• 대한기계학회논문집B
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• 제30권12호
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• pp.1203-1210
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• 2006

The filmwise condensation heat transfer coefficients of R-134a on the horizontal copper and stainless steel tubes were measured and analyzed. The outside diameter of the tubes was 15.88 mm, and the tube thickness ranged from 0.89 to 1.65 mm. The polished stainless steel tube had an RMS surface roughness($R_q$) of 0.37 $\mu$m, and commercial stainless steel tubes had an surface roughness($R_q$) of 1.855 $\mu$m. The tests were conducted at the saturation temperatures of 20 and $30^{\circ}C$, and the liquid wall subcoolings from 0.4 to $2.1^{\circ}C$. The measured condensation heat transfer coefficients were significantly lower than the predicted data by the Nusselt analysis. This trend in the stainless steel tube was explained by the effects of thermal resistance of tube material and surface roughness. Based on the experimental data with respect to wall thickness and surface roughness, it was suggested that the existing correlation on external condensation should be modified by considering material and surface roughness factors. The revised correlation was developed by introducing the effects of wall thickness and surface roughness into the Nusselt equation. The average deviation of the revised correlation was 13.0 %.

• 구강회복응용과학지
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• 제16권3호
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• pp.197-210
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• 2000

Surface roughness is one of implant surface topography and it's found that surface roughness characterizations, such as surface energy, oxide layer thickness and its chemical composition, are closely correlated if the roughness is changed. Several studies showed the importance of analyzing surface structure so the surface structure of thread implant was analyzed to measure the implant quality exactly. In this study, surface roughness of 4 implants - MK $II^{(R)}$(Nobel Biocare), $RBM^{(R)}$(Life-Core, USA), $Osseotite^{(R)}$(3i, USA), $TPS^{(R)}$(Life-Core, USA) - were measured using $Accura^{(R)}$ and 40 implants were installed into 4 sets of ten bovine ribs based on the parameters from the measurements. From this test, the following conclusions for the initial stability were drawn by measuring and comparing RFA, Periotest Value (PTV), Removal Torgue Value (RTV). 1. $R_a$ value in surface roughness measurement was increasing by the order of $MKII^{(R)}$, $Osseotite^{(R)}$, $RBM^{(R)}$, $TPS^{(R)}$ and $R_q$ value was the same order. 2. $R_q$ value in each section was observed to increase by the order of $MKII^{(R)}$, $Osseotite^{(R)}$, $RBM^{(R)}$, $TPS^{(R)}$ in top and $MKII^{(R)}$, $RBM^{(R)}$, $Osseotite^{(R)}$, $TPS^{(R)}$ in mid-section but the value of $MKII^{(R)}$ bottom was the lowest, followed by $Osseotite^{(R)}$, $RBM^{(R)}$ and $TPS^{(R)}$. 3. RFA increased by the order of $RBM^{(R)}$(7042Hz), $MKII^{(R)}$(7047Hz), $Osseotite^{(R)}$(7076Hz), $TPS^{(R)}$(7168Hz) and there was no significance between each group. 4. PTV was increasing by the order of $MKII^{(R)}$(-1.62), $TPS^{(R)}$(-1.92), $Osseotite^{(R)}$ & $RBM^{(R)}$(-2.08) and there was no significance, either. 5. Removal torque in RTV measurement showed the increasing order of $MKII^{(R)}(5.31kgf{\cdot}cm)$, $Oeeotite^{(R)}(5.71kgf{\cdot}cm)$, $TPS^{(R)}(5.92kgf{\cdot}cm)$ and $RBM^{(R)}(7.24kgf{\cdot}cm)$ and there was no significance among groups. Above observations explains that surface roughness does not make any impact on the initial stability of implants installation.

• Tribology and Lubricants
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• 제21권1호
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• pp.1-7
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• 2005

Effect of Surface roughness on nanoscale adhesion was studied experimentally by using colloidal probe technique. Glass micro balls having the radius of $3.3\~17.4{\mu}m$ were glued at the end of AFM cantilevers to prepare colloidal probes. Adhesion force between the colloidal probe and Si-wafer was measured using pull-off force measuring method. Results showed that the measured adhesion forces are not the function of the radius of the glued balls because the ball surfaces are rough. It is also found that roughness parameters such as $R_a,\;R_q\;and\;R_{max}$ do not have important role on nanoscale adhesion. In order to find the effect of surface roughness on nanoscale adhesion, the bearing areas were extracted from the measured topography of glued balls. After normalizing the measured adhesion force with the bearing area, it was found that the normalized adhesion force kept constant as function of the radius of glued ball.

