• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.1
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• pp.401-408
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• 2019

This study numerically examined the maximum wind pressure distribution of a billboard on the roof of a middle-rise building. The deformation caused by the maximum wind pressure was examined. For the numerical analysis, the signboard was assumed to be installed on $(b)20m{\times}(d)10m{\times}(h)$ buildings. The maximum wind pressure was measured using four models with the standard model and different sizes of the signboard. The numerical analysis showed that the horizontal deformation predominantly occurs as the shape of the signboard becomes closer to a rectangle, and high wind pressure and deformation occur at the corners of both ends. As the height of the signboard increases, vertical deformation predominantly occurs, and static pressure forms on the backside. When the height is lower than the width of the signboard, the wind pressure is concentrated on the center of the roof. Therefore, the distribution of the maximum wind pressure is stable, and the effect of the wind pressure is relatively low as the height-to-width ratio approaches 1.

• Journal of the Korean Institute of Gas
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• v.16 no.6
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• pp.1-6
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• 2012

Using the Siwek 20 L spherical explosion vessel, the explosion properties have been examined to understand the influence of magnesium content in Mg-Al alloy dusts with different concentration. For this purpose, the Mg-Al alloy dusts (volume mean diameter : $151{\sim}160{\mu}m$) with magnesium content ratio were used. As the results, the increase of Mg content in Mg-Al alloy causes an decreased minimum explosion concentration and an increased maximum explosion pressure. Also the maximum explosion pressure and maximum rate of pressure rise in Mg-Al alloy dusts mainly depended on the dust concentrations. However, for the explosion index (Kst) of Mg-Al (40:60 wt%), Mg-Al (50:50 wt%) and Mg-Al (60:40 wt%), it was founded to increase the Kst with increasing of magnesium content ratio.

• International Journal of Fluid Machinery and Systems
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• v.10 no.1
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• pp.63-75
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• 2017

Many axial fans have circular arc blades with constant thickness. It is still a challenging task to calculate their performance, i.e. to predict how large their pressure rise and pressure losses are. For this task a need for cascade data exists. Therefore, the designer needs a method which works quickly for design purposes. In the present contribution a design method for such cascades consisting of circular arc blades with constant thickness is described. It is based on a singularity method which is combined with a CFD-data-based flow loss model. The flow loss model uses CFD-data to predict the total pressure losses. An interpolation method for the CFD-data are applied and described in detail. Data of measurements are used to validate the CFD-data and parameter variations are conducted. The parameter variations include the variation of the camber angle, pitch chord ratio and the Reynolds number. Additionally, flow patterns of two dimensional cascades consisting of circular arc blades with constant thickness are shown.

• Aerospace Engineering and Technology
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• v.1 no.2
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• pp.113-122
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• 2002

A numerical analysis on the uniformity of propellant injection velocity of KSR-III has been carried out to give design improvements. Injector holes were approximated as porous media with the same pressure drop . The injection velocity is higher at the opposite side of the inlet for both LOX and fuel due to the static pressure rise in the stagnation region. Flow passages at the vertical circular plate in the LOX dome increase the uniformity of LOX injection. Little change was observed in the injection uniformity and pressure drop for the slanted LOX passage. Also provided were the O/ F ratio distributions from the oxidizer/ fuel injection velocity analysis.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2961-2966
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• 2007

When the pressure at the weak spot established at a certain part of a high pressure vessel or piping system exceeds a design pressure, this weak spot is burst, and the pressurized gas emitted through the weak spot will cause a compression wave system. In this connection, in the present study, an experimental study by using a conventional shock tube facility is performed to estimate the effects of the material of diaphragm, curvature radius and thickness of materials on the valve opening time in diaphragm. Pressure sensor having 500kHz in natural frequency is installed at 35mm downstream of the rupture diaphragm to measure the static pressure history of propagating and being accumulated compression wave. 4 kinds of materials are used as diaphragm that is aluminium, copper, stainless steel and zinc. The diaphragm radii of curvature R are ${\infty}$, 120mm and 60, respectively. And the depth for $90^{\circ}$ groove is 0.04mm. It is found that the smaller the tensile strength and elongation of the rupture diaphragm is, the smaller the radius of curvature of the rupture diaphragm is, and for the same conditions the thinner the thickness of the rupture diaphragm is, the shorter the valve opening time becomes. Also, the tensile strength, elongation and the radius of curvature of the rupture diaphragm for the same conditions are smaller, the maximum pressure rise caused by the coalescences of the compression wave is smaller. Finally the pressure ratio is higher, the valve opening time is shortened and gradient of pressure increment is more steepen.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.22
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• pp.10027-10031
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• 2014

