• Title/Summary/Keyword: surface friction drag

검색결과 55건 처리시간 0.025초

구상 선수 주위의 유동과 기포 공급 효과에 관한 실험적 연구 (On the Variation of Resistance Components due to Air Bubble Blowing on Bulb Surface of a Ship)

  • 임근태;김효철
    • 대한조선학회논문집
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    • 제33권1호
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    • pp.54-64
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    • 1996
  • 편저형 선형의 구상 선수에서 기포를 공급하면 기포가 선저 표면에 공급되고, 기포 공급의 효과로 물과 선저 표면이 직접 접촉하는 면적이 줄어들게 되어 선박의 마찰 저항을 감소시킬 수 있을 것이다. 이를 실험적으로 확인하기 위하여 구상 선수 선형에 대하여, 우선 선수 주변에서의 한계유선을 관측하고, 국부적 압력 분포 및 마찰 응력을 계측하였다. 다음으로, 기포 공급 조건을 바꾸며 실험한 결과, 국부 표면 마찰 저항의 감소를 확인 할 수 있었다. 또한, 기포 공급시 일어나는 운동량 변화가 저항 성분이 되는 것으로 확인되었다. 이러한 실험 결과는 실용 선형에서 기포법으로 저항 감소를 얻어내기 위한 기초적 연구가 될 수 있을 것으로 판단된다.

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평판 위 흐름 Defect Law 영역의 난류 특성 연구 (Investigation of Turbulence Characteristics of Defect Law Region over Flat plate)

  • 서성부;박일룡;정광효;임정관;김광수;김진
    • 한국해양공학회지
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    • 제28권4호
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    • pp.268-273
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    • 2014
  • To investigate the turbulence characteristics within the boundary layer over a flat plate, an experimental study was performed using a PIV technique in a circular water channel. For two water velocities, 0.92 and 1.99 m/s, the water velocity profiles were taken and analyzed to determine turbulent characteristics such as the Reynolds stress, Taylor micro-length scale, and Kolmogorov length scale within the defect law region of the boundary layer. These analysis methods may be applied to research on the friction drag reduction technology using micro-bubbles or an air sheet over the surface of a ship's hull, because the physical reason for the friction drag reduction could be found by understanding the variation of the turbulence characteristics and structures in the boundary layer.

난류발생기를 가지는 원형 파이프내에서의 마찰저감 및 열전달율에 관한 실험적 연구 (Experimental Study on the Drag Reduction & Heat Transfer Ratio in the Circular Pipe with Swirl Generater)

  • 김성수;조성환;윤석만
    • 대한설비공학회:학술대회논문집
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    • 대한설비공학회 2008년도 하계학술발표대회 논문집
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    • pp.430-435
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    • 2008
  • Total lengths of domestic pipe network for district heating system are above about 2,500Km. A lots of pumping power for heat transportation through long pipe are required by the flow friction of pipe surface. Until now there have been considered about various methods to reduce the flow friction for district heating system such as using surfactants and turbulence promoters by swirl flow and baffles etc. At this study, swirl flow generator was tested about the possibility to increase the heat transfer ratio at the heat exchanger in the case which the suppling water temperature increased from $50^{\circ}C$ until $120^{\circ}C$. Experimental results showed that the heat transfer ratio increased and also pressure increase ratio increased simultaneously in the case which swirl flow generator installed. The amount of the increasing ratio for heat transfer and pressure were reached until 4.33% and 11% at the case of $120^{\circ}C$ suppling temperature which domestic district heating system were using.

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인체와 노면간의 마찰계수 추정에 관한 연구 (Estimation of Drag Factors Between Roadway Surface and Human Body)

