• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1460-1465
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• 2004

Flow patterns around a rotating circular cylinder having square dimpled surface were visualized by the hydrogen bubble technique at velocity ratios from a=0 to 4.8 and Reynolds number of $Re=1.0{\times}10^{4}$. The wake region of the cylinder was reduced as the velocity ratios increase and was smaller than that of the smooth cylinder without dimples at the same velocity ratio. The hydrodynamic characteristics on the cylinder was investigated by measuring of lift and drag at velocity ratios from a=0 to 4.1 and Reynolds number from $Re=1.2{\times}10^{4}$ to $Re=2.0{\times}10^{4}$. As the velocity ratios increase, the average lift and drag coefficients were increased and at the same velocity ratio, the average lift was larger but the average drag was smaller than that of the smooth cylinder.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.4
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• pp.486-492
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• 2004

Flow patterns around a rotating circular cylinder having square dimpled surface were visualized by the hydrogen bubble technique at velocity ratios from a=0 to 4.8 and Reynolds number of Re=1.0${\times}$10$^4$. The wake region of the cylinder was reduced as the velocity ratios increase and was smaller than that of the smooth cylinder without dimples at the same velocity ratio. The hydrodynamic characteristics on the cylinder was investigated by measuring of lift and drag at velocity ratios from a=0 to 4.1 and Reynolds number from Re=1.2${\times}$10$^4$ to Re=2.0${\times}$10$^4$. As the velocity ratios increase, the average lift and drag coefficients were increased and at the same velocity ratio, the average lift was larger but the average drag was smaller than that of the smooth cylinder.

• The KSFM Journal of Fluid Machinery
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• v.14 no.3
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• pp.50-58
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• 2011

To utilize wind resources effectively around buildings in urban area, the magnitudes of wind velocity and turbulence intensity are important, which means the need of the information about the relationship between the magnitude of wind velocity and that of fluctuating wind velocity. In the paper, wind-tunnel experiments were performed to provide the information about Characteristic of Wind flow around buildings with the spanwise distance and the side ratio of buildings as variables. For a single building with the side ratios of one and two, the average velocity ratio was 1.4 and the velocity standard deviation ratio ranged from 1.4 to 2.6 at the height of 0.02m at the corner of the windward side, in which flow separation occurred. For twin buildings with the side ratios of one and two, the velocity ratio ranged from 2 to 2.5 as the spanwise distance varied at the height of 0.02m, and the velocity standard deviation ratio varied near 1.25. For twin buildings with the side ratios of one and two, the maximum velocity ratio was 1.75 at the height of 0.6m, and the maximum velocity standard deviation ratio was 2.1. It was also found from the results of CFD analysis and wind-tunnel experiments that for twin buildings with the side ratios of one and two, the difference between the velocity ratio of CFD analysis and that of wind-tunnel experiments at streamwise distances was near 0.75.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.1
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• pp.52-61
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• 2009

This experiment was conducted in attempt of improving hydrodynamic efficiency of the propulsion mechanism by installing a spring to the wing so that the opening angle of the wing in one stroke can be changed automatically, compared to the existing method of fixed maximum opening angle in Weis-Fogh type ship propulsion mechanism. Average thrust coefficient was almost fixed with all velocity ratio with the prototype, but with the spring type, thrust coefficient increased sharply as velocity ratio increased. Average propulsive efficiency was larger with bigger opening angle in the prototype, but in the spring type, the one with smaller spring coefficient had larger value. In the range over 1.0 in velocity ratio where big thrust can be generated, spring type had more than twice of propulsive efficiency increase compared to the prototype.

• Journal of the Korea institute for structural maintenance and inspection
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• v.5 no.3
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• pp.123-130
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• 2001

The purpose of this study is to suggest the non-destructive equation for the estimation of concrete strength by ultrasonic pulse velocity at the Age of 28day compressive strength of $600{\sim}1000kg/cm^2$. For this purpose, selected test variables were water-hinder ratio, replacement ratio of silica fume, binder content, maximum size of coarse aggregate and sand-aggregate ratio. From the results, the average increase or decrease of ultrasonic pulse velocity is 61m/sec for each 1% of moisture content. And the correlation equation between the ultrasonic pulse velocity and the compressive strength of concrete is as follows. $F_c=896.3V_p-3514$ ($R^2$ = 0.81) where, $F_c$ : compressive strength($kgf/cm^2$), $V_p$ : ultrasonic velocity(km/sec).

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1993.10a
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• pp.1043-1052
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• 1993

Field experiments were conducted to determine the optimum combination of performance parameters of a single-shank, tractor-mounted oscillating subsoiler. Tests were conducted at frequencies of oscillation of 3.7 , 5.67, 7.58, 9.48 and 11.456Hz ; amplitudes of 18, 21, 23.5, 34 and 36.5 mm ; and forward speeds of 1.84, 2.19 and 3.42 kmph at moisture content close to the plastic limit of the soil. It was observed that there was a reduction in average draft but an a increase in average total power requirement for oscillating than non-oscillating subsoiling. The draft and power ratios were significantly affected by the forward speed, frequency and amplitude. Their combined interaction expressed in terms of the velocity ratio parameter( the ratio of peak tool velocity and forward speed) however has the strongest influence. At the same velocity ratio, the draft reduction and power increase were less at higher amplitude of oscillation . As the oscillating frequency is increased toward the soil resonance the draft requirement becomes less. For the field conditions tested. the optimum operation was obtained at an amplitude of 36.5mm, frequency of 9.48Hz and speed of 2.19 kmph with a draft ratio of 0.33 and a power ratio of only 1.24.

