• 소성∙가공
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• 제8권6호
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• pp.604-611
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• 1999

This paper is concerned with the family of parts that generally feature a central hub with radial protrusions. As opposed to conventional forward and backward extrusion, in which the material flows in a direction parallel to that of the punch or die motion, the material flows perpendicular to the punch motion in radial extrusion. Three variants of radial extrusion of a collar or flange are investigated. Case I involves forcing a cylindrical billet against a flat die, Case II involves deformation against a stationary punch recessed in the lower die, and Case III involves both the upper and lower punches moving together toward the center of the billet. Extensive simulational work is performed with each case to see the process conditions in terms of forging load, balanced and symmetrical flow in the flange. Also, the effect of the gap size and die corner radii to the material flow are investigated. In this study, the forming characteristics of radial extrusion will be considered by comparing the forces, shapes etc. The design factors during radial extrusion are investigated by the rigid-plastic FEM simulation.

• 한국초전도ㆍ저온공학회논문지
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• 제15권3호
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• pp.35-39
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• 2013

In this paper, we present test results of developed 100 W class linear compressor for Stirling-type pulse tube refrigerator. The fabricated linear compressor has dual-opposed configuration, free piston and moving magnet type linear motor. Power transfer, efficiency and required pressure waveform are predicted with designed and measured specifications. In experiments, room temperature test with flow impedance is conducted to evaluate performance of developed linear compressor. Flow impedance is loaded to compressor with metering valve for flow resistance, inertance tube for flow inertance and buffer volumes for flow compliance. Several operating parameters such as input voltage, current, piston displacement and pressure wave are measured for various operating frequency and fixed input current level. Behaviors of dynamics and performance of linear compressor as varying flow impedance are discussed with measured experimental results. The developed linear compressor shows 124 W of input power, 86 % of motor efficiency and 60 % of compressor efficiency at its resonant operating condition.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.637-642
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• 2001

Performance and cavitation characteristics of a turbo pump inducer which is designed for oxygen pump is experimentally investigated. It is found that the static performance of inducer is dependent on the location of inlet pressure measurement and that enough distance from inducer is ensured for accurate evaluation of performance. With the increase of flow rate. NPSH tends to decrease as opposed to pump characteristics, which seems to be due to the cavitation region.

• 한국항공우주학회지
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• 제36권2호
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• pp.131-136
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• 2008

본 연구는 다양한 배열 상태에 놓인 2원주 주위의 유동장 특성을 PIV를 이용하여 파악한 것이다. 직렬배열에서 하류측 원주의 후방에서 측정한 Strouhal 수는 수평 간격비가 클수록 작게 나타났다. 직렬배열에서 2원주 사이의 흐름은 거의 정체되어 있으며, 상류측 원주에 가까울수록 정체 범위가 크게 나타났다. 직렬배열에서 자유류와 2원주의 중심선이 이루는 받음각()의 미소 변화(${\alpha}$=${\pm}1.0^{\circ}$)에 따라 2원주 사이에는 서로 반대 방향의 와류가 생성되었다. 병렬배열에서 수직 간격비가 클수록 2원주 사이의 유속이 크게 나타났다.

• 대한기계학회논문집B
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• 제29권10호
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• pp.1156-1162
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• 2005

In this study, a noble method is proposed to prevent the edge overcoating (EOC) that may develop near the edge of the steel strip in the gas wiping process of continuous hot-dip galvanizing. In our past study (Trans. of the KSME (B), Vol. 27, No. 8, pp. $1105\~1113$), it was found that EOC is caused by the alternating vortices which are generated by the collision of two opposed jets in the region outside the steel strip. When the two opposed jets collide at an angle much less than $180^{o}$, non-alternating stable vortices are established symmetrically outside the steel strip, which lead to nearly uniform pressure on the strip surface. In order to deflect both jets downward by a certain angle, a cylinder with small diameter is installed tangentially to the exit of the lower lip of the two-dimensional jet. In order to find an optimum cylinder diameter, the three dimensional flow field is analysed numerically by using the commercial code, STAR-CD. And the coating thickness is calculated by using an integral analysis method to solve the boundary layer momentum equation. In order to compare the present noble method with the conventional baffle plate method to prevent the EOC, the flow field with a baffle plate is also calculated. The calculation results show that the tangentially installed cylinder at the bottom lip of the jet exit is more effective than the baffle plate to prevent EOC.

