• 인터넷정보학회논문지
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• 제23권3호
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• pp.67-76
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• 2022

현대에는 전자기파를 이용한 전력 및 신호 전달이 필수적인데, 전자기파를 원하는 경로를 통해 효율적으로 전달하기 위해서는 도파 구조(guided structure)가 필요하다. 본 논문에서는 먼저 전파해석 기법인 유한요소법(FEM : Finite Element Method)을 적용하여 도파 구조 중 하나인 2-D/3-D 도파관(waveguide)에 대해 직접 in-house code를 작성하여 전자기 시뮬레이션하였다. 이후 in-house code의 해석 결과를 대표적인 전자파 상용 시뮬레이션 소프트웨어인 HFSS의 결과와 비교하여 해석의 정확성을 검증하였다. 아울러, 전자기 해석에 있어 무한대의 해석 영역을 잘라 해석하기 위해 필수적인 흡수경계조건(ABC : Absorbing Boundary Condition)의 성능을 분석한 후, 병렬화 기법의 적용에 따른 성능 향상을 제시하였다.

• 설비공학논문집
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• 제13권9호
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• pp.888-894
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• 2001

Advanced gas turbine engines employ turbine entry temperatures so high that cooling of the turbine blades is essential. The coolant flow introduces losses which need to be minimized, and therefore it is important that the minimum amount of coolant should be used. This work presents the result of the one-dimensional analysis and the effect of the boundary conditions on coolant flow rate in gas turbine blades.

• 대한수학회지
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• 제58권5호
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• pp.1109-1129
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• 2021

This paper considers an anisotropic polytropic infiltration equation with a source term $$u_t={\sum\limits_{i=1}^{N}}{\frac{{\partial}}{{\partial}x_i}}\(a_1(x){\mid}u{\mid}^{{\alpha}_i}{\mid}u_{x_i}{\mid}^{p_i-2}u_{x_i}\)+f(x,t,u)$$, where p_i > 1, α_i > 0, a_i(x) ≥ 0. The existence of weak solution is proved by parabolically regularized method. Based on local integrability $u_{x_i}{\in}W_{loc}^{1,p_i}(\Omega)$, the stability of weak solutions is proved without boundary value condition by the weak characteristic function method. One of the essential characteristics of an anisotropic equation different from an isotropic equation is found originally.

• 한국지반공학회논문집
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• 제37권12호
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• pp.25-31
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• 2021

지반의 열-수리 현상에 대한 수치해석에서 경계조건은 해석결과의 정확도에 중요한 역할을 한다. 본 연구에서는 지반과 대기의 상호작용을 고려한 열-수리 경계조건을 제시하였다. 지면의 에너지 평형은 태양복사, 지구복사, 바람에 의한 대류, 수분 증발에 대한 잠열 그리고 지중으로의 열전도로 구성된다. 각각의 열흐름에 대한 방정식을 제시하고, 불포화 지반의 열-수리 현상에 대한 해석프로그램과 연계하여 수치해석을 수행하였다. 울산기상대에서 관측된 기상데이터를 이용한 수리-열적 해석에서 실측된 지표면 온도와 수치해석 결과가 매우 유사하였다. 낮시간의 수분 증발에 의한 잠재열은 비포장 지면의 온도를 낮추며, 야간시간에는 지면조건의 영향이 감소한 열적평형 상태에 도달하였다. 지면의 온도변화는 지중으로 깊어질수록 열확산으로 감소하였다. 지표면의 온도가 주요 관심사인 수치해석에서는 지반과 대기의 열-수리적 상호작용을 고려한 수치해석을 수행해야 한다.

• 한국분무공학회지
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• 제9권4호
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• pp.53-66
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• 2004

An experimental study was carried out in order to investigate the influence of flow conditions on a boundary layer in the near-wake of a flat plate. The flow conditions in the vicinity of the trailing edge that is influenced by upstream condition history are an essential factor that determines the physical characteristics of a near-wake. Tripping wires attached at various positions were selected to change flow conditions of a boundary layer. The flows such as laminar, transitional, and turbulent boundary layer at 0.98C from the leading edge are imposed in order to investigate the evolution of symmetric and asymmetric wake. An x-type hot-wire probe(55P61) is employed to measure at 8 stations in the near-wake. Test results show that the near-wake for the case of a turbulent boundary layer is relatively insensitive to instability after separating at the trailing edge, and Reynolds shear stress in the near-wake for the case of a turbulent boundary layer collapses due to turbulent kinetic energy.

• 한국연소학회지
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• 제11권3호
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• pp.8-17
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• 2006

When a flame is stabilized in a tube of a finite thickness, a conductive heat transfer through the tube significantly changes the wall temperature and affects the flame characteristics. Thus the tube length and thermal boundary conditions affect on the structure of the flame in a conductive tube. A one-dimensional analytical study was conducted by employing two energy equations for tubes and mixtures and a species equation for the mixture. Variation of the maximum temperatures and indicating displacements were observed. A parametric study on the effects of inner Peclet numbers, normalized wall conductivities, and heat transfer conditions of the tube was conducted. This study provides essential data for a more efficient computational simulation of the flame stabilized in conductive tubes.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2995-3000
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• 2008

Understanding of the impinging behavior of an electrically charged spray is essential in determining appropriate operating conditions for electro-spraying of paints, surface coating materials and insecticides. In the present work, the wall impact behavior of an electrically charged drop has been investigated and compared with that of a neutral drop experimentally. The critical Sommerfeld number representing the spread-splash boundary for the charged drop impacting on the dielectric substrate turned out to be larger compared to that for the neutral drop with the same surface condition. The change of the transition boundary is due to the increase in the surface wettability of the drop on the substrate. However, with the electrically conducting substrates, the charging effect on the transition boundary appeared negligible. This is because the electric discharging time is much shorter than the time required for the flattened drop to reach its maximum extent.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 봄 학술발표회 논문집
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• pp.12-18
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• 2002

For the analysis of Kirchhoff plate bending problems, a new meshless method is implemented. For the satisfaction of the C¹ continuity condition in which the first derivative is treated as another primary variable, Hermite interpolation is enforced on standard reproducing kernel particle method. In order to impose essential boundary conditions on solving C¹ continuity problems, shape function modifications are adopted. Through numerical tests, the characteristics and accuracy of the HRKPM are investigated and compared with the finite element analysis. By this implementation, it is shown that high accuracy is achieved by using HRKPM fur solving Kirchhoff plate bending problems.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제1권1호
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• pp.1-34
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• 1997

In this study, various available meshless methods are briefly reviewed and the connection among them is investigated. The objective of meshless methods is to eliminate some difficulties which are originated from reliance on a mesh by constructing the approximation entirely in terms of nodes. Especially, focusing on Element Free Galerkin Method(EFGM) based on moving least square interpolants(MLSI), a new implementation is developed based on a variational principle with penalty function method were used to enforce the essential boundary condition. In addition, the weighted orthogonal basis functions are constructed to overcome disadvantage of MLSI.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 춘계학술대회논문집
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• pp.355-362
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• 2009

Most material of engineering interest undergoes solidification process from liquid to solid state. Identifying the underlying mechanism during solidification process is essential to determine the microstructure of material which governs the physical properties of final product. In this paper, we expand our previous two-dimensional numerical technique to three-dimensional simulation for computing dendritic solidification process with fluid convection. We used Level Contour Reconstruction Method to track the moving liquid-solid interface and Sharp Interface Technique to correctly implement phase changing boundary condition. Three-dimensional results showed clear difference compared to two-dimensional simulation on tip growth rate and velocity.