• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.131-134
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• 2002

Braided carbon fiber reinforced Al matrix composites were developed and characterized. Braided carbon fiber preforms with braiding angles of $30^{\circ}$, $45^{\circ}$ and $60^{\circ}$ were manufactured by using a braiding machine. The manufactured braided carbon fibers were used as reinforcement to fabricate Al matrix composites by employing a pressure infiltration casting method. In the processing of pressure infiltration casting, important processing parameters such as melting temperature, preheating temperature of preform and applied pressure were optimized. Prediction of elastic constants on composites was performed by using the volume averaging method, which utilizes the coordinate transformation and the averaging of stiffeness and compliance constants based upon the volume of each reinforcement and matrix material. The elastic moduli of composites were evaluated by using Resonant Ultrasound Spectroscopy(RUS) method and compared with the elastic moduli obtained from static tensile test method.

• Steel and Composite Structures
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• 제28권2호
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• pp.195-207
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• 2018

First-order reliability method (FORM) is enhanced based on the search direction using relaxed conjugate reliability (RCR) approach for the embedded nanocomposite beam under buckling failure mode. The RCR method is formulated using discrete conjugate map with a limited scalar factor. A dynamical relaxed factor is proposed to control instability of proposed RCR, which is adjusted using sufficient descent condition. The characteristic of equivalent materials for nanocomposite beam are obtained by micro-electro-mechanical model. The probabilistic model of nanocomposite beam is simulated using the sinusoidal shear deformation theory (SSDT). The beam is subjected to external applied voltage in thickness direction and the surrounding elastic medium is modeled by Pasternak foundation. The governing equations are derived in terms of energy method and Hamilton's principal. Using exact solution, the implicit buckling limit state function of nanocomposite beam is proposed, which is involved various random variables including thickness of beam, length of beam, spring constant of foundation, shear constant of foundation, applied voltage, and volume fraction of ZnO nanoparticles in polymer. The robustness, accuracy and efficiency of proposed RCR method are evaluated for this engineering structural reliability problem. The results demonstrate that proposed RCR method is more accurate and robust than the excising reliability methods-based FORM. The volume fraction of ZnO nanoparticles and the applied voltage are the sensitive variables on the reliable levels of the nanocomposite beams.

• 대한기계학회논문집B
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• 제24권12호
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• pp.1608-1614
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• 2000

For the purpose of obtaining fundamental data which is needed to develope combustion system of LPG engine, we made constant volume chamber and analyzed flame propagation characteristics under different intial temperature, initial pressure and equivalence ratio which affect combustion of LPG. We investigated flame propagation speed of each fuel using laser deflection method and compared with the investigated flame propagation speed of each fuel using laser deflection method and compared with the results of image processing of flame. As a result, the maximum flame propagation speed was found at equivalence ratio 1.0 and 1.1 for LPG and gasoline, respectively. In the lean region, we can see that flame propagation speed of LPG surpasses that of gasoline. On the contrary, flame propagation speed of gasoline surpasses LPG in the rich region. As initial temperature and initial pressure were higher, flame propagation speed was faster. And, as equivalence ratio was larger and initial temperature was higher, combustion duration was shorter and maximum combustion pressure was higher.

• Steel and Composite Structures
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• 제41권6호
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• pp.821-829
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• 2021

Nonlinear dynamic response of a sandwich beam considering porous core and nano-composite face sheet on nonlinear viscoelastic foundation with temperature-variable material properties is investigated in this research. The Hamilton's principle and beam theory are used to drive the equations of motion. The nonlinear differential equations of sandwich beam respect to time are obtained to solve nonlinear differential equations by Homotopy perturbation method (HPM). The effects of various parameters such as linear and nonlinear damping coefficient, linear and nonlinear spring constant, shear constant of Pasternak type for elastic foundation, temperature variation, volume fraction of carbon nanotube, porosity distribution and porosity coefficient on nonlinear dynamic response of sandwich beam are presented. The results of this paper could be used to analysis of dynamic modeling for a flexible structure in many industries such as automobiles, Shipbuilding, aircrafts and spacecraft with solar easured at current time step and the velocity and displacement were estimated through linear integration.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.3073-3078
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• 2008

In this study to find out the amount of soot, LII method, which utilizes a laser, was used in laminar diffusion flame and based upon the temperature and soot measured from the turbulent Diesel diffusion flame in the constant-volume chamber using the two-color method. Through these experiments, we could know that the LII signal is generally proportional to the soot amount in a laminar diffusion flame. And we could acquire the temperature and soot using the two-color method in a turbulent Diesel diffusion flame effectively. In addition to, this experiment revealed that the KL factor was high on parts of the chamber where the temperature dropped. On the other hand, the KL factor was low where the temperature increased rapidly. Also, it was possible to measure the highest temperature of a turbulent Diesel diffusion flame is approximately 2300K.

