• Tribology and Lubricants
• /
• 제38권6호
• /
• pp.281-286
• /
• 2022

In this study, the effects of Elasto-hydrodynamic lubrication pressure on the critical shoulder height of raceway in an angular contact ball bearing were investigated. Both 3D contact analyses using an influence function and the EHL analysis were conducted for the contact geometry between the ball and raceways. The pressure distributions by 3D contact analysis and EHL analysis for an example bearing were compared. The effect of ellipse truncation on the minimum film thickness also investigated from EHL analysis. The critical shoulder height in the dry contact and the EHL state were compared for various applied loads. It is shown that when the ellipse truncation occurs, the pressure spike for the EHL conjunction is higher than that for the dry contact, and its location moves more inward of the contact center. The steep pressure gradients would increase the flow rate, so in order to maintain flow continuity a significant reduction in film thickness and an abrupt rise in pressure occurs in the edge of shoulder. Significant reduction of the minimum film thickness occurs near the edge of shoulder. The critical shoulder heights in the EHL state are calculated as higher values compared with in the dry contact. This results shows that the determination of critical shoulder height by the EHL analysis is more proper.

• 한국기계연구소 소보
• /
• 통권18호
• /
• pp.163-168
• /
• 1988

Impregnation of molten thermoplastic resin into continuous unidirectional fiber bundles was investigated. The degree of impregnation is defined as the ratio between the number of impregnated fibers and the total number of fibers of a bundle. The degree of impregnation was modeled as a function of time, impregnation pressure, temperature and tow size assuming the radial inward flow through the fiber bundle is governed by the Darcy's law. The permeability was assumed to be constant. Experiments were performed to evaluate the validity of the medel. Today's T300 graphite fiber bundles and Polyetheretherketone(PEEK) resin was used. A fiber bundle and resin powder were put into a mold and pressure and temperature were applied. After a predetermined time, the sample was taken out and microphotographs of the cross-section were taken. From the microphotographs, the number of impregnated fibers was counted and then the degree of impregnation was determined. Experiments were also performed for different tow sizes. Good agreements were found between the model and the experiments rendering a confidence in the model.

• International Journal of Fluid Machinery and Systems
• /
• 제2권2호
• /
• pp.147-155
• /
• 2009

Dynamic characteristics of the clearance flow between an axially oscillating rotational disk and a stationary disk were examined by experiments and computations based on a bulk flow model. In the case without pressure fluctuations at the inlet and outlet of the clearance, parallel and contracting flow paths had an effect to stabilize the axial oscillation of the rotating disk. The enlarged flow path had an effect to destabilize the axial oscillation due to the negative damping and stiffness for outward and inward flows, respectively. It was shown that the fluid force can be decomposed into the component caused by the inlet or outlet pressure fluctuation without the axial oscillation and that due to the axial oscillation without the inlet or outlet pressure fluctuation. A method to predict the stiffness and damping coefficients is proposed for general cases when the device is combined with an arbitrary flow system.

• 한국지반공학회논문집
• /
• 제29권3호
• /
• pp.15-27
• /
• 2013

기존 성토재하 방식의 연약지반 개량공법에서 제기된 여러 가지 문제에 의해 진공압 재하방식의 개량공법이 개발되었으며, 국내 적용사례가 증가하고 있다. 현장에서의 침하관리시 동일한 하중을 재하하였을 경우의 진공압재하공법과 성토재하공법에 대한 침하량 비교 연구가 진행되어 왔다. 본 연구에서는 두 공법의 발생침하량에 관한 이론 및 사례 연구를 수행하였다. 그 결과 연약지반 개량을 위해 진공압이 적용되면 내향의 수평변위가 발생하고 동일한 하중재하 대비 침하량이 감소하였다. Hooke의 탄성이론을 바탕으로 한 경우 0.54~0.67, 국내 설계기준에서는 0.50~0.75, 과거 국내 시공사례를 바탕으로 한 경우 0.91, 실내시험을 바탕으로 한 경우 0.81, 탄성론과 체적압축계수법을 바탕으로 한 경우 0.75, 최근 국내 대심도 시공 사례의 경우 0.77~0.93의 범위를 보이는 것으로 나타났다.

• 한국환경보건학회지
• /
• 제46권1호
• /
• pp.78-87
• /
• 2020

Objectives: To identify the degree of physical burden, a determination was undertaken of dust collection efficiency, inhalation pressure, and CO₂ concentration related to health masks certified by the Ministry of Food and Drug Safety (MFDS). Methods: Twenty health masks were purchased on the market. Dust collection efficiency and inhalation pressure were determined in the same manner as in MFDS certification testing, respectively using TSI Model 8130 (TSI, U.S.) and ART Plus (Korea). CO₂ concentrations for 20 subjects using a CO₂ analyzer (G100, G150, Geotechnical Instrument Ltd., UK) were measured with a similar method as a total inward leakage test. In addition to CO₂ levels, dead space volumes in the masks was determined for predicting concentrations of CO₂ in inhalation air. Results: Most of the dust collection efficiencies found for the 20 masks were far higher than the standard. Four KF94s met KF99 and four KF80s even met KF94. Most inhalation pressures were also much lower than the standard, with many almost one-half of the standard. The mean and standard deviation of CO₂ concentration in the mask were 2.9±0.44%. Considering dead volume, the prediction for CO₂ concentration in the inhalation air was 4,395±1,266 ppm. Conclusions: For healthy men and women, the dust collection efficiency and inhalation pressure of health masks were not at a level that would affect their health. Although CO₂ levels in the inhalation air were predicted not to affect health, research on the physiological effects of health masks on Koreans is needed for more precise research.

