1,721,000 research outputs found
Electro-magneto-mechanical formulation of a sandwich shell subjected to electro-magneto-mechanical considering thickness stretching
No full textThickness stretching included formulation of a multi-layered doubly curved shell in small scale is studied in the present work. Out-of-plane normal strain is accounted in our formulation based on a higher-order theory. Based on this theory, the total transverse deflection is divided into three portions named as bending, shear and stretching parts. Transient formulation of the nanoshell is derived using Hamilton’s principle and nonlocal formulation. The natural frequencies of the nanoshell are obtained in terms of main input parameters, such as initial electric and magnetic potentials, nonlocal parameters, aspect ratio, radii ratio and foundation parameters
Adaptive Neural Stabilizing Controller for a Class of Mismatched Uncertain Nonlinear Systems by State and Output Feedback
Full text linkIn this paper, first, an adaptive neural network (NN) state-feedback controller for a class of nonlinear systems with mismatched uncertainties is proposed. By using a radial basis function NN (RBFNN), a bound of unknown nonlinear functions is approximated so that no information about the upper bound of mismatched uncertainties is required. Then, an observer-based adaptive controller based on RBFNN is designed to stabilize uncertain nonlinear systems with immeasurable states. The state-feedback and observer-based controllers are based on Lyapunov and strictly positive real-Lyapunov stability theory, respectively, and it is shown that the asymptotic convergence of the closed-loop system to zero is achieved while maintaining bounded states at the same time. The presented methods are more general than the previous approaches, handling systems with no restriction on the dimension of the system and the number of inputs. Simulation results confirm the effectiveness of the proposed methods in the stabilization of mismatched nonlinear systems
Free vibrations of functionally graded polymer composite nanoplates reinforced with graphene nanoplatelets
No full textA two-variable sinusoidal shear deformation theory (SSDT) and a nonlocal elasticity theory are applied in this paper to analyze the free vibration behavior of functionally graded (FG) polymer composite nanoplates reinforced with graphene nanoplatelets (GNPs), resting on a Pasternak foundation. Based on the proposed theory, the transverse deflection is assumed as summation of bending and shear transverse deformations. Four different FG reinforcement patterns are here employed, namely a uniform distribution UD, and non-uniform distributions FG-O, FG-X and FG-A. The effective elastic modulus, the Poisson’s ratio and the density of composite nanoplates are computed using the Halpin-Tsai model and the rule of mixture, respectively. The numerical results are validated through a comparative assessment of the results with respect to predictions from literature, including nanoplates and FG polymer composite plates. A wide parametric investigation shows the influence of some significant parameters, such as nonlocal parameters, total number of layers, weight fraction, as well as parameters related to the Pasternak foundation and geometry, on the free vibration response of FG polymer composite nanoplates reinforced with GNPs
Adaptive output feedback neural network control of uncertain non-affine systems with unknown control direction
Full text linkThis paper deals with the problem of adaptive output feedback neural network controller design for a SISO non-affine nonlinear system. Since in practice all system states are not available in output measurement, an observer is designed to estimate these states. In comparison with the existing approaches, the current method does not require any information about the sign of control gain. In order to handle the unknown sign of the control direction, the Nussbaum-type function is utilized. In order to approximate the unknown nonlinear function, neural network is firstly exploited, and then to compensate the approximation error and external disturbance a robustifying term is employed. The proposed controller is designed based on strict-positive-real (SPR) Lyapunov stability theory to ensure the asymptotic stability of the closed-loop system. Finally, two simulation studies are presented to demonstrate the effectiveness of the developed scheme. © 2014 The Franklin Institute
Higher-order thermo-elastic analysis of FG-CNTRC cylindrical vessels surrounded by a pasternak foundation
No full textThis study analyses the two-dimensional thermo-elastic response of functionally graded carbon nanotubes reinforced composite (FG-CNTRC) cylindrical pressure vessels, by applying the third-order shear deformation theory (TSDT). The effective properties of FG-CNTRC cylindrical pressure vessels are computed for different patterns of reinforcement, according to the rule of mixture. The governing equations of the problem are derived from the principle of virtual works and are solved as a classical eigenproblem under the assumption of clamped supported boundary conditions. A large parametric investigation aims at showing the influence of some meaningful parameters on the thermo-elastic response, such as the type of pattern, the volume fraction of CNTs, and the Pasternak coefficients related to the elastic foundation
Nonlocal bending analysis of curved nanobeams reinforced by graphene nanoplatelets
No full textThe paper presents a large parametric investigation on the bending response of Functionally Graded (FG) polymer composite curved beams reinforced by graphene nanoplatelets resting on a Pasternak foundation. The theoretical framework is based on the First-order Shear Deformation Theory (FSDT) and the nonlocal elasticity theory. The governing equations are obtained by means of the principle of virtual works. Four different patterns are considered to describe the through-the-thickness distribution of the reinforcing phase. The effective Young’s modulus and Poisson’s ratio are evaluated through the application of the Halpin-Tsai model and the rule of mixture, respectively. The numerical results are presented in terms of some significant parameters, such as the weight fraction and geometric features of the graphene nanoplatelets, the total number of layers, the foundation properties and the nonlocal parameter. The effect of these quantities on the kinematic and static behavior is discussed
Application of sinusoidal shear deformation theory and physical neutral surface to analysis of functionally graded piezoelectric plate
No full textThe concept of neutral surface for a Functionally Graded Piezoelectric (FGP) plate is developed in this paper. The electro-elastic analysis of a FGP plate resting on Winkler-Pasternak foundation is performed in the theoretical framework provided by a two-variable sinusoidal shear deformation theory, including the aforementioned concept of neutral surface. First, the location of neutral surface is defined with respect to the position of the middle surface and then the governing bending equations are derived using the principle of virtual work. An analytical method is presented to investigate the influence on the displacement and stress components of the main parameters of the model, which are volume fraction exponent of the constituents, the electric potential and foundation parameters. The numerical results are validated through the comparison with available references. The numerical results prove that the value of transverse bending deflection is greater than the corresponding shear deflection. In addition, it can be observed that the volume fraction exponent has peculiar influence on the distribution of displacements and stresses
Two-dimensional thermo-elastic analysis of FG-CNTRC cylindrical pressure vessels
No full textThis paper focuses on the application of the first-order shear deformation theory (FSDT) to thermo-elastic static problems of functionally graded carbon nanotubes reinforced composite (FG-CNTRC) cylindrical pressure vessels. A symmetric displacement-field is considered as unknown functions along the longitudinal direction, whereas a linear distribution is assumed along the thickness direction. The cylindrical pressure vessel is subjected to an inner and outer pressure under a temperature increase. Different patterns of reinforcement are applied as distributions of CNTs. The effective material properties of FG-CNTRC cylindrical pressure vessels are measured based on the rule of mixture, whereas the governing equations of the problem are here derived through the principle of virtual works. A large parametric investigation studies the effect of some significant parameters, such as the pattern and volume fraction of CNTs, on the longitudinal distribution of deformation, strain and stress components, as useful tool for practical engineering applications
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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