• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.496-497
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• 2009

In this paper the power flow finite element method (PFFEM) has been used to analyze the vibration of a plate partially covered with a damping sheet. Experiments have been performed to measure the loss factor and frequency response functions of the plate partially covered with the damping sheet. The data for the loss factor has been used as the input data to predict the vibration of the coupled plates with PFFEM. The comparison between the experimental results and the predicted PFFEM results for the frequency response functions has been performed. It showed that PFFEM can be effectively used to predict structural vibration in medium-to-high frequency ranges.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.95-101
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• 1997

A general method is presented for the analysis of the damping effectiveness of viscoelastic layer applied to elastic beam. The damping is attributed to the shear deformations of the treatment. Specific results are then given for sandwich beams with dissipative cores. The calculated results by this method are validated by comparison with the experimental results. Optimum design of a viscoelastic damping layer which is constrainedly cohered on a steel beam is discussed from the viewpoint of the modal loss factor. An object function is a loss factor of 3-layered beam and design variable is the thickness of constraining layer and viscoelastic layer. Optimum thickness can be obtained when 3-layered beam has a maximum loss factor.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1256-1259
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• 2006

The purpose of this study was to investigate the current status and influence factor in measuring the dynamic stiffness of damping materials. The property of the dynamic stiffness of damping materials was tested and analysed in condition such as the size of test samples and the change of relative humidity in heating chamber. Test results showed that the dynamic stiffness of after-heating was lower than that of before-heating in most samples and the change of relative humidity in heating chamber got little influence of the dynamic stiffness. The resonant frequency of test sample decreased $2{\sim}7Hz$ as the decrease of the size of sample. Because it was increased that total mass per unit area of sample, the change of dynamic stiffness had little influence.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.9 s.90
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• pp.852-860
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• 2004

There are many standard methods for measuring vibration damping properties of the beam type material. Among them, three standards ASTM E 756, ISO 6721 and JIS G 0602, are compared. Loss factor and Young's modulus of the steel beam are evaluated by using five different methods and their results are compared. Logarithmic decay method and half-power bandwidth method are used to calculate the loss factor. It was observed that Young’s modulus is agree well, but loss factors are different from test to test. So the same test method must be applied to measure damping properties.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.364-366
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• 2012

Quantification of acoustic amplification in a model chamber has been studied for combustion stabilization induced by passive control devices. DMD(Dynamic mode Decomposition) method is adopted and the results from method are compared with those from damping factor approach. The model chamber has a faceplate with baffled injectors, where damping factor has its maximum at a specific baffle gap. They show a good agreement with the results from the previous method.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.7 s.112
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• pp.690-696
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• 2006

Thickness of damping layer in sandwich plate needs to be optimized in order to make modal loss factor of the sandwich plate maximum. Since previous studies were interested in noise reductions over high frequency range, the modal properties were derived based on simply supported boundaries. This conventional formula is approximately applicable to other boundary conditions over high frequency range only. The purpose of this study is to propose a method to determine optimum damping layer thickness of sandwich plate for maximum modal damping in low frequency range when the boundary condition is not a simple support. The conventional RKU equation based on simply supported boundary is modified to reflect other boundary conditions and the modified RKU equation is subsequently applied to determine the optimum damping layer thickness for arbitrary conditions. In order to reflect frequency-dependent characteristics of elastic modulus of the damping layer, an iteration method is proposed in determining the modal properties. Test results on sandwich plates for optimum damping layer thickness are compared with predictions by the proposed method and conventional method.

• Smart Structures and Systems
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• v.19 no.1
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• pp.57-66
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• 2017

Nanocomposites reinforced with carbon nanotube fibers exhibit greater stiffness, strength and damping properties in comparison to conventional composites reinforced with carbon/glass fibers. Consequently, most of the nanocomposite research is focused in understanding the dynamic characteristics, which are highly useful in applications such as vibration control and energy harvesting. It has been observed that those nanocomposites show better stiffness when the geometry of nanotubes is straight as compared to curvilinear although nanotube agglomeration may exist. In this work the damping behavior of the nanocomposite is characterized in terms of loss factor under the presence of nanotube agglomerations. A micro stick-slip damping model is used to compute the damping properties of the nanocomposites with multiwall carbon nanotubes. The present formulation considers the slippage between the interface of the matrix and the nanotubes as well as the slippage between the interlayers in the nanotubes. The nanotube agglomerations model is also presented. Results are computed based on the loss factor expressed in terms of strain amplitude and nanotube agglomerations. The results show that although-among the various factors such as the material properties (moduli of nanotubes and polymer matrix) and the geometric properties (number of nanotubes, volume fraction of nanotubes, and critical interfacial shear stresses), the agglomeration of nanotubes significantly influences the damping properties of the nanocomposites. Therefore the full potential of nanocomposites to be used for damping applications needs to be analyzed under the influence of nanotube agglomerations.

• Earthquakes and Structures
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• v.4 no.5
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• pp.489-508
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• 2013

Design spectra for damping ratios higher than 5% have several important applications in the design of earthquake-resistant structures. These highly damped spectra are usually derived from a 5%-damped reference pseudo-acceleration spectrum by using a damping modification factor. In cases of high damping, the absolute acceleration and the relative velocity spectra instead of the pseudo-acceleration and the pseudo-velocity spectra should be used. This paper elaborates on the recovery of spectral absolute acceleration and spectral relative velocity from their pseudo-spectral counterparts. This is accomplished with the aid of correction factors obtained through extensive parametric studies, which come out to be functions of period and damping ratio.

• Earthquakes and Structures
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• v.8 no.5
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• pp.1091-1111
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• 2015

Base isolation is an effective method for protecting structures against earthquake hazard. It elongates the period of vibration and introduces supplemental damping to the structural system. The stiffness, damping and displacement are coupled forcing the code seismic design procedure to be unnecessarily complicated. In addition, the force reduction factor -a key parameter in the design procedurehas not been well addressed by seismic design codes at the high levels of damping due to the pronounced difference between pseudo and actual accelerations. In this study, a comparison has been conducted to evaluate eight different methods, in the literature, for calculating the force reduction factor due to damping. Accordingly, a simplified seismic analysis procedure has been proposed based on the well documented N2 method. Comprehensive analysis has been performed for base-isolated structure models for direct application and verification of the proposed procedure. The results have been compared with those of the European code EC8, the nonlinear time history analysis and investigations in the literature, where good agreement has been reported. In addition, a discussion has been elaborated for the resulted response of the base-isolated structure models with respect to the dynamic characteristics of the base isolation system.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.3
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• pp.421-432
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• 2002

In this study the modal characteristics and responses of an asymmetric structure with added viscoelastic dampers were investigated for design parameters such as eccentricity of stiffness and added dampers, the loss factor of the damping materials used. For modal characteristics, variation of the quantities such as natural frequencies, modal damping ratios, modal participation factors, and dynamic amplification factors were observed, and displacements at flexible and stiff edges, and at center of mass were obtained. Based on the results, the problem of the optimum damper distribution to minimize the torsional effects was addressed, and the proposed method for optimum damper distribution was applied to a multi-story structure to verify the applicability Finally the effect of viscous and viscoelastic dampers were compared by varying the loss factor of the viscoelastic material.