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دسترسی آزاد مقاله
1 - Finite element formulation for the free vibration analysis of embedded double-walled carbon nanotubes based on nonlocal Timoshenko beam theory
Milad Hemmatnezhad Reza AnsariAbstractThe present paper is concerned with the free vibration analysis of double-walled carbon nanotubes embedded in an elastic medium and based on Eringen's nonlocal elasticity theory. The effects of the transverse shear deformation and rotary inertia are included acc چکیده کاملAbstractThe present paper is concerned with the free vibration analysis of double-walled carbon nanotubes embedded in an elastic medium and based on Eringen's nonlocal elasticity theory. The effects of the transverse shear deformation and rotary inertia are included according to the Timoshenko beam theory. The governing equations of motion which are coupled with each other via the van der Waals interlayer forces have been derived using Hamilton's principle. The thermal effect is also incorporated into the formulation. Using the statically exact beam element with displacement fields based on the first order shear deformation theory, the finite element method is employed to discretize the coupled governing equations which are then solved to find the natural frequencies. The effects of the small scale parameter, boundary conditions, thermal effect, changes in material constant of the surrounding elastic medium, and geometric parameters on the vibration characteristics are investigated. Furthermore, our analysis includes nonlocal double-walled carbon nanotubes with different boundary conditions between inner and outer tubes which seem to be scarcely considered in the literature, and the corresponding given results for this case can be considered as a benchmark for further studies. Comparison of the present numerical results with those from the open literature shows an excellent agreement. پرونده مقاله -
دسترسی آزاد مقاله
2 - Modelling of Non-Uniform Piezoelectric Micro-Cantilever in Different Environments
Mitra Taghizade A. H. Korayem M. H. KorayemIn recent years, Atomic Force Microscopy (AFM) has been known as a powerful and efficient tool for surface imaging in different environment. To enhance image quality and more precise prediction of Micro-cantilever (MC) behaviour, accuracy in the MC modeling and simulati چکیده کاملIn recent years, Atomic Force Microscopy (AFM) has been known as a powerful and efficient tool for surface imaging in different environment. To enhance image quality and more precise prediction of Micro-cantilever (MC) behaviour, accuracy in the MC modeling and simulation and detecting the MC sensitivity to geometric parameters has great importance. To model the vibration motion of the AFM non-uniform piezoelectric MC, Timoshenko beam theory is used in order to consider the effect of shear effect in air and liquid environment. In addition, the effect of the forces imposed by the ambient and sample surface is considered. Frequency response has been studied in the air and different liquid environments and the obtained results have been compared with experiential results as well as with results obtained from Euler-Bernoulli beam theory that is reflective of higher precision exercised in the modeling in respect to Euler-Bernoulli beam theory. Efast statistical method, which is found efficient and quick in the survey of linear and nonlinear models and takes the inter-parameter coupling effect into consideration besides calculating the sensitivities unique to each of the factors, has been applied in order to analyse the geometrical parameters’ effects on the MC natural frequencies in the air and water environments. پرونده مقاله -
دسترسی آزاد مقاله
3 - Minimum Stiffness and Optimal Position of an Intermediate Elastic Support to Maximize the Fundamental Frequency of a Vibrating Timoshenko Beam using Finite Element Method and Multi-Objective Genetic Algorithm
Hossein Ebrahimi Farshad Kakavand Hasan SeidiThis paper explores the optimal position and minimum stiffness of two intermediate supports to maximize the fundamental natural frequency of a vibrating cantilever Timoshenko beam with tip mass using Finite Element Method (FEM) and a multi-objective genetic algorithm (G چکیده کاملThis paper explores the optimal position and minimum stiffness of two intermediate supports to maximize the fundamental natural frequency of a vibrating cantilever Timoshenko beam with tip mass using Finite Element Method (FEM) and a multi-objective genetic algorithm (GA). After validating the results by comparison to previous works, the effects of the mass ratio and the position and stiffness of intermediate elastic support on the fundamental frequency are investigated. The numerical results demonstrated that as mass ratio increases, the optimal position moves toward the tip mass, and minimum stiffness increases. In many practical applications, it is not possible to place intermediate support in the optimal position; therefore, the minimum stiffness does not exist. In order to overcome this issue, a tolerance zone is considered, and design curves are proposed. The simultaneous optimization of the first and second natural frequencies of the beam with two intermediate supports was carried out using the genetic algorithm (GA) and the multi-objective GA. It was found that the optimization of the first and second natural frequencies did not require the two supports to have the same and high stiffness. The stiffness and optimal positions of the two supports differ at different mass ratios. Moreover, to optimize the first natural frequency, the second support should be stiffer, while the optimization of the second natural frequency requires the higher stiffness of the first support. پرونده مقاله -
