• Title, Summary, Keyword: roughness

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EHL Analysis for Rough Surface with Directional Roughness (거친 표면의 돌기 방향성에 따른 EHL 해석)

  • Kim, Tae-Wan;Cho, Yong-Joo
    • Tribology and Lubricants
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    • v.25 no.5
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    • pp.342-347
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    • 2009
  • This paper presents EHL analysis for rough surfaces with directional roughness. Three different types of surfaces with pure longitudinal roughness, pure transversal roughness and isotropic roughness are generated. For the surfaces with longitudinal and transversal roughness, two cases are analyzed; one is a case of asperity peak on a spherical contact center, the other one is of valley on a spherical contact center. As a results, the surface with pure transversal roughness gives higher pressure and smaller minimum film thickness than the surface with pure longitudinal roughness, and the surface with isotropic roughness has similar EHL behavior with the surface with pure transversal roughness.

Digital Signal Processing for the Optical Surfaece Roughness System (광학식 표면 거칠기 계의 디지탈 신호처리)

  • Kim, Hee-Nam;Heo, Woong;Gu, Man-Seo
    • Journal of the Korean Society of Safety
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    • v.6 no.2
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    • pp.21-30
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    • 1991
  • In this paper, we study effect of waveness at the optical surface roughness measurement. In generally, waveness components cause errors in calculation of the roughness value of metal surface. We study about surface roughness signals In the frequency domain for separate two signal component of real roughness and waveness by digital signal processing methods. Thereafter, determine low and high Component of frequency spectrum. By this separating frequency value we design liner low and high pass filter which cutoff frequency is 1 Hz. After this process, converted each filtered spectrum by inverse discrete fourier transformation to time domain waveness and real roughness signals We calculate surface roughness value from filtered roughness signals. For evaluate this method, we use five specimens roughness signal which obtained from optical surface roughness measuring system in 3mm/s moving speed with 0.1 mm laser beam spot size As a result, we obtain more linerized roughness value than that of unfiltered roughness signals.

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Effective Wall Roughness corresponding to Roughness Coefficient of Open Channel Flow (개수로 조도계수에 따른 유효 벽면거칠기)

  • Choi, Jun-Woo;Kwon, Kab-Keun;Kim, Hyung-Seok;Yoon, Sung-Bum
    • 한국전산유체공학회:학술대회논문집
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    • pp.176-179
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    • 2008
  • In a numerical simulation of open channel turbulent flows, the determination of wall roughness height for wall function was studied. The roughness constant, based on the law-of-the -wall for flow on rough walls, obtained by experimental works for pipe flows is employed in general wall functions. However, this constant of wall function is the function of Froude number in open channel flows. Thus, the wall roughness should be determined by taking into account the effect of Froude number. In addition, the wall roughness should be corresponding to Manning's roughness coefficient widely used for open channels. In this study, the relation between wall roughness height as an input condition and Manning's roughness coefficient was investigated, and an equation for effective wall roughness height considering the characteristics of numerical models was proposed as a function of Manning's roughness coefficient.

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Effect of surface roughness on laminar flow in a micro-channel by using lattice Boltzmann method (격자 볼츠만 방법을 이용한 미소채널 내에서의 층류 유동에 대한 표면 거칠기의 영향)

  • Shin, Myung-Seob;Yoon, Joon-Yong;Byun, Sung-Joon;Kim, Kak-Joong
    • 유체기계공업학회:학술대회논문집
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    • pp.179-183
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    • 2006
  • Surface roughness is present in most of the microfluidic devices due to the microfabrication techniques. This paper presents lattice Boltzmann method (LBM) results for laminar flow in a microchannel with surface roughness. The surface roughness is modeled by an array of rectangular modules placed on top and bottom side of a parallel-plate channel. In this study, LBGK D2Q9 code in lattice Boltzmann Method is used to simulate flow field for low Reynolds number in a micro-channel. The effects of relative surface roughness, roughness distribution, roughness size and the results are presented in the form of the product of friction factor and Reynolds number. Finally, a significant increase in Poiseuille number is detected as the surface roughness is considered, while the effect of roughness on the microflow field depends on the surface roughness.

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Roughness Mobilization Characteristics of Artificial Triangular Asperities (인공 삼각 돌출부의 거칠기 발현특성)

  • Hong, Eun-Soo;Choi, Sung-Oong;Lee, In-Mo
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.760-767
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    • 2006
  • Underestimation of rock joint shear strength comes from an inadequate consideration of roughness mobilization behavior, which is changed by asperity size as well applied normal load. In this study, we performed rock joint shear tests, and studied the roughness mobilization characteristics related with the scale of normal stress and asperities. Test specimens with artificial triangular asperities were manufactured. The specimens consisted of 3 types, and each type represented unevenness, waviness and total roughness(superposition of unevenness and waviness). The experimental results show that the roughness mobilization characteristics are varied by the scale of normal stress and asperities. Furthermore, the investigation shows that the rate of geometrical component and mechanical component in the total roughness is also varied by the scale of normal stress and asperities. These results suggest that we should consider the roughness mobilization characteristics for the roughness quantification and the shear strength modelling.

