• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.454-454
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• 2012

Magnetron sputtering에서, 영구자석의 자속은 target 표면 가까이에 전자를 구속한다. 구속된 전자는 Ar중성기체와 충돌하여 Ar이온을 발생시킬 수 있으므로, target 근처에서의 플라즈마 밀도를 높여, 자석이 없을 때보다 낮은 압력 또는 낮은 전압에서 방전할 수 있다. 구속 전자가 밀집된 공간에서 sputtering 현상이 주로 발생하기 때문에, planar target을 사용할 경우에는 target이 불균일하게 식각되어 target의 사용효율이 좋지 못하다. 이에 대한 한 가지 대안은 target을 원통형으로 만들어 회전시키는 것이다. Cylindrical target 의 내부에 위치한 영구자석은 고정시키고, target만을 회전시키면 비교적 균일하게 식각되므로 target의 사용효율을 높일 수 있다. 본 연구에서는 기존의 planar target에 대한 Particle-In-Cell Simulation을 Cylindrical target 에 적용시키기 위한 방법을 알아본다. 또한, 개발된 Simulator를 이용하여, Sputtering 조건의 변화에 대한 I-V curve의 변화를 살펴본다.

• 한국전산유체공학회지
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• 제19권2호
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• pp.72-78
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• 2014

A hybrid particle-mesh method as the combination between the Vortex-In-Cell (VIC) method and penalization method has been achieved in recent years. The VIC method, which is based on the vorticity-velocity formulation, offers particle-mesh algorithms to numerically simulate flows past a solid body. The penalization method is used to enforce boundary conditions at a body surface with a decoupling between body boundaries and computational grids. The main advantage of the hybrid particle-mesh method is an efficient implementation for solid boundaries of arbitrary complexity on Cartesian grids. However, a numerical simulation of flows in large domains is still not too easy. In this study, a multi-domain approach is thus proposed to further reduce computation cost and easily implement it. We validate the implementation by numerical simulations of an incompressible viscous flow around an impulsively started circular cylinder.

• 천문학회보
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• 제37권1호
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• pp.67.1-67.1
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• 2012

Shocks are evolved when the relativistic jets in active galactic nuclei (AGNs), black hole binaries, supernova remnants (SNR) and gamma-ray bursts (GRBs) interact with the surrounding medium. The high energy particles are believed to be accelerated by the diffusive shock acceleration and the strong magnetic field is generated by Weibel instability in the shock. When ultrarelativistic electrons with strong magnetic field cool by the synchrotron emission, the radiation is observed in gamma-ray burst and the near-equipartitioned magnetic field in the external shock delays the afterglow emission. In this paper, we performed the 3D particle-in-cell (PIC) simulations to understand the characteristics of these relativistic shock and particle acceleration. Forward and reverse shocks are shaped while the unmagnetized injecting jet interacts with the unmagnetized ambient medium. Both upstream and downstream become thermalized and the particle accelerations are shown in each transition region of the shock structures.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3197-3202
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• 2007

An analysis program for pedestrian flow has been developed to investigate the flow patterns of passenger in railway stations. Analysis algorithms for pedestrian flow based on DEM(Discrete Element Method) are newly developed. There are lots of similarity between particle-laden two phase flow and passenger flow. The velocity component of 1st phase corresponds to the unit vector of calculation cell, each particle to passenger, volume fraction to population density and the particle velocity to the walking velocity, etc. And, the walking velocity of passenger is also represented by the function of population density. Key algorithms are developed to determine the position of passenger, population density and numbering to each passenger. By using the developed program, we compared the simulation results of the effects of the location and size of exit and elapsed time.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.407-413
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• 2011

VIC (Vortex-In-Cell) method for viscous incompressible flow is presented to simulate the wake behind a modified NACA16 foil. With uniform rectangular grid, the velocity in field is calculated using streamfunction from vorticity field by solving the Poisson equation in which FFT(Fast Fourier Transform) is combined with 2nd order finite difference scheme. Here, LES(Large Eddy Simulation) with Smagorinsky model is applied for turbulence calculation. Effective viscosity is formulated using magnitude of strain tensor(or vorticity). Then the turbulent diffusion as well as viscous diffusion becomes particle strength exchange(PSE) with averaged eddy viscosity. The well-established panel method is combined to obtain the irrotational velocity and to apply the no-penetration boundary condition on the body panel. And wall diffusion is used for no-slip condition numerical results of turbulent stresses are compared with experimental results (Bourgoyne, 2003). Before comparing process, LES(Large Eddy Simulation) SGS(Subgrid scale) stress is transformed Reynolds averaged stress (Winckelmans, 2001).

