• 한국소음진동공학회논문집
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• 제15권12호
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• pp.1347-1354
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• 2005

The free vibration characteristics of Al cantilever square plates with a brass inclusion were analyzed experimentally and numerically The experimentally obtained natural frequencies and mode shapes were compared with the FEM analysis results. The impulse exciting method was used for experiment and ANSYS software package was used for FEM analysis. The natural frequencies obtained iron experiment and numerical analysis matched within $0\%$. It was found that the natural frequencies of the Al cantilever square plates with a brass inclusion decrease as the size of inclusion increases. For the third mode shape, comparing the nodal line of the Al plate and the Al plate with a inclusion, the mode shape showed the reversed quadratic curve. The natural frequencies of inclusion plate were decreased as the location of inclusion moves from the clamped edge to the tree edge.

• 대한건축학회논문집:구조계
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• 제34권2호
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• pp.3-10
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• 2018

Damage location and extent of structure could be detected by the inverse analysis on dynamic response properties such as frequencies and mode shapes. In practice the measured difference of natural frequencies represent the stiffness change reliably, however the measured mode shape is insensitive for stiffness change, but provides spatial information of damage. The damage detection index on shear building structures is formulated in this study. The damage detection index could be estimated from mode shape and srory stiffness of undamaged structure and frequency difference between undamaged and damaged structure. For the verification of the observed damage detection method, the numerical analysis of Matlab and MIDAS and shacking table test were performed. In results, the damage index of damaged story was estimated so higher than undamaged stories that indicates the damaged story apparently.

• Smart Structures and Systems
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• 제9권4호
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• pp.335-353
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• 2012

This study suggests a simple two-step method for structural vibration-based health monitoring for beam-like structures which only utilizes mode shape curvature and few natural frequencies of the structures in order to detect and localize cracks. The method is firstly based on the application of wavelet transform to detect crack locations from mode shape curvature. Then particle swarm optimization is applied to evaluate crack depth. As the Rayleigh quotient is introduced to estimate natural frequencies of cracked beams, the relationship of natural frequencies and crack depths can be easily obtained with only a simple formula. The method is demonstrated and validated numerically, using the numerical examples (cantilever beam and simply supported shaft) in the literature, and experimentally for a cantilever beam. Our results show that mode shape curvature and few estimated natural frequencies can be used to detect crack locations and depths precisely even under a certain level of noise. The method can be extended for health monitoring of other more complicated structures.

• 소음진동
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• 제11권2호
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• pp.323-328
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• 2001

The paper describes a theoretical study on the flexural vibration of an elastic rectangular plate with periodically nonuniform material properties. The approximate solution of the natural frequency and mode shape has been obtained using the perturbation technique for sinusoidal modulation of the flexural rigidity and mass density. It has been shown that distributed modes exist in the plate which Is a two-dimensional model of the flat panel speaker.

• 한국소음진동공학회논문집
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• 제24권10호
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• pp.780-787
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• 2014

This paper experimentally deals with the vibration characteristics of flat ring transducers used for ultrasonic sensors and actuators. Radial vibration mode, which is the fundamental mode of a thin piezoelectric transducer, was measured by a laser in-plane vibrometer. An impedance analyzer was used to measure natural frequencies. The results measured by experiments verified theoretical predictions. The vibration characteristics of ring transducers were identified according to the outer diameter size. The shape of the fundamental mode is almost uniform but slightly decreases from the inner to the outer circumferential surfaces. The natural frequency of the fundamental mode decreases as the outer diameter increases. It appears that the ring type transducer is suitable to excite uniformly distributed vibration on a flat surface.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문초록집
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• pp.396.1-396
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• 2002

The AVT under traffic-induced vibrations was carried out on Namhae Suspension bridge in Korea. Mode shapes as well as natural frequencies up to the 15th mode were acquired exactly, and the effect of traffic mass and temperature on measured natural frequencies was investigated. The results from the AVT are compared with those from forced vibration test(FVT) and FE analysis. (omitted)

• 한국농공학회:학술대회논문집
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• 한국농공학회 1999년도 Proceedings of the 1999 Annual Conference The Korean Society of Agricutural Engineers
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• pp.206-211
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• 1999

The purpose of this study is to investigate the natural frequencies and mode shapes of beam-columns on the non-homogeneous foundaion. The beam model is based on the classical Bernoulli-Euler beam theory. The linear foundation modulus is chosen as the non-homogeneous foundation in this study . The differentidal equation goeverning free vibrations of such beam-columns subjected to axial load is derived and solved numerically for calculting the natural frquencies and mode shapes. In numerical fivekinds of end constraint are considered, and the lowest four natural frquencies and corresponding mode shape are obtained as the non-dimensional forms.

• Nuclear Engineering and Technology
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• 제36권4호
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• pp.364-373
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• 2004

This study investigates the fluidelastic instability characteristics of helical steam generator type tubes used in operating nuclear power plants. To obtain a natural frequency, corresponding mode shape, and participation factor, modal analyses using various conditions are performed for helical type tubes. Investigated are the effects of the number of turns, the number of supports, and the status of the inner fluid on the modal and fluidelastic instability characteristics of the tubes, which are expressed in terms of the natural frequency, the corresponding mode shape, and the stability ratio.

• 대한기계학회논문집A
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• 제28권9호
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• pp.1359-1367
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• 2004

The purpose of this study is to predict the dynamic transmission error of the helical gear system. To do so, the equations of motion in the helical gear system which consists of motor, coupling, gear, torque sensor, and brake are derived. As the input parameters, the mass moment of inertia by a 3D CAD software and the equivalent stiffness of the bearings and shaft are calculated and the coupling stiffness is measured. The static transmission error as an excitation is calculated by in-house program. Dynamic transmission error is predicted by solving the equations of motion. Mode shape, the dynamic mesh force and the bearing force are also calculated. In this analysis, the relationship between the dynamic mesh force and the bearing force and mode shape behavior in gear mesh are checked. As a result, the magnitude of mesh force is highly related with the gear mesh behavior in mode shape. The finite element analysis is conducted to find out the natural frequency of gear system. The natural frequencies by finite element analysis have a good agreement with the results by equation of motion. Finally, dynamic transmission error is measured by the specially designed experiment and the results by equation of motion are validated.

• Steel and Composite Structures
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• 제2권3호
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• pp.223-236
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• 2002

An analytical procedure based on the transfer matrix method to estimate not only the natural frequencies but also vibration mode shapes of the thin-walled members composed of interconnected cylindrical shell panels is presented. The transfer matrix is derived from the differential equations for the cylindrical shell panels. The point matrix relating the state vectors between consecutive shell panels are used to allow the transfer procedures over the cross section of the members. As a result, the interactions between the shell panels of the cross sections of the members can be considered. Although the transfer matrix method is naturally a solution procedure for the one-dimensional problems, this method is well applied to thin-walled members by introducing the trigonometric series into the governing equations of the problem. The natural frequencies and vibration mode shapes of the thin-walled members composed of number of interconnected cylindrical shell panels are observed in this analysis. In addition, the effects of the number of shell panels on the natural frequencies and vibration mode shapes are also examined.