• 한국자동차공학회논문집
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• 제12권2호
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• pp.54-61
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• 2004

The engine-out flow is highly transient and hot, and may place tremendous thermal and inertial loads on a closed-coupled catalyst. Therefore, time-dependent and detailed flow and thermal field simulation may be crucial. The aim of this study is to develop combined chemical reaction and multi-dimensional fluid dynamic mathematical model and to study the effect of unsteady pulsating thermal and flow characteristics on thermal reliability of closed-coupled catalyst. The effect of cell density on the conversion performance under real running condition is also investigated. Unlike previous studies, the present study focuses on coupling between the problems of pulsating flow pattern and catalyst thermal response and conversion efficiency. The results are expressed in terms of temporal evolution of flow, pollutant and temperature distribution as well as transient characteristics of conversion efficiency. Fundamental understanding of the flow and thermal phenomena of closed-coupled catalyst under real running condition is presented. It is shown that instants of significantly low values of flow uniformity and conversion efficiency exist during exhaust blowdown and the temporal varaition of flow uniformity is very similar in pattern to one of conversion efficiency. It is also found that the location of hot spot in monolith is directly affected by transient flow pattern in closed-coupled catalyst.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2003년도 종합학술발표회 논문집 Vol.13 No.1
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• pp.371-375
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• 2003

In this paper, a new design method for coupled-line filters with tapped input/output has been developed. The design equations for this tapped filter have been obtained using a new equivalent circuit model of tapped lines. From an edge coupled-line filter, tapped lines replaces the input/output coupled lines which tend to have very narrow gaps (few mils). Therefore, tapped coupled-line filters tend to be less sensitive to filter fabrication tolerances and to be easily fabricated using milling tools. The new filter design algorithm allows very accurate filter design for frequencies less than 20 GHz and bandwidth less than 20%. Above 20 GHz, the filter performance can be optimized starting from the filter design algorithm in this paper. Simulation problems with 2-D EM tools to characterize filter performance at high frequencies have shown to be solved by providing a channel for the filter to eliminate higher order modes.

• 한국정밀공학회지
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• 제22권11호
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• pp.111-117
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• 2005

The vibration problems associated with gear coupled rotors have been the focus of much engineering work. These systems are complex and difficult to analyze in that they have the problems associated with conventional rotors plus those additional problems associated with the gear couplings. This paper examines the problems peculiar to the gear mesh. Because of the meshing action of gears, the elasticity of the gear teeth introduces time-varying stiffness coefficients into the governing equations of motion. This means that system response must be thought of in terms of Mathieu-type equations, where multiple-frequency response occur due to the periodic coefficients. The meshing action of the gears also couples the lateral and torsional gear motions. Gear errors, such as tooth profile and spacing errors, produce forces and torque that excite the system at multiple frequencies, some of which are much higher than shaft rotational speed. To investigate how to the time-varying stiffness in the gear teeth and the gear errors act one the dynamic response of the gear coupled rotors, a three-dimensional dynamic model with lateral-tortional oscillation is developed. The harmonic balance technique is employed to solve this mathieu-type problem.

• 한국전산구조공학회논문집
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• 제27권3호
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• pp.137-145
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• 2014

본 논문에서는 브리징 스케일 분해를 기반으로 멀티스케일 문제에 대한 설계민감도 해석법을 개발하였다. 나노 기술의 급속한 발전으로 인해 나노 수준의 해석의 필요성이 지속적으로 증가하고 있다. 최근 분자동역학과 연속체역학의 연성문제에서 많은 해석 방법들이 개발되었다. 본 논문에서는 연성시스템 해석을 위해 브리징 스케일 기법을 사용한다. 전체 영역의 분자동역학 시스템의 해석은 많은 양의 계산 비용이 들기때문에 분자동역학과 연속체 시뮬레이션의 연성시스템을 선호한다. 분자동역학과 연속체 수준 사이의 정보 교환은 분자동역학과 연속체의 경계에서 일어난다. 브리징 스케일 법에서 일반화된 랑지벵 방정식은 축소된 영역의 분자동역학 시스템 해석을 위하여 요구되고, 시간이력 커널을 사용하여 구한 GLE 힘은 분자동역학 시스템에서 경계에 있는 원자들에 작용한다. 그러므로 분자동역학과 연속체 수준의 시뮬레이션을 분리해서 해석할 수 있으며 계산 과정을 가속시킬 수 있다. 연성문제의 시뮬레이션 이후에는 설계의 최적화를 위해 설계민감도 해석의 필요성이 자연스럽게 나타나며 전체 시스템의 성능은 나노 스케일의 효과를 고려해서 최적화된다. 설계구배 기반 최적화에서 설계민감도가 요구되지만 유한차분법으로 구한 민감도는 문제가 대형화될 때 계산비용의 제한때문에 비실용적이나 해석적 설계민감도는 효율적인 강점을 갖는다. 본 연구에서는 연성된 분자동역학-연속체 멀티스케일 문제에서 해석적 설계민감도를 유도하여 정확성과 향후 최적설계로의 활용 가능성을 확인하였다.

