• Journal of Electrical Engineering and Technology
• /
• 제10권2호
• /
• pp.647-652
• /
• 2015

A fully coupled finite element analysis (FEA) technique was developed for analyzing the discharge phenomena and dielectric liquid flow while considering surface charge density effects in dielectric flow guidance. In addition, the simulated speed of surface charge propagation was compared and verified with the experimental results shown in the literature. Recently, electrohydrodynamics (EHD) techniques have been widely applied to enhance the cooling performance of electromagnetic systems by utilizing gaseous or liquid media. The main advantage of EHD techniques is the non-contact and low-noise nature of smart control using an electric field. In some cases, flow can be achieved using only a main electric field source. The driving sources in EHD flow are ionization in the breakdown region and ionic dissociation in the sub-breakdown region. Dielectric guidance can be used to enhance the speed of discharge propagation and fluidic flow along the direction of the electric field. To analyze this EHD phenomenon, in this study, the fully coupled FEA was composed of Poisson's equation for an electric field, charge continuity equations in the form of the Nernst-Planck equation for ions, and the Navier-Stokes equation for an incompressible fluidic flow. To develop a generalized numerical technique for various EHD phenomena that considers fluidic flow effects including dielectric flow guidance, we examined the surface charge accumulation on a dielectric surface and ionization, dissociation, and recombination effects.

• 전기학회논문지
• /
• 제56권1호
• /
• pp.117-122
• /
• 2007

LB method is one of the most interesting technique to arrange certain molecular groups at precise position relative to others. Also, the LB deposition technique can fabricate extremely thin organic films with a high degree of control over their thickness and molecular architecture. In this way, new thin film materials can be built up at the molecular level, and the relationship between these artificial structures and the properties of materials can be explored. In this paper, evaluation of physical properties was made for dielectric relaxation phenomena by the detection of the surface pressures and displacements current on the monolayer films of phospolipid monomolecular DLPC. Lipid thin films were manufacture by detecting deposition for the accumulation and the current was measured after the electric bias was applied across the manufactured MIM device. It is found that the phospolipid monolayer of dielectric relaxation takes a little time and depend on the molecular area. When electric bias is applied across the manufactured MIM device by the deposition condition of phospolipid mono-layer, it wasn't breakdown when the higher electric field to impress by increase of deposition layers.

• Nuclear Engineering and Technology
• /
• 제34권4호
• /
• pp.396-405
• /
• 2002

An experimental study on counter-current flow limitation phenomena in narrow annular passages was carried out The gap sizes tested were 1, 2 and 3 mm. This is very small compared with the outer diameter of the annular passage, 500 mm. It was visually observed that a CCFL might occur in some part of the periphery while the other part is remained in a counter current flow pattern. That is, non-uniform behaviour of fluids due 4o a 2-dimensional effect appear in a large diameter facility. Because of this non-uniformity, a CCFL is defined in the present work as the situation where net water accumulation is sustained. That is, some amount of water should not be allowed to penetrate the gap and accumulate over the gap at CCFL criterion. The measured data are presented in the form of Wallis＇type correlation with characteristic length of gap size. It was found that the present correlation is in good agreement with other empirical correlation based on measurements whose test section diameter is close and the gap size is much larger than that of the present test section.

• Tribology and Lubricants
• /
• 제34권6호
• /
• pp.292-299
• /
• 2018

The objective of this research is to investigate the impact of engine oil aging on PM(Particulate Matter), exhaust gases, and DPF. It is widely known that the specification of a lubricant and its consumption in an ICE considerably influences the release of regulated harmful emissions under normal engine operating conditions. Considering DPF clogging phenomena associated with lubricant-derived soot/ash components, a simulated aging mode is designed for DPF to facilitate engine dynamometer testing. A PM/ash accumulation cycle is developed by considering real-world engine operating conditions for the increment of engine oil consumption and natural DPF regeneration for ash accumulation. The test duration for DPF aging is approximately 300 h with high- and low-SAPs engine oils. Detailed engine lubricant properties of new and aged oils are analyzed to evaluate the effect of engine oil degradation on vehicle mileage. Furthermore, physical and chemical analyses are performed using X-CT, ICP, and TGA/DSC to quantify the engine oil contribution on the PM composition. This is achieved by sampling with various filters using specially designed PM sampling equipment. Using high SAPs engine oil causes more PM/ash accumulation compared with low SAPs engine oils and this could accelerate fouling of the EGR in the engine, which results in an increase in harmful exhaust gas emissions. These test results on engine lubricants under operating conditions will assist in the establishment of regulated and unregulated toxic emissions policies and lubricant quality standards.

