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In this study, dynamic properties of fluid-conveying flexoelectric cylindrical nanoshells subjected to an electric field are examined throughout the wave propagation approach. Employing nonlocal strain gradient theory (NSGT) and constitutive flexoelectric relations for shell-type structure, a new model has been represented regarding the Love shell theory. Governing motion equations are derived exploiting Hamilton's principle and are then solved numerically to acquire the wave propagation properties. A discussion on numerical results is then implemented to highlight the exact wave propagation response of the structure against the flexoelectric effect, electric field, flow velocity and external force. The results reveal a remarkable effect of flexoelectricity on wave propagation response especially for some modes in specific wave number domains. As a prominent result, the flexoelectricity effect on wave dispersion response is found more pronounced for second and third modes, compared to the first mode. In addition, this effect is more tangible for lower wave numbers. The applied positive or negative electric and mechanical force exhibits a decreasing or increasing effect on the phase velocity of all the modes. The presented investigation and the reported results may be useful in designing the systems which are benefiting from wave propagation phenomenon properties of cylindrical nanoshells. [ABSTRACT FROM AUTHOR]

This paper investigates the dynamical responses and performances of mono-, bi-, and tri-stable nonlinear energy sinks in simultaneous vibration suppression and energy harvesting as well as solely vibration mitigation. To this end, a realizable multi-stable nonlinear energy sink composed of a bimorph cantilever beam and arrays of magnets is considered for vibration mitigation. The target vibrating structure is a simply-supported beam under a harmonic excitation. The proposed absorber can exhibit multi-stability based on the magnet gaps. First, using extended Hamilton's principle, the coupled continuous magneto-electromechanical equations governing the system are obtained. Next, the bifurcations of the absorber fixed points that lead to different stability states are analyzed. Then, the time- and frequency-responses of the coupled system are studied using time integration. The results show that the bi- and tri-stable absorbers perform well in case of strongly modulated responses. Furthermore, the response of the coupled system is verified using the harmonic balance method and pseudo-arclength continuation. Next, the potential well escape method based on the harmonic balance solution is exploited to investigate the strongly modulated response emergence and disappearance as well as its variations with the system parameters. The coupling mechanism of the nonlinear absorber to the host beam is also studied using linearization and compared with the harmonic balance solution. In addition, in order to compare the performances of the bi-stable and tri-stable absorbers, energy-based analyses are performed. The results reveal the average harvested power per average kinetic energy of the main system for a bi-stable absorber is higher than a tri-stable absorber. Furthermore, the bi-stable absorber can mitigate the host structure vibration more than the tri-stable absorber. Finally, it is observed that the bi-stable absorber suppresses the vibration more than its corresponding mono-stable absorber and harvests more energy over a broader frequency region. [ABSTRACT FROM AUTHOR]

The advantages of carbon nanotubes (CNTs) in fortifying the glass fiber reinforced polymeric (GFRP) composites are discussed in this paper. Bolted steel straps are utilized at the edges of composite plate to establish clamped conditions in the test setup. To minimize uncertainties caused by bolt attachments, a genetic algorithm-based model updating approach has been implemented by introducing artificial linear springs at the margins to achieve a better balance between theory and reality. The accuracy of the plate's results (natural frequencies and mode shapes) is verified, and the mechanical properties of randomly dispersed CNTs are incorporated in the formulations of folded plates. Remarkably, the motion equations are brought forward by the first order shear deformation theory (FSDT). Thereafter, two-directional generalized differential quadrature (2D-GDQ) technique is employed to determine natural frequencies from available motion, continuity, and boundary equations. The results of the folded plate are validated first by an experimental modal testing and finally some effective parameters such as folding angle, CNT weight ratio, boundary condition and flange-shape length are examined. [ABSTRACT FROM AUTHOR]

