• 한국자동차공학회논문집
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• 제10권3호
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• pp.28-35
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• 2002

The objective of this paper is to quantitatively investigate the effects of alcohol mixture on the combustion improvement of main fuel in supplying alcohol to direct injection diesel engine by auxiliary injection method and blend method. If alcohol is supplied, engine performance greatly improves in high load range. In case of supplying ethanol, BSFC improves, the emission of smoke and NO decreases by delaying main fuel injection timing 5$\^{C}$A. The maximum delivery quantity of alcohol is limited to approximately 50% of total fuel delivery due to misfire and knocking. The limit quantity of main fuel injection that does not accompany misfire and the deterioration of BSFC was approximately 15∼18.5mg/st.

• 한국경영과학회:학술대회논문집
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• 한국경영과학회 1993년도 추계학술대회발표논문집; 서강대학교, 서울; 25 Sep. 1993
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• pp.31-39
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• 1993

This paper considers a procedure for the economic design of a cumulative score(CUSCORE) control chart and more sensitive than X-type control chart for small shift to control the mean of a process with a exponentially distributed quality characteristic. An expected loss - cost model as a function of design variables(sample size, sampling interval, scoring limit and decision limit) is derived. Direct search techniques are used to optimize the model subject to ARL in control. Numerical examples and sensitivity analysis of the model are presented. For selected values of situation parameters a comparison study with CUSUM charts is given. CUSCORE control charts compare favourably with CUSUM charts in cost for speedy production process. The proposed control chart can be directly applied for controlling the lifetime characteristics.

• Structural Engineering and Mechanics
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• 제34권4호
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• pp.417-447
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• 2010

The uncertainty often observed in experimental strengths of masonry constituents makes critical the selection of the appropriate inputs in finite element analysis of complex masonry buildings, as well as requires modelling the building ultimate load as a random variable. On the other hand, the utilization of expensive Monte Carlo simulations to estimate collapse load probability distributions may become computationally impractical when a single analysis of a complex building requires hours of computer calculations. To reduce the computational cost of Monte Carlo simulations, direct computer calculations can be replaced with inexpensive Response Surface (RS) models. This work investigates the use of RS models in Monte Carlo analysis of complex masonry buildings with random input parameters. The accuracy of the estimated RS models, as well as the good estimations of the collapse load cumulative distributions obtained via polynomial RS models, show how the proposed approach could be a useful tool in problems of technical interest.

• 한국수소및신에너지학회논문집
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• 제22권5호
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• pp.735-740
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• 2011

본 연구에서는 직접분사식 CNG기관의 희박한계를 보다 확장하여 고효율 및 저배기 공해를 실현시키고자 실린더 내에 고압의 천연가스를 직접분사함과 동시에 흡입과정 중 흡기관 내에 소량의 저압천연가스를 보조분사하는 경우의 희박한계 확장 및 제반특성에 대해 검토하였다. 그 결과, 흡기보조분사가 없을 경우 희박한계가 ${\lambda}$ = 1.4 까지였으나, 흡기보조분사율이 5~15% 정도에서는 희박한계가 ${\lambda}$ = 1.5 까지 확장되었다. 이는 흡기보조분사에 따른 혼합기의 혼합율 향상에 기인한 것으로 해석하였다. 연소기간은 줄어들었지만, 흡기보조분사의 효과는 주연소기간에서 조기연소기간보다 강하게 나타났다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2015년도 제51회 KOSCO SYMPOSIUM 초록집
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• pp.123-125
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• 2015

A study has been conducted to investigate the effect of swirl angle in low swirl combustor. In this study, the employed swirl angles were $28^{\circ}$, $32^{\circ}$ and $37^{\circ}$. Direct flame photos show that the width of the flame is expanded and the length of the flame is shortened when swirl angle is increased. Also, as the swirl angle was increased, the flame stability region could be widened due to the expansion of lower flammable limit. Between 3 and 7kW, CO emissions was below 10 ppm and NOx emissions was also below 27 ppm at $O_2$ 15% basis over the lean burning range of 0.6 < ${\Phi}$ < 0.9. From this investigation of stability expansion effect and emission performance, it was identified that the swirl angle $37^{\circ}$ is most suitable swirling condition in the low swirl model combustor.

• Structural Engineering and Mechanics
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• 제41권3호
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• pp.339-348
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• 2012

The slope stability analysis is usually done using the methods of calculation to rupture. The problem lies in determining the critical failure surface and the corresponding factor of safety (FOS). To evaluate the slope stability by a method of limit equilibrium, there are linear and nonlinear methods. The linear methods are direct methods of calculation of FOS but nonlinear methods require an iterative process. The nonlinear simplified Bishop method's is popular because it can quickly calculate FOS for different slopes. This paper concerns the use of inverse analysis by genetic algorithm (GA) to find out the factor of safety for the slopes using the Bishop simplified method. The analysis is formulated to solve the nonlinear equilibrium equation and find the critical failure surface and the corresponding safety factor. The results obtained by this approach compared with those available in literature illustrate the effectiveness of this inverse method.