• 한국수자원학회논문집
• /
• 제57권1호
• /
• pp.35-44
• /
• 2024

댐유입량 예측에 대하여 데이터 기반 머신러닝 및 딥러닝(Machine Learning & Deep Learning, ML&DL) 분석도구들이 공개되어 다양한 분야에서 ML&DL의 적용연구가 활발히 진행되고 있으며, 모델의 자체 성능향상 뿐만 아니라 모델의 특성을 고려한 데이터의 전처리도 댐유입량을 정확하게 예측하게 하는 중요한 모델성능 향상의 요소라고 할 수 있다. 특히 기존 강우자료는 적설량을 열선 설비를 통하여 녹여 강우량으로 환산되어 있으므로, 융적설에 따른 강우와 유입량의 상관관계를 왜곡하게 된다. 따라서 본연구에서는 소양강댐과 같이 융적설의 영향을 받는 댐유역에 대한 댐일유입량 예측시 겨울에 강설량이 적설이 되어 적게 유출되는 현상과, 봄에 융설로 인하여 무강우나 적은 비에도 많은 유출이 일어나는 물리적 현상을 ML&DL모델로 적용하기 위하여 필요한 강우 데이터의 전처리에 대한 연구를 수행 하였다. 강우계열, 유입량계열을 조합하여 3가지 머신러닝(SVM, RF, LGBM)과 2가지 딥러닝(LSTM, TCN) 모델을 구축하고, 최적 하이퍼파라메터 튜닝을 통하여 적합 모델을 적용하고 한 결과, NSE 0.842~0.894로 높은 수준의 예측성능을 나타내었다. 또한 융적설을 반영한 강우보정 데이터를 만들기 위하여 융적설 모의 알고리즘을 개발하고, 이를 통하여 산정된 보정강우를 머신러닝 및 딥러닝 모델에 적용한 결과 NSE 0.841~0.896 으로 융적설 적용전과 비슷한 높은 수준의 예측 성능을 나타내었으나, 융적설 기간에는 조정된 강우로 학습되어 예측되었을 때 실측유입량에 근접하는 모의결과를 나타내었다. 결론적으로, 융적설이 영향을 미치는 유역에서의 데이터 모델 적용시에는 입력자료 구축시 적설 및 융설이 물리적으로 타당한 강우-유출 반응에 적합하도록 전처리과정이 중요함을 밝혔다.

• 대한기계학회논문집A
• /
• 제23권6호
• /
• pp.881-894
• /
• 1999

Cylindrical plunge grinding is widely used for final machining process of precision parts such as automobile, aircraft, measurement units. But in order to make parts which have high precision accuracy and high surface integrity, it is necessary to consider grinding characteristics due to accumulation phenomena of grinding wheel in plunge grinding process. In this study, in order to examine closely plunge grinding process, grinding power, grinding force, real depth of cut are monitored in transient state, steady state and spark out state. As the result, it is shown that grinding power and force are affected by dressing condition, depth of cut and speed ratio and that there exist threshold grinding force and it also affected by dressing condition. Also considered effects of grinding conditions on surface roughness and roundness of workpiece

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 1998년도 추계학술대회 논문집
• /
• pp.211-214
• /
• 1998

DC breakdown characteristics and formation of space charge at the interfaces of crosslinked polyethylene (XLPE) /ethylene propylene diene terpolymer (EPDM) laminates were studied. Effects of silicone grease and some chemicals such as crosslinking coagent on the interfacial charge were also studied. Interfacial charge develops at the interface of XLPE/EPDM laminates, which changes depending on heat treatment conditions and types of chemicals coated at the interface. Some chemicals such as maleic anhydride reduce the accumulation of interfacial charge in the XLPE/EPDM laminates. Breakdown strength of EPDM/XLPE laminate through the interface was highest when silicone oil was pasted in the interfaces. Interfacial breakdown strength decreased with the increase of MAH content.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2002년도 하계학술대회 논문집 Vol.3 No.2
• /
• pp.927-930
• /
• 2002

The HFPD measurement method is a technique to analyze aging state of high voltage insulation materials and detect higher frequency signals than conventional PD measurement method therefore it takes less noise effect and could execute active line measurement. It is possible to analyze main discharge phenomena and obtain access to aging progress occurred in insulation materials through accumulation of HFPD signals during determined interval and expression of fractal dimension using statistical process of accumulated signals. In this study, the statistical parameters (skewness & kurtosis) and fractal dimensions are changed by discharge patterns that is shown up different characteristics with applied voltages and times.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2010년도 하계학술대회 논문집
• /
• pp.94-94
• /
• 2010

The result was estimated on the fractal characteristics as possibilities of identification of manufacture state for long period stabilities. At the second, the dangerous area was easily found to the recurrent phenomena of FD output. However, such area is very difficult to analysis of mechanism and to predict the lifetime in present state, it is possible to discriminate by means of data accumulation.

• 한국기계가공학회지
• /
• 제8권4호
• /
• pp.1-6
• /
• 2009

Air drying technology was developed as an equipment for reducing of moisture content from wastewater treatment and waterworks sludge cake and reproducing it by reusable matter. Advantage of cyclone type pneumatic dehydrator is simple and excellent drying performance. The air drying equipment was composed to the air ejector which made high-speed fluid field, and cyclone which made circling fluid field. Dewatered cake was crushed at the high-speed zone as first step, and formed with dried powder of sphere shape by the collision between particles at the circling fluid zone. In this study, a CFD analysis has been performed to predict air-sludge particles flow in cyclone and ejector of pneumatic dehydrator. The computational results showed typical Rankine vortex structure which was frequently found in swirling flow phenomena. And the conical type wedge in lower part of a cyclone prevented accumulation of the sludge particles in the cyclone. Therefore, this technology was effective in drying of dehydrated cake of waterworks sludge.