دسترسی آزاد مقاله
4 - Vibration Analysis of Rotary Tapered Axially Functionally Graded Timoshenko Nanobeam in Thermal Environment
N Shafiei M Hamisi M GhadiriIn this paper, vibration analysis of rotary tapered axially functionally graded (AFG) Timoshenko nanobeam is investigated in a thermal environment based on nonlocal theory. The governing equations of motion and the related boundary conditions are derived by means of Ham چکیده کاملIn this paper, vibration analysis of rotary tapered axially functionally graded (AFG) Timoshenko nanobeam is investigated in a thermal environment based on nonlocal theory. The governing equations of motion and the related boundary conditions are derived by means of Hamilton’s principle based on the first order shear deformation theory of beams. The solution method is considered using generalized differential quadrature element (GDQE) method. The accuracy of results are validated by other results reported in other references. The effect of various parameters such as AFG index, rate of cross section change, angular velocity, size effect and boundary conditions on natural frequencies are discussed comprehensively. The results show that with increasing angular velocity, non-dimensional frequency is increased and it depends on size effect parameter. Also, in the zero angular velocity, it can be seen with increasing AFG index, the frequencies are reducing, but in non-zero angular velocity, AFG index shows complex behavior on frequency. پرونده مقاله -
دسترسی آزاد مقاله
5 - An Approximate Solution of Functionally Graded Timoshenko Beam Using B-Spline Collocation Method
D Mahapatra Sh Sanyal Sh BhowmickCollocation methods are popular in providing numerical approximations to complicated governing equations owing to their simplicity in implementation. However, point collocation methods have limitations regarding accuracy and have been modified upon with the application چکیده کاملCollocation methods are popular in providing numerical approximations to complicated governing equations owing to their simplicity in implementation. However, point collocation methods have limitations regarding accuracy and have been modified upon with the application of B-spline approximations. The present study reports the stress and deformation behavior of shear deformable functionally graded cantilever beam using B-spline collocation technique. The material grading is along the beam height and varies according to power law. Poisson’s ratio is assumed to be a constant. The equations are derived using virtual work principle in the framework of Timoshenko beams to obtain a unified formulation for such beams. A sixth order basis function is used for approximation and collocation points are generated using Greville abscissa. Deformation and stresses; bending (axial) stresses and transverse (shear) stresses, and position of neutral axis are studied for a wide range of power law index values. The results are reported along the beam cross-section and beam length. پرونده مقاله -
دسترسی آزاد مقاله
6 - Nonlinear Modeling of Bolted Lap Jointed Structure with Large Amplitude Vibration of Timoshenko Beams
M Jamal-Omidi F AdelThis paper aims at investigating the nonlinear behavior of a system which is consisting of two free-free beams which are connected by a nonlinear joint. The nonlinear system is modelled as an in-extensional beam with Timoshenko beam theory. In addition, large amplitude چکیده کاملThis paper aims at investigating the nonlinear behavior of a system which is consisting of two free-free beams which are connected by a nonlinear joint. The nonlinear system is modelled as an in-extensional beam with Timoshenko beam theory. In addition, large amplitude vibration assumption is taken into account in order to obtain exact results. The nonlinear assumption in the system necessities existence of the curvature-related and inertia-related nonlinearities. The nonlinear partial differential equations of motion for the longitudinal, transverse, and rotation are derived using the Hamilton’s principle. A set of coupled nonlinear ordinary differential equations are further obtained with the aid of Galerkin method. The frequency-response curves are presented in the section of numerical results to demonstrate the effect of the different dimensionless parameters. It is shown that the nonlinear bolted-lap joint structure exhibits a hardening-type behavior. Furthermore, it is found that by adding a nonlinear spring the system exhibits a stronger hardening-type behavior. In addition, it is found that the system shows nonlinear behavior even in the absence of the nonlinear spring due to the nonlocal nonlinearity assumption. Moreover, it is shown that considering different engineering beam theories lead to different results and it is found that the Euler-Bernoulli beam theory over-predict the resonance frequency of the structure by ignoring rotary inertia and shear deformation. پرونده مقاله -
دسترسی آزاد مقاله