Background: We investigated the risk of cancer mortality according to obesity status and metabolic health status using sampled cohort data from the National Health Insurance system. Materials and Methods: Data on body mass index and fasting blood glucose in the sampled cohort database (n=363,881) were used to estimate risk of cancer mortality. Data were analyzed using a Cox proportional hazard model (Model 1 was adjusted for age, sex, systolic blood pressure, diastolic blood pressure, total cholesterol level and urinary protein; Model 2 was adjusted for Model 1 plus smoking status, alcohol intake and physical activity). Results: According to the obesity status, the mean hazard ratios were 0.82 [95% confidence interval (CI), 0.75-0.89] and 0.79 (95% CI, 0.72-0.85) for the overweight and obese groups, respectively, compared with the normal weight group. According to the metabolic health status, the mean hazard ratio was 1.26 (95% CI, 1.14-1.40) for the metabolically unhealthy group compared with the metabolically healthy group. The interaction between obesity status and metabolic health status on the risk of cancer mortality was not statistically significant (p=0.31). Conclusions: We found that the risk of cancer mortality decreased according to the obesity status and increased according to the metabolic health status. Given the rise in the rate of metabolic dysfunction, the mortality from cancer is also likely to rise. Treatment strategies targeting metabolic dysfunction may lead to reductions in the risk of death from cancer.

• Wind and Structures
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• v.16 no.1
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• pp.93-115
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• 2013

This paper describes a study of the influence of a dynamically flexible building structure on pressures inside and net pressures on the roof of low-rise buildings with a dominant opening. It is shown that dynamic interaction between the flexible roof and the internal pressure results in a coupled system that is similar to a two-degree-of-freedom mechanical system consisting of two mass-spring-damper systems with excitation forces acting on both the masses. Two resonant modes are present, the natural frequencies of which can readily be obtained from the model. As observed with quasi-static building flexibility, the effect of increased dynamic flexibility is to reduce the first natural frequency as well as the corresponding peak value of the admittance, the latter being the result of increased damping effects. Consequently, it is found that the internal and net roof pressure fluctuations (RMS coefficients) are also reduced with dynamic flexibility. This model has been validated from experiments conducted using a cylindrical model with a leeward end flexible diaphragm, whereby good match between predicted and measured natural frequencies, and trends in peak admittances and RMS responses with flexibility, were obtained. Furthermore, since significant differences exist between internal and net roof pressure responses obtained from the dynamic flexibility model and those obtained from the quasi-static flexibility model, it is concluded that the quasi-static flexibility assumption may not be applicable to dynamically flexible buildings. Additionally, since sensitivity analyses reveal that the responses are sensitive to both the opening loss coefficient and the roof damping ratio, careful estimates should therefore be made to these parameters first, if predictions from such models are to have significance to real buildings.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.23-26
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• 2002

Two modes of shock waves propagating in He II (superfluid helium), this is a compression and a thermal shock waves, were studied experimentally by using superconductive temperature sensors, piezo pressure transducers and Schlieren visualization method with an ultra-high-speed video camera (40,500 pictures/sec). The shock waves are induced by a gas dynamic shock wave impingement upon a He II free surface. It is found that the shock Mach number of a transmitted compression shock wave is up to 1.16, and the shock Mach number of a thermal shock wave coincides well with the second sound velocity under each compressed He II state condition. The temperature rise ratio of an induced thermal shock wave to that of an incident gas dynamic shock wave was found to be very small, as small as 0.003 at 1.80K.

• Journal of the korean Society of Automotive Engineers
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• v.11 no.4
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• pp.35-42
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• 1989

The major purpose of this paper is a study on the effect of die profile radius on the formability of spring-type blankholder system in deep drawing process. By drawing the various materials, formability is studied by means of checking the drawing force, blankholding force variation, limiting drawing ratio and wall wrinkling phenomenon. As the die profile radius increases, the maximum drawing force and maximum blankholding force decrease regardless of lubrication condition. Because better lubrication induces blankholding force to rise, spring type blankholder system is better to protect flange wrinkling phenomenon than constant pressure type. And wall wrinkling phenomenon was not detected in experimental die radius range, so the Miyakawa's upper wrinkling limit is understimated in case of material tested.

• Wind and Structures
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• v.17 no.5
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• pp.537-552
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• 2013

Wind tunnel experiments were performed to study the wind loads on an inclined flat plate with and without a guide plate. Highly turbulent flow, which corresponded to free-stream turbulence intensity on the flat roof of low-rise buildings, was produced by a turbulence generation grid at the inlet of the test section. The test model could represent a typical solar collector panel of a solar water heater. There are up-stream movements of the separation bubble and side-edge vortices, more intense fluctuating pressure and a higher bending moment in the turbulent flow. A guide plate would result in higher lift coefficient, particularly with an increased projected area ratio of a guide plate to an inclined flat plate. The value of lift coefficient is considerably lower with increased free-stream turbulent intensity.