• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.5 no.1
• /
• pp.75-81
• /
• 1985

The behavior of a plane buoyant jet within the zone of flow establishment(ZFE) which is discharged vertically upward into a stagnant uniform environment, is analyzed by the integral equations of mass, momentum and tracer conservation. The analysis includes the spreading ratio with Froude number and geometry of the potential core of ZFE and the length of ZFE. The central velocity at the end of ZFE is found to be influenced significantly by buoyancy, especially at low discharge Froude number. The results provide the necessary initial conditions for the investigation of the zone of established flow.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.2
• /
• pp.456-466
• /
• 1994

Experimental investigation was made to study the mechanism of fluid and thermal oscillation phenomena of surface-tension driven flow in a cylindrical liquid column heated from above which is the low-gravity floating zone simulated on earth. Hexadecane, octadecane, silicon oil (10cs), FC-40 and water are used as the test liquids. The onset of the oscillatory thermocapillary convection appears when Marangoni number exceeds its criteria value and is found to be due to the coupling among velocity and temperature field with the free surface deformation. The frequency of temperature oscillation decreases with increasing aspect ratio for a given diameter and Marangoni number and the oscillation level increases with Marangoni number. The flow pattern in the liquid column appears either as symmetric or asymmetric 3-D flow due to the oscillatory flow in the azimuthal direction. The free surface deformation also occurs either as symmetric or asymmetric mode and its frequency is consistent with those of flow and temperature oscillations. The amplitude of surface deformation also increases with Marangoni number.

• Fire Science and Engineering
• /
• v.27 no.1
• /
• pp.20-25
• /
• 2013

This study is experimentally analyzed to extract the major parameters affecting the performance of the smoke-control system and the relations of pressure difference between vestibule and supply air pressure zone effect of supply mass flow rate and leakage area in the smoke-control zone. To obtain this, the mock-up building of three-story scale with a total of 10 compartments was constructed, and several apparatus were also installed for in-situ measurement of the ventilation flow rate, pressure difference between compartments, smoke defensive air velocity, the opening-closing force of door, etc. This article show that pressure difference in the smoke-control zone is significantly related with leakage area of vestibule in low pressure region, leakage area of supply air pressure in over pressure region and both of them in pressure control region when the pressure control range of damper is 45 Pa~55 Pa.

• Economic and Environmental Geology
• /
• v.43 no.6
• /
• pp.615-623
• /
• 2010

Seismic refraction survey is a geophysical method that delineates subsurface velocity structure using direct wave and critically refracted wave. The generalized reciprocal method(GRM) is an inversion technique which uses travel-time data from several forward and reverse shots and which can provide the geometry of irregular inclined refractors and structures underlain by hidden layer such as low velocity zone and thin layer. In this study, a simple Excel-GRM routine was tested for fast mapping of the interface between weathering layer and bedrock during the survey, with employing a pair of forward and reverse shots. This routine was proved to control the maximum dip of approximately $30^{\circ}C$ and maximum velocity contrast of 0.6, based on the panel tests in terms of dipping angle and velocity contrast for the two-layer inclined models. In contrast with conventional operation of five to seven shots with sufficient offset distance and indoor data analysis thereafter, this routine was performed in the field shortly after data acquisition. Depth to the bedrock provided by Excel-GRM, during the field survey for Cheongju granite area, correlates well with the elevation of the surface of soft rock from the drill core and SPS logging data. This cost-effective routine developed for quickly delineating the bedrock surface in the field survey will be readily applicable to mapping of weathering zone in narrow zone with small variation of elevation of bedrock.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.28 no.10
• /
• pp.1210-1218
• /
• 2004

Experimental study was performed to investigate the flow behavior in boundary layer on the blade suction surface of a multi-stage axial flow compressor, which was focused on the third stage of the 4-stage Low Speed Research Compressor. Flow measurements in the boundary layer were obtained using a boundary layer hot wire probe, which was traversed normal to the blade suction surface at small increments by the probe traverse specially designed. Detailed boundary layer flow measurements covering most of the stator suction surface were taken and are described using time mean and ensemble averaged velocity profiles. Amplitude of the velocity fluctuation and turbulence intensity in the boundary layer flow are also discussed. At midspan, narrow but strong wake zone due to passing wake disturbances is generated in the boundary layer near the blade leading edge for the rotor blade passing period. Corner separation is observed at the tip region near the trailing edge, which causes to increase steeply the boundary layer thickness.

• Wind and Structures
• /
• v.22 no.6
• /
• pp.685-701
• /
• 2016

Downbursts are of great harm to transmission lines and many towers can even be destroyed. The downburst wind field model by Chen and Letchford was applied, and the wind loads of two typical transmission towers in inland areas and littoral areas were calculated separately. Spatial finite element models of the transmission towers were established by elastic beam and link elements. The wind loads as well as the dead loads of conductors and insulators were simplified and applied on the suspension points by concentrated form. Structural analysis on two typical transmission towers under normal wind and downburst was completed. The bearing characteristics and the failure modes of the transmission towers under downburst were determined. The failure state of tower members can be judged by the calculated stress ratios. It shows that stress states of the tower members were mainly controlled by 45 degree wind load. For the inland areas with low deign wind velocity, though the structural height is not in the highest wind velocity zone of downburst, the wind load under downburst is much higher than that under normal wind. The main members above the transverse separator of the legs will be firstly destroyed. For the littoral areas with high deign wind velocity, the wind load under downburst is lower than under normal wind. Transmission towers are not controlled by the wind loads from downbursts in design process.

