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دسترسی آزاد مقاله
1 - Study on Vibration Band Gap Characteristics of a Branched Shape Periodic Structure Using the GDQR
M Hajhosseini A AbshahiIn this study, a new periodic structure with special vibration band gap properties is introduced. This structure consists of a main beam and several cantilever beam elements connected to this main beam in the branched shape. Two models with different number of beam elem چکیده کاملIn this study, a new periodic structure with special vibration band gap properties is introduced. This structure consists of a main beam and several cantilever beam elements connected to this main beam in the branched shape. Two models with different number of beam elements and geometrical parameters are considered for this periodic structure. The transverse vibrations of beams are solved using the generalized differential quadrature rule (GDQR) method to calculate the first four band gaps of each model. Investigating the influences of geometrical parameters on the band gaps shows that some bands are close to each other for specific ranges of geometrical parameters values. Furthermore, as the number of beam elements increases, the number of close band gaps increases. Having more than two close band gaps means that this periodic structure has a relatively wide band gap in total. Furthermore, this wide band can move to low frequency ranges by changing the geometrical parameters. Absorbing vibrations over a wide band gap at low frequency ranges makes this periodic structure a good vibration absorber. Verification of the analytical method using ANSYS software shows that the GDQR method can be used for vibration analysis of beam-like structures with high accuracy. پرونده مقاله -
دسترسی آزاد مقاله
2 - Exact Closed Form Characteristic Equations for Transverse Vibration of Timoshenko Beams
Shahriar Hosseini-Hashemi K Hosseini-Hashemi R NazemnezhadThe dimensionless equations of motion are derived based on the Timoshenko beam theory to study the transverse vibration of beams without further usage of any approximate method. The exact closed form characteristic equations are given within the validity of the Timoshen چکیده کاملThe dimensionless equations of motion are derived based on the Timoshenko beam theory to study the transverse vibration of beams without further usage of any approximate method. The exact closed form characteristic equations are given within the validity of the Timoshenko beam theory for beams having various boundary conditions. Accurate Eigen frequency parameters are presented for a different length to height ratio for each case. The exact closed form mode shapes related to deflection, slope due to bending and stress resultants are also presented and illustrated for some cases. The modal tests are performed for beams with clamped-Free and Free-Free boundary conditions. Finally, the effect of boundary conditions, length to height ratio on the eigenvalues parameters and vibratory behavior of each distinct case are studied. Validity of the derived closed form characteristic equations are checked through comparison of numerical solutions with the available results. It is believed that in the present work, the exact closed form characteristic equations and their associated Eigen functions, except for the beams with simply supported ends, for the rest of considered cases are obtained for the first time. پرونده مقاله -
دسترسی آزاد مقاله
3 - A New Approach to the Study of Transverse Vibrations of a Rectangular Plate Having a Circular Central Hole
K Torabi A.R AzadiIn this study, the analysis of transverse vibrations of rectangular plate with circular central hole with different boundary conditions is studied and the natural frequencies and natural modes of a rectangular plate with circular hole have been obtained. To solve the pr چکیده کاملIn this study, the analysis of transverse vibrations of rectangular plate with circular central hole with different boundary conditions is studied and the natural frequencies and natural modes of a rectangular plate with circular hole have been obtained. To solve the problem, it is necessary to use both Cartesian and polar coordinate system. The complexity of the method is to apply an appropriate model, which can solve the problem of transverse vibrations of a plate. So, it has been tried that the functions of the deflection of plate, in the form of polynomial functionsproportionate with finite degrees, to be replaced by Bessel function, which is used in the analysis of the vibrations of a circular plate. Then with the help of a semi-analytical method and orthogonality properties of the eliminated position angle, without any need to analyze so many points on the edges of the rectangular plate, we can prevent the coefficients matrix from becoming so much large as well as the equations from becoming complicated. The above mentioned functions will lead to reducing the calculation time and simplifying the equations as well as speeding up the convergence. پرونده مقاله -
دسترسی آزاد مقاله
4 - Axial and Transverse Vibration of SWBNNT System Coupled Pasternak Foundation Under a Moving Nanoparticle Using Timoshenko Beam Theory
