Showing papers on "Shell (structure) published in 2020"

Thermal buckling and forced vibration characteristics of a porous GNP reinforced nanocomposite cylindrical shell

Abstract: In this research, thermal buckling and forced vibration characteristics of the imperfect composite cylindrical nanoshell reinforced with graphene nanoplatelets (GNP) in thermal environments are presented. Halpin–Tsai nanomechanical model is used to determine the material properties of each layer. The size-dependent effects of GNPRC nanoshell is analyzed using modified couple stress theory. For the first time, in the present study, porous functionally graded multilayer couple stress (FMCS) parameter which changes along the thickness is considered. The novelty of the current study is to consider the effects of porosity, GNPRC, FMCS and thermal environment on the resonance frequencies, thermal buckling and dynamic deflections of a nanoshell using FMCS parameter. The governing equations and boundary conditions are developed using Hamilton’s principle and solved by an analytical method. The results show that, porosity, GNP distribution pattern, modified couple stress parameter, length to radius ratio, mode number and the effect of thermal environment have an important role on the resonance frequencies, relative frequency change, thermal buckling, and dynamic deflections of the porous GNPRC cylindrical nanoshell using FMCS parameter. The results of current study can be useful in the field of materials science, micro-electro-mechanical systems and nano electromechanical systems such as microactuators and microsensors.

Three-dimensional static and free vibration analysis of graphene platelet–reinforced porous composite cylindrical shell:

Abstract: Because of promoted thermomechanical performance of functionally graded graphene platelet–reinforced composite ultralight porous structural components, this article investigates bending and free vi...

Generalized variational principles for buckling analysis of circular cylinders

Abstract: A generalized variational principle and a parameterized generalized variational principle are obtained for large deformation analysis of circular cylinders by the semi-inverse method; all known variational principles in the literature are special cases of the obtained parameterized functional. In this approach, a trial functional is constructed with an energy-like integral involving an unknown function, which is identified step by step. The present paper provides a quite straightforward but rigorous tool to the construction of a variational principle for the shell or plate buckling.

Influence of system parameters on buckling and frequency analysis of a spinning cantilever cylindrical 3D shell coupled with piezoelectric actuator

Abstract: In this research, buckling and vibrational characteristics of a spinning cylindrical moderately thick shell covered with piezoelectric actuator carrying spring-mass systems are performed. This stru...

Vibration Control of a Smart Shell Reinforced by Graphene Nanoplatelets

Abstract: Smart control and dynamic investigation of a graphene nanoplatelets reinforced composite (GPLRC) cylindrical shell surrounded by a piezoelectric layer as actuator and sensor based on a numerical so...

Application of nanomaterial for thermal unit including tube fitted with turbulator

Abstract: In the present article, double pipe with installed tape was offered as a system to use the hot gas energy. The shell side was full of nanofluid (CuO-H2O) and counter flow was considered. Both zones contain turbulent regime and k–ɛ model has been implemented for simulation. Single phase model in predicting the feature of nanomaterial help us to decrease the computation cost. Modeling based on FVM was employed to extract the contours in various sections in shell region and calculation of f and Nu. In outputs, influences of revolution (N) and Re were examined. Go through the shell side, temperature goes up and velocity increases. When Re* = 5, N = 7, going from inlet to outlet sections leads to intensification of velocity and temperature about 36.1% and 5.63%. Changing N makes temperature to decline about 2.83% and 4.3% when Re = 5000 and 2000, respectively. Moreover, augment of revolution in Re* = 2 and 5 makes velocity to intensify about 16.15% and 12.53%. When N = 3, temperature declines about 4.11% with intensification of inlet velocity while velocity augments about 157.69%. Given Re* = 2, rise of N up to 5 causes Nu and f to intensify to about 17.4% and 33.15%, respectively. With intensification of Re at N = 3, Darcy factor declines to about 15.73% while Nu intensifies to about 100.59%.

