• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2004.11a
• /
• pp.155-159
• /
• 2004

In this paper, it was analyzed the characteristics of electrical and acoustical variations for loudspeaker due to fabrication processes. First, mass of each components of loudspeaker was measured by electric precision scale and performed statistical analysis. Second. Thiele-Small parameters of sample loudspeakers produced by unskilled students were identified by known mass parameter identification method using electrical impedance method and investigated on the variations of each parameter. Electrical impedance tests and acoustic frequency responses were measured on sample loudspeakers and variations were examined to grasp relationship between components variation and fabrication processes. Main factors to effect the changes of electrical impedance were concluded by fabrication processes errors not by components of loudspeaker.

• Structural Engineering and Mechanics
• /
• v.21 no.3
• /
• pp.255-273
• /
• 2005

Based on the random vibration theory, a response spectrum method is developed for seismic response analysis of linear, multi-degree-of-freedom structures under multi-support excitations is developed. Various response quantities, including the mean and variance of the peak response, the response mean frequency, are obtained from proposed combination rules in terms of the mean response spectrum. This method makes it possible to apply the response spectrum to the seismic reliability analysis of structures subjected to multi-support excitations. Considering that the tedious numerical integration is required to compute the spectral parameters and correlation coefficients in above combination rules, this paper further offers simplified procedures for their computation, which enhance dramatically the computational efficiency of the suggested method. The proposed procedure is demonstrated for tow numerical examples: (1) two-span continuous beam; (2) two-tower cabled-stayed bridge by using Monte Carlo simulation (MC). For this purpose, this paper also presents an approach to simulation of ground motions, which can take into account both mean and variation properties of response spectrum. Computed results based on the response spectrum method are in good agreement with Monte Carlo simulation results. And compared with the MSRS method, a well-developed multi-support response spectrum method, the proposed method has an incomparable computational efficiency.

• Structural Engineering and Mechanics
• /
• v.46 no.3
• /
• pp.371-385
• /
• 2013

Vibration isolators and anti-vibration mounts are ideal, for example, in creating floating floors for gymnasiums, or performance spaces. However, it is well-known that there are great difficulties on isolating vibration transmission in structural steel components, especially steel floors. Besides, the selection of inertia blocks, which are usually used by engineers as an effective vibration control measure, is usually based on crude methods or the experience of the engineers. Thus, no simple method or indices have been available for assessing the effect of inertia blocks on vibration isolation or stability of vibratory systems. Thus, the aims of this research are to provide further background description using a FE model and present and implement a modal approach, that was validated experimentally, the latter assisting in providing improved understanding of the vibration transmission phenomenon in steel buildings excited by a velocity-source type of excitation. A better visualization of the mean-square velocity distribution in the frequency domain is presented using the concept of modal expansion. Finally, the variation of the mean-square velocity with frequency, whilst varying mass and/or stiffness of the coupled system, is presented.

• Smart Structures and Systems
• /
• v.9 no.1
• /
• pp.55-70
• /
• 2012

It is not easy to experimentally obtain the FRF (Frequency Response Function) matrix corresponding to a full set of DOFs (degrees of freedom) for a dynamic system. Utilizing FRF data measured at specific positions, with DOFs less than that of the system, as constraints to describe a damaged system, this study identifies parameter matrices such as mass, stiffness and damping matrices of the system, and provides a damage identification method from their variations. The proposed parameter identification method is compared to Lee and Kim's method and Fritzen's method. The validity of the proposed damage identification method is illustrated in a simple dynamic system.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2000.11a
• /
• pp.389-392
• /
• 2000

This paper presents a performance Analysis of electrically exhaust gas recirculation valve using commercial electromagnetic simulation software, Flux2D. Under the assumption of 2D axi-symmetric magnetic field, the characteristics of EEGR valve by revising the design parameter, has ken investigated by estimating the variation of thrust force with respect to the pintle position. The mode shapes and the frequency response functions were computed by using three dimensional finite element modeling of the whole EEGR valve and their accuracies were verified with experimental FFT analysis technique.

