• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.12
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• pp.125-130
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• 2019

A gas-spring has been used in many areas and its use is increasing because it can be designed for a range of purposes. In this study, the behavior of a piston with an orifice hole inside the gas-spring cylinder was predicted using computational fluid dynamics (CFD). The piston was designed to reduce the reaction force if the gas-spring is compressed and to move at a low speed when it is returned. The analysis showed that if the initial gas pressure in the gas-spring is increased to a certain level, the speed of the piston would not decrease with time but will remain constant. The effects of orifice hall size on the piston return speed were investigated. Reducing the size of the orifice hole will increase the pressure difference on both sides of the piston, reduce the piston speed, and make it more constant. On the assumption of a constant speed of the piston, a theoretical solution to the return speed of the piston was derived according to the initial gas pressure, and the results for several initial gas pressures were compared with those of CFD. Comparison studies showed similar results for both methods.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.11a
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• pp.377-378
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• 2007

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2012.06a
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• pp.158-158
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• 2012

• 한국가스학회:학술대회논문집
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• 2003.05a
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• pp.219-223
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• 2003

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.8 no.2
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• pp.83-89
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• 2009

An air-fuel ratio control is essential in reducing hazardous exhaust emissions from a compressed natural gas(CNG) engine, and can be accomplished by accurate control of gas injection flow. In this study, theoretical research was conducted on injection characteristics of a solenoid gas injector, and injection experiments for calibration and analysis were performed. Various factors for gas injection flow such as injection pressure, gas temperature, and supply voltage are studied. A dynamic flow equation of the natural gas was proposed on the basis of flow dynamics theories and results of the injection experiment. The verification of the dynamic flow equation of the solenoid injector was carried out with a large CNG-engine applied to an urban bus. Air-fuel ratio control experiments were conducted in both steady and transient state. Results of injection experiments for the solenoid injector and the CNG-engine was proved the control method proposed herein to be effective.

• 에너지협의회보
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• s.67
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• pp.30-39
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• 2004

• Journal of the Korean Society of Visualization
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• v.6 no.2
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• pp.53-57
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• 2008

• The Journal of Asian Finance, Economics and Business
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• v.5 no.2
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• pp.25-33
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• 2018

In the globalization and free trade era, the current account deficit problem is a common phenomenon experienced by most countries, both developing and developed countries. Also with managed floating regime of exchange rate, it becomes very important to analyze the dynamics of current account balance which determine the trade. The deficit condition has lasted for four years in Indonesia, as well the deficit value above the value of the surplus that has been experienced during the period 2005-2011. This study is firstly aim to examine the condition of the deficit which happens in the export and import, manufactured goods and oil and gas, whether related to the transaction of goods and services. We try to build a predicted model which near the actual. Then, the focuses examines an exchange rate volatility impact on current account deficit. The model used in this research is a simultaneous model of Indonesia current account deficit from 2005 to 2014. The simulation result indicated that depreciation increase surplus to current account deficit. The decrease of export manufactured goods (non oil and gas) higher than the increase of import. For the oil and gas sector, depreciation of the rupiah against the US dollar results in an increased burden of higher oil and gas imports due to import transactions.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.12
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• pp.1092-1100
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• 2005

We investigated a carbon nanotube (CNT) oscillator controlled by the thermal gas expansion using classical molecular dynamics simulations. When the temperature rapidly increased, the force on the CNT oscillator induced by the thermal gas expansion rapidly increased and pushed out the CNT oscillator. As the CNT oscillator extruded from the outer nanotube, the suction force on the CNT oscillator increased by the excess van der Waals(vdW) energy. When the CNT oscillator reached at the maximum extrusion point, the CNT oscillator was encapsulated into the outer nanotube by the suction force. Therefore, the CNT oscillator could be oscillated by both the gas expansion and the excess vdW interaction. As the temperature increased, the amplitude of the CNT oscillator increased. At the high temperatures, the CNT oscillator escaped from the outer nanotube, because the force on the CNT oscillator due to the thermal gas expansion was higher than the suction force due to the excess vdW energy. By the appropriate temperature controls, such as the maximum temperature, the heating rate, and the cooling rate, the CNT oscillator could be operated.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.5
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• pp.439-446
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• 2017

This paper deals with an experimental study of the dynamics of an underwater bubbles and shock waves, generated by rapid underwater release of highly compressed gas. Aribag inflators, which are used for automobile's airbag system, are used to generate the extremely-rapid underwater gas release. Experimental studies of the complex underwater bubble dynamics as well as underwater shock wave were carried out in a specifically designed cylindrical water tank. The water tank is equipped with a high-speed camera and pressure sensors. The high-speed camera was used to capture the expansion and collapse of the gas bubble created by inflators, while pressure sensors was used to measure the underwater shock propagation and magnitudes. The experimental results were compared against the results of explosion of pentolite explosive. Several physical phenomena that has been observed and discussed, which are different from the explosive underwater explosion.