• 대한기계학회논문집A
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• 제38권7호
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• pp.751-756
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• 2014

우리 주변에는 수많은 알갱이들이 서로 상호작용하면서 운동하는 모습을 주로 볼 수 있다. 본 연구에서는 수많은 알갱이들의 접촉에 따른 동적 거동을 분석하였다. 접촉에 의한 각 요소의 거동을 해석하기 위해 이산 요소법(Discrete element method)을 사용하였다. 접촉 관계에 있어서 접촉 판별을 위해 Neighboring-Cell 알고리즘을 사용하였고, 접촉력 계산에 Hertzian contact model과 Tangential sliding friction contact 모델을 사용하였다. 수많은 알갱이의 접촉해석을 위해 GPU 기반의 병렬 프로그램을 구성하였다. 해석을 검증하기 위해서 댐 붕괴 실험을 수행하였다. 거동 종료시점에 입자들의 쌓인 형상을 시뮬레이션 결과와 비교하여 해석 프로그램의 신뢰성을 검증하였다.

• 전기학회논문지
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• 제61권12호
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• pp.1880-1885
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• 2012

Nonlinear dynamical behaviors in thermionic low pressure discharge are investigated using a particle-in-cell(PIC) simulation. An electrostatic PIC code is developed to model the plasma discharge system including the kinetic effects. The elastic collision, excitation collision, ionization collision, and electron-ion recombination collision are considered in this code. The generated electrons and ions are traced to analyze physical characteristics of the plasma. The simulation results show that the nonlinear oscillation structures are observed for cold plasma in the system and the similar structures are observed for warm plasma with a shift in values of the bifurcation parameter. The detailed oscillation process can be subdivided into three distinct mode; anode-glow, temperature-limited, and double-layer modes.

• Korea-Australia Rheology Journal
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• 제18권4호
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• pp.171-181
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• 2006

We present a short review for authors' previous work on direct numerical simulations for inertialess hard particle suspensions formulated either with a Newtonian fluid or with viscoelastic polymeric fluids to understand the microstructural evolution and the bulk material behavior. We employ two well-defined bi-periodic domain concepts such that a single cell problem with a small number of particles may represent a large number of repeated structures: one is the sliding bi-periodic frame for simple shear flow and the other is the extensional bi-periodic frame for planar elongational flow. For implicit treatment of hydrodynamic interaction between particle and fluid, we use the finite-element/fictitious-domain method similar to the distributed Lagrangian multiplier (DLM) method together with the rigid ring description. The bi-periodic boundary conditions can be effectively incorportated as constraint equations and implemented by Lagrangian multipliers. The bulk stress can be evaluated by simple boundary integrals of stresslets on the particle boundary in such formulations. Some 2-D example results are presented to show effects of the solid fraction and the particle configuration on the shear and elongational viscosity along with the micro-structural evolution for both particles and fluid. Effects of the fluid elasticity has been also presented.

• 한국진공학회지
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• 제10권1호
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• pp.112-118
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• 2001

본 논문에서는 축 방향으로 자화된 용량결합형 13.65 MHz/40 KHz RF 방전에서 Langmuir Probe, Emissive Probe를 통해 이온 전류 밀도, 전자 온도, 플라즈마 전위의 자장 의존성 및 자기 바이어스 전위를 조사하였다. 자장을 인가함으로서 실험변수 범위 내에서 최대 3배의 이온 전류밀도증가를 얻었고 점화가능한 기체 압력의 최저값을 줄일 수 있었다. 플라즈마가 자화된 경우 공간 전위는 평균적으로 감소하였고 RF 전압의 한주기 동안 시 변동폭이 크게 증가하였다. 플라즈마 전위의 자장 의존성은 Particle-in-Cell Simulation을 수행하여 실험 결과와 비교하였다. 대표적 실험 조건에서 전자 온도는 자장에 따라 약 4 eV에서 5 eV로 약간 증가하는 경향을 보였으나 방전 주파수를 40 KHz로 줄인 경우 1.8 eV에서 0.8 eV로 감소하였다. 실험 장치의 응용 예로서 플루오로 카본 가스에 의한 식각실험이 수행되었다. 자화 플라즈마의 산화막 식각속도 증가를 확인함으로서 축방향 자장이 실제 공정에 긍정정인 영향을 미침을 확인 할 수 있었다.

• International Journal of Aeronautical and Space Sciences
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• 제16권4호
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• pp.548-559
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• 2015

We performed a numerical simulation based on the two-dimensional (2-D) unsteady Euler's equation with a single-step Arrhenius reaction model in order to investigate the detonation wave front propagation of an Argon (Ar) diluted oxy-hydrogen mixture ($2H_2+O_2+12Ar$). This simulation operates in the detonation frame of reference. We examine the effect of grid size and the performance impact of integrated quantities such as mass flow. For a given set of baseline conditions, the minimal and maximum grid resolutions required to simulate the respective detonation waves and the detonation cell structures are determined. Tertiary shock wave behavior for various grids and pre-exponential factors are analyzed. We found that particle fluctuation can be weakened by controlling the mass flow going through the oblique shock waves.