• Proceedings of the KIEE Conference
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• 1997.07a
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• pp.174-176
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• 1997

편미분 방정식의 형태로 나타나는 많은 전자기장 문제들을 유한요소법이나 유한차분법 등의 수치해석적 방법으로 해결하려는 경우 시스템 행렬을 구성하게 된다. 이때 해석영역의 요소수가 많을수록 행렬의 조건수(condition number)는 다항식(polynomial) 증가를 갖게 되며, 이는 풀어야 할 선형시스템에서 반복 연산 과정의 속도를 떨어뜨리는 결과를 야기한다. 이러한 결과를 wavelet을 기저 함수로 쓰게 되면, 더 높은 분해능(resolution)의 해를 유한 요소법이나 유한 차분법에서와 같은 요소 분할 과정이 없이 Mallat 변환이라는 간단한 과정을 통해 구할 수 있으며, 본 논문에서는 Daubechies의 wavelet 함수를 기저 함수로 사용하여 전자기장 문제에 적용함으로서 수치해석에 있어서 wavelet 함수의 적용이 많은 장점을 갖고 있음을 보인다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.3
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• pp.408-418
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• 1986

본 연구에서는 표면은 단단하고 내면은 강인한 조직을 얻기위하여 대형 성형 탄 로울에 대하여 노에서의 급속가열 및 대기 상태에서의 자연냉각의 열처리가 수행 되어진다. 급속가열 및 냉각시 성형탄 로울 내부의 온도 분포 예측을 위하여 대류 및 복사 열전달 경계조건을 가지는 1차원 비정상 열전도 방정식이 유한 차분법을 사 용하여 해석되어졌다. 여기서 급속가열시 연소가스로 부터 기체복사에 의하여 성 형탄 로울의 바깥표면을 통하여 흡수되는 열량은

• The Korean Journal of Rheology
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• v.7 no.2
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• pp.110-119
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• 1995

본 연구에서는 Upper Convected Maxwll 유체 및 Leonov-like-Giesekus 유체모형 을 이용하여 축대칭 4:1수축을 지나는 점탄서유체의 유동을 수치해석하였다. 이러한 점탄성 유체의 대한 지배방정식이 타원형-쌍곡선형으로 형식변화되므로 이를 적절히 고려할수 있 는 형태의 와도방정식을 이용하여 수치해석을 수행하였다. 와도방정식의 수치해석에서는 형 식에 따른 차분법을 도입하였다. 두 유체모형에 대해서 Weissenberg수를 증가시키면서 탄 성의 효과가 모서리와류의 크기, 응력의 분포 지배방정식의 형식변화에 미치는 영향을 살펴 보았다. 수치해석결과 탄성의 효과가 증가할수록 모서리와류가 커지며, 평면유동의 경우보다 훨씬 큰 모서리와류가 관찰되어 기존의 실험결과와 잘 일치하는 것을 볼수 있었다. 또한 수 치해석 결과로부터 와도방정식의 형식변화를 확인할수 있었다.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2000.11a
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• pp.130-134
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• 2000

본 논문에서는 확장된 시간영역 유한차분법(Extended finite difference time domain method)을 이용하여 마이크로파 중폭기를 해석하였다. 회로에 포함되어 있는 능동 소자는 고주파 등가 회로를 이용하여 모델링 하였다. 고주파 등가 회로를 통하여 계산한 게어트와 드레인의 전류를 FDTD의 전계 계산식에 첨가향으로개 마이크로스트립 회로의 전자기파와 능동 소자와의 상호 작용을 특성 지었다. 해석 결과는 주파수 영역 회로 해석법(Frequency-domain circuit analysis)을 이용한 결과와의 비교를 통하여 정확성을 입증했다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.1
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• pp.67-76
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• 2024

