• 한국경영과학회지
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• 제35권2호
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• pp.19-35
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• 2010

Many papers have used a two-stage approach of first calculating DEA efficiency scores and then seeking to correlate these scores with various environmental variables. Most of the studies have not checked whether such a two-stage approach is statistically valid for identifying significant environmental variables. Recently Simar and Wilson (2007) (SW) introduce a sensible data generating process and bootstrap procedure based on truncated regression for the two-stage approach. Banker and Natarajan (2008) (BN) provide a statistical foundation for the two-stage approach comprising a DEA followed by an ordinary least squares or maximum likelihood estimation. Researchers have to identify an approach suitable for their research circumstances in terms of properties, merits, demerits, and robustness to plausible departures from its chosen data generating process. We summarize the foundations and properties of the two-stage procedures suggested by SW and BN. And we discuss merits and demerits of those procedures. Also using Monte Carlo simulation we assess their relative performance under several misspecified settings.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.589-592
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• 2002

A commercial CFD code is applied to analyze the 3-D viscous flow field within vertical multi-stage centrifugal pump including impeller of centrifugal pump with 6 blades and guide vain with 11 blades. The numerical analysis of vertical multi-stage centrifugal pump is performed by changing flow rate from $8\;to\;26\;m^{3}/h$ at the constant 3500rpm. The characteristics such as total pressure coefficient, total head, water horse power, power efficiency are represented according to flow rate changing. In the future, we will need to perform flow calculation of vertical multi-stage centrifugal pump by considering meridional shape of impeller.

• Journal of Advanced Marine Engineering and Technology
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• 제22권1호
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• pp.42-51
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• 1998

A 150 m$\^$3//hr, 30 kg/cm$\^$2/, air-cooled 3-stage reciprocating air compressor is designed to be used in starting large diesel engines of ships. A basic design procedure is presented to meet the targeted pressure and flow rate, and especially a volumetric efficiency of 80%. Temperature and stress analysis of the 1st stage cylinder are performed using axisymmetric FEM modelings. The dynamics of valve system is analyzed and stress at the 1st stage valve seat caused by valve impact is evaluated. To reduce friction loss and wear at the compressor engine system tribological design issues are reviewed and good design practices are suggested. Finally, forced-air pin-type interstage coolers are designed to dissipate generated compression heat at each stage.

• 한국공작기계학회논문집
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• 제15권3호
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• pp.82-90
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• 2006

Recently the electrostatic 2-axis MEMS stages have been fabricated for the purpose of an application to PSD (Probe-based Storage Device). However, all of the components(platform, comb electrodes, springs, anchors, etc.) in those stages are placed in-plane so that they have low areal efficienceis, which is undesirable as data storage devices. In this paper, we present a novel structure of an electrostatic 2-axis MEMS stage that is characterized by having large area platform. for obtaining large area efficiency, the actuator part consisting of mainly comb electrodes and springs is placed right below the platform. The structure and operational principle of the MEMS stage are described, followed by a design procedure, structural and modal analyses using FEM(Finite Element Method). The areal efficiency of the MEMS stage was designed to be about 25%, which is very large compared with the conventional ones having a few percentage.

• 한국항만경제학회지
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• 제25권3호
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• pp.139-164
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• 2009

지금까지 본 연구에서는 첫째, 항만투자의 단계별 가치사슬효율성과 관련된 기존연구들을 검토하였으며, 또한 선진국의 항만투자의 가치사슬효율성과 관련된 제도를 간략하게 소개하였으며, 둘째, 설문지조사법을 통해서 국내항만관련 교수 및 유관기관의 전문가들이 생각하는 항만투자의 가치사슬 효율성을 평가하기 위한 모형을 파악하여 제시하였다. 셋째, 다년도 패널자료에 의한 단계별 가치사슬효율성을 측정하기 위한 모형을 개발하는 한편 그러한 모형에 따라서 실증분석을 하고 해석하였다. 실증분석결과를 요약해 보면 다음과 같다. 첫째, 전체 패널자료를 이용한 제1모형의 단계별 효율성의 순위를 살펴보면, 2단계, 3-1단계, 1단계, 3-2단계의 순서가 8개 항만(인천, 장항, 목포, 완도, 여수, 제주, 서귀포, 부산)에서 시현되었으며, 전체의 단계별 효율성을 평균한 순위는 2단계, 1단계, 3-1단계, 3-2단계 순위였다. 제2모형의 단계별 효율성 순위를 살펴보면, 9개항만 중에서 3개항만 (인천, 목포, 제주)이 2단계, 3-2단계, 3-1단계, 1단계의 순서를 보였으며, 전체의 단계별 효율성을 평균한 순위도 2단계, 3-2단계, 3-1단계, 1단계의 순서였다. 둘째, 가치사슬효율성 수치사이의 차이를 전체평균적인 측면에서 살펴보면, 제1모형에서는 2단계와 1단계를 비교한 가치사슬효율성 수치를 제외하고는 다른 모든 비교단계의 효율성은 악화된 것으로 나타났다. 제2모형에서는 2단계가 1단계에 비해서 가치사슬효율성이 크게 증진되었으며, 1단계에 비교된 3-1단계, 3-2단계, 그리고 3-2단계에 비교된 3-1단계에서는 가치사슬 효율성이 증진되었으며, 2단계에 비교된 3-1단계, 3-2단계에서는 오히려 악화되었다. 실증분석 결과는 다음과 같은 정책적인 함의를 갖고 있다. 즉, 국토해양부의 항만투자와 관리를 담당하는 담당자는 본 논문의 실증분석결과에서 제시하고 있는 단계별, 항만별, 가치사슬효율성 자료를 검토하여 가치사슬 효율성수치가 높게 시현된 항만들의 모형별 가치사슬단계에 주목하여 항만투자를 집행함으로써 그 효과를 증대시키는 노력을 해야만 한다.

