• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.100-109
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• 2004

Is this study, results of static pile load tests of in-situ cast piles in weak or uncemented sedimentary rock layers have been analyzed and presented. Consdierations on the characteristics of soils sedimentary rocks have been made. From the measurements of strain gauges and extensometers the relationship of unit skim friction versus displacement and that of unit end bearing versus displacement have been obatined to verity the characteristics of bearing capacity of this uncemented sedimentary rock layers. Also, a comparison has been made between ultimate skin friction in compression and tension.

• Journal of Power System Engineering
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• v.5 no.2
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• pp.30-35
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• 2001

A comparison of fully developed heat transfer and friction factor characteristics has been made in rectangular ducts with one wall roughened by five different shapes. The effects of rib shape geometries and Reynolds number are examined. The rib height-to-duct hydraulic diameter, pitch-to-height ratio, and aspect ratio of channel width to height are fixed at $e/D_e=0.0476$, P/e=8, and W/H=2.33, respectively. To understand the mechanisms of the heat transfer enhancements, the measurements of the friction factors are also conducted in the smooth and rough channels. The data indicate that the triangular type rib has a substantially higher efficiency index than any other ones in the range we studied.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.7
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• pp.1597-1603
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• 1995

A prediction model on forward slip has been developed for presetting rolling speed of each finish mill stand in the continuous hot strip roduction. Those factors such as neutral point, friction coefficient, volume fractions undergoing width spread, shape of deformation zone at each side of entry and delivery of the rolls were taken into account. To reduce the speed unbalance between adjacent stands a refining method of adjusting friction coefficient has also been developed. On-line application of the model showed a good agreement in rolling speeds between the predictions and the actual measurements, and gave an outstanding improvement in the travelling stability of strip passing through the finishing mill train.

• Transactions of Materials Processing
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• v.22 no.7
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• pp.394-400
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• 2013

Microforming is a very efficient and economical technology to fabricate very small metallic parts in various applications. In order to extend the use of this forming technology for the production of microparts, the size effect, which occurs with the reduction of part size and affects the forming process significantly, must be thoroughly investigated. In this study, the tribological size effect in microforming was studied using modeling and scaled ring compression experiments. A micro-scale friction approach based on the slip-line field theory and lubricant pocket model was used to understand the friction mechanism and explain the tribological size effect. Ring compression tests were performed to analyze the interfacial friction condition from the deformation characteristics of the ring specimens. In addition, finite element analysis results were utilized to quantitatively determine the size-dependent frictional behavior of materials in various process conditions. By comparing theoretical results and experimental measurements for different size factors, the accuracy and reliability of the model were verified.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.1
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• pp.1-9
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• 2007

Water condensate accumulated on the surface of a fin-and-tube heat exchanger significantly affects its thermal and hydraulic performance. The purpose of this study is to investigate the effect of condensate retention on the air-side heat transfer performance and flow friction. Total 12 samples of slit and plate fin-and-tube heat exchangers with varying fin spacing and number of tube rows are tested under dry and wet conditions. The thermal fluid measurements are made using a psychometric calorimeter. Frontal air velocity varies in the range from 0.7 m/s to 1.5 m/s. Using the experimental data, presented are the heat transfer coefficients in terms of Colburn j-factor and friction factor.

• Journal of KSNVE
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• v.9 no.2
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• pp.258-264
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• 1999

The purpose of this paper is to investigate the damping behavior of a flexible joint. The slip at a structrual joint is selected at the tips of two identical cantilever beams adjoining each other. Both the direction of normal force and its magnitude varies due to the global deformation of the structure from mode to mode in the friction model. The friction dependent on vibration displacements resultsin the same functional behavior of the hysteretic material damping. Linearized energy loss factors are obtained as functions of both linear and torsional spring stiffness for their groups of symmetric and anti-symmetric modes, respectively. Experimental measurements as made for comparisons with analytical estimations by controlling the magnitude of fastening torque in the fastener, Hi-Lite. Trends on damping levelsmeasured in a very common vibration test method make an excellent agreement on the estimated damping levels.