• 한국압력기기공학회 논문집
• /
• 제7권2호
• /
• pp.26-33
• /
• 2011

To evaluate steam oxidation behaviours of Alloy 617 and Haynes 230, oxidation test were performed at $900^{\circ}C$ in steam and $steam+20\;vol.-%\;H_2$ environments. Oxidation rate in steam condition was similar to that in air for Alloy 617, while it was slightly lower for Haynes 230. When hydrogen was added to steam, oxidation rate was enhanced. Isolated $MnTiO_3$ particle were formed on $Cr_2O_3$ oxide layer and sub layer $Cr_2O_3$ were formed in steam and $steam+20\;vol.-%\;H_2$ for Alloy 617. On the other hands, $MnCr_2O_3$ layer were formed on top of $Cr_2O_3$ oxide layer for Haynes 230. The extensive sub layer $Cr_2O_3$ formation was resulted from the oxygen inward diffusion in such environments. When hydrogen was added, the oxide morphology was changed from polygonal to platelet because of the accelerated diffusion of cations under the oxide layer. In addition, decarburized zone was extended as hydrogen participated into the reactions causing carbide dissolution.

• 열처리공학회지
• /
• 제13권5호
• /
• pp.337-345
• /
• 2000

As a case hardening process for stainless steels, nitriding is more preferred and widely used than carburizing which deterioates corrosion resistance severely. In order to add the nitrogen into the stainless steels, passive film on the surface must be removed effectively before nitriding. Conventional gas nitriding process is performed in the temperature range of 500 to $600^{\circ}C$ with $NH_3$ gas, which often leads to sensitization of stainless steels. In this study, we tried to activate passive film of austenitic stainless steels by heating at low pressure. ($900^{\circ}C$, $5{\times}10^{-2}$ Torr.) Nitriding was performed at the solution treatment temperature of $1100^{\circ}C$ with nitrogen molecules instead of $NH_3$ gas. An attainable nitrogen content in a case depends on the nitrogen gas pressure at constant nitriding temperature. A case depth is proportional to the square root of solution time, which suggests that inward diffusion of nitrogen follows the Fick's 2nd law. Surface nitrogen atoms are dissolved as interstitial solutes, or precipitated in the form of MN, $M_2N$ nitrides, which increase the case hardeness. Dissolved nitrogen in the case enhances the cavitation resistance of austenitic stainless steels dramatically.

• 천문학회보
• /
• 제35권2호
• /
• pp.54-54
• /
• 2010

Interplanetary space is filled with dust particles originating mainly from comets and asteroids. Such interplanetary dust particles lose their angular momentum by olar radiation pressure, causing the dust grains to slowly spiral inward Poynting-Robertson effect). As dust particles move into the Sun under the influence of Poynting-Robertson drag force, they may encounter regions of resonance just outside planetary orbits, and be trapped by their gravities, forming the density enhancements in the dust cloud (circumsolar resonance ring). The circumsolar resonance ring near the Earth orbit was detected in the zodiacal cloud through observations of infrared space telescopes. So far, there is no observational evidence other than Earth because of the detection difficulty from Earth bounded orbit. A Venus Climate Orbiter, AKATSUKI, will provide a unique opportunity to study the Venusian resonance ring. It equips a near-infrared camera for the observations of the zodiacal light during the cruising phase. Here we consider whether Venus gravity produces the circumsolar resonance ring around the orbit. We thus perform the dynamical simulation of micron-sized dust particles released outside the Earth orbit. We consider solar radiation pressure, solar gravity, and planetary perturbations. It is found that about 40 % of the dust particles passing through the Venus orbit are trapped by the gravity. Based on the simulation, we estimate the brightness of the Venusian resonance ring from AKATSUKI's locations.

• 동아시아경상학회지
• /
• 제9권4호
• /
• pp.81-92
• /
• 2021

Purpose - Work stress environment is expanding alongside the speed of worldwide change and psychological well-being concerns are coming about because pressure over-burden can bring about lost workdays, lower representative usefulness, and high occupation turnover rates. For this reason, this study investigates to provide how practitioners can manage employee work stress using health psychology based on prior studies. Research design, Data, and methodology - Qualitative textual research involves collecting and analyzing various non-numeric data to establish different concepts or opinions in prior literature. That means that the present researcher carried out qualitative research in multiple ways, investigating many kinds of previous textual data, such as prior published peer-reviewed resources and case studies analysis. Result - The results revealed that directed symbolism has been displayed to improve prosperity and tranquility among employees with an assortment of persistent infections. Like diaphragmatic breathing, reflection practices consolidate zeroing in on a particular article or sensation (like breathing) while at the same time separating from other distracters and controlling inward encounters (for example, feelings, musings) through non-critical acknowledgment. Conclusion - This research proposes that intellectual rebuilding or figuring out how to perceive maladaptive musings and change them to reflect more versatile; judicious idea examples can fundamentally further develop temperament, diminish pressure, and reduction negative feelings for employees.

• 대한기계학회논문집B
• /
• 제24권1호
• /
• pp.75-84
• /
• 2000

Performance and flow characteristics of a small forward swept propeller fan for home refrigerators are studied experimentally. An unusual discontinuity is observed in the performance curve of the fan. Mean flow fields measured with as-hole Pitot probe reveal that the flow is axial at the high flow rate and radial at the low flow rate. The flow structure changes abruptly across the discontinuity. Unsteady flow measurements with a set of hot-wire probes indicate that near the discontinuity a single-cell stall rotates at 40% speed of the fan speed, while away from the discontinuity the flow shows periodic variation corresponding to the blade passage frequency. Phase-lock averaged flow fields measured with a triple-sensor hot-wire probe show that there appears radially inward flow over the pressure side of the blade and the outward passage flow over the tip.