• Advances in materials Research
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• v.7 no.3
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• pp.163-174
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• 2018

This article studies the free and forced vibrations of the carbon nanotubes CNTs embedded in an elastic medium including thermal and dynamic load effects based on nonlocal Euler-Bernoulli beam. A Winkler type elastic foundation is employed to model the interaction of carbon nanotube and the surrounding elastic medium. Influence of all parameters such as nonlocal small-scale effects, high temperature change, Winkler modulus parameter, vibration mode and aspect ratio of short carbon nanotubes on the vibration frequency are analyzed and discussed. The non-local Euler-Bernoulli beam model predicts lower resonance frequencies. The research work reveals the significance of the small-scale coefficient, the vibrational mode number, the elastic medium and the temperature change on the non-dimensional natural frequency.

• The Journal of the Acoustical Society of Korea
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• v.18 no.2
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• pp.83-89
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• 1999

The forced vibration of a finite cylindrical shell has been analyzed from an elastic wave viewpoint. The displacement vector is used to formulate the vibration field, that is regarded as a superposition of disturbances due to elastic waves propagating on the shell. The reflection matrix is also used in the formulation of the vibration field, that is easily derived in the present approach. It allows one to easily identify the wave conversion of elastic waves at the ends of the shell. The present approach is used to predict the vibration field of the cylindrical shell with free-free boundary conditions. The contribution of each type of elastic waves into the vibration field was identified, and the wave conversion at the ends of the shell was observed. Those results showed that the present approach can be effectively used to analyze the forced vibration of the cylindrical shell from an elastic wave viewpoint.

• Journal of Korean Association for Spatial Structures
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• v.6 no.2 s.20
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• pp.115-121
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• 2006

In recent years vibration control damper made of low yield point steel is expected to play an important role in controlling structural vibration induced earthquake and wind. But their dynamic characteristics and energy dissipation effects on the whole structure model are not clarified. In this paper, firstly, we presents the results of cyclic tests on low yield steel dampers. Secondly, forced vibration tests on existence three stories steel structure model with low yield point steel dampers are presented. Lastly, it is estimated energy amount which is dissipated through the hysteresis dampers by using two types of analytical models, hysteresis model and equivalent linear model.

• Journal of Energy Engineering
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• v.13 no.4
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• pp.275-280
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• 2004

Augmentation of heat transfer by ultrasonic vibration in pipes are investigated. Measurements of convective heat transfer coefficients on circular pipe walls are made with and without ultrasonic vibration applied to water. These data are compared with each other to quantify the effects of ultrasonic vibration on heat transfer enhancement. Numerical analysis has been also performed in order to extend the ranges of examined temperature and flow rate. FLUENT Ver.6.1 is used to simulate velocity and temperature fields and evaluate heat transfer coefficient with and without ultrasonic vibration. The results show that the ultra- sonic vibration enhances the Nusselt number of forced convection flow and the increase rate strongly depends on flow rate.

• Advances in nano research
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• v.8 no.1
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• pp.25-36
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• 2020

Rotating systems concern with torsional vibration, and it should be considered in vibration analysis. To do this, the time-dependent torsional vibrations in a single-walled carbon nanotube (SWCNT) under the linear and harmonic external torque, are investigated in this paper. Eringen's nonlocal elasticity theory is considered to demonstrate the nonlocality and constitutive relations. Hamilton's principle is established to derive the governing equation of motion and consequently related boundary conditions. An analytical method, called the Galerkin method, is utilized to discretize the driven differential equations. Linear and harmonic torsional loads, along with determined amplitude, are applied to the SWCNT as the external torques. SWCNT is considered under the clamped-clamped end supports. In free vibration, analysis of small scale effect reveals the capability of natural frequencies in different modes, and this results desirably are in coincidence with another study. The forced torsional vibration in the time domain, especially for carbon nanotubes, has not been done before in the previous works. The previous forced studies were devoted to the transverse vibrations. It should be emphasized that the dynamical analysis of torsion is novel, workable, and at the beginning of the path. The variations of nonlocal parameter, CNT's thickness, and the influence of excitation frequency on time-dependent angular displacement and nondimensional angular displacement are investigated in the context.

