• 유체기계공업학회:학술대회논문집
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• 1998.12a
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• pp.105-114
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• 1998

Flow field and near-field noise of a centrifugal fan has been studied with an efrcient compressible method and STAR-CD. The flow field of the centrifugal fan is assumed two-dimensional. Most of the compressible studies has been done by inviscid solver because viscous simulation shows little difference. The near field noise is estimated in term s of sound pressure level in frequency domain transformed from the computed pressure fluctuations using FFT. The simulation has been done on various design elements such as impeller blade shapes, the number of blades and cut-off clearance. The comparison shows that the number of blades has a significant effect on near-field noise without losing aerodynamic performance.

• 전기의세계
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• v.24 no.6
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• pp.77-84
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• 1975

This paper treats A.C. arc movement in a transverse A.C. magnetic field at atmospheric pressure with the purpose of selecting electrode materials and obtaining detailed data for design of A.C. air circuit breaker, plasma accelerator and plasma jet. Arc velocities in transverse magnetic field are measured by varying arc current, arc voltage, gap length, magnetic flux density and the erosion of electrode surface, which influence arc velocities. The main results are; 1)Arc velocities in transverse magnetic field have different values according to electrodes of various materials and decrease in a descending order of cold cathode, medium cathode and hot cathode. 2)Arc velocities in transverse magnetic field increases with arc current, arc voltage, gap length and magnetic flux densith and on the other hand decrease with the increase of electrode surface erosion. 3)D.C.arc velocity in D.C. magnetic field is higher than A.C. arc velocity in A.C. magnetic field of the same value.

• The KSFM Journal of Fluid Machinery
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• v.2 no.1 s.2
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• pp.43-49
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• 1999

Flow field and near-field noise of a centrifugal fan has been studied with an efficient compressible method and STAR-CD. The flow field of the centrifugal fan is assumed to be two-dimensional. Most of the compressible studies have been done by inviscid solver because viscous simulation shows little difference. The near field noise is estimated in terms of sound pressure level in frequency domain transformed from the computed pressure fluctuations using FFT. The simulation has been done on various design elements such as impeller blade shapes, the number of blades and cut-off clearance. The comparison shows that the number of blades has a significant effect on near-field noise without losing aerodynamic performance.

• Proceedings of the IEEK Conference
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• 2001.10a
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• pp.443-447
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• 2001

A laboratory-scale electrodewatering system for enhancing conventional filter pressure dewatering by an electric field has been developed to decrease the water content of sludge generated in the wastewater treatment. It consists of a piston-typed filter press, a power supply and data acquisition system. The offset of electrodewatering is investigated as a function of applied pressure, applied voltage, sludge type and filtration time. Also the optimal conditions for maximizing the dewatering efficiency in the eletrodewatering system are investigated. Electric field strength and mechanical pressure are in the range of from 0 to 120 V/cm and from 98.1 to 392.4 kPa. The dewatering rates increased with increasing electric strength. These experiments produced a final sludge cake with water content of 60 wt% using electrodewatering technology, compared with a 80 wt% using pressure filtration alone. The conventional filtration system using the electrodewatering shows the potential to be effective method for improving dewatering Sludge.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.7 s.172
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• pp.130-136
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• 2005

A new MR cylinder with built-in valves using MR fluid (MR valve) is suggested and fabricated fur fluid control systems. The MR fluid is a newly developed functional fluid whose obvious viscosity is controlled by the applied magnetic field intensity. The MR cylinder is composed of cylinder with small clearance and piston with electromagnet. The differential pressure is controlled by the applied magnetic field intensity. It has the characteristics of simple, compact and reliable structure. The size of MR cylinder and piston has $\varphi30mm\times300mm$ and $\varphi28.5mm\times120mm$ in face size, respectively and 0.8mm in gap length. Through experiments, it was found that the differential pressure is controlled by the applied magnetic field intensity under little influence of the flow rate, which corresponds to a pressure control valve. The differential pressure of 0.47MPa was obtained with the input current of 1.5A. The rising time was 2.3s in step response of a manipulator using the MR cylinder. The effectiveness of the MR cylinder was also demonstrated through the position control.

• 한국가시화정보학회:학술대회논문집
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• 2004.12a
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• pp.75-80
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• 2004

Aerospike nozzles have been expected to be used for an engine of a reusable space shuttle to respond to growing demand for rocket-launching and its cost reduction. In this study, the flow field structures in any cross sections around clustered linear aerospike nozzles are visualized and analyzed, using laser induced fluorescence (LIF) of nitrogen monoxide seeded in the carrier gas of nitrogen. Since flow field structures are affected mainly by pressure ratio, the clustered linear aerospike nozzle is set inside a vacuum chamber to carry out the experiments in the wide range of pressure ratios from 75 to 200. Flow fields are visualized in several cross-sections, demonstrating the complicated three-dimensional flow field structures. Pressure sensitive paint (PSP) of PtTFPP bound by poly- IBM -co-TFEM is also applied to measurement of the complicated pressure distribution on the spike surface, and to verification of contribution of a truncation plane to the thrust. Finally, to examine the effect of the sidewalls attached to the aerospike nozzle, the flow fields around the nozzle with the sidewalls are compared with those without sidewalls.

