• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 춘계학술대회 논문집
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• pp.680-689
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• 2011

A dynamic analysis procedure is developed to provide a comprehensive estimation of the dynamic response spectrum for locomotive's wheels running over a Pre-Stressed Concrete (PSC) box girder bridge on the Korea high speed railway. The wheel force spectrum with the bridge behavior are analyzed as the dynamic procedure for various running speeds (50~450km/h). The high-speed railway locomotive (KTX) is used as 38-degree of freedom system. Three displacements(vertical, lateral, and longitudinal) and three rotational components (pitching, rolling, and yawing). For one car-body and two bogies as well as five movements except pitching rotation components for four wheel axes forces are considered in the 38-degree of freedom model. Three dimensional frame element is used to model of the PSC box girder bridges, simply supported span length of 40m. The irregulation of rail-way is derived using the exponential spectrum density function under assumption of twelve level tracks conditions based on the normal probability procedure. The dynamic responses of bridge passing through the railway locomotive with high-speed analyzed by Newmark-${\beta}$ method and Runge-Kutta method are compared and contrasted considering the developed models of bridge, track and locomotive comprehensively. The dynamic analyses of wheel forces by Runge-Kutta method which are able to analyze the forces with high frequency running on the bridge and ground rail-way are conducted. Additionally, wheel forces spectrum and three rotational components of vehicle body for three typical running speeds is also presented.

• 대한토목학회논문집
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• 제33권6호
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• pp.2473-2481
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• 2013

2차로 양방향 교통류의 주요한 특징은 저속차량으로 인한 차량군과 차량추월이다. 따라서 교통류 모의실험을 이용하여 2차로 도로 교통류의 미시적 분석하기 위해서는 차량군의 행태와 더불어 대항차로를 이용한 추월 행태를 동시에 구현하는 차량모형의 개발이 필수적이다. 이에 따라 국내에서는 이산적 시공간을 기반으로 2차로 양방향 교통류 모형이 소개 되었다(윤병조, 2011). 그러나 선행연구는 임계밀도 이하의 안정 교통류 상태에서 차량추월 행태의 설명력이 우수한 반면, 불안정 교통류상태에서 차량추월의 행태를 설명하기에는 단점을 가지고 있었다. 따라서 본 연구에서는 선행연구를 기반으로 불안정 교통류 상태에서 보다 현실적으로 차량추월을 구현하는 모형을 수정/개발하였다. 개발된 모형의 평가를 위하여 모의실험을 수행한 결과, 차량추종모형은 교통류의 미시적 특성중 하나인 가다서다(Stop-and-go) 현상을 설명하면서 거시적 교통류 관계를 효과적으로 구현 하였으며, 추월모형은 대향방향 교통류와 차량추월 확률변수의 조건에 따라 불안정 교통류상태에서도 합리적으로 차량추월을 설명하였다. 따라서 본 논문에서 제시된 차량모형은 보다 더 현실적으로 2차로 도로 교통류의 분석에 활용될 수 있을 것으로 판단된다.

• 천문학회보
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• 제40권1호
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• pp.48.4-49
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• 2015

Stellar spiral arms and magnetic fields in disk galaxies are important in the formation of gaseous structures such as spurs/feathers and wiggles as well as in angular momentum transport between stars and gas. We present our recent results of global magnetohydrodynamic simulations to study nonlinear responses of self-gravitating and magnetized gas to an imposed stellar spiral potential. We vary the arm strength, the arm pattern speed, and magnetic field strength to explore various galactic situations. Magnetic fields not only reduce the peak density of galactic spiral shocks but also make angular momentum transport more efficient via magnetic pressure and tension forces. The extent and shapes of gaseous arms as well as the radial mass drift rate depend rather sensitively on the magnetic field strength. The wiggle instability apparent in unmagnetized models is suppressed with increasing magnetic field strength, while magnetic fields promote the development of magneto-Jeans instability of the arms and magnetic islands in between arms. We quantify the angular momentum transport by spiral shocks, focusing on the effects of magnetic fields. We also present physical interpretations of our numerical results and discuss astronomical implications of our findings.

