-wave interactions plays a central role in spectral evolution. Since huge calculation time is required to exact computation of the resulting Boltzmann integral, however, the exact nonlinear energy transfer has not been directly introduced into operational wave models. Thus, effective calculation methods were examined in the present study which exploit the scale property of a scattering coefficient and the detailed balance of interactions. The improved Webb's method (IWM) has inherent stability because singularities degenerate into a negligible point. The improved Masuda's method (IMM) makes a quasi-analytical treatment of the inherent singularities and requires only 1.3 seconds of computer time via Pentium 300MHz processor. The IMM is, therefore, projected to be very useful for theoretical researches in spectral evolution with fetch- or duration-limited situations.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1998.09a
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• pp.106-116
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• 1998

Hasselmann(1963b)은 Neumann 스펙트럼에 대한 비선형에너지 전달함수의 수치계산을 처음으로 행하였다. 그 후 Sell and Hassetmann(1972)은 동일한 계산법을 JONSWAP 스펙트럼에 적용하여 비선형에너지 전달에 의하여 스펙트럼의 첨두가 저주파 영역으로 천이하는 현상을 발견하였다. 그러나 이 계산법은 방대한 시간을 필요로 하며 또한 수치적인 불안정성 때문에 계산 정도가 떨어지는 단점을 갖고 있다. (중략)

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.11 no.1
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• pp.20-33
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• 1999

The evolution of deep-sea waves is driven by energy input from wind, nonlinear energy transfer between wave components, and dissipation through whitecaps. A comparative study was implemented by the use of two wave models in which only the computation methods of nonlinear wave-wave interactions are different from each other. It was reaffirmed that the nonlinear interaction plays a central role in such phenomena that occurred during the spectral growth of wind-seas as down-shift of the spectral peak frequency, overshoot, undershoot, and formation of self-similar spectrum. Specifically, the directional distribution at high frequencies develops into bimodal form, which is attributed to the nonlinear interactions. As saturation stage is reached, spectral density at high frequencies becomes proportional to negative 4 power to the frequency. Perturbations introduced into the spectrum quickly vanished through the actions of the self-similar mechanism. Thus, the nonlinear transfer has important contribution to the stability of numerical ocean wave models.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.2
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• pp.19-25
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• 2004

The linear analysis for the balance of linear momentum of a structure is relatively easy to perform, but the error becomes large when the structure experiences large deformation. Therefore, the material and geometric nonlinearity need to be considered for the precise calculations in that case. The plastic flow of a ductile steel-like metal mainly transforms its dissipated mechanical energy into heat, which transfers under the first and second law of thermodynamics. This heat increases the temperature of the material and the strength of the material decreases accordingly, which affects mechanical behavior of the given structure. This paper presents a finite-strain thermo-elasto-plastic steel model. This model can handle large deformation and thermal load simultaneously, which is common during earthquake periods. Two 3-dimensional finite element analyses verify this formulation.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.3
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• pp.11-22
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• 2010

An analysis method is proposed for the transient linear or nonlinear analysis of dynamic interactions between a flexible dam body and reservoir impounding compressible water under earthquake loadings. The coupled dam-reservoir system consists of three substructures: (1) a dam body with linear or nonlinear behavior; (2) a semi-infinite fluid region with constant depth; and (3) an irregular fluid region between the dam body and far field. The dam body is modeled with linear and/or nonlinear finite elements. The far field is formulated as a displacement-based transmitting boundary in the frequency domain that can radiate energy into infinity. Then the transmitting boundary is transformed for the direct coupling in the time domain. The near field region is modeled as a compressible fluid contained between two substructures. The developed method is verified and applied to various earthquake response analyses of dam-reservoir systems. Also, the method is applied to a nonlinear analysis of a concrete gravity dam. The results show the location and severity of damage demonstrating the applicability to the seismic evaluation of existing and new dams.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.52 no.12
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• pp.595-601
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• 2003

For a control of CPS(Contactless Power Supply), the paper deals with the results which are simulated by a equivalent electric circuit on the LIPT(Linear Inductive Power Transmission). In order to control the CPS, the output values is handled with the driving frequency according to the change of a load. The method that controls the driving frequency for adjusting the output power is reasonable to be applied to the controller. But, when the driving frequency meets the resonant frequency and passes, it lead to a serious problem. Therefore, the controlled region of the driving frequency has to be predicted and determined by the simulation of a electric circuit.

• Journal of Korean Society of Steel Construction
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• v.9 no.4 s.33
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• pp.625-635
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• 1997

The base isolation technique and its benefits in reducing the transmitted earthquake energy into a structure have gained increasing recognition during the last two decades. Unfortunately, the current available design procedures, especially for base-isolated bridges, seem inadequate and too restrictive. As a result, practical design procedure still relies upon a series of deterministic time history analyses. In this study, the evaluation of the possibility of the normal mode method to predict the nonlinear seismic responses of base isolated bridges has been performed. The applicability has been examined through the numerical approach with isolator's elastic or plastic states of the base isolated bridges. Numerical results show that the 1st. mode period and the various responses are varied with the state but are conversed. And, the result show that the normal mode method is applicable to predict the seismic responses and to design the babe isolated bridge. Various analysis method to bridges with bilinearized hysteresis isolator and various pier heights are evalulated.

• The Journal of the Acoustical Society of Korea
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• v.25 no.4
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• pp.184-190
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• 2006

Recently, Lee et al. have proposed an algorithm utilizing the signals from different paths by using bottom mounted simple linear array to estimate 3-D location of oceanic target. But this algorithm assumes that sound velocity is constant along depth of sea. Consequently, serious performance loss is appeared in real oceanic environment that sound speed is changed variously. In this paper, we present a 3-D near field localization algorithm for inhomogeneous sound speed. The proposed algorithm adopt localization function that utilize ray propagation model for multipath environment with linear sound speed profile(SSP), after that, the proposed algorithm searches for the instantaneous azimuth angle, range and depth from the localization cost function. Several simulations using linear SSP and non linear SSP similar to that of real oceans are used to demonstrate the performance of the proposed algorithm. The estimation error in range and depth is decreased by 100m and 50m respectively.

• Computational Structural Engineering
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• v.3 no.3
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• pp.113-123
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• 1990

The paper is concerned with the elasto-plastic and geometrically nonlinear analysis of shell structures using an improved degenerated shell element. In the formulation of the element stiffness, the combined use of three different techniques was made. They are; 1) an enhanced interpolation of transverse shear strains in the natural coordinate system to overcome the shear locking problem ; 2) the reduced integration technique in in-plane strains to avoid the membrane locking behavior ; and 3) selective addition of the nonconforming displacement modes to improve the element performances. This element is free of serious shear/membrane locking problems and undesirable compatible/commutable spurious kinematic deformation modes. In the formulation for plastic deformation, the concept of a layered element model is used and the material is assumed von Mises yield criterion. An incremental total Lagrangian formulation is presented which allows the calculation of arbitrarily large displacements and rotations. The resulting non-linear equilibrium equations are solved by the Netwon-Raphson method combined with load or displacement increment. The versatility and accuracy of this improved degenerated shell element are demonstrated by solving several numerical examples.