• Title/Summary/Keyword: RMS(Root mean square) roughness

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A Study on Failure Analysis of Low Pressure Turbine Blade Subject to Fatigue Load (피로하중을 받은 저압 터빈 블레이드의 파손해석에 관한 연구)

  • 홍순혁;이동우;조석수;주원식
    • Journal of Welding and Joining
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    • v.19 no.3
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    • pp.298-304
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    • 2001
  • Turbine blade is subject to force of three types ; the torsional force by torsional mount, the centrifugal force by the rotation of rotor and the cyclic bending force by steam pressure. The cyclic bending force was a main factor on fatigue strength. SEM fractography in root of turbine blade showed micro-clack width was not dependent on stress intensity factor range. Especially, fatigue did not exist on SEM photograph in root of turbine blade. To clear out the fracture mechanism of turbine blade, nanofractography was needed on 3-dimensional crack initiation and crack growth with high magnification. Fatigue striation partially existed on AFM photograph in root of turbine blade. Therefore, to find a fracture mechanism of the torsion-mounted blade in nuclear power plant, the relation between stress intensity factor range and surface roughness measured by AFM was estimated, and then the load amplitude ΔP applied to turbine blade was predicted exactly by root mean square roughness.

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A study on statistical characteristics of time-varying underwater acoustic communication channel influenced by surface roughness (수면 거칠기에 따른 수면 경로의 시변 통신채널 통계적 특성 분석)

  • In-Seong Hwang;Kang-Hoon Choi;Jee Woong Choi
    • The Journal of the Acoustical Society of Korea
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    • v.42 no.6
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    • pp.491-499
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    • 2023
  • Scattering by Sea surface roughness occurs due to sea level roughness, communication performance deteriorates by causing frequency spread in communication signals and time variation in communication channels. In order to compare the difference in time variation of underwater acoustic communication channel according to the surface roughness, an experiment was performed in a tank owned by Hanyang University Ocean Acoustics Lab. Artificial surface roughness was created in the tank and communication signals with three bandwidths were used (8 kHz, 16 kHz, 32 kHz). The measured surface roughness was converted into a Rayleigh parameter and used as a roughness parameter, and statistical analysis was performed on the time-varying channel characteristics of the surface path using Doppler spread and correlation time. For the Doppler spread of the surface path, the Weighted Root Mean Square Doppler spread (wfσν) that corrected the effect of the carrier frequency and bandwidth of the communication signal was used. Using the correlation time of the surface path and the energy ratio of the direct path and the surface path, the correlation of total channels was simulated and compared with the measured correlation time of total channels. In this study, we propose a method for efficient communication signal design in an arbitrary marine environment by using the time-varying characteristics of the sea surface path according to the sea surface roughness.

Reduction of surface roughness during high speed thinning of silicon wafer

  • Heo, W.;Ahn, J.H.;Lee, N.E.
    • Proceedings of the Korean Vacuum Society Conference
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    • 2010.02a
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    • pp.392-392
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    • 2010
  • In this study, high-speed chemical dry thinning process of Si wafer and evolution of surface roughness were investigated. Direct injection of NO gas into the reactor during the supply of F radicals from $NF_3$ remote plasmas was very effective in increasing the Si thinning rate due to the NO-induced enhancement of surface reaction but thinned Si surface became roughened significantly. Addition of Ar gas, together with NO gas, decreased root mean square (RMS) surface roughness of thinned Si wafer significantly. The process regime for the thinning rate enhancement with reduced surface roughness was extended at higher Ar gas flow rate. Si wafer thinning rate as high as $22.8\;{\mu}m/min$ and root-mean-squared (RMS) surface roughness as small as 0.75 nm could be obtained. It is expected that high-speed chemical dry thinning process has possibility of application to ultra-thin Si wafer thinning with no mechanical damage.

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A Study on the Detection of the Chatter Using Current Signal in Turning (선삭가공시 전류신호를 이용한 채터 검출에 관한 연구)

  • 서한원;유기현;오석형;서남석
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1997.04a
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    • pp.947-951
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    • 1997
  • Recently, the necessity of the detection of abnormal machining process is being emphasized in order to improve the machining accuracy and reduce the cost in unmanned operating system. The vibration by chatter generated in cutting processes within machine tools is a relative motion between tools and workpieces. So, if the chatter occurs, the surface roughness and accuracy of workpieces will be deteriorate and it leads to the rapid wear of tools. The author intended to use the I /sab/RMS (current of root mean square) of current sigals and the movimg C.V. (coefficient of variation) of each phase for the detection method of chatter.

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LTPS Technology in ERSO

  • Liu, David N.;Yeh, Yung-Hui
    • 한국정보디스플레이학회:학술대회논문집
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    • 2004.08a
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    • pp.124-128
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    • 2004
  • A Poly-Si and a ITO films with surface roughness 1.8 nm and 0.5 nm of root mean square ($R_{rms}$ vakue) values were developed, respectively. A 3 inch UXGA LTPS TFT-LCD with 667 ppi resolution and a 10 inch VGA LTPS OLED have been developed and demonstrated using PMOS technology.

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Assessing the effect of stylus tip radius on surface roughness measurement by accumulation spectral analysis

  • Kwon Ki-Hwan;Cho Nahm-Gyoo
    • International Journal of Precision Engineering and Manufacturing
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    • v.7 no.1
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    • pp.9-12
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    • 2006
  • A spectral analysis and numerical simulation are employed to assess the effects of the stylus tip radius on measuring surface profiles. Original profiles with fractal spectral densities are generated and then are numerically traced with circular tipped stylus. Instead of their spectral densities, the accumulative power spectrums of traced profiles are analyzed. It is shown that the minimum wavelength of traced profile relates directly to the radius r of the stylus tip and the root-mean-square (rms) roughness ${\sigma}_o$ of original profile. From this accumulation spectral analysis, a formula is developed to estimate the minimum wavelength of traced profile. By using the concept of the minimum wavelength, an appropriate stylus tip radius can be chosen for the given rms roughness ${\sigma}_o$ of the profile.