7 - Size-Dependent Forced Vibration Analysis of Three Nonlocal Strain Gradient Beam Models with Surface Effects Subjected to Moving Harmonic Loads
K Rajabi Sh Hosseini Hashemi A.R NezamabadiThe forced vibration behaviors are examined for nonlocal strain gradient nanobeams with surface effects subjected to a moving harmonic load travelling with a constant velocity in terms of three beam models namely, the Euler-Bernoulli, Timoshenko and modified Timoshenko چکیده کاملThe forced vibration behaviors are examined for nonlocal strain gradient nanobeams with surface effects subjected to a moving harmonic load travelling with a constant velocity in terms of three beam models namely, the Euler-Bernoulli, Timoshenko and modified Timoshenko beam models. The modification for nonlocal strain gradient Timoshenko nanobeams is exerted to the constitutive equations by exclusion of the nonlocality in the shear constitutive relation. Some analytical closed-form solutions for three nonlocal strain gradient beam models with simply supported boundary conditions are derived by using the Galerkin discretization method in conjunction with the Laplace transform method. The effects of the three beam models, the nonlocal and material length scale parameters, the velocity and excitation frequency of the moving harmonic load on the dynamic behaviors of nanobeams are discussed in some detail. Specifically, the critical velocities are examined in some detail. Numerical results have shown that the aforementioned parameters are very important factors for determining the dynamic behavior of the nanobeams accurately. پرونده مقاله -
دسترسی آزاد مقاله
8 - Vibration of Timoshenko Beam-Soil Foundation Interaction by Using the Spectral Element Method
S Hamioud S Khalfallah S BoudaaThis article presents an analysis of free vibration of elastically supported Timoshenko beams by using the spectral element method. The governing partial differential equation is elaborated to formulate the spectral stiffness matrix. Effectively, the non classical end b چکیده کاملThis article presents an analysis of free vibration of elastically supported Timoshenko beams by using the spectral element method. The governing partial differential equation is elaborated to formulate the spectral stiffness matrix. Effectively, the non classical end boundary conditions of the beam are the primordial task to calibrate the phenomenon of the Timoshenko beam-soil foundation interaction. Non-dimensional natural frequencies and shape modes are obtained by solving the partial differential equations, numerically. Upon solving the eigenvalue problem, non-dimensional frequencies are computed for the first three modes of vibration. Obtained results of this study are intended to describe multiple objects, such as: (1) the establishment of the modal analysis with and without elastic springs, (2) the quantification of the influence of the beam soil foundation interaction, (3) the influence of soil foundation stiffness’ on free vibration characteristics of Timoshenko beam. For this propose, the first three eigenvalues of Timoshenko beam are calculated and plotted for various stiffness of translational and rotational springs. پرونده مقاله -
دسترسی آزاد مقاله
9 - A Comparison Between the Linear and Nonlinear Dynamic Vibration Absorber for a Timoshenko Beam
H Kouhi R Ansari E Salahshoor B Miripour FardDynamic vibration absorbers (DVAs) play an important role in the energy dissipation of a vibrating system. Undesirable vibrations of structures can be reduced by using the absorbers. This paper investigates the effect of an attached energy sink on the energy dissipation چکیده کاملDynamic vibration absorbers (DVAs) play an important role in the energy dissipation of a vibrating system. Undesirable vibrations of structures can be reduced by using the absorbers. This paper investigates the effect of an attached energy sink on the energy dissipation of a simply supported beam subjected to harmonic excitation. The aim is to design an optimal linear energy sink (LES) and a nonlinear energy sink (NES) and then compare them with each other. Each absorber includes a spring, a mass, and a damper. For each absorber, the optimum mass, stiffness, and damping coefficients are obtained in order to minimize the beam’s maximum amplitude at the resonant frequencies. The optimization problem is minimizing the maximum amplitude of the beam subjected to an arbitrary harmonic force excitation. For consideration of the effects of rotary inertia and shear deformation, the Timoshenko beam theory is used. The mathematical model of beam with DVA is verified by using the ANSYS WORKBENCH software. Finally, by considering the uncertainty on the DVA parameters it was observed that the LES is more robust than the NES. پرونده مقاله -
دسترسی آزاد مقاله
10 - Nonlinear Free Vibration Analysis of Functionally Graded Sandwich Beam with Magnetorheological Fluid Core Using Timoshenko Beam Theory
