• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 봄 학술발표회 논문집
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• pp.121-128
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• 1999

This paper presents a time domain method for soil-structure interaction analysis for seismic loadings. It is based on the finite element formulation incorporating analytical frequency-dependent infinite elements for the far field soil. The dynamic stiffness matrices of the far field region formulated using the present method in frequency domain can be easily transformed into the corresponding matrices in time domain. At first, the equivalent earthquake forces are evaluated along the interface between the near and the far fields from the free-field response analysis carried out in frequency domain, and the results are transformed into the time domain. An efficient procedure is developed for the convolution integrals to evaluate the interaction force along the interface, which depends on the response on the interface at the past time instances as well as the concurrent instance. Then, the dynamic responses are obtained for the equivalent earthquake force and the interaction force using Newmark direct integration technique. Since the response analysis is carried out in time domain, it can be easily extended to the nonlinear analysis. Example analysis has been carried out to verify the present method in a multi-layered half-space.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권2호
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• pp.495-513
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• 2020

The correlation identification of the subsurface is a novel electrical prospecting method which could suppress stochastic noise. This method is increasingly being utilized by geophysicists. It achieves the frequency response of the underground media through division of the cross spectrum of the input & output signal and the auto spectrum of the input signal. This is subject to the spectral leakage when the cross spectrum and the auto spectrum are computed from cross correlation and autocorrelation function by Discrete Fourier Transformation (DFT, "To obtain an accurate frequency response of the earth system, we propose an improved correlation identification method which uses all phase Fast Fourier Transform (APFFT) to acquire the cross spectrum and the auto spectrum. Simulation and engineering application results show that compared to existing correlation identification algorithm the new approach demonstrates more precise frequency response, especially the phase response of the system under identification.

• 한국실천공학교육학회논문지
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• 제3권1호
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• pp.45-50
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• 2011

유한요소 해석(FEA: finite element analysis)의 발달로 복잡한 기계나 자동차 및 구조물에 대해서도 상세한 진동해석을 할 수 있게 되었다. 그러나, 복잡한 구조물을 정확하게 모형화하기 어렵고, 특히 접합부의 강성과 감쇠 특성을 알기 어렵고, 복잡한 형상을 단순화하는 과정에서 발생하는 오차 등의 이유로 유한요소해석 결과는 부정확할 수 있다. 반면에 실제 구조물의 실험 데이터로부터 추출한 실험적 모드해석(modal testing) 결과는 상세하지는 않지만 정확하다고 볼 수 있다. 그러나 실험 결과가 구조물의 진동 특성을 정확하게 나타낸다는 가정은 여러 가지 측정 오차로 인하여 정확하지 않을 수 있다. 이 논문에서는 실험적 모드해석의 기본이 되는 FRF(frequency response function; 주파수 응답함수)의 측정에 영향을 미치는 오차들을 측정 오차와 신호처리 오차로 구분하여 각각에 대해 세밀히 살펴보고, 그러한 오차들을 감소함으로써 보다 정확한 FRF를 구하는 방법에 대해서 고찰해보았다.

• 한국지능시스템학회논문지
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• 제12권1호
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• pp.39-43
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• 2002

모달법을 사용하는 주파수 응답해석에서, 주파수 응답함수 계산에 포함할 모드의 수를 결정하는 것이 매우 중요하다 대부분의 전문가들은 자신의 경험에 의해 모드 축약을 수행한다. 그러나, 비전문가의 입장에서 다양한 문제에 대하여 모드 축약을 합리적으로 수행하는 것은 어려운 일이다. 본 연구에서는 퍼지이론을 이용하여 경험적인 모드 축약법을 표준화하여 전문가뿐만 아니라, 비전문가도 적절한 모드 축약을 쉽게 할 수 있도록 하였다. 퍼지 룰 베이스는 유한요소법 프로그램을 이용한 시뮬레이션 결과를 바탕으로 작성되었다. 시뮬레이션 결과 퍼지이론을 이용한 모드 축약법이 해석에 포함할 모드의 수를 결정하는데 있어서 매우 효과적인 것으로 나타났다.

• 한국자동차공학회논문집
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• 제15권6호
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• pp.177-182
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• 2007

In this paper, automotive hydraulic pipeline systems are modeled in which a straight blocked pipe, two pipes with sudden expansion or contraction are connected in series and terminated with a chamber. The frequency response characteristics of these composite pipeline systems are investigated experimentally. The theoretical analysis for various pipe configurations is base on transfer matrix method with frequency dependent viscous friction distributed parameter pipeline model. The gain and phase of transfer functions are included for comparison with experimental results. There is close agreement between the results of experimental and theoretical determination of pressure response in automotive hydraulic pipeline systems.

