• The KSFM Journal of Fluid Machinery
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• v.7 no.3 s.24
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• pp.39-47
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• 2004

Micro gas turbines are designed with low turbine inlet temperature and pressure ratio. To overcome the efficiency defect of the simple cycle, adoption of the recuperator is an inevitable choice. In addition to the design performance, we should also pay attention to the off-design performance of gas turbines since they usually operate at part-load conditions lot a considerable amount of their lifetime. This study analyzes off-design performance characteristics of micro gas turbines and addresses the importance of the recuperation process doting the part load operation. Comparative analyses have been performed to evaluate the part load performance differences among various design and operating options : simple vs recuperative cycles, single vs two shaft configurations, various operating strategies for the single shaft configuration, and current vs advanced engines. Major finding is that maintaining high turbine exhaust temperature is crucial for efficient operation of micro gas turbines.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.1 no.2
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• pp.70-73
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• 1987

This paper itltroduces a simple stair-case PWM using the pseudo-sinusoidal method. In a configuration of controller, the value of sine as a fundamental factor divided into stair-case level and the three-phase PWM inverter is composed by digital compound for each value of stair-case level. The three-phase output pulse at a fixed carrier frequency and a variable reference frequency is obtained under the effect of reduced harmonics. In this experiment, using the power FET as the switching device, 0.5 H.P. induction motor operation is performed when the switching frequency is 20KHz.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.9 no.3
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• pp.108-112
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• 1984

The motivation in this paper is in obtaining an adaptive observer with simple configuaration and faster adapting speed. The identification and state estimation are seperated to increase the adapting speed of the adaptive observer. The method of identification proposed by Ichikawa is modified. And the adaptive observer is constructed by using the output of state variable filters that are used in identification. Finally, the digital simulation results to the proposed system are presented.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.824_825
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• 2009

This paper deals with the characteristics of SPMSM for hydraulic actuator according to the slot number. As a design variable, slot number affects the winding configuration and this leads to the total variation of motor characteristic. Therefore number of slot should be cautiously determined. Three SPMSMs are designed and THD of back emf, cogging torque, and torque ripple are compared. Among three SPMSMs, 36slots with 12 pole is chosen for further development considering motor characteristics and manufacturing.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1167_1168
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• 2009

This paper presents new configuration of a.c. traction power supply system. The proposed system includes autotransformer with variable tab. The voltage drop in traction power supply system can be reduced due to tap change of autotransformer. In this paper, fault current and Impedance is investigated, when fault occurs in traction power supply system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.1085-1089
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• 2007

An acoustic topology optimization method is developed to optimize the acoustic attenuation capability of a muffler. The transmission loss of the muffler is calculated by using the three-point method based on finite element analysis. Each element of the finite element model is assumed to have the variable acoustic properties, which are penalized by a carefully-selected interpolation function to yield clear expansion chamber shapes at the end of topology optimization. The objective of the acoustic topology optimization problem formulated in this work is to maximize the transmission loss at a target frequency. The transmission loss value at a deep frequency of a nominal muffler configuration can be dramatically increased by the proposed optimization method. Optimal muffler configurations are also obtained for other frequencies.

• Transactions of the Korean Society of Automotive Engineers
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• v.1 no.1
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• pp.1-13
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• 1993

The three-dimensional numerical analysis for in-cylinder flow of four-valve engine without intake port has been successfully computed. These computations have been performed using technique of the general coordinate transformation based on the finite-volume method and body-fitted non-orthogenal grids using staggered control volume and covariant variable as dependent one. Computations are started at intake valve opening and are carried through top-dead-center of compression. A k-$\varepsilon$model is used to represent turbulent transport of momentum. The principal study is the evolution of interaction between mean flow and turbulence and of the role of swirl and tumble in generating near TDC turbulence. Results for three different inlet flow configuration are presented. From these results, complex flow pattern may be effective for promoting combustion in spark-ignition engines and kinetic energy of mean flow near TDC is well converted into turbulent kinetic energy.

• Computers and Concrete
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• v.9 no.5
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• pp.357-374
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• 2012

The aim of this paper is to develop a procedure able to calculate the long-term stress and strain patterns in modern prestressed composite structures which are largely influenced by creep and shrinkage and whose final static configuration is the result of many phases of loading and restraints conditions. The introduction of equivalent moduli, depending on the viscous and elastic features of materials, can guarantee a significant simplification of the problem presented above. The proposed calculation model has been used to design the "Quattroquercie Viaduct" located on the highway "A3" Salerno-Reggio Calabria, Italy.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.501-506
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• 1999

The purpose of this study is to experimentally investigate the strength and ductility of reinforced high strength concrete columns under uniaxial load and several test variables. To do this, we have conducted tests on thirteen 20$\times$20$\times$60cm specimens with 8 and 12 longitudinal steel bars subjected to monotonic uniaxial compression. The main variables considered in this test are the configuration of ties, the space the ties, the diameter of ties and yield strength of ties. The results indicate that the strength and the ductility of reinforced high strength concrete columns have been influenced on these variables except yield strength of ties. Judging from test results, real stress of ties at peak concrete stress is suitable variable than yield strength of ties for estimation of the strength gain factor(Ks).

• KIEAE Journal
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• v.4 no.3
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• pp.27-35
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• 2004

The conventional way to acquire sufficient amount of daylight in interiors is to provide large openings with clear glass. The use of clear glass on the whole facade, however, might cause a sort of visual problem because of the harness of direct sun and brighter sky surface than expected. They should be filtered in opticalway or bounced in the architectural. One of the common solutions for the problem might be the use of photometric glasses with various transmittances for the glass walls. This paper deals with performance data related to the impact of various transmittal glazing materials for window systems in terms of daylighting. A series of scale model measurements was carried out with the fundamental configuration of a commonly used all-glass facades. Additionally some experimental performance index was issued for the better expression of the need of natural lighting.