• Title, Summary, Keyword: friction factor

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Test Results of Friction Factor for Round-Hole Roughness Surfaces in Closely Spaced Channel Flow of Water

  • Ha, Tae Woong
    • Journal of Mechanical Science and Technology
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    • v.18 no.10
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    • pp.1849-1858
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    • 2004
  • For examining friction-factor characteristics of round-hole pattern surfaces which are usually applied on damper seals, flat plate test apparatus is designed and fabricated. The measurement method of leakage and pressure distribution along round-hole pattern specimen with different hole area is described and a method for determining the Fanning friction factor is discussed. Results show that the round-hole pattern surfaces provide a much larger friction factor than smooth surface, and the friction factor vs. clearance behavior yields that the friction factor generally decreases as the clearance increases unlike the results of Nava's flat plate test. As the hole depth is decreased, the friction factor is increased, and maximum friction factor is obtained for 50% of hole area. Since the present experimental friction factor results show coincident characteristics with Moody's friction factor model, empirical friction factors for round-hole pattern surfaces are obtained by using the Moody's formula based on curve-fit of the experimental data. Results of Villasmil's 2D CFD simulation support the present experimental test result.

The Characteristic of Friction-Factor on Honeycomb Surfaces (Part II : Friction-Factor Jump Phenomenon) (허니콤 표면의 마찰계수 특성에 관한 연구 (Part 2 : 마찰계수 급상승현상에 관한 고찰))

  • 하태웅
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.6
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    • pp.1439-1447
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    • 1994
  • Test results of friction-factor for the flow of air in a narrow channel lined with various honeycomb geometries show that, generally, the friction-factor is nearly constant or slightly decreases as the Reynolds number(or Mach number) increases, a characteristic common to turbulent flow in pipes. However, in some test geometries this trend is remarkably different. The friction factor dramatically drops and then rises as the Mach number increases. This phenomenon can be characterized as a "friction-factor jump." Further investigations of the acoustic spectrum indicate that the "friction-factor jump" phenomenon is accompanied by an onset of a normal mode resonance excited coherent flow fluctuation structure, which occurs at Reynolds number of the order of $10^4$. New empirical friction-factor model for "friction-factor jump" cases is developed as a function of Mach number and local pressure.ach number and local pressure.

The Effect of Surface-Friction-Factor-Jump Characteristics on Retordynamics of a Seal (마찰계수 급상승 특성이 실의 로터다이나믹 특성에 미치는 영향)

  • 하태웅
    • Journal of KSNVE
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    • v.6 no.2
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    • pp.197-203
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    • 1996
  • This study is to analyze the rotordynamic effect of surface-friction- factor characteristics on an annular seal. The honeycomb geometry which shows friction-factor-jump phenomena is used in this study. A rotordynamic analysis for a contered annular seal has been developed by incorporating empirical friction-factor model for honeycomb stator surfaces. The results of the analysis for the honeycomb seal showing the friction-factor jump is compared to the non- friction-factor-jump case. The results yield that the friction-factor-jump decreasesdirect stiffness and cross coupled stiffness coefficients, and increases damping coefficient to stabilize rotating machinery in a rotordynamic point of view. The analysis of the honeyeomb seal for the friction-factor-jump case shows reasonably good compared to experimental results, especially, for cross coupled and damping coeffcients.

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Characteristics of Friction Factor for Artificially Roughened Surfaces (임의로 거칠게 한 표면의 점성 마찰특성)

  • Ha, Tae-Woong;Ju, Young-Chan;Lee, Yong-Bok;Kim, Chang-Ho
    • The KSFM Journal of Fluid Machinery
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    • v.6 no.3
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    • pp.15-20
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    • 2003
  • For measuring friction factor of artificially-roughened surfaces which are usually applied to damper seals, flat plate test apparatus is designed and fabricated. The measurements of leakage flow and pressure distribution through round-hole patterned specimen with different hole areas are described, and a method is discussed for determining the friction factor experimentally. Results show that the friction factor of the round-hole patterned surface is bigger than that of smooth surface, and increases as increasing the hole area. A empirical friction factor model for the round-hole patterned surface can be descrived by the Moody's friction factor formula.

A Study for Distribution Methods Between Superelevation and Side Friction Factor Reflecting Ergonomic Characteristics by Increasing Design Speed (설계속도 상향에 따른 인간공학적 특성을 반영한 편경사와 횡방향마찰계수 분배방법에 관한 연구)

  • Jeong, Seungwon;Kim, Sangyoup;Choi, Jaisung;Kim, Hongjin;Jang, Taeyoun
    • International Journal of Highway Engineering
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    • v.15 no.3
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    • pp.103-115
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    • 2013
  • PURPOSES: The purpose of this study is to develop a method for distribution between superelevation and side friction factor by increasing design speed. METHODS: First of all, a method for distribution between superelevation and side friction factor and a theory for the functional formula of side friction factor in compliance with horizontal radius applied in South Korea and the United States are considered. Especially, design speed of 140km/h and numerical value of design elements are applied to the theory for the functional formula of side friction factor in AASHTO's methods. Also, the anxiety EEG upon running speed is measured to reflect ergonomic characteristics through field experiments at seven curve sections of the West Coast Freeway, and this data is applied to graph for the functional formula of side friction factor. RESULTS : Matching side friction factor against the anxiety EEG, the results that a critical points of driver's anxiety EEG sharply increase locate under existing parabola are figured out. CONCLUSIONS : Therefore, we could get a new type of the functional formula that driver's driving comfortability is guaranteed if the existing the functional formula of side friction factor goes down under boundary of the critical points of the anxiety EEG.