Harmonic resonances of graphene-reinforced nonlinear cylindrical shells: effects of spinning motion and thermal environment

Abstract: This work investigates nonlinear harmonic resonance behaviors of graded graphene-reinforced composite spinning thin cylindrical shells subjected to a thermal load and an external excitation. The volume fraction of graphene platelets varies continuously in the shell’s thickness direction, which generates position-dependent useful material properties. Natural frequencies of shell traveling waves are derived by considering influences of the initial hoop tension, centrifugal and Coriolis forces, thermal expansion deformation, and thermal conductivity. A new Airy stress function is introduced. Harmonic resonance behaviors and their stable solutions for the spinning cylindrical shell are analyzed based on an equation of motion which is established by adopting Donnell’s nonlinear shell theory. The necessary and sufficient conditions for the existence of the subharmonic resonance of the spinning composite cylindrical shell are given. Besides the shell’s intrinsic structural damping, the Coriolis effect due to the spinning motion has a contribution to the damping terms of the system as well. Comparisons between the present analytical results and those in other papers are made to validate the existing solutions. Influences of main factors on vibration characteristics, primary resonance, and subharmonic resonance behaviors of the novel composite cylindrical shell are discussed. Furthermore, the mechanism of how the spinning motion affects the amplitude–frequency curves of harmonic resonances of the cylindrical shell is analyzed.

Influence of the Position of Artificial Boundary on Computation Accuracy of Conjugated Infinite Element for a Finite Length Cylindrical Shell

Abstract: Structural finite element coupled with the conjugated infinite element method is an efficient numerical technique for solving the acoustic radiation problem due to the vibration of underwater objects. However, for large complex structures, the total acoustic mesh would become very large if the artificial boundary is too far away from the structural wetted surface. Thus, the calculation time can become too long to confine the application of the conjugated infinite element method. On the other hand, if the artificial boundary is close to the structural wetted surface, it will lead to computation accuracy losing due to the near-field effects. Consequently, it is essential to present some guidelines based on the physical mechanism of structural acoustics to choose a suitable artificial boundary that optimizes calculation accuracy and efficiency. In present work, the evanescent wave theory of an infinite length cylindrical shell is adopted to theoretically analyze the decay characteristic of evanescent waves in near field. Then, the effect of the position of artificial boundary on computation accuracy of conjugated infinite element for a finite length ring-stiffened cylindrical shell is numerically investigated. Results suggested that for the cylindrical shell mentioned in this study, the artificial boundary can be placed at least 0.4 times the acoustic wavelength away from the structural wetted surface. What’s more, for high frequencies or large-scale structures, the required non-dimensional distance between the artificial boundary and the structural wetted surface increases.

Wave based method for free vibration characteristics of functionally graded cylindrical shells with arbitrary boundary conditions

Abstract: The wave based method (WBM) is used to analyze the free vibration characteristics of functionally graded material (FGM) cylindrical shell with arbitrary boundary conditions. The motion relationship is described by the first-order shear deformation shell theory (FSDST). The displacement components and transverse rotations are expressed as wave function expansions. In accordance with the dynamic relationship, the final governing equation and global matrix are assembled by incorporating the boundary matrices. The natural frequency of the system is obtained by solving the determinant of the global matrix. By comparing the results with those in the literature, the validity of the proposed method is verified. In addition, the influences of power-law exponents and boundary conditions on natural frequencies are analyzed. The effects of geometric parameters including the ratio of thickness to radius and the ratio of length to the radius on natural frequencies are discussed. The purpose of this paper is to demonstrate the ease of application of the WBM for the free vibration of FGM cylindrical shells with arbitrary boundary conditions. Furthermore, the advantage of the WBM are: (1) the global matrix is easy to construct; (2) different boundary conditions can be conveniently adjusted; (3) it is with high computational efficiency and precision.

Buckling analyses of functionally graded graphene-reinforced porous cylindrical shell using the Rayleigh–Ritz method

Abstract: In this article, buckling analysis of a porous nanocomposite cylindrical shell reinforced with graphene platelets (GPLs) using first-order shear deformation theory is carried out. Internal pores and GPLs are scattered uniformly and/or nonuniformly in the thickness direction. The mechanical properties such as the effective modulus of elasticity through the thickness direction are computed by the modified Halpin–Tsai micromechanics approach, whereas density and Poisson ratio are in accordance with the rule of mixtures. The Rayleigh–Ritz method is employed to obtain a critical buckling load of the graphene-reinforced porous cylindrical shell. The accuracy of the obtained formulation is validated by comparing the numerical results with those reported in the available literature as well as with the software ABAQUS. Moreover, the effects of patterns of internal pores and GPLs distribution, GPLs weight fraction, density and size of internal pores, different boundary conditions, geometric factors such as mid-radius to thickness ratio and shape of graphene platelets on the buckling performance of the functionally graded graphene platelet-reinforced composite porous cylindrical shell are explored.