O Miraliyari S Jafari Mehrabadi M.M NajafizadehIn this paper, the analysis of nonlinear free vibrations of beams made of functionally graded materials with magnetorheological fluid as core is investigated. It is assumed that the beam is made of three layers including constraining layer, magnetorheological fluid and چکیده کاملIn this paper, the analysis of nonlinear free vibrations of beams made of functionally graded materials with magnetorheological fluid as core is investigated. It is assumed that the beam is made of three layers including constraining layer, magnetorheological fluid and base layer and is located on Simply-Simply, Clamped-Simply and Clamped–Clamped supports. The governing equations of the beam are derived using the Hamilton’s principle. To obtain the vibrational frequencies, the theory of Timoshenko beam is used by the Generalized Differential Quadrature method. The effects of magnetic field intensity, power law exponents, core thickness and constraining layer thickness and the length of the beam on natural frequency and modal loss factor related to different frequencies modes for the three boundary conditions have been investigated. The results show the effects of physical and geometrical parameters regarding the natural frequency and modal loss factor of the sandwich beam with different modes. Also, the frequency and loss factor values obtained from Generalized Differential Quadrature method are very close to the results obtained by the Finite Element method. This shows the accuracy and precision of this method. پرونده مقاله -
دسترسی آزاد مقاله
11 - 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
12 - A Nonlocal First Order Shear Deformation Theory for Vibration Analysis of Size Dependent Functionally Graded Nano beam with Attached Tip Mass: an Exact Solution
M Ghadiri A JafariIn this article, transverse vibration of a cantilever nano- beam with functionally graded materials and carrying a concentrated mass at the free end is studied. Material properties of FG beam are supposed to vary through thickness direction of the constituents according چکیده کاملIn this article, transverse vibration of a cantilever nano- beam with functionally graded materials and carrying a concentrated mass at the free end is studied. Material properties of FG beam are supposed to vary through thickness direction of the constituents according to power-law distribution (P-FGM). The small scale effect is taken into consideration based on nonlocal elasticity theory of Eringen. The nonlocal equations of motion are derived based on Timoshenko beam theory in order to consider the effect of shear deformation and rotary inertia. Hamilton’s principle is applied to obtain the governing differential equation of motion and boundary conditions and they are solved applying analytical solution. The purpose is to study the effects of parameters such as tip mass, small scale, beam thickness, power-law exponent and slenderness on the natural frequencies of FG cantilever nano beam with a point mass at the free end. It is explicitly shown that the vibration behavior of a FG Nano beam is significantly influenced by these effects. The response of Timoshenko Nano beams obtained using an exact solution in a special case is compared with those obtained in the literature and is found to be in good agreement. Numerical results are presented to serve as benchmarks for future analyses of FGM cantilever Nano beams with tip mass. پرونده مقاله -
دسترسی آزاد مقاله
13 - Non Uniform Rational B Spline (NURBS) Based Non-Linear Analysis of Straight Beams with Mixed Formulations
R Ranjan J.N ReddyDisplacement finite element models of various beam theories have been developed traditionally using conventional finite element basis functions (i.e., cubic Hermite, equi-spaced Lagrange interpolation functions, or spectral/hp Legendre functions). Various finite element چکیده کاملDisplacement finite element models of various beam theories have been developed traditionally using conventional finite element basis functions (i.e., cubic Hermite, equi-spaced Lagrange interpolation functions, or spectral/hp Legendre functions). Various finite element models of beams differ from each other in the choice of the interpolation functions used for the transverse deflection w, total rotation , and/or shear strain , as well as the variational method used (e.g., collocation, weak form Galerkin, or least-squares). When nonlinear shear deformation theories are used, the displacement finite element models experience membrane and shear locking. The present study is concerned with development of alternative beam finite elements using both uniform and non-uniform rational b-splines (NURBS) to eliminate shear and membrane locking in an hpk finite element setting for both the Euler-Bernoulli beam and Timoshenko beam theories. Both linear and non-linear analysis are performed using mixed finite element models of the beam theories studied. Results obtained are compared with analytical (series) solutions and non-linear finite element and spectral/hp solutions available in the literature, and excellent agreement is found for all cases. پرونده مقاله -
دسترسی آزاد مقاله
14 - Nonlinear Finite Element Analysis of Bending of Straight Beams Using hp-Spectral Approximations