The current paper is focused on the frequency features of spinning coupled functionally graded carbon nanotube reinforced (FG-CNTRC) cone-cone shells undergoing high temperatures. The physic of the structures is based on two conical shell segments with different semi-vertex angles that are merges via the ideal bonding at the junctures. Simultaneous consideration of environmental thermal effects and rotation about the structure's axis in dealing with conditions near and also far from critical speeds and buckling temperatures could add the novelty of the available paper. The frequency inspections include the study of free vibration behavior, frequency bifurcation of traveling waves and also identifying instability regions with regard to critical thermal buckling and critical speed phenomena. A two-step procedure based on first order shear deformation theory (FSDT) and von Kármán assumptions is employed to access the system's formulation. Firstly, the initial thermal stress resultants are captured upon static step and then utilized through the dynamic step. Afterward, generalized differential quadrature (GDQ) method is implemented on the set of governing equations. After verifying the precision of results, some parametric studies are provided to investigate the effects of temperature and rotary speed elevations, radius and position of conjunction, CNT volume fraction and distribution schemes on the dynamic attributes of the spinning structure. [ABSTRACT FROM AUTHOR]

Sound transmission loss (STL) can be augmented in buildings using graphene nanoplatelets (GPLs) and metamaterials. The present study established an analytical model grounded on the three-dimensional (3D) elasticity theory to predict STL in a doubly curved shell with a 3D re-entrant auxetic cellular core (3D-RACS) and GPLs as the top layer. The state space method was used to offer an analytical solution, where each part of the structure was divided into a number of layers and each layer into several sublayers. The stiffness matrix of the core was developed according to elastic properties such as Young's modulus, shear modulus, and Poisson's ratio out of the plane. The findings revealed that GPLs as the top layer had a tremendous impact on the structure's performance. Furthermore, the effects of 3D-RACS and GPL parameters on the structure's STL were investigated in the stiffness and mass control domains. Accordingly, the addition of the core material significantly affected high frequencies, particularly in the mass control domain. Finally, the results indicated that curvature and coincidence frequencies could be changed by optimizing 3D-RACS and GPL parameters. Doubly curved structures have different applications in different industries, and due to the complexity of their modelling, they have been used less in research. Nowadays, structural vulnerability to acoustic waves is a concern in the industry, and designers seek to prevent the transmission of acoustic waves into the structure. This is why the study of sound transmission loss is so broad. One of the best methods is to increase the rigidity of the structure because increasing the stiffness of the structure increases the sound transmission loss. In this regard, auxetic materials (3D-RACS) used as a type of metamaterial can have a significant impact on increasing the loss of sound transmission. Due to the use of a sandwich structure in this research, however, GPL material is used for the outer wall exposed to waves. This material can increase the structural rigidity of a structure despite its lightness. Finally, by designing such a structure and comparing the results, a very effective output has been obtained. [ABSTRACT FROM AUTHOR]

Thickness size effect is known as a size-dependent effect which might play an important role in mechanical behavior of nano-sized structures. This effect has not been considered so far for nano-energy harvester's behavior analysis. This paper aims to elucidate the size-dependent nonlinear vibrational response of flexoelectric nano-energy harvesters considering the effect of strain gradient, surface elasticity and thickness size effect. The fundamental equations are established based on the constitutive relations for a flexoelectric bulk, surface elasticity, Maxwell theory and Gauss law. Also, Euler–Bernoulli beam theorem together with nonlinearity of von-Karman is employed. The obtained governing equations of motion throughout Hamiltonian's principle are then discretized via single-mode discretization based on Galerkin's approach. Static condensation methodology is employed to decline the number of the acquired time-dependent equations. The multiple timescales method as a solution approach is hired to solve the resulted nonlinear equations analytically. According to the obtained frequency response, the maximum amplitude of the generated voltage and power is calculated and corresponding curves are presented. A comprehensive numerical investigation is finally implemented to analyze the size-dependent behavior of the harvested energy against various involved factors, namely thickness size effect, flexoelectricity and surface effects, load resistance and base excitation, considering energy harvesters with different thicknesses. As a paramount result, it is concluded that the thickness size effect has an essential influence on the nano-scale energy harvester's dynamics, especially for those with lower thicknesses. It is disclosed that similar to the surface effect and flexoelectric phenomenon, the thickness effect is also size-dependent. The results disclose that in addition to the surface and flexoelectric effects, thickness size effect could also be considered in mathematical formulation of nano-energy harvesters to modify the conventional models. This might lead to reach nano-energy harvesters with higher performance and efficiency. [ABSTRACT FROM AUTHOR]

