• Geomechanics and Engineering
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• v.32 no.1
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• pp.97-110
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• 2023

The coefficient of lateral earth pressure at rest in loose sand during virgin loading, K₀ , and during unloading, K'₀ , have been determined from laterally confined load-unload tests. The tests included measurement of lateral pressure with null pressure gauges, side wall friction with newly designed friction meters and applied pressure and base pressure with load cells. The importance of accounting for side-wall friction when evaluating the distribution of vertical pressure over the height of the soil specimen was demonstrated. Relatively uniform friction was observed during loading, but this was not the case during unloading unless friction reduction measures were employed. While the measured value of K₀ was found to be close to, if slightly higher than the value commonly estimated on the basis of friction angle, φ', the ratio of K'₀ to K₀ was found to reasonably fit an expression of the form K'₀/K₀ = 1 + C·log(OCR), with C equal to 1 in the present tests.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.1
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• pp.53-62
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• 1989

In order to determine the form and the length of saline wedge, it is necessary to evaluate interfacial friction factor. Hetherto one dimensional two-layer flow model which assumed pressure as the hydrostatic pressure distribution has been well used to the calculation of saline wedge form, it just then stands in need of relevant interfacial friction factor. For example, in the case where we calculate back to interfacial friction factor out of saline wedge form obtained at a laboratory open channel with comparatively narrow width, it is needed to correct the side-wall effect of a channel, if generally negligible in the river. In this study, we confirmed the influence of a side-wall upon the lateral velocity distributions at laboratory channel and then examined in detail the value of interfacial friction factor in the case where it was corrected by the side-wall effect and not corrected. And then we make clear the influence of a side-wall upon the arrested saline wedge and interfacial faction factor from these results.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.03a
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• pp.53-57
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• 1998

In order to investigate the effects of the variables during the stamping process upon the side wall curl behavior, experiments and finite element analyses were done using a 90 degree draw-bending test. The variables considered were the die radius, the forming speed, the restraint force, the lubrication and the sheet grade. The experiments and simulation conditions were selected according to the design of experiment (DOE) approach. The effects of the restraint force, the lubrication and the forming speed were the same for both high strength and mild steels, but the effects of the die radius on the side wall curl were dependent on the magnitude of the die radius and the sheet grade. A straight side wall was observed for both high strength and mild steels when the die radius was about 2∼3 times of the sheet thickness. It was recommended that the restraint force, the forming speed and the friction be increased in order to reduce the side wall curl.

• Journal of the Korea Institute of Military Science and Technology
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• v.3 no.2
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• pp.213-218
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• 2000

An experimental study was performed to investigate the effect of surface temperature mismatch on measurements of skin friction using a plug-type skin friction gage mounted on the side wall of a supersonic wind tunnel. The freestream Mach number was 2.4 and Reynolds number per meter was $5.25 {\times}10^7$ with total pressure of 50 psi and total temperature of 275K. Temperature mismatch between the gage surface and surrounding wall surface was generated by hot water injection using the active temperature control system. Results of the tests showed that the temperature mismatch made sizable effects on the measurements of skin friction.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.5
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• pp.365-374
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• 2011

For the first time, the present study has measured the velocity distribution function in circular open channel flow in a three-dimensional shape using a stereoscopic PIV system. For a given channel slope, water depth was varied from 30% to 80% of the channel diameter. Then, the characteristics of the velocity distribution function was compared according to the change of the water depth. Unlike a rectangular channel, the present experiment exhibited quite different shapes in the velocity distribution function whether the water depth is higher than 50% or not. Especially, the position of maximum velocity in the central and side wall changes in a different manner for the water depth above 50%. By differentiating the velocity distribution function, local wall friction coefficient was evaluated as a function of wall position. If the water depth goes down, the difference between the maximum and minimum values in the local wall friction coefficient increases, and the averaged value a1so increases.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.10
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• pp.809-820
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• 2003

