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دسترسی آزاد مقاله
1 - 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
2 - 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
3 - 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
4 - Analysis of Nonlinear Vibrations for Multi-walled Carbon Nanotubes Embedded in an Elastic Medium
A Ghorbanpour Arani H Rabbani S Amir Z Khoddami Maraghi M Mohammadimehr E HaghparastNonlinear free vibration analysis of double-walled carbon nanotubes (DWCNTs) embedded in an elastic medium is studied in this paper based on classical (local) Euler-Bernoulli beam theory. Using the averaging method, the nonlinear free vibration responses of DWCNTs are o چکیده کاملNonlinear free vibration analysis of double-walled carbon nanotubes (DWCNTs) embedded in an elastic medium is studied in this paper based on classical (local) Euler-Bernoulli beam theory. Using the averaging method, the nonlinear free vibration responses of DWCNTs are obtained. The result is compared with the obtained results from the harmonic balance method for single-walled carbon nanotubes (SWCNTs) and DWCNTs. The effects of the surrounding elastic medium, van der waals (vdW) forces and aspect ratio of SWCNTs and DWCNTs on the vibration amplitude are discussed. The error percentage of the nonlinear free vibration frequencies between two theories decreases with increasing the spring constant of elastic medium. Results are also shown that if the value of the spring constant is lower than (), the nonlinear free vibration frequencies are increased. In this case, the effect of the spring constant on frequency responses is significant, while if the value of the spring constant is higher than (), the curve of frequency responses has a constant value near to 1 and therefore the effect of the spring constant on frequency responses is negligible. پرونده مقاله -
دسترسی آزاد مقاله
5 - Influence of Temperature Change on Modal Analysis of Rotary Functionally Graded Nano-beam in Thermal Environment
E Shahabinejad N Shafiei M GhadiriThe free vibration analysis of rotating functionally graded (FG) nano-beams under an in-plane thermal loading is provided for the first time in this paper. The formulation used is based on Euler-Bernoulli beam theory through Hamilton’s principle and the small scal چکیده کاملThe free vibration analysis of rotating functionally graded (FG) nano-beams under an in-plane thermal loading is provided for the first time in this paper. The formulation used is based on Euler-Bernoulli beam theory through Hamilton’s principle and the small scale effect has been formulated using the Eringen elasticity theory. Then, they are solved by a generalized differential quadrature method (GDQM). It is supposed that, according to the power-law form (P-FGM), the thermal distribution is non-linear and material properties are dependent to temperature and are changing continuously through the thickness. Free vibration frequencies are obtained for two types of boundary conditions; cantilever and propped cantilever. The novelty of this work is related to vibration analysis of rotating FG nano-beam under different distributions of temperature with different boundary conditions using nonlocal Euler-Bernoulli beam theory. Presented theoretical results are validated by comparing the obtained results with literature. Numerical results are presented in both cantilever and propped cantilever nano-beams and the influences of the thermal, nonlocal small-scale, angular velocity, hub radius, FG index and higher modes number on the natural frequencies of the FG nano-beams are investigated in detail. پرونده مقاله -
دسترسی آزاد مقاله
6 - Effect of the Interparticle Interactions on Adsorption-Induced Frequency Shift of Nano-beam-Based Nanoscale Mass-Sensors: A Theoretical Study
K Rajabi Sh Hosseini-HashemiIt is well-known that the Interparticle interactions between adsorbates and surface of an adsorbent can affect the surface morphology. One of the consequences of this issue is that the resonant frequency of a nanoscale resonator can be changed due to adsorption. In this چکیده کاملIt is well-known that the Interparticle interactions between adsorbates and surface of an adsorbent can affect the surface morphology. One of the consequences of this issue is that the resonant frequency of a nanoscale resonator can be changed due to adsorption. In this study we have chosen a cantilever-based nanoscale mass-sensor with a single nanoparticle at its tip. Using the classical continuum mechanics and the Euler-Bernoulli beam theory we have derived the governing equation of free vibration of the proposed sensor. By the assumption of physisorption, the weak van der Waals forces between