A Ghorbanpour Arani A Karamali Ravandi M.A Roudbari M.B Azizkhani A Hafizi BidgoliIn this study, a semi analytical method for transverse and axial vibration of single-walled boron nitride nanotube (SWBNNT) under moving a nanoparticle is presented. The surrounding elastic medium as Pasternak foundation and surface stress effect are included in the for چکیده کاملIn this study, a semi analytical method for transverse and axial vibration of single-walled boron nitride nanotube (SWBNNT) under moving a nanoparticle is presented. The surrounding elastic medium as Pasternak foundation and surface stress effect are included in the formulations of the proposed model. Using Timoshenko beam theory (TBT), Hamilton’s principle and nonlocal piezoelasticity theory, the higher order governing equation is derived. The influences of surface stress effects, spring and shear parameters of Pasternak foundation and aspect ratio are also investigated on the free and forced vibration behavior of SWBNNT under moving a nanoparticle. Through an inclusive parametric study, the importance of using surrounding elastic medium in decrease of normalized dynamic deflection is proposed. It is demonstrated that the values of shear modulus have significant role on the vibration behavior of SWBNNT. The influences of surface stresses on the amplitude of normalized dynamic deflection are also discussed. The output result's of this study has significant influences in design and production of micro electro mechanical system (MEMS) and nano electro mechanical system (NEMS) for advanced applications. پرونده مقاله -
دسترسی آزاد مقاله
5 - Longitudinal-Torsional and Two Plane Transverse Vibrations of a Composite Timoshenko Rotor
M Irani Rahagi A Mohebbi H AfshariIn this paper, two kinds of vibrations are considered for a composite Timoshenko rotor: longitudinal-torsional vibration and two plane transverse one. The kinetic and potential energies and virtual work due to the gyroscopic effects are calculated and the set of six gov چکیده کاملIn this paper, two kinds of vibrations are considered for a composite Timoshenko rotor: longitudinal-torsional vibration and two plane transverse one. The kinetic and potential energies and virtual work due to the gyroscopic effects are calculated and the set of six governing equations and boundary conditions are derived using Hamilton principle. Differential quadrature method (DQM) is used as a strong numerical method and natural frequencies and mode shapes are derived. Effects of the rotating speed and the lamination angle on the natural frequencies are studied for various boundary conditions; meanwhile, critical speeds of the rotor are determined. Two kinds of critical speeds are considered for the rotor: the resonance speed, which happens as rotor rotates near one of the natural frequencies, and the instability speed, which occurs as value of the first natural frequency decreases to zero and rotor becomes instable. پرونده مقاله -
دسترسی آزاد مقاله
6 - Spectral Finite Element Method for Free Vibration of Axially Moving Plates Based on First-Order Shear Deformation Theory
M.R Bahrami S HatamiIn this paper, the free vibration analysis of moderately thick rectangular plates axially moving with constant velocity and subjected to uniform in-plane loads is investigated by the spectral finite element method. Two parallel edges of the plate are assumed to be simpl چکیده کاملIn this paper, the free vibration analysis of moderately thick rectangular plates axially moving with constant velocity and subjected to uniform in-plane loads is investigated by the spectral finite element method. Two parallel edges of the plate are assumed to be simply supported and the remaining edges have any arbitrary boundary conditions. Using Hamilton’s principle, three equations of motion for the plate are developed based on first-order shear deformation theory. The equations are transformed from the time domain into the frequency domain by assuming harmonic solutions. Then, the frequency-dependent dynamic shape functions obtained from the exact solution of the governing differential equations is used to develop the spectral stiffness matrix. By solving a non-standard eigenvalue problem, the natural frequencies and the critical speeds of the moving plates are obtained. The exactness and validity of the results are verified by comparing them with the results in previous studies. By the developed method some examples for vibration of stationary and moving moderately thick plates with different boundary conditions are presented. The effects of some parameters such as the axially speed of plate motion, the in-plane forces, aspect ratio and length to thickness ratio on the natural frequencies and the critical speeds of the moving plate are investigated. These results can be used as a benchmark for comparing the accuracy and precision of the other analytical and numerical methods. پرونده مقاله -
دسترسی آزاد مقاله
7 - Exact Closed-Form Solution for Vibration Analysis of Truncated Conical and Tapered Beams Carrying Multiple Concentrated Masses