Nonlinear dynamic analysis of piezoelectric functionally graded porous truncated conical panel in thermal environments

Abstract: In this article, the nonlinear dynamic response and free vibration of functionally graded porous (FGP) truncated conical panel with piezoelectric actuators in thermal environments are investigated by an analytical method. The panel resting on an elastic foundation which is modeled according to the Winkler–Pasternak theory. The material properties including Young's modulus, shear modulus, and density are assumed to smoothly through the shell thickness. Three types of porosity distribution across the thickness, namely, symmetric porosity distribution, non-symmetric porosity, and uniform porosity distribution, are considered. Theoretical formulations are presented based on the first-order shear deformation shell theory with a von Karman-Donnell type of kinematic nonlinearity. The non-linear motion equations and resulting equations are derived by using Hamilton's principle, Galerkin's method, and Runge-Kutta method. Lastly, some numerical results are presented to study the effects of shell characteristics, porosity distribution, porosity coefficient, applied actuator voltage, temperature increment and elastic foundations on the nonlinear dynamic response and the natural frequencies of the piezoelectric FGP truncated conical panel.

Variation of shell thickness in ZnO-SnO2 core-shell nanowires for optimizing sensing behaviors to CO, C6H6, and C7H8 gases

Abstract: ZnO-SnO2 core-shell nanowires (C-S NWs) with different shell thicknesses (0–120 nm) were prepared and their sensing behavior was systematically studied. ZnO-SnO2 C-S NWs were prepared using a two-step synthesis procedure, where core ZnO NWs were synthesized by a vapor-liquid-solid growth technique, and subsequently these cores were coated with SnO2 shell layers by using an advanced atomic layer deposition technique. The sensors were exposed to 10-ppm CO, C6H6, and C7H8 gases at an optimal working temperature. The shell thickness was optimized to be 40 nm, for which the sensor revealed the highest sensitivity and fastest dynamics to the above-mentioned gases. The sensing mechanism was discussed in detail and the dominant mechanism was related to the radial modulation effect as well as the volume fraction of the shell to the total volume of C-S NWs.

Free vibration analysis of FG-CNTRC shell structures using the meshfree radial point interpolation method

Abstract: This study conducts the first-known free vibration analysis of functionally graded carbon nanotubes-reinforced (FG-CNTRC) shell structures using the meshfree radial point interpolation method (RPIM). The modified first-order shear deformation theory (modified FSDT) is implemented to get the realistic effect of the transverse shear deformation with its parabolic distribution. Numerical examples are carried out to examine the convergence and accuracy of the element-free RPIM method in its application to the free vibration FG-CNTRC analysis of shell structures. Results obtained using the proposed meshfree method, demonstrate that the improved FSDT is very successful compared to closed-form solutions and finite element results using different shell theories.

A novel design, analysis and 3D printing of Ti-6Al-4V alloy bio-inspired porous femoral stem

Abstract: The current study is proposing a design envelope for porous Ti-6Al-4V alloy femoral stems to survive under fatigue loads. Numerical computational analysis of these stems with a body-centered-cube (BCC) structure is conducted in ABAQUS. Femoral stems without shell and with various outer dense shell thicknesses (0.5, 1.0, 1.5, and 2 mm) and inner cores (porosities of 90, 77, 63, 47, 30, and 18%) are analyzed. A design space (envelope) is derived by using stem stiffnesses close to that of the femur bone, maximum fatigue stresses of 0.3σys in the porous part, and endurance limits of the dense part of the stems. The Soderberg approach is successfully employed to compute the factor of safety Nf > 1.1. Fully porous stems without dense shells are concluded to fail under fatigue load. It is thus safe to use the porous stems with a shell thickness of 1.5 and 2 mm for all porosities (18–90%), 1 mm shell with 18 and 30% porosities, and 0.5 mm shell with 18% porosity. The reduction in stress shielding was achieved by 28%. Porous stems incorporated BCC structures with dense shells and beads were successfully printed.

