• 한국주조공학회지
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• 제38권5호
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• pp.95-102
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• 2018

The dependence of the tensile properties on variations in the porosity of A356 aluminium alloys was investigated in terms of the quality index of the tensile properties based upon the ultimate tensile strength and elongation as well as the variation of the strength coefficient and strain-hardening exponent with regard to a T6 treatment. The test specimens were prepared by low-pressure die-casting and a subsequent T6 treatment, and the experimental results of a tensile test carried out at room temperature were compared to the theoretical description using a modified constitutive model. The nominal value of the quality index of A356 alloys increases gradually with a lapse of the ageing time upon a T6 treatment, despite the fact that this value is temporarily decreased during the initial stage of ageing from a solutionised condition. Additionally, the quality index depends practically upon the porosity variation with a power law relationship without regard to whether in solutionised or artificial aged conditions. The theoretical description indicates that the strength coefficient directly determines the nominal level of the quality index. Moreover, the overall dependence of the quality index on the porosity variation is remarkably weakened with an increase in the tensile strain, whereas the quality index depends sensitively upon the porosity variation with a low value of the strain-hardening exponent.

• 한국추진공학회지
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• 제21권2호
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• pp.18-25
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• 2017

무노즐 부스터에 사용하는 추진제의 연소특성에 관한 연구를 수행하였다. 밀도비추력을 향상키기기 위하여 고체 추진제의 조성에 Al와 Zr의 금속연료들이 도입되었으며 무노즐 부스터를 설계하기 위하여 낮은 압력지수 및 고 연소속도가 추진제의 주요 연소특성으로 연구되었다. Zr을 함유하는 추진제는 Al을 함유하는 추진제보다 높은 연소속도를 보였으며, $13{\mu}m$ Zr을 함유하는 추진제는 연소속도는 35 mm/s (at 1000 psi)와 압력지수 0.3282를 보였다. 이러한 결과로부터, 무노즐 부스터에서 Al와 Zr을 함유하는 추진제를 사용하는 이점을 보였다.

• 한국분무공학회지
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• 제9권1호
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• pp.30-36
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• 2004

The purpose of this study was to investigate the fuel spray characteristics that made most important at an homogeneous air fuel mixture, in a common rail direct injection type HCCI engine. As a study conducted relation which a back pressure and injection pressure are influenced to air fuel mixture characteristics, we tried to offer date even through we select suitable to a HCCI engine running condition of the fuel injection condition. To accomplish the study, to measure a injection rate of common rail type injector and to visualize and simulate a fuel spray was conducted. From the result of injection rate, a common rail injector was confirmed to appear a initial delay of 0.3msec and a latter period delay of 0.7msec. Therefore, real injection duration was determined by about 0.5msec increasing. From the result of fuel spray, the spray penetration was proportional to 1/4 exponent of atmosphere pressure. An experimental equation was deduced from the spray penetration of spray visualization experiment and the relation of injection duration and penetration was estimated in HCCI engine using an experimental equation.

• 대한기계학회논문집B
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• 제26권2호
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• pp.177-183
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• 2002

The field tests on the waterhammer were carried out in the pump pipeline system with an air chamber. The effects of the input variables and the design parameters for the air chamber were investigated by both the numerical calculations and the experiments. Because the waterhammer problems as a result of the pump power failure were the most important, these situations were carefully studied. Among the input variables used in the waterhammer analysis, the polytropic exponent, the discharge coefficient and the wavespeed had influence on the simulated results in that order, and were calibrated in comparison with the experimental results. As the initial air volume in a vessel increased, the period of waterhammer increased and the pressure variation decreased, resulting from the reduction of the rate of pressure change in the air chamber. Using smaller orifice in the bypass pipe, the pressure rise was suppressed in some degree and the pressure surge was dissipated more rapidly as time passed. The simulations were in fairly good agreement with the measured values until 1∼2 periods of waterhammer. Not only the maximum and minimum pressures in the pipe1ine but also those occurring times were reasonably predicted. The computer program developed in this study will be useful in designing the optimum parameters of an air chamber for the real pump pipeline system.