• Journal of Biosystems Engineering
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• v.9 no.1
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• pp.22-33
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• 1984

Husk separator is an indispensable equipment in rice milling plants. However, any basic research on the designing and operating criteria of the husk separator have rarely been conducted in Korea. According to the survey results reported recently, grain loss occurs in the process of rice husk separation at custom rice milling plants in Korea and the performance of husk separator has also not been identified. With this regard this study was conducted with a typical commercial husk separator to investigate the effect of the operational factors such as feed rate, blower speed and opening ratio on the velocity distribution in the air duct and the performance of the separator. The results are summerized as follows: 1. The average wind velocity in the primary air duct increased linearly with the blower rpm and the size of air inlet port in both cases of double type and single type operations. 2. The coefficient of variation in the horizontal wind velocities in the primary air duct was the minimum when the opening ratio was 0.22 ($0.052m^2$ of air inlet port) in both cases of single type and double type operations regardless of the blower speeds used in this test. The average wind velocity at the upper part of air duct was greater by 2-5 m/s than the velocity at the bottom part in double type operation. In case of single type operation, however, the average velocity in the middle part was greater than the upper or bottom part when the opening ratio was greater than 0.74. 3. The relationship between the overall effectiveness of separation(Ed for double type and Es for single type) and the average wind velocity (Va) in the primary air duct was expressed in the following quadratic functions. $$Ed=-190.84+106.18Va-10.052Va^2$$ ($r^2$ = 0.97782) $$Es=-223.76+106.23Va-9.1935Va^2$$ ($r^2$ = 0.97029) The average wind velocity required to obtain the overall effectiveness of separation more than 80% ranged from 4.04 m/sec to 5.84 m/sec in case of double type operation, and from 4.70 m/sec to 6.20 m/sec in case of single type. 4. An optimum wind velocity can be obtained with an increase in the blower speed or the size of air inlet port as presented in Figure 8. There was a tendency that the faster the blower speed, the narrower the control range of the air inlet port. 5. The feed rates (1850kg/hr and 2100kg/hr) adopted in this experiment did not bring about a significant difference in both the overall effectiveness of separation and the power consumption. 6. The energy consumption increased cubically with the blower speed but linearly with the size of the air inlet port. On the basis of the results described in items 1, 3, and 6, it would be more economic to adjust the size of the air inlet port larger with a relatively low blower speed than to adjust the size smaller with a relatively high speed.

• Journal of computational fluids engineering
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• v.13 no.1
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• pp.21-27
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• 2008

A numerical study for laminar flow in the entrance region of helical tubes for uniform inlet velocity conditions is carried out by means of the finite volume method to investigate the effects of Reynolds number, pitch and curvature ratio on the flow development. This results cover a curvature ratio range of 1/10$\sim$1/320, a pitch range of 0.0$\sim$3.2, and a Reynolds number range of 125$\sim$2000. It has been found that the curvature ratio does significantly effect on the angle of flow development, but the pitch and Reynolds number do not. The characteristic angle $\phi_c(=\phi/\sqrt{\delta})$, or the non-dimensional length $\overline{l}(=l\sqrt{\delta}cos(atan\lambda)/d)$ can be used to represent the flow development for uniform inlet velocity conditions. In uniform inlet velocity conditions, the growth of boundary layer delays the flow development attributed to centrifugal force, and in which conditions the amplitude of flow oscillations is smaller than that in parabolic inlet velocity conditions. If the pitch increases or if the curvature ratio or Reynolds number decreases, the minimum friction factor and the fully developed average friction factor normalized with the friction factor of a straight tube and the flow oscillations decrease.

• Journal of the Korean Society of Combustion
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• v.18 no.2
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• pp.8-16
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• 2013

The flameless combustion has been considered as one of the promising combustion technology for high thermal efficiency, reducing NOx and CO emissions. In this paper, the effect of air and fuel injection condition on formation of flameless combustion was analyzed using three dimensional numerical simulation. The results show that the high temperature region and the average temperature was decreased due to increase of recirculation ratio when air velocity is increased. The average temperature was also affected by entrainment length. Generally mixing effect was enhanced at low entrainment length and dilution was dominated at high entrainment length. This entrainment length was greatly affected by air and fuel injection velocity and distance between air and fuel. It is also found that the recirculation ratio and dilution effect were generally increased by entrainment length and the recirculation ratio, mixing and dilution effect are the significant factor for design of flameless combustion system.

• The Journal of the Acoustical Society of Korea
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• v.25 no.2E
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• pp.49-55
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• 2006

Compressional wave velocity (Vp), shear wave velocity (Vs), elastic and physical properties, and electrical resistivity for two core sediments obtained from Southeastern Yellow Sea Mud (SEYSM) were measured and computed. The sediments consist of homogeneous mud (mostly silt and clay) with shells and shell fragments. As a result, the mean grain size is uniform ($7.5-8.5{\Phi}$ throughout the core sediments. However, physical properties such as wet bulk density and porosity show slightly increasing and decreasing patterns with depth, compared to the mean grain size. The compressional (about 1475 m/s in average) and shear wave (about 60 m/s in average) velocities with depth accurately reflect the pattern of wet bulk density and porosity. Electrical resistivity is more closely correlated with compressional wave velocity than physical properties. The computed Vp/Vs and Poisson's ratios are relatively higher (more than 10) and lower (approximately 0.002) than Hamilton's (1979) data, respectively, suggesting the typical characteristics of soft and fully water-saturated marine sediments. Thus, the Vp/Vs ratio in soft and unconsolidated sediments is not likely sufficient to examine lithology and sediment properties. Relationships between the elastic constant and physical properties are correlated well. The elastic constants (Poisson's ratio, bulk modulus, shear modulus) given in this paper can be used to characterize soft marine sediments saturated with seawater.