Showing papers on "Shell (structure) published in 2016"

Design of highly stable and selective core/yolk–shell nanocatalysts—A review

Abstract: In recent decades, increasing interests have been put on improving the stability and selectivity of nanocatalysts for clean energy production due to the decrease of fossil fuels. Despite the prominent feature of high catalytic activity, nanocatalysts are prone to sintering. Structural design of nanocatalysts to form core/yolk shell structure has been proven to be the most effective method to enhance their catalytic stability. In this review, design strategies for core/yolk shell nanocatalysts to attain high stability in energy related applications at high temperatures such as hydrocarbon reforming reactions for syngas production and high temperature fuel cells such as SOFC and MCFC are summarized and exemplified with the advancements made in the recent three years. In addition, measures taken to obtain outstanding selectivity for F-T synthesis and C C bond hydrogenation reactions are also presented. Further, excellent shape and size selectivity design examples are also introduced. Finally, unsolved problems and challenges for core/yolk shell nanocatalysts design are proposed as the final part of this review.

Design and Analysis of a Soft Pneumatic Actuator with Origami Shell Reinforcement

Abstract: Soft pneumatic actuators (SPAs) are versatile robotic components enabling diverse and complex soft robot hardware design. However, due to inherent material characteristics exhibited by their primary constitutive material, silicone rubber, they often lack robustness and repeatability in performance. In this article, we present a novel SPA-based bending module design with shell reinforcement. The bidirectional soft actuator presented here is enveloped in a Yoshimura patterned origami shell, which acts as an additional protection layer covering the SPA while providing specific bending resilience throughout the actuator's range of motion. Mechanical tests are performed to characterize several shell folding patterns and their effect on the actuator performance. Details on design decisions and experimental results using the SPA with origami shell modules and performance analysis are presented; the performance of the bending module is significantly enhanced when reinforcement is provided by the shell. W...

Batch adsorption of cephalexin antibiotic from aqueous solution by walnut shell-based activated carbon

Abstract: The batch adsorption experiments were investigated for the adsorption of cephalexin (CFX) antibiotic on walnut shell activated carbon (AC). The adsorbent was prepared by chemical activation method in the presence of ZnCl 2 . Several adsorption parameters including the adsorbent dosage, the initial CFX concentration, contact time, temperature, and pH were studied. The adsorption isotherm was analyzed by different isotherm models. It was found that the Freundlich and Toth models provided the best fit for the experimental data for two and three parameter models, respectively. The maximum adsorption capacity was obtained 233.1 mg/g based on the Langmuir model. The kinetic data were well represented by pseudo-second order model. Thermodynamics analysis showed endothermic nature of CFX adsorption on walnut shell AC under examined conditions.

Au@MoS2 Core–Shell Heterostructures with Strong Light–Matter Interactions

Abstract: There are emerging opportunities to harness diverse and complex geometric architectures based on nominal two-dimensional atomically layered structures. Herein we report synthesis and properties of a new core–shell heterostructure, termed Au@MoS2, where the Au nanoparticle is snugly and contiguously encapsulated by few shells of MoS2 atomic layers. The heterostructures were synthesized by direct growth of multilayer fullerene-like MoS2 shell on Au nanoparticle cores. The Au@MoS2 heterostructures exhibit interesting light–matter interactions due to the structural curvature of MoS2 shell and the plasmonic effect from the underlying Au nanoparticle core. We observed significantly enhanced Raman scattering and photoluminescence emission on these heterostructures. We attribute these enhancements to the surface plasmon-induced electric field, which simulations show to mainly localize within the MoS2 shell. We also found potential evidence for the charge transfer-induced doping effect on the MoS2 shell. The DFT c...

Analytical solution for nonlinear postbuckling of functionally graded carbon nanotube-reinforced composite shells with piezoelectric layers

Abstract: This paper presents an analytical solution procedure for the nonlinear postbuckling analysis of piezoelectric functionally graded carbon nanotubes reinforced composite (FG-CNTRC) cylindrical shells subjected to combined electro-thermal loadings, axial compression and lateral loads. The carbon nanotubes are assumed to be aligned and straight with uniform and functionally graded distributions in the thickness direction. The kinematics and constitutive relations are written on the basis of the classic theory and the von Karman nonlinear strain–displacement relations of large deformation. Applying the Ritz energy approach, analytical solutions are proposed for the nonlinear critical axial load, lateral pressure as well as the load-shortening ratio of the piezoelectric FG-CNTRC shell. Numerical results are presented to study the effects of dimensional parameters, CNT volume fraction, distribution type of the reinforcement and piezoelectric thickness on the nonlinear buckling behavior of the piezoelectric nanocomposite shell. It is revealed that the carrying capacity of the structure increases as the shell is integrated by the piezoelectric layers and reinforced by higher CNT volume fraction. Furthermore, FGX- and FGO- CNTRC piezoelectric shells are indicated to have higher and lower carrying capacities compared to UD-CNTRC piezoelectric shells, respectively.

