• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.3
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• pp.65-73
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• 2004

The bolier systems of coal fired power plants are large, non-linear systems with numerous interactions between its component parts. In the analysis of such complex systems, dynamic simulation is recognized as a powerful method of keeping track of the myriad of interactions. The boiler system consists of air/gas system and water/steam system. Due to recent reinforcement of environmental regulation on pollutant discharge and requirements of design validation on properites of boiler, the commercial programs are used for the analysis of boiler system. This paper addressed to the development of model using MMS(Modular Modeling System) developed by EPRI(Electric Power Research Institute) as the simulation tool. The developed model using MMS is tested for the design and local data on boiler combustion system of korea standard coal fired power plant boiler. The simulation results show that the developed model well reproduces responses of the combustion system with less than ${\pm}$5% error under steady state and transient state conditions. The developed model for analysis of the combustion system in this paper is general and applicable to any type of coal fired power plant.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.298-298
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• 2011

다양한 수문학적 순환 성분들의 영향을 받는 유역의 포화과정은 토양층의 공간적 이질성과 맞물려 매우 복잡한 거동특성을 보이는 것으로 알려져 왔다. 이와 관련하여 주목해 볼 만한 지형인자 중의 하나로서 지형지수(topographic index)를 들 수 있다. 지형지수는 TOPMODEL의 주요한 입력변수 중의 하나로서 그 공간적 분포에 따라 유역의 상대적인 포화도를 용이하게 평가할 수 있는 객관적인 수단을 제공한다. 하지만 신뢰성 있는 지형지수의 산정은 상당히 까다로운 작업으로서 정확한 지형지수를 산정할 수 있는 절대적인 방법은 존재하지 않는 것으로 알려져 있다. 이는 지금까지 개발된 DEM을 기반으로 한 각종 흐름방향 모의기술의 수준이 아직 자연적인 지형형상을 완전히 반영하지 못함에 기인한다. 본 연구에서는 8-흐름방향방법의 단점을 보완하기 위하여 개발된 바 있는 $\infty$-흐름방향방법에 따라 지형지수를 산정하여 유역이 공간적으로 포화되어 가는 과정을 모의하여 보았다. $\infty$-흐름방향방법은 각도의 형태로 흐름방향을 산정하여 고정된 흐름방향의 구속에서 벗어남과 동시에 최소한의 흐름분산(flow dispersion) 모의를 허용하여 유역규모의 포화과정을 효율적으로 모의할 수 있는 수단으로 판단된다. 대상유역으로는 설마천 유역을 선택하였으며 지형분석 과정에는 Arc GIS를 기반으로 운용되는 software 중의 하나인 TauDEM을 적용하였다. 아래 그림은 각각 포화도 20%, 50%, 90%에 해당하는 포화역을 도시한 것으로 하천망으로 중심으로 유역이 공간적으로 포화되어 가는 과정을 효율적으로 나타내고 있음을 확인할 수 있다. 본 연구를 통하여 제시되는 방법론은 자연유역의 유출응답 속에 내재하는 동적특성이나 비선형특성에 대한 체계적인 접근을 가능하게 하는 효율적인 수단을 제공할 수 있을 것으로 기대된다.

• The Transactions of the Korean Institute of Power Electronics
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• v.5 no.4
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• pp.335-342
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• 2000

A new control method for a single-phase active power filter, based on a load current estimation using a DC capacitor voltage of active power filter without sensing nonlinear load current, is proposed in this paper. Because the method proposed can remove the load current sensor in comparison with a conventional method sensing the load current and DC capacitor voltage together, it can make the active power filter easy installation, low cost, small size with no performance detriment. In addition, sample-hold technique and proportional control method is adopted to control the DC capacitor voltage and as no delay element such as LPF or PI control in the conventional method is used, the transient response is fast and good. Operation of a single-phase active power filter which consist of eight mode is explained according to utility voltage, compensation current and switch state, and compensation characteristics of active power filter using proposed method is verified by experiment.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.1
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• pp.333-342
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• 2012

This paper presents a vowel onset point (VOP) detection method based on the human auditory system. This method maps the "perceptual" frequency scale, i.e. Mel scale onto a linear acoustic frequency, and then establishes a series of Triangular Mel-weighted Filter Bank simulate the function of band pass filtering in human ear. This nonlinear critical-band filter bank helps greatly reduce the data dimensionality, and eliminate the effect of harmonic waves to make the formants more prominent in the nonlinear spaced Mel spectrum. The sum of mel spectrum peaks energy is extracted as feature for each frame, and the instinct at which the energy amplitude starts rising sharply is detected as VOP, by convolving with Gabor window. For the single-word database which contains 12 vowels articulated with different kinds of consonants, the experimental results showed a good average detection rate of 72.73%, higher than other vowel detection methods based on short-time energy and zero-crossing rate.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.6
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• pp.83-91
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• 2006