• Geomechanics and Engineering
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• 제21권3호
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• pp.279-288
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• 2020

The permeation grouting is a commonly used technique to improve the engineering geology condition of the soft ground. It is of great significance to predict the permeation range of the grout so as to ensure the effects of grouting. This paper conducts a theoretical analysis of jet-grouting effects in ground improvement and rotary grouting pile installation by utilizing deformation-permeation coupled poroelastic solutions based on Biot's theory and Laplace-Fourier integral transform technique. The exponential function and the intermittent trigonometric function are chosen to represent time-dependent grouting pressure usually encountered in ground improvement and rotary grouting pile installation process, respectively. The results, including the radial displacement, the hoop stress, the excess pore fluid pressure, the radial discharge, and the permeation radius of grout, are presented for different grouting time, radial positions and grouting lengths. Parametric study is conducted to explore the effects of variation of the exponent in the exponential grouting pressure-time relationship on grouting-induced responses. It is expected that the proposed solutions can be used to estimate the permeation range of grouting in ground improvement and rotary grouting pile installation.

• 한국자동차공학회논문집
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• 제8권6호
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• pp.60-69
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• 2000

In order to obtain underwater or underground power sources, the closed cycle diesel engine is operated in the non air-breathing circuit system where the major species of the working fluid include oxygen, argon, and recycled exhaust gas. In the present study, the closed cycle diesel engine is designed to operate at the intake pressure between 2 and 3 bar. For operating in the open-cycle and closed-cycle situations, experimental apparatus using this diesel engine is made with ACAP as data acquisition system. In open, semi-open, and closed cycle modes, the predicted p-$\theta$ and P-V are compared with load bank power. Computation have been performed for wide range of major experimental parameters such as the specific fuel and oxygen concentrations, fuel conversion efficiency and polytropic exponent, IMEP and maximum cylinder pressure.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집
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• pp.439-442
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• 2002

The interface between two different materials in the insulation systems is the weak-link in the underground power transmission systems, In this paper, Optimum conditions of the interface between Epoxy and EPDM is studied. The variation factor condition of interface is roughness of surface, spreading of oils, interfacial pressure and temperature. The breakdown times under the constant voltage below the breakdown voltage were also gained. The breakdown voltage at the after laying time equivalent to is calculated by the V-t characteristic and the inverse power law. When this is done, the characteristic life exponent n is used and the long time breakdown voltage can be evaluated.

• International Journal of Air-Conditioning and Refrigeration
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• 제9권2호
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• pp.51-61
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• 2001

A numerical study has been conducted to characterize the transient pressure in a simple water supply pipe system with an air chamber by utilizing a commercial code that employs the method of characteristics. Some results produced for validation in the study agree quite well with the previously reported. Several parameters are than varied. Among them are the valve closure time, the wave speed, the static pressure, the polytropic exponent, the air chamber volume, the diameter and the shape of orifice in the air chamber, etc, while the water temperature and velocity are kept constant at $20^\circ{C}$ and 0.8m/s, respectively. Results reported in this parametric study may be useful to understand the unsteady behavior of the system.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
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• pp.472-475
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• 2010

나노 알루미늄과 물의 연소 반응을 정상상태 층류 연소로 모델링하여 이론적 접근을 하였으며 압력에 따른 화염전파속도의 영향을 조사하였다. 물의 상변화에 따른 증발열을 고려하였으며 다양한 압력 영역(0.1MPa ~ 10MPa)에 대한 연소 특성을 살펴보았다. 모델링 영역을 1)물+알루미늄 2)증기+알루미늄 3)반응영역으로 나누었으며 영역의 방정식을 구성하고 화염속도에 대한 해석적 해를 구하였다. 입자크기에 따른 연소실 압력의 영향을 도출하여 시험결과와 비교, 분석 하였다.

• 에너지공학
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• 제10권3호
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• pp.278-285
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• 2001

본 연구에서는 경수로 사용후핵연료를 모사하는 모의 핵연료 제조 공정 중 소결체 특성에 미치는 변수들의 영향에 관하여 기술하였다. 주로 성형압, 소결 온도 및 시간이 소결체의 밀도에 미치는 영향에 관하여 분석하였다. 성형압은 1 ton/$\textrm{cm}^2$에서 4ton/$\textrm{cm}^2$, 소결 온도는 167$0^{\circ}C$, 173$0^{\circ}C$, 178$0^{\circ}C$, 소결 시간은 4시간, 8시간, 24시간으로 변화시키면서 실험을 수행하였다. 성형밀도는 성형압의 1/3승에 비례하며, 이론 밀도의 약 90.5%에서 99.6%까지의 소결 밀도를 갖는 모의 핵연료를 제조하였다. 결정립 성장지수와 활성화에너지는 각각 2.5와 287.97kJ/mo1 이었다.