• Journal of Power System Engineering
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• v.22 no.1
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• pp.87-93
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• 2018

Specimens were machined out from hot-rolled AZ31 magnesium alloy, and deformed at 623K with rolling reduction of 30%. After hot rolling, specimens were annealed at various range of temperature and time. In this study, static recrystallization was occurred during heat treatment, however, variation of main component and intensity of texture was not revealed. The results of microstructure observation, damping capacity test and dislocation mechanism indicated that increasing of damping capacity was caused by grain growth. It means that grain size is effective factor to damping capacity.

• Journal of the Korean Wood Science and Technology
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• v.25 no.2
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• pp.61-66
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• 1997

Paulownia wood has been used as sound board for Korean traditional musical instruments such as Keomungo(Korean lute), Kayagum(twelve-stringed Korean harp) and Changgu(hour-glass shaped drum), etc. The acoustic properties of wood affected not only by dimensions but also by density and stiffness of wood. Due to inhomogeneity and hygroscopicity of wood. the acoustic properties of wood are inconsistent. To clarify the effect of moisture content and air dry density on acoustic properties, longitudinal vibration experiment was accomplished in 3 moisture content levels of 9.6, 11.1 and 12.5% and in 3 air dry density levels of 0.22, 0.25 and 0.28g/$cm^3$. The results were as follows: As the moisture content increased, the fundamental frequency. specific dynamic Young's modulus and sound velocity decreased, but the internal friction increased so that loss of energy increased. The values in damping of sound radiation were rapidly decreased at 12.5%. It meant that the damping of internal friction was larger than damping of sound radiation at high moisture content. As the air dry density increased, the fundamental frequency, specific dynamic Young's modulus and sound velocity increased, but the internal friction and damping of sound radiation decreased so that loss of energy decreased. And acoustic converting efficiency was hardly influenced by increasing air drying density.

• East Asian mathematical journal
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• v.32 no.3
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• pp.355-364
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• 2016

In this paper, we study exponential stabilization of the vibrations of the Kelvin-Voigt type wave equation with Balakrishnan-Taylor damping and acoustic boundary in a bounded domain in $R^n$. To stabilize the systems, we incorporate separately, the internal material damping in the model as like Kang [3]. Energy decay rate are obtained by the exponential stability of solutions by using multiplier technique.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.189-195
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• 2008

The vibration isolator system(VIS) which has very low natural frequency could be designed by applying an axial compressive force to the beam-column flexure(BCF). In this paper a new shape of the BCF is suggested. It has stepwise axially varying properties by viscoelastic damping layer. So it has internal structural damping by damping layer during deformation. First the analytic solution is obtained for the BCF. And its critical load, buckling mode, stiffness and stress distributions are investigated. Also the dynamic properties of the VIS consist of the damping layered BCF are studied. Finally the optimal design procedure of damping layered BCF for the VIS is suggested. The improved performance of suggested VIS is verified by some experiments.

• Advances in concrete construction
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• v.13 no.6
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• pp.423-431
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• 2022

Although the influence of moisture content on the mechanical properties of concrete has been studied for a long time, research related to its influence on the damping and energy dissipation property of concrete structure is still very limited. In this paper, the relationship between damping property and moisture content of concrete using cyclic uniaxial compression is firstly presented, and the mechanism of the influence of moisture content on concrete damping and energy dissipation capacity is analyzed. Based on the experimental research, moisture-related damping and energy dissipation model is proposed. Results show that the dissipated energy of concrete and loss factor increase as the moisture content increasing. The energy dissipation coefficient reflecting the influence of stress level of concrete under cyclic load, decreases first and then increases as the moisture content increasing. The mechanism of moisture-related energy dissipation behavior can be divided into the reactive force of water, the development of the internal micro cracks and the pore water pressure. Finally, the proposed moisture-related damping and energy dissipation model are verified.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.6_spc
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• pp.635-643
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• 2016

A stability theory of a damped cantilever column under sub-tangential follower forces is first summarized based on the stability map. It is then demonstrated that internal and external damping can be exactly transformed to Rayleigh damping so that the damping coefficients can be effectively determined using proportional damping. Particularly a parametric study with variation of damping coefficients is performed in association with flutter loads of Beck's column and it is shown that two damping coefficients can be correctly estimated for real systems under the assumption of Rayleigh damping. Finally a frequency equation of a cantilever beam subjected to both a sub-tangentially follower force and two kinds of damping forces is presented in the closed-form and its stability maps are constructed and compared with FE solutions in the practical range of damping coefficients.