K Torabi H Afshari M Sadeghi H ToghianIn this paper, an exact closed-form solution is presented for free vibration analysis of Euler-Bernoulli conical and tapered beams carrying any desired number of attached masses. The concentrated masses are modeled by Dirac’s delta functions which creates no need چکیده کاملIn this paper, an exact closed-form solution is presented for free vibration analysis of Euler-Bernoulli conical and tapered beams carrying any desired number of attached masses. The concentrated masses are modeled by Dirac’s delta functions which creates no need for implementation of compatibility conditions. The proposed technique explicitly provides frequency equation and corresponding mode as functions with only two integration constants which leads to solution of a two by two eigenvalue problem for any number of attached masses. Using Basic functions which are made of the appropriate linear composition of Bessel functions leads to make implementation of boundary conditions much easier. The proposed technique is employed to study effect of quantity, position and translational inertia of the concentrated masses on the natural frequencies and corresponding modes of conical and tapered beams for all standard boundary conditions. Unlike many of previous exact approaches, presented solution has no limitation in number of concentrated masses. In other words, by increase in number of attached masses, there is no considerable increase in computational effort. پرونده مقاله -
دسترسی آزاد مقاله
8 - Free and Forced Transverse Vibration Analysis of Moderately Thick Orthotropic Plates Using Spectral Finite Element Method
M.R Bahrami S HatamiIn the present study, a spectral finite element method is developed for free and forced transverse vibration of Levy-type moderately thick rectangular orthotropic plates based on first-order shear deformation theory. Levy solution assumption was used to convert the two- چکیده کاملIn the present study, a spectral finite element method is developed for free and forced transverse vibration of Levy-type moderately thick rectangular orthotropic plates based on first-order shear deformation theory. Levy solution assumption was used to convert the two-dimensional problem into a one-dimensional problem. In the first step, the governing out-of-plane differential equations are transformed from time domain into frequency domain by discrete Fourier transform theory. Then, the spectral stiffness matrix is formulated, using frequency-dependent dynamic shape functions which are obtained from the exact solution of the governing differential equations. An efficient numerical algorithm, using drawing method is used to extract the natural frequencies. The frequency domain dynamic responses are obtained from solution of the spectral element equation. Also, the time domain dynamic responses are derived by using inverse discrete Fourier transform algorithm. The accuracy and excellent performance of the spectral finite element method is then compared with the results obtained from closed form solution methods in previous studies. Finally, comprehensive results for out-of-plane natural frequencies and transverse displacement of the moderately thick rectangular plates with six different combinations of boundary conditions are presented. These results can serve as a benchmark to compare the accuracy and precision of the numerical methods used. پرونده مقاله -
دسترسی آزاد مقاله
9 - Investigation of Dynamical Behavior (Transverse Vibration) and Instability Analysis of Carbon Nanotubes Conveying Nanofluid
سهیل اویسی حسن نحوی داود طغراییThis work focuses on the dynamical behavior of carbon nanotubes, including vibration, wave propagation and fluid-structure interaction. In the present research, transverse vibration of nano fluid conveying carbon nanotubes is investigated. To this end, based on the nonl چکیده کاملThis work focuses on the dynamical behavior of carbon nanotubes, including vibration, wave propagation and fluid-structure interaction. In the present research, transverse vibration of nano fluid conveying carbon nanotubes is investigated. To this end, based on the nonlocal and strain-inertia gradient continuum elasticity theories and by using rod and Euler-Bernoulli beam models, the system’s dynamical behavior is modeled and then, the governing equation of motion is solved and discretized by applying the weighted-residual Galerkin approximate method. Moreover, effect of considering nano-scale fluid flowing through the nanotube, the boundary conditions, the different elastic mediums and the van der Walls interaction between the layers of multi-walled carbon nanotubes on the natural frequencies, critical velocities and stability of the system are considered. The results show that the passing fluid flow and the axially moving of nanotube decrease the system’s natural frequencies especially for nanotubes with large internal radius and in high fluid flow and axially moving speeds of nanotube. In addition, it is observed that the natural frequencies and stability of the system strongly depend on the small-scale parameter (nano-scale), mainly in the longitudinal vibration پرونده مقاله
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