• 대한기계학회논문집A
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• 제28권9호
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• pp.1306-1313
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• 2004

This paper addresses a theoretical approach to calculate the amount of the stored energy during high strain-rate deformations using atomistic level simulation. The dynamic behavior of materials at high strain-rate deformation are of great interest. At high strain-rates deformations, materials generate heat due to plastic work and the temperature rise can be significant, affecting various properties of the material. It is well known that a small percent of the energy input is stored in the material, and most of input energy is converted into heat. However, microscopic analysis has not been completed without construction of a material model, which can simulate the movement of dislocations and vacancies. A major cause of the temperature rise within materials is traditionally credited to dislocations, vacancies and other defects. In this study, an atomistic material model for FCC such as copper is used to calculate the stored energy.

• JSTS:Journal of Semiconductor Technology and Science
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• 제6권1호
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• pp.1-9
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• 2006

We introduce our in-house program, NANOCAD, for the modeling and simulation of carrier transport in nanoscale MOSFET devices including quantum-mechanical effects, which implements two kinds of modeling approaches: the top-down approach based on the macroscopic quantum correction model and the bottom-up approach based on the microscopic non-equilibrium Green’s function formalism. We briefly review these two approaches and show their applications to the nanoscale bulk MOSFET device and silicon nanowire transistor, respectively.

• 대한기계학회논문집B
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• 제34권6호
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• pp.569-577
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• 2010

다상 유체 시스템에 적용할 수 있는 다중스케일 입자 시뮬레이션 기법을 개발하였다. 거시 모델과 미시모델이 만나는 경계영역에서 세가지로 구별되는 기능을 수행하도록 하였다. 먼저, 기상과 액상을 분리하여 연결하기 위해 벽을 설정하였다. 또 경계영역을 근처에서 경계의 위치를 측정하고 이것에 벽의 각도와 위치가 연동하여 접촉각 값을 미시모델에서 거시모델로 전달하게 하였다. 마지막으로, 입자의 삽입과 제거를 통해 경계영역의 질량과 온도를 거시적 조건에 맞추도록 하였다. 이 알고리즘들을 적용한 완전습윤과 부분습윤시스템들은 좋은 결합 결과를 보였다.

• Structural Engineering and Mechanics
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• 제74권3호
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• pp.407-423
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• 2020

The pre-peak cyclic shear mechanism of two-order asperity degradation of rock joints in the direct shear tests with static constant normal loads (CNL) are investigated using experimental and numerical methods. The laboratory testing rock specimens contains the idealized and regular two-order triangular-shaped asperities, which represent the specific geometrical conditions of natural and irregular waviness and unevenness of rock joint surfaces, in the pre-peak cyclic shear tests. Three different shear failure patterns of two-order triangular-shaped rock joints can be found in the experiments at constant horizontal shear velocity and various static constant normal loads in the direct and pre-peak cyclic shear tests. The discrete element method is adopted to simulate the pre-peak shear failure behaviors of rock joints with two-order triangular-shaped asperities. The rock joint interfaces are simulated using a modified smooth joint model, where microscopic scale slip surfaces are applied at contacts between discrete particles in the upper and lower rock blocks. Comparing the discrete numerical results with the experimental results, the microscopic bond particle model parameters are calibrated. Effects of cyclic shear loading amplitude, static constant normal loads and initial waviness asperity angles on the pre-peak cyclic shear failure behaviors of triangular-shaped rock joints are also numerically investigated.

• Current Applied Physics
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• 제18권11호
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• pp.1388-1392
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• 2018

Metal thin films are used widely to solve the vibration problem. However, damping mechanism is still not clear, which limits the further improvement of the damping properties for film and the development of multi-functional damping coating. In this paper, Damping microscopic mechanism of porous metal films was investigated at both macroscopically and microscopically mixed levels. Molecular dynamics simulation method was used to model and simulate the loading-unloading numerical experiment on the micro-pore and vacancy model to get the stress-strain curve and the microstructure diagram of different defects. And damping factor was calculated by the stress-strain curve. The results show that dislocations and new vacancies appear in the micro-pores when metal film is stretched. The energetic consumption from the motion of dislocation is the main reason for the damping properties of materials. Micro-mechanism of damping properties is discussed with the results of in-situ experiment.

• Geomechanics and Engineering
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• 제35권5호
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• pp.475-486
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• 2023

Ballast particles have an irregular shape and are discrete in nature. Due to the discrete nature of ballast, it exhibits complex mechanical behaviour under loading conditions. The discrete element method (DEM) can model the behaviour of discrete particles under a multitude of loading conditions. DEM is used in this paper to simulate a series of three-dimensional direct shear tests in order to investigate the shear behaviour of railway ballast and its interaction at the microscopic level. Particle flow code in three dimension (PFC3D) models the irregular shape of ballast particles as clump particles. To investigate the influence of particle size distribution (PSD), real PSD of Indian railway ballast specification IRS:GE:1:2004, China high-speed rail (HSR) and French rail specifications are generated. PFC3D built-in linear contact model is used to simulate the interaction of ballast particles under various normal stresses, shearing rate and shear box sizes. The results indicate how shear resistance and volumetric changes in ballast assembly are affected by normal stress, shearing rate, PSD and shear box size. In addition to macroscopic behaviour, DEM represents the microscopic behaviour of ballast particles in the form of particle displacement at different stages of the shearing process.

