• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2648-2653
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• 2007

Recently, increasing demand on not only lighter but also extremely mobile battery make micro fuel cell device very attractive alternative. By reducing the size of fuel cell, surface tension becomes dominant factor with minor gravitational effect. Therefore, it is very difficult to detach the $CO_2$ bubble generating on a cathode side in ${\mu}DMFC$ (micro direct methanol fuel cell). The degassing of a $CO_2$ bubble has drawn quite attention especially for ${\mu}DMFC$ due to its considerable effect on overall machine performance. Our attention has been paid to the dynamic behavior of immiscible bubble attached to the one side of the wall on 2D rectangular channel subject to external shear flow. We use Level Contour Reconstruction Method (LCRM) which is simplified version of front tracking method to track the bubble interface motion. Effects of Reynolds number, Weber number, advancing/receding contact angle and property ratio on bubble detachment characteristic has been numerically identified.

• Tribology and Lubricants
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• v.19 no.3
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• pp.159-166
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• 2003

This research for replacement of chlorine or sulfur based EP(extreme pressure) -additives which is restricted materials by environmental regulation. The subject of this study is as follows, 4-ball test and friction coefficient test were experimented in accordance with temperature and velocity, compounding with several organic or inorganic metallic elements. After 4-ball test, wear area of steel ball was analysed by SEM-EDX. As the analysis, organic and inorganic elements make a effect for extreme pressure lubricity. It is shown that the friction coefficient of lubricant which includes chlorine or sulfur additives, the scoring phenomenon is found accord-ing to temperature and the scuffing phenomenon at 200$^{\circ}C$. Applying to Na, P, S, Zn, Ca based on inorganic and organic elements, the result showed that friction coefficient is decreased more and more, as increasing temperature of lubricant. The additive based on S, Cl, P elements is effect far extreme pressure in the sample#1 and Na, P, S, Zn, Ca in sample #2. These elements are environmental contaminants and S, Cl based on EP additives which are very popular in domestic industry, when they are properly composed with non-chlorine based on additives and Na, P, S, Zn, Ca organic or inorganic elements. It is showed that lubricity and excellent anti-wear properties.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.4
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• pp.2330-2334
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• 2014

In this study, we confirmed the frequency characteristics of planar spiral inductor based on non-contact method AC coupling for wireless signal transmission. The dielectric constant variation of the substrate does not directly effect the inductance of device but effect the electrostatic capacity of device. Therefore, its change self-resonance frequency. The thickness increment of the substrate increase inductance but decrease self-resonance frequency. Because, the thickness decrement of the substrate make the inside electrostatic capacity increment.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.1
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• pp.101-108
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• 2011

Understanding the exhaust gas recirculation (EGR) cooler fouling in diesel engine is important factor in the durability characteristic of a EGR system. We develope a test rig and PM feeder using carbon black to examine the effect of fouling on EGR cooler devices those were consisted of flat and shell & tube type. The EGR cooler fouling process is a complex interaction involving heat exchanger shape, boundary condition, constitutes, chemistry and operating mode. As the soot deposited to EGR cooler, these formed a thin deposit layer that was less heat exchange than the fresh status of tube enclosing the exhaust gas, resulting in lower heat exchange effectiveness in both type coolers. But these deposits caused different results in pressure drop, it is increased in flat type, but decreased in Shell & tube type of EGR cooler. A cause was estimated from a change of the flow structure and a decrease of contact area as the EGR cooler fouling.

• Journal of the Ergonomics Society of Korea
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• v.19 no.2
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• pp.63-74
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• 2000

This paper is to clarify a thermal physiological index that can account for the effects of local thermal environment. For this purpose two young female subjects exposing themselves to the above while sitting on a chair, sitting on the floor and lying on the floor were measured. These three representative postures accompanied the different contact surface areas, thereby the heat conduction rate between the floor and subject was quantitatively measured for each posture. It made the present study deal with the effect of heat conduction concerning the modified mean skin temperature and finally propose new weighting coefficients for the mean skin temperature calculation based on the Hardy & DuBois' formulas. In order to verify the proposed model, the experiment was carried out using a floor heating system. The comparison between the experimental result and prediction revealed that the proposed model should be about 10% more accurate than the conventional one in the case of lying on the floor which the heat conduction effect becomes important.

