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여경민 ( Kyeong-min Yeo ),서정우 ( Jung-woo Seo ),이석원 ( Suk-won Lee ),이준호 ( June-ho Yi ) 한국정보처리학회 2010 한국정보처리학회 학술대회논문집 Vol.17 No.1
평판 디스플레이(flat panel display)의 크기가 커짐에 따라 다양한 기판을 이용한 제조 방법이 개발되고 있다. 디스플레이 제조 공정 중 기판의 결함을 찾아서 분류하는 검사 시스템은 최종 제품의 품질을 결정하는 매우 중요한 부분이다. 본 연구는 머신비전 기술을 이용하여 불투명하고 반사율이 높은 기판 표면의 결함을 찾아내고, 이 결함을 스크래치(scratch), 흑결함(dark defect), 백결함(white defect)으로 분류하는 장치를 구현하는데 목적이 있다[4]. 이를 구현하기 위해 본 논문에서는 정밀 스테이지(stage)와 라인 카메라(line CCD camera)을 이용한 광학계를 활용하여 검사 시스템을 구현하였다. 구축된 시스템을 이용하여 취득한 이미지를 12 개의 영역으로 등분하여 각각의 국부 영역에 대한 문턱값 연산(thresholding)을 적용함으로써 조명의 불균일을 의한 검출 에러율을 획기적으로 낮추었다. 간단한 컴퓨터비전 알고리듬의 채용으로도 검사 시스템의 구현이 가능함을 보였다.
여경민(Kyongmin Yeo),이창훈(Changhoon Lee) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
The intermittent characteristics of fluid particle accelerations near the wall are investigated with the<br/> higher-order statistics and the probability density functions (PDF) by using a direct numerical simulation of<br/> turbulent channel flow. Also, the behaviors of acceleration associated with the coherent structures are<br/> discussed. The flatness factor of wall-normal acceleration is extremely high near the wall and it exceeds the<br/> previously reported value obtained in isotropic turbulence. The presence of the wall seems to make the<br/> accelerations more intermittent and the associated mechanism is explained with the PDFs. The skewness<br/> factor of wall-normal acceleration indicates that accelerations are associated with the streamwise vortices.
김병구(Byung-Gu Kim),여경민(Kyeongmin Yeo),이창훈(Changhoon Lee) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
We investigated modification of near-wall turbulence in the stably stratified turbulent channel flow by using direct numerical simulation. Detailed investigation revealed that the baroclinic torque plays an important role in generation and intensification of small-sized vortical structures. Thus typical length scale of vortical structures becomes smaller under stratification, whereas the length scale associated with temperature variation becomes larger. Both streamwise and spanwise component of baroclinic torque showed strongly intermittent behaviors. In addition to, streamwise baroclinic torque showed that it's non-gaussian behavior returned to like gaussian as stability was increased. As we increased stability, angle of strong vortical structure makes with the horizontal was increased in buffer layer, while decreased in the outer layer.
정재달(Jaedal Jeong),여경민(Kyongmin Yeo),이창훈(Changhoon Lee) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
Particle suspension is frequently observed in many natural flows such as in the atmosphere and the ocean as well as in various engineering flows. Recently, airborne micro or nano-scale particles in atmosphere attract much attention from environmental society since small particle cause serious environmental problems in the industrialized areas. Also, such heavy particles' behavior is quite different from its pure fluid particles because the inertia force and buoyance force acting on the heavy particles are different than those acting on fluid particles, so that heavy particles do not follow the trajectories of the fluid particle. Therefore, our studies is to investigate the characteristics of the behavior of heavy particles considering the inertia effect under gravity. However, we do not consider modification of turbulence by the particles, that is one-way interaction. We carried out direct numerical simulation of isotropic turbulence with particles under the Stokes drag assumption for a spherical particle. These results can be used in the development of a stochastic model for predicting particle's dispersion.
정재달(Jaedal Jung),여경민(Kyongmin Yeo),이창훈(Changhoon Lee) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-
Particle suspension is frequently observed in many natural flows such as in the atmosphere and the ocean as well as in various engineering flows. Recently, airborne micro or nano-scale particles in atmosphere attract much attention from environmental society since small particle cause serious environmental problems in the industrialized areas. Also, the characteristics of such heavy particles' behavior is quite different from its fluid particles because the inertia force and buoyance force acting on the heavy particles are different than those acting on fluid particles. Therefore, our studies is to investigate the characteristics of the behavior of heavy particles considering the inertia effect with or without gravity effect, but do not consider modification of turbulence by the particles, that is one-way interaction. We carried out direct numerical simulation of isotropic turbulence with particles under the Stokes drag assumption for a spherical particle. These results can be used in the development of a stochastic model for predicting particle's behavior.
조성기(Seonggee Cho),여경민(Kyongmin Yeo),이창훈(Changhoon Lee) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
The motion of small heavy particles in homogeneous isotropic turbulence in the present of gravity is investigated using Direct Numerical Simulations (DNS) at moderate Reynolds number. The Lagrangian velocity and acceleration statistics of particles and of flow for a wide range of Stokes number, defined as the ratio of the particle response time to Kolmogorov time scale of turbulence, were obtained for the direction of the gravity and normal direction, respectively. It is found that particles lose their correation faster than the case without gravity. Then, a significant increase in the average settling velocity was observed for a certain range of Stokes number. Our focus is placed on gravitational effect on very small particles. Our simulations show that as the Stokes number reduces to zero, their mean settling velocity aproaches the terminal velocity in still fluid.
정재달(Jaedal Jeong),여경민(Kyongmin Yeo),이창훈(Changhoon Lee) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
Particle-laden turbulence is frequently observed in nature such as the atmosphere and ocean, as well as in many engineering flows. Recently, as the dispersion of pollutant in environmental problem is of more interest, the study on the particle-laden turbulence is more important both for predicting the behavior of particles and for understanding the fundamental characteristics. Isotropic turbulence is a good example of turbulence for understanding its the properties because if Reynolds number is high, small scale turbulence has universal characteristics of isotropic turbulence without relevance to large scale turbulence. Thus, using direct numerical simulation of particle-laden isotropic turbulence, we investigate the correlation of fluid velocities along particle trajectories for finding fluid-particle interaction mechanism. Furthermore, the results of present study can be applied to development of a solid particle dispersion model.