• Tribology and Lubricants
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• v.18 no.4
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• pp.291-298
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• 2002

In this study, a numerical analysis f3r the piston secondary dynamics and lubrication characteristics of small refrigeration reciprocating compressors is presented. In general, the length of cylinder in this class of compressors is shortened to diminish the frictional losses of the piston-cylinder system. So, the contacting length between piston and cylinder wall is in variable with the rotating crank angle around the BDC of the reciprocating piston. In the problem formulation of the piston dynamics, the change in bearing length of the piston and all corresponding forces and moments are considered in order to determine the piston trajectory, velocity and acceleration at each step. A Newton-Raphson procedure was employed in solving the secondary dynamic equations of the piston. The developed computer program can be used to calculate the entire piston trajectory and the hydrodynamic forces and moments as functions of crank angle under compressor running conditions. The results explored the effects of the radial clearance, lubricant viscosity, and pin location on the stability of the piston, the oil leakage, and friction losses.

• Journal of information and communication convergence engineering
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• v.14 no.2
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• pp.122-128
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• 2016

In the future, hybrid power management systems using fuel cells (FCs) and batteries will be used as the driving power systems of ships. These systems consist of an FC, a converter, an inverter, and a battery. In general, an FC provides steady-state energy; a battery provides the dynamic energy in the start state of a ship for enabling a smooth operation, and provides or absorbs the peak or dynamic power when the load varies and the FC cannot respond immediately. The FC voltage range is very wide and depends on the load; Therefore, the FC cannot directly connect to the inverter. In this paper, we propose a power management strategy and design process involving a unidirectional converter, a bidirectional converter, and an inverter, considering the ship's operating conditions and the power conditions of the FC and the battery. The presented experimental results were verified through a simulation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.737-740
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• 2002

Pressure fluctuation in the cylinder is one of the major sources on noise emission in oil hydraulic piston pumps. This paper reports an experimental study of pressure fluctuation characteristics in the cylinder of oil hydraulic piston pumps. We measured pressure fluctuation at BDC with delivery pressure, rotational speed. Because the pre-compression and the V-grooves in the valve plate is known of noise reduction, we investigated also the effect of pre-compression and V-grooves at the ends of the kidney ports with four types valve plates. We found that the pre-compression and the V-grooves in valve plate could reduce the noise of oil hydraulic piston pumps.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.1
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• pp.74-81
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• 2001

Dynamic pressure is one of the major sources on noise emission in oil hydraulic piston pump. This paper reports an experimental study of dynamic pressure characteristics in the cylinder bore of oil hydraulic piston pump. We experimently measured dynamic pressure at BDC with delivery pressure, rotational speed and oil temperature. Because the V-grooves at the ends of the kidney ports with three types valve plates. We hope this paper help to design of the valve plate in oil hydraulic piston pump.

• Applied Chemistry for Engineering
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• v.33 no.1
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• pp.11-16
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• 2022

Metal-organic frameworks (MOFs) are porous materials with nano-sized pores. The degree of gas adsorption and pore size can be controlled according to types of metal ions and organic ligands. Many studies have been conducted on MOFs in the fields of gas storage and separation, and gas sensors. For rapid and quantitative gas adsorption/desorption analyses, it is necessary to form various MOF structures in uniform films on a sensor surface. In this review, some of representative direct methods for uniformly synthesizing MOFs such as MIL-53 (Al), ZIF-8, and Cu-BDC from anodized aluminum oxide, zinc oxide nanorods, and copper thin films, respectively on the surface of a microresonator are highlighted. In addition, the operation principle of quartz crystal microbalance and microcantilever, which are representative microresonators, and the interpretation of signals that change when gas is adsorbed to MOFs are covered. This is intended to enhance the understanding of gas adsorption/desorption analysis of MOFs using microresonators.

• Aerospace Engineering and Technology
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• v.4 no.1
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• pp.162-170
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• 2005

In KSLV-I, actuation system for thrust vector control of kick motor was configured as electro-hydraulic servo actuation system and consisted of actuators, hydraulic power supply system, hydraulic power distribution system and control system. In case of hydraulic power supply system, we use EMDP(Electric Motor Driven Pump) to supply hydraulic power. Generally, we use brushed DC motor for EMDP but it is not easy to operate EMDP using brushed DC motor at a high altitude. Hence, we are developing EMDP using brushless DC motor to use at a high altitude. In this study, we will explain control system for BLDC motor to drive hydraulic pump.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1617-1620
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• 1999

In this work, the effect of blend on physical and electrical properties investigated. The two kinds of low-density polyethylene (LDPE) whose densities are evaluated at $0.9179[g/cm^3]$ and $0.9192[g/cm^3]$, respectively, were used and blended according to the different blend ratio. The LDPE with the blend ratio of 50[wt%] represented the lowest impulse breakdown strength, $F_{BImp}$ at $30[^{\circ}C]$, but the highest $F_{BImp}$ at $90[^{\circ}C]$. DC breakdown strength, $F_{BDC}$. decreased with the increase of blend ratio at $30[^{\circ}C$, but increased at $60[^{\circ}C]$. The current density decreased with a blend ratio up to 75 [wt%] at $90[^{\circ}C]$. By analyzing the diffraction patterns of XRD, we found that the LDPE with the blend ratio of 50 [wt%] represented the largest crystal size of (020) plane. We investigated the relationship between the effect of blend and electrical properties and these results are discussed.

• Transactions of the Korean hydrogen and new energy society
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• v.22 no.3
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• pp.299-304
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• 2011

A hydrogen fueled 2 stroke free-piston engine with reverse uni-flow scavenging have a advantageous structure for the backfire occurrence, but it can reduce thermal efficiency by the circuit-flow to go through a exhaust-port. In this research, varied boost pressure, SVOT and exhaust pressure are used in a 2stroke free-piston engine with hydrogen fueled for studying the possibility of increasing thermal efficiency of free-piston hydrogen engine. As a result, to increase thermal efficiency of free-piston are suitable to supply the mixture after port closed the exhaust rater than to use the scanvenging. And it was increased by the exhaust pressure, to achieve it must be used the lean-mixture at SVOT aBDC $34^{\circ}$.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.934-939
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• 2001

In computational study of the flow in piston engines and the flow through moving valves, the use of moving vertices is essential for modelling flows with moving boundaries. The positions of cell vertices in such cases must be allowed to vary with time. To simulate 3-dimensional port-valve and piston-cylinder of HIMSEN 6H21/32 engine, a commercially available code, STAR-CD, was used. Changes in mesh geometry was specified by PROSTAR commands.(i.e. the Change Grid operation in the EVENTS command module.) Control of the intake flow is expected to play an important role as designers seek to obtain better fuel spray characteristics, fuel mixing and mixture preparation, combustion performance, and emissions reductions to meet national standards. As a result of analysis, velocity fields indicate the presence of a structured flow comprised of one pair of counter-rotating vortices under the intake valve during the early induction process. These flow structures remain visible for most of the intake process. As the piston moves towards BDC, these vortices develops into a larger tumbling motion that dominates the flow structure.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.6
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• pp.503-510
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• 2014

This study proposes a bi-directional interleaved current-fed resonant converter (CRC) with reduced size of the output filter for a fuel cell electric vehicle. The proposed CRC achieves zero-current switching turn on and off of switches and diodes and makes ripple current of the output capacitor theoretically zero. As a result, the cost and volume of the output capacitor are significantly reduced. The two-stage power conversion technique is also applied for wide input and output voltage range operations. A 2kW prototype of the proposed converter is built and tested to verify the validity of the proposed operation.