• 해양환경안전학회지
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• 제18권2호
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• pp.139-144
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• 2012

매연 생성에 대하여 톨루엔의 영향을 알아보기 위하여 순수에틸렌 대향류 확산화염에 톨루엔을 소량 혼합하여 수치해석을 수행하였다. 톨루엔($C_7H_8$)의 혼합 비율은 3%, 5%, 10%, 및 20%로 하였다. 계산에는 CHEMKIN III 기반의 Senkin 코드와 oppdif 코드를 이용하여 0-D 계산과 1-D 계산을 수행하였다. 0-D의 Senkin 계산에서는 톨루엔의 혼합율이 증가할수록 메틸라디칼의 농도는 증가하고 이에 따른 벤젠의 농도도 증가하였다. 이는 순수 에틸렌 화염에 톨루엔을 혼합할 경우 더 많은 매연이 생성될 것이라는 걸 의미한다. oppdif 코드에 의한 1-D 계산에서는 10% 톨루엔 반응식으로부터는 H 라디칼의 생성율이 결정적인 역할을 한다는 것을 알 수 있었다. 위 결과들로부터 확산화염 내 매연 생성에 있어 메틸라디칼, 벤젠과 H 라디칼이 중요한 역할을 한다는 것을 알 수 있었다.

• 한국수산과학회지
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• 제27권2호
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• pp.173-182
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• 1994

A numerical experiment on the effective discharge of waste materials caused in recirculating aquaculture basins was performed. The numerical model used in this study was a 4-level hydrodynamic and advection-diffusion model. Flow structures and settling processes of ss in the various mathematical model basins are discussed. The calculated flow fields of the numerical basin corresponded well with the measured velocity in field basin. In the cases of steep bottom slopes in 4/30, the non-dimensional tractive force($U{\ast}/U{\ast}_c$) which is all important parameter for the deposition pattern of waste materials was stronger than with the mild slope one. The settling pattern of ss depended considerably on the degree of bottom slope of basin. To concentrate deposited waste materials into the center discharge pipe, it is useful to design a cylindrical basin with a steeply conical bottom. In addition, to prevent movement of the deposit area away from the center, it is necessary to locate the circulating ducts at diametrically opposed points on the basin sides.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2012년도 제44회 KOSCO SYMPOSIUM 초록집
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• pp.241-243
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• 2012

Experiments were conducted to get the design concepts for the continuous aluminum particle feeding system. Two opposed cylinders were used. Aluminum particles in one cylinder were ejected to the air by the supplying gas and the pressure of the other cylinder. It was not possible to eject more aluminum mass flowrate than that of gas if particles were just thrust by the pressure difference between two cylinders. Aluminum particle/air mixture in the flow system was successfully ignited by the electric spark.

• Journal of Advanced Marine Engineering and Technology
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• 제31권2호
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• pp.159-165
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• 2007

The Characteristics of the flowfield around two circular cylinders in tandem arrangement was investigated by PIV. Strouhal numbers. velocity vectors and velocity profiles were observed at centre-to-centre space ratios of P/D= 1.5. 2.0 and 2.5, and Reynolds number of $Re=3.0{\times}10^3{\sim}5.0{\times}10^3$. As the results the Strouhal numbers measured in the rear region of the cylinder of wake side were decreased with the space ratios. The flow between two cylinders was almost stagnated and the size of the stagnated region was larger in the close side than in the far side of the front cylinder. The direction of vortex between two cylinders was opposed each other with the small difference(${\alpha}\;{\pm}1.0^{\circ}$) of the attack angle ${\alpha}$.

• 전기학회논문지
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• 제57권11호
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• pp.1954-1961
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• 2008

Microgrid usually consists of a cluster of distributed generators(DGs), energy storage systems and loads, and can operate in the grid-connected mode and the islanded mode. This paper presents detailed descriptions of two different options for controlling the active power of DGs in the microgrid. One is regulating the power injected by the unit to a desired amount(Unit output power control) and the other is to regulate the flow of active power in the feeder where the unit is installed to a constant(Feeder flow control). Frequency-droop characteristics are used to achieve good active power sharing when the microgrid operates in the islanded mode. The change in the frequency and the active power output of DGs are investigated according to the control mode and the configuration of DGs when the microgrid is disconnected from the main grid. From the analysis, this paper proposes a method to determine the droop constant of DGs operating in the feeder flow control mode. Simulation results using the PSCAD/EMTDC are presented to validate the approach, which shows good performance as opposed to the conventional one.