• 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 Materials Processing
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• v.15 no.9 s.90
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• pp.660-666
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• 2006

This study examined the mechanical properties and bending formability evaluation of spring strip materials(SK5 CSPH, STS 301 CSP-EH, C7701-H). The hardness test and tensile test were performed at room temperature($20^{\circ}C$) for mechanical properties. The U-bending test were carried out at various conditions of punch corner radius(Rp), ratio of punch comer radius/thickness(Rp/t) and ratio of clearance/thickness(Rp/t) and ratio of clearance/thickness(C/t) for bending formability evaluation.

• Journal of the korean Society of Automotive Engineers
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• v.6 no.1
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• pp.71-77
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• 1984

Stress analysis of split ring with four different radius ratios under the compressive load is made by the photoelastic experiment and the numerical analysis through the FEM. The results of the two methods agreed well. Above results are also compared with those of the theoretical formula in order to confirm the range in which the formula of the curved bar is applied in connection with the radius ratio. The results of the two methods agreed well with those of the formula for the radius ratio, 3/2 and 9/7 within small errors of around 7% and 5% respectively.

• Journal of Korean Society for Atmospheric Environment
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• v.29 no.2
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• pp.211-216
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• 2013

For diffusion limited cluster agglomerates the ratio of the mobility radius to the radius of gyration $R_m/R_g$ vs. N and the ratio of the mobility radius to the radius of primary particle $R_m$/a are determined using experimental data obtained with DMA-APM and tandem DMA over a range of Knudsen numbers extending into the transition region where there is a lack of data. It was found that in slip regime with the number of primary particles between 100 and 400, datapoints are found to be between the two asymptotic lines for the continuum and free molecular regimes as those datapoints are plotted in both $R_m/R_g$ vs. N and $R_m$/a vs. N.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.1
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• pp.43-55
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• 2008

The complexity of determining strain associated with shear modulus and damping ratio in torsional tests has been resolved by means of several approaches. Particularly, the modified equivalent radius approach is adequate to when generating the plots of equivalent radius ratio versus strain more effectively over any range of strains in resonant column and torsional shear (RC/TS) tests. The modified equivalent radius approach was applied for hyperbolic, modified hyperbolic, and Ramberg-Osgood models in evaluating damping ratio. Results showed that using a single value of equivalent radius ratio based on conventional equivalent radius approach is not appropriate. A new model was developed to consider the soil damping behavior at small strains as well as hysteretic damping and it was attempted to determine adjustments are required in evaluating strain associated damping when combining the two damping components.

• Journal of Mechanical Science and Technology
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• v.17 no.8
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• pp.1226-1233
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• 2003

Experimental heat transfer data for single-phase water flow in the annuli with corrugated inner tubes are presented. In the annuli with parallel flow, ten different annular arrangements are considered. For water flow rate in 1,700${\gamma}$$\^$*/). As P/e becomes closer to 8 in the range below the radius ratio (${\gamma}$$\^$*/) of 0.5, Nusselt numbers increase. However, Nusselt numbers decrease in the range above the radius ratio (${\gamma}$$\^$*/) of 0.5 because flow reattachment position becomes farther in the narrower clearance.

• Journal of Ocean Engineering and Technology
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• v.24 no.6
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• pp.61-70
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• 2010

This study presents free vibration analyses of perforates steel plates with various cutouts. Four different parameters (shape, size, curvature radius ratio, and rotation of cutouts) were considered to investigate the effects of those parameters on the free vibration characteristics, such as natural frequencies of the perforated steel plates. Three different shapes of cutouts are circle, square, and triangle, and the considered sizes are 5, 10, 15, 20, and 25 mm. For the triangular and square cutouts, the characteristic radii of the inscribed circles of those cutouts were defined. In addition, the curvature radius ratio was defined as the ratio of curvature radius of bluntness and the characteristic radius. Then, total seven different curvature radius ratios (0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1) were considered. To investigate the rotation effect of the cutouts, it was considered four rotations ($0^{\circ}$, $15^{\circ}$, $30^{\circ}$, and $45^{\circ}$) for the square cutouts and three rotations (0, 15, and 30) for the triangular cutouts. All the free vibration analyses were conducted using a general purpose finite element program. From the analyses we found that the most influential parameter for the free vibration response of the perforated plates is the size of cutout. The other factors such as the shape, curvature radius ratio, and rotation are minors; they mainly change the natural frequency as long as the size effect is accompanied.

• Journal of computational fluids engineering
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• v.21 no.3
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• pp.1-7
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• 2016

In the present study, the homogeneous model is used to simulate the natural convection heat transfer of the CuO-water nanofluid in a concentric annular enclosure. Simulations have been carried while the Rayleigh number ranges from $10^3$ to $10^6$, solid volume fraction ranges from 0.01 to 0.04 and the radius ratio varies between 0.1 and 0.7. Results are presented in the form of streamlines, isotherm patterns and averaged Nusselt numbers for different values of solid volume fraction, radius ratio of the annulus and Rayleigh numbers. The results show that by decreasing the radius ratio and/or increasing the Rayleigh number, the averaged Nusselt number increases. Also the heat transfer rate increases as increased solid volume fractions.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.108.2-108.2
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• 2012

Recent results from microlensing surveys show that a free-floating planet or a wide-separation planet is more numerous than a main-sequence star in the Galaxy. Moreover, the detection efficiency of the planets will be improved in next-generation experiments with a high survey monitoring frequency. However, microlensing events produced by both planets appear similar light curves with a short duration timescale, thus it is difficult to distinguish them. In this paper, we investigated the detectable separation range of a wide-separation planet as the planet bound to its host star. We construct the fractional deviation maps using the magnifications of the planetary lensing and the single-lensing by planet itself for various parameters such as a mass ratio, separation, and source radius. As a result, we found that the pattern of the fractional deviation is related to the ratio of source radius to caustic size, and the ratio satisfying the detection criterion (i.e., ${\geq}5%$ in the fractional deviation) varies with a separation. Hence, we derived a fitting formula as the function of a mass ratio and a source radius to reflect the variation in the calculations of the detectable separation range of a wide-separation planet as the planet bound to its host star. In addition, we estimated the condition that a wide-separation planet can be detected as a single-lensing event under the finite source effect. We found that such a case is possible provided that the source radius is smaller than ~2.5 times of Einstein ring radius of a planet, regardless of a separation or a mass ratio.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.642-645
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• 2008

A pin fin with variable fin base thickness is analysed by using the one dimensional analytic method. Heat loss and fin thermal resistance are presented as a function of the fin base thickness, pin fin outer radius and convection characteristic numbers ratio. The relationship between the fin outer radius and fin base thickness for the same amount of heat loss is shown. One of the results indicates the fin thermal resistance decreases as the fin outer radius and/or convection characteristic numbers ratio increase whereas the fin thermal resistance is independent on the variation of fin base thickness.