• Title, Summary, Keyword: Artificial diffusion technique

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Hydrodynamic Modeling for Discharge Analysis in a Dielectric Medium with the Finite Element Method under Lightning Impulse

  • Lee, Ho-Young;Lee, Se-Hee
    • Journal of Electrical Engineering and Technology
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    • v.6 no.3
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    • pp.397-401
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    • 2011
  • The response of lightning impulse voltage was explored in dielectric liquids employing hydrodynamic modeling with three charge carriers using the finite element method. To understand the physical behavior of discharge phenomena in dielectric liquids, the response of step voltage has been extensively studied recently using numerical techniques. That of lightning impulse voltage, however, has rarely been investigated in technical literature. Therefore, in this paper, we tested impulse response with a tip-sphere electrode which is explained in IEC standard #60897 in detail. Electric field-dependent molecular ionization is a common term for the breakdown process, so two ionization factors were tested and compared for selecting a suitable coefficient with the lightning impulse voltage. To stabilize our numerical setup, the artificial diffusion technique was adopted, and finer mesh segmentation was generated along with the axial axis. We found that the velocity from the numerical result agrees with that from the experimental result on lightning impulse breakdown testing in the literature.

Image Classification Using Modified Anisotropic Diffusion Restoration (수정 이방성 분산 복원을 이용한 영상 분류)

  • 이상훈
    • Korean Journal of Remote Sensing
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    • v.19 no.6
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    • pp.479-490
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    • 2003
  • This study proposed a modified anisotropic diffusion restoration for image classification. The anisotropic diffusion restoration uses a probabilistic model based on Markov random field, which represents geographical connectedness existing in many remotely sensed images, and restores them through an iterative diffusion processing. In every iteration, the bonding-strength coefficient associated with the spatial connectedness is adaptively estimated as a function of brightness gradient. The gradient function involves a constant called "temperature", which determines the amount of discontinuity and is continuously decreased in the iterations. In this study, the proposed method has been extensively evaluated using simulated images that were generated from various patterns. These patterns represent the types of natural and artificial land-use. The simulated images were restored by the modified anisotropic diffusion technique, and then classified by a multistage hierarchical clustering classification. The classification results were compared to them of the non-restored simulation images. The restoration with an appropriate temperature considerably reduces error in classification, especially for noisy images. This study made experiments on the satellite images remotely sensed on the Korean peninsula. The experimental results show that the proposed approach is also very effective on image classification in remote sensing.

Discharge Analysis in Dielectric Media Considering Ionic Dissociation And Thermal Characteristics Employing Multiphysics Analyzing Technique (다중물리해석기법에 의한 이온의 해리 및 열특성을 고려한 유전체의 방전해석)

  • Lee, Ho-Young;Lee, Se-Hee
    • Proceedings of the KIEE Conference
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    • pp.1584-1585
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    • 2011
  • 분자의 전리(ionization)작용과 이온의 해리(dissociation)작용에 의한 유전체 내 방전해석을 위해서 전자, 양이온, 음이온의 생성과 소멸, 전자부착, 재결합 과정을 포함한 전하연속방정식, 전계에 의한 푸아송 방정식, 유전체 온도에 관한 열확산 방정식을 결합하여 해석하였다. 전계 방출 조건과 열전자 방출 조건이 경계조건으로 부여되었고 에너지 최소화 정류조건을 따르는 유한요소법(finite element method)을 이용하여 해석하였다. 비교적 작은 값을 가지는 확산성을 무시하고 대류성에 역점을 두어 발생하는 수치적 불안정은 인공확산항(artificial diffusion technique)을 도입하여 안정화하였다. 본 논문에서는 IEC standard 60897의 표준규격에 따른 2차원 축대칭 침-구 전극에 적용하여 제안된 다중물리해석기법의 타당성을 입증하였다.

