• Title/Summary/Keyword: Roughness factor

Search Result 455, Processing Time 0.033 seconds

Study of Mass and Flow Resistance in a Square Ribbed Microchannel using Lattice Boltzmann Method

  • Taher, Mohammad Abu;Kim, Heuy-Dong;Lee, Yeon-Won
    • Journal of Power System Engineering
    • /
    • v.18 no.6
    • /
    • pp.207-214
    • /
    • 2014
  • Mass and flow resistance in a square ribbed microchannel have been studied numerically using the Lattice Boltzmann Method. It has been build up on two dimensional nine velocity vectors model with single relaxation time method called the Lattice Bhatnagor-Gross-Krook model. To analyze the roughness effect on the flow resistance namely the friction factor and mass flow has been discussed at the slip flow regime, $0.01{\leq}Kn{\leq}0.10$, where Kn is the Knudsen number. The wall roughness is considered by square microelements with a relative roughness height up to maximum 10% of channel height. The velocity profiles in terms of streamlines near the riblets are demonstrated to be responsible for the roughness effect. It is found that the roughness effect leads to increase the flow resistance with roughness height but it is decreased significantly with increasing the space between two roughness elements as well as the Knudsen number. In addition, the mass flow decreased linearly with increasing both roughness height and gap but significantly changed at the slip flow regime.

Variation of Moving Dynamic Vehicle Loads According to Surface Smoothness of Pavement Systems (도로포장 표면평탄성에 따른 주행차량의 동적 하중 변화 특성)

  • Kim, Seong-Min;Rhee, Suk-Keun
    • International Journal of Highway Engineering
    • /
    • v.10 no.1
    • /
    • pp.135-144
    • /
    • 2008
  • The dynamic loads imposed by moving vehicles have variations in the magnitude due to the surface roughness of the pavement systems and the larger dynamic loads than the design loads may affect the pavement performance. This paper presents variations of the moving dynamic vehicle loads due to the pavement surface roughness. This study was performed as a basic study to apply the pay factor to the surface roughness for the improvement of pavement quality and performance. The profile data was obtained from the old and new pavements and the analysis was performed to investigate the dynamic loads when vehicles move on the pavements having those profiles. The artificial profiles were also developed to find the effects of the vehicle speed, wavelength and amplitude of the surface roughness on the dynamic vehicle loads. The increase in the load magnitude due to the surface roughness affects the stresses and strains of pavements and finally reduces the pavement life. The methodology to obtain the relationship between the surface roughness and the pavement performance was proposed in this study.

  • PDF

A Comparison of Roughness Measurement and Load Transfer Test for the Calculation of Unit Skin Friction of Pile Foundation in Soft Rocks (기초 연암부 벽면거칠기 시험과 하중전이 시험 결과의 비교 및 단위주면마찰력의 산정에 대한 연구)

  • Hong, Seok-Woo;Hwang, Geun-Bae
    • Journal of the Korean Geotechnical Society
    • /
    • v.39 no.6
    • /
    • pp.21-30
    • /
    • 2023
  • One of the methods for calculating unit skin friction of soft-rock-socket parts for cast-in-place piles involves the roughness measurement of the parts. The measurements are conducted during the excavation stage. A roughness measuring device is installed in the excavation hole and the unit skin friction is calculated from the measured surface roughness of the rock socket. Herein, the results of roughness measurement of rock-socket parts in cast-in-place piles and that of load transfer tests are analyzed and compared. The unit skin friction from the roughness measurements can be converted into unit skin friction corresponding to the displacement of a pile generated in a load transfer test. A reduction factor is given as Rf = -0.14n + 1.48.

The Effect of Surface Roughness on Breakdown in Air (공기중 절연파괴에 있어서 전극표면의 요철에 의한 영향)

  • 오철한;김미태
    • 전기의세계
    • /
    • v.28 no.11
    • /
    • pp.33-36
    • /
    • 1979
  • In a uniform field, when an electrode with a hemispherical protrusion is set in atmosphere, by applying the streamer breakdown criterion and the surface roughness factor, the effect of field distortion due to electrode surface roughness on breakdown is investigated theoretically. A quantitative relation between the threshold of breakdown and the air pressure times the heigh of protrusion is derived by the aid of a computor and the results are compared with that of SF$_{6}$./.

  • PDF

Numerical Simulation Model of Alternative Refrigerants Flow Through Capillary Tubes (대체냉매의 모세관내 유동 시뮬레이션)

  • 장세동;노승택
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.8 no.1
    • /
    • pp.55-64
    • /
    • 1996
  • A numerical model of refrigerant flow through a capillary tube is developed, which considers the effects of underpressure for vaporization, kinetic energy, and roughness of capillary tube. The numerical model is based on homogeneous flow assumptions for the two-phase flow region. A characteristic chart of HFC refrigerants flow through capillary tubes and correction factor chart of geometry and relative roughness of capillary tube to select a proper capillary for refrigerating machines using alternative refrigerants is presented by this numerical model.

