• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.2
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• pp.197-207
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• 2002

Energy dissipation capacity and earthquake responses of steel structures installed with unbonded braces(UB) were investigated. Parametric studies were performed for a single-degree-of-freedom structure under harmonic loads, and optimum yield strength of unbonded braces were derived. Nonlinear dynamic time history analyses were carried out to investigate the seismic response of multi-story model structures with UB having various size and strength. Various techniques were applied to determine proper story-wise distribution of UB in multi-story structures. The analysis results show that the maximum displacements of structures generally decrease as the stiffness of UB increases. However for some natural frequencies and seismic loads the maximum displacement and accumulated damage increases as the stiffness of UB increases.

• Journal of Power System Engineering
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• v.16 no.4
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• pp.60-65
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• 2012

This study was carried out to investigate the effect of reverse transformation on the damping capacity in high manganese austenitic stainless steel. ${\alpha}^{\prime}$-martensite was formed with the specific direction and surface relief by deformation. Over 95% of the austenite phase was transformed to deformation-induced ${\alpha}^{\prime}$-martensite by 70% cold rolling. Reverse transformation became rapid above an annealing temperature of $550^{\circ}C$, but there was no significant transformation above $700^{\circ}C$. In addition, with increasing annealing time at $700^{\circ}C$, reverse transformation was induced rapidly, but the transformation was almost completed at 10 min. Damping capacity was increased up to $700^{\circ}C$, and than unchanged with the increasing annealing temperature. Damping capacity increased steeply with an increasing reverse treatment time up to 10min, whereas there were no significant change with a treatment time of more than 10 min. Damping capacity increased with an increasing the reversed austenite and was strongly affected by reversed austenite.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.12
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• pp.27-34
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• 2018

This paper considers the seismic performance of lever-type tuned mass damper(TMD). The lever-type TMD is designed utilizing the seismic-performance of TMD and the control force required for constraining story drift. The TMD is basically designed by tuning the frequency of primary structure. Thus, the TMD plays an important role to reduce the dynamic responses. The lever-type TMD has a merit to control more displacement responses than the existing TMD due to the control forces. It is shown that the optimum design of lever-type TMD is affected by the ratio of the TMD mass with respect to the mass of the primary structure, the damping ration of the primary structure, and the length ratio of the lever. A numerical example exhibits the effectiveness of the dynamic control by the lever-type TMD and its validity is illustrated in a three-story building structure subjected to earthquake.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.5
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• pp.698-705
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• 1986

The dynamic behaviour of bearing-rotor system with flexible and damped supports is systematically investigated. To find out the obvious trend of the influence of the external damping on the resonance peak of a rolling bearing-rotor system and on the stability linit of a cylindrical journal bearing-rotor system, some important characteristic design parameters are derived. Those are the dimensionless stiffness and damping ratio of the external damping refered to the rotor stiffness. For an optimal design of the external damping a relation between the stiffness and damping coefficients can be obtained from the dynamic analysis of the whole system.

• Journal of the KSME
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• v.33 no.10
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• pp.884-891
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• 1993

최근 승용차의 설계는 일반적으로 고속화, 경량화 추세에 있다. 이에 따라 심각하게 대두되고 있는 것이 진동문제로서, 그중에서도 조향계(steering system)의 진동은 보다 쾌적한 승차감 내지 조정성능을 저해하고 운전자에게 불쾌감을 초래하는 진동으로서 이에 대한 개선책이 요구되어 왔다. 따라서 이러한 조향계의 진동인 쉬미(shimmy)현상을 저감시키기 위해서는 다음과 같은 방법등이 있다. 1) 가진원이 되는 타이어의 불균형 질량을 줄이거나 타이어의 정밀도를 증가시키는 방법. 2) 진동전달 경고상의 감쇠특성과 조향계의 강성을 변화시켜 전달률을 줄이는 방법. 3) 차체의 동특성 변화를 통하여 고유진동수를 변화시켜 공진영역을 옮기는 방법. 이 글에서는 쉬미에 큰 영향을 줄 것으로 생각되어지는 여러 중요한 인자들을 단계적으로 포함 시켜가면서 이론해석 결과와 실험결과를 비교 . 검토 . 보완해갈 것이며, 그 결과 이론적으로 쉬미현상을 예측할 수 있는 방안을 제시하고자 한다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.1
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• pp.9-16
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• 2020

The objective of this study is to propose closed-form solutions to the free vibration response of single-degree-of-freedom (SDOF) systems, as part of fundamental research on dynamic systems with Coulomb friction. The motion of a dynamic system with Coulomb friction is described by a nonlinear differential equation, and, due to the variation in the sign of friction force term with the direction of motion, it is difficult to obtain the closed-form solution. To solve this problem, the nonlinear differential equation is directly computed by numerical integration, or an approximated solution is indirectly obtained using a linear differential equation wherein the damping effect due to Coulomb friction is replaced by an equivalent viscous damping term. However, these conventional methods do not provide a closed-form solution from a mathematical point of view. In this regard, closed-form solutions to the free vibration response of SDOF systems with Coulomb friction are derived herein by considering that the sign of the friction force term is reversed in each half-cycle of motion and by expanding it to the entire time history using the power series function. In addition, for a given initial condition, both the number of free vibration half-cycles and the response at the instant when free vibration motion stops are predicted under the condition that the motion of free vibration is stopped when the amplitude of the friction force is higher than that of the restoring force due to stiffness.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.7 s.250
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• pp.750-756
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• 2006

This study predicts the modified eigenvectors and eigenvalues of the non-proportional damped structure due to the change in the mass, damping and stiffness of structure by iterative method of the sensitivity coefficient using the original dynamic characteristic. The method is applied to the non-proportional damped 3 degree of freedom system by modifying the mass, damping and stiffness. The predicted dynamic characteristics are showed a good agreement with these from the structural reanalysis using the modified mass, damping and stiffness.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.04a
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• pp.86-91
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• 1996

In this study, the modal analysis is adopted for the investigation of vibratory characteristics of a rolling stock. A governing equation for this system is deverived on a condition that the rolling stock is in proportional viscous damping and proportional hysteretic damping. By applying this method a computational modal analysis software is developed. The validity and reliability of this method is verified by comparing the results for the above case and with those of a system having proportional viscous damping and a system having general viscous damping. A system that has non-linearity, an error from the calculation may occur in the analysis. In this case, we applied the piecewise linear method to estimate the modal parameters.

• Journal of KSNVE
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• v.7 no.6
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• pp.1039-1048
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• 1997

This paper describes the effects of dual dynamic vibration absorbers attached to a primary vibration system with damping. The efficiency of dual dynamic vibration absorbers was investigated with the height of amplitude ratio at the resonance frequency ratio of the damped vibration system according to mass ratio, natural frequency ratio and damping ratio. The variation of amplitude ratio related to frequency ratio of primary vibration system is verified experimentally and theoretically according to dual dynamic vibration systems using computer program designed to find mutual relationship between two absorbers.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.12
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• pp.129-135
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• 1996

This paper presents the effectiveness of the dynamic vibration absorber consisting of a single mass, coil springs and oil damper on the resonance freauency ratio and amplitude ratio for damped linear systems, that is, primary vibration system with damping. The effects of the dynamic vibration absorber are investigated numerically and experimentally for values of mass ratio, natural frequency ratio, and damping ratio. The experimental results show good agreement with calculated ones. As a result, the characteristics shown by the present work are useful in optimal tuning the dynamic vibration absorber in practice.