R RanjanDisplacement finite element models of various beam theories have been developed using traditional finite element interpolations (i.e., Hermite cubic or equi-spaced Lagrange functions). Various finite element models of beams differ from each other in the choice of the in چکیده کاملDisplacement finite element models of various beam theories have been developed using traditional finite element interpolations (i.e., Hermite cubic or equi-spaced Lagrange functions). Various finite element models of beams differ from each other in the choice of the interpolation functions used for the transverse deflection w, total rotation φ and/or shear strain γxz, or in the integral form used (e.g., weak form or least-squares) to develop the finite element model. The present study is concerned with the development of alternative beam finite elements using hp-spectral nodal expansions to eliminate shear and membrane locking. Both linear and non-linear analysis are carried out using both displacement and mixed finite element models of the beam theories studied. Results obtained are compared with both analytical (series) solutions and non-linear finite element solutions from literature, and excellent agreement is found for all cases. پرونده مقاله -
دسترسی آزاد مقاله
15 - A Comparative Study of Least-Squares and the Weak-Form Galerkin Finite Element Models for the Nonlinear Analysis of Timoshenko Beams
W Kim J.N ReddyIn this paper, a comparison of weak-form Galerkin and least-squares finite element models of Timoshenko beam theory with the von Kármán strains is presented. Computational characteristics of the two models and the influence of the polynomial orders used on چکیده کاملIn this paper, a comparison of weak-form Galerkin and least-squares finite element models of Timoshenko beam theory with the von Kármán strains is presented. Computational characteristics of the two models and the influence of the polynomial orders used on the relative accuracies of the two models are discussed. The degree of approximation functions used varied from linear to the 5th order. In the linear analysis, numerical results of beam bending under different types of boundary conditions are presented along with exact solutions to investigate the degree of shear locking in the newly developed mixed finite element models. In the nonlinear analysis, convergences of nonlinear finite element solutions of newly developed mixed finite element models are presented along with those of existing traditional model to compare the performance. پرونده مقاله -
دسترسی آزاد مقاله
16 - Vibration Response of an Elastically Connected Double-Smart Nanobeam-System Based Nano-Electro-Mechanical Sensor
A Ghorbanpour Arani S.A Mortazavi R Kolahchi A.H Ghorbanpour AraniNonlocal vibration of double-smart nanobeam-systems (DSNBSs) under a moving nanoparticle is investigated in the present study based on Timoshenko beam model. The two smart nanobeams (SNB) are coupled by an enclosing elastic medium which is simulated by Pasternak foundat چکیده کاملNonlocal vibration of double-smart nanobeam-systems (DSNBSs) under a moving nanoparticle is investigated in the present study based on Timoshenko beam model. The two smart nanobeams (SNB) are coupled by an enclosing elastic medium which is simulated by Pasternak foundation. The energy method and Hamilton’s principle are used to establish the equations of motion. The detailed parametric study is conducted, focusing on the combined effects of the nonlocal parameter, elastic medium coefficients, external voltage, length of SNB and the mass of attached nanoparticle on the frequency of piezoelectric nanobeam. The results depict that the imposed external voltage is an effective controlling parameter for vibration of the piezoelectric nanobeam. Also increase in the mass of attached nanoparticle gives rise to a decrease in the natural frequency. This study might be useful for the design and smart control of nano-devices. پرونده مقاله -
دسترسی آزاد مقاله
17 - A New Finite Element Formulation for Buckling and Free Vibration Analysis of Timoshenko Beams on Variable Elastic Foundation
A Mirzabeigy M Haghpanahi R MadoliatIn this study, the buckling and free vibration of Timoshenko beams resting on variable elastic foundation analyzed by means of a new finite element formulation. The Winkler model has been applied for elastic foundation. A two-node element with four degrees of freedom is چکیده کاملIn this study, the buckling and free vibration of Timoshenko beams resting on variable elastic foundation analyzed by means of a new finite element formulation. The Winkler model has been applied for elastic foundation. A two-node element with four degrees of freedom is suggested for finite element formulation. Displacement and rotational fields are approximated by cubic and quadratic polynomial interpolation functions, respectively. The length of the element is assumed to be so small, so that linear variation could be considered for elastic foundation through the length of the element. By these assumptions and using energy method, stiffness matrix, mass matrix and geometric stiffness matrix of the proposed beam element are obtained and applied to buckling and free vibration analysis. Accuracy of obtained formulation is approved by comparison with the special cases of present problem in other studies. Present formulation shows faster convergence in comparison with conventional finite element formulation. The effects of different parameters on the stability and free vibration of Timoshenko beams investigated and results are completely new. پرونده مقاله -
دسترسی آزاد مقاله
18 - Theoretical Formulations for Finite Element Models of Functionally Graded Beams with Piezoelectric Layers