  • 김민태;이상수;이철기
    • 한국ITS학회 논문지
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    • 제9권6호
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    • pp.54-62
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    • 2010
  • 차 대 보행자 교통사고는 다른 유형의 사고에 비해 피해가 매우 크고 사고의 비중도 높으나 사고의 특성 상 과학적 접근이 어렵다. 기존 보행자 사고에 관한 연구의 대부분은 차 대 보행자의 충돌 실험에 대한 실험식 도출에 집중되어 있고, 실험식에서 중요한 변수로 작용되는 인체 활주 마찰 계수에 대한 연구가 부족한 실정이다. 본 연구에서는 인체와 노면간의 마찰계수에 대한 현장실험을 실시하여 이에 대한 실험값을 측정하여 제시하였다. 본 연구에서 조사된 인체노면 마찰계수 값은 건조한 아스팔트 도로에서 0.59~0.62, 건조한 콘크리트 도로는 0.59~0.61로 측정되었다. 또한, 젖은 아스팔트와 콘크리트 도로에서는 각각 0.56~0.59, 0.51~0.54로 나타나 건조한 노면 상태와 비교하여 5.0%와 8.3% 감소하는 것으로 파악되었다. 도출된 마찰계수를 시뮬레이션 프로그램을 이용하여 검증한 바, 실험 수치와 시뮬레이션 결과가 유사함을 확인하였다. 본 연구결과를 활용하여 국내 교통사고 조사 시 사용되는 인체 마찰계수의 적용 값의 범위를 축소할 수 있고, 이는 사고 조사의 정확성 향상에 큰 도움을 줄 것으로 기대한다.

Bioinspired Nanoengineering of Multifunctional Superhydrophobic Surfaces

  • Choi, Chang-Hwan
    • 한국표면공학회:학술대회논문집
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    • 한국표면공학회 2015년도 추계학술대회 논문집
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    • pp.102-133
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    • 2015
  • Nature, such as plants, insects, and marine animals, uses micro/nano-textured surfaces in their components (e.g., leaves, wings, eyes, legs, and skins) for multiple purposes, such as water-repellency, anti-adhesiveness, and self-cleanness. Such multifunctional surface properties are attributed to three-dimensional surface structures with modulated surface wettability. Especially, hydrophobic surface structures create a composite interface with liquid by retaining air between the structures, minimizing the contact area with liquid. Such non-wetting surface property, so-called superhydrophobicity, can offer numerous application potentials, such as hydrodynamic drag reduction, anti-biofouling, anti-corrosion, anti-fogging, anti-frosting, and anti-icing. Over the last couple of decades, we have witnessed a significant advancement in the understanding of surface superhydrophobicity as well as the design, fabrication, and applications of superhydrophobic coatings/surfaces/materials. In this talk, the designs, fabrications, and applications of superhydrophobic surfaces for multifunctionalities will be presented, including hydrodynamic friction reduction, anti-biofouling, anti-corrosion, and anti-icing.

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표면 거칠기가 가스 포일 스러스트 베어링의 성능에 미치는 영향 (Effects of Surface Roughness on the Performance of a Gas Foil Thrust Bearing)

  • 황성호;김대연;김태호
    • Tribology and Lubricants
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    • 제39권2호
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    • pp.81-85
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    • 2023
  • This study presents an experimental investigation of the effects of surface roughness on gas foil thrust bearing (GFTB) performance. A high-speed motor with the maximum speed of 80 krpm rotates a thrust runner and a pneumatic cylinder applies static loads to the test GFTB. When the motor speed increases and reaches a specific speed at which a hydrodynamic film pressure generated within the gap between the thrust runner and test GFTB is enough to support the applied static load, the thrust runner lifts off from the test GFTB and the friction mechanism changes from the boundary lubrication to the hydrodynamic lubrication. The experiment shows a series of lift-off test and load-carrying capacity test for two thrust runners with different surface roughnesses. For a constant static load of 15 N, thrust runner A with its lower surface roughness exhibits a higher start-up torque but lower lift-off torque than thrust runner B with a higher surface roughness. The load capacity test at a rotor speed of 60 krpm reveals that runner A results in a higher maximum load capacity than runner B. Runner A also shows a lower drag torque, friction coefficient, and bearing temperature than runner B at constant static loads. The results imply that maintaining a consistent surface roughness for a thrust runner may improve its static GFTB performance.

