• Journal of Power System Engineering
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• v.18 no.5
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• pp.74-79
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• 2014

This article aims at investigating the effect of applied load and sliding speed on wear behavior of thermally spraryed STS316 coating. STS316 coatings were fabricated by flame spray process according to optimal parameters on steel substrates. Dry sliding wear tests were performed on STS316 coating using four different applied load as 10, 15, 20 and 25 N and four different sliding speed as 15, 30, 45 and 60 rpm. Wear behavior on worn surface was investigated using scanning electron microscope(SEM) and energy disperive X-ray spectroscopy(EDS). The dominant wear mechanism of STS316 coating under low applied load and sliding speed was oxidation on worn surface. However, under high applied load and sliding speed the principal wear mechanism was abrasion on oxidation film and damage of oxidation film.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1992.11a
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• pp.31-37
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• 1992

금형을 이용하는 소성가공에서는 형 사이에서 셩형되는 소재가 소성변형되지만 이때 소재는 형의 표면을 따라 미끄러지면서 유동하므로 형재료와 소재간에는 큰 마찰력이 작용하고, 형재료는 이 마찰력에 의하여 전단응력이 작용하게 된다. 따라서 이러한 전단응력이 반복하여 작용하는 프레스가공 등에서는 형의 수명이 항상 문제가 된다. 물론 형의 수명은 형재료가 프레스압력에 견디지 못하여 형이 균열되거나 펀치가 절단되는 것 같은 형재료의 강인성이 불충분하기 때문에 비교적 조기에 일어나는 파손에 의하여 수명의 대상으로 되는 경우도 있지만 무엇보다도 형의 수명을 죄우하는 가장 중요한 사항은 형재료의 내마멸성이다. 따라서 본 연구에서서는 이들 제인자를 고려하여 Die 및 Punch의 재료로 널리 사용되는 냉간성형용 Die강인 STD 11의 마멸특성을 알기 위하여 미끄럼 속도, 접촉압력 및 미끄럼 거리등을 변화시켜 내마멸성을 나타내는 최적사용조건을 찾고자 하는 것을 목적으로 하였다.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.2011-2016
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• 2004

In order to develop a high efficiency fire pump, its performance characteristics with various operating conditions are investigated. The governing equations are derived from making using of three-dimensional Navier-Stokes equations with the standard ${\kappa}-{\varepsilon}$ turbulence model and SIMPLE algorithm. Using a commercial code, CFX, pressure distribution and flow fields in a fire pump are calculated with various ranges of rotating speed 800-2400 rpm. Particularly, calculations with multiple frames of reference method between the rotating and stationary parts of the domain are carried out. With the help of numerical results, correlation formula between the casing pressure and the efficiency is derived.

• International Journal of Highway Engineering
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• v.10 no.2
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• pp.125-133
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• 2008

Achieving consistent geometric design is an important goal in highway design to ensure obtaining safe, economical and smooth traffic operation. Most evaluation of consistency is based on 'speed change' in speed profile. According to literature, the speed depends on geometric elements, speed on tangent section prior to a curve, and background around roads. Especially, the radius is the most main element mentioned in various literature. Therefore, this paper shows two ways of calculating horizontal radius on real road, that is, three-dimensional road. First of all, the radius of horizontal curve is calculated based on physical method. The calculated radius contains not only superelevation but also longitudinal grade while the current minimum radius is calculated by considering superelevation and side friction according to the point-mass equation. Secondly, the problem of composed curves with distorted appearance by overlaying sag or crest vertical alignment has been known. To quantify the extent of distortion effects, the method of calculation of real seen so called 'Perspective Radius' is developed. The paper presents the perspective radius and recommended perspective radius.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1989.06b
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• pp.48-59
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• 1989

최근 터어보 샤프트, 터어보 팬, 터어보 쳇트 엔진, 가스 터어빈, 공작기계의 주축, 그리고 섬유기계 섬유봉등의 회전기계류 설계에서 단위 무게당 출력의 비율을 높이기 위해서 회전속도의 고속화가 요구되고 있다. 이러한 경우 회전축계의 진동특성에 크게 영향을 미치는 감쇠특성을 부각시키기 위하여 베어링의 외부에 스퀴즈-필름 댐퍼 (Squeeze-film Damper)를 부가하고 회전축계를 유연하게 지지하여 줌으로써 진동문제를 간단히 해결하며 회전속도의 고속화를 가능하게 할 수 있다. 적합하게 설계된 스퀴즈-필름 댐퍼의 잇점은 다음과 같다. (a) 회전축의 위험속도를 작은 공진쪽으로서 통과하는 것이 가능. (b) 베어링과 지지구조물에 전달되는 하중이 감소 (c) 장기간 사용중, 마모 및 브레이드 파손에 의해 진폭이 증가된 불평형 강제진동에서도 안정된 운전이 가능 (d) 미끄럼 저어널 베어링에 지지된 회전축계의 고속회전에서 불안정한 자려진동이 나타나는 안정 한계속도를 높히는 것이 가능

• Journal of Energy Engineering
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• v.18 no.2
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• pp.87-92
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• 2009