• Journal of the Korean Society of Industry Convergence
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• v.26 no.3
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• pp.381-387
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• 2023

This study conducts the flow analysis on the basis of the impeller RPM of water measuring valve and differential pressure at valve inlet and outlet. The software used for the flow analysis is STAR-CCM+. In terms of the structure of the measuring valve, it has an impeller installed inside, and a metering chamber has inlet and outlet holes. The flow analysis on the water measuring valve drew the following conclusions: The flow rate and flow coefficient distribution according to the impeller RPM and differential pressure were on the linear increase. Regarding the flow field in the valve, the increased differential pressure had the highest velocity distribution, and complex flow field was generated in the measuring chamber. In particular, since the path between the inlet and outlet holes in the measuring chamber and the valve body was narrow, there was a section that had flow field interference. Given that, it showed the feature of the valve used for water measuring on the basis of the impeller RPM.

• Journal of Biosystems Engineering
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• v.36 no.5
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• pp.303-313
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• 2011

This study was conducted to investigate the effects of axle weight distribution and inflation pressure of tire on the fuel economy of tractors as well as operational range of tractor engine in terms of engine speed and power when a 4WD tractor of 38.2 kW rated power at 2500 rpm is used for plowing and flooded-field rotavating in paddy fields. (1) Plowing operation required an average engine power of 9.6~13.5 kW which equals 25~35% of rated PTO power. Engine speed ranged from 1,320.4 to 1,737.4 rpm, work velocity from 3.4 to 4.8 km/h, and fuel consumption from 3.2 to 4.2 L/h, respectively. (2) Flooded-field rotavating required an average engine power of 11.5~18.5 kW which equals 30~48.4% of rated PTO power. Out of this 6.2~12.2 kW was used for PTO power. Engine speed ranged from 1,557 to 2,067 rpm, work velocity from 2.5~5.4 km/h and fuel consumption from 3.2~5.5 L/h, respectively. (3) Axle weight distribution, inflation pressure of tire and moisture content of soil did not affect significantly the specific volumetric fuel consumption but affected significantly the fuel consumption per unit area of operation. Fuel savings amounted to 65% in plowing operation and 20% in flooded-field rotavating when the axle weight distribution and inflation pressure of tire were optimally adjusted. (4) Optimal adjustment of axle weight distribution and inflation pressure of tire are expected to save fuel consumption by 10~65% per unit area of operation in plowing and 10~20% in flooded-field rotavating.

• Tunnel and Underground Space
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• v.13 no.2
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• pp.125-137
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• 2003

Field measurements were carried out in this study to investigate the behavior of cut and cover tunnel such as the distribution and the magnitude of the earth pressure during back fill process. Three kinds of measuring instruments, such as the earth pressure load cell, the concrete strain gauge and the reinforcing bar meter of embedded type in concrete structure were installed and measured. Earth pressure load cells measured the outside forces acting on the tunnel lining with radial directions. Three load cells were installed at the crown, the right and the left shoulder of the tunnel, respectively. Three sets of reinforcing bar meter were installed in the double reinforcements of the tunnel lining and their locations were the same with the position of the earth pressure load cells. Concrete strain gauge was installed only one site of the upper compressive part at the tunnel crown. Based on the measurements, the deformation and the earth pressure acting on the tunnel lining were investigated with the back fill process. Considerations on the validity of the field measurements were paid.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.4
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• pp.429-440
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• 2015

In this study, model test equipment was developed to evaluate the hydraulic pressure reduction in appling the drainage shield tunnel and the model test for hydraulic pressure difference was performed in case of drainage and undrained conditions. In the result of model test, increase ratio of pore water pressure was decreased in drainage condition and total stress in drainage condition was smaller than that in undrained condition, so the hydraulic pressure was reduced by the groundwater inflow into the model tunnel. In the result of field instrumentation, the hydraulic pressure in the back ground of shield tunnel was small by 11~22% in comparison with the calculated hydraulic pressure ($r_w{\cdot}H$) in same groundwater level. In the result of model test and field instrumentation, it was appeared in drainage and undrained conditions that the difference between the theoretical hydraulic pressure and the real hydraulic pressure. It shows that it is possible to apply the reduced hydraulic pressure in applying the drainage shield tunnel and to reduce the segment section due to hydraulic pressure reduction.