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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]

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]