An experimental investigation is conducted to study a 2-phase vertically upward hydraulic transport of solid particles by water and non-Newtonian fluids in a slim hole concentric annulus with rotation of the inner cylinder. Rheology of particulate suspensions in viscoelastic fluids is of importance in many applications such as particle removal from surfaces, transport of proppants in fractured reservoir and cleaning of drilling holes, etc. In this study, a clear acrylic pipe was used in order to observe the movement of solid particles. Annular velocities varied from 0.3 m/s to 2.0 m/s. The mud systems included fresh water and CMC solutions. Main parameters considered in the study were inner-pipe rotation speed, fluid flow regime and particle injection rate. A particle rising velocity and pressure drop in annulus have been measured for fully developed flows of water and of aqueous solutions. For both water and 0.2% CMC solutions, the higher the concentration of the solid particles is, the larger the pressure gradients become.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.1
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• pp.179-186
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• 2002

The absolute longitudinal speed of a vehicle is estimated by using vehicle acceleration data from an accelerometer and wheel speed data from standard 50-tooth antiknock braking system wheel speed sensors. An intuitive solution to this problem is, "When wheel slip is low, calculate absolute velocities from the wheel speeds; when wheel slip is high, calculate absolute velocity by integrating the accelerometer." Fuzzy logic is introduced to implement the above idea and a new algorithm of "modified velocities with step integration" is proposed. This algorithm is verified experimentally to estimate speed of a vehicle, and is also shown to estimate absolute longitudinal vehicle speed with a 6% worst-case error during a hard braking maneuver lasting three seconds.

• Journal of the korean Society of Automotive Engineers
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• v.5 no.3
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• pp.56-63
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• 1983

강성체로된 견인물체가 탄성무한경면으로 지지된 점탄성층 위를 미끄러져 갈 때 접촉구간에서의 압력분포와 마찰 특성을 고찰하였다. 즉, 접촉구간에서의 강성체의 모양과 압력분포에 관한 적분 방정식을 구하고, 점탄성층의 두께가 접촉구간에 비하여 충분히 두꺼울 때 압력분포와 마찰계 수의 근사해를 구하였다. 압력분포의 모양은 점탄성층의 물성을 표시하는 지수값, 즉 .alpha.<1/2, .alpha.=1/2, .alpha.>1/2에 따라서 크게 다르다. 한편, 수치해석에 의하면 마찰 계수에 대한 근 사해는 강성체의 미끄럼 속도, 점탄성 층의 두께, 탄성체의 영율 (E$_{o}$ )과 점탄성층의 시효 성탄성계수 (E$_{v}$ )의 차, 즉 E$_{o}$ /E$_{v}$ 에 따라 변화함을 알 수 있다. 즉, 탄성체가 점탄성층에 비하여 딱딱하면 할수록, 또 강성체 속도가 느리면 느릴수록 마찰계수는 작아진다. 그리고 불성의 지수(.alpha.)가 커지면 커질수록 근사해의 수렵 속도는 느려지게 되고 지 수(.alpha.)가 1에 가까워지면 점탄성층의 탄성효과는 점성효과에 비하여 거의 무시할 수 있으며 근사해는 의미가 없어지게 된다.

• Tribology and Lubricants
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• v.25 no.1
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• pp.25-30
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• 2009

본 연구에서는 pin-on-disk 마찰 시험기를 통하여 Hexagonal 배열 $40{\mu}m$ Dimple 패턴의 효과를 실험하였다. 마찰 실험은 미끄럼 속도가 $0.06{\sim}0.34m/s$로 하였으며 마찰하중은 $20{\sim}100\;N$의 범위로 하였고, Dimple의 밀도는 $10{\sim}25%$의 범위로 제작하여 실험을 행하였다. 일반적으로 속도가 증가하고 하중이 감소할수록 마찰계수는 감소하는 경향을 나타내었으며, Dimple에 의한 마찰저감 효과는 속도가 $0.14{\sim}0.26m/s$의 범위에서 나타났다. $40{\mu}m$ Hexagonal 배열 Dimple 패턴의 마찰 특성에서는 밀도가 12.5%에서 가장 좋은 경향을 나타내었다.

• International Journal of Highway Engineering
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• v.11 no.2
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• pp.1-15
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• 2009

Surface of exposed aggregate concrete pavements is consists of exposed coarse aggregate by removing upper 2$\sim$3mm mortar of concrete slab. Exposed aggregate concrete pavements have advantages of maintaining low-noise and adequate skid-resistance level during the performance period. In order to provide the successful exposed concrete aggregate pavement, uniform distribution of the coarse aggregate on pavement surface through adequate the mix design and exposing method. The mix design in concrete pavement is generally designed on the basis of strength, but mix design of exposed aggregate pavement employed in this study includes the consideration of noise and skid resistance, as well as strength. Smaller of maximum coarse aggregate is known to be effective for reduce noise level. Optimum mix design and exposing method of fine-size exposed aggregate portland cement concrete pavement that can reducing the noise and maintain the adequate level of skid resistance are proposed in this study. To consider the variation of optimum exposing time due to the hardening speed of mortar by climatic condition, quantitative is also suggested measurement of hardening state.