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장연상(Yanshuang Zhang),정병호(Byung Ho Jeong) 한국경영과학회 2012 韓國經營科學會誌 Vol.37 No.4
The existing DEA models have been devoted to evaluate relative efficiency of DMUs based on multiple input and output factors of a same period. However, a certain kind of lead time can be required to produce outputs using inputs in an organization. R&D evaluation is a typical area with this kinds of time lag. Thus, the purpose of this paper is to develop a new DEA model to deal with time lag effect in performance evaluation. The proposed model is to find relative efficiency of each DMU for each period considering the time lag effect. A case example using a real data set is also given to show the usage or implication of the suggested model. The results are compared with the ones of the CCR model and the multi-periods input model.
2중 분류를 형성하는 가솔린 연료분사기들의 분무 특성에 관한 연구
장연상(Y.S.Chang),김원태(W.T.Kim),강신재(S.J.Kang),노병준(B.J.Rho) 한국자동차공학회 1998 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1998 No.11_1
The fuel injector of 4-Valve gasoline engine, is required dual-stream. Thus, in this study spray behavior and atomization characteristics of the injectors forming dual-stream, is investigated by spray visualization and 3D PDPA measurement. As a result, the atomization performance of 4-hole injector is superior to 2-hole injector about 30%. And the atomization performance of air shroud 4-hole injector is very excellent but it doesn't form dual stream over 20kPa air shroud. Air shroud injector with separator maintains dual stream up to 80kPa air shroud, it is expected about 45% improvement of atomization.<br/>
A Multi-Period Input DEA Model with Consistent Time Lag Effects
정병호,장연상,이태한 한국산업경영시스템학회 2019 한국산업경영시스템학회지 Vol.42 No.3
Most of the data envelopment analysis (DEA) models evaluate the relative efficiency of a decision making unit (DMU) based on the assumption that inputs in a specific period are consumed to produce the output in the same period of time. However, there may be some time lag between the consumption of input resources and the production of outputs. A few models to handle the concept of the time lag effect have been proposed. This paper suggests a new multi-period input DEA model considering the consistent time lag effects. Consistency of time lag effect means that the time delay for the same input factor or output factor are consistent throughout the periods. It is more realistic than the time lag effect for the same output or input factor can vary over the periods. The suggested model is an output-oriented model in order to adopt the consistent time lag effect. We analyze the results of the suggested model and the existing multi period input model with a sample data set from a long-term national research and development program in Korea. We show that the suggested model may have the better discrimination power than existing model while the ranking of DMUs is not different by two nonparametric tests.
윤덕영 ( Duk Young Yoon ),장연상 ( Yeon Sang Jang ) 한국항공경영학회 2009 한국항공경영학회 추계학술대회 Vol.2009 No.-
As finding and purchasing travel product through travel agency`s website has become general practices in the market place, travel agencies exert themselves to improve quality of web site to draw maximum user satisfaction which directly linked to market competitiveness, this study takes empirical research on which and how the combined attributes affect website quality and suggest travel agencies more effective way for strengthening their position under highly competitive environment.
회전컵에 의해 분무된 물방울의 크기분포 및 분무실내 거동
이영수,박균영,이형주,장연상 한국화학공학회 2000 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.38 No.4
직경 120㎝의 분무실 내에서 회전컵을 이용한물의 분무실험을 수행하였다. 물의 공급량 3-l0㎏/h, 컵의 회전속도 10,0000-20,000 rpm 범위에서 컵 회전속도와 물 공급량이 분무액적 크기에 미치는 영향을 관찰하고, 이미 제안된 실험식에 의한 예측값과 비교하였다. 본 실험에서 측정된 액적크기와 예측값 사이에는 상당한 차이가 있음을 알 수 있었다. 선회공기 주입하에 분무실내 액적분포 측정 및 공기흐름조사를 통하여 분무된 액적이 공기흐름을 타고 축 아래로 갈수록 벽 쪽으로 이동하며, 일부는 분무실에 형성된 재순환 기류에 의해 분무실 중심쪽으로 이동함을 알았다. 선회공기의 영향을 받아 액적의 분무실내 체류시간이 증가하고, 분무실내에 존재하는 난류현상으로 액적의 충돌 합체가 이루어져, 축 아래로 내려갈수록 액적의 크기가 증가하였다. Experiments on the spray of water have been carried out using a rotating cup in a chamber of 120 ㎝ in diameter. The feed rate of water was varied from 3 to 10 ㎏/h and the rotation speed of the cup from 10,000 to 20,000 rpm. Measured drop sizes were compared with those predicted by empirical equations; there existed considerable discrepancies between experimental data and predicted values. In the presence of a swirling air in the chamber, the water drops ejected from the cup moved toward the wall as they fall down, following the main stream of the air. Some of the drops moved toward the center of the chamber by a recirculating air flow. The dmp size increased in the axial direction toward the bottom, probably due to coalescence between water drops. The turbulence of the air and the extension of the residence time of the drops by the swirling action of the air must have increased the chance of the coalescence.
이강웅(K.W.Lee),장연상(Y.S.Chang),김원태(W.T.Kim),강신재(S.J.Kang),노병준(B.J.Rho) 한국자동차공학회 1997 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1997 No.11_1
This study is investigated to the atomization characteristics of pintle type gasoline injector with air swirl adaptors. Air swirl adaptors have four swirl angle such as 0˚, 15˚, 30˚, 45˚, In this study, injector is used air and unlead gasoline fuel as working fluids. Spray visualization and PDPA measurements were carried out under the various assisted air pressure and the fixed fuel pressure. For analysis the atomization characteristics, distributions of mean diameter, number probability density, and SMD are examined with swirl angles of adoptor, axial and radial distance, etc.<br/>