Corrugated structures are widely being used in industrial applications, which raises the demand for careful analysis of their behavior. To fill the gap for vibroacoustic characteristics, this paper focuses on proposing a model to investigate sound transmission through double-walled cylindrical shells with a circumferentially corrugated core. The structure is composed of outer and inner isotropic layers and a corrugated core. The outer layer is subjected to an oblige plane wave, and also a subsonic flow is traveling outside the double-walled shell. An equivalent method is applied to replace the corrugated core as axial, radial, and rotational springs with specific stiffness coefficients. The first-order shear deformation theory (FSDT) is applied to describe the behavior of isotropic shells. A considerable parametric study is established concerning both the incident wave and structural characteristics. The results show that the presence of the corrugated core improves sound transmission loss (STL) of the structure in the mass-controlled region, and it has a negative effect on STL in the coincidence-controlled region; therefore, using such a core for sound insulation depends on the desired frequency domain. [ABSTRACT FROM AUTHOR]

This paper is dedicated to examine the size-dependent nonlinear forced dynamics of MRE-cored sandwich micro-pipes in existence of external distributed load and internal flow. For this aim, Euler-Bernoulli beam theory, considering von-Karman nonlinearity, together with the modified couple stress theory (MCST) are exploited to attain a mathematical formulation of the problem. Employing Galerkin's approach with consideration of two axial and transverse modes, the obtained nonlinear partial differential equations are discretized, from which nonlinear ordinary equations are achieved. Thereafter, static condensation method is utilized in order to reduce the number of the obtained ordinary equations. The acquired nonlinear equations are then solved according to the method of multiple scales, which leads to nonlinear natural frequencies and frequency-response curves of the system. Throughout the numerical analysis, the effect of a smart MRE core existence on the system's response, considering various boundary conditions, is explored. Additionally, a numerical investigation is implemented to highlight the influences of MRE-related intrinsic properties namely the intensity of the applied magnetic potential and MRE core thickness on the natural frequencies, frequency-response and load-response curves of the system. Totally, the substantial role of the MRE core and its intrinsic characteristics on the dynamic response of the system is explored, which implies that, this smart core could be a good candidate in such sandwich structures in order to control and boost the dynamic properties and response of the mechanical systems. [ABSTRACT FROM AUTHOR]

A viscoelastic model is proposed in this approach to determine the sound transmission loss coefficient of a sandwich shell system with double curvature. The structure is composed of a double-walled composite shell subjected to a viscoelastic core. Investigating the efficient impresses of rotary inertia and shear deformation, vibration equations of both outer and inner shells are extracted within the framework of shear deformation shallow shell theory. Besides, the Zener mathematical model is used for viscoelastic material, which is based on a spring connected in series with a parallel mixture of spring and dashpot. This model presents the dynamic response in the whole frequency domain at which shear modulus and bulk complex modulus are frequency dependent. Since the performed studies on the sound transmission loss of this kind of structures are insignificant, the outcomes of plate models with a viscoelastic core are used to provide a reliable sound transmission loss comparison. The results show that the applied strategy can improve the acoustic characteristics of the system at high frequencies compared to that of a single-layer one with the same mass. This issue is more highlighted while the thickness of the viscoelastic layer enhances, which confirms the positive performance of the viscoelastic materials in this range of frequency, particularly in the resonant frequency. In addition to the curvature effect on acoustic features, the vibration response of the system is configured based on various frequencies and materials. [ABSTRACT FROM AUTHOR]

The present study is concerned with an analytical solution for calculating sound transmission loss through an infinite double-walled circular cylindrical shell with two isotropic skins and a polymeric foam core. Accordingly, the two-walled cylindrical shell is stimulated applying an acoustic oblique plane wave. The equations of motion are derived according to Hamilton's principle using the first-order shear deformation theory for every three layers of the construction. Additionally, by the aid of employing the Zener mathematical model for the core of polymeric foam, mechanical properties are determined. To authenticate the results of this study, the damping of the core layer goes to zero. Therefore, the numerical results in this special case are compared with those of isotropic shells. The results prove that the presented model has high accuracy. It is also designated that decreasing the power-law exponent of the core leads to improving the sound transmission loss through the thickness of the construction. Besides, in addition to probe some configurations versus alterations of frequencies and dimensions, the convergence algorithm is provided. Consequently, it is realized that by increasing the excitation frequency, the minimum number of modes to find the convergence conditions is enhanced. The results also contain a comparison between the sound transmission loss coefficient for four different models of a core of a sandwiched cylindrical shell. It is comprehended that the presented model has a transmission loss coefficient more than the other types of the core at high frequencies. [ABSTRACT FROM AUTHOR]