• 천문학회지
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• 제49권3호
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• pp.109-122
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• 2016

[Fe II] emission lines are prominent in the infrared (IR) and important as diagnostic tools for radiative atomic shocks. We investigate the emission characteristics of [Fe II] lines using a shock code developed by Raymond (1979) with updated atomic parameters. We first review general characteristics of the IR [Fe II] emission lines from shocked gas, and derive their fluxes as a function of shock speed and ambient density. We have compiled available IR [Fe II] line observations of interstellar shocks and compare them to the ratios predicted from our model. The sample includes both young and old supernova remnants in the Galaxy and the Large Magellanic Cloud and several Herbig-Haro objects. We find that the observed ratios of the IR [Fe II] lines generally fall on our grid of shock models, but the ratios of some mid-IR lines, e.g., [Fe II] 35.35 µm/[Fe II] 25.99 µm, [Fe II] 5.340 µm/[Fe II] 25.99 µm, and [Fe II] 5.340 µm/[Fe II] 17.94 µm, are significantly offset from our model grid. We discuss possible explanations and conclude that while uncertainties in the shock modeling and the observations certainly exist, the uncertainty in atomic rates appears to be the major source of discrepancy.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2000년도 춘계종합학술대회
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• pp.470-473
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• 2000

지난 10여 년 동안 MOSFET는 전력감소, 도핑농도 증가, 캐리어 속도 증가를 위해서 많은 변화를 가져왔다. 이러한 변화를 받아들이기 위해서, 채널의 길이와 공급되어지는 전압이 감소해야만했으며, 그것으로 인해 소자가 더욱 작아지게 되었다. 그러므로 본 논문은 이러한 변화를 위해 채널의 길이와 전압에 의한 MOSFET 구조에서의 변화를 관찰하고, 드레인과 게이트 사이에서의 임팩트 이온화의 변화를 관찰하였다. 본 논문은 세 가지의 모델 즉, conventional MOSFET와 LDD(lightly doped drain) MOSFET, EPI MOSFET을 제시하였다. 게이트 길이는 0.15um, 0.075um을 사용하였고, 스케일링계수는 λ = 2를 사용하였다 스케일링방법은 Constant-Voltage 스케일링으로 하였고, TCAD를 사용하여, 스케일링에 의한 MOSFET의 특성과 임팩트 이온화, 전계를 비교 분석하였으며, 최적의 채널과 도필 농도에 대하여 분석하였다.

• Journal of Biosystems Engineering
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• 제14권4호
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• pp.242-250
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• 1989

The performance of a vertical type centrifugal distributor of granular materials was studied by means of mathematical models and experimental investigations. To develop the mathematical description of particle motion, some assumptions were made. The distribution process consisted of three stages: the entrance of a particle to the blade, the motion of the particle on the blade, and the motion of the particle in the air. The physical properties of fertilizer, which affected the particle motion, were investigated: bluk density, coefficient of friction, coefficient of restitution, and particle size distribution. The particle motion were simulated by using a computer. A prototype distributor was designed and constructed for experimental tests. The following conclusions were drawn from the computer simulation and experiment results. 1. The fertilizer may slide or roll at the point of contact when they impact on the blade and move along the blade. 2. The interaction among fertilizers may prevent them from bouncing. 3. When fertilizers roll on the blade, rolling resistance is one of the factors affecting the particle's motion. 4. The trajectory angle and position of fertilizers from a disc depend on the blade position and particle shape, but the rotating speed of the disc affected them only slightly.

