• Structural Engineering and Mechanics
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• v.12 no.4
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• pp.449-457
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• 2001

In the design of industrial chimneys and towers, structural engineers must assume a level of the inherent damping in the structures. In order to better estimate the dynamic response of those structures, actual damping was measured from wind-induced vibration signals of chimneys and towers and its characteristics with respect to the response levels, the structural systems, and the wind direction were discussed. Damping ratio and natural frequency for three chimneys and two towers were calculated using random decrement technique.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.228-232
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• 2004

This paper is to identify the position of random disturbance on flexible dynamic system, and the position of the piezo ceramic actuator 0 minimize tip response. Correlation of the output signals from each parts on flexible system is used to identify the position of random disturbance. Except the correlation with an output signal from the position of random disturbance, other correlations have time delay. This is a base idea to identify the position on this study.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.5
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• pp.381-389
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• 2014

This study is concerned with the estimation of vibration-field of a cylindrical structure by modal expansion method(MEM). MEM is a technique that identifies modal participation factors using some of vibration signals and natural modes of the structure: The selection of sensor locations has a big influence on predicted vibration results. Therefore, this paper deals with four optimal sensor placement( OSP) methods, EFI, EFI-DPR, EVP, AutoMAC, for the estimation of vibration field. It also finds optimal sensor locations of the cylindrical structure by each OSP method and then performs MEMs. Predicted vibration results compared with reference ones obtained by forced response analysis. The standard deviations of errors between reference and predicted results were also calculated. It is utilized to select the most suitable OSP method for estimation of vibration field of the cylindrical structure.

• Composites Research
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• v.13 no.1
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• pp.89-97
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• 2000

Fatigue damage detection and vibration sensing for a laminated composites and impact location detection for a steel beam have been carried out using optical fiber sensor. Intensity based optical fiber sensor is constructed by placing two cleaved fiber end in a hollow glass tube, and multiple reflection within the cavity is considered. Fatigue signals are measured by embedded optical fiber, surface mounted optical fiber sensor and strain gage simultaneously. For vibration sensing, optical fiber sensor is mounted on the carbon fiber composite beam and its response to free vibration and forced vibration is investigated. In impact location detection, two optical fiber sensors are used and the information obtained from two sensors is arrival time delay of vibration caused by impact. Impact location can be calculated from this time delay. The obtained results show that the intensity based optical fiber sensor provide reliable data during long-term fatigue loading, unlike strain gage which deteriorate during the early part of the fatigue test. Optical fiber sensor signals coincide with gap sensor in vibration sensing. The precise locations of impact can be detected within 4.1% error limit.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.6
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• pp.437-443
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• 2014

Vibration testing is conducted for evaluate the fatigue resistance of responsible system over excitation situations and two kinds of vibration profiles, harmonic or random, are widely used in engineering fields. Harmonic excitation profile is adequate for the rotating machinery that is primarily exposed to the orderly excited force subjected for a rotating speed; Random profile is suitable for the non-stationary vibration input, that is a ground excitation for example. Recently, the sine on random(SOR) testing method was sometimes considered to represent the real excitation conditions since the measured response signals of a target system, expecially for moving mobility, shows usually a mixture of them. So, it is important to understand the accumulated fatigue damage over different excitation patterns, harmonic and/or random, to determine the efficient vibration profile of a target system. A uniaxial vibration testing with a notched simple beam was introduced to evaluate the fatigue damage for different excitation profiles and the best choice of vibration profile was concluded from those comparison of calculated fatigue damages.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.340-345
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• 2014

Vibration testing is conducted for evaluate the fatigue resistance of responsible system over excitation situations and two kinds of vibration profiles, harmonic or random, are widely used in engineering fields. Harmonic excitation profile is adequate for the rotating machinery that is primarily exposed to the orderly excited force subjected for a rotating speed; Random profile is suitable for the non-stationary vibration input, that is a ground excitation for example. Recently, the sine on random (SOR) testing method was sometimes considered to represent the real excitation conditions since the measured response signals of a target system, expecially for moving mobility, shows usually a mixture of them. So, it is important to understand the accumulated fatigue damage over different excitation patterns, harmonic and/or random, to determine the efficient vibration profile of a target system. A uniaxial vibration testing with a notched simple beam was introduced to evaluate the fatigue damage for different excitation profiles and the best choice of vibration profile was concluded from those comparison of calculated fatigue damages.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.10
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• pp.677-684
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• 2015

It is often necessary to predict the vibration patterns of the structures from the signals of finite number of vibration sensors. This study presents the optimal placement of vibration sensors by applying the genetic algorithm and the modal expansion method. The modal expansion method is used to estimate the vibration response of the whole structure. The genetic algorithm is used to estimate the optimal placement of vibration sensors. Optimal sensor placement can be obtained so that the fitness function is minimized in the genetic algorithm. This paper discusses the comparison of the performances of two types of fitness functions, modal assurance criteria(MAC) and condition number( CN). As a result, the estimation using MAC shows better performance than using CN.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.80-85
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• 2008

In general, deflection limit criteria of bridge design specifications have been considered based on static serviceability and structural stability. Dynamic serviceability induced from bridge vibration actually has not been included in the criteria. Thus, it is necessary for comfort limit to be considered in order to check dynamic serviceability on bridge vibration. In this study, the comfort limit of bridge structures based on the RMQ and VDV considering the signal fluctuation effectively and the time duration exposed has been constructed. The comfort limit developed in time domain was verified by using vibration signals directly measured from the existing bridges. Comparing the developed comfort limit with the conventional ones defined in frequency domain, it is shown that the comfort limit developed in time domain would be more feasible for evaluating quantitatively the serviceability due to bridge vibration. Using the Bridge-train interaction analysis program, dynamic response of the bridge by the stiffness change were obtained for several railway bridges. And, a stiffness limit satisfying the bridge vibration serviceability was estimated by compared with comport limit. From the results, a new deflection limit on bridge structures satisfying the vibration serviceability could be proposed by comparing with the conventional deflection limit criteria.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.4
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• pp.414-420
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• 2015

In this study, the linear quadratic Guassian loop transfer recovery (LQG/LTR) control technique was combined with an integrator and applied to an inchworm having piezoelectric actuators for precise motion tracking. The piezoelectric actuator showed nonlinear response characteristics, including hysteresis, due to its ferroelectric characteristics and the residual displacement phenomenon. This paper proposes a feedback control scheme using the LQG/LTR controller with an integrator to improve the ability to track the response to complex input signals and to suppress the phenomenon of hysteresis and residual vibration. Experimental results show that the developed feedback control system for an inchworm can track the various motion contours quickly without residual vibration or overshoot.

• Journal of KSNVE
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• v.10 no.6
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• pp.949-954
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• 2000

Applicability of the vibration signal phase for predicting the modal damping properties of structures is investigated. For uniform plates with different internal damping levels, the phase delay as a function of the frequency span as well as a function of the distance between the excitation and response measurement points are experimentally obtained. Dependence of the phase characteristics on the amount of structural damping is elucidated -more heavily damped plate shows notably reduced phase delay at intermediate distances. The experimental results compare favorably with analytical predictions, and show much promise for further refinement as a tool for estimating structural properties.