This article presents the numerical results for acoustic transmission through relatively thick functionally graded carbon nanotube-reinforced composite (FG-CNTRC) cylindrical shells. The vibration behavior of cylindrical shell is modeled using the first-order shear deformation theory (FSDT) which takes into account the transverse shear strains averaged over the wall thickness. Effective properties of materials of the shell reinforced by single-walled carbon nanotubes (SWCNTs) are estimated through a micromechanical model based on the extended rule of mixture. Furthermore, four different types of distribution of carbon nanotubes (CNTs) along the thickness direction, i.e., UD, FG-V, FG-O, and FG-X, are considered. The shell is submerged in a fluid with an external airflow and an oblique plane wave excites on the external sidewall of the shell. In order to obtain an analytical solution of sound transmission loss (STL), the motion equations of the shell and acoustic wave equations are simultaneously solved. Then, natural frequencies and STL are extracted and they are compared with those available in the literature. Finally, the obtained results are discussed to demonstrate the effectiveness of the CNT distribution, volume fraction of CNTs, shell thickness, and Mach number on STL. [ABSTRACT FROM AUTHOR]

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This article is provided to investigate the free vibrational behaviors accompanied by buckling characteristics of carbon nanotube-reinforced conical shells via the Haar wavelet technique. For a better performance in the thermal environments, materials used in the structure obey the temperature-dependent relations. On the other hand, carbon nanotubes are embedded across the thickness uniformly or functionally. Using Hamilton's principle through the first-order shear deformation theory yields governing equations. Both dynamic and stability states are evaluated in the vicinity of equilibrium state and are also derived with regard to initial thermal stresses that are obtained via linear membrane technique in static analysis. The obtained partial differential equations are converted into ordinary ones with the aid of separating variable technique. Subsequently, the Haar wavelet approach is used to discretize the equations meridionally and transform them into new algebraic ones. Capability of this approach in calculation of frequencies with only a few numbers of the collocation points is demonstrated. Finally, to verify the integrity and precision of the proposed approach, some comparison studies are made with those of relevant results in the literature primarily. Thereafter, some effective parameters such as the geometry of nanotube, different boundary conditions, temperatures, and material properties are studied. [ABSTRACT FROM AUTHOR]

A theory is proposed to study the vibrations of homogenous isotropic circular cylindrical shells based on a developed plate vibration theory. By proposing a novel distribution of the shear stress and strain across the thickness of the shell, the arguments are adjusted such that the transverse shear strains and stresses equal zero at the shell surfaces. Due to the existing curvature in the circumferential direction, the defined shear stress and strain distributions consider a change in the position of the neutral plane toward the center of curvature. In the presented Two-Separated Lateral Displacement (TSLD) theory, the lateral displacement is defined by two bending and shear parts to provide an analytical model, referred to as the four-variable refined plate theory. The similarity to classical theory and involving only four unknowns are significant features of the introduced theory. The TSLD theory is verified against the available data in the literature. It is shown that the provided stress and stress distributions lead to more accurate results, especially in moderately thick cylinders. The proposed theory is remarkably more precise than classical shell theory and First-order Shear Deformation Theory (FSDT). Results of the TSLD theory are as accurate as the Higher-Order Shear Deformation Theory (HOST12) for the higher frequency parameters and more thick shells, while the TSLD theory implementation is much simpler than the HOST12. [ABSTRACT FROM AUTHOR]

