Yazar "Sofiyev, Abdullah H." seçeneğine göre listele

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    Analytical Solution of Stability Problem of Nanocomposite Cylindrical Shells under Combined Loadings in Thermal Environments
    (MDPI, 2023) Avey, Mahmure; Fantuzzi, Nicholas; Sofiyev, Abdullah H.
    The mathematical modeling of the stability problem of nanocomposite cylindrical shells is one of the applications of partial differential equations (PDEs). In this study, the stability behavior of inhomogeneous nanocomposite cylindrical shells (INH-NCCSs), under combined axial compression and hydrostatic pressure in the thermal environment, is investigated by means of the first-order shear deformation theory (FSDT). The nanocomposite material is modeled as homogeneous and heterogeneous and is based on a carbon nanotube (CNT)-reinforced polymer with the linear variation of the mechanical properties throughout the thickness. In the heterogeneous case, the mechanical properties are modeled as the linear function of the thickness coordinate. The basic equations are derived as partial differential equations and solved in a closed form, using the Galerkin procedure, to determine the critical combined loads for the selected structure in thermal environments. To test the reliability of the proposed formulation, comparisons with the results obtained by finite element and numerical methods in the literature are accompanied by a systematic study aimed at testing the sensitivity of the design response to the loading parameters, CNT models, and thermal environment.
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    The Application of the Modified Lindstedt-Poincaré Method to Solve the Nonlinear Vibration Problem of Exponentially Graded Laminated Plates on Elastic Foundations
    (MDPI, 2024) Avey, Mahmure; Tornabene, Francesco; Aslanova, Nigar Mahar; Sofiyev, Abdullah H.
    The solution of the nonlinear (NL) vibration problem of the interaction of laminated plates made of exponentially graded orthotropic layers (EGOLs) with elastic foundations within the Kirchhoff–Love theory (KLT) is developed using the modified Lindstedt–Poincaré method for the first time. Young’s modulus and the material density of the orthotropic layers of laminated plates are assumed to vary exponentially in the direction of thickness, and Poisson’s ratio is assumed to be constant. The governing equations are derived as equations of motion and compatibility using the stress–strain relationship within the framework of KLT and von Karman-type nonlinear theory. NL partial differential equations are reduced to NL ordinary differential equations by the Galerkin method and solved by using the modified Lindstedt–Poincaré method to obtain unique amplitude-dependent expressions for the NL frequency. The proposed solution is validated by comparing the results for laminated plates consisting of exponentially graded orthotropic layers with the results for laminated homogeneous orthotropic plates. Finally, a series of examples are presented to illustrate numerical results on the nonlinear frequency of rectangular plates composed of homogeneous and exponentially graded layers. The effects of the exponential change in the material gradient in the layers, the arrangement and number of the layers, the elastic foundations, the plate aspect ratio and the nonlinearity of the frequency are investigated.
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    Buckling Behavior of Nanocomposite Plates with Functionally Graded Properties under Compressive Loads in Elastic and Thermal Environments
    (Shahid Chamran University of Ahvaz, 2023) Ipek, Cengiz; Sofiyev, Abdullah H.; Fantuzzi, Nicholas; Efendiyeva, Sadige P.
    The buckling behavior of functionally graded carbon nanotube (FG-CNT) reinforced polymer-based moderately-thick plates subjected to in-plane biaxial compressive loads in elastic and thermal environments in the framework of first-order shear deformation plate theory (FSDPT) is investigated. First, the temperature-dependent properties of CNTs and nanocomposites are defined and their constitutive relations are established, then the stability and strain compatibility equations in elastic media are derived in the framework of the FSDPT. Then, by applying the Galerkin method to the basic equations, a closed-form solution is obtained for the critical biaxial compressive loads. The specific numerical analyzes and interpretations are made for various plate sizes and CNT patterns on the Winkler elastic foundation and in thermal environments within FSDPT and classical plate theory (CPT).
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    Buckling behavior of sandwich cylindrical shells covered by functionally graded coatings with clamped boundary conditions under hydrostatic pressure
    (MDPI, 2022) Sofiyev, Abdullah H.; Fantuzzi, Nicholas; Ipek, Cengiz; Tekin, Gülçin
    The buckling behavior of sandwich shells with functionally graded (FG) coatings operating under different external pressures was generally investigated under simply supported boundary conditions. Since it is very difficult to determine the approximation functions satisfying clamped boundary conditions and to solve the basic equations analytically within the framework of first order shear deformation theory (FOST), the number of publications on this subject is very limited. An analytical solution to the buckling problem of FG-coated cylindrical shells under clamped boundary conditions subjected to uniform hydrostatic pressure within the FOST framework is presented for the first time. By mathematical modeling of the FG coatings, the constitutive relations and basic equations of sandwich cylindrical shells within the FOST framework are obtained. Analytical solutions of the basic equations in the framework of the Donnell shell theory, obtained using the Galerkin method, is carried out using new approximation functions that satisfy clamped boundary conditions. Finally, the influences of FG models and volume fractions on the hydrostatic buckling pressure within the FOST and classical shell theory (CT) frameworks are investigated in detail.
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    Dynamic Behavior of Shafts, Couplings and Working Body of the Machine under Torsional Impact Moment
    (Shahid Chamran University of Ahvaz, 2024) Khalilov, Isa Ali; Sofiyev, Abdullah H.
