• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.2
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• pp.211-216
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• 2012

The availability of thermal energy has been widely recognized recently, and the cascade usage of thermal energy from combustion has been encouraged. Within this framework, a 1-kW-class Stirling-engine.based cogeneration system has been proposed as a unit of a distributed energy system. The capacity has been designed to be adequate for domestic usage, which requires high compactness as well as low emissions and noise. To develop a highly efficient system satisfying these requirements, a premixed slot-type short-flame burner has been proposed, and a series of experiments has been performed to understand its combustion characteristics. Flame images have been captured to observe the dependence of the flame mode on the combustion load and air/fuel ratio. The exhaust gas has been sampled and analyzed to study the emission characteristics for each flame mode.

• Korean Journal of Optics and Photonics
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• v.11 no.6
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• pp.405-410
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• 2000

We propose a novel design concept to improve extinction ratio by minimizing $Cv_e-Cv_o$ . Improvements of loss and fabrication error limit are also obtained by this hybrid design of the lateral shift and curved waveguide to control transfer coefficients, $Cv_e and Cv_o$ . The concept of lateral shift merges two transfer coefficients, and additional curved waveguide controls mode profile asymmetrically to help this minimizing effect of $Cv_e-Cv_o$ with no serious decrease in transfer efficiency. For a given InP based waveguide structure, the mode propagation analysis with an effective index approximation provided a calculational improvement of extinction ratio to -39 dB and fabrication error limit to $57.19\mu\textrm{m}$, with a structure design of $300\mu\textrm{m}$ waveguide curvature and $0.1\mu\textrm{m}$lateral shift. shift.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2A
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• pp.207-214
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• 2008

This study presents a way to validate the quality level of the proposed connection type and verify the experimental test, and performs a 3D nonlinear analysis corresponding to the experimental test. Two mixed-structure beams were cast and tested under a four-point static loading. Force-displacement relation, force-strain relation, force-opening width, and failure mode were observed from comparing the numerical results of the adopted FE model. Nonlinear analysis of mixed structures was carried out by utilizing the contact elements of a general purpose structural analysis computer program (ABAQUS). The results of numerical and experimental simulation show that the proposed L-shaped connection has greater stiffness under flexural loading and better structural performance with regard to the connection.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.6
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• pp.201-212
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• 2007

This study presents experimental results of Steel-PSC mixed structural system having front-rear plate connection between Steel and Prestressed Concrete. Two kinds of Steel-PSC mixed structural system of 5.4m length were tested to evaluate flexural behaviors under four point loading, and 4 kinds of specimens with and without prestressing force at R & L type connection were tested to observe the shear behavior. Based on the test results of load-deflection curves and failure modes of specimens, it is found that the proposed L shape connection with front-rear plate connection between Steel and Prestressed Concrete has higher strength and stiffness. From the study, Steel-PSC mixed structural system with L shaped connection has a better structural performance in connection part.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.4
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• pp.19-33
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• 2008

Dynamic response measurements from natural excitation were carried out for 25- and 42-story buildings to evaluate their inherent properties, such as natural frequencies, mode shapes and damping ratios. Both are reinforced concrete buildings adopting a core wall, or with shear walls as the major lateral force resisting system, but frames are added in the plan or elevation. In particular, shear walls in a 25-story building are converted to frames from the 4th floor level downwards while maintaining a core wall throughout, resulting in a fairly complex structure. Due to this, along with similar stiffness characteristics in the principal directions, significantly coupled and closely spaced modes of motion are expected in this building, making identification rather difficult. By using various state-of-the-art system identification methods, the modal parameters are extracted, and the results are then compared. Three frequency-domain and four time-domain based operational modal identification methods are considered. Overall, all natural frequencies and damping ratios estimated from the different identification methods showed a greater consistency for both buildings, while mode shapes exhibited some degree of discrepancy, varying from method to method. On the other hand, in comparison with analysis results obtained using the initial finite element(FE) models, test results exhibited a significant difference of about doubled frequencies, at least for the three lower modes in both buildings. To improve the correlation between test and analysis, a few manual schemes of FE model updating based on plausible reasons have been applied, and acceptable results are obtained. The advantages and disadvantages of each identification method used are addressed, and some difficulties that might arise from the updating of FE models, including automatic procedures, for such large structures are carefully discussed.

