• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.756_757
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• 2009

This paper deal with the efficiency evaluations in a Synchronous reluctance motor(SynRM) Vs. PMASynRM using a coupled transient finite element methed(FEM) and preisach modeling, which is presented to analyze the characteristics under the effect of saturation and hysteresis loss. The focus of this paper is the efficiency evaluation relative to hysteresis loss, copper loss, etc. on the basis of load condition in a SynRM and PMASynRM. Computer simulation and experimental result for the efficiency using dynamometer shoe the propriety of the proposed method.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.437-442
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• 2004

The optimization of a blade sweep for a transonic axial compressor rotor (NASA rotor 37) has been performed using a response surface method and a Reynolds-averaged Wavier-Stokes (RANS) flow simulation. Two shape variables of the rotor blade, which are used to define a blade sweep, are introduced to increase an adiabatic efficiency. Data points for response evaluations have been selected by D-optimal design, and linear programming method has been used for an optimization on a response surface. The result shows that the adiabatic efficiency is increased to about 1 percent compared to that of the reference shape of the rotor blade. Relatively high increasement of the adiabatic efficiency is obtained between 20 and 60 percent span. In the present study, backward swept blade is more effective to increase the adiabatic efficiency In the axial compressor rotor.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.29 no.2
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• pp.1-6
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• 2006

This study proposes a new approach which combines Data Envelopment Analysis(DEA) and the Analytic Hierarchy Process(AHP) techniques to effectively evaluate Decision Making Units(DMUs). While DEA evaluates a quantitative data set, employs linear programming to obtain input and output weights and ranks the performance of DMUs, AHP evaluates the qualitative data retrieved from expert opinions and other managerial information in specifying weights. The objective of this research is to design a decision support process for managers to incorporate positive aspects of DEA's absolute numerical evaluations and AHP's human preference structure values. It is believed that a pragmatic manager will be more receptive to the results that include subjective opinions incorporated into the evaluation of the efficiency of each DMU efficiency. The WPDEA method provides better discrimination than the DEA method by reducing the number of efficient units.

• Journal of Power Electronics
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• v.16 no.1
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• pp.121-132
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• 2016

In this paper, high-efficiency design methodology of a zero-voltage-switching full-bridge (ZVS-FB) pulse width modulation (PWM) converter for server-computer power supply is discussed based on self-driven synchronous rectifier (SR) performance. The design approach focuses on rectifier conduction loss on the secondary side because of high output current application. Various-number parallel-connected SRs are evaluated to reduce high conduction loss. For this approach, the reliability of gate control signals produced from a self-driver is analyzed in detail to determine whether the converter achieves high efficiency. A laboratory prototype that operates at 80 kHz and rated 1 kW/12 V is built for various-number parallel combination of SRs to verify the proposed theoretical analysis and evaluations. Measurement results show that the best efficiency of the converter is 95.16%.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1092-1094
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• 2005

This paper deal with the efficiency evaluations in a Synchronous reluctance motor(SynRM) Vs. PMASynRM using a coupled transient finite element method(FEM) and preisach modeling, which is presented to analyze the characteristics under the effect of saturation and hysteresis loss. The focus of this paper is the efficiency evaluation relative to hysteresis loss, copper loss, etc. on the basis of load condition in a SynRM and PMASynRM. Computer simulation and experiment at result for the efficiency using dynamometer shoe the propriety of the proposed method.

• Management Science and Financial Engineering
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• v.14 no.2
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• pp.67-87
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• 2008

Data envelopment analysis (DEA) has proven to be a useful tool for assessing efficiency or productivity of organizations which is of vital practical importance in managerial decision making. While DEA assumes exact input and output data, the development of imprecise DEA (IDEA) broadens the scope of applications to efficiency evaluations involving imprecise information which implies various forms of ordinal and bounded data possibly or often occurring in practice. The primary purpose of this article is to characterize the variable efficiency in IDEA. Since DEA describes a pair of primal and dual models, also called envelopment and multiplier models, we can basically consider two IDEA models: One incorporates imprecise data into envelopment model and the other includes the same imprecise data in multiplier model. The issues of rising importance are thus the relationships between the two models and how to solve them. The groundwork we will make includes a duality study which makes it possible to characterize the efficiency solutions from the two models. This also relates to why we take into account the variable efficiency and its bounds in IDEA that some of the published IDEA studies have made. We also present computational aspects of the efficiency bounds and how to interpret the efficiency solutions.