    In this study, the influence of the torsional rigidity of the connected shafts, couplings and the working body of the machine, as well as the damping capacity of the coupling, on the torsional impact moment generated in the machine transmission is investigated. Unlike existing classical calculation models, the torsional stiffness of the connected shafts, the torsional damping ability of the coupling and the effects of the moment ratio are taken into consideration together. Under these conditions an analytical expression for the shock moment or resonance coefficient is obtained. The main novelties in obtaining of this expression are the ratio of the torsional stiffness of the connected shafts with the torsional stiffness of the coupling and the acceptance of the moment of resistance of the working body of the machine depending on the torsional stiffness. It has been found that the considered factors have a significant effect on the resonance zone. Finally, different and overlapping conditions are determined when determining the value of the resonance coefficient characterizing the torque impact moment, calculated according to the classical and proposed models. © 2024 Published by Shahid Chamran University of Ahvaz
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    Modeling and solution of eigenvalue problems of laminated cylindrical shells consisting of nanocomposite plies in thermal environments
    (Springer Science and Business Media Deutschland GmbH, 2024) Sofiyev, Abdullah H.
    This work is dedicated to the modeling and solution of eigenvalue problems within shear deformation theory (SDT) of laminated cylindrical shells containing nanocomposite plies subjected to axial compressive load in thermal environments. In this study, the shear deformation theory for homogeneous laminated shells is extended to laminated shells consisting of functionally graded (FG) nanocomposite layers. The nanocomposite plies of laminated cylindrical shells (LCSs) are arranged in a piecewise FG distribution along the thickness direction. Temperature-dependent material properties of FG-nanocomposite plies are estimated through a micromechanical model, and CNT efficiency parameters are calibrated based on polymer material properties obtained from molecular dynamics simulations. After mathematical modeling, second-order time-dependent and fourth-order coordinate-dependent partial differential equations are derived within SDT, and a closed-form solution for the dimensionless frequency parameter and critical axial load is obtained for first time. After the accuracy of the applied methodology is confirmed by numerical comparisons, the unique influences of ply models, the number and sequence of plies and the temperature on the critical axial load and vibration frequency parameter within SDT and Kirchhoff–Love theory (KLT) are presented with numerical examples.
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    Size-dependent nonlinear vibration of functionally graded composite micro-beams reinforced by carbon nanotubes with piezoelectric layers in thermal environments
    (Springer, 2022) Gia Phi, Bui; Van Hieu, Dang; Sedighi, Hamid M.; Sofiyev, Abdullah H.
    Nonlinear free vibration characteristics of functionally graded (FG) composite micro-beams reinforced by carbon nanotubes (CNTs) with piezoelectric layers in thermal environment are investigated in this work. The uniform distribution and four nonuniform distribution types of the CNTs reinforcements are examined. The equations of motion are derived based on the Euler–Bernoulli beam theory with von Karman’s assumption, the nonlocal strain gradient theory and the Hamilton’s principle. The approximate nonlinear frequencies of FG-carbon nanotube-reinforced composite (CNTRC) micro-beams for simply supported and clamped–clamped boundary conditions are obtained by using two analytical methods including the equivalent linearization method and the energy balance method. The accuracy of the obtained results has been verified. The influences of the nonlocal parameter, material length scale parameter, geometric property of micro-beam, temperature change, applied voltage, distribution pattern and volume fraction of the CNTs on the nonlinear free vibration behaviors of the FG-CNTRC micro-beams are performed and discussed in detail.
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    Stability Analysis of Shear Deformable Inhomogeneous Nanocomposite Cylindrical Shells under Hydrostatic Pressure in Thermal Environment
    (Multidisciplinary Digital Publishing Institute (MDPI), 2023) Sofiyev, Abdullah H.; Fantuzzi, Nicholas
    In this study, the stability of inhomogeneous nanocomposite cylindrical shells (INCCSs) under hydrostatic pressure in a thermal environment is presented. The effective material properties of the inhomogeneous nanocomposite cylindrical shell are modeled on the basis of the extended mixture rule. Based on the effective material properties, the fundamental relations and stability equations are derived for thermal environments. In this process, the first-order shear deformation theory (FSDT) for the homogeneous orthotropic shell is generalized to the inhomogeneous shell theory. This is accomplished using the modified Donnell-type shell theory. The analytical expressions are obtained for hydrostatic buckling pressure of INCCSs in the framework of FSDT and classical shell theory (CST) by obtaining a solution based on Galerkin’s procedure. The numerical examples presented include both comparisons and original results. The last section shows the influences of carbon nanotube (CNT) models, volume fraction, and shell characteristics on the hydrostatic buckling pressure in the thermal environment.
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    Thermoelastic behavior of an isotropic solid sphere under a non-uniform heat flow according to the MGT thermoelastic model
    (Taylor & Francis, 2022) Abouelregal, Ahmed E.; Saidi, Anouar; Mohammad-Sedighi, Hamid; Shirazi, Ali H.; Sofiyev, Abdullah H.
    Moore-Gibson-Thompson (MGT) is an equation which appropriately describes the spread of sound waves in gasses and fluids as well as thermal/mechanical waves in elastic bodies. The objective of this article is to theoretically analyze the generalized thermoelasticity models that have been presented as the development of the Fourier’s law dealing with the paradox of unlimited propagation velocities of thermal waves. For this purpose, a new model is presented which combines the third type of Green and Naghdi model (GN-III) with the generalized theory including the relaxation time based on the MGT equation. The proposed model may be considered as a generalization of previous thermoelastic theories. To examine the introduced approach, the behavior of thermoelastic waves within a homogeneous isotropic sphere in which its surface is exposed to thermal shock with varying heat source is investigated. The variations in different physical fields of a given substance have been computed by means of Laplace transform technique and an efficient numerical technique is implemented in Laplace inversion procedure. The effect of different forms of heat source are also examined and several comparisons for various thermoelasticity approaches are comprehensively conducted.