• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.5
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• pp.463-469
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• 2016

In this study, a virtual specimen with a linear continuous gradient of void ratio (FGM: Functional Graded Material) is constructed using low-order probability functions of two real cement paste specimens. Two real specimens with difference void ratios are taken from X-ray CT to construct the virtual specimen. A virtual specimen with a gradient void distribution, whose average void ratio is between void ratios of two homogeneous real specimens, is constructed using a stochastic optimization approach. The void ratio distribution is assumed to be linear, and continuously varies in the vertical direction. In this study, a gradient term of void ratio is incorporated into the objective function as well as low-order probability functions from the previous research. To confirm the effect of gradient void distribution on the material response, air permeability is evaluated using finite element analysis. The analysis results are compared with experimental results, and confirm the effect of gradient void distribution on permeability.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.612-613
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• 2008

맥스웰 응력텐서T와 맥스웰 응력 n.T는 물리적인 의미가 없는 가상적인 양이라는 것을 논문 I에서 논하였다. 본 논문 II 에서는 물리적 실체를 가지는 맥스웰 응력텐서의 발산양인 ${\nabla}{\cdot}T$의 계산을 위하여 가상공극을 도입하고, 그 것의 계산법에 대하여 제시한다. 가상공극법은 기존의 여러 전자기력 계산법의 상위개념으로 적용할 수 있는 접근법으로서 매체간에 접촉시에 전자기력 계산을 위하여 개발이 된 것이다. 이 방법을 각 유한요소에 적용함으로서 체적력밀도를 구할 수 있음을 보인다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.5
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• pp.1061-1071
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• 2015

In the present study, the Navier-Stokes (N-S) equations delineating water flows inside porous media were derived applying Reynolds transport theorem in order to provide a basis for analyzing water wave problems inside the porous media. Then, the derived N-S equations were compared with the same species of equations in existing researches. Based on the N-S equations, a set of Boussinesq equations was then derived in such a form that the dispersiveness and nonlinearity of water waves inside the porous media can be properly reproduced. Finally, numerical analyses were carried out to demonstrate the validity of the equations. The reflection and transmission coefficients of porous breakwaters were calculated and compared with the results of existing hydraulic experiments. The numerical results showed a rather sensitive dependency on the virtual mass coefficient of grains constituting the porous media. The selection of the coefficient with zero turned out to give nice agreements with numerical and experimental results.

• Journal of the Korean Magnetics Society
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• v.26 no.6
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• pp.206-212
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• 2016

The shape of a iron bed supporting a permanent magnet in a large-sized motor is a important factor for determining the coupling strength with the yoke. In a large-sized motor, there is a difference in electromagnetic force with the yoke depending on the shape of the iron bed. In this paper, we show the differences and problems by calculating the electromagnetic force between the double bed and the single bed through the virtual air gap, and show that the single bed is superior in terms of the binding force. It is also shown that the binding force between the bed and the yoke is improved by carving the groove shape under the bed.

• Journal of the Korean Magnetics Society
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• v.21 no.5
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• pp.174-179
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• 2011

Magnetic force calculation methods such as Maxwell stress, virtual work principle, equivalent magnetic charge, and equivalent magnetizing current are widely used until now. The force density is still controversial issue even though it is common sense that all of these methods have legitimate results. The surface force densities of each method are quite different with each other in the point of numerical result and final expression. In this paper, it is shown that a unified expression of body force density is derived using virtual air-gap scheme for an analytic model in which cylindrical magnetic material with a vertical current runs through its center.