An advanced method of Relaxed Static Stability (RSS) is utilized for improving the aerodynamic performance of modern version supersonic jet fighter aircraft. The flight control system utilizes RSS criteria in longitudinal axis to achieve performance enhancements and improve stability. The flight control law of T-50 advanced trainer employs RSS concept in order to improve the aerodynamic performance and guarantee aircraft stability. The longitudinal center of gravity(X-c.g) varies as a function of external stores, fuel state and gear position. Shifts in X-c.g relate directly to longitudinal static margin in aircraft stability. This paper deals the maximum aft X-c.g for critical aircraft loadings and checks static margin limits using sensitivity such as damping, natural frequency, gain and phase margin. And nonlinear analysis was conducted for such as short period input. And also, this paper shows the T-50 aircraft stability based on the result of high angle of attack flight such as upright and inverted departure.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.5
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• pp.1805-1813
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• 2010

This paper presented regarding an parametric study to investigate seismic capacity evaluation of semi-rigid steel frame infilled with composit panel. In order to propose the optimum retrofit of the steel frame, we analysed the various pattern of retrofitted steel frame subjected to weak/medium earthquake. Steel frame with composit panel was analysed by Time history analyses analysis. The model were analysed using the suites of ground motion developed by NEHRP project on steel moment resisting frame. These earthquakes consist of 20 horizontal ground acceleration record each, i.e., a 10%, 50% probability of accidence in a 50 year period. We considered the semi-rigid connection which are commonly used in field, and modeled the nonlinear connection element (GAP) between panel and frame. It was shown that how is the steel frame with composit panel effected. We also examined the response of retrofitted frame.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.88-97
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• 2012

The objective of this research is to investigate the seismic performance and flexure-shear behavior of square reinforced concrete bridge piers with solid and hollow cross section. Test specimens were nonseismically designed with the aspect ratio 4.5 Two reinforced concrete columns were tested under constant axial load while subjected to lateral load reversals with increasing drift levels. Longitudinal steel ratio was 2.217 percent. The transverse reinforcement ratio As/($s{\cdot}h$), corresponding to 58 percent of the minimum lateral reinforcement required by Korean Bridge Design Specifications for seismic detailing, which represent existing columns not designed by the current seismic design specifications or designed by limited ductility concept. This study are to provide quantitative reference data for the limited ductility design concept and tendency for performance or damage assessment based on the performance levels such as cracking, yielding, collapse, etc. Failure behavior, ultimate displacement/drift ratio, displacement ductility, response modification factor, equivalent viscous damping ratio, residual deformation, effective stiffness, plastic hinge length, strain of reinforcements and nonlinear analysis are investigated and discussed in this paper.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.1
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• pp.39-45
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• 1989

Many mechanical systems including ships and/or offshore structures have poor dynamic response characteristics such as undesirable natural frequencies and undesirable mode shapes. It is mandatory to redesign the structure. In this paper a procedure for the dynamic redesign of an undamped structural system is presented. The method which uses a penalty function with a penalty term containing error in equilibrium for a given vibration mode may have a shortcoming. This method includes unconstrained eigenvector degrees of freedom as unknowns. In the work developed here, only constrained mode shape changes are used in the solution procedure, resulting in a reduction of the unnecessary calculations. Among the set of equations which characterizes the redesign of the structural systems, the under constrained problem is discussed here and formulated as an optimization problem, with an optimal criterion such as minimum change or minimum structural weight of the system. Four simple numerical applications illustrate the efficiency of the method. The method can be applied to the vibration problems of ships and/or offshore structures with an implementation of the commercial FE codes.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.2
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• pp.271-278
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• 2000

In this study the effect and applicability of viscoelastic dampers on the seismic reinforcement of steel framed structures are investigated in the context of the performance based design approach. The effect of the damper on dissipating the input seismic energy was investigated with a single degree of freedom system. For analysis models a five-story steel frame subjected to gravity load, a ten-story and twenty-story structure subjected to gravity and wind load were designed. The code-specified design spectrums were constructed for each soil type and performance objective, and artificial ground excitation records to be used in the nonlinear time history analysis were generated based on the design spectrums. Inter-story drift was adopted as the primary performance criterion. According to the analysis results, all model structures turned out to satisfy the performance level for most of the soil conditions except for the soft soil(operational level). It was also found that the seismic performance could be greatly enhanced, and the structures were led to behave elastically by installing viscoelastic dampers on appropriate locations.

• The Journal of the Acoustical Society of Korea
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• v.15 no.1
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• pp.23-33
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• 1996

In this paper we point out that if the classical principal domain for bispectra is utilized to determine a second-order Volterra model's output, such and output will be incomplete. This deficiency is associated with the periodic nature of the DFT. For this reason, the objective of this paper is to present an "extended" principal domain for Volterra kernels which leads to an improved estimate of the nonlinear system's response. In order to define the extended principal domain, we derive a new discrete frequency-domain Volterra model from a discrete time-domain Volterra model utilizing 2-dimensional DFT and the relationship between the quadratic component of the Volterra model and a square filter. The effect of the extended domain on the model output is interpreted in terms of the periodicity of DFT. Through computer simulations, we demonstrate the effects of the extended principal domain on the Volterra modeling. The simulation results indicate that the extended principal domain plays and important role in computing Volterra model outputs and estimating Volterra model coefficients.