열전달 증진을 위한 딤플형상의 최적설계 (Design Optimization of Dimple Shape to Enhance Heat Transfer)

  • 최지용;김광용
    • 유체기계공업학회:학술대회논문집
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    • 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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    • pp.285-288
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    • 2004
  • This study presents a numerical procedure to optimize the shape of dimple surface to enhance turbulent heat transfer in rectangular channel. The response surface based optimization method is used as an optimization technique with Reynolds-averaged Wavier-Stokes analysis of fluid flow and heat transfer with shear stress transport (SST) turbulence model. The dimple depth-to -dimple print diameter ratio, channel height- to- dimple print diameter ratio. and dimple print diameter-to-pitch ratio are chosen as design variables. The objective function is defined as a linear combination of heat transfer coefficient and friction drag coefficient with a weighting factor. Full factorial method is used to determine the training points as a mean of design of experiment.

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활주 직전과 제동 직전 속도의 상관관계 규명에 관한 연구 (Relationships Between Pre-Skidding and Pre-Braking Speed)

  • 류태선;전진우;박홍한;이수범
    • 대한교통학회지
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    • 제27권1호
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    • pp.43-51
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    • 2009
  • 이 논문은 타이어-노면간 마찰계수(drag factor)와 노면에 발생된 스키드마크를 통해 제동직전 속도(pre-braking speed) 산정을 정확하게 하기 위한 방법론을 제시하고자 한다. 제동직전 속도(pre-braking speed)와 활주직전 속도(pre-skidding speed)간 어떠한 상관관계가 있는지 판단하기 위해 실차 주행 및 제동실험을 통해 데이터가 수집되었다. 두 대의 차량에 fifth wheel(오륜) 장비, 스피드건, vericom 2000 등 다양한 측정장비를 탑재하여 제동실험이 수행되었으며, 자동차 속도, 제동거리, 활주거리, 감속도 등이 정밀 측정되었다. 실험자료의 분석을 통해 노면 마찰계수값과 활주직전 속도를 산정하고, 이후 활주직전 속도와 제동직전 속도를 비교하여 이들간의 상관관계를 규명하였다. 결과적으로 산정된 마찰계수값은 현재 일반적으로 적용되고 있는 0.8보다 높았으며, 제동직전 속도는 활주직전 속도보다 $5{\sim}10km/h$ 정도 높은 것으로 나타났다. 향후에는 다양한 차종과 노면조건에 대한 후속실험을 통해 더욱 정교한 한국형 분석모형의 개발과 실무적용이 필요할 것으로 판단된다.

Shape Optimization of A Surface Roughened by Staggered Ribs To Enhance Turbulent Heat Transfer

  • Kim Hong-Min;Kim Kwang-Yong
    • 한국전산유체공학회:학술대회논문집
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    • 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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    • pp.237-239
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    • 2003
  • The present study investigates on design optimization of rib-roughened two-dimensional channel to enhance turbulent heat transfer. Response surface method with Reynolds-averaged Navier-Stokes analysis is used as an optimization technique. Standard $k-{\varepsilon}$model with wall functions is adopted as a turbulence closure. The objective function is defined as a linear combination of heat transfer and friction drag coefficients with weighting factor. Computational results for overall heat transfer rate show good agreements with experimental data. Four design variables are optimized for weighting factor of 0.02.

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Brass fillers in friction composite materials: Tribological and brake squeal characterization for suitable effect evaluation

  • Kchaou, Mohamed;Sellami, Amira;Abu Bakar, Abd. Rahim;Lazim, Ahmad Razimi Mat;Elleuch, Riadh;Kumar, Senthil
    • Steel and Composite Structures
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    • 제19권4호
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    • pp.939-952
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    • 2015
  • In this paper, brake pad performance of two organic matrix composites namely, Sample 1 (contains no brass filler) and Sample 2 (contains 1.5% brass filler), is studied based on tribological and squeal noise behavior. In the first stage, a pin-on-disc tribometer is used to evaluate the frictional behavior of the two pads. On the following stage, these pads are tested on squeal noise occurrence using a drag-type brake dynamometer. From the two type of tests, the results show that; (i) brass fillers play a dual role; firstly as reinforcing element of the brake pad providing primary contact sites, and secondly as solid lubricant by contributing to the formation of a layer of granular material providing velocity accommodation between the pad and the disc; (ii) brass fillers contribute to friction force stabilization and smooth sliding behavior; (iii) the presence of small weight quantity of brass filler strongly contributes to squeal occurrences; (iv) there is close correlation between pin-on-disc tribometer and brake dynamometer tests in terms of tribological aspect.