This paper investigates simultaneous vibration suppression and energy harvesting through a continuous dynamic vibration absorber (DVA) with piezoelectric coupling, both numerically and analytically. The proposed system is composed of a simply supported host beam that is under a periodic external forcing or transient excitation in the form of an initial condition. Besides, a DVA is attached to the host beam. First, the governing electromechanical equations of the coupled system are derived. Next, convergence analyses are performed to find the effects of the considering higher modes of the host and absorber beam. Furthermore, the frequency response curves of the mechanical and electrical responses are obtained. It is observed that the DVA can effectively annihilate the host structure vibrations, up to 98.5%, and at the same time harvest considerable levels of voltage/power. Moreover, comprehensive investigations on the role of various mechanical and electrical parameters on the system responses are carried out. To validate the numerical results, an analytical solution is provided and a great agreement between these solution schemes is observed. Also, the dynamics of the considered system under an initial condition is inspected. Finally, the effects of the PZT layers in vibration isolation performance are studied. Results divulged that, upon the proper tuning of the mechanical and electrical parameters, the proposed DVA can significantly scavenge energy and mitigate vibrations. [ABSTRACT FROM AUTHOR]

Wave dispersion response of a fluid-carrying piezoelectric nanotube is studied in this paper utilizing an improved model for piezoelectric materials which capture a new effect known as flexoelectricity in conjunction with the surface elasticity. For this aim, a higher order shear deformation theory is employed to model the problem. Furthermore, strain gradient effect as well as nonlocal effect is taken into consideration throughout using the nonlocal strain gradient theory (NSGT). Surface elasticity is also considered to make an accurate size-dependent formulation. Additionally, a non-compressible and non-viscous fluid is taken into consideration to model the flow effect. The wave propagation solution is then implemented to the governing equations obtained by Hamiltonian’s approach. The phase velocity and group velocity of the nanotube is determined for three wave modes (i.e. shear, longitudinal and bending waves) to study the influence of various involved factors including strain gradient, nonlocality, flexoelectricity and surface elasticity and flow velocity on the wave dispersion curves. Results reveal a considerable effect of the flexoelectric phenomenon on the wave propagation properties especially at a specific domain of the wave number. The size-dependency of this effect is disclosed. Overall, it is found that the flexoelectricity exhibits a substantial influence on wave dispersion properties of the smart fluid-conveying systems. Hence, such size-dependent effect should be considered to achieve exact and accurate knowledge on wave propagation characteristics of the system. [ABSTRACT FROM AUTHOR]

The present approach considers hybrid control strategy to reduce the amount of transmitted sound through a multilayered doubly curved sandwich shell equipped with piezoelectric layer and shunt circuit. The construction is composed of some piezoelectric actuator and sensor layers as an active controller as well as resistance–inductance shunt circuit as passive controller. In addition, a layer made of isotropic material is also sandwiched as a core. Firstly, in order to obtain the electromechanical equations of curved shell integrated with piezoelectric layers, Hamilton's principle, and shear deformation shallow shell theory are employed. After presenting the sound transmission loss of structure, the reliability of the formulation is checked by the aid of previous outcomes. In the following, the piezoelectric layers coupled with shunt circuit are employed to inspect the influence of these patches on the control of transmitted sound through structure. The results indicate that the shunt circuit is able to enhance the sound transmission loss at resonant frequency with no need source of energy. Since in designing the engineering structures, the transmitted noise control is important especially in the resonant frequency, the influence of using several parallel shunt circuits with each piezoelectric layer is also examined. It is shown that increment of the number of parallel shunt circuits implies substantial reduction of transmitted sound to the structure in the resonant frequency. Finally, the solution process is followed to study the effect of active control on the acoustic transmission. Then, it is found that employing the simultaneous active and passive controllers not only cause to reduce the transmitted noise in the resonant frequency but also make to improve the behavior of sound transmission loss in entire range of frequency. [ABSTRACT FROM AUTHOR]

Multi-objective vibroacoustic optimization of the double-walled doubly curved composite shells having poroelastic lining in its core in a diffuse field is performed based on Non-dominated sorting Genetic Algorithm-II. To present an analytical model on the basis of multi-objective optimization, the summation of sound transmission loss and transverse displacement along with weight of the structure are considered as two cost functions, which should be optimized in a diffuse field. In fact, the significant achievement of this work is to design an optimization algorithm to improve vibroacoustic fitness and weight of the sandwich doubly curved shells. In the first part of the paper, a general formulation is prepared to analyze the dynamic of the poroelastic composite sandwich structures. Likewise, some validation configurations are presented to confirm the accuracy of the current formulation. Consequently, an optimization algorithm is provided on the basis of considering some appropriate design variables including material and porous types as well as stacking sequences. In this regard, a batch of 19 benchmarks of porous core is investigated. Furthermore, a configuration of optimized points in the Pareto front is plotted in which the simultaneous effects of optimizing the weight and vibroacoustic fitness can be observed. As a result, a new approach is made through optimization of the transverse displacement of the structure as a function of various incidence and azimuth angles in three dimensional configurations with respect to different frequencies. [ABSTRACT FROM AUTHOR]