J.N Reddy S Doshi A MulianaIn this paper an overview of functionally graded materials and constitutive relations of electro elasticity for three-dimensional deformable solids is presented, and governing equations of the Bernoulli–Euler and Timoshenko beam theories which account for through- چکیده کاملIn this paper an overview of functionally graded materials and constitutive relations of electro elasticity for three-dimensional deformable solids is presented, and governing equations of the Bernoulli–Euler and Timoshenko beam theories which account for through-thickness power-law variation of a two-constituent material and piezoelectric layers are developed using the principle of virtual displacements. The formulation is based on a power-law variation of the material in the core with piezoelectric layers at the top and bottom. Virtual work statements of the two theories are also developed and their finite element models are presented. The theoretical formulations and finite element models presented herein can be used in the analysis of piezolaminated and adaptive structures such as beams and plates. پرونده مقاله -
دسترسی آزاد مقاله
19 - Vibration Analysis of Multi-Step Bernoulli-Euler and Timoshenko Beams Carrying Concentrated Masses
K Torabi H Afshari H NajafiIn this paper, vibration analysis of multiple-stepped Bernoulli-Euler and Timoshenko beams carrying point masses is presented analytically for various boundary conditions. Each attached element is considered to have both translational and rotational inertias. The method چکیده کاملIn this paper, vibration analysis of multiple-stepped Bernoulli-Euler and Timoshenko beams carrying point masses is presented analytically for various boundary conditions. Each attached element is considered to have both translational and rotational inertias. The method of solution is “transfer matrix method” which is based on the changes in the vibration modes at the vicinity of any discontinuity in geometrical and natural parameters; these changes are shown by transfer matrices depended on the geometry of each step or value of the translational and rotational inertias of each attached element. First, natural frequencies and corresponding normal mode shapes are obtained by implementation of the compatibility conditions and external boundary conditions; Then, the precision of the proposed method is checked by comparison of the results with other exact solutions; Finally, the effect of the translational and rotational inertias and position of the attached elements on the natural frequencies of multi-stepped beams are investigated for various boundary conditions. پرونده مقاله -
دسترسی آزاد مقاله
20 - Optimal Locations on Timoshenko Beam with PZT S/A for Suppressing 2Dof Vibration Based on LQR-MOPSO
M Hasanlu A BagheriNeutralization of external stimuli in dynamic systems has the major role in health, life, and function of the system. Today, dynamic systems are exposed to unpredicted factors. If the factors are not considered, it will lead to irreparable damages in energy consumption چکیده کاملNeutralization of external stimuli in dynamic systems has the major role in health, life, and function of the system. Today, dynamic systems are exposed to unpredicted factors. If the factors are not considered, it will lead to irreparable damages in energy consumption and manufacturing systems. Continuous systems such as beams, plates, shells, and panels that have many applications in different industries as the main body of a dynamic system are no exceptions for the damages, but paying attention to the primary design of model the automatic control against disturbances has highly met the objectives of designers and also has saved much of current costs. Beam structure has many applications in constructing blades of gas and wind turbines and robots. When it is exposed to external loads, it will have displacements in different directions. Now, it is the control approach that prevents from many vibrations by designing an automated system. In this study, a cantilever beam has been modeled by finite element and Timoshenko Theory. Using piezoelectric as sensor and actuator, it controls the beam under vibration by LQR controller. Now, in order to increase controllability of the system and reduce the costs, there are only spots of the beam where most displacement occurs. By controlling the spots and applying force on them, it has the most effect on the beam. By multi-objective particle swarm optimization or MOPSO algorithm, the best weighting matrices coefficients of LQR controller are determined due to sensor and actuator displacement or the beam vibration is controlled by doing a control loop. پرونده مقاله -
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21 - تحلیل ارتعاشات آزاد تیر تیموشینکو ساخته شده از مواد تابعی دو بعدی
محمد رحیم ترشیزیان عبدالحسین اخوت پوردر این تحقیق ارتعاشات آزاد یک تیر از جنس ماده تابعی دو بعدی با در نظر گرفتن تئوری تیر تیموشینکو بررسی شده است. تغییرات خواص مواد در دو جهت ضخامت و طول تیر به صورت تابع نمائی فرض شده است. معادلات حرکت با استفاده از اصل همیلتون بدست آمده که در آن اثر اینرسی های عمودی و دو چکیده کاملدر این تحقیق ارتعاشات آزاد یک تیر از جنس ماده تابعی دو بعدی با در نظر گرفتن تئوری تیر تیموشینکو بررسی شده است. تغییرات خواص مواد در دو جهت ضخامت و طول تیر به صورت تابع نمائی فرض شده است. معادلات حرکت با استفاده از اصل همیلتون بدست آمده که در آن اثر اینرسی های عمودی و دورانی نیز در نظر گرفته شده است. حل معادلات حرکت از روش لوی با رهیافتی از روش فضای حالت انجام گرفته و فرکانس های طبیعی تیر محاسبه شده اند. اثر تغییرات نسبت طول به ضخامت تیر، پارامتر های غیر همگونی ماده و شرایط مرزی، بر روی فرکانس های طبیعی تیر بررسی گردیده است. نتایج نشان می دهد، با افزایش نسبت طول به ضخامت تیر فرکانس های طبیعی افزایش می یابد و همچنین مقدار فرکانس های طبیعی برای تیر از ماده تابعی دو بعدی در شرایط یکسان بیشتر از مقدار آن در تیر از ماده تابعی یک بعدی می باشد. پرونده مقاله -