• 한국안전학회지
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• 제15권3호
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• pp.14-22
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• 2000

A numerical analysis has been performed on the two-dimensional rectangular gallium melting problem using the enthalpy method. The major advantage of this method is that the physical domain is discretized with fixed grids without transforming variables and the interface conditions of phase change are accounted for the definition of suitable source terms in the governing equations. But in the fixed method, there is some ambiguity in defining the porosity constant which has no physical interpretation. If the velocity correction is included in the momentum equation, for the appropriate range of porosity constant, the realistic predictions are obtained. The object of the present work is to predict the phase change within the molten steel with thin riser slab using the modified enthalpy-porosity method. The computational procedures for predicting velocity and temperature are based on the finite volume method and the non-staggered grid system. The influence of natural convection on the melting process is considered. A comparison with the experimental results shows that the modified method is better than the previous one.

• 대한토목학회논문집
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• 제29권2A호
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• pp.155-162
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• 2009

이 논문은 정다각형 중실단면을 갖는 최강보에 관한 연구이다. 이 연구에서 보의 체적은 항상 일정하다. 이러한 보에 집중하중과 만재 사다리꼴 분포하중이 작용하는 경우에 탄성곡선의 미분방정식을 유도하고 이를 수치해석하여 정적 거동을 산정하였다. 미분방정식은 Runge-Kutta법을 이용하여 수치적분을 하였고 미지수인 보의 초기치는 shooting method를 이용하여 산정하였다. 수치해석 예에서는 단순보를 채택하였고, 단면깊이의 형상함수로는 선형, 포물선형 및 정현형의 함수를 채택하였다. 이 연구에서 얻은 수치해석의 결과로부터 보의 정적 최대거동값이 최소가 되는 단면형상 즉 최강단면비를 산정하였다.

• 한국자동차공학회논문집
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• 제12권5호
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• pp.58-65
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• 2004

A cylindrical constant volume combustion chamber was used to investigate the combustion characteristics of stratified methane-air mixture under several initial charge conditions in the author's previous reports. The results showed that the improvement of thermal efficiency and reduction of heat loss was realized simultaneously by using 2-stage injection method. This paper deals with the reason why the stratified combustion has showed better combustion rate through the measurement and analysis of chemiluminescence of C $H^{*}$ and $C_{2}$$^{*}$ radicals. An optic fiber bundle is used to measure the local emission of C $H^{*}$ and $C_{2}$$^{*}$ radicals to map the relationship between the excess air ratio and local radical intensity ratio in the combustion vessel at 5 mm apart form the geometric center. The results show that there exist a relationship between the intensity ratio and the air-fuel ratio. It is revealed that the improvement of combustion rate in a lean-stratified mixture is realized through the 2-stage injection method. method.

• 한국분무공학회지
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• 제8권4호
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• pp.31-38
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• 2003

Constant volume combustion chamber has been designed to investigate diesel spray characteristics with Common-Rail injection system to realize high pressure injection. In this study, two methods of measurements, Schlieren shadowgraphy and Mie scattering imaging method ate applied experimentally to study spray form and liquid phase zone in high pressure, high temperature conditions. Diesel fuel is injected at the point which ignited mixture gas is completely burned. The effect of injection pressure, injector hole diameter, ambient gas temperature and density are investigated experimentally.

• International Journal of Automotive Technology
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• 제6권6호
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• pp.555-561
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• 2005

This experimental study was executed to obtain basic data for actual engine operation using radical induced ignition method (RI) which can achieve emission reduction and high efficiency due to the rapid bulk combustion. In this study, a direct injection diesel engine was converted into SI type engine with a sparkplug. The modified SI type engine can be divided into two classes. One is the SI engine with a sparkplug only at the cylinder head, and the other is the SI engine with the sparkplug which is enveloped in a sub-chamber. Also, a basic experimental was conducted in order to investigate combustion mechanism of radical induced injection before the experiment execution for actual engine using the modified SI engine. The bulk combustion phenomenon of radical induced ignition method was analyzed from the basic experiment by using a constant volume chamber. Volume value of sub-chamber used in this experiment is approximately $0.2\%$ of one of the main combustion chamber. In this paper, combustion characteristics using radical induced injection method was compared with that of using spark ignition method according to change in the engine speed and equivalence ratio. As a result, in the case of the radical induced injection engine, the combustion duration and cycle variation were respectively reduced ranged from $\Phi$(equivalence ratio)=0.8 (lean mixture ratio) to $\Phi$=1.0 (stoichiometric ratio).