Fluid-conveying micro/Nano structures are key tools in MEMS and NEMS applications especially for drug delivery systems to attack a specific tumor like cancer cells. Vibrational characteristics of such tools play a crucial role in delivering efficient and reliable performance in various applications. As a result, vibration and instability control of such systems is of great importance. Vibration and instability response of magnetostrictive sandwich cantilever fluid-conveying micro-pipes is investigated in this paper utilizing smart magnetostrictive layers as actuators. Euler–Bernoulli beam model together with modified couple stress theory (MCST) are used to model the problem. As main properties of these smart layers, magnetic intensity effect, velocity feedback gain and thermal effects are taken into account in the modeling. The governing equation is extracted employing Hamilton's principle. Extended Galerkin procedure is applied to discretize the governing equation and obtain the eigenvalue problem which is solved straightforwardly to reach the eigenvalues. Afterwards, eigenvalue diagrams are studied to analyze the vibrational characteristics and possible instabilities (flutter and bifurcation) occurring in first three modes of the system. Throughout this analysis, the role of various intrinsic properties of the magnetostrictive layers on the critical flow velocity and frequency is studied in detail. The numerical results show a good ability for the used smart layers to control the instability of fluid-conveying micro-pipes. Therefore, these sandwich structures may be helpful for achieving a novel design for such systems. [ABSTRACT FROM AUTHOR]

This paper presents an analytical model to embed porous materials in a finite cylindrical shell in order to obtain the sound transmission loss coefficient. Although the circumferential modes are considered only for calculating the amount of the transmitted noise through an infinitely long cylinder, the present study employs the longitudinal modes in addition to circumferential ones to analyze the vibroacoustic performance of a simply supported cylinder subjected to the porous core based on the first order shear deformation theory. To achieve this goal, the structure is immersed in a fluid and excited by an acoustic wave. In addition, the acoustic pressures and the displacements are developed in the form of double Fourier series. Since these series consist of infinite modes, it is essential to terminate this process by considering adequate modes. Hence, the convergence checking algorithm is employed in the form of some three-dimensional configurations with respect to length, frequency and radius. Afterwards, some figures are plotted to confirm the accuracy of the present formulation. In these configurations, the obtained sound transmission loss from the present study is compared with that of the infinite one. It is shown that by increasing the length of the structure, the results are approached to sound transmission loss of the infinite shells. Moreover, a new approach is proposed to show the transverse displacement of a finite poroelastic cylinder at different frequencies. Based on the outcomes, it is found that by enhancing the length of the poroelastic cylinder, the amount of the transmitted sound into the structure is reduced at the high frequency domain. However, the sound insulation property of the structure is improved at the low frequency region when the radius of the shell is decreased. [ABSTRACT FROM AUTHOR]

In this study, a robust controller against the uncertainties in piezoelectric patches including sensor and actuator is designed based on sliding mode method to control the radiated sound from cylindrical shells. Accordingly, in order to extract and discretize the dynamic equations of a smart cylinder equipped with piezoelectric patches, the Hamilton's principle and the Rayleigh-Ritz method are, respectively, used. The radiated sound is estimated by the Kirchhoff-Helmholtz integral and the acoustic structural sensing method. Furthermore, an innovative approach is proposed on sliding mode control to model system uncertainties and design robust control signals against these disturbances. Using effective control signals for each mode is the applied methodology for establishing independent sliding surfaces. In fact, it is attempted to relate between actuator matrix determinant and system control ability in generating the efficient control signals and error reduction due to actuators uncertainties. By the aid of this relation, optimization of the actuators position according to the genetic algorithm is implemented. The obtained results show that by optimizing the actuators position not only the appropriate performance of the system in controlling the radiated sound from the structure is enhanced but also the essential control voltage for each actuator is significantly decreased. [ABSTRACT FROM AUTHOR]