دسترسی آزاد مقاله
22 - تحلیل و طراحی کنترل کننده بهینه به منظور دستیابی به میرایی ارتعاشی تیر هوشمند تیموشنکو در بازه های مختلف
مجتبی حسنلو اجمد باقری فرید نجفیمیرایی ارتعاشی تیر تیموشنکو براساس یافتن مکان، تعداد بهینه حسگر و عملگر پیزوالکتریک با استفاده از کنترلر LQR و الگوریتم MOPSO موضوع مورد بررسی در این تحقیق محسوب میشود. امروزه برای اینکه یک سازه دارای عمر، هزینه ساخت، مصرف انرژِ قابلیت اطمینان بهینهای باشد تلاشهای فر چکیده کاملمیرایی ارتعاشی تیر تیموشنکو براساس یافتن مکان، تعداد بهینه حسگر و عملگر پیزوالکتریک با استفاده از کنترلر LQR و الگوریتم MOPSO موضوع مورد بررسی در این تحقیق محسوب میشود. امروزه برای اینکه یک سازه دارای عمر، هزینه ساخت، مصرف انرژِ قابلیت اطمینان بهینهای باشد تلاشهای فراوانی از سوی محققین این حوزه صورت پذیرفتهاست. یکی از تحقیقات تامین سازه هوشمند بهینه و کنترلشده با استفاده از حسگر و عملگر پیزوالکتریک است بگونهای این حسگر و عملگر بتواند به محض دریافت یک ارتعاش توسط حسگر و با انتقال سیگنال ارتعاشی به کنترلر، بهترین بهره کنترلی را براساس نوع نگرش طراحی شده در کنترلر اتخاذ شده و آنگاه سیگنال مناسبی را به عملگر انتقال دهد. در واقع این عملگر است که تمام تلاش خود را برای خنثیسازی ارتعاش سازه به ظهور میرساند تا سازهای با عمر بیشتر و خرابی کمتر داشتهباشد و بتواند هدف طراح را به بهترین نحوه تامین نماید. حال در این پژوهش با استفاده از الگوریتم MOPSO و تعریف متغیرهای طراحی، بهترین تعداد و مکان جهت نصب حسگر و عملگر پیزوالکتریک در پایین و بالای سازه تیر یکسرگیردار در بازهای مشخص را امکانپذیر جستجو نموده و آنگاه یک مدل بهینه از طراحی سازه هوشمند ارائه نماید. پرونده مقاله -
دسترسی آزاد مقاله
23 - آنالیز ارتعاش آزاد نانولولههای ویسکوالاستیک تحت میدان مغناطیسی طولی بر اساس گرادیان کرنش غیرموضعی مدل تیر تیموشنکو
پرویز قزوینیاندر این مقاله ارتعاش آزاد نانولولههای ویسکوالاستیک تحت میدان مغناطیسی طولی مورد بررسی قرار گرفته است. معادله حاکم با استفاده از مدل تیر تیموشنکو و مدل کلوین-ویت بر اساس تئوری گرادیان کرنش غیرموضعی فرمولبندی شده است. در رویه آنالیز از روش تربیع دیفرانسیلی تطبیقی موضعی ( چکیده کاملدر این مقاله ارتعاش آزاد نانولولههای ویسکوالاستیک تحت میدان مغناطیسی طولی مورد بررسی قرار گرفته است. معادله حاکم با استفاده از مدل تیر تیموشنکو و مدل کلوین-ویت بر اساس تئوری گرادیان کرنش غیرموضعی فرمولبندی شده است. در رویه آنالیز از روش تربیع دیفرانسیلی تطبیقی موضعی (LADQM) استفاده شده است. همچنین اثر پارامترهای غیرموضعی، ضریب استهلاک سازهای، پارامتر مقیاس طول ماده و میدان مغناطیسی طولی بر فرکانسهای طبیعی سیستم مورد بررسی قرار گرفته است. ممکن است نتایج این تحقیق برای درک کاربرد بالقوه نانولولهها در سیستم نانو الکترومکانیکی مفید باشد. پرونده مقاله -
دسترسی آزاد مقاله
24 - تحلیل دینامیکی تیر تیموشنکو از جنس ماده مرکب روی بستر ویسکوالاستیک تحت تاثیر بار متمرکز متحرک و نیروی محوری
محمدجواد رضوانی محمدحسین کارگرنویندر این مقاله، تحلیل دینامیکی تیر تیموشنکو از جنس ماده مرکب روی بستر ویسکو الاستیک تعمیم یافته پسترنک تحت اثر بار متمرکز متحرک و نیروی محوری از دیدگاه تئوری مرتبه اول برشی مطالعه شده است. اصولاً تیرهای تحت نیروی محوری ستون نامیده میشوند که برای از بین بردن اثر مرزی تیر چکیده کاملدر این مقاله، تحلیل دینامیکی تیر تیموشنکو از جنس ماده مرکب روی بستر ویسکو الاستیک تعمیم یافته پسترنک تحت اثر بار متمرکز متحرک و نیروی محوری از دیدگاه تئوری مرتبه اول برشی مطالعه شده است. اصولاً تیرهای تحت نیروی محوری ستون نامیده میشوند که برای از بین بردن اثر مرزی تیر متناهی، فرض میشود که تیر تا بینهایت گسترده شده باشد. سرعت حرکت بار و خصوصیات هندسی و مکانیکی تیر در طول آن ثابت میباشد. بستر در نظر گرفته شده شامل سه عامل استهلاک اعم از میرایی قائم، میرایی دورانی و ویسکوزیته لایه برشی و دو عامل سفتی شامل سفتی قائم و دورانی میباشد. با استفاده از نرمافزارMathematica روند تحلیل در قالب یک برنامه کامپیوتری درآمده و نتایج به صورت نمودارهای خیز، نیروی برشی و تنش برحسب فاصله از بار متحرک و تغییر پارامترهای ذکر شده در فوق رسم گردیدهاند. نتایج حاصل از تحلیل، با نتایج موجود در دیگر مراجع مقایسه شده است. پرونده مقاله -
دسترسی آزاد مقاله
25 - Vibration Analysis of Timoshenko Beam reinforced with Boron-Nitride Nanotube on Elastic Bed
ایلدا عبداللهی محمدحسین یاسIn this paper, free vibration analysis of a polymer-based nano-composite beam reinforced by boron-nitride nanotubes and subjected on elastic foundation, is studied. Smooth and defect-free nanotubes with uniform and directly- orientated in matrix are intended. Also, nano چکیده کاملIn this paper, free vibration analysis of a polymer-based nano-composite beam reinforced by boron-nitride nanotubes and subjected on elastic foundation, is studied. Smooth and defect-free nanotubes with uniform and directly- orientated in matrix are intended. Also, nanotubes’ distribution in the thickness direction of beam is regarded as a uniform distribution of the three different targeted ones. The properties of nano-beam are obtained by using a micromechanical model. The governing equations based on Timoshenko beam theory are derived by using the Hamilton principle. The equations are solved by the extended differential Quadrature and the natural frequencies are obtained. The effect of various parameters such as volume fraction of nanotubes, carbon-nanotube (CNT) distribution in the thickness direction of the beam, elastic media, boundary conditions and the aspect ratio is investigated on the natural frequency. The results show that a change on these parameters has a significant impact on the natural frequency. پرونده مقاله -