• 터널과지하공간
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• 제28권6호
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• pp.584-595
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• 2018

흙의 전단강도의 적절한 기준을 제시하기 위해 모래질, 점토질, 자갈질의 약 290 여개의 재료에 대하여 직접전단시험을 수행하였다. 흙의 대분류에 의한 모래질 흙의 전단강도는 모래 함유율이 많은 흙일수록 내부마찰각은 증가하는 경향이 뚜렷하게 나타났으며, 그 범위는 $23.5^{\circ}{\sim}34.9^{\circ}$에 분포하고 있는 것으로 나타났고, 점착력은 2.0 kPa~15.7 kPa 사이에서 골고루 분포하는 것으로 나타났다. 탄성계수는 하중단계에 따라 뚜렷하게 구분할 수 있었으며, 수직하중이 증가할수록 약 80%씩 증가하였다. 점토질 흙의 내부마찰각은 $15.0^{\circ}{\sim}28.6^{\circ}$의 범위에서 점토성분 함유율이 많아질수록 감소하는 경향이 나타났고, 점착력은 일정한 범위로 증가하는 경향이 나타났다. 점토질 흙의 탄성계수는 거의 같은 증가비로 초기탄성계수만 약간 증가하는 경향을 나타내었다. 자갈질 흙의 내부마찰각은 $29.9^{\circ}{\sim}36.7^{\circ}$의 범위로 뚜렷한 특성을 파악할 수 없었다. 세부분류에 따른 SW(입도분포가 좋은 모래), SP(입도분포가 나쁜 모래), SC(점토 섞인 모래), SM(실트 섞인 모래)의 점착력은 실트함유율이 가장 많은 SM 시료에 비해 SC는 약 94%, SW는 약 78%, SP는 약 59% 정도 값을 나타내었다. 또한 내부마찰각은 ML(액성한계가 낮은 실트)과 CL(액성한계가 낮은 점토)이 거의 같은 거동 특성을 나타내었고, MH(액성한계가 높은 실트)는 ML의 약 88% 값을 나타내었다. 점착력에 대한 변화는 거의 비슷한 증가비를 나타내었다.

• Bulletin of the Korean Chemical Society
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• 제33권3호
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• pp.1015-1019
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• 2012

The direct calculation method is generalized to the excited-state diffusion-influenced reversible reaction of a neutral and a charged particle under an external field with two different lifetimes and quenching in three dimensions. The present method provides an alternative way to calculate the binding probability density functions and the survival probabilities from the corresponding irreversible results. The solutions are obtained as the series solutions by the diagonal approximation due to the anisotropy of the unidirectional external field. The numerical results are found to be in good agreement with those of the previous study [S. Y. Reigh et al. J. Chem. Phys. 132, 164112 (2010)] within a weak field limit. The solutions of two approaches show qualitatively the same overall behavior including the power laws at long times.

• Bulletin of the Korean Chemical Society
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• 제27권10호
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• pp.1613-1617
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• 2006

Optimum analytical conditions for cyclic voltammetry (CV) and square wave (SW) stripping voltammetry were determined using mercury-mixed carbon nanotube paste electrode (PE). The results approached the microgram working ranges of SW: 10.0-80.0 $ugL^{-1}$ and CV: 100-700 $ugL^{-1}$ Cd (II); working conditions of 300-Hz frequency, 100 mV amplitude, 1.6 V accumulation potential, 400 sec accumulation time, and 40 mV increment potential. First, analysis was performed through direct assay of cadmium ions deep into the fishs brain core and plant tissue in real time with a preconcentration time of 400 sec. The relative standard deviation of 10.0 $mgL^{-1}$ Cd (II) observed was 0.064 (n = 12) at optimum conditions. The low detection limit (S/N) was set at 0.6 $ugL^{-1}$ ($5.33{\times}10^{-9}$ M). The methods can be used in direct analysis in vivo or in real-time monitoring of plant tissue.

• 한국자동차공학회논문집
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• 제6권3호
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• pp.78-87
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• 1998

A dynamic model of direct-acting OHC valve train system has been used to determine the load conditions in the system. The modified equations for calculating the friction forces between cam and HLA, and at a camshaft bearing have been defined considering the lubrication conditions. Then, to understand the frictional characteristics in the system, a parameter study has been performed. As the results of the analysis, valve spring stiffness and preload have great effects on the friction in the system, but the effects of other parameters are negligible. So, how to design the valve train system with respect to the reduction of friction is to minimize the valve spring stiffness and preload in the limit of satisfying the dynamic constraints.