• Journal of Korea Water Resources Association
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• v.45 no.5
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• pp.455-464
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• 2012

In this study, a combined unsteady friction model has been developed to simulate the waterhammer phenomenon for the pipeline system. The method of characteristics has been employed as the modeling platform for the integration of the acceleration based model and the frequency dependant model for unsteady friction. Both Zielke's model and Ramos model were also compared with pressure measurements of a pilot plant pipeline system. In order to validate the modeling approach, a pipeline system equipped with the high frequency pressure data acquisition system was fabricated. The time series of pressure, introduced by a sudden valve closure, were obtained for two Reynolds numbers. A trial and error method was used to calibrate parameters for unsteady friction model. The comparison between different unsteady friction contributions in pressure variation provided the comprehensive understanding in the pressure damping mechanism of waterhammer. The proper evaluation of unsteady friction impact is a critical factor for accurate simulation of hydraulic transient.

• Korean Journal of Oriental Medicine
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• v.14 no.3
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• pp.103-111
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• 2008

Recently, skin diagnosis has been suggested as a promising tool for discrimination of Sasang Constitution, reported by examining the skin characteristics such as thickness, stiffness, slip, and skin textures like wrinkles and furrows. However, the works had a limitation in that clinical decision on the skin characteristics was made by relying upon oriental medicine doctors' subjective sense of touch. In order to objectify the skin diagnosis and claim its efficacy on the discrimination of the Sasang Constitutions, it is necessary to demonstrate its discrimination capability by providing numerical values in terms of physical quantities obtained from measurements using today's sensors and equipment technologies, which motivated this work as a priliminary step towards objectification of skin diagnosis. The skin characteristics focused in this work is the slip property of the back-hand skin that has been exploited using the dynamic friction measurement system. First, curved geometric effects of the back-hand skin on the measured lateral/vertical force signals were estimated using the artificially designed silicon coated structures, which led to a suggestion on a quality controlled experimental design based upon a empirical analysis model. Second, the experimental design thus suggested has been applied to the measurement of dynamic friction coefficients for two healthy male subjects of Taeumin (TE) and Soyangin (SY), respectively. The result shows that the dynamic friction coefficient is less for the SY subject than for the TE subject around the area of the skin used for diagnosis by the oriental medicine doctor, implying the TE subject's skin is more slippery than the SE subject's that is consistent with the oriental medicine doctor's diagnosis. Hopefully, this work can provide guidelines for obtaining quality data in friction measurement to be collected for discussion on the efficacy of the skin diagnosis and its objectification through statistical analysis.

• Tribology and Lubricants
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• v.24 no.2
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• pp.63-71
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• 2008

Friction and adhesion tests were conducted to investigate tribological characteristics of materials for MEMS/NEMS using atomic force microscope (AFM). AFM Si tips were chemically modified with a self-assembled monolayer (SAM) derived from trichlorosilane like octadecyltrichlorosilane (OTS) and (1H, 1H, 2H, 2H-perfluorooctyl) trichlorosilane (FOTS), and various materials, such as Si, Al, Au, Cu, Ti and PMMA films, were prepared for the tests. SAMs were coated on Si wafer by dipping method prior to AFM tip to determine a proper dipping time. The proper dipping time was determined from the measurements of contact angle, surface energy and thickness of the SAMs. AFM tips were then coated with SAMs by using the same coating condition. Friction and adhesion forces between the AFM Si tip modified with SAM and MEMS/NEMS materials were measured. These forces were compared to those when AFM tip was uncoated. According to the results, after coating OTS and FOTS, the friction and adhesion forces on all materials used in the tests decreased; however, the effect of SAM on the reduction of friction and adhesion forces could be changed according to counterpart materials. OTS was the most effective to reduce the friction and adhesion forces when counterpart material was Cu film. In case of FOTS, friction and adhesion forces decreased the most effectively on Au films.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.1077-1078
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• 2013