Two-Neutron Halo is Unveiled in ^{29}F.

Abstract: We report the measurement of reaction cross sections (σ_{R}^{ex}) of ^{27,29}F with a carbon target at RIKEN. The unexpectedly large σ_{R}^{ex} and derived matter radius identify ^{29}F as the heaviest two-neutron Borromean halo to date. The halo is attributed to neutrons occupying the 2p_{3/2} orbital, thereby vanishing the shell closure associated with the neutron number N=20. The results are explained by state-of-the-art shell model calculations. Coupled-cluster computations based on effective field theories of the strong nuclear force describe the matter radius of ^{27}F but are challenged for ^{29}F.

Critical Role of Shell in Enhanced Fluorescence of Metal–Dielectric Core–Shell Nanoparticles

Abstract: Large-scale simulations are performed by means of the transfer-matrix method to reveal optimal conditions for metal–dielectric core–shell particles to induce the largest fluorescence on their surfa...

Localization in spherical shell buckling

Abstract: This paper addresses localization of the deformation due to buckling that occurs immediately following the onset of bifurcation in the axisymmetric buckling of a perfect spherical elastic shell subject to external pressure. The localization process is so abrupt that the buckling mode of the classical eigenvalue analysis, which undulates over the entire shell, becomes modified immediately after bifurcation transitioning to an isolated dimple surrounded by an unbuckled expanse of the shell. The paper begins by revisiting earlier attempts to analyze the initial post-buckling behavior of the spherical shell, illustrating their severely limited range of validity. The unsuccessful attempts are followed by an approximate Rayleigh-Ritz solution which captures the essence of the localization process. The approximate solution reveals the pathway that begins at bifurcation from the classical mode shape to the localized dimple buckle. The second part of the paper presents an exact asymptotic expansion of the initial post-buckling behavior which accounts for localization and which further exposes the analytic details of the abruptness of the transition.

General Strategy for Designing Highly Selective Gas-Sensing Nanoreactors: Morphological Control of SnO2 Hollow Spheres and Configurational Tuning of Au Catalysts.

Abstract: Catalyst-loaded hollow spheres are effective at detecting ethanol with high chemical reactivity. However, this has limited the widespread use of catalyst-loaded hollow spheres in designing highly selective gas sensors to less-reactive gases such as aromatics (e.g., xylene). Herein, we report the preparation of xylene-selective Au-SnO2 nanoreactors by loading Au nanoclusters on the inner surface of SnO2 hollow shells using the layer-by-layer assembly technique. The results revealed that the sensor based on SnO2 hollow spheres loaded with Au nanoclusters on the inner surface exhibited unprecedentedly high xylene selectivity and an ultrahigh xylene response, high enough to be used for indoor air quality monitoring, whereas the sensor based on SnO2 hollow spheres loaded with Au nanoclusters on the outer surface exhibited the typical ethanol-sensitive sensing behaviors as frequently reported in the literature. In addition, the xylene selectivity and response were optimized when the hollow shell was sufficiently thin (∼25 nm) and semipermeable (pore size = ∼3.5 nm), while the selectivity and response decreased when the shell was thick or highly gas permeable with large mesopores (∼30 nm). Accordingly, the underlying mechanism responsible for the unprecedentedly high xylene sensing performance is discussed in relation to the configuration of the loaded Au nanoclusters and the morphological characteristics including shell thickness and pore size distribution. This novel nanoreactor concept can be widely used to design highly selective gas sensors especially to less-reactive gases such as aromatics, aldehydes, and ketones.

Origin and Shell-Driven Optimization of the Heating Power in Core/Shell Bimagnetic Nanoparticles

Abstract: The magnetic properties of core/shell nanoparticles can be finely tuned through the exchange coupling at the interface, enabling large heating powers under alternating magnetic fields. However, the...

High-Accuracy Approach for Thermomechanical Vibration Analysis of FG-Gplrc Fluid-Conveying Viscoelastic Thick Cylindrical Shell

Abstract: High importance of fluid-conveying structures in multifarious engineering applications arises the necessity of enhancing the mechanical characteristics of these systems in an effective way. Accordi...