In this paper, we present a DIP-MLS testing method that combines digital image processing with a rigid body-based MLS differencing approach to measure mechanical variables and analyze the impact of target location and image resolution. This method assesses the displacement of the target attached to the sample through digital image processing and allocates this displacement to the node displacement of the MLS differencing method, which solely employs nodes to calculate mechanical variables such as stress and strain of the studied object. We propose an effective method to measure the displacement of the target's center of gravity using digital image processing. The calculation of mechanical variables through the MLS differencing method, incorporating image-based target displacement, facilitates easy computation of mechanical variables at arbitrary positions without constraints from meshes or grids. This is achieved by acquiring the accurate displacement history of the test specimen and utilizing the displacement of tracking points with low rigidity. The developed testing method was validated by comparing the measurement results of the sensor with those of the DIP-MLS testing method in a three-point bending test of a rubber beam. Additionally, numerical analysis results simulated only by the MLS differencing method were compared, confirming that the developed method accurately reproduces the actual test and shows good agreement with numerical analysis results before significant deformation. Furthermore, we analyzed the effects of boundary points by applying 46 tracking points, including corner points, to the DIP-MLS testing method. This was compared with using only the internal points of the target, determining the optimal image resolution for this testing method. Through this, we demonstrated that the developed method efficiently addresses the limitations of direct experiments or existing mesh-based simulations. It also suggests that digitalization of the experimental-simulation process is achievable to a considerable extent.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.4
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• pp.667-673
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• 2000

This paper presents the modeling method of nonlinear circuits with lumped elements by using a hybrid Haar -wavelet MRTD/FDTD techniques. To analyze nonlinear circuits with lumped elements, the Haar-wavelet MRTD scheme is applied to the entire structure of interest and the conventional FDTD scheme is locally used to describe the characteristics of the lumped elements. To validate the scheme, microstrip structure with lumped elements and a single diode mixer are simulated.

• Journal of Wetlands Research
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• v.10 no.2
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• pp.67-79
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• 2008

The one-dimensional (1D) finite-difference method (FDM) with Abbott-Ionescu scheme and the two-dimensional (2D) finite-volume method (FVM) with an approximate Riemann solver (Osher scheme) for unsteady flow calculation in river are described. The two models have been applied to several problems including flow in a straight channel, flow in a slightly meandering channel and a flow in a meandering channel. The uniform rectangular channel was employed for the purpose of comparing results. A comparison is made between the results of computation on 1D and 2D flows including straight channel, slightly meandering channel and meandering channel application. The implementation of the finite-volume method allows complex boundary geometry represented. Agreement between FVM and FDM results regarding the discharge and stage is considered very satisfactory in straight channel application. It was concluded that a 1D analysis is sufficient if the channel is prismatic and remains straight. For curved (meandering) channels, a 2D or 3D model must be used in order to model the flow accurately.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.4
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• pp.1-6
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• 1992

The finite difference simulation method for ship waves is introduced for hull form improvement. Numerical simulations were performed for a series of modified hull forms and the simulated results were used for the determination of the better hull forms. A 4,400 TEU container carrier which was designed and experimented in towing tank was chosen for the purpose. The calculation results are compared with those of model test, of simplified Neumann-kelvin problems and of Rankine source method. In this study, it is shown that the combination of the computer simulation by our method with the experiment provides one of the most economical and reliable procedures of hull form improvement and that the degree of accuracy of this method is so high that it can cope with very practical design purposes.

• Geophysics and Geophysical Exploration
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• v.5 no.2
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• pp.99-107
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• 2002

An analytical forward modeling algorithm was developed for the efficient application to the geotechnical engineering in SASW (Spectral Analysis of Surface Waves) method. for the theoretical dispersion curve, the finite difference method using motion stress vector, which was proposed by Aki and Richards, was employed and verified with two earth models. For the stable and fast calculation, it was found that the model size depending on the frequency range is suitable $1.5\~2$ times bigger than the wavelength.

• Geophysics and Geophysical Exploration
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• v.6 no.2
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• pp.77-86
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• 2003

We designed a new time-domain, finite-difference, elastic wave modeling technique, based on a displacement formulation. which yields nearly correct solutions to Lamb's problem. Unlike the conventional, displacement-based, finite-difference method using a node-based grid set (where both displacements and material properties such as density and Lame constants are assigned to nodal points), in our new finite-difference method, we use a cell-based grid set (where displacements are still defined at nodal points but material properties within cells). In the case of using the cell-based grid set, stress-free conditions at the free surface are naturally described by the changes in the material properties without any additional free-surface boundary condition. Through numerical tests, we confirmed that the new second-order finite differences formulated in the cell-based grid let generate numerical solutions compatible with analytic solutions unlike the old second-order finite-differences formulated in the node-based grid set.