• 전산구조공학
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• 제25권4호
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• pp.28-39
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• 2012

• 융합신호처리학회논문지
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• 제12권3호
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• pp.217-221
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• 2011

GaAs 나 InP 기반의 HEMT(High Electron Mobility Transistor)들은 우수한 마이크로파 및 밀리미터파 주파수 특성 및 이에 따른 우수한 저잡음 특성을 가지고 있다. GaAs 기반 MHEMT(Metamorphic HEMT)는 InP 기반의 HEMT에 비해 비용 측면에서 커다란 장점을 가지고 있다. 본 논문에서는 마이크로파 및 밀리미터파 응용 시스템에 필수적인 MHEMT의 RF 특성을 예측 평가하기 위하여 MHEMT의 RF 소신호 특성 회로를 시뮬레이션하고 분석하였다. 본 논문에서의 시뮬레이션을 통한 RF 소신호 주파수 분석은 MHEMT를 이용한 밀리미터파 응용 시스템 설계에 도움을 제공할 수 있을 것으로 기대된다.

• 전기의세계
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• 제17권3호
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• pp.29-38
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• 1968

The development of the frequency converter using semiconductor enables to easily control the speed of A.C. motors. It is now technically possible and economically feasible to provide them with power at variable frequency, using silicon-controlled-rectifier (or thyristor) inverters. In such a case, if an induction motor is to be operated efficiently over a wide speed range, it must be supplied from a variable-frequency source whose frequency is adjustable over a range similar to that required for the motor speed. It is desired to observe how several characteristics are changed such as primary current, torque-speed, etc. Although the characteristics could be obtained by means of the conventional method, it requires very complicated calculation. It is assumed that the charateristics above are easily investigated by means of current diagram method from variable circuit constants relating to the motor which is designed in rated frequency. In this paper, the results of the study on the current-diagram method and its application are described as follows; (1) In order to discuss the construction of current diagram, the equation of the stator current with adjustable frequency was derived for applying the Current Diagram Method. (2) The radius, the center of the current circle and current vector locus at any desired frequency could be easily determined with the aid of both above mentioned equation and the standard current diagram at reference frequency. (3) This method could be applicable to the various types of Induction Motors, and this paper has dealt with its application to the capacitor, split-phase and 2-phase types of motors.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
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• pp.1-6
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• 2001

In this article, the fundamental concept, characteristics and application potentials of coreless printed-circuit-board (PCB) transformers are described. Coreless PCB transformers do not have the limitations associated with magnetic cores, such as the frequency limitation, magnetic saturation and core losses. In addition, they eliminate the manual winding process and its associated problems, including labor cost, reliability problems and difficulties in ensuring transformer quality in the manufacturing process. The parameters of the printed windings can be precisely controlled in modern PCB technology. Because of the drastic reduction in the vertical dimension, coreless PCB transformers can achieve high power density and are suitable for applications in which stringent height requirements for the circuits have to be met. A transformer's power density of $24W/cm^2$ has been reported in a power conversion application. When used in an isolation amplifier application, coreless PCB transformers tested so far enable the amplifier to achieve a remarkable linear frequency range of 1MHz, which is almost eight times higher than the frequency range of 120kHz in existing Integrated-Circuit products. PCB materials offer extremely high isolation voltage, typically from 15kV to 40kV, which is higher than many other isolation means such as optocouplers. It is envisaged that coreless PCB transformers can replace traditional core-based transformers in some industrial applications. Their application potentials deserve more attention and exploration.

• Structural Engineering and Mechanics
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• 제25권6호
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• pp.653-674
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• 2007

This paper discusses the application of piezoelectric sensors used for evaluation of damping ratio of PVC plastics. The development of the mathematical formulation based on the Empirical Mode Decomposition for calculating the damping coefficient and natural frequency of the system is presented. A systematic experimental and analytical investigation was also carried out to demonstrate the integrity of several methods commonly used to evaluate the damping of materials based on a single degree freedom formulation. The influence of the sensors' location was also investigated. Besides the commonly used methods, a newly emerging time-frequency method, namely the Empirical Mode decomposition, is also employed. Mathematical formulations based on the Hilbert-Huang formulation, and a frequency spacing technique were also developed for establishing the natural frequency and damping ratio based on the output voltage of a single piezoelectric sensor. An experimental investigation was also conducted and the results were compared and verified with Finite Element Analysis (FEA), revealing good agreement.