• Structural Engineering and Mechanics
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• 제21권4호
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• pp.437-450
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• 2005

In this study, a complete analysis of soil-structure interaction problems is presented which includes a modelling of the near surrounding of the building (near-field) and a special description of the wave propagation process in larger distances (far-field). In order to reduce the computational effort which can be very high for time domain analysis of wave propagation problems, a special approach based on similarity transformation of the infinite domain on the near-field/far-field interface is applied for the wave radiation of the far-field. The near-field is discretised with standard Finite Elements, which also allows to introduce non-linear material behaviour. In this paper, a new approach to calculate the involved convolution integrals is presented. This approximation in time leads to a dramatically reduced computational effort for long simulation times, while the accuracy of the method is not affected. Finally, some benchmark examples are presented, which are compared to a coupled Finite Element/Boundary Element approach. The results are in excellent agreement with those of the coupled Finite Element/Boundary Element procedure, while the accuracy is not reduced. Furthermore, the presented approach is easy to incorporate in any Finite Element code, so the practical relevance is high.

• Nuclear Engineering and Technology
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• 제46권2호
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• pp.263-272
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• 2014

Scattering source calculations using conventional spherical harmonic expansion may require lots of computation time to treat full-coupled three-dimensional photon-electron transport in a highly anisotropic scattering medium where their scattering cross sections should be expanded with very high order (e.g., $P_7$ or higher) Legendre expansions. In this paper, we introduce a modified scattering kernel approach to avoid the unnecessarily repeated calculations involved with the scattering source calculation, and used it with parallel computing to effectively reduce the computation time. Its computational efficiency was tested for three-dimensional full-coupled photon-electron transport problems using our computer program which solves the multi-group discrete ordinates transport equation by using the discontinuous finite element method with unstructured tetrahedral meshes for complicated geometrical problems. The numerical tests show that we can improve speed up to 17~42 times for the elapsed time per iteration using the modified scattering kernel, not only in the single CPU calculation but also in the parallel computing with several CPUs.

• 한국전산구조공학회논문집
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• 제30권4호
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• pp.351-361
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• 2017

본 연구에서는 다양한 변수를 갖는 병렬 RC 구조벽체시스템에 대한 성능기반설계의 타당성과 이에 따른 모멘트 재분배 개념의 적용성을 분석하기 위해 횡력을 지지하는 병렬 RC 구조벽체시스템에 대한 비선형해석을 수행하였다. 설계변수(철근비, 콘크리트변형률, 벽체높이)가 병렬 RC 구조벽체시스템의 거동에 미치는 영향을 분석하였으며 이를 기반으로 병렬 RC 구조벽체시스템의 성능기반 설계를 위한 고려사항을 제안하였다. 비선형해석 결과, 병렬 RC 구조벽체시스템 성능기반 설계와 모멘트 재분배 개념의 적용을 위해서는 연결보의 항복여부에 대한 고려가 필요한 것으로 나타났다. 높은 벽체의 경우, 연결보가 항복하지 않고 탄성 상태로 거동할 수 있기 때문에 고층 병렬 RC 구조벽체시스템에 대해 성능기반 설계 및 모멘트 재분배 개념을 적용하기 위해서는 벽체에 높은 수준의 소성변형능력을 필요로 하며, 이를 위해 벽체 압축단부에 횡보강을 필수적으로 실시해야 한다.

• 충청수학회지
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• 제35권1호
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• pp.53-67
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• 2022

Nonlinear system of initial value problems involving R-L fractional derivative is studied. Monotone iterative technique coupled with lower and upper solutions is developed for the problem. It is successfully applied to study qualitative properties of solutions of nonlinear system of initial value problem when the function on the right hand side is nondecreasing.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 ITC-CSCC -1
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• pp.70-73
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• 2002

High frequency digital LSI circuits are usually composed of many sub-circuits coupled with interconnects. They sometimes causes serious problems of the fault switching by time-delays, crosstalks, reflections of signals and so on. Therefore, it is very important to develop a user-friendly simulator for solving these problems. Although a moment matching method is widely used as the reduction technique of interconnects, it may happen to arise erroneous results for evaluating the poles far from the origin. In this paper, we show an asymptotic method in the complex frequency-domain, where we calculate the exact poles and residues giving large effect to the transient responses. Then, the interconnects are replaced by the asymptotic equivalent circuits using the poles and residues. Thus, we can develop a users-friendly simulator using the equivalent circuits.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집C
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• pp.170-175
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• 2001

The design cycle associated with large engineering systems requires an initial decomposition of the complex system into design processes which are coupled through the transference of output data. Some of these design processes may be grouped into iterative subcycles. In analyzing or optimizing such a coupled system, it is essential to determine the best order of the processes within these subcycles to reduce design cycle time and cost. This is accomplished by decomposing large multidisciplinary problems into several multidisciplinary analysis subsystems (MDASS) and processing it in parallel. This paper proposes new strategy for parallel decomposition of multidisciplinary problems to improve design efficiency by using the multiple objective genetic algorithm (MOGA), and a sample test case is presented to show the effects of optimizing the sequence with MOGA.