• The Transactions of the Korea Information Processing Society
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• v.2 no.4
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• pp.567-580
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• 1995

A transition-based Objet-oriented programming system(TOPS) is a transition-based object-oriented system suitable for development of various concurrent systems.A TOPS consists of a collection of interacting structural active objects(SAOs),and their behaviors are determined by the transition statements provided in their class definitions.Furthermore,SAOs can be structurally and hierarchcally composed from their component SAOs like hardware commponents. These features allow SAOs to model components for circuit simulation more naturally than passive objects used in ordinary object-oriented programming. Also,we can easily add new kinds of components by using the inheritance mechanism.Executions of transition statements may be eventand/or time-driven, and hence digital,and mixed-mode simulation is possible.Prototype simulation programs with graphical user interfaces have been developed as TOPS progrms for digital,analog,and mixed-mode circuit simulation.

• Journal of KIISE:Computer Systems and Theory
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• v.27 no.7
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• pp.675-683
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• 2000

For real time services of multimedia applications, storage systems should provide data without degrading their performance. Since it is very important to recover data immediately at a disk failure, the disk recovery system is required. This paper presents a hybrid recovery scheme which prevents degraded the performance on a single disk failure at RAID level 5 architecture until the failed disk is replaced with a new disk. The proposed scheme is very economical compared to previous spare disk schemes because it does not use extra disks. The performance of the proposed scheme is evaluated and analyzed with that of the RAID level 5 for various requested sizes through the simulation. The results show that the performance of the proposed scheme is improved up to 20 percents at the failure mode and 80 percents at the reconfigured mode. After a multimedia server system has been built with a RAID controller and hard disks, the data recovery performance of the propose scheme are compared with the results of simulation.

• The Journal of the Acoustical Society of Korea
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• v.19 no.3
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• pp.26-34
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• 2000

In this paper, we propose a 4kbps speech coder that combines the harmonic vector excitation coding with time-separated transition coding. The harmonic vector excitation coding uses the harmonic excitation coding in the voiced frame and uses the vector excitation coding with the structure of analysis-by-synthesis in the unvoiced frame, respectively. But two mode coding method is not effective for transition frame mixed in voiced and unvoiced signal and a new method beyond using unvoiced/voiced mode coding is needed. Thus, we designed a time-separated transition coding method for transition frame in which a voiced/unvoiced decision algorithm separates unvoiced and voiced duration in a frame, and harmonic-harmonic excitation coding and vector-harmonic excitation coding method is selectively used depending on the previous frame U/V decision. In the decoder, the voiced excitation signals are generated efficiently through the inverse FFT of harmonic magnitudes and the unvoiced excitation signals are made by the inverse vector quantization. The reconstructed speech signal are synthesized by the Overlap/Add method.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.1
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• pp.24-33
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• 2020

In this study, model combustion tests were conducted to investigate the combustion instability characteristics of swirl coaxial injectors for a liquid rocket engine. To examine the effects of the combustion chamber resonant frequency and the injector mixing conditions, pressure fluctuations in the combustion chamber were measured by changing the combustion chamber length, injector recess length, and propellant mixture ratio. From the test results, the variation in the pressure fluctuations for each experimental condition was confirmed and the combustion stability was evaluated by stability mapping. It was found that the longitudinal mode and Kelvin-Helmholtz instabilities occurred due to the change in the combustion chamber and recess lengths.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.4
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• pp.83-90
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• 2004

In this paper, we proposed a new instruction set(X32Y ISA) with 3 different types of instruction mode. The proposed instruction set organizes 32-bit, 24-bit, 16-bit instruction in order to solves a problem of memory size limitation in an embedded microprocessor. We designed a 32-bit 5 stage pipeline RISC microprocessor based on the X32V ISA. To verify the proposed the X32V ISA and a microprocessor, we estimated a program code size of multimedia application programs using a X32V simulator. In result, we verified that the Light mode and the Ultra Light mode obtains 8%, 27% reduction of a program code size through comparison with the Default mode. The proposed microprocessor was verified all X32V instructions execution at Xilinx FPGA with 33MHz operating frequency,