• 한국산림과학회지
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• 제112권3호
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• pp.374-381
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• 2023

산지하천에서 발생하는 돌발홍수는 특정 지점의 점(Point) 유속보다는 전체 구간의 평균 유속에 따라 이동속도가 결정되며, 구간 평균유속은 하천경사, 하상재료, 수리적 거칠기에 많은 영향을 받는다. 이 연구에서는 하천경사 및 거칠기 높이를 이용하여 산지하천의 구간 평균유속 추정방법을 개발하였다. 염료추적자법(Dye Tracing)을 이용하여 특정 구간의 평균유속을 측정하고, LiDAR 영상으로부터 하천 지형 및 형상을 추출하였다. 거칠기 높이를 산정하기 위해 표면 거칠기 변수(R_a, R_max, R_z )와 하상재료의 크기(D₅₀, D₈₄)를 이용하였다. 현장 계측자료로부터 무차원 접근법을 이용하여 구간 평균유속과 유량과의 관계식 v = 0.5499Q^0.6165 을 도출하였으며, R² =0.77의 설명력을 나타냈다. 이 연구에 이용된 5개의 거칠기 높이 중 평균 거칠기 높이(R_a)의 RMSE가 0.45로서 다른 거칠기 높이의 범위(0.47-1.04)보다 낮게 나타나 평균 거칠기 높이(R_a)가 구간 평균유속 산정을 위한 거칠기 높이 인자로 가장 적합하다고 판단되었다.

• 한국정밀공학회지
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• 제18권10호
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• pp.61-68
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• 2001

Turbine blade in nuclear plant is subject to cyclic bending fatigue by high steam pressure. Especially, fatigue fracture is caused by low stress below yielding stress. Photograph by SEM doesn't have striation but photograph by AFM has striation on the fatigue fractured surface of 12% Cr steel used in turbine blade. Surface roughness $R_q$ has the linear relation with respect to stress intensity factor range ΔK and is increased linearly according to load amplitude $\textit{\Delta}P$. In this study loading condition applied to turbine blade is predicted by the relation between the gradient of $R_q$ to $\textit{\Delta}K$ and load amplitude $\textit{\Delta}P$.

• 한국응용과학기술학회지
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• 제34권1호
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• pp.152-162
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• 2017

태양광 발전의 효율을 높이기 위한 실란 커플링제와 나노 무기산화물을 첨가한 계면활성제를 이용한 친수성 코팅액을 제조하여 태양광 모듈의 유리 표면에 도포하여 김서림 방지(antifogging) 및 내오염성(antifouling)을 부여하였다. 1% 친수성 코팅액에 나노 무기산화물인 $Ludox^{(R)}$를 첨가한 경우 $Ludox^{(R)}$의 농도에 관계없이 초친수성과 우수한 antifogging 효과를 나타내었다. 그러나 유리에 대한 antifouling 효과는 $Ludox^{(R)}$를 10% 이상 첨가하였을 때부터 발현되었다. 또한, pH 4에서 가수분해한 TEOS를 첨가한 코팅액의 경우 TEOS를 0.7% 첨가한 경우 steam test 결과 antifogging 효과를 유지하였으며, 코팅한 유리 표면을 젖은 킴와이프로 100회 문지른 후에도 pollution test 결과 antifouling 효과를 유지하였다. 또한, AFM을 이용하여 표면 거칠기($R_q$)를 확인한 결과 TEOS를 너무 많이 첨가하면 가장 높은 표면 거칠기 값을 보였으며 코팅된 표면의 상태도 매우 불규칙하였다. TEOS가 0.7% 첨가된 경우 비교적 높은 표면 거칠기 값과 안정된 표면 상태를 나타내었다. 결론적으로 김서림 방지 특성만을 위하여는 나노 무기산화물인 $Ludox^{(R)}$는 필요없으나, antifouling의 효과를 나타내기 위해서는 최소 10%의 $Ludox^{(R)}$가 첨가되어야 하며, 우수한 내구성을 나타내기 위해서는 0.7%의 TEOS를 첨가해야 한다.

• 한국정밀공학회지
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• 제27권4호
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• pp.40-45
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• 2010

Evaluation of uncertainty is an ongoing process that can consume time and resources. It can also require the service of someone who is familiar with data analysis techniques. Therefore, it is important for laboratory personnel who are approaching uncertainty analysis for the first time to be aware of the resources required. International inclination of measurement filed to guarantee the traceability and confidence of measurement results discards the error concept and instead analyzes the measurement uncertainty. In this paper, we analyzed the elements of measurement uncertainty on surface roughness test which are the important things in mechanical parts test. Repeat the test by 3 men, the measurement uncertainty could be calculated.