Characteristics of Friction Factor for Artificially Roughened Surfaces (임의로 거칠게한 표면의 점성 마찰특성)

  • Ha, Tae Woong;Ju, Young Chan;Lee, Yong-Bok;Kim, Chang-Ho
    • 유체기계공업학회:학술대회논문집
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    • pp.465-470
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    • 2002
  • For measuring friction-factor of artificially-roughened surfaces which are usually applied on damper seals, flat plate test apparatus is designed and fabricated. the measurement of leakage and pressure distribution through round-hole pattern specimen with different hole area is described and a method is discussed for determining the friction-factor experimentally. Results show that the friction-factor of the round-hole pattern surfaces is bigger than that of smooth surface and increases as increasing the hole area. A empirical friction factor model for round-hole pattern surface is defined as the Moody's friction factor formula.

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Determination of Flow Stress and Friction Factor by the Ring Compression Test (II) (링압축실험에 의한 유동응력 및 마찰인자의 결정 (II))

  • 최영민;김낙수
    • Transactions of Materials Processing
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    • v.3 no.2
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    • pp.215-228
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    • 1994
  • The purpose of this paper is to pursue a general method to determine both the flow stress of a material and the friction factor by ring compression test. The materials are assumed to obey the expanded n-power hardening rule including the strain-rate effect. Ring compression is simulated by the rigid-plastic finite element method to obtain the database used in determining the flow stress and friction factor. The Simulation is conducted for various strain hardening exponent, strain-rate sensitivity, friction factor, and compressing speed, as variables. It is assumed that the friction factor is constant during the compression process. To evaluate the compatibility of the database, experiments are carried out at room and evaluated temperature using specimens of aluminum 6061-T6 under dry and grease lubrication condition. It is shown that the proposed test method is useful and easy to use in determining the flow stress and the friction factor.

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The Characteristic of Friction-Factor on Honeycomb Surfaces (Part I : Experimantal Tests and Friction-Factor Modeling) (허니콤 표면의 마찰계수 특성에 관한 연구 (Part 1 : 표면 마찰계수 측정 및 모델링))

  • 하태웅
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.6
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    • pp.1430-1438
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    • 1994
  • Friction-factors for honeycomb surfaces are measured with a flat plate tester. The flat plate test apparatus is described and method is discussed for determining the friction-factor experimentally. The friction-factor is calculated for the flat plate test based on the Fanno-line flow. The test parameters are honeycomb cell width, depth, clearance, inlet pressure, and Reynolds number(or Mach number). A new empirical friction-factor model for honeycomb surfaces are developed as a function of these parameters.

A New Measure of Asset Pricing: Friction-Adjusted Three-Factor Model

  • NURHAYATI, Immas;ENDRI, Endri
    • The Journal of Asian Finance, Economics and Business
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    • v.7 no.12
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    • pp.605-613
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    • 2020
  • In unfrictionless markets, one measure of asset pricing is its height of friction. This study develops a three-factor model by loosening the assumptions about stocks without friction, without risk, and perfectly liquid. Friction is used as an indicator of transaction costs to be included in the model as a variable that will reduce individual profits. This approach is used to estimate return, beta and other variable for firms listed on the Indonesian Stock Exchange (IDX). To test the efficacy of friction-adjusted three-factor model, we use intraday data from July 2016 to October 2018. The sample includes all listed firms; intraday data chosen purposively from regular market are sorted by capitalization, which represents each tick size from the biggest to smallest. We run 3,065,835 intraday data of asking price, bid price, and trading price to get proportional quoted half-spread and proportional effective half-spread. We find evidence of adjusted friction on the three-factor model. High/low trading friction will cause a significant/insignificant return difference before and after adjustment. The difference in average beta that reflects market risk is able to explain the existence of trading friction, while the difference between SMB and HML in all observation periods cannot explain returns and the existence of trading friction.

Rotordynamic Analysis of a Labyrinth Seal Using the Moody's Friction-Factor Model (Moody 마찰계수식을 사용한 래버린스 실의 회전체 동역학적 해석)

  • Ha, Tae Woong
    • The KSFM Journal of Fluid Machinery
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    • v.2 no.3
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    • pp.52-58
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    • 1999
  • The leakage and rotordynamic coefficients of see-through type gas labyrinth seals are determined using a two-control-volume-model analysis with Moody's wall-friction-factor formula which is defined with a large range of Reynolds number and relative roughness. Jet flow theory are used for the calculation of the recirculation velocity in the cavity. For the reaction force from the labyrinth seal, linearized zeroth-order and the first-order perturbation equations are developed for small motion about a centered position. The leakage and rotordynamic coefficient results of the present analysis are compared with Scharrer's theoretical analysis using Blasius' wall-friction-factor formula and Pelletti's experimental results. The comparison shows that the present analysis using Moody's wall-friction-factor formula and Scharrer's theoretical analysis using Blasius' wall-friction-factor formula give the same results for a smooth seal surface and the range of Reynolds number less than $10^5$.

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