• Journal of the Korea Society of Computer and Information
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• v.25 no.5
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• pp.107-116
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• 2020

The purpose of this study was to compare the pattern of two men's pants for education and two for industry, and to analyze the patterning method that is most suitable for the body shape of middle-aged men. As a result of appearance evaluation for 3D simulation, J pattern was evaluated as the best in most items, and H pattern was analyzed to be the most inappropriate. As a result of measuring the airgap, all four patterns of the waist circumference were evaluated to have very small airgap, and the J pattern had the smallest airgap for the pants. J pattern was analyzed as the most suitable pattern for middle-aged men's body shape by synthesizing the appearance evaluation of virtual wear, color distribution, sectional view, airgap, etc. However, in the case of J pattern, it was analyzed that the pants length needs to be modified. Since this study compared and analyzed only two patterns for education and two for industry, it is thought that the development of pants for middle-aged men should be developed through actual wearing experiments with J patterns.

• Journal of Soil and Groundwater Environment
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• v.8 no.4
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• pp.12-20
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• 2003

This study presents a mathematical model for simulating the fate and transport of a reactive organic contaminant, TCE, degraded by cometabolism in dual-porosity soils during the installation of in situ biobarrier. To investigate the effect of dual-porosity on transport and biodegradation of organic hydrocarbons, a bimodal approach was incorporated into the model. Modified Monod kinetics and a microcolony concept were employed to represent the effects of biodegrading microbes on the transport and biodegradation of an organic contaminant. The effect of permeability reduction in biobarrier due to biomass accumulation on the flow field were examined in the simulation of a hypothetical field-scale in situ bioaugmentation. Simulation results indicate that the presence of the immobile region can decrease the bioavailability of biodegradable contaminants and that the placement of microbes and nutrients injection wells should be considered for an effective installation of biobarrier during in situ bioaugmentation scheme.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.610-611
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• 2008

맥스웰 응력텐서는 전기기기의 전자기력을 해석함에 현재 가장 널리 사용되는 방법 중 하나이다. 본 논문에서는, 맥스웰 응력텐서 자체는 물리적인 의미가 없는 가상적인 응력텐서이며, 고체역학 또는 동역학적인 해석을 위해 이를 물리적인 기계력으로 취하면 안 된다는 것을 보이고자 한다. 물리적 의미를 부여할 수 있는 것은 응력텐서의 발산인 ${\nabla}{\cdot}T$ 이며 이는 전자기 체적력을 의미하고, 중력과 같은 원격 힘이다. 맥스웰 응력텐서의 유도과정을 에너지적인 접근에서 관찰하여 그 과정으로부터 본 결론을 유도 할 수 있음을 보인다. 본 논문은 두 개로 구성되는 데, 본 논문인 I에는 유효성의 한계에 대한 논의, 별도의 연작논문인 II에서는 대안으로서 가상공극을 사용한 체적력 계산법을 제시한다.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.659-660
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• 2006

전기기기에서의 전자기력 계산은 기기의 성능뿐 아니라 기계적 변형, 진동을 예측하는 주요 파라미터이다. 지금까지는 Maxwell stress tensor법이나 자하법, 가상변위법등에 의해 전체 전자기력 또는 토크를 계산하여 왔으나, 이 방법들은 모두 분포 전자기력을 계산할 수 없었다. 본 논문에서는 기기 내부의 체적 전자기력분포를 계산하는 방법을 제시하고, 그 예로써 영구자석형 전동기의 전자기력 분포를 보여준다. 체적력의 계산은 저자에 의해 제안 된 가상공극법에 기반하여 구현할 수 있다.

• Proceedings of the KIPE Conference
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• 2020.08a
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• pp.435-436
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• 2020

본 논문에서는 단상 영구자석 동기 전동기의 센서리스 운전을 위한 회전자 자극 검출 기법을 제안한다. 제안한 회전자 초기 자극 검출 방법은 비대칭 공극을 갖는 단상 영구자석 동기 전동기에 고주파 전압 및 옵셋 전류를 인가하여 회전자 자극 위치에 따른 전류 옵셋의 크기를 검출함에 있다. 이를 위해 가상의 dq축 모델을 이용한 고정자 전류의 크기를 비교하여 회전자 자극을 검출하고자 한다. 제안된 방법은 다수의 실험 결과를 통해 타당성을 입증하였다.