• The Journal of Korea Robotics Society
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• v.12 no.3
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• pp.332-338
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• 2017

As an interpretation of existing jamming effects, the main variables affecting the increase in stiffness due to jamming are known as system density, jamming density, pressure, and particulate temperature. The main variable, jamming density, is closely related to the distribution of particle size and contact properties such as particle shape and friction. However, the complexity of these variables makes it difficult to fully understand the mechanism of the jamming effect. In this paper, we focus on the jamming effects of particles that have more elastic properties than particles such as sand and coffee powder, which are commonly used as constituent particles of existing jamming, in order to reduce complicated factors such as temperature and concentrate on jamming effects based on elastic characteristics of particles. It was experimentally explored the possibility of increasing stiffness by mixing particles of different sizes rather than simply increasing the bending stiffness by controlling the particle size. Through simulations and experiments, we found a case where the stiffness of each particle size distribution is larger than the stiffness of each particle size.

• Journal of Electrical Engineering and Technology
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• v.12 no.2
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• pp.944-949
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• 2017

Recently, the demand of maglev systems in the manufacturing industry for LCD and OLED display panels, which are required to be very clean and possess vacuum systems, has been increasing due to their characteristics such as being non-contact, noise free and eco-friendly. However, it is still a challenge to simultaneously control both the propulsion and levitation for their interactive effect difficult to be exactly measured. In this paper, we proposed a new tuning method for controlling the magnetic levitation force robustly against the levitation disturbance caused by a propulsion system, based on LQ servo optimal control. The disturbance torque of the LSM propulsion system is calculated through FEM analysis in such a way that the LQ servo controller is determined in order to minimize the effect of the disturbance. The robust performance of the proposed LQ servo control method for the in-track type magnetic levitation systems is demonstrated via simulations and experiments.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.12
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• pp.1251-1256
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• 2015

This study investigates the friction noise characteristic in relation to the corrosion of metal by using the frictional reciprocating and pin-on-disk system. From the experiments, it is found that the corrosion of metal advances the onset time and increases the magnitude of friction noise. Further, it is observed that the effect of corrosion on friction noise stems from the alteration of tribo-surface during repetitive frictional motion. The alteration of the corrosive contact surface induces a negative friction-velocity slope, by which the corrosion of metal can generate dynamic instability faster than non-corrosion of metal.

• Geomechanics and Engineering
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• v.11 no.2
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• pp.197-209
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• 2016

Clayey rock has large clay mineral content. When in contact with water, this expands considerably and may present a significant hazard to the stability of the rock in geotechnical engineering applications. This is particularly important in the present work, which focused on mitigating some unwelcomed properties of clayey rock. Changes in its physical properties were simulated by subjecting the rock to a low voltage direct current (DC) using copper, steel and aluminum electrodes. The modified mechanism of the coupled electrical and chemical fields acting on the clayey rock was analyzed. It was concluded that the essence of clayey rock electrochemical modification is the electrokinetic effect of the DC field, together with the coupled hydraulic and electrical potential gradients in fine-grained clayey rock, including ion migration, electrophoresis and electro-osmosis. The aluminum cathodes were corroded and generated gibbsite at the anode; the steel and copper cathodes showed no obvious change. The electrical resistivity and uniaxial compressive strength (UCS) of the modified specimens from the anode, intermediate and cathode zones tended to decrease. Samples taken from these zones showed a positive correlation between electric resistivity and UCS.

• Journal of rehabilitation welfare engineering & assistive technology
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• v.2 no.1
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• pp.19-25
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• 2009

Pes planus is a condition where the arch of the foot collapses and comes in contact with the ground. The purpose of study was to confirm the effect of a patient-customized insole on both feet velocity of pes planus with and without the insole, in order to establish both feet velocity as a rehabilitation evaluation factor of pes planus in future. As a result, the average velocity shifts of both feet showed that left foot is 2.96%, right foot is 1.09% via gait experiment with 13 pes planus patients with and without insole. Therefore this study verified that the patient-customized insole effects on both feet velocity of pes planus. However further study needs to demonstrate both feet velocity as a rehabilitation evaluation factor in pes planus.