• Steel and Composite Structures
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• 제35권4호
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• pp.545-554
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• 2020

The present paper explores nonlinear dynamical properties of piezo-magnetic beams based on a nonlocal refined higher-order beam formulation and piezoelectric phase effect. The piezoelectric phase increment may lead to improved vibrational behaviors for the smart beams subjected to magnetic fields and external harmonic excitation. Nonlinear governing equations of a nonlocal intelligent beam have been achieved based upon the refined beam model and a numerical provided has been introduced to calculate nonlinear vibrational curves. The present study indicates that variation in the volume fraction of piezoelectric ingredient has a substantial impact on vibrational behaviors of intelligent nanobeam under electrical and magnetic fields. Also, it can be seen that nonlinear free/forced vibrational behaviors of intelligent nanobeam have dependency on the magnitudes of induced electrical voltages, magnetic potential, stiffening elastic substrate and shear deformation.

• Computers and Concrete
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• 제24권6호
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• pp.579-586
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• 2019

In this research paper, the free vibrational behavior of the simply supported FG nano-plate is studied using the nonlocal two variables integral refined plate theory. The present model takes into account the small scale effect. The effective's properties of the plate change according to the power law variation (P-FGM). The equations of motion of the system are determined and resolved via Hamilton's principle and Navier procedure, respectively. The validity and efficiency of the current model are confirmed by comparing the results with those given in the literature. At the last section, several numerical results are presented to show the various parameters influencing the vibrational behavior such as the small-scale effect, geometry ratio, material index and aspect ratio.

• Steel and Composite Structures
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• 제46권3호
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• pp.367-383
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• 2023

In this investigation, an improved integral trigonometric shear deformation theory is employed to examine the vibrational behavior of the functionally graded (FG) sandwich plates resting on visco-Pasternak foundations. The studied structure is modelled with only four unknowns' variables displacements functions. The simplicity of the developed model being in the reduced number of variables which was made with the help of the use of the indeterminate integral in the formulation. The current kinematic takes into consideration the shear deformation effect and does not require any shear correction factors as used in the first shear deformation theory. The equations of motion are determined from Hamilton's principle with including the effect of the reaction of the visco-Pasternak's foundation. A Galerkin technique is proposed to solve the differentials governing equations, which enables one to obtain the semi-analytical solutions of natural frequencies for various clamped and simply supported FG sandwich plates resting on visco-Pasternak foundations. The validity of proposed model is checked with others solutions found in the literature. Parametric studies are performed to illustrate the impact of various parameters as plate dimension, layer thickness ratio, inhomogeneity index, damping coefficient, vibrational mode and elastic foundation on the vibrational behavior of the FG sandwich plates.

• Earthquakes and Structures
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• 제24권2호
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• pp.127-140
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• 2023

The vibration of microtubule in human cells is the source of electrical field around it and inside cell structure. The induction of electrical field is a direct result of the existence of dipoles on the surface of the microtubules. Measuring the electrical fields could be performed using nano-scale sensors and the data could be transformed to other computers using internet of things (IoT) technology. Processing these data is feasible by artificial intelligence-based methods. However, the first step in analyzing the vibrational behavior is to study the mechanics of microtubules. In this regard, the vibrational behavior of the microtubules is investigated in the present study. A shell model is utilized to represent the microtubules' structure. The displacement field is assumed to obey first order shear deformation theory and classical theory of elasticity for anisotropic homogenous materials is utilized. The governing equations obtained by Hamilton's principle are further solved using analytical method engaging Navier's solution procedure. The results of the analytical solution are used to train, validate and test of the deep neural network. The results of the present study are validated by comparing to other results in the literature. The results indicate that several geometrical and material factors affect the vibrational behavior of microtubules.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 춘계학술대회논문집; 경주코오롱호텔; 22-23 May 1997
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• pp.229-234
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• 1997

The dynamic behavior of underground structures is complex due to the effects of vibrational characteristics of the structure and the rock. In this study, dynamic displacement responses at the structure surface by the elastic stress waves are considered as the vibrational characteristics, and evaluated by the form of the frequency spectrum. The variation of the vibrational characteristic is simulated by numerical analysis at the case of the structure has internal defections. The results reveals the possibility of the experimental detection of void existence and size. Furthermore, the verification of the dynamic response can be used for rating the stability of a tunnel.