• Smart Structures and Systems
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• v.26 no.5
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• pp.575-589
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• 2020

For vibration control of stay cables in cable-stayed bridges, viscous dampers are frequently used, and they are regularly installed between the cable and the bridge deck. In practice, neoprene rubber bushings (or of other types) are also widely installed inside the cable guide pipe, mainly for reducing the bending stresses of the cable near its anchorages. Therefore, it is important to understand the effect of the bushings on the performance of the external damper. Besides, for long cables, external dampers installed at a single position near a cable end can no longer provide enough damping due to the sag effect and the limited installation distance. It is thus of interest to improve cable damping by additionally installing dampers inside the guide pipe. This paper hence studies the combined effects of an external damper and an internal damper (which can also model the bushings) on a stay cable. The internal damper is assumed to be a High Damping Rubber (HDR) damper, and the external damper is considered to be a viscous damper with intrinsic stiffness, and the cable sag is also considered. Both the cases when the two dampers are installed close to one cable end and respectively close to the two cable ends are studied. Asymptotic design formulas are derived for both cases considering that the dampers are close to the cable ends. It is shown that when the two dampers are placed close to different cable ends, their combined damping effects are approximately the sum of their separate contributions, regardless of small cable sag and damper intrinsic stiffness. When the two dampers are installed close to the same end, maximum damping that can be achieved by the external damper is generally degraded, regardless of properties of the HDR damper. Field tests on an existing cable-stayed bridge have further validated the influence of the internal damper on the performance of the external damper. The results suggest that the HDR is optimally placed in the guide pipe of the cable-pylon anchorage when installing viscous dampers at one position is insufficient. When an HDR damper or the bushing has to be installed near the external damper, their combined damping effects need to be evaluated using the presented methods.

• Coupled systems mechanics
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• v.5 no.2
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• pp.157-190
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• 2016

This paper deals with frequency analysis of Euler-Bernoulli beams carrying an arbitrary number of Kelvin-Voigt viscoelastic dampers, subjected to harmonic loads. Multiple external/internal dampers occurring at the same position along the beam axis, modeling external damping devices and internal damping due to damage or imperfect connections, are considered. The challenge is to handle simultaneous discontinuities of the response, in particular bending-moment/rotation discontinuities at the location of external/internal rotational dampers, shear-force/deflection discontinuities at the location of external/internal translational dampers. Following a generalized function approach, the paper will show that exact closed-form expressions of the frequency response under point/polynomial loads can readily be derived, for any number of dampers. Also, the exact dynamic stiffness matrix and load vector of the beam will be built in a closed analytical form, to be used in a standard assemblage procedure for exact frequency response analysis of frames.

• Korean Journal of Materials Research
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• v.28 no.3
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• pp.129-134
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• 2018

This study was carried out to investigate the effect of grain size on the damping capacity of the Fe-26Mn-4Co-2Al damping alloy. ${\alpha}^{\prime}$ and ${\varepsilon}-martensite$ were formed by cold working, and these martensites were formed with a specific direction and surface relief. With an increase in grain size, the volume fraction of ${\alpha}^{\prime}$ and ${\varepsilon}-martensite$ increased by decrement the austenite phase stability. This volume fraction more rapidly increased in cold-rolled specimen than in the specimen that was not cold-rolled. The damping capacity also increased more with the augmentation an increased grain size and more rapidly increased in cold-rolled specimen than in the specimen that was not cold rolled. The effect of grain size on the damping capacity was larger in the cold-rolled specimen than the specimen that was not cold-rolled. Damping capacity linearly increased with an increase in volume fraction of ${\varepsilon}-martensite$. Thus, the damping capacity was affected by the ${\varepsilon}-martensite$.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.188-191
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• 1997

In the recent sheet metal forming simulations, it increases to adopt the dynamic explicit method for an effective computation and the elastic-plastic formulation for stress recovery. It is inevitable in the dynamic explicit method that some noises occur and sometimes partly spoil results of simulations. It is severer when complicated contact conditions are included in simulations. An effective method to control these noises is introduction of damping effects. In this paper, the concept of contact damping is introduced in order to suppress noises due to complicated contact conditions. This is checked by analyzing a simple sheet metal forming process(U-bending). From the computational results, it is shown that the contact damping can effectively control the noises due to contacts and develop more reliable internal stress states.