دسترسی آزاد مقاله
26 - Nonlinear Vibration Analysis of Multi-Walled Carbon Nanotubes in Thermal Environment using the Nonlocal Timoshenko Beam Model
ابوالحسن نظری نژاد گیاشی رضا انصاری حبیب رمضان نژاد آزاربنیIn this paper, based on the nonlocal Timoshenko beam theory, a nonlinear model is presented for the vibrational behavior of carbon nanotubes (CNTs) embedded in elastic medium in thermal environment. Using the Timoshenko beam theory and nonlocal elasticity of Eringen, th چکیده کاملIn this paper, based on the nonlocal Timoshenko beam theory, a nonlinear model is presented for the vibrational behavior of carbon nanotubes (CNTs) embedded in elastic medium in thermal environment. Using the Timoshenko beam theory and nonlocal elasticity of Eringen, the influences of rotary inertia, transverse shear deformation and small scale effect are taken into account. To model the interaction forces between walls, whether adjacent or non-adjacent, the van der Waals interlayer interactions are considered. The harmonic balance method (HBM) is used for the solution of the set of nonlinear governing equations and the frequency function of the system for the simply-supported boundary conditions is derived. Compared to the incremental harmonic balance method which has been employed in the previous studies, the HBM is simpler and has a reasonable accuracy. The effects of geometrical parameters of nanotubes such as the number of walls, the ratio of length to outer diameter and environmental conditions such as elastic medium modulus, temperature and also the effect of nonlocal parameter on the nonlinear frequency are investigated. The presented nonlinear vibration analysis is of a general form, so that they are applicable for CNTs with arbitrary number of walls. The obtained results for single-, double- and triple-walled CNTs indicate that with an increase in the number of walls, elastic medium modulus, aspect ratio and temperature, the value of nonlinear frequency tends to that of its linear counterpart. Also, a comparison between the results of the Timoshenko beam theory and those of Euler-Bernoulli beam theory shows that the difference between the frequency responses of these theories is significant for short CNTs, but, as the length increases, the difference between the results becomes negligible. پرونده مقاله -
دسترسی آزاد مقاله
27 - Effect of Bed and Crack on the Natural Frequency for the Timoshenko Beam Using Finite Element Method
افشین منوچهری فر فرید ابطحیIn this study, the natural frequencies and mode shapes of beams without cracks and cracked Timoshenko beams is calculated with different boundary conditions using finite element method. The energy method is used to solve the equations. Hardness and softness matrices for چکیده کاملIn this study, the natural frequencies and mode shapes of beams without cracks and cracked Timoshenko beams is calculated with different boundary conditions using finite element method. The energy method is used to solve the equations. Hardness and softness matrices for Timoshenko beam without crack are obtained by solving the potential and kinetic energy equations. Then for investigation of cracked condition, the cracked element stiffness matrix is used and the beam natural frequencies are obtained by entering the boundary conditions of the beam. After that the effect of bed is investigated by addition of it to the equations. پرونده مقاله -
دسترسی آزاد مقاله
28 - Sensitivity Analysis of Frequency Response of Atomic Force Microscopy in Liquid Environment on Cantilever's Geometrical Parameters
مهرنوش دمیرچلیIn this paper, the non-linear dynamic response of rectangular atomic force microscopy in tapping mode is considered. The effect of cantilever’s geometrical parameters (e.g., cantilever length, width, thickness, tip length and the angle between the cantilever and t چکیده کاملIn this paper, the non-linear dynamic response of rectangular atomic force microscopy in tapping mode is considered. The effect of cantilever’s geometrical parameters (e.g., cantilever length, width, thickness, tip length and the angle between the cantilever and the sample's surface in liquid environment has been studied by taking into account the interaction forces. Results indicate that the resonant frequency, amplitude and phase are very sensitive to changes of geometrical parameters. In order to improve and optimize the system's behavior, the sensitive analysis (SA) of geometrical parameters on the first resonant frequency and amplitude of cantilever's vertical displacement has been conducted using Sobol's method. Results show that the influence of each geometrical variable on frequency response of the system can play a crucial role in designing the optimum cantilever in liquid medium for soft and sensitive biological samples. Also, one way to speed up the imaging process is to use short cantilevers. For short beams, the Timoshenko model seems to be more accurate compared to other models such as the Euler-Bernoulli. By using the Timoshenko beam model, the effects of rotational inertia and shear deformation are taken into consideration. In this paper, this model has been used to obtain more accurate results پرونده مقاله
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