In this paper, thermal buckling and free vibration of orthogonally stiffened functionally graded truncated conical shells in thermal environment is investigated. Conical shell has been stiffened by rings and stringers, and the influences of the stiffeners are evaluated by the aid of smearing method. The material properties of the structure are assumed to be changed continuously in the thickness direction. First, the initial thermal stresses are obtained accurately by solving the thermoelastic equilibrium equations. Then, by taking into account the initial thermal stresses, equations of motion as well as boundary conditions are obtained, applying the Hamilton's principle and the first-order shear deformation theory. The natural frequencies of the system have been achieved, solving these governing equations with considering Differential Quadrature Method (DQM). In addition to Eigen frequency analysis, the critical buckling-temperature of the conical shell has been computed. Moreover, the effects of geometrical parameters, number of stiffeners, thermal environment and various boundary conditions on natural frequency of the system have been investigated. Finally, in order to validate the present work, the results are compared with those of other researches available in literature. [ABSTRACT FROM AUTHOR]

In this article, an approximate solution using differential quadrature method is presented to investigate the effects of thermo-mechanical loads and stiffeners on the natural frequency and critical speed of stiffened rotating functionally graded cylindrical shells. Transverse shear deformation and rotary inertia, based on first-order shear deformation shell theory (FSDT), are taken into consideration. The equations of motion are derived by the Hamilton's principle while the stiffeners are treated as discrete elements. Material properties are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fraction of the constituents. The temperature field is assumed to be varied in the thickness direction. The equations of motion as well as the boundary condition equations are transformed into a set of algebraic equations applying the DQM. The results obtained include the relationship between frequency characteristics of different power-law index, rotating velocities, thermal loading and amplitude of axial load. To validate the present analysis, the comparison is made with a number of particular cases in literature. Excellent agreement is observed and a new range of results are presented for stiffened rotating FG cylindrical shell under thermo-mechanical loads which can be used as a benchmark to approximate solutions. [ABSTRACT FROM AUTHOR]

Composite structures are often used in the aerospace industry due to the advantages offered by a high strength to weight ratio. Sound transmission through an infinite laminated composite cylindrical shell is studied in the context of the transmission of airborne sound into the aircraft interior. The shell is immersed in an external fluid medium and contains internal fluid. Airflow in the external fluid medium moves with a constant velocity. An exact solution is obtained by simultaneously solving the first-order shear deformation theory (FSDT) of a laminated composite shell and the acoustic wave equations. Transmission losses (TL) obtained from numerical solutions are compared with those of other authors. The effects of structural properties and flight conditions on TL are studied for a range of values, especially, the Mach number, stack sequences, and the angle of warp. Additionally, comparisons of the transmission losses are made between the classical thin shell theory (CST) and FSDT for laminated composite and isotropic cylindrical shells. [ABSTRACT FROM AUTHOR]

In this paper, size-dependent wave dispersion behavior of smart piezoelectric nanotubes conveying viscous fluid is analyzed considering surface stress effects and slip boundary conditions. The size effects of the nanotube are taken into account by making use of the nonlocal strain gradient theory (NSGT). To take the slip boundary conditions into consideration, the average velocity correction factor is utilized. The Newtonian method, in conjunction with the Rayleigh beam theory, is incorporated within the constitutive stress-strain relations of the surface and bulk of a piezoelectric material to derive the governing equations. The obtained equations involve size-dependent parameters, surface effects, slip boundary conditions, fluid viscosity and piezoelectric voltage. As a consequence, an analytical solution is applied to extract the wave dispersion relation of the nanotube. In addition, the influences of different factors, including nonlocal parameter, length scale parameter, surface effects, piezoelectric voltage, surface elastic modulus and surface residual stress on the wave dispersion characteristics of the piezoelectric nanotube, are examined. The effects of the piezoelectric voltage on the damping ratio of the nanotube are also studied. The obtained results in this paper are expected to be useful for more accurate prediction of the mechanical behaviors as well as of the wave propagation characteristics of viscous-fluid-conveying piezoelectric smart nanotubes. Meanwhile, the results will be helpful for efficient applications of piezoelectric nanotubes designing smart mechanical systems on a nanotechnology basis. [ABSTRACT FROM AUTHOR]