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ahmadian--m--t
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Energy Optimization of an Arm with Seven Degrees of Freedom Using Imperialistic Competitive Algorithm (ICA) and Designing an Artificial Neural Network
, M.Sc. Thesis Sharif University of Technology ; Ahmadian, M.T (Supervisor) ; Asghari, M (Supervisor)
Abstract
In recent years, great attention has been devoted to the design of artificial arms. The most crucial problem in such a design is the trajectory of movement. In this paper, a seven degree of freedom arm is modeled and simulated. Also, the optimization method named “Imperialistic Competitive Algorithm” has been modified and better performance of the new version is presented. Energy optimization is performed based on trajectory of the arm with angular velocity, angular acceleration and joint angles using modified imperialistic competitive algorithm (ICA). Considering ICA as a fast optimization algorithm, it would be reasonable to use this algorithm for robotic purposes for online answering. The...
Nonlinear forced vibration of strain gradient microbeams
, Article Applied Mathematical Modelling ; Volume 37, Issue 18-19 , 1 October , 2013 , pp. 8363-8382 ; ISSN: 0307904X ; Kahrobaiyan, M. H ; Alasty, A ; Ahmadian, M. T ; Sharif University of Technology
Abstract
In this paper, the strain gradient theory, a non-classical continuum theory able to capture the size effect happening in micro-scale structures, is employed in order to investigate the size-dependent nonlinear forced vibration of Euler-Bernoulli microbeams. The nonlinearities are caused by mid-plane stretching and nonlinear external forces such as van-der-Waals force. The nonlinear governing equations of the microbeams are solved analytically utilizing the perturbation techniques. The primary, super-harmonic and sub-harmonic resonances of a microbeam are studied and the size-dependency of the frequency responses is assessed. The results indicate that the nonlinear forced vibration behavior...
Nonlinear forced vibration of strain gradient microbeams
, Article Applied Mathematical Modelling ; Volume 37, Issue 18-19 , 2013 , Pages 8363-8382 ; 0307904X (ISSN) ; Kahrobaiyan, M. H ; Alasty, A ; Ahmadian, M. T ; Sharif University of Technology
2013
Abstract
In this paper, the strain gradient theory, a non-classical continuum theory able to capture the size effect happening in micro-scale structures, is employed in order to investigate the size-dependent nonlinear forced vibration of Euler-Bernoulli microbeams. The nonlinearities are caused by mid-plane stretching and nonlinear external forces such as van-der-Waals force. The nonlinear governing equations of the microbeams are solved analytically utilizing the perturbation techniques. The primary, super-harmonic and sub-harmonic resonances of a microbeam are studied and the size-dependency of the frequency responses is assessed. The results indicate that the nonlinear forced vibration behavior...
Static analysis of electrically actuated nano to micron scale beams using nonlocal theory
, Article Proceedings of the ASME Design Engineering Technical Conference, 28 August 2011 through 31 August 2011 ; Volume 7 , August , 2011 , Pages 391-396 ; 9780791854846 (ISBN) ; Pasharavesh, A ; Ahmadian, M. T ; Fallah, A ; Sharif University of Technology
2011
Abstract
In this paper, size dependent static behavior of micro and nano cantilevers actuated by a static electric field including deflection and pull-in instability, is analyzed implementing nonlocal theory. Euler-bernoulli assumptions are made to model the relation between deflection of the beam and bending moment. Differential form of the constitutive equation of nonlocal theory is used to find the revised equation for bending moment and substituting in the equilibrium equation of electrostatically actuated beams final nonlinear ordinary differential equation is arrived. Also the boundary conditions for solving the equation are revised and to analyze the size effect better governing equation is...
Free vibration analysis of cylindrical panels with spiral cross section
, Article International Journal of Mechanical Sciences ; Volume 133 , 2017 , Pages 376-386 ; 00207403 (ISSN) ; Ahmadian, M. T ; Asghari, M ; Pugno, N. M ; Sharif University of Technology
Abstract
In this paper, free vibration of open noncircular cylinders with spiral cross section are studied under arbitrary boundary conditions. For deriving the strain energy function, Kirchhoff-Love hypotheses are employed. To obtain the solutions, Rayleigh-Ritz technique is implemented by selecting Chebyshev orthogonal polynomials of first kind as admissible displacement functions in three directions. Convergence of the proposed formulation is verified for spiral cylindrical panel and the results are compared with those of ABAQUS. Parametric study is undertaken to highlight the effect of inner radius, separation distance, subtended angle, thickness, and length of the spiral cylinders on the free...