• 한국항공운항학회지
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• 제27권1호
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• pp.20-25
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• 2019

To prepare for the ever-increasing demand for air transport, airport operators should be well aware of the timing of the saturation of the facility and increase the capacity of the airport through extension or extension. The capacity of an airport is determined by the smallest value of the facilities that make up the airport, but it is generally customary to determine the capacity of the costly and time-consuming runway as a whole for the airport. For analyzing the capacity of the runway capacity, the study used the most accurate microscopic air traffic simulation, Simmod-PRO, to analyze the saturation time of three runways currently in Incheon International Airport's operation, and calculate the appropriate time for operation of the 4th runway. The study also calculate the relocation of Airport's high-speed exit taxiway for analyzing the increasing of capacity.

• 대한교통학회지
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• 제33권2호
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• pp.214-222
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• 2015

계속되는 항공수요 증가와 국지적인 기상요인으로 제주국제공항은 우리나라 공항가운데 가장 높은 항공기 지연율을 보이고 있다. 현재의 항공수요 증가추세를 감안할 때 이러한 제주국제공항의 항공기 지연현상은 앞으로 더욱 악화되어 공항의 처리능력 한계에 다다를 것으로 예상된다. 공항의 처리능력을 가늠할 수 있는 활주로의 연간용량 산정은 장래 공항계획 수립을 위한 필수적인 작업이다. 하지만 현재 실무에서는 FAA에서 제시한 산정식을 적용하여 연간용량을 산정하고 있으나, 변수에 대한 명확한 정의가 이루어지고 있지 않아 사용자의 해석에 따라 상이한 결과값이 도출될 가능성이 있으며, 항공기의 지연이 고려되지 않는다는 점에서 실무적 제약이 내재되어 있다. 이러한 실무적 한계를 개선하기 위한 방법으로, 본 논문에서는 미시적 항공교통 시뮬레이션 모형을 활용하여 활주로를 이용하는 항공기의 평균 지연시간을 측정하고, 이를 기준으로 제주국제공항 활주로의 일일용량을 분석, 최종적으로 연간용량을 산정하는 방법을 소개하였다. 또한, 시뮬레이션 모형구축 및 검증을 위한 자료수집, 분석과정과 검증결과를 설명하였다. 제주국제공항의 일일용량 및 연간용량 분석 결과, 각각 약 460회, 약 169,000회로 산정되었다.

• 대한교통학회지
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• 제19권5호
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• pp.7-18
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• 2001

본 연구는 도시물류 문제를 미시적 및 거시적 관점으로 정의하고, 국내외 문헌의 현황 및 한계점을 밝히고, 향후 연구방향을 제시하며, 정책 대안을 평가하는 모형을 개념적으로 제시하는 것을 목적으로 하였다. 문헌의 한계점을 바탕으로 하여 추후 연구 방향으로서는 도시내 물류활동 주체인 화주, 제품공급업자 등을 고려하는 미시적 관점의 연구가 강화되어야 한다는 점과 다양한 정책 대안들을 보다 효과적으로 평가할 수 있는 개념적 평가 모형 정립의 필요성 그리고 물류활동 주체와 도시 교통 문제를 함께 평가할 수 있는 통합 모형의 구축을 제의하였다. 도시물류 개선 대안을 평가하기 위한 모형을 개념적으로 제시하는 데 있어서 거시적 관점과 미시적 관점의 상관관계를 정리하고, 미시적 관점에서 관련 주체별 평가 요소를 도출하고 이를 바탕으로 평가 모형을 구체화하였다. 특히, 최근 시도된 시뮬레이션 기법을 이용한 화물차량경로 예측 방법을 제시하고, 모형을 통하여 도시물류 개선을 위한 정책 대안이 각 물류활동의 주체에게 미치는 영향을 미시적 및 거시적 관점에서 평가할 수 있음을 밝혔다. 또한 향후 본 연구에서 제시된 모형들을 보다 구체화하는 노력이 필요할 뿐 아니라 재고관리 시스템을 통한 수요예측 기법 등의 기초 연구가 계속되어야 함을 강조하였다.

• Geomechanics and Engineering
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• 제34권5호
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• pp.577-595
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• 2023

A dynamic triaxial discrete element numerical model of lightweight soil was established using the discrete element method to study the microscopic mechanism of expanded polystyrene (EPS) particles in the soil under cyclic loading. The microscopic parameters of the discrete element model of the lightweight soil were calibrated depending on the dynamic triaxial test hysteresis curves. Based on the calibration results, the effects of the EPS particles volume ratio and amplitude on the contact force, displacement field, and velocity field of the lightweight soil under different accumulated strains were studied. The results showed that the hysteresis curves of lightweight soil exhibit nonlinearity, hysteresis, and strain accumulation. The strain accumulated in remolded soil is mainly tensile strain, and that in lightweight soil is mainly compressive strain. As the volume ratio of EPS particles increased, the contact force first increased and then decreased, and the displacement and velocity of the particles increased accordingly. With an increase in amplitude, the dynamic stress of the particle system increased, and the accumulation rate of the dynamic strain of the samples also increased. At 5% compressive strain, the contact force of the particles changed significantly and the number of particles deflected in the direction of velocity also increased considerably. These results indicated that the cemented structure of the lightweight soil began to fail at a compressive strain of 5%. Thus, a compressive strain of 5% is more reasonable than the dynamic strength failure standard of lightweight soil.