• 소음진동
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• 제10권4호
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• pp.642-647
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• 2000

Conventional cepstrum has been widely used to detect echo and fault signals embedded in noise. One of the problems of finding impulse signals using the conventional cepstrum in that it is normally very sensitive to signal to noise ratio (SNR). This paper proposes a signal processing method to detect impulse signal in noisy environment. Because the proposed method minimizes the variance of signal power at a cepstrum domain, it is suggested to be called as minimum variance cepstrum (MV cepstrum). Computer simulations have been performed to understand the characteristics of the MV cepstrum. Both mathematical approach and computer simulations confirmed that the MV cepstrum is a useful technique to detect impulse in noisy environment.

• 대한기계학회논문집
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• 제18권2호
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• pp.372-379
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• 1994

In this study, the describing function is adopted to represent nonlinearity in the system equations. The compliance can be obtained by solving nonlinear simultaneous algebraic quations for multi-degrees-of-freedom system with multinonlinearities. When the technique is applied, the nonlinearity of the system can be identified from the compliance which is obtained from the sinusoidal excitation of the system. By employing the describing function in the Building Block Analysis, we can extensively develop the BBA into investigation of the continuous systems with nonlinearities. The evaluated compliance can quantitatively show the effects of nonlinearity such as the transfer of the natural frequency, the variance of the compliance at the natural frequency, and the jump phenomena which occur during sweeping of the excitation frequency.

• 소음진동
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• 제10권6호
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• pp.985-990
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• 2000

The signals that can be obtained from rotating machines often convey the information of machine. For example, if the machine under investigation has faults, then these signals often have pulse signals, embedded in noise. Therefore the ability to detect the fault signal in noise is major concern of fault diagnosis of rotating machine, In this paper, minimum variance cepstrum (MV cepstrum) . which can easily detect impulse in noise, has been applied to detect the type of faults of ball bearing system. To test the performance of this technique. various experiments have been performed for ball bearing elements that have man made faults. Results show that minimum variance cepstrum can easily detect the periodicity due to faults and also shows the pattern of excitation by the faults.

• 소음진동
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• 제7권2호
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• pp.223-229
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• 1997

Presented is a method to estimate system parameters of a system with polynomial non-linerities from the measured higher order frequency response functions. Higher order FRFs can be measured on some restricted regions by sinusoidally exciting a non-linear system with various input amplitudes and measuring the response component at the excitation frequency. These higher order FRFs can be expressed in terms of system parameter, and the system parameters can be estimated from the measured FRFs. Since the expressions for higher order FRFs are complicated, system parameters can be estimated from them using an optimization technique. The present method has been applied to a simulated single degree of freedom system with non-linear stiffness and damping, and has estimated accurate system parameters.

• 한국농공학회지
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• 제43권5호
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• pp.106-115
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• 2001

This paper deals with the free vibrations of horizontally curved beams partially supported on elastic foundations. Taking account of the effects of rotatory inertia and shear deformation, differential equations governing the free vibrations of such beams are derived, in which the Pasternak foundation model is considered as the elastic foundation. Differential equations are numerically solved to calculate natural frequencies and mode shapes. The experiments were performed in which the free vibration frequencies of such curved beams in laboratorial scale were measured and these results agreed quite well with the present studies. In numerical examples, the circular, parabolic, sinusoidal and elliptic curved members are considered. The parametric studies are performed and the lowest four frequency parameters are reported in tables and figures as the non-dimensional forms. Also the typical mode shapes are presented.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 B
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• pp.815-816
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• 2006

This paper proposes a novel design method for flux barrier which built in q-axis in rotor of IPM type BLDC motor. It aims to reduce the motor vibration with reduced cogging torque and lessened torque ripple by the sinusoidal waveform distribution of flux generated in the permanent magnet, which results from designed flux barriers. Design of flux barrier optimized using the Taguchi methods that considered multiple quality characteristics, such as cogging torque, average torque and efficiency are considered. The result of proposed method is compared and verified with 2D finite element method (FEM).

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1998년도 봄 학술발표회 논문집
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• pp.441-448
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• 1998

In this study, an explicit transient analysis program considering material and geometric nolinearities has been developed and used to analyze the dynamic behaviors of circular, parabolic, sinusoidal and catenary arches according to the change of shapes and boundary conditions. To understand dynamic behaviors of arches, first of all, the results of free vibration analysis for four kinds of arches are discussed. The results of transient analysis under impact loads we discussed in respect of boundary condition, change of height, and arch-shape. The dynamic behaviors of arches by nonlinear transient analysis considering both material and geometric nolinearities are also discussed.

• 한국농공학회:학술대회논문집
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• 한국농공학회 2000년도 학술발표회 발표논문집
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• pp.213-218
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• 2000

This paper deals with the free vibrations of shallow arches resting on elastic foundations. Foundations are assumed to follow the hypothesis proposed by Pasternak. The governing differential equation is derived for the in-plane free vibration of linearly elastic arches of uniform stiffness and constant mass per unit length. Sinusoidal arches with hinged-hinged and clamped-clamped end constraints are considered in analysis. The frequency equations (lowest symmetical and antisymmetrical natural frequency equations) are obtained by Galerkin's method. The effects of arch rise, Winkler foundation parameter and shear foundation parameter on the lowest two natural frequencies are investigated.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제48권11호
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• pp.587-596
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• 1999

The use of Switching elements in power systems causes the current or voltage to involve harmonic waves. Harmonics bring about registration errors of the equipment for measuring power. In case the induction watthour meter designed on sinusoidal source is used in the measurement of power with harmonics, the precise measurement of power has many problems because harmonics cause a decrease of power factor and vibration by the unstable driving force on the aluminum disc. In this paper, analysis and test results on the harmonic sensitivity of an induction watthour meter is reported when the input voltage and current with harmonics were supplied to single-phase watthour meter.

• 한국통신학회논문지
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• 제12권5호
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• pp.527-534
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• 1987

진동에 관한 비선형 1계연립미분방정식을 아나로그 시뮬레이션으로 2상전압제어발진을 시켜 유용성을 확인하였다. 2상신호를 각각 제곱하여 합성하는 부분과 곱셈부분의 실제회로 구성시 복잡하고 가격이 높아지므로 정류 회로와 스위칭회로로 대치하여 회로의 단순화와 가격 저렴화를 이루었다. 본 논문에서 제시된 회로는 제어 압력전압에 주파수가 정확한 비례관계를 가졌고, 응답 속도가 비교적 빠르고 또한 위상오차가 매우 적었으며 주파수비가 10:1 이상에서도 저왜율과 정진폭으로 동작하였다.