• Advances in nano research
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• v.14 no.4
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• pp.335-353
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• 2023

The possibility of energy harvesting as well as controlled vibration of a three-layered beam consisting of two piezoelectric layer and one core layer made of nonpiezoelectric material is investigated using paradox-free local/nonlocal theory. The three-layered nanobeam is resting on an elastic foundation and subjected to a blast load. Also, the core layer is made of Nano-composites reinforced by CNTs and carbon fibers (MHCD). Governing equations as well as boundary conditions are obtained using Hamilton,s principle. The equations discretized by Generalized Differential Quadrature Method (GDQM) and solved by Newmark beta method. In addition, two differential and integral gains are employed for controlling the forced vibration. The size-dependency of the elastic foundation is considered using two-phase elasticity. The effect of elastic foundation, control gains, nonlocal factor, as well as parameters affecting the core material on the forced vibration and energy harvesting is investigated in detail. The equations as well as solution procedure is validated utilizing some compassion studies. This work can be a basis for future studies on energy harvesting and controlled vibration in small scales.

• Steel and Composite Structures
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• v.35 no.6
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• pp.765-777
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• 2020

In the context of classic conical shell formulation, nonlinear forced vibration analysis of truncated conical shells and annular plates made of multi-scale epoxy/CNT/fiberglass composites has been presented. The composite material is reinforced by carbon nanotube (CNT) and also fiberglass for which the material properties are defined according to a 3D Mori-Tanaka micromechanical scheme. By utilizing the Jacobi elliptic functions, the frequency-deflection curves of truncated conical shells and annular plates related to their forced vibrations have been derived. The main focus is to study the influences of CNT amount, fiberglass volume, open angle, fiber angle, truncated distance and force magnitude on forced vibrational behaviors of multi-scale truncated conical shells and annular plates.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.6
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• pp.175-180
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• 2001

Dynamic response localization of simple mistuned periodic structures is presented in this paper Mistuning in periodic structures can cause forced responses that are much larger than those of perfectly tuned structures. So mistuning results in the critical impact on high cycle fatigue of structures. Thus, it is of great importance to predict the mistuned forced response in an efficient way. In this paper, forced responses of coupled pendulum systems are investigated to identify the localization effect of periodic structures. The effects of mistuning and damping on the maximum forced response are examined. It is found that certain conditions of mistuning and coupling can cause strong localization and the localization becomes significant under weak damping. It is also found that the maximum forced response increases as the number of Periodic structures increases.

• Computers and Concrete
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• v.32 no.6
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• pp.553-565
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• 2023

This work is the first to apply nonlocal theory and a variety of deformation plate theories to study the issue of forced vibration and buckling in organic nanoplates, where the effect of the drag parameter inside the structure has been taken into consideration. Whereas previous research on nanostructures has treated the nonlocal parameter as a fixed value, this study accounts for its effect, and finds that its value fluctuates with the thickness of each layer. This is also a new point that no works have mentioned for organic plates. On the foundation of the notion of potential movement, the equilibrium equation is derived, the buckling issue is handled using Navier's solution, and the forced oscillation problem is solved using the finite element approach. Additionally, a set of numerical examples exhibiting the forced vibration and buckling response of organic nanoplates are shown. These findings indicate that the nonlocal parameter and the drag parameter of the structure have a substantial effect on the mechanical responses of organic nanoplates.

• Smart Structures and Systems
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• v.18 no.6
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• pp.1125-1143
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• 2016

Forced vibration analysis of a simple supported viscoelastic nanobeam is studied based on modified couple stress theory (MCST). The nanobeam is excited by a transverse triangular force impulse modulated by a harmonic motion. The elastic medium is considered as Winkler-Pasternak elastic foundation.The damping effect is considered by using the Kelvin-Voigt viscoelastic model. The inclusion of an additional material parameter enables the new beam model to capture the size effect. The new non-classical beam model reduces to the classical beam model when the length scale parameter is set to zero. The considered problem is investigated within the Timoshenko beam theory by using finite element method. The effects of the transverse shear deformation and rotary inertia are included according to the Timoshenko beam theory. The obtained system of differential equations is reduced to a linear algebraic equation system and solved in the time domain by using Newmark average acceleration method. Numerical results are presented to investigate the influences the material length scale parameter, the parameter of the elastic medium and aspect ratio on the dynamic response of the nanobeam. Also, the difference between the classical beam theory (CBT) and modified couple stress theory is investigated for forced vibration responses of nanobeams.