• 한국정밀공학회지
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• 제5권1호
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• pp.78-83
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• 1988

The purpose of this study is to understand the cutting characteristics of glass-fiber rein- forced plastic (GFRP) by investigating the variation of cutting force and surface roughness, depending on the amount fo flank wear and cutting conditions. And a Taylor type tool life equation is derived using the regression analysis. The present study reveals that, 1. Taylor's eqquation can be applicable to GFRP nd the constants n (0.170-0.175) and C (53.7- 64.4) are smaller than those in cutting of steel. 2. Principal cutting force increases sharply with the increase of feed rate, but feed force and radial force are almost constant. This result is quite different from that of metal cutting. 3. Cutting forces ($F_P, \;F_Q, \;F_R$) increase with the increase of flank wear, and feed force especially increases sharply with the increase of flank wear. 4. Surface roughness changes very much along the circumference of the workpiece and the amount of flank wear has almost no effect on surface roughness.

• 전자공학회논문지A
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• 제32A권3호
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• pp.471-481
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• 1995

Measurement factors for the dielectric properties of low dielectric loss materials (tan${\dalta}{\le}10^{-4}$) were investigated using the dielectric rod resonator method. It was shown that the relative conductivity (${\sigma}_{r}$) should be controlled within a 5% to obtain the standard deviations of less than 0.07 for permittivity .epsilon.r and 0.06${\times}10^{-4}$ for tan.delta.respectively. Surface resistivity (R$_s$) could be reduced when the surface roughness of parallelled conducting plate was less than 0.07 .mu.m. Measurement error for the permittivity was $\pm$0.02% independent of probe loop size, whereas the error in Q value was reduced with the decrease in probe loop size and also with the increase in the absolute values of Q. Reliable Q values were determined with the probe loop size of less than 4mm. The accurate for the distance between the measuring probe loop and the sample could be obtained when the insertion loss of resonant frequency ranged -15dB - -30dB.

• 한국농공학회지
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• 제18권2호
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• pp.4116-4120
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• 1976

With the use of many rivers increased nearly to the capacity, the need for information concerning daily quantities of water and the total annual or seasonal runoff has became increased. A systematic record of the flow of a river is commonly made in terms of the mean daily discharge Since. a single observation of stage is converted into discharge by means of rating curve, it is essential that the stage discharge relations shall be accurately established. All rating curves have the looping effect due chiefly to channel storage and variation in surface slope. Loop rating curves are most characteristic on streams with somewhat flatter gradients and more constricted channels. The great majority of gauge readings are taken by unskilled observers once a day without any indication of whether the stage is rising or falling. Therefore, normal rating curves shall show one discharge for one gauge height, regardless of falling or rising stage. The above reasons call for the correction of the discharge measurements taken on either side of flood waves to the theoretical steady-state condition. The correction of the discharge measurement is to consider channel storage and variation in surface slope. (1) Channel storage As the surface elevation of a river rises, water is temporarily stored in the river channel. There fore, the actual discharge at the control section can be attained by substracting the rate of change of storage from the measured discharge. (2) Variation in surface slope From the Manning equation, the steady state discharge Q in a channel of given roughness and cross-section, is given as {{{{Q PROPTO SQRT { 1} }}}} When the slope is not equal, the actual discharge will be {{{{ { Q}_{r CDOT f } PROPTO SQRT { 1 +- TRIANGLE I} CDOT TRIANGLE I }}}} may be expressed in the form of {{{{ TRIANGLE I= { dh/dt} over {c } }}}} and the celerity is approximately equal to 1.3 times the mean watrr velocity. Therefore, The steady-state discharge can be estimated from the following equation. {{{{Q= { { Q}_{r CDOT f } } over { SQRT { (1 +- { A CDOT dh/dt} over {1.3 { Q}_{r CDOT f }I } )} } }}}} If a sufficient number of observations are available, an alternative procedure can be applied. A rating curve may be drawn as a median line through the uncorrected values. The values of {{{{ { 1} over {cI } }}}} can be yielded from the measured quantities of Qr$.$f and dh/dt by use of Eq. (7) and (8). From the 1/cI v. stage relationship, new vlues of 1/cI are obtained and inserted in Eq. (7) and (8) to yield the steady-state discharge Q. The new values of Q are then plotted against stage as the corrected steadystate curve.