  • PDF

Friction Factor and Heat Transfer in Equilateral Triangular Ducts with Surface Roughness

  • Ahn, Soo-Whan
    • Journal of Mechanical Science and Technology
    • /
    • v.15 no.5
    • /
    • pp.639-645
    • /
    • 2001
  • Experimental investigations were conducted to study forced convection of fully developed turbulent flows in horizontal equilateral triangular ducts with different surface roughness pitch ratios (P/e) of 4, 8, and 16 on one side. The ducts bottom wall was heated uniformly and the other surfaces were thermally insulated. To understand heat transfer enhancement mechanism, heat transfer rates were measured. Smooth triangular ducts were also tested for benchmark purposes. The results were compared with previous results for similarly configured channels, at which they were roughened by regularly spaced transverse ribs in the rectangular and circular channels.

  • PDF

An Effect of Load on Surface Roughness on Surface Rolling of Ground Mild Steel (연삭가공된 강재의 표면 Rolling시 가압력이 표면 조도에 미치는 영향)

  • Kim, Hee-Nam
    • Journal of the Korean Society of Safety
    • /
    • v.2 no.1
    • /
    • pp.31-41
    • /
    • 1987
  • The surface rolling method which is one of the plastic deformation processes increases the surface roughness with reduction of diameter and hardness. In this study, three NACHI 6000 ZZ bearing were used for surface rolling tool on a mild steel. The following results have been obtained with the mild steel. 1) The load is major factor in getting fine surface roughness of roller fininshing after grinding. The optimal surface roughness of SS40 steel can be obtained at the contact pressure of $210kgf/cm^2$. But, Better surface roughness can not be expected, Due to flaking phenomena at more than 300 kgf/cm of contact pressure. 2) At the contact pressure range of $200kgf/cm^2{\sim}210kgf/cm^2$ for optimal surface roughness, The surface hardness increased to Hv 200~Hv 240 from Hv 125 before surface rolling. 3) Within the diameter variation of $13{\mu}m$ the surface roughness and the surface hardness were increased, but out of variation of $14{\mu}m$. The surface roughness become worse and the surface hardness was increased.

  • PDF

A Study on the Characteristics of Ultra Precision Machining of a Al Cone Mirror (Al 원추경 초정밀가공 특성에 관한 연구)

  • 현동훈;조언정;이승준;권용재;김영찬
    • Proceedings of the Korean Society for Technology of Plasticity Conference
    • /
    • 2003.05a
    • /
    • pp.397-401
    • /
    • 2003
  • In this work, diamond turning process is used to produce mirror surface on a Al cone. The Al cone as used as a mirror which can reflect a laser beam without scattering and, hence, it is critical to minimize the surface roughness of a Al cone. During diamond turning, feedrate and tool nose radius are changed to investigate characteristics of the ultra precision machined surface of a Al cone. A laser beam of 633 nm is applied to examine the effect of surface roughness on the characteristics of reflectivity. It is found that surface roughness is not significantly affected by feedrate. The main factor influencing surface roughness is tool nose radius. The line patterns of reflected laser beams show that the minimum surface roughness of 0.08 $\mu\textrm{m}$ (Ra) is required to avoid scattering phenomena of reflectivity.

  • PDF

Extraction of Factors Effecting Surface Roughness Using the System of Experiments in the Ultra-precision Mirror Surface Finishing (실험 계획법을 이용한 초정밀 경면 연마 가공에서 표면 거칠기에 영향을 미치는 인자의 검출)

  • 배명일;김홍배;김기수;남궁석
    • Journal of the Korean Society for Precision Engineering
    • /
    • v.15 no.2
    • /
    • pp.53-60
    • /
    • 1998
  • In this study, it is experimented to find factors effecting surface roughness using the system of experiments. in the mirror surface finishing system. (1) The film feed and oscillation frequency in $40{\mu}m$ abrasive film, grinding speed in $30{\mu}m$, and machining time in $15{\mu}m$15 are the main factors effecting the surface roughness. (2) Applying the optimal finishing condition to $40{\mu}m$, $30{\mu}m$, $15{\mu}m$ abrasive finishing film in sequence, it is possible to obtian about Ra 10 nm surface roughness on SM45C workpiece. (3) Application of the system of experments to the micro abrasive grain film finishing was very effective method in the extraction of main factor and optimal condition.

  • PDF

The OMM system for machined form and surface roughness measurement concerned with volumetric error (기계 체적오차가 고려된 가공형상-거칠기 측정 OMM 시스템)

  • 이상준;김선호;김옥현
    • Proceedings of the Korean Society of Precision Engineering Conference
    • /
    • 2000.05a
    • /
    • pp.681-686
    • /
    • 2000
  • Machining information such as machined form and surface roughness accuracy is an important factor for manufacturing precise parts. To this regard, OMM(On the Machine Measurement) has been issued for last several decades to alternate with CMM. In this research, measuring system consisting of a laser probe is developed for machined form and surface roughness measurement on the machine tool. The obtained machined form accuracy is compared with reference one defined in CAD model. The measured surface roughness data is compared with measured master surface beforehand. Furthermore, using the pre-defined volumetric error map approach compensates the geometric accuracy of the machine tool. The overall performance is compared with CMM, and verified the feasibility of the measurement system.

  • PDF