• 한국정보통신학회논문지
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• 제10권11호
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• pp.2032-2038
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• 2006

연속되는 이미지 중에서 인간의 동작을 인식하는 것은 인간과 컴퓨터 의 상호 작용에서 매우 중요하고 도전할 분야이다. 본 논문에서는 CONDENSATION 알고리즘을 이용하여 입자 필터(particle filter)에 기반한 동작 인식 알고리즘을 제안한다. 입자 필터는 조건 확률 전파 모델(Conditional Density Propagation)인 베이시안(Bayesian) 추정 규칙을 적용하는 추적구조를 갖고 있기 때문에 다른 어떤 종류의 추적 알고리즘보다 뛰어난 성능을 보인다. 본 논문에서는 알고리즘의 성능평가를 위해서 두 개의 동작 모델을 가정하였고, 영상에 대한 전처리를 위해서는 MATLAB를 이용하였으며 입자필터는 고속 처리를 위하여 C++로 구현하였다. 두 개의 동작 실험 결과를 통해, 동작 인식 입자 필터가 복잡한 환경 속에서 강인한 추적 성능을 나타냄을 확인하였다.

• 한국정보통신학회논문지
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• 제11권3호
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• pp.584-591
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• 2007

연속되는 이미지 중에서 인간의 동작을 인식하는 것은 인간과 컴퓨터의 상호 작용에서 매우 중요하고 도전할 분야이다. 본 논문에서는 CONDENSATION 알고리즘을 이용하여 입자 필터(particle filter)에 기반한 동작 인식 알고리즘을 제안한다. 입자 필터는 조건 확률 전파 모델(Conditional Density Propagation)인 베이시안(Bayesian) 추정 규칙을 적용하는 추적구조를 갖고 있기 때문에 일반적으로 기존 추적 알고리즘보다 뛰어난 성능을 갖는 경향이 있다. 본 논문에서는 알고리즘의 성능 평가를 위해서 두 개의 동작 모델을 가정하였고, 영상에 대한 전처리를 위해서는 MATLAB를 이용하였으며 입자필터는 고속 처리를 위하여 C++로 구현하였다. 두 개의 동작 실험 결과를 통해, 동작 인식 입자 필터가 근접한 동작 환경 속에서 강인한 추적 성능을 나타냄을 확인하였다.

• 한국해양공학회지
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• 제33권3호
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• pp.236-244
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• 2019

Internal waves occur at the interface between two layers caused by a seawater density difference. The internal waves generated by a body moving in a two-layer fluid are also related to the generation of surface waves because of their interaction. In these complex flow phenomena, the experimental measurements and experimental set-up for the wave patterns of the internal waves and surface waves are very difficult to perform in a laboratory. Therefore, studies have mainly been carried out using numerical analysis. However, model tests are needed to evaluate the accuracy of numerical models. In this study, the various experimental conditions were evaluated using CFD simulations before experiments to measure the wave patterns of the internal waves and surface waves in a stratified two-layer fluid. The numerical simulation conditions included variations in the densities of the fluids, depth of the two-layer fluid, and moving speed of the underwater body.

• Steel and Composite Structures
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• 제47권5호
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• pp.569-585
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• 2023

This paper proposes an efficient approach for the structural topology optimization of bi-directional functionally graded structures by incorporating popular radial basis functions (RBFs) into an implicit level set (ILS) method. Compared to traditional element density-based methods, a level set (LS) description of material boundaries produces a smoother boundary description of the design. The paper develops RBF implicit modeling with multiquadric (MQ) splines, thin-plate spline (TPS), exponential spline (ES), and Gaussians (GS) to define the ILS function with high accuracy and smoothness. The optimization problem is formulated by considering RBF-based nodal densities as design variables and minimizing the compliance objective function. A LS-RBF optimization method is proposed to transform a Hamilton-Jacobi partial differential equation (PDE) into a system of coupled non-linear ordinary differential equations (ODEs) over the entire design domain using a collocation formulation of the method of lines design variables. The paper presents detailed mathematical expressions for BiDFG beams topology optimization with two different material models: continuum functionally graded (CFG) and mechanical functionally graded (MFG). Several numerical examples are presented to verify the method's efficiency, reliability, and success in accuracy, convergence speed, and insensitivity to initial designs in the topology optimization of two-dimensional (2D) structures. Overall, the paper presents a novel and efficient approach to topology optimization that can handle bi-directional functionally graded structures with complex geometries.