• Proceedings of the KIEE Conference
• /
• 1991.07a
• /
• pp.281-285
• /
• 1991

In this paper, response characteristics by applying impulse into transformer windings in order to precaution diagonosis of power electric instrument are studied. A sample oilless transformer, an aging transformer and a good transformer are slected for models. The experimented results show that for testing the windings distortion and impedanced change of transformer the LVI method are suitable. Also, variation characteristic of output waveforms at time and frequency domain in order to efficient analysis is discussed. The results response that waveforms at frequency domain is very higher resolution at time domain.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.21 no.1
• /
• pp.41-48
• /
• 2022

Vehicle vibration was introduced in the time and frequency domains using fast Fourier transform (FFT) analysis. In particular, a vibration mode analysis and characteristics of the frequency response function (FRF) in a sport utility vehicle (SUV) passing over a bump barrier at different speeds was performed systematically. The response behavior of the theoretical acceleration was obtained using a numerical method applied to the forced vibration model. The amplitude and frequency of the external force on the vehicle cause various power spectra with individual intrinsic system frequencies. In this regard, several modes of power spectra were acquired from the spectra and are discussed in this paper. The proposed technique can be used for monitoring the acceleration in a vehicle passing over a bump barrier. To acquire acceleration signals, various experimental runs were performed using the SUV. These acceleration signals were then used to acquire the FRF and to conduct mode analysis. The vehicle characteristics according to the vehicle condition were analyzed using FRF. In addition, the vehicle structural system and bump passing frequencies were discriminated based on their power spectra and other FRF spectra.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.26 no.11
• /
• pp.1736-1742
• /
• 1989

In this thesis, to verify input-output characteristics of GaAs MESFET, light is illuminated to C-band oscillator which already designed and manufactured, thus input-output variation of GaAs MESFET is to be shown. Experimental results of two kinds of optical effects, optical tuning and opticla switching, of GaAs MESFET Oscillators are presented. For optical tuning, the Oscillation frequency decreases with optical illumination and the Oscillator power output generally increases with optical illumination, the increase being around 1 to 3 dBm at 1mW/mm\ulcornerlight intensity. While the DC-lingt illuminated Oscillator response data provide information of the optical senditivity of GaAs-MESFET Oscillators. Pulse-light illuminated transient response data can be invoked to understand the detailed optical-electrical interaction mechanisms response. Thus, it is shown that direct control of micro-devices is realisable, if we use optical effect of GaAs semiconductor compound.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.15 no.6
• /
• pp.11-18
• /
• 2011

Accurate modal identification analysis is required to reasonably perform a seismic qualification of safety-related electric equipment installed in nuclear power plants (NPPs). This study evaluates a variation of the modal properties of an electric equipment cabinet structure in NPPs according to the excitation levels. For the study, an actual electric equipment cabinet was selected as a specimen and was dynamically tested by using a portable exciter in accordance with the level of input vibration energy. Tests were classified into two sets: with-door cases, and without-door cases. Frequency response functions were computed from the signals of the acceleration responses and input motions measured from the vibration tests. A polynomial curve fitting algorithm was used to extract the modal properties from the frequency response functions. This study reviews the variation of the modal properties according to the variation of the excitation levels. The results of the study show that the modal frequencies and the modal dampings of the object specimen varies nonlinearly according to the excitation level of the test motion. Attaching the door increases the modal damping of the cabinet.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.37 no.1
• /
• pp.19-28
• /
• 2000

The parallel inverter is widely utilized because of its fault-tolerance capability, high-current output at constant voltages and system modularity. The conventional paralled inverter usually employes an active and reactive power control or a frequency and voltage droop control. However, these approaches have the disadvantages that the response time of parallel inverter control is slow against load and system parameter variation to calculate active, reactive power, frequency and voltage. This paper describes novel control scheme for equalization of output power between the parallel connected inverters. The proposed scheme has a fast power balance control response, a simplicity of implementation, and inherent peak current limiting capability since it employes a instantaneous current/voltage control with output voltage and current balance and output voltage regulation. A design procedure for the proposed parallel inverter controller is presented. Futhermore, the proposed constrol scheme is verified through the simulation in various cases such as the system parameter variation, the control parameter variation and the nonlinear load condition.