The present study investigates effects of flow velocity on the convective heat/mass transfer characteristics in wavy ducts of a primary surface heat exchanger application. Local heat/mass transfer coefficients on the wavy duct sidewall are determined by using a naphthalene sublimation technique. The flow visualization technique is used to understand the overall flow structures inside the duct. The aspect ratio and corrugation angle of the wavy duct is fixed at 7.3 and 145$^{\circ}$ respectively, and the Reynolds numbers, based on the duct hydraulic diameter, vary from 100 to 5,000. The results show that there exist complex secondary flows and transfer processes resulting in non-uniform distributions of the heat/mass transfer coefficients on the duct side walls. At low Re (Re<1000), relatively high heat/mass transfer regions like cell shape appear on both pressure and suction side wall due to the secondary vortex flows called Taylor-Gortler vortices perpendicular to the main flow direction. However, at high Re (Re>1000), these secondary flow cells disappear and boundary layer type flow characteristics are observed on pressure side wall and high heat/mass transfer region by the flow reattachment appears on the suction side wall. The average heat/mass transfer coefficients are higher than those of the smooth circular duct due to the secondary flows inside wavy duct. And also friction factors are about two times greater than those of the smooth circular duct.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.2
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• pp.17-23
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• 2000

Experimental investigations were conducted to study the forced convection of fully-developed turbulent flow in horizontal equilateral duct fabricated with the same length and equivalent diameter, but different surface roughness pitch ratio(P/e) of 4, 8 and 16 on the one side wall only. The experiments were performed with the hydraulic diameter based Reynolds number ranged from 70,000 to 10,000. The entire bottom wall of the duct was heated uniformly and the other surfaces were thermally insulated. To understand the mechanisms of the heat transfer enhancement, measurements of the heat transfer were done to investigate the contributive factor of heat transfer promotion, namely, the fin effect. And the results were compared with those of previous investigations for similarly configured channels, at which they were roughened by regularly spaced transverse ribs in the rectangular and circular channels.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.65-70
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• 2000

Experimental investigations were conducted to study the forced convection of fully-developed turbulent f)on· in horizontal equilateral duct fabricated with the same length and equivalent diameter, but different surface roughness Pitch ratio(P/e) of 4, 8 and 16 on the one side wall only The experiments were performed with the hydraulic diameter based Reynolds number ranged from 70.000 to 10,000 The entire bottom wall of the duct was heated uniformly and the other surfaces were thermally insulated. To understand the mechanisms of the heat transfer enhancement. measurements of the heat transfer were done to investigate the contributive factor of heat transfer promotion. namely the fin effect. And the results were compared with those of Previous investigations for similarly configured channels, at which they were roughened by regularly spaced transverse ribs in the rectangular and circular channels.

• Journal of the Korean Geotechnical Society
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• v.15 no.4
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• pp.235-246
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• 1999

Some of the underground structures such as subway tunnels are constructed by open cut method, in which the ground is excavated, a structure installed, and after that the excavated space is backfilled. In this case, because of their narrow and constrained boundary conditions, the earth pressure induced by self-weight of the backfilled soil acting on the underground structures is different from that of the classical theory. The vertical and horizontal earth pressures acting on upper slab and side wall of the underground structures constructed by open cut method are affected by the backfill geometry. The laboratory model tests were performed in the conditions of a variety of the shapes of backfill geometry and wall friction. And their results were compared with those from theories. As a result, it was observed that the distribution of the earth pressure acting on the underground structure is affected by the shapes of backfill geometry, the width of backfill, the angle of excavation and the wall friction.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.8
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• pp.783-789
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• 2012

In this study, turbulent flow and heat transfer characteristics in a helically coiled tube have been numerically investigated. Helically coiled tubes are commonly used in heat exchange systems to enhance the heat transfer rate. Accordingly, they have been widely studied experimentally; however, most studies have focused on the pressure drop and heat transfer correlations. The centrifugal force caused by a helical tube increases the wall shear stress and heat transfer rate on the outer side of the helical tube while decreasing those on the inner side of the tube. Therefore, this study quantitatively shows the variation of the local Nusselt number and friction factor along the circumference at the wall of a helical tube by varying the coil diameter and Reynolds number. It is seen that the local heat transfer rate and wall shear stress greatly decrease near the inner side of the tube, which can affect the safety of the tube materials. Moreover, this study verifies the previous experimental correlations for the friction factor and Nusselt number, and it shows that the correlation between the two in a straight tube can be applied to a helical tube. It is expected that the results of this study can be used as important data for the safety evaluation of heat exchangers and steam generators.