• Steel and Composite Structures
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• 제25권6호
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• pp.649-661
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• 2017

This paper is motivated by the lack of studies in the technical literature concerning to the influence of carbon nanotubes (CNTs) waviness and aspect ratio on the vibrational behavior of functionally graded nanocomposite annular sector plates resting on two-parameter elastic foundations. The carbon nanotube-reinforced (CNTR) plate has smooth variation of CNT fraction based on the power-law distribution in the thickness direction, and the material properties are also estimated by the extended rule of mixture. In this study, the classical theory concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube random contact, which explicitly accounts for the progressive reduction of the tubes' effective aspect ratio as the filler content increases. Parametric studies are carried out to highlight the influence of CNTs volume fraction, waviness and aspect ratio, boundary conditions and elastic foundation on vibrational behavior of FG-CNT thick sectorial plates. The study is carried out based on three-dimensional theory of elasticity and in contrary to two-dimensional theories, such as classical, the first- and the higher-order shear deformation plate theories, this approach does not neglect transverse normal deformations. The annular sector plate is assumed to be simply supported in the radial edges while any arbitrary boundary conditions are applied to the other two circular edges including simply supported, clamped and free. For an overall comprehension on 3-D vibration of annular sector plates, some mode shape contour plots are reported in this research work.

• Geomechanics and Engineering
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• 제35권4호
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• pp.367-383
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• 2023

The present paper examines the natural frequency responses of the bi-directional (n_x-n_y, n_y-n_z and n_z-n_x) and multidirectional (n_x-n_y-n_z) functionally graded (FG) plate and curved structures with and without porosity. The even and uneven kind of porosity pattern are considered to observe the influence of porosity type and porosity index. The numerical findings have been obtained using a higher order shear deformation theory (HSDT) based isometric finite element (FE) approach generated in a MATLAB platform. According to the convergence and validation investigation, the proposed HSDT based FE model is adequate to predict free vibrational responses of multidirectional porous FG plates and curved structures. Further a parametric analysis is carried out by taking various design parameters into account. The free vibrational behavior of bidirectional (2D) and multidirectional (3D) perfect-imperfect FGM structure is examined against various power law index, support conditions, aspect, and thickness ratio, and for the curvature of curved structures. The results indicate that the maximum non-dimensional fundamental frequency (NFF) value is observed in perfect FGM plates and curved structures compared to porous FGM plates and curved structures and it is maximum for FGM plates and curved structures with uneven kind of porosity than even porosity.

• Bulletin of the Korean Chemical Society
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• 제27권12호
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• pp.2028-2036
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• 2006

The combined ab initio and vibrational predissociation (VP) spectroscopic studies on methylammonium-$(water)_4$ complex aimed at understanding the hydration behavior of an amphiphilic ion core are described. The ab initio calculations predicted eleven low-energy isomers forming cyclic, tripod, chain, and caged structures, and their relative stabilities, total hydration energies and thermodynamic functions at 298 K and 150 K. The excellent correlation between the observed VP spectra and ab initio spectra for bonded N-H, bonded O-H and free O-H stretches suggested co-existence of five cyclic isomers and two non-cyclic isomers in ion beam at 150 K, consistent with the trends of calculated Gibbs free energies.

• Bulletin of the Korean Chemical Society
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• 제13권4호
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• pp.385-388
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• 1992

The transition probabilities for the thermal intramolecular electron transfer and the optical intervalence transfer band for a symmetric mixed-valence Cu(I)-Cu(II) compound were used to extract the PKS parameters $\varepsilon$ = -1.15, ${\lambda}$ = 2.839, and ${\nu}g$- = 923 $cm^{-1}$. These parameters determine the potential energy surfaces and vibronic energy levels. Three pairs of vibrational levels are below the top of the energy barrier in the lower potential surface. The contribution of each vibrational state to the intramolecular electron transfer was calculated. It is shown that the three pairs of vibrational states below the top of the barrier are responsible for most of the electron transfer at 261-306 K. So the intramolecular electron transfer in this system is a tunneling process. The transition probability exhibits the usual high-temperature Arrhenius behavior, but at lower temperature falls off to a temperature-independent value as tunneling from the lowest levels becomes the limiting process.

• Bulletin of the Korean Chemical Society
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• 제15권3호
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• pp.228-236
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• 1994

The effect of the vibration mode coupling induced by the vibration-rotation interaction on total energy was investigated for the states with zero total angular momentum(J=0) in a quasilinear symmetric triatomic molecule of $AB_2$ type using a model potential function with a slight potential barrier to linearity. It is found that the coupling energy becomes larger for the levels of bend and asymmetric stretch modes and smaller for symmetric stretch mode as the excitation of the vibrational modes occurs. The results for the real molecule of $CH_2^+$, which is quasilinear, generally agree with the results for the model potential function in that common mode selective dependence of coupling energy is exhibited in both cases. The differences between the results for the model and real potential function in H-C-H system are analyzed and explained in terms of heavy mixing of the symmetric stretch and bend mode in excited vibrational states of the real molecule of $CH_2^+$. It is shown that the vibrational mode coupling in the potential energy function is primarily responsible for the broken nodal structure and chaotic behavior in highly excited levels of $CH_2^+$ for J= 0.