• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.795-800
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• 2007

In the previous study, a simple but effective analysis procedure, named as an Improved Modal Pushover Analysis (IMPA) was proposed to estimates the seismic capacities of multi-span continuous bridge structures, on the basis of the modal pushover analysis which considers all the dynamic modes of a structure. Differently from other previous studies, IMPA maintains the simplicity of the capacity-demand curve method and also gives a better estimation of the maximum dynamic response of a structure. Nevertheless, its applicability has never been approved for multi-span continuous bridges with large differences in the length of their adjacent piers. This paper, accordingly, concentrates on a parametric study to verify the efficiency and limitation in application of IMPA through a correlation study between various analytical models including the Equivalent Single Degree Of Freedom (ESDOF) and Modal Pushover Analysis (MPA) usually used in the seismic design of structures. Based on the obtained numerical results, this paper introduces a practical guidance and/or limitation for using IMPA to predict the seismic response of a bridge effectively.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.3
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• pp.127-132
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• 2010

Eigensolutions associated with self-excited vibration of disc brake system can be obtained by complex eigenvalue analysis. The eigenvalue sensitivity to change in contact stiffness can be used to demonstrate stability criteria and eigenvalue veering. Dynamic instability on eigenvalue loci with respect to the variation of contact stiffness is found to be related to mode interaction between two adjacent modes. This modal interaction can be effectively shown by mode shape visualization. This paper presents the methodology to construct the mode shape of disc brake system where a disc and two brake pads are coupled with contact stiffness.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.102-106
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• 2003

An experimental modal analysis and dynamic stiffness evaluation of a moving body structure of a high speed machining center are presented in this paper. The natural frequencies and corresponding modes, and dynamic compliance of a moving body structure of high speed machining center are investigated by using F.E.M., hydraulic exciter test, and impulse hammer test. The lowest three natural frequencies were found to be 56.6 Hz, 112.7 Hz, and 142.7 Hz by FEA respectively, while those were 55 Hz, 112 Hz, 131 Hz by experimental analysis. Furthermore, both computed and measured absolute dynamic compliances of the moving body structure in iso-direction showed good agreement especially at the first two mode frequencies. With our experimental data, the dynamic characteristics of the machining center can be exploited to get a new development of structural dynamic design and modification.

• Structural Monitoring and Maintenance
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• v.5 no.3
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• pp.379-390
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• 2018

In this paper, a novel and effective damage diagnosis algorithm is proposed to detect and estimate damage using two stages least squares support vector machine (LS-SVM) and limited number of attached sensors on structures. In the first stage, LS-SVM1 is used to predict the unmeasured mode shapes data based on limited measured modal data and in the second stage, LS-SVM2 is used to predicting the damage location and severity using the complete modal data from the first-stage LS-SVM1. The presented methods are applied to a three story irregular frame and cantilever plate. To investigate the noise effects and modeling errors, two uncertainty levels have been considered. Moreover, the performance of the proposed methods has been verified through using experimental modal data of a mass-stiffness system. The obtained damage identification results show the suitable performance of the proposed damage identification method for structures in spite of different uncertainty levels.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.3 s.168
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• pp.61-67
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• 2005

A dynamic model for flexure hinge-based compliant mechanisms is derived. The dynamic model of the previous works do not well describe the behaviors of rigid bodies in the compliant mechanism when the length of the flexure hinge is long. In this study, the effect on the length of the flexure hinge is pointed out and then the dynamic model is derived to overcome the length effect. For verification, modal analyses are carried out using the proposed dynamic model and FEM (Finite Element Method). Finally they are compared by the terms of modal frequency. As the result, the proposed dynamic model can be used in design and analysis of the compliant mechanism.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.109-114
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• 2007

Analytical method to analyze the effect of tolerance on the modal characteristic of multi-body systems in dynamic equilibrium position is suggested in this paper. Monte-Carlo Method is conventionally employed to perform the tolerance analysis. However, Monte-Carlo Method spends too much time for analysis and has a greater or less accuracy depending on sample condition. To resolve these problems, an analytical method is suggested in this paper. By employing the sensitivity information of mass, damping and stiffness matrices, the sensitivities of damped natural frequencies and the transfer function can be calculated at the dynamic equilibrium position. The effect of tolerance on the modal characteristic can be analyzed from tolerance analysis method.

• Structural Engineering and Mechanics
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• v.2 no.1
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• pp.95-112
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• 1994

This paper describes the formulation and application of a dynamic model for a conventional rail track subjected to arbitary loading functions that simulate wheel/rail impact forces. The rail track is idealized as a periodic elastically coupled beam system resting on a Winkler foundation. Modal parameters of the track structure are first obtained from the natural vibration characteristics of the beam system, which is discretized into a periodic assembly of a specially-constructed track element and a single beam element characterized by their exact dynamic stiffness matrices. An equivalent frequency-dependent spring coefficient representing the resilient, flexural and inertial characteristics of the rail support components is introduced to reduce the degrees of freedom of the track element. The forced vibration equations of motion of the track subjected to a series of loading functions are then formulated by using beam bending theories and are reduced to second order ordinary differential equations through the use of mode summation with non-proportional modal damping. Numerical examples for the dynamic responses of a typical track are presented, and the solutions resulting from different rail/tie beam theories are compared.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.09a
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• pp.125-130
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• 2001

It is well known that many real systems have asymmetric mass, damping and stiffness matrices. In this case, the method for calculating eigenpair sensitivity is different from that of symmetric system. To determine the derivatives of the eigenpairs in asymmetric damped case, a modal method was recently developed by Adhikari. When a dynamic system has many degrees of freedom, only a few lower modes are available, and because the higher modes should be truncated to use the modal method, the errors may become significant. In this paper a procedure for determining the sensitivities of the eigenpairs of asymmetric damped system using a few lowest set of modes is proposed. Numerical examples show that proposed method achieves better calculating efficiency and highly accurate results when a few modes are used.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.571-575
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• 2000

The physical properties of the spatial model, mass, stiffness and damping matrix, can be defined by a specific natural frequency, damping ratio and mode shape. These modal parameters can be determined from a set of frequency response function(FRF) measured by exciting the structure and measuring the responses at various points around the structure. In this paper, The Transfer Matrix is obtained by experimental modal analysis for the 3-story scaled building model which TMD is installed on top and the physical properties of the spatial model is determined using the residue matrix and the location of poles from FRF measurement using polynomial curve fitting methods.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.9 s.180
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• pp.2266-2273
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• 2000

Equations of motion of a multi-beam system undergoing overall rigid body motion are derived by employing finite element method. An orientation angle is employed to allow the arbitrary orientation o f the beam element. Modal coordinate reduction technique, which has been successfully utilized in the conventional linear modeling method, is employed for the present modeling method to reduce the computational effort. Different from the conventional linear modeling method, the present modeling method captures the motion-induced stiffness variations which are important for the dynamic analysis of structures undergoing overall rigid body motion. The numerical results are compared to those of a commercial program to verify the reliability of the present method.