• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.735-741
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• 2008

Identification of asymmetry and anisotropy of rotor system is important for diagnosis of rotating machinery. Directional frequency response functions (dFRFs) are known to be a powerful tool in effectively detecting the presence of asymmetry or anisotropy. In this paper, an input noise effect of dFRFs for rotors is estimated, when both asymmetry and anisotropy are present. The normalized random errors of the dFRFs are calculated to verify the validity of the method, which is demonstrated by numerical simulation with a simple rotor model.

• Tribology and Lubricants
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• v.15 no.1
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• pp.68-76
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• 1999

This paper presents the nonlinear characteristics of the oil lubricated hydrodynamic journal bearing. The traditional approach is to characterize the behavior and performance of fluid film hydrodynamic journal bearings by means of linearized bearing analysis. The objective of this paper is to examine the nonlinear characteristics of the journal bearing when an external sinusoidal shock is given to the system. The oil film force is obtained by solving the finite width Reynolds equation at each time step by the solution of the column method. Frequency response function and journal orbit obtained from both linear and nonlinear bearing simulations are compared with each other.

• 제어로봇시스템학회:학술대회논문집
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• 1998.10a
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• pp.289-294
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• 1998

The distributed-parameter structures expressed with the partial differential equations are considered as the infinite-dimensional dynamic system. For implementation of a controller in multivariate systems, it is necessary to derive the state-space reduced order model. By the eigensystem realization algorithm, we can yield tile subspace system with the Markov parameters derived from the measured frequency response function by the inverse discrete Fourier transformation. We also review the necessary conditions for the convergence of the approximation system and the error bounds in terms of the singular values of Markov-parameter matrices. To determine the natural frequencies and modal damping ratios, the modal coordinate transformation is applied to the realization system. The vibration test for a smart structure is performed to provide the records of frequency response functions used in the subspace system realization.

• Structural Engineering and Mechanics
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• v.89 no.6
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• pp.549-556
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• 2024

A serial pendulum dynamic vibration absorber (DVA) was designed to suppress the vibration of two degrees of freedom (Two-DOF) structure model. The optimal DVA parameters are selected using a genetic algorithm (GA) by minimizing the fitness function formulated from the system's frequency response function (FRF). Two fitness function criteria, using one and two target frequency ranges, were utilized to calculate the optimal DVA parameters. The optimized serial pendulum DVA parameters were used to reduce structural vibration under free and forced excitation conditions. The simulation study found that the serial pendulum DVA can effectively reduce the vibration response for a small excitation amplitude. However, the DVA performance decreases for a large excitation amplitude due to the nonlinearity of pendulum motion, and the percentage of vibration response attenuation is smaller than that obtained using a small excitation amplitude.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.6
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• pp.117-124
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• 2005

This study developes the vibration model to estimate the vibration energy of compact disc player's mainbase assembly which is supported by dampers and springs, and this model is verified by experiment. From frequency response function, we investigate the natural frequency and mode shape in the up/down direction for mainbase assembly. In order to determine the analysis frequency band, we investigate the excitation frequency of road from the vehicle test. As the characteristics of dampers and springs are changed, we carry out the sensitivity analysis of vibration energy for mainbase assembly which include optical pick-up and feeding system. And we found out that the properties of damper were dominant element in the vibration energy of mainbase assembly's CG(center of gravity).

• Journal of the Korean Society for Precision Engineering
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• v.14 no.10
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• pp.164-169
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• 1997

The aim of this paper is to present some results of sensitivity analysis in frequency domain. The sensitivity fonctions in frequency domain is not depend on the external excitation but depend on the frequency of the system's resonance. The sensitivity functions are determined as function of partial derivatives of system transfer functions taken with respect to system design parameters. The logarithmic sensitivity function is the dimensionless sensitivity funciton available, making it useful to compare the influence of various parameters on system variables. Two degree of fredom system is used to illustrate the procedure for sensitivity analysis proposed in this paper.

• Proceedings of the KSR Conference
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• 2005.05a
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• pp.718-721
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• 2005

The purpose of the study is to evaluate the usage of microtremor in estimation of subsurface structure and ground response to ground motion. Ground motion amplification based on site condition of an area is an important parameter for dynamic design. Microtremor cover the characteristics in a low frequency range, while forced vibrations cover them in a high-frequency range. Microtremor consider ground characteristics and offer transfer function in area. To determine the dominant frequency, the passive microtremor measurement is performed and to determine the transfer function of test site, active microtremor measurement is performed. Microtremor measurement in the site is compared with theoretical transfer function calculated from the known structures.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.4
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• pp.369-373
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• 2016

Accurate identification of damping matrix in structures is very important for predicting vibration responses and estimating parameters or other characteristics affected by energy dissipation. In this paper, damping matrix identification method that use normal frequency response functions, which were estimated from complex frequency response functions, is proposed. The complex frequency response functions were obtained from the experimental data of the structure. The nonproportional damping matrix was identified through the proposed method. Two numerical examples (lumped-mass model and cantilever beam model) were considered to verify the performance of the proposed method. As a result, the damping matrix of the nonproportional system was accurately identified.

• The Journal of Korean Institute for Practical Engineering Education
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• v.3 no.1
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• pp.45-50
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• 2011

Despite the highly sophisticated development of finite element analysis, a finite element model for structural dynamic analysis can be inaccurate or even incorrect due to the difficulties of correct modelling, uncertainties on the finite element input data and geometrical oversimplification, while the modal data extracted from measurement are supposed to be correct, even though incomplete. The assumption that the test results represent the true dynamic behaviour of the structure, however, may not be correct because of various measurement errors. The measurement errors are investigated and their effects on estimated frequency response functions(FRFs) are also investigated.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.2
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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.