• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.805-812
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• 2006

An optimization formulation is proposed to minimize sound pressures in a two-dimensional cavity by controlling the attachment area of unconstrained damping materials. For the analysis of structural-acoustic systems, a hybrid approach that uses finite elements for structures and boundary elements for cavity is adopted. Four-parameter fractional derivative model is used to accurately represent dynamic characteristics oJ the viscoelastic materials with frequency and temperature. Optimal layouts of the unconstrained damping layer on structural wall of cavity are identified according to temperatures and the amount of damping material by using a numerical search algorithm.

• International Journal of High-Rise Buildings
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• v.5 no.1
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• pp.51-62
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• 2016

The concept of introducing viscous damping devices between outriggers and perimeter columns in tall buildings to provide supplementary damping and improve performance, reduce structural costs, and increase available usable area was developed and implemented by Smith and Willford (2007). It was recognized that the relative vertical movement that would occur between the ends of outriggers and columns, if they were not connected, could be used to generate damping. The movements, and correspondingly damping, can potentially be significantly increased by amplifying them using simple "mechanisms". The mechanisms also make it possible to increase the number of available dampers and thus further increase supplementary damping. The feasibility of mechanisms to amplify supplementary damping and enhance structural performance of tall, slender buildings is studied with particular focus on its efficacy in improving structural performance in wind loads.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.131-134
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• 2002

Supersonic flutter analysis of cylindrical composite panels with structural damping treatments has been performed using the finite element method based on the layerwise shell theory. The natural frequencies and loss factors of cylindrical viscoelastic composites are computed considering the effects of transversely shear deformation. The panel flutter of cylindrical composite panels is analyzed considering structural damping effect. Various damping characteristics for unconstrained layer damping, constrained layer damping, and symmetrically co-cured sandwich laminates are compared with those of an original base panel in view of aeroelastic stabilities.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.10a
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• pp.459-466
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• 2002

The purpose of this study is to propose a new method for evaluating equivalent damping ratios of a structure with supplemental damping devices to assess their control effect quantitatively. A MDOF system is transformed to an equivalent SDOF system based on the assumption that the first mode dominates structural response. Approximate closed-form formulas for the evaluation of the first damping ratio are presented for various damping devices. Through numerical analysis of a ten-story building equipped with damping devices, the effectiveness of equivalent SDOF model and closed form formulas are verified.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.1025-1032
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• 2006

The PVRC(Pressure Vessel Research Council) damping is for the response spectrum analysis of the piping system. In this study, the possibility to apply it to the time history analysis is evaluated to reduce the higher conservatism for the structural integrity. The evaluation was performed for the surge line connecting the pressurizer to the hot-leg, and the whole mode includes the RCS and the building structures with the surge line. The analyses were performed using ANSYS code. The first modal analysis shows the modes of the surge line are isolated from those of the other structures. The composite modal damping was calculated with PVRC damping for the surge line and RG 1.60 damping for the other structures by using ANSYS routines. Of the calculated composite modal damping values, the composite modal damping values related to the modes of the surge line were replaced with the PVRC damping values with respect to its frequencies. With this replacement, the composite modal damping values of the other structures were not changed. Based on this decouple characteristics, the time history analyses for the seismic events with PVRC damping for the surge line were performed. And the results show the resultant loads can be reduced by up to 50%.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.333-337
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• 2003

The use of reactive shearing structural intensity to place small patches of constrained layer damping material in order to achieve the largest reduction in the radiated sound power of Air-conditioner outdoor unit is described. The normal surface velocity of each panel was measured using a laser doppler vibrometer. Experimental results indicated that patches of constrained layer damping material placed over areas of high reactive structural intensity reduced the radiated sound power significantly more than patches of the same area placed over areas of low reactive structural intensity

• Wind and Structures
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• v.10 no.5
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• pp.401-420
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• 2007

Field measurements of the wind-induced response of two residential reinforced concrete buildings, among the tallest in the world, have been performed during two typhoons. Natural periods and damping values have been determined and compared with other field measurements and empirical predictors. Suitable and common empirical predictors of natural period and structural damping have been obtained that describe the trend of tall, reinforced concrete buildings whose structural vibrations have been measured in the collection of studies in Hong Kong compiled by the authors. This data is especially important as the amount of information known about the dynamic parameters of buildings of these heights is limited. Effects of the variation of the natural period and damping values on the alongwind response of a tall building for serviceability-level wind conditions have been profiled using the gust response factor approach. When using this approach on these two buildings, the often overestimated natural periods and structural damping values suggested by empirical predictors tended to offset each other. Gust response factors calculated using the natural periods and structural damping values measured in the field were smaller than if calculated using design-stage values.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.835-838
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• 2008

In this study, long-term compression displacement of damping materials used to reduce floor impact noise and compressive load that crack begins to happen in Ondol layers including the material were measured as basic research to make guide line for right choice of damping material considering structural stability of Ondol layer. From the result, it was found that compression displacement by elapsed time as well as early displacement of damping material when load is applied on Ondol layer are should be included in the guide line for the choice of damping materials. And no problem is expected to be in structural stability of Ondol layer in case choose a damping material that compression displacement at three months later from inflict load is within 10% than initial thickness.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.2
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• pp.145-152
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• 2015

In the study, the effects of damping devices on damping ratio increase and wind-load reduction were investigated based on the computational platform, which is one of the parametric modeling methods. The computational platform helps the designers or engineers to evaluate the efficacy of the numerous alternative structural systems for irregular Super-Tall building, which is crucial in determining the capacity and the number of the supplemental damping devices for adding the required damping ratios to the building. The inherent damping ratio was estimated based on the related domestic and foreign researches conducted by using real wind-load records. Two types of damping devices were considered: One is inter-story installation type passive control devices and the other is mass type active control devices. The supplemental damping ratio due to the damping devices was calculated by means of equivalent static analysis using an equation suggested by FEMA. The optimal design of the damping devices was conducted by using the computational platform. The structural element quantity reduction effect resulting from the installation of the damping devices could be simply assessed by proposing a wind-load reduction factor, and the effectiveness of the proposed method was verified by a numerical example of a 455m high-rise building. The comparison between roof displacement and the story shear forces by the nonlinear time history analysis and the proposed method indicated that the proposed method could simply but approximately estimate the effects of the supplemental damping devices on the roof displacement and the member force reduction.

• Aerospace Engineering and Technology
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• v.4 no.1
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• pp.9-17
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• 2005

The aeroelastic stability enhancement of composite hingeless rotor system through the structural damping increase has been investigated. In order to increase structural damping of the rotor system, constrained layer damping (CLD) treatment is applied to the composite flexures. Modal analysis of composite flexures with attached viscoelastic and constraining layers are performed using MSC/NASTRAN, and the effectiveness of CLD treatments are validated through modal test. The composite flexures with CLD are applied to a hingeless rotor system. The rotor system is tested in hovering condition and it is shown that in-plane damping is increased by means of CLD treatments.