• Structural Engineering and Mechanics
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• v.7 no.1
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• pp.53-67
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• 1999

The natural frequencies and modes of free vibration of specially orthotropic elliptic and circular plates are analysed using the Rayleigh-Ritz method. The assumed functions used are two-dimensional boundary characteristic orthogonal polynomials which are generated using the Gram-Schmidt orthogonalization procedure. The first five natural frequencies are reported here for various values of aspect ratio of the ellipse. Results are given for various boundary conditions at the edges i.e., the boundary may be any of clamped, simply-supported or fret. Numerical results are presented here for several orthotropic material properties. For rectilinear orthotropic circular plates, a few results are available in the existing literature, which are compared with the present results and are found to be in good agreement.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.10
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• pp.924-933
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• 2011

The possibility of noncontact excitation of vibrations in a shaft was investigated in order to enable online structural health monitoring of a shaft during its rotating condition without stop operation. The proposed noncontact exciter was devised to exclusively generate one of two shaft vibration modes, so called longitudinal and flexural. Using the prototypes and a lot of experiments on them, it was proven that bias magnetic field, exciting voltage, center frequency, and geometry of yokes have crucial impacts on its output characteristics.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.18 no.4
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• pp.355-361
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• 2009

In this paper, an analysis technique is presented for performing the effective design of bus structure. Sensitivity analysis is carried out for the natural frequency of component structures consisting of bus B.I.W. Local vibration modes of substructure, which large affect on the global vibration mode of the bus B.I.W., are obtained through the sensitivity analysis technique using the mathematical chain rule. And also the design variables, which are determined from the sensitivity analysis, are redesigned through optimum design process. The proposed analysis technique shows that the bus structure can be effectively designed considering the vibration characteristics.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2005.05a
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• pp.364-369
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• 2005

In the semiconductor and optical industry the non-contact transportation is required for reducing the damages. The ultrasonic levitation is the solution of the problem. In this paper, the ultrasonic levitation system and 3 disk-type stator for levitation various object are proposed. The vibration modes of disks are analyzed with FEM and designed with the analysis results. The 3D vibration profiles of the disks are measured by Laser scanning vibrometer for verifying the vibration characteristics of the system. The amplitudes of the disks and the levitation heights of object are measured for evaluating the performance.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.10
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• pp.968-973
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• 2012

Slam testing is a mandatory testing process to evaluate the fatigue resistance of a door plate module before delivering it to car makers. This process is very hard job to complete it since the testing facilities are considerably expensive and the required testing time is relatively very long, i.e. more than eight days for a single specimen. In this paper, an accelerated testing method of a door plate module is proposed using vibration test equipment instead of the current one by exposing to the critical excitation of a door glass. Under the proposed excitation method, the similar testing result can be evaluated within less than two hours. The suitability of the proposed testing method was demonstrated by comparing failure modes of both the current testing method and the proposed one.

• 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.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.647-651
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• 2002

This study dealt with the free vibration of two identical rectangular plates coupled with fluid. In order to investigate the vibration characteristics of fluid-coupled rectangular plates, an analytical method based on the finite Fourier series expansion and Rayleigh-Ritz method was suggested. A commercial computer code, ANSYS was used to perform finite element analysis and we investigated the vibration characteristics with mode shapes and natural frequencies. As a result, the transverse vibration modes, in-phase and out-of-phase, were observed alternately in the fluid-coupled system. The effect of fluid bounding and plate boundary condition on the fluid-coupled natural frequency were investigated. It was shown that the mode numbers increased, the normalized natural frequencies monotonically increased.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.3
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• pp.110-115
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• 2010

This paper studies the vibration characteristics of a vehicle seat on several driving conditions. Modal test for a vehicle seat is conducted for the three different boundary conditions: on the rigid jig, BIW and the full vehicle. In driving on various road conditions and speeds, vibration level is measured at several locations including seat mounting and seat-back. The vibration pattern for each driving condition is found where the suspension mode and the 1st bending and torsion modes of the seat make the major contribution on it.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.452-458
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• 2003

This paper presents a robust vibration control methodology of smart structural systems. The governing equations and associated boundary conditions are derived by Hamilton's principle. A robust controller is designed using a linear matrix inequality (LMI) approach to the multiobjective synthesis. The design objectives are to achieve a mix of H$\sub$$\infty$/ performance and H$_2$ performance satisfying constraints on the closed-loop pole locations in the face of model uncertainties. Numerical examples are presented to demonstrate the effectiveness of LMI approach in damping out the multiple modes of vibration of the piezo/beam system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.260-265
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• 1996

Active control of forced vibration response of a fixed-fixed beam implementing PZT sensor/actuator was conducted. Among various control scheme, PPF control was chosen due to its amenability and natural robustness. For a single frequency excitation, the PPF control provided reasonable controllability with the appropriate damping ratio of the compensator. Without increasing actuator voltage, best controllability can be obtained by the exact tuning between the natural frequency of the structure and the cut-off frequency of the compensator. Even the multi-frequency excitation, the PPF provided good vibration suppression for corresponding mode of interest, even though residual modes should be controlled with independent compensators for each mode.