A shell model for free vibration analysis of carbon nanoscroll
, Article Materials ; Volume 10, Issue 4 , 2017 ; 19961944 (ISSN) ; Ahmadian, M. T ; Asghari, M ; Pugno, N. M ; Sharif University of Technology
Abstract
Carbon nanoscroll (CNS) is a graphene sheet rolled into a spiral structure with great potential for different applications in nanotechnology. In this paper, an equivalent open shell model is presented to study the vibration behavior of a CNS with arbitrary boundary conditions. The equivalent parameters used for modeling the carbon nanotubes are implemented to simulate the CNS. The interactions between the layers of CNS due to van der Waals forces are included in the model. The uniformly distributed translational and torsional springs along the boundaries are considered to achieve a unified solution for different boundary conditions. To study the vibration characteristics of CNS, total energy...
Mechanical behavior analysis of size-dependent micro-scaled functionally graded Timoshenko beams by strain gradient elasticity theory
, Article Composite Structures ; Volume 102 , 2013 , Pages 72-80 ; 02638223 (ISSN) ; Rahaeifard, M ; Kahrobaiyan, M. H ; Movahhedy, M. R ; Akbari, J ; Ahmadian, M. T ; Sharif University of Technology
2013
Abstract
In this paper, a size-dependent formulation is developed for Timoshenko beams made of functionally graded materials (FGMs). The developed formulation is based on the strain gradient theory; a non-classical continuum theory able to capture the size-effect in micro-scaled structures. Five new equivalent length scale parameters are introduced as functions of the constituents' length scale parameters. It is shown that the size-dependent static and dynamic behavior of FG micro-beams can be described using these equivalent length scales. The governing differential equations of motion and both classical and non-classical sets of boundary conditions are derived for the proposed strain gradient FG...
Mechanical behavior analysis of micro-scaled functionally graded timoshenko beams by the strain gradient theory
, Article Proceedings of the ASME Design Engineering Technical Conference ; Volume 5 , 2012 , Pages 67-73 ; 9780791845042 (ISBN) ; Kahrobaiyan, M. H ; Rahaeifard, M ; Ahmadian, M. T ; Movahhedy, M. R ; Akbari, J ; Sharif University of Technology
2012
Abstract
In this paper, a size-dependent formulation is developed for Timoshenko beams made of functionally graded materials (FGM). The developed formulation is based on the strain gradient theory;a non-classical continuum theory able to capture the size-effect in micro-scaled structures. Considering the material length scale parameters of the FG beams vary through the thickness, the new equivalent length scale parameters are proposed as functions of the constituents' length scale parameters to describe the size-dependent static and dynamic behavior of FG microbeams. The governing differential equations of equilibrium and both classical and nonclassical sets of boundary conditions are derived for the...
Effect of geometric nonlinearity on dynamic pull-in behavior of coupled-domain microstructures based on classical and shear deformation plate theories
, Article European Journal of Mechanics, A/Solids ; Volume 28, Issue 5 , 2009 , Pages 916-925 ; 09977538 (ISSN) ; Moghimi Zand, M ; Ahmadian, M. T ; Sharif University of Technology
2009
Abstract
This paper investigates the dynamic pull-in behavior of microplates actuated by a suddenly applied electrostatic force. Electrostatic, elastic and fluid domains are involved in modeling. First-order shear deformation plate theory and classical plate theory are used to model the geometrically nonlinear microplates. The equations of motion are descritized by the finite element method. The effects of nonlinearity, fluid pressure, initial stress and different geometric parameters on dynamic behavior are examined. In addition, the influences of initial stress and actuation voltage on oscillatory behavior of microplates are evaluated. © 2009 Elsevier Masson SAS. All rights reserved
Dynamic analysis of electrically actuated rectangular microplates with nonlinear plate theory under squeeze-film damping effect
, Article 2008 ASME International Mechanical Engineering Congress and Exposition, IMECE 2008, Boston, MA, 31 October 2008 through 6 November 2008 ; Volume 13, Issue PART A , 2009 , Pages 401-408 ; 9780791848746 (ISBN) ; Moghimi Zand, M ; Ahmadian, M. T ; Sharif University of Technology
2009
Abstract
In this paper, dynamic behavior and pull-in phenomenon of electrically actuated rectangular micro plates under the effect of squeeze-film damping and nonlinear electrostatic force is studied. Finite element method is implemented in order to drive weak formulations of linear and nonlinear micro plate equations of motion based on classical plate theory (CPT) (for thin microplates with moderate nonlinearity) and squeeze-film damping based on Reynolds nonlinear equation. Finally, an efficient reduced-order model contingent on singular value decomposition method (SVD) is used to study dynamic pull-in phenomenon. This model is constructed by the global basis functions achieved from a few runs of...
