• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.656-661
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• 2005

An optimization formulation of unconstrained damping treatment on beams is proposed to minimize vibration responses using a numerical search method. The fractional derivative model is combined with RUK's equivalent stiffness approach in order to represent nonlinearity of complex modulus of damping materials with frequency and temperature. The loss factors of partially covered unconstrained beam are calculated by the modal strain energy method. Vibration responses are calculated by using the modal superposition method, and of which design sensitivity formula with respect to damping layout is derived analytically. Plugging the sensitivity formula into optimization software, we can determine optimally damping treatment region that gives minimum forced response under a given boundary condition. A numerical example shows that the proposed method is very effective in minimizing vibration responses with unconstrained damping layer treatment.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.570-575
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• 2002

Servo performance of a disk drive is greatly affected by the mechanical resonance frequencies of the head gimbal assembly (HSA). It is important factor to allow broader bandwidths for servo system in improving overall drive performance. In this paper, an optimal design for ODD suspension is attempted to increase resonance frequencies in tracking direction. Initial model was designed and the design parameter was defined to the model. The mode frequency variation for the change of design parameter was observed by modal analysis using the finite element method(FEM). The sensitivity matrix was calculated from the observed data and so through sensitivity analysis, an optimized ODD suspension was designed to have the higher resonant frequency than the initial model.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.7 s.124
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• pp.579-586
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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. Sensitivity equations for damped natural frequencies and the transfer function are derived at the dynamic equilibrium position. By employing the sensitivity information of mass, damping and stiffness matrices, the sensitivities of damped natural frequencies and the transfer function can be calculated.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.05a
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• pp.221-224
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• 2001

The dynamic characteristics of a hydraulic press for micro-stamping are investigated by Finite Element Analysis. This machine requires high precision in producing milli-structure of electric products such as TFT-LCD back-up light reflector. First, the modal analysis of the parts and the assembly of the hydraulic press is performed. Then, the sensitivity analysis is carried out. The results show that the bearing stiffness and the base mounting stiffness affect the specific mode shapes.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.114-121
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• 1998

This paper presents the model updating of an equipment panel by using modal test and sensitivity analysis. The equipment panel is one of the major structures of communication satellite, on which broadcasting and communication equipments are mounted. For high rigidity and light weight, the panel was designed as an aluminum honeycomb sandwich panel. In addition, heat pipes were embedded in the panel for thermal control. It is essential to improve the finite element model of a satellite by using modal test in order to verify the satellite is designed with adequate margin under launch environment. In this paper, Young's modulus of aluminum facesheet was selected as a modified parameter by sensitivity analysis. The effect of rotational springs of boundary points was also considered.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.244-249
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• 1998

The present paper improves the direct identification scheme based upon the equation error formulation with incomplete modal data. First, an indirect estimation technique is considered for estimating unmeasured elements of latent vectors by the combined use of a model and measured incomplete eigen vectors. It is used for estimating the other elements of eigen vectors, which are essential for identification but not available. Next an index is introduced here to indicate the quality of estimation with respect to the mode and the measured positions. A sensitivity formula for eigenvalues with respect to the unknown joint coefficient is also derived to select the modes appropriate for identification. An identification strategy is suggested to meet with practical problems with the help of the index and sensitivity formula. The index and the sensitivity are proved to be useful for selecting measurement positions and modes appropriate for identification A comprehensive simulation study is performed to test the proposed method.

• Structural Engineering and Mechanics
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• v.68 no.1
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• pp.39-51
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• 2018

In this study, a frequency domain model updating method is presented using power spectral density (PSD) data. It uses the sensitivity of PSD function with respect to the unknown structural parameters through a decomposed form of transfer function. The stiffness parameters are captured with high accuracy through solving the sensitivity equations utilizing the least square approach. Using numerically noise polluted data, the model updating results of a truss model prove robustness of the method against measurement and mass modelling errors. Results prove the capabilities of the method for parameter estimation using highly noise polluted data of low ranges of excitation frequency.

• Proceedings of the KIEE Conference
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• 1999.11b
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• pp.193-196
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• 1999

This paper presents a new systematic contingency selection and screening method for transient stability. The variation of modal synchronizing torque coefficient(MSTC) is computed using eigen-sensitivity analysis of the electromechanical oscillation modes in small signal stability model and contingencies are ranked in decreasing order of the sensitivities of the MSTC(SMSTC). The relevant clusters are identified using the eigenvector or participating factor. The proposed algorithm is tested on the KEPCO system. Ranking obtained by the SMSTC is consistent with the time simulation results by PSS/E.

• Journal of KSNVE
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• v.9 no.2
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• pp.248-257
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• 1999

This paper presents the model updating of an equipment panel by using modal test and sensitivity analysis. The equipment panel is one of the major structures of communication satelite, on which broadcasting and communication equipments are mounted. For high rigidity and light weight, the panel was designed as an aluminum honeycomb sandwich panel. In addition, heat pipes were embedded in the panel for thermal control. It is essential to improve the finite element model of a spacecraft structure by using modal test in order to verify that the satellite is designed and fabricated with adequate margin under launch environment. In this paper, Young's modulus of aluminumfacesheet was selected as a modified parameter in the sensitivity analysis. The effect of boundary conditions on model improvement was also investigated.

• Smart Structures and Systems
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• v.6 no.2
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• pp.115-133
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• 2010

A modal filter is a tool used to extract the modal coordinates of each individual mode from a system's output. This is achieved by mapping the response vector from the physical space to the modal space. It decomposes the system's responses into modal coordinates, and thus, on the output of the filter, the frequency response with only one peak corresponding to the natural frequency to which the filter was tuned can be obtained. As was shown in the paper (Deraemecker and Preumont 2006), structural modification (e.g. a drop in stiffness or mass due to damage) causes the appearance of spurious peaks on the output of the modal filter. A modal filter is, therefore, a great indicator of damage detection, with such advantages as low computational effort due to data reduction, ease of automation and lack of sensitivity to environmental changes. This paper presents the application of modal filters for the detection of stiffness changes. Two experiments were conducted: the first one using the simulation data obtained from the numerical 7DOF model, and the second one on the experimental data from a laboratory stand in 4 states of damage.