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Modelling of Rock Joint Shear Strength Using Surface Roughness Parameter, Rs (표면 거칠기 계수 Rs를 이용한 암석 절리면 전단강도 모델)

  • 이석원;배석일;이인모
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.73-80
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    • 2001
  • The shear strength of jointed rock is influenced by effective normal stress, joint wall compressive strength, joint roughness and so on. Since joint roughness makes considerable influences on shear strength of jointed rock, many studies tried to get quantitative joint roughness parameter. Until now, Joint Roughness Coefficient, JRC proposed by Barton has been prevalently used as a rock joint roughness parameter In spite of its disadvantages. In this study, a quantification of rock joint roughness is performed using surface roughness parameter, Rs. Proposed method is applied to rock core specimens, field joint surfaces, and JRC profiles. The scale of fluctuation is introduced to extend the suggested method to the large scale field joint surface roughness. Based on the quantification of joint surface roughness, joint shear tests are performed with the portable shear box. The relationship between joint surface roughness and joint shear strength is investigated and finally, a rock joint shear strength equation is derived from these results. The equation has considerable credibility and originality in that it is obtained from laboratory tests and expressed with quantified parameter.

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A New Quantification Method of Rock Joint Roughness (I) - A Close Assessment of Problems (암석 절리면 거칠기의 정량화에 대한 연구 (I) - 문제점의 규명)

  • Hong, Eun-Soo;Nam, Seok-Woo;Lee, In-Mo
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.7 no.4
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    • pp.269-283
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    • 2005
  • To figure out the cause of underestimating the roughness and shear strength of rock joints suggested by numerous researchers, we analyzed roughness mobilization characteristics, characteristics of roughness parameters, effects of sampling interval, and waviness for roughness parameters. It was found out that lack of understanding of the roughness mobilization characteristics, inappropriate applications of roughness parameters, and effect of aliasing provide a main reasons for those problems. Several practical alternatives for improving those problems were suggested. As far as digitizing methods are concerned, we can find that using a 3D scanner can give a relatively effective result. To avoid aliasing, sampling interval should be less than one-quarter of the minimum asperities. As for the quantification of roughness, it was analyzed that the roughness parameter should be classified into two components depending on the scale of roughness to apply the shear strength model. For classifying the roughness, a framework of the criterion was suggested based on the plastic flow concept for the asperity failure, and the basis for proposing a new alternative shear strength model was established.

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Analysis of Surface Roughness by FFT Analyzer in Turning Operation (선반작업(旋盤作業)에서의 FFT Analyzer에 의한 표면(表面)거칠기 해석(解析))

  • Kim, Gyung-Nyun;Choi, Eun-Soon
    • Journal of the Korean Society for Nondestructive Testing
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    • v.12 no.3
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    • pp.12-19
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    • 1992
  • This paper shows that the identified and unidentified components of surface roughness in NC turning lathe which can not be analyzed in time domain such as $R_{max},\;R_a$ can be isolated in frequency domain by FFT analyzer. By interfacing FFT analyzer with stylus surface roughness instrument, surface roughness on change of working condition, especially tool feed, such as 0.1, 0.15, 0.2, 0.25, 0.3(mm/rev) can be analyzed in frequency domain as follows. 1. By frequency analysis of surface roughness profile, the basic wave length of surface roughness can be obtained to isolate the identified and unidentified components of surface roughness. 2. With increase of tool feed, the unidentified components of surface roughness increase. 3. Since $R_{max}$, which can be obtained by stylus surface roughness is proportion to the output voltage of FFT analyzer, FFT analyzer also can be used to measure surface roughness in time domain such $R_a,\;R_{max}$.

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Vibration of vehicle-bridge coupling system with measured correlated road surface roughness

  • Han, Wanshui;Yuan, Sujing;Ma, Lin
    • Structural Engineering and Mechanics
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    • v.51 no.2
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    • pp.315-331
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    • 2014
  • The present study investigated the effect of the correlation of the measured road roughness profiles corresponding to the left and right wheels of a vehicle on the vibration of a vehicle-bridge coupling system. Four sets of road roughness profiles were measured by a laser road-testing vehicle. A correlation analysis was carried out on the four roughness samples, and two samples with the strongest correlation and weakest correlation were selected for the power spectral density, autocorrelation and cross-correlation analyses. The scenario of a three-axle truck moving across a rigid-frame arch bridge was used as an example. The two selected road roughness profiles were used as inputs to the vehicle-bridge coupling system. Three different input modes were adopted in the numerical analysis: (1) using the measured road roughness profile of the left wheel for the input of both wheels in the numerical simulation; (2) using the measured road roughness profile of the right wheel for both wheels; and (3) using the measured road roughness profiles corresponding to left and right wheels for the input corresponding to the vehicle's left and right wheels, respectively. The influence of the three input modes on the vibration of the vehicle-bridge system was analyzed and compared in detail. The results show that the correlation of the road roughness profiles corresponding to left and right wheels and the selected roughness input mode both have a significant influence on the vibration of the vehicle-bridge coupling system.

The Effect of surface roughness on Finished Surface orientation of Friction Characteristics (가공방향의 마찰특성에 대한 표면거칠기 영향)

  • 유응대;김태완;조용주
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • pp.267-272
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    • 2001
  • The effect of characteristic of surface roughness and roughness patterns on frictioin was studied experimentally in boundary lubrication with reciprocating tribometer. Roughness was changed from Ra=0.2 $\mu\textrm{m}$ to Ra=1.2 $\mu\textrm{m}$. Three roughness patterns-transverse, oblique, longitudinal- were tested for various load. Ra=1.0 $\mu\textrm{m}$ roughness showed lower friction coefficient and transversal pattern showed lower friction and high scuffing load in the test conditions.

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