Effect of squeeze-film damping on the dynamic behavior of circular and rectangular microplates
, Article 2007 International Semiconductor Device Research Symposium, ISDRS, College Park, MD, 12 December 2007 through 14 December 2007 ; January , 2007 ; 1424418917 (ISBN); 9781424418916 (ISBN) ; Ahmadian, M. T ; Sadeghian, H ; Sharif University of Technology
2007
Transparency enhancement of haptic systems based on compensation of device dynamics
, Article ASME International Mechanical Engineering Congress and Exposition, Proceedings, 13 November 2009 through 19 November 2009 ; Volume 10, Issue PART A , 2010 , Pages 103-110 ; 9780791843833 (ISBN) ; Ahmadian, M. T ; Vossoughi, G. R ; Motamedi, M ; Sharif University of Technology
Abstract
Transparency is a measure of performance in haptic devices. In order to improve transparency and reduce the difference between the impedance transmitted to the user and the target impedance it is necessary to compensate for the dynamics of the haptic device. Due to stability reasons improvement of transparency is limited. Passivity as a stability criterion has been used widely in design and analysis of haptic devices, Since passivity is a conservative criterion, it acts as an obstacle in improving transparency of the haptic interfaces. In this paper instead of passivity, robust stability of the interaction is studied in the presence of parametric uncertainties due to variations in user hand...
Nonlinear oscillations of viscoelastic microcantilever beam based on modified strain gradient theory
, Article Scientia Iranica ; Volume 28, Issue 2 , 2021 , Pages 785-794 ; 10263098 (ISSN) ; Ahmadian, M. T ; Firoozbakhsh, K ; Sharif University of Technology
Sharif University of Technology
2021
Abstract
A viscoelastic microcantilever beam is analytically analyzed based on the modified strain gradient theory. Kelvin-Voigt scheme is used to model beam viscoelasticity. By applying Euler-Bernoulli inextensibility of the centerline condition based on Hamilton's principle, the nonlinear equation of motion and the related boundary conditions are derived from shortening effect theory and discretized by Galerkin method. Inner damping, nonlinear curvature effect, and nonlinear inertia terms are also taken into account. In the present study, the generalized derived formulation allows modeling any nonlinear combination such as nonlinear terms that arise due to inertia, damping, and stiffness, as well...
Size effects on stability and bifurcation of nonlinear viscoelastic microcantilevers based on strain gradient
, Article Journal of the Brazilian Society of Mechanical Sciences and Engineering ; Volume 44, Issue 1 , 2022 ; 16785878 (ISSN) ; Ahmadian, M. T ; Monfared, V ; Toghraie, D ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2022
Abstract
Analytical frequency analysis of a nonlinear viscoelastic microcantilever is performed based on strain gradient theory. The Kelvin–Voigt scheme is utilized to model the viscoelasticity effect. Due to the microcantilever shortening effect via Euler–Bernoulli inextensibility condition, geometric, inertia, stiffness, and inherent damping nonlinearities are considered. The equation of motion is derived from Hamilton’s principle, and discretized using Galerkin method. The multiple timescale perturbation method is performed to solve the time response equation. Implying steady-state condition, the nonlinear relation between detuning parameter and amplitude of the vibration of a nonlinear...
Application of a new cylindrical element formulation in finite element structural analysis of FGM hollow cylinders
, Article Finite Elements in Analysis and Design ; Volume 50 , March , 2012 , Pages 1-7 ; 0168874X (ISSN) ; Bonakdar, M ; Ahmadian, M. T ; Sharif University of Technology
Abstract
A finite element formulation is derived for the structural analysis of functionally graded hollow cylinders. The power-law distribution model is used for the composition of the constituent material in the thickness direction. According to property variation in FG cylinders, it is difficult to analyze them using the conventional element formulation. In order to facilitate the process of modeling and analyzing the FG cylinders, the finite element formulation is based on a newly designed cylindrical element. The new cylindrical element allows for property variations along the thickness, which results in considerable reduction of the required elements and eliminates the need to mesh the cross...