• 한국공간구조학회논문집
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• 제16권2호
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• pp.47-54
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• 2016

It is very important to calculate natural frequency of the observatory tower correctly because it is keenly affected by wind response vibration due to its large slenderness ratio, weight and small damping ratio. Additionally, suggestion equation of natural frequency being used in the design phase has considerable difference between actual measured value thereby making it inappropriate to be used in the serviceability design of the observatory tower. Therefore, this paper conducted an ambient vibration measuring on 10 observatory towers through mobile-phone application thereby calculating the natural frequency and comparing the result with the domestic and foreign standards and that of the eigen-value analysis. This paper suggested approximate equation of the natural frequency of the observatory tower; T=0.0266H. The square of the corelation coefficient is 0.940, which is high.

• 한국공간구조학회논문집
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• 제15권4호
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• pp.99-105
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• 2015

The serviceability design of the high-rise building is affected by the wind response vibration such as the acceleration, at this time it is important to calculate the natural frequency correctly. Since the suggestion equation of the natural frequency being used in the design phase is not the regression equation obtained from the vibration measurement of the high-rise building, the verification to use for the serviceability design of the high-rise building is necessary. This thesis conducted an ambient vibration measuring on the high-rise building through the mobile-phone application to calculate the natural frequency and suggested a natural frequency approximate expression following the building's height, and compared with the domestic/foreign standard and the result of the eigen-value analysis.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.55-60
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• 2000

Constant ${\Delta}K$ fatigue crack growth tests were performed applying an intermediate multiple overload for SM45C steel. The purpose of the present study is to investigate the effects of specimen thickness at various baseline stress intensity levels$({\Delta}K_b)$, overload application frequency(a/W) and overload application frequency$(OL_{HZ})$ on fatigue crack growth retardation behavior. The principal results are summarized as follows. The amount of retardation for a given ${\Delta}K_b$ level is increased with increasing the baseline stress intensity level in all specimen thickness. The normalized minimum crack growth rate is increased with increasing the specimen thickness, except for ${\Delta}K=45MPa \sqrt m$. The retardation cycle is decreased with increasing the overload application position and increased with the overload application frequency.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2002년도 춘계학술대회논문집
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• pp.213-217
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• 2002

Recently the subject of "wavelet analysis" has be drawn by both mathematical and engineering application fields such as Signal Processing, Compression/Decomposition, Wavelet-Neural Network, Statistics and etc. Even though its similar to courier analysis, wavelet is a versatile tool with much mathematical content and great potential for applications. Especially, wavelet transform uses localizable various mother wavelet functions in time-frequency domain. Therefore, wavelet transform has good time-analysis ability for high frequency component, and has good frequency-analysis ability for low frequency component. Using the discriminative ability is more easy method than other conventional techniques. In this paper, Morlet wavelet transform was applied to discriminate the kind of line fault by acquired data from real power transformation network. The experimental result presented that Morlet wavelet transform is easier, and more useful method than the FFW (Fast courier Transform).ransform).

• 한국산학기술학회논문지
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• 제10권8호
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• pp.1824-1831
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• 2009

본 논문은 대규모 전력 송전망에서 발전기가 사고로 인해 순간적으로 전력공급을 중단하게 되었을 때 과도기간 동안 나타나는 전력계통 주파수의 급강하가 탈락된 발전기의 위치로부터 전력 송전망 전체로 파급되어 가는 전파속도를 분석한다. 이러한 전력계통 주파수 동요의 전파속도는 전력계통 고유의 특성에 따라 다르게 나타나기 때문에 광역적 측면에서 전력 수송망의 특성을 이해하는데 중요한 파라미터이며, 최근 미국의 전력 송전망을 대상으로 운영중인 광역 전력계통 주파수 감시스템(FNET)을 활용한 전력 IT 적용연구에서 중요한 파라미터로 활용되고 있다. 본 논문에서는 방대한 규모를 가진 미 동부의 전력송전 연계계통에 대해 최근의 동적모델을 사용하여 다양한 위치에서의 발전기 탈락을 모의한 후 이에 따른 전력계통주파수 동요의 전파 특성을 분석하고 그 전파속도를 제시한다.