• 한국추진공학회지
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• 제17권5호
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• pp.54-59
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• 2013

현재 Micro Shock Tube는 다양한 공학응용분야에 적용되고 있으며, 특히 우주항공 및 연소기술 그리고 약물전달 등의 분야에서 광범위한 잠재력을 가진 장치 중 하나이다. 그러나 Micro Shock Tube에서의 유동 특성은 작은 직경으로 인해 형성되는 매우 낮은 Reynolds Number와 높은 Knudsen Number의 영향으로 일반적으로 잘 알려진 Macro Shock Tube의 유동 특성과 상이하게 나타난다. 본 연구에서는 이러한 Micro Shock Tube의 유동 특성을 상세히 연구하기 위해 직경이 다른 두 가지 Micro Shock Tube의 실험을 수행하였다. 충격파 전파를 측정하기 위해 고압관의 파막압력 그리고 저압관의 세 지점에 센서를 설치하여 압력을 측정하고 분석하였다. 본 연구로부터, 동일한 파막압력에서 Micro Shock Tube 직경의 증가에 따라 충격파 전파속도가 증가하였고, 반사파의 영향도 더 크게 받았다.

• Tribology and Lubricants
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• 제25권5호
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• pp.305-310
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• 2009

Laser surface texturing (LST) methods are applied recently to generate micro-dimples in machine components having parallel sliding surfaces such as thrust bearings, mechanical face seals and piston rings, etc. And it is experimentally reported by several researchers that the micro-dimpled bearing surfaces can reduce friction force. Until now, however, theoretical results for various dimple parameters are not fully presented. In this paper, a commercial computational fluid dynamics (CFD) code, FLUENT is used to investigate the effect of dimple depth on the lubrication characteristics of parallel thrust bearing. The results show that the pressure, velocity and density distributions within dimples are highly affected by dimple depths and cavitation conditions. Adoption of micro-dimple on the bearing surface can reduce the friction force highly and its levels are affected by dimple depth. The numerical methods and results can be use in design of optimum dimple characteristics to improve thrust bearing performance.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.113-115
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• 2003

Droplet impinging into a cavity at micro-scale is one of important fluidic issues for microfabrications, e.g. bio-chip applications and inkjet deposition processes in the PLED panel manufacturing. The droplets generally dispensing from an inkjet head, which contains an array of nozzles, have a volume in several picoliters, while each nozzle jets the droplets into cavities with micron-meter size located on substrates. Due to measurement difficulties at micro-scale, the numerical simulation could serve as an efficient and preliminary way to evaluate the micro-sized droplet impinging behavior into a cavity. The micro-fluidic flow is computed by solving the three-dimensional Navier-Stokes equations through a finite volume discretization. The droplet front is predicted by a volume-of-fluid approach, in which the surface tension is modeled as a function of the fluid concentration. This paper discusses the influence of fluid properties, such as surface tension and fluid viscosity, on micro-fluidic characteristics at different jetting speeds in the deposition process via the proposed numerical approach.

• Steel and Composite Structures
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• 제26권4호
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• pp.421-437
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• 2018

Free vibration analysis of a three-layered microbeam including an elastic micro-core and two piezo-magnetic face-sheets resting on Pasternak's foundation are studied in this paper. Strain gradient theory is used for size-dependent modeling of microbeam. In addition, three-unknown shear and normal deformations theory is employed for description of displacement field. Hamilton's principle is used for derivation of the governing equations of motion in electro-magneto-mechanical loads. Three micro-length-scale parameters based on strain gradient theory are employed for prediction of vibrational characteristics of structure in micro-scale. The results show that increase of three micro-length-scale parameters leads to significant increase of three natural frequencies especially for increase of second micro-length-scale parameter. This result is according to this fact that stiffness of a micro-scale structure is increased with increase of micro-length-scale parameters.

• 대한기계학회논문집B
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• 제28권5호
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• pp.587-593
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• 2004

In this paper, flow characteristics of plasma flow in a micro-tube were investigated experimentally using micro particle image velocimetry(micro-PIV). For comparison, the experiments were repeated for deionized(DI) wale. instead of plasma. Both velocity profiles of plasma and do-ionized water are well agreed with the theoretical velocity distribution of newtonian fluid. We also carried out generating plasma-in-oil droplet formation at a Y-junction microchannel. In order to clarify the hydrodynamic aspects involved in plasma droplet formation, Rhodamine-B were mixed with plasma only for visualization of plasma droplet. With oil as the continuous phase and plasma as the dispersed phase, plasma droplet can be generated in a continuous phase flow at a Y-junction. For given experimental parameters, regular-sized droplets are reproducibly formed at a uniform flow conditions.

• Journal of Mechanical Science and Technology
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• 제19권2호
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• pp.664-673
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• 2005

The heat transfer characteristics of rarefied flows in a micro-actuator are studied numerically. The effect of Knudsen number (Kn) on the heat transfer of the micro-actuator flows is also examined. The Kn based on gas density and characteristic dimension is varied from near-continuum to highly rarefied conditions. Direct simulation Monte Carlo calculations have been performed to estimate the performance of the micro-actuator. The results show that the magnitude of the temperature jump at the wall increases with Kn. Also, the heat transfer to the isothermal wall is found to increase significantly with Kn.

• 공업화학
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• 제16권2호
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• pp.275-281
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• 2005

본 연구에서는 격자 볼츠만 방법 중 Scalar Passive 코드를 사용하여 미소채널 내에서의 수동형 믹서의 혼합에 대하여 계산을 수행하였다. 미소채널 내에서의 수동형 믹서의 혼합에 대하여 유선과 압력분포를 통해 혼합과 압력 강하를 물리적으로 규명하였으며, 혼합에 영향을 주는 인자에 대해서 알아보았다. 수동형 믹서의 경우 고정물의 간격보다는 고정물의 개수와 고정물의 크기가 혼합효율과 압력강하에 큰 영향을 주었다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.236-239
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• 2005

This study investigated the effect of ovariectomy (OVX) on the rat bone fur long term (22 weeks). In previous researches, there were many studies for morphology of OVX-induced osteoporotic bones based on micro-Computed Tomography (micro-CT). However, there were few studies fpr detecting and tracking changes of mechanical characteristics in the lumbar vertebrae of OVX rat fur long-term. For this study, one female Sprague-Dawley rat was used: an OVX rat. The 4th lumbar of the OVX rat was utilized as a specimen. Morphological characteristics could be investigated fur the lumbar vertebrae in an OVX rat by using in-vivo Micro-CT. An OVX rat was scanned at week 0 (just before surgery), at week 4, at week 8, at week 16 and at week 22 after surgery. Micro finite element $({\mu}FE)$ analysis was used to investigate mechanical characteristics in the lumbar vertebrae for an OVX rat.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2012년도 춘계학술대회 논문집
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• pp.193-194
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• 2012

• 대한기계학회논문집B
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• 제32권11호
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• pp.870-877
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• 2008

Numerical analysis is applied to model Pt-catalyzed reaction in a micro-scale combustor fueled by butane. The reaction constants of catalytic oxidation are determined from plug flow model with the experimental data. Orders of magnitude between the chemical reaction rate and the mass transfer rate are carefully compared to reveal which mechanism plays a dominant role in the total fuel conversion rate. For various conditions of fuel flow rate and surface temperature, the profiles of Sherwood number are investigated to study the characteristics of the mass transport phenomena in the micro-tube combustor.