• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.850-854
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• 2009

Approximate analysis for a building installed with a friction damper is revisited to get insight of its dynamic behavior. Energy balance equation is used to have a closed analytical form solution of dynamic magnification factor (DMF) for the building with combined viscous and friction damping. It is found out that DMF is dependent on friction force ratio and resonance frequency. Linear transfer function from input external force to output building displacement is obtained by simplifying DMF equation. Root mean square of building displacement is derived under earthquake-like random excitation. Finally, design of friction damper is proposed by processing target control ratio, damping ratio factor, and friction force in sequence.

• Journal of Power System Engineering
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• v.17 no.1
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• pp.64-70
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• 2013

The heat transfer and friction factor characteristics of turbulent flows in three stationary channels have been investigated experimentally to check out the effect of divergence ratio. These are a constant cross-sectional channel and two diverging channels with ratio of divergence(Dho/Dhi) of 1.16 and 1.49. The measurement was conducted within the range of Reynolds numbers from 15,000 to 89,000 and the dimension of uniform cross-sectional test section is $100mm{\times}100mm$ at the cross section and 1,000 mm in length. The measurements of heat transfer coefficients and friction factors in the uniform channels were conducted as a reference. Because of the streamwise flow deceleration, the heat transfer and friction factor characteristics in the diverging channel were quite different from those of the constant cross-sectional channel. The effective friction factors and convective heat transfer coefficients increased with increasing the ratio of divergence of the channel.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.5
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• pp.587-592
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• 1999

The combined effects of radius ratio and roughness pitch ratio on the turbulent fluid flow characteristics of the fully developed flow in the annullar tubes with rib-roughened core walls were determined for Reynolds number ranging from 12,000 to 66,000. To understand the underlying physical phenomena responsible for friction factor enhancement, measurements of velocity profiles and zero shear stress and maximum velocity positions were combined to propose the friction factor correlation. Friction factors were found to be a function of the roughness pitch ratio and radius ratio.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.1
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• pp.22-28
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• 2010

Approximate analysis for a building installed with a friction damper is performed to get insight of its dynamic behavior. Energy balance equation is used to have a closed analytical form solution of dynamic magnification factor(DMF). It is found out that DMF is dependent on friction force ratio and resonance frequency. Approximation of DMF and equivalent damping ratio of a friction damper is proposed with such assumption that the building with a friction damper shows harmonic steady-state response and narrow banded response behavior near resonance frequency. Linear transfer function from input external force to output building displacement is suggested from the simplified DMF equation. Root mean square of a building displacement is derived under earthquake-like random excitation. Finally, design procedure of a friction damper is proposed by finding friction force corresponding to target control ratio. Numerical analysis is carried out to verify the proposed design procedure.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.105-111
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• 2000

A numerical study has been performed to obtain the heat transfer and pressure drop characteristics for shell-and-tube heat exchanger with various shapes of tubes. The Tubes have variation of Aspect Ratio, Pitch and Rotation. Results are presented as plots of Colburn j factor and friction factor f against Aspect Ratio, Pitch and Rotation. As Aspect Ratio increases, j factor and f factor decreases. As Pitch increases, j factor decreases. j/f have optimized Pitch for each Aspect Ratio. Accordingly, there is fitness of Aspect Ratio and Pitch fur most effective cases. The Rotation of tubes are of no meaning for both heat transfer and pressure drop.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.831-836
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• 1989

It was found that the effect of the friction between the roll and the workpiece on the spread ratio in flat rolling processes varies with the width-to-height ratio and the reduction in height by Tozawa, Oh and kobayashi numerically. In the present study, the barrelling profile accompanying the width spread was predicted by using the energy method proposed by Kato, which is known to be one of the most advanced method for the three dimensional analysis of the rolling process. The modified velocity field was applied to compute the width spread and the result was verified by experiments. the analysis by the energy method gave the result that the spread ratio increases with the friction factor when the width-to-height ratio is 1 and decreases when the ratio is larger then 2, being consistent with the results of Tozawa and Oh. Nevertheless the cold rolling experiment for pure aluminium showed that the spread ratio decreases with the increasing friction factor irrespective of the width-to-hight ratio.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.3
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• pp.281-289
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• 2005

An experimental study on the heat transfer and friction characteristics of a fully developed turbulent air flow in a square channel with $45^{\circ}$ inclined ribs on one, two, and four walls is reported. Tests were performed for Reynolds number ranging from 7,600 to 24,900. The pitch-to-rib height ratio, p/e, was kept at 8 and rib height-to-channel hydraulic diameter ratio, $e/D_h$, was kept at 0.0667. The heat transfer coefficient and friction factor values were enhanced with the increase in the number of ribbed walls. Results of this investigation could be used in various applications of internal channel turbulent flows involving different number of roughened walls.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.4
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• pp.175-180
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• 2014

Experimental investigations of the heat transfer and friction factors in the ribbed divergent rectangular channel with the channel exit hydraulic diameter to inlet hydraulic diameter ratio of 1.16 were performed. The surface heaters were mounted onto the two opposite walls. The main experimental parameter is the ratio of rib pitch (p) to height (e), at which the ratios (p/e) of 6, 10, and 14 are considered in the channel with ribs on one wall only. The straight ribbed square channel is also considered as a comparison. The major findings are that the ratio of p/e = 6 shows the highest values in the heat transfer and the ratio of p/e = 10 indicates the greatest friction factor in the ribbed divergent channel. Editor's note:No major changes or corrections needed. Well written.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.241-247
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• 2001

A comparison of fully developed heat transfer and friction factor characteristics has been made in rectangular ducts with ones 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/De=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 indicates that the triangular type rib has a substantially higher heat transfer performance than any other ones in the range we studied.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.5
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• pp.341-347
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• 2001

A comparison of fully developed heat transfer and friction factor characteristics has been made in rectangular ducts with ones 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 $e$/De=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 indicates that the triangular type rib has a substantially higher heat transfer performance than any other ones in the range we studied.