Formulation for static behavior of the viscoelastic Euler-Bernoulli micro-beam based on the modified couple stress theory
, Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) ; Volume 9, Issue PARTS A AND B , 2012 , Pages 129-135 ; 9780791845257 (ISBN) ; Nikfar, M ; Ahmadian, M. T ; Sharif University of Technology
2012
Abstract
In this work an analytical solution is presented for a viscoelastic micro-beam based on the modified couple stress theory which is a non-classical theory in continuum mechanics. The modified couple stress theory has the ability to consider small size effects in micro-structures. It is strongly emphasized that without considering these effects in such structures the solution will be wrong and not suitable for designing systems in micro-scales. In this study correspondence principle is used for deriving constitutive equations for viscoelastic material based on the modified couple stress theory. Governing equilibrium equations are obtained by considering an element of micro-beam. Closedform...
On size-dependent nonlinear free vibration of carbon nanotube-reinforced beams based on the nonlocal elasticity theory: Perturbation technique
, Article Mechanics Based Design of Structures and Machines ; 2020 ; Borjalilou, V ; Fallah, F ; Ahmadian, M. T ; Sharif University of Technology
Taylor and Francis Inc
2020
Abstract
Based on the first-order shear deformation (FSD) model and nonlocal elasticity theory, the simultaneous effects of shear and small scale on the nonlinear vibration behavior of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) beams are investigated for the first time. To this end, the governing equations of bending and stretching with von Kármán geometric nonlinearity are decoupled into one fourth-order partial differential equation in terms of transverse deflection. A closed-form solution of the nonlinear natural frequency, which can be used in conceptual design and optimization algorithms of FG- CNTRC beams with different boundary conditions, is developed using a hybrid...
Closed-form solution for free vibration of variable-thickness cylindrical shells rotating with a constant angular velocity
, Article Thin-Walled Structures ; Volume 166 , 2021 ; 02638231 (ISSN) ; Fallah, F ; Ahmadian, M. T ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
Based on the classical Donnell's and Love's shell theories, free vibration behavior of variable-thickness thin cylindrical shells rotating with a constant angular velocity is analyzed. The equations of motion and corresponding boundary conditions of rotating homogenous cylindrical shells with axisymmetric variation of thickness are derived using Hamilton's principle. This formulation includes effects of initial hoop tension due to the centrifugal force as well as Coriolis and centrifugal accelerations. Considering the variation of stiffness coefficients in axial direction, the classical Love's theory results in a coupled system of two second-order and one fourth-order partial differential...
On nonlinear free vibration of externally compressible fluid-loaded sandwich cylindrical shells: Curvature nonlinearity in bending and impermeability condition
, Article Thin-Walled Structures ; Volume 179 , 2022 ; 02638231 (ISSN) ; Fallah, F ; Ahmadian, M. T ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
A nonlinear fluid–structure interaction (FSI) model is presented for nonlinear vibration analysis of sandwich cylindrical shells subjected to an external compressible flow by considering the curvature nonlinearity in impermeability condition and bending. The sandwich shells are made of two face sheets and a central core of advanced materials including functionally graded (FG), metal foam, and anisogrid lattice composite. Based on the Kirchhoff–love hypotheses with the geometric nonlinearities in the normal strain and curvature of mid-surface, one decoupled nonlinear integral–differential equation is obtained for axisymmetric bending vibration of sandwich cylindrical shells. For the first...
On size-dependent nonlinear free vibration of carbon nanotube-reinforced beams based on the nonlocal elasticity theory: Perturbation technique
, Article Mechanics Based Design of Structures and Machines ; Volume 50, Issue 6 , 2022 , Pages 2124-2146 ; 15397734 (ISSN) ; Borjalilou, V ; Fallah, and, F ; Ahmadian, M. T ; Sharif University of Technology
Taylor and Francis Ltd
2022
Abstract
Based on the first-order shear deformation (FSD) model and nonlocal elasticity theory, the simultaneous effects of shear and small scale on the nonlinear vibration behavior of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) beams are investigated for the first time. To this end, the governing equations of bending and stretching with von Kármán geometric nonlinearity are decoupled into one fourth-order partial differential equation in terms of transverse deflection. A closed-form solution of the nonlinear natural frequency, which can be used in conceptual design and optimization algorithms of FG- CNTRC beams with different boundary conditions, is developed using a hybrid...