• Proceedings of the KIEE Conference
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• summer
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• pp.917-919
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• 2004

This paper deals with the stator design solution of a synchronous reluctance motor (SynRM) with various slot number by loss & torque evaluations related to the slot open, teeth width using coupled Preisach modeling & FEM. The coupled Finite Elements Analysis (FEA) & Preisach model have been used to evaluate the nonlinear solution. Comparisons are given with characteristics of a SynRM according to the stator winding, slot number, slot open, teeth width variation, respectively

• Proceedings of the Korea Society for Industrial Systems Conference
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• 2008.10b
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• pp.316-321
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• 2008

In the present emerging global economy, as the focus is shifted from manufacturing to service sector, the efficiency of service operations is crucial for the county's sustainable growth and development. As one of the fastest growing service sector industries in South Korea, the call center has become an inevitable part of customer service for most companies. Despite of the strategic importance of the call center, there has been no empirical study on the efficiency of call center service operations in the literature. The main purpose of this study is to evaluate the technical efficiency of call center services so as to not only identify the current status of call center service operations, but also suggest ways to improve service operations efficiency. For this purpose, we apply a non-parametric efficiency measurement method, DEA (Data Envelopment Analysis), to domestic call centers in order to compare their relative efficiency. Based on DEA evaluations, we provided specific directions for the inefficient call centers to possibly improve their operation efficiencies. It is expected that the measurement methods suggested in this study can be applied to various issues such as service KS certification, service operations management, and the productivity analysis of service personnel.

• JSTS:Journal of Semiconductor Technology and Science
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• v.15 no.1
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• pp.145-149
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• 2015

A reconfigurable lighting engine for widely used lighting models is proposed for low-power GPU shaders. Conventionally, lighting operations that involve many complex arithmetic operations were calculated by the shader programs on the GPU, which led to a significant energy overhead. In this letter, we propose a lighting engine to improve the energy-efficiency by supporting the widely used advanced lighting models in hardware. It supports the Blinn-Phong, Oren-Nayar, and Cook-Torrance models, by exploiting the logarithmic arithmetic and optimizing the trigonometric function evaluations for the energy-efficiency. Experimental results demonstrate 12.7%, 42.5%, and 35.5% reductions in terms of power-delay product from the shader program implementations for each lighting model. Moreover, our work shows 10.1% higher energy-efficiency for the Blinn-Phong model compared to the prior art.

• Health Policy and Management
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• v.10 no.4
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• pp.75-98
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• 2000

This study applied Data Envelopment Analysis(DEA) and Ratio Analysis and Regression Analysis to a set of Korean Public Corporation Medical Centers to evaluate their relative human resource efficiencies. The output measure used in this study was based on health insurance system which was used in both in-patient departments and out-patient departments. Inputs included working time of the doctors, nurses, technicians, and managerial department staff. Based on the data provided on the inputs and outputs, the analysis showed 23 of the 34 hospitals to be relatively inefficient. Each hospital with an efficiency rating of less than 1 was considered relatively inefficient. In addition, managerial strategies based on dual variables were constructed to indicate the manner In which inefficient hospitals may be made efficient. A subsequent analysis of t-test revealed that the bed occupancy rate, medical revenue per 100beds, value added revenue per staff, medical revenue per staff were statistically significant. The results of this study suggest the DEA is a promising tool for evaluating relative human resource efficiency in hospitals which have multiple inputs and outputs and where the efficient production function is not specifiable with any precision. But it is considered that efficiency evaluations may be most effective]y accomplished by Incorporating a combination of methodologies such as ratio analysis and regression analysis.