Development of a 3D Roughness Measurement System of Rock Joint Using Laser Type Displacement Meter (레이저 변위계를 이용한 암석 절리면의 3차원 거칠기 측정기 개발)

  • 배기윤;이정인
    • Tunnel and Underground Space
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    • v.12 no.4
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    • pp.268-276
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    • 2002
  • In this study, a 3D coordinate measurement system equipped with a laser displacement meter for digitizing rock joint surface was established and the digitized data were used to calculate several roughness parameters. The parameters used in this study were micro avenge inclination $angle(i_{ave})$, average slope of joint $asperity(SL_{ ave})$, root mean square of $i-angle(i_{rms})$, standard deviation of height(SDH), standard deviation of $i-angle(SD_i)$, roughness profile $index(R_P)$, and fractal dimension(D). The relationships between the roughness parameters based on the digitzation of the surface profile were analyzed. Since the measured value varied according to the degree of reflection and the variation of colors at the measuring point, rock joint surface was painted in white to minimize the influence of the surface conditions. The comparison of the measured values and roughness parameters before and after painting revealed the better consequence from measurement on the painted surfaces. Also, effect of measuring interval was studied. As measured interval was increased, roughness parameters were exponentially decreased. The incremental sequence of degree of decrease was $SDH\; i_{ave},\; i_{rms},\; SD_i,\;and\; R_ p-1$. As a result of comparison of parameters from pin-type measurement system and laser type measurement system, all value of parameters were higher when laser-type measurement system was used, except SDH.

Accuracy Verification of Theoretical Models for Estimating Microwave Reflection from Rough Sea Surfaces (거친 바다표면의 마이크로파 반사 계산을 위한 이론적 모델 정확도 검증)

  • Park, Sinmyong;Oh, Yisok
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.28 no.10
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    • pp.788-793
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    • 2017
  • This paper presents the verification of accuracies of theoretical models for calculating the microwave reflections from rough sea surfaces. First of all, the Pierson-Moskowitz ocean spectrum was used to generate the rough sea surfaces. Then the relationship between the significant wave heights, root-mean-square(RMS) heights and wind speed was derived by estimating the significant wave heights and RMS heights of the generated sea surfaces according to various wind speeds, and compared the derived relationship with other measurement data sets. The reflection coefficients of the sea surfaces were calculated by using a numerical method(the moment method). Then, the numerical results were compared with Ament model, PO(Physical Optics) model, GO(Geometrical Optics) model and B-M(Brown-Miller) model for various roughness conditions(wind speed) and incidence angles. It was found that the Ament model is not accurate except for a very low roughness conditions($kh_{rms}$<0.4, k is wavenumber and $h_{rms}$ is RMS height). It was also found that at incidence angles lower than $70^{\circ}$, the PO and the GO models agree well with the numerical results, while the B-M model agrees well with the numerical analysis results at incidence angles higher than $80^{\circ}$ for very rough sea surfaces with $kh_{rms}$>10.

An Evaluation Method for Three-Dimensional Morphologies of Discontinuities considering the Shear Direction

  • Zhang, Qingzhao;Luo, Zejun;Pan, Qing;Shi, Zhenming;Jang, Bo-An
    • The Journal of Engineering Geology
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    • v.32 no.1
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    • pp.85-99
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    • 2022
  • Rock discontinuities, as weak interfaces in rock, control mechanical properties of rock mass. Presence of discontinuities complicates the engineering properties of rock, which is the root of anisotropy and heterogeneity that have nonnegligible influences on the rock engineering. Morphological characteristics of discontinuities in natural rock are an important factor influencing the mechanical properties, particularly roughness, of discontinuities. Therefore, the accurate measurement and characterization of morphologies of discontinuities are preconditions for studying mechanical properties of discontinuities. Taking discontinuities in red sandstone as research objects, the research obtained three-dimensional (3D) morphologies of discontinuities in natural rock by carrying out 3D morphological scanning tests. The waviness and roughness were separated from 3D morphologies of rock discontinuities through wavelet transform. In addition, the calculation method for the overall slope root mean square (RMS) as well as slope RMSs of waviness and roughness of 3D morphologies of discontinuities considering the shear direction was proposed. The research finally determined an evaluation method for 3D morphologies of discontinuities by quantitatively characterizing 3D morphologies with the mean value of the three slope RMSs.

Dependence of Q Factor on Surface Roughness in a Plasmonic Cavity

  • Kim, Yoon-Ho;Kwon, Soon-Hong;Ee, Ho-Seok;Hwang, Yongsop;No, You-Shin;Park, Hong-Gyu
    • Journal of the Optical Society of Korea
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    • v.20 no.1
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    • pp.188-191
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    • 2016
  • We investigated surface-roughness-dependent optical loss in a plasmonic cavity consisting of a semiconductor nanodisk/silver nanopan structure. Numerical simulations show that the quality factors of plasmonic resonant modes significantly depend on the surface roughness of the dielectric-metal interface in the cavity structure. In the transverse-magnetic-like whispering-gallery plasmonic mode excited in a structure with disk diameter of 1000 nm, the total quality factor decreased from 260 to 130 with increasing root-mean-square (rms) surface roughness from 0 to 5 nm. This quantitative theoretical study shows that the smooth metal surface plays a critical role in high-performance plasmonic devices.