• 한국초전도ㆍ저온공학회논문지
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• 제3권2호
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• pp.62-68
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• 2001

This paper presents manufacturing process and test results in the optimum pressure and operating frequency for the free piston free displacer(FPFD) Stirling cryocooler designed and manufactured by Korea Institute of Machinery &Materials (KIMM). FPFD Stirling cryocooler is currently under development uses opposed linear motors to drive opposed pistons . The performance of FPFD Stirling cryocooler is evaluated as a function fo charging pressure and operating frequency. In general as the operating frequency of the compressor is increaed but natural frequency of the displacer is almost constant. The prototype has achieved no load temperature of 49K and cooling capacity of 0.5W at 7.2K.

• 한국초전도ㆍ저온공학회논문지
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• 제3권2호
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• pp.49-54
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• 2001

The purpose of this study is to analyze the characteristics of the linear compressor for Stirling refrigerator. To ensure high performance and long life of the FPFD(Free Piston. Free Displacer) type Stirling refrigerator, the operating parameters of the linear compressor should be optimized. The experimental results show that the operating frequency of the linear compressor has significant effect on the input power characteristics. and that the compressor with higher charging pressure of working fluid has high pressure ratio. For the high performance of the linear compressor. compressor should be operated at the resonance frequency with respect to the given charging pressure.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 추계학술대회 논문집
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• pp.235-241
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• 1998

Flow characteristics of a compressible gas flow through a rotating disc-type rotary valve are investigated experimentally under various conditions. It is known that the mass flow rate through poppet valves of 4-stroke cycle engines and through piston valves of 2-stroke cycle engines decrease with increase in engine speed. Rotary valve is one means by which air maybe made to flow intermittently through a pipe. In this paper a exhaust system simulator of engine was used to experimentally analyzer the decrease inflow rate at high rotation speeds and to determine what variables, other than rotational speed, give rise to the observed behaviour. These variables have been included in an empirical equation which is representative of the measured flow characteristics.

• 한국정밀공학회지
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• 제15권1호
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• pp.137-144
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• 1998

For a model system consisted of four pneumatic cylinders with strokes of 10, 20, 40 and 80 mm, investigation was carried out experimentally and numerically about the reliability of system with elastic and viscous load. The elastic load affects the performance of each cylinder in cylinder series, and changes the time lag and the velocity of the piston which makes the positioning control rather difficult. Taking the effects of the elastic load into consideration, positioning can be carried out comparatively smoothly by only adjusting the driving timing. The effect of a viscous load reduces the vibration of each moving body in the cylinder series and also reduces the over-travelled distance which happens when several cylinders move at the same time. For reasons, a positioning with a viscous load can be relatively smoothly carried out even without the timing control.

• 드라이브 ㆍ 컨트롤
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• 제9권2호
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• pp.8-14
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• 2012

Electro-hydraulic spring return actuator(ESRA) is utilized for air conditioning facilities in a nuclear power plant. It features self-contained, hydraulic power that is integrally coupled to a single acting hydraulic cylinder and provides efficient and precise linear control of valves as well as return of the actuator to the de-energized position upon loss of power. In this paper, the algebraic equations of ESRA at steady-state have been developed for the analysis of static characteristics that includes control pressure and valve displacement of pressure reducing valve, flow force on flapper as well as its displacement over the entire operating range. Also, the effect of external load on piston deviation is investigated in terms of linear system analysis. The results of static characteristics show the unique feature of force balance mechanism and can be applied to the stable self-controlled mechanical system design of ESAR.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.871-874
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• 2002

Many malfunctions take place in container crane spreader due to impact. So we designed a 2DOF hydraulic impact absorbing system with multi-step damping coefficient and studied the effect of orifice's interval and damping coefficient. The damping coefficient of upper piston was found to be 180 N.s/m, and the orifice's interval to be 9mm, the max reaction force and the average reaction force might be lowest. Compared with a general 2-DOF impact absorbing system, the max reaction force reduced by 46%., and average reaction force reduced by 5%.

• 설비공학논문집
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• 제13권8호
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• pp.763-770
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• 2001

The high pressure side rotary compressor is investigated in this study. The temperatures at 29 points of main components and the refrigerant and the performance of the instrumented compressor are measured at various operating conditions. The complex heat transfer mechanism between the components, such s cylinder, suction pipe and stator of motor, is fairly clarified. It is also confirmed that the achievement of a high efficiency by reducing the heat transfer loss in the rotary compressor is possible.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.695-700
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• 2003

This paper dealt with friction-induced vibrations in engineering practice, specifically arising at the moment of counterturn of two friction surfaces. The harshness of the vibrations are attributed to the sharp change of the friction coefficients from kinetic to static near zero relative velocity, which is one of the examples of the stick slip. But the experimental results and numerical analysis of piston and cylinder operation showed that transition of the friction coefficient from kinetic to static is insignificant in vibrations. Dry friction itself dominates the harshness of vibrations. This study shows that how dry friction triggers the vibrations and demonstrates the effect of sharp transition from kinetic to static friction coefficient on the vibrations.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.838-843
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• 2005

The nonlinear characteristics of a suspension is directly related to the ride quality of a passenger car. In this study, a dynamic experiment for a spring and a damper of a passenger car is performed to analyze the nonlinear characteristics using MTS 1-axial testing machine and a mathematical nonlinear dynamic suspension model based on experimental data is devised to estimate the ride quality using Billings' method. The devised nonlinear model is applied to the ride quality analysis using K factor and the effect of suspension parameters is examined. As a result, the friction between the cylinder and the piston of a damper is the most effective parameter for the ride quality of a passenger car.

• 한국산업융합학회 논문집
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• 제5권4호
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• pp.313-320
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• 2002

A 2-dimensional $k-{\varepsilon}$ numerical model was developed to explore the effects of vehicle movement, jet fan and wind speed for the ventilation of road tunnels. To consider the temperature distribution in the tunnel, the energy equation was solved with a source term of the energy exhausted from vehicles. Although the tunnel ventilation can be made by the piston effect of vehicle movement, an additional ventilation is necessary when a head wind is existing. Jet fans may assist the air flow in the tunnel. However, more efficient ventilation system should be necessary, because the exhaust gas from vehicles flow along the road surface and it cannot be diffused in the longitudinal tunnel.