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PIV measurement of oscillatory flow in a micro-channel as a bronchiole model

  • LEE Won-je;KAWAHASHI Massaki;HIRAHARA Hiroyuki
    • 한국가시화정보학회:학술대회논문집
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    • pp.125-134
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    • 2004
  • The improvement of artificial respiration method has brought about the decrease in mortality of pulmonary diseases patients. Various respiratory curative methods, inclusive of HFOV (High Frequency Oscillatory Ventilation), have been developed for more effectual and less harmful management of acute respiratory failure. However, the mechanism of gas transfer and diffusion in a bronchiole has not yet been clarified in detail. As a first approach to the problem, we measured oscillatory flows in a Y-shaped micro-channels as bronchiole model by micro Particle Image Velocimetry(micro PIV). In order to establish the fundamental technique of PIV measurements on oscillatory air flow in a micro-channel, we used about 500-nm-diameter incense smoke particles, a diode laser, a high speed camera including an objective lens, and a HFOV, which is effective technique for medical care of pulmonary disease patients, especially, infants. The bronchiole model size is that parent tube is $500\{mu}m$ width and $500\{mu}m$ depth, and daughter tubes are $450\{mu}m$ width and $500\{mu}m$ depth. From this study made on the phenomenon of fluid in micro size bronchus branch of a lung, we succeeded to get time series velocity distribution in a micro scale bronchial mode. The experimental results of velocity distribution changing with time obtained by micro PIV can give fundamental knowledge on oscillatory airflow in micro-channel.

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Analysis of Space Charge Propagation in a Dielectric liquid Employing Field-Thermal Electron Emission Model and Finite Element Method (유한요소법과 전계-열전자 방출 모델에 의한 절연유체 내 공간전하 전파해석)

  • Lee, Ho-Young;Lee, Se-Hee
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.58 no.10
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    • pp.2011-2015
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    • 2009
  • In an insulating dielectric liquid such as transformer oil, space charge injection and propagation were analyzed under the Fowler-Nordheim and Richardson-Dushman's thermal emission charge injection conditions for blade-plane electrodes stressed by a step voltage. The governing equations were composed of all five equations such as the Poisson's equation for electric fields, three continuity equations for electrons, negative, and positive ions, and energy balanced equation for temperature distributions. The governing equations for each carrier, the continuity equations, belong to the hyperbolic-type PDE of which the solution has a step change at the space charge front resulting in numerical instabilities. To decrease these instabilities, the governing equations were solved simultaneously by the Finite Element Method (FEM) employing the artificial diffusion scheme as a stabilization technique. Additionally, the terminal current was calculated by using the generalized energy method which is based on the Poynting's theorem, and represents more reliable and stable approach for evaluating discharge current. To verify the proposed method, the discharge phenomena were successfully applied to the blade~plane electrodes, where the radius of blade cap was $50{\mu}m$.

Explanation of Foaming Mechanism and Experimental Application of Foam Reduction Techniques in the Treated Wastewater Outlet of Wastewater Treatment Plant Connected to a Tidal River, Korea (감조하천에 연결된 하수처리장 방류구의 거품 형성기작 해석 및 거품발생 저감기술의 실험적 현장적용)

  • Shin, Jae-Ki;Cho, Youngsoo;Kim, Youngsung;Kang, Bok-Gyoo;Hwang, Soon-Jin
    • Korean Journal of Ecology and Environment
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    • v.49 no.3
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    • pp.187-196
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    • 2016
  • This study was performed to improve the foaming generated in the effluent of wastewater treatment plant from March 2015 to July 2016. The main cause of foaming was air entrainment by an impinging jet and the internal accumulation by the diffusion barrier. Particularly, the foam growth was most active when there is low tide and larger discharge. To solve this problem, we experimented after installing fine mesh screen and the artificial channel device with underwater discharging outlet in the treated wastewater discharge channel and the outlet, respectively. As a result, the effects of foam reduction by devices ranged 85.0~92.0% and 70.7~85.6%, respectively. In addition, the foam and the noise were easily solved, first of all look to contribute to the prevention of complaints. Our device studies were applied to a single wastewater treatment plant. However, it is considered to be able to apply in other similar cases of domestic sewage treatment plants.