• Tribology and Lubricants
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• 제39권6호
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• pp.221-227
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• 2023

A rotordynamic system consists of components that undergo rotational motion. These components include shafts, impellers, thrust collars, and components that support rotation, such as bearings and seals. The motion of this type of rotating system can be modeled as two-dimensional motion and, accordingly, the equation of motion for the rotordynamic system can be represented using complex coordinates. The directional frequency response function (dFRF) can be derived from this complex coordinate system and used as an effective analytical tool for rotating machinery. However, the dFRF is not widely used in the field because most previous studies and commercial software are based on real coordinate systems. The objective of the current study is to introduce the dFRF and show that it can be an effective tool in rotordynamic analysis. In this study, the normal frequency response function (nFRF) and dFRF are compared under rotordynamic analysis for isotropic and unisotropic rotors. Results show that in the nFRF, the magnitude of the response is the same for both positive and negative frequencies, and the response is similar under all modes. Consequently, the severity of the mode cannot be identified. However, in the dFRF, the forward and backward modes are clearly distinguishable in the frequency domain of the isotropic rotor, and the severity of the mode can be identified for the unisotropic rotor.

• Journal of Power Electronics
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• 제12권2호
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• pp.317-325
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• 2012

Resonant immittance converter (RIC) topologies can transform a current source into a voltage source (Type-I RICs) and vice versa (Type-II RICs), thereby making them suitable for many power electronics applications. RICs are operated at a fixed frequency where the resonant immittance network (RIN) exhibits immittance conversion characteristics. It is observed that the low-frequency response of Type-II RINs is relatively flat and that the state variables associated with Type-II RINs affect the response only at the high frequencies in the vicinity of the switching frequency. The overall response of a Type-II RIC is thus dominated by the filter response, which is particularly important for the controller design. Therefore, an approximate equivalent circuit model and a small-signal model of Type-II RICs are proposed in this paper, neglecting the high-frequency response of Type-II RINs. While the proposed models greatly simplify and speed-up the analysis, it adequately predicts the open-loop transient and small-signal ac behavior of Type-II RICs. The validity of the proposed models is confirmed by comparisons of their results with those obtained from a cycle-by-cycle simulation and with an experimental prototype.

• 한국농업기계학회:학술대회논문집
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• 한국농업기계학회 2000년도 THE THIRD INTERNATIONAL CONFERENCE ON AGRICULTURAL MACHINERY ENGINEERING. V.III
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• pp.533-542
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• 2000

Instrumentation and technologies are described for determining the vibration response characteristics of the pear with frequency range 5 to 320Hz. The computer program for controlling the vibration exciter and the function generator and for measuring the vibration response characteristics of the pear was developed. Mechanical properties such bioyield deformation, rupture deformation and apparent elastic modulus etc. were compared with the vibration response characteristics of the pear. The resonant frequency of the pear ranged from 53 to 102Hz and the amplitude at resonance was between 1.08 and 2.48g-rms. The resonant frequency and amplitude at resonance decreased with the increase of the sample mass, and they were slightly affected by mechanical properties such as bioyield deformation and rupture deformation. Regression analysis was performed among the relatively high correlated parameters from the results of correlation coefficient analysis.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.320-325
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• 2003

Acoustic-Pressure Response of diluted hydrogen-air diffusion flames is investigated numerically by adopting a fully unsteady analysis of flame structures. In the low-pressure regime, the amplification index remains low and constant at low frequencies. As acoustic frequency increases, finite-rate chemistry is enhanced through a nonlinear accumulation of heat release rate, leading to a high amplification index. Finally, the flame responses decrease at high frequency due to the response lag of the transport zone. For a medium-pressure operation and low-frequency excitation, the amplification index is low and constant. It then decreases at moderate frequencies. As frequency increases further, the amplification index increases appreciably due to an intense accumulation effect.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 제6회 학술대회 논문집 일렉트렛트 및 응용기술연구회
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• pp.5-8
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• 2004

We have investigated equivalent-circuit analysis of organic light-emitting diodes using frequency-dependent response of $ITO/Alq_3(60nm)/Al$ device at two different bias voltages. Complex impedance Z of the device was measured in the frequency range of 40Hz~1MHz. A Cole-Cole plot shows that there are two dielectric relaxations at the bias below turn-on voltage, and one relaxation at the bias above turn-on voltage. We are able to interpret the frequency-dependent response in terms of equivalent-circuit model of contact resistance $R_s$ in series with parallel combination of resistance $R_p$ and capacitance $C_p$. We have obtained contact resistance $R_s$ around $90{\Omega}$, mainly from the ITO anode.