• Geophysics and Geophysical Exploration
• /
• v.13 no.2
• /
• pp.153-158
• /
• 2010

To investigate the velocity structure in the central and southern parts of the Korean peninsula, a 299-km NW-SE seismic refraction profile KCRT-2008was obtained across major tectonic boundaries. Seismic waves were generated by detonating 250 ~ 1500 kg explosives at depths of 50 ~ 100 m in eight drill holes located at intervals of 21 ~ 113 km. The seismic signals were detected by 4.5 Hz geophones at a nominal interval of 500 m. The first-arrival times were inverted to derive a velocity tomogram. The raypaths indicate several mid-crust interfaces including those at approximate depths of 2 ~ 3, 11 ~ 13, and 20 km. The Moho discontinuity with refraction velocity of 7.7 to 8.1 km/s has a maximum depth of 34.5 km under the central portion of the peninsula. The Moho becomes shallower as the Yellow Sea and the East Sea are approached on the west and east coasts of the peninsula, respectively. The depth of the 7.6 km/s velocity contour varies from 31.3 km to 34.4 km. The velocity tomogram shows the existence of a 129 km wide low-velocity zone centered at 7.2 km depth under the Okchon fold belt and Gyeonggi massif and low-velocity(< 5.4 km/s) rocks in the Gyeongsang sedimentary basin with a maximum thickness of 2.6 km

• Clean Technology
• /
• v.13 no.4
• /
• pp.300-307
• /
• 2007

The combustion characteristics of diffusion flame formed in the wake of a cylindrical stabilizer with varying fuel injection angle were studied. This study was performed by measuring the flame stability limits, lengths and temperatures of recirculation zones of flames, turbulence intensity in the wake of stabilizer, and concentration distribution of combustion gas, and by taking photographs of flames. The flame stability limits are dependent on fuel injection angle and main air velocity. The length and temperature of recirculation zone are dependent on fuel injection angle. As the length of the recirculation zone is decreased, the flame shows more stable behavior. The temperature of recirculation zone has a maximum value at the condition of theoretical mixture. The flame stability is enhanced when the temperature in the recirculation zone decreases. The turbulence intensity in the wake of stabilizer is independent of the fuel injection angle, but it is affected by stabilizer itself and main air flow condition. If the stabilization characteristics of flame is good, the concentration of $C_3H_8$ is high, but the concentration of $CO_2$ is low at the boundary of recirculation zone. The combustion characteristics of diffusion flame can be controlled by changing the fuel injection angles. The appropriate fuel injection angle should be selected to get high combustion efficiency, high load power, low environmental pollution, and clean combustion condition of fuel.

• Journal of the Korean Society of Safety
• /
• v.35 no.2
• /
• pp.111-117
• /
• 2020

When KS C IEC 60069-10-1(2015) standard is applied to estimate a hazardous area, the chart showing the relationship between a hazardous area distance and release characteristic is used as a guide to determine the extent of hazardous zones for various forms of release. Three release characteristic lines based on the three types of release as an unimpeded jet release with high velocity, a diffusive jet release with low velocity, and a release of heavy gases or vapours that spread along horizontal surfaces are given. As these characteristic lines have the low limit threshold, it is difficult to estimate the hazardous area distance when the value of release characteristic is under the low limit threshold. And KS C IEC 60079-10-1(2015) standard shows the concept for a zone of Negligible extent(NE) which can be considered as non hazardous area, but it is also difficult to apply the concept of a Negligible extent. The purpose of this paper is to suggest the guideline for the release characteristic to decide a hazardous area distance and the Negligible extent(NE) being considered as non-hazardous area when deciding a hazardous area distances by the KS C IEC 60079-10-1 standard.

• Journal of the Semiconductor & Display Technology
• /
• v.22 no.4
• /
• pp.32-37
• /
• 2023

For the potential applications in large-area OLED lightings, hydrogen fuel cells, and secondary batteries, we have performed an intermittent coating of high-viscosity polydimethylsiloxane using roll-to-roll slot die coater. During intermittent coating, dead zones inevitably appear where the thickness of PDMS patch films becomes non-uniform, especially at the leading/trailing edge. To reduce it, we have coated the PDMS patches by varying the process parameters such as the installation angle of the slot die head, coating speed, and patch interval. It is observed that the PDMS solution flows down and thus the thickness profile is non-uniform for horizonal intermittent coating, whereas the PDMS solution remaining on the head lip causes an increase in the PDMS thickness at the leading/trailing edges for vertical intermittent coating when the coating velocity is low. As the coating speed increases, however, the dead zone is shown to be reduced. It is addressed that the overall dead zone (the dead zone at the leading edge + the dead zone at the trailing edge) is smaller with horizontal intermittent coating than with vertical intermittent coating.