• 품질경영학회지
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• 제44권4호
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• pp.785-798
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• 2016

Purpose: This paper developed the framework for extracting strategies of research and business development (R&BD) based on the data envelopment analysis(DEA). Methods: DEA has been widely utilized in evaluating R&D efficiency. Even though, technology transfer and commercialization has been regarded as the important factors for practical R&D efficiency evaluation, most research have evaluated R&D efficiency by just using the DEA outputs such as the number of patents and papers. The technology transfer, commercialization and relations among costs and generated technology and commercialization are needed to be considered for more practical R&D efficiency evaluation. Thus, this research addressed a method on how to incorporate the commercialization factors into the R&DB efficiency evaluation, and improve the efficiency strategically in terms of R&D and B&D. To achieve this, this research utilized a two-stage network DEA model for R&BD efficiency evaluation. Results: The proposed framework was applied to the 15 public research institutes and the 34 universities for validation. R&BD efficiency for the 15 public research institutes and the 34 universities was evaluated, and the differentiated improvement strategies for the inefficient DMUs to improve their efficient were proposed. Conclusion: The R&BD efficiency would be effectively analyzed based on two-stage network DEA. It would be utilized for the effective strategy planning for cultivating R&BD.

• 동력기계공학회지
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• 제20권1호
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• pp.11-17
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• 2016

In this study, the simulation for performance comparison between basic single stage organic rankine cycle, multi stage reheater cycle and multi stage reheater & recuperator cycle was carried out. The multi stage reheater cycle and multi stage reheater & recuperator cycle was designed to improve the efficiency for organic rankine cycle using heat source from industrial waste heat and heat sink from deep ocean water. R245fa was selected as a refrigerant for the cycle and system efficiencies were simulated by the variation of the heat sink temperature and the cycle classification. Performance characteristics were simulated by using the Aspen HYSYS. It was confirmed that the system efficiency was decreased by the increase of heat sink temperature. These results can be considered to be applied as geo-ocean thermal energy conversion in where plenty of geothermal or ocean thermal resource exist.

• Journal of Communications and Networks
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• 제18권4호
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• pp.600-609
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• 2016

In this paper, we propose a two-stage base station (BS) sleeping scheme to save energy consumption in cellular networks. The BS sleeping mode is divided into a light sleeping stage and a deep sleeping stage according to whether there is a user in the BS's coverage. In the light sleeping stage, a BS will retain its coverage and frequently switch between the on state and the doze state according to the service characteristics. While in the deep sleeping stage analysis, the BS will shut down its coverage, and neighbor BSs will patch the coverage hole. Several closed-form formulas are derived to demonstrate the power consumption in each sleeping stage and the stage switching conditions are discussed to minimize the average power consumption. The average traffic delay caused by BS sleeping and the average deep sleeping rate under a given traffic load have also been studied. In addition, it is shown that BS sleeping is not always possible because of the limited quality of service (QoS) requirements. Simulation results show that the proposed scheme can effectively reduce the average BS power consumption, at the cost of some extra traffic delay. In summary, our proposed framework provides an essential understanding of the design of future green networks that aim to take full advantage of different stages of BS sleeping to obtain the best energy efficiency.

• 디자인학연구
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• 제16권2호
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• pp.355-364
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• 2003

본 연구는 디자인의 프로세스를 2단계모델과 3단계모델로 구분하고 이들 각 모델의 효율성에 대하여 검증하였다. 2단계모델은 디자이너의 창의적인 마인드를 바탕으로 주관적이고 감각적으로 수행하는 디자인활동을 의미하며 반대로 3단계모델인 경우 객관적이고 논리적인 소비자 중심적자인 활동을 의미한다. 기존 연구에서는 이러한 두 가지 모델에 대하여 상대적으로 어떤 모델이 더 효과적인가에 대하여 의견의 일치를 이루어내지 못하였다. 본 연구에서는 이들 두 모델에 대하여 시장선도전략(market leader strategy)과 시장탐색전략(market seeker strategy)의 개념을 통해 각각의 효율성을 제시하였다 즉, 실증분석을 통해 명성브랜드라면 2단계모델을 바탕으로 한 시장선도전략이 그리고 비명성브랜드인 경우에는 3단계 모델을 바탕으로 한 시장탐색전략이 더 효율적이라는 상황적 입장을 제시하였으며 다만 어떤 상황에서 어떤 모델이 더 효율적인지에 대한 다각적인 검토가 더 필요하다고 제안하고 있다.

• 한국전산유체공학회지
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• 제11권4호
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• pp.1-8
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• 2006

Clocking effects of a stator on the performance and internal flow in an UTRC 1.5 stage axial turbine are investigated using a three-dimensional unsteady flow simulation. Six relative positions of two rows of stator are investigated by positioning the second stator being clocked in a step of 1/6 pitch. The relative efficiency benefit of about 1% is obtained depending on the clocking positions. However, internal flows have some different characteristics from that in the previous study at the best and worst efficiency positions, since the first stator wake is mixed out with the rotor wake before arriving at the leading edge of the second stator. Instead of the first stator wake, it is found that the wake interaction of the first stator and rotor has a important role on a relative efficiency variation at each clocking position. The time-averaged local efficiency along the span at the maximum efficiency is more uniform than that at the minimum efficiency. That is, the spanwise efficiency distribution at the minimum efficiency has larger values in mid-span but smaller values near the hub and casing in comparison to those at the maximum efficiency. Moreover, the difference between maximum and minimum instantaneous efficiencies during one period is found to be smaller at the maximum efficiency than at the minimum efficiency.