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Viet L.D.,Vien Co Hoc
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science | Year: 2012

A dynamic vibration absorber moving in the tangential or in the normal direction of a pendulum's orbit can reduce the free vibration of the pendulum. This article discusses the problem of a pendulum structure attached with two dynamic vibration absorbers moving orthogonally at the same time. The analytical optimization is proposed to be done in two steps, in which the parameters of the linear dynamic vibration absorber moving in tangential direction and the non-linear dynamic vibration absorber moving in normal direction are chosen sequentially based on the stability maximization criterion. The analytical analysis shows that the two-dynamic vibration absorber scheme has small benefit in comparison with the single-dynamic vibration absorber scheme. The analytical conclusions are verified by numerical calculations. Although the conclusion of the article is unexpected, it is important in practice because the two-dynamic vibration absorber arrangement can be excluded in the design. © IMechE 2012. Source


Duc Chinh P.,Vien Co Hoc
Journal of the Mechanics and Physics of Solids | Year: 2011

Upper and lower bounds on the effective conductivity of statistically isotropic multicomponent materials in d dimensions (d=2 or 3) are constructed from the minimum energy principles and appropriate trial fields. The trial fields, involving harmonic potentials and free parameters to be optimized, lead to the bounds containing up to three-point correlation information about the microgeometry of a composite. The bounds are applied to give estimates for the symmetric cell materials, which are optimal over some ranges of parameters, and asymmetric multicoated spheres, which yield the exact effective conductivity in certain cases. The results also agree with many known ones. New bounds for random cell polycrystals are obtained and illustrated on a number of polycrystalline aggregates. © 2011 Elsevier Ltd. All rights reserved. Source


Viet L.D.,Vien Co Hoc | Anh N.D.,Vien Co Hoc | Matsuhisa H.,Kyoto University
Journal of Sound and Vibration | Year: 2011

In this paper, the vibration reduction of a pendulum structure with dynamic vibration absorber (DVA) using Coriolis force is investigated. When the pendulum structure is subjected to a single harmonic excitation, the effective damping of Coriolis force is used with the second-order approximations to obtain the closed forms of optimal parameters of the DVA. The closed forms obtained show that the natural frequency of the absorber should be tuned to twice that of the pendulum. The closed forms of optimal parameters are verified by numerical optimization. The modified forms of optimal parameters are proposed to be used in case of general excitation. Base on this modified form, the design procedure is demonstrated by the numerical calculation of the free vibration and wind-induced vibration of a ropeway gondola. © 2010 Elsevier Ltd. All rights reserved. Source


Viet L.D.,Vien Co Hoc | Anh N.D.,Vien Co Hoc | Matsuhisa H.,Kyoto University
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science | Year: 2011

There are two types of dynamic vibration absorbers (DVAs) for vibration reduction of a pendulum structure. The first one moving in the tangential direction of the pendulum's orbit can reduce all kinds of vibrations but the effectiveness is quite poor when the DVA locates near the centre of oscillation. Conversely, the second one moving in the normal direction of the pendulum's orbit can only reduce large vibration but has a good effect when the DVA's location is near the centre of oscillation. In this article, the authors propose the DVA, which can move in the normal and tangential directions at the same time. The proposed DVA can overcome the shortcoming of two DVAs moving in only one direction. Because the system's non-linearity is quite complex, a numerical method is used for obtaining the optimal parameters. Then, the authors introduce the convenient empirical formulas of optimal parameters based on the numerical results. The effect of the proposed DVA is demonstrated by the numerical calculations of free vibration of a ropeway gondola. Source


La V.D.,Vien Co Hoc
Journal of Sound and Vibration | Year: 2012

A passive dynamic vibration absorber (DVA) moving along a pendulum can cause the nonlinear Coriolis damping to reduce the pendulum swing. This paper proposes a simple semi-active on-off damping controller to improve the passive Coriolis DVA. The aim of the on-off damping control is to amplify the DVA resonance motion to increase the energy dissipated. Moreover, the paper finds the analytical solution of the harmonic vibration of semi-active controlled system. The accuracy of the analytical formulas and the superior performance of the semi-active DVA are verified by numerical simulations. © 2012 Elsevier Ltd. All rights reserved. Source

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