the attached nanoparticle and the upper surface atoms have been taken into account. Effect of this interparticle interaction on the frequency response of the mass sensor is examined. Accordingly, the classical equation of motion has been modified by an additional termon the dynamics behavior of the sensor with a variable coefficient. It has been shown that the effect of this additional term is the same as that of an elastic foundation with variable modulus. Numerical results have shown that this additional term has significant effect on the frequency shift of a nanoscale mass-sensor in such a way that by approaching the nanoparticle towards the sensor, the frequency shift of the sensor will increase significantly. The smaller is the nanoparticle, the higher is the frequency shift. پرونده مقاله -
دسترسی آزاد مقاله
7 - بررسی ارتعاشات آزاد و پایداری نانوتیوب دوار حامل جریان
مهدی صالحی محمد ارمغانیدر تحقیق حاضر محور دوار با استفاده از مدل تیر اویلر-برنولی شبیهسازی میشود. نیروهای وارد بر تیر تحت اثر ارتعاشات آن از سمت جریان داخلی، با استفاده از تئوری بدنههای باریک (Slender body theorem) شبیهسازی میشود. برای انتقال معادلات از فضای محلی به غیر محلی از تئوری اری چکیده کاملدر تحقیق حاضر محور دوار با استفاده از مدل تیر اویلر-برنولی شبیهسازی میشود. نیروهای وارد بر تیر تحت اثر ارتعاشات آن از سمت جریان داخلی، با استفاده از تئوری بدنههای باریک (Slender body theorem) شبیهسازی میشود. برای انتقال معادلات از فضای محلی به غیر محلی از تئوری ارینگن استفاده شده است. سپس با ترکیب معادلات حاکم بر محور دوار با نیروهای داخلی وارد شده از طرف جریان، معادلات خطیسازی شدهی همگیر سیستم استخراج میشود. سپس با استفاده از روشهای تحلیل بردار ویژه، فرکانسهای طبیعی ارتعاشات محور و پایداری آن در سرعتهای دورانی مختلف مطالعه میشود. همچنین اثر پارامترهایی چون سرعت دورانی، نسبت جرمی جریان داخلی به جرم محور، ضریب لاغری محور بر مرز پایداری بررسی خواهد شد. پرونده مقاله -
دسترسی آزاد مقاله
8 - Implementing Basic Displacement Function to Analyze Free Vibration Rotation of Non-Prismatic Euler-Bernoulli Beams
Pouria Hajikarimi Reza AttarnejadRotating beams have been considerably appealing to engineers and designers of complex structures i.e. aircraft’s propeller and windmill turbines. In this paper, a new flexibility-based method is proposed for the dynamic analysis of rotating non-prismatic Euler-Ber چکیده کاملRotating beams have been considerably appealing to engineers and designers of complex structures i.e. aircraft’s propeller and windmill turbines. In this paper, a new flexibility-based method is proposed for the dynamic analysis of rotating non-prismatic Euler-Bernoulli beams. The flexibility basis of the method ensures the true satisfaction of equilibrium equations at any interior point of the elements. Following structural/mechanical principles, exact shape functions and consequently exact structural matrices i.e. consistent mass, geometric stiffness and flexural stiffness matrices are derived in terms of special so-called “Basic Displacement Functions”. The method is considered as the logical extension of conventional finite element method. Being straightforward formulated, the method can be incorporated into any standard finite element programs. The method poses no restrictions on either type of cross-section or variation of cross-sectional dimensions. The effects of rotational speed parameter and taper ratio on the variation of natural frequencies are studied and the results compare well with the other existing methods in the technical literature. پرونده مقاله -
دسترسی آزاد مقاله
9 - Nonlinear Vibration Analysis of an Euler-Bernoulli Beam Resting on a Nonlinear Elastic Foundation under Compressive Axial Force
احمد مامندی محمدحسین کارگرنوینThis paper studies the nonlinear vibration analysis of a simply supported Euler-Bernoulli beam resting on a nonlinear elastic foundation under compressive axial load using nonlinear normal modes concept in the case of three-to-one (3:1) internal resonance. The beam&rsqu چکیده کاملThis paper studies the nonlinear vibration analysis of a simply supported Euler-Bernoulli beam resting on a nonlinear elastic foundation under compressive axial load using nonlinear normal modes concept in the case of three-to-one (3:1) internal resonance. The beam’s governing nonlinear PDE of motion and also its boundary conditions are derived and then solved using the method of Multiple Time Scales. Under three to-one-internal resonance condition applying nonlinear normal modes the steady state stability analysis of the beam’s vibrations is performed. Then the effect of changing the value of different parameters on the beam’s dynamic response and the steady state stability analysis is investigated. پرونده مقاله
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