Enceladus's and Dione's floating ice shells supported by minimum stress isostasy

Abstract: Enceladus' gravity and shape have been explained in terms of a thick isostatic ice shell floating on a global ocean, in contradiction of the thin shell implied by librations. Here we propose a new isostatic model minimizing crustal deviatoric stress, and demonstrate that gravity and shape data predict a 38 ± 4km-thick ocean beneath a 23 ± 4km-thick shell agreeing with – but independent from – libration data. Isostatic and tidal stresses are comparable in magnitude. South polar crust is only 7 ± 4km thick, facilitating the opening of water conduits and enhancing tidal dissipation through stress concentration. Enceladus' resonant companion, Dione, is in a similar state of minimum stress isostasy. Its gravity and shape can be explained in terms of a 99 ± 23km-thick isostatic shell overlying a 65 ± 30km-thick global ocean, thus providing the first clear evidence for a present-day ocean within Dione.

Slow-Injection Growth of Seeded CdSe/CdS Nanorods with Unity Fluorescence Quantum Yield and Complete Shell to Core Energy Transfer

Abstract: A two-step process has been developed for growing the shell of CdSe/CdS core/shell nanorods. The method combines an established fast-injection-based step to create the initial elongated shell with a second slow-injection growth that allows for a systematic variation of the shell thickness while maintaining a high degree of monodispersity at the batch level and enhancing the uniformity at the single-nanorod level. The second growth step resulted in nanorods exhibiting a fluorescence quantum yield up to 100% as well as effectively complete energy transfer from the shell to the core. This improvement suggests that the second step is associated with a strong suppression of the nonradiative channels operating both before and after the thermalization of the exciton. This hypothesis is supported by the suppression of a defect band, ubiquitous to CdSe-based nanocrystals after the second growth.

Stability of Non-Linear Vibrations of Doubly Curved Shallow Shells

Abstract: Large amplitude (geometrically non-linear) vibrations of doubly curved shallow shells with rectangular boundary, simply supported at the four edges and subjected to harmonicexcitation normal to the surface in the spectral neighbourhood of the fundamental mode are subject of investigation in this paper. The first part of the study was presented by the authors in [M. Amabili et al. Nonlinear Vibrations of Doubly Curved Shallow Shells. Herald of Kazan Technological University, 2015, 18(6), 158-163, in Russian]. Two different non-linear strain-displacement relationships, from the Donnell’s and Novozhilov’s shell theories, are used to calculate the elastic strain energy. In-plane inertia and geometricimperfections are taken into account. The solution is obtained by Lagrangian approach. The non-linear equations of motion are studied by using (i) a code based on arclengthcontinuation method that allows bifurcation analysis and (ii) direct time integration. Numerical results are compared to those available in the literature and convergence of the solution is shown. Interaction of modes having integer ratio between their natural frequencies, giving rise to internal resonances, is discussed. Shell stability under dynamic load is also investigated by using continuation method, bifurcation diagram from direct time integration and calculation of the Lyapunov exponents and Lyapunov dimension. Interesting phenomena such as (i) snap-through instability, (ii) subharmonic response, (iii) period doubling bifurcations and (iv) chaotic behavior have been observed.

Higher-order structural theories for the static analysis of doubly-curved laminated composite panels reinforced by curvilinear fibers

Abstract: The main aim of this paper is the evaluation of the through-the-thickness profiles of strain, stress and displacement components of several doubly-curved panels reinforced by curvilinear fibers. The placement of the reinforcing phase along curved paths allows to obtain mechanical properties which change point by point and affects the static behavior of shell structures. Some numerical applications based on both higher-order Equivalent Single Layer (ESL) and Layer-Wise (LW) theories are shown in order to underline the curvilinear fiber influence on the static analysis. The structural model, which is based on the so-called Carrera Unified Formulation (CUF), is completely general and can deal easily with variable stiffness shells. An appropriate recovery procedure based on the three-dimensional elasticity equations in principal curvilinear coordinates is presented to compute strains and stresses. The equation system which governs the static problem under consideration is solved numerically through the Generalized Differential Quadrature (GDQ) method. The same numerical technique is employed to evaluate the geometrical parameters needed for the characterization of the shell reference surface, according to the differential geometry.

The local GDQ method for the natural frequencies of doubly-curved shells with variable thickness: A general formulation

Abstract: The present paper aims to evaluate the natural frequencies of several doubly-curved shells with variable thickness. The general theoretical formulation allows to take into account various higher-order Equivalent Single Layer (ESL) theories in a unified manner, including the Murakami's function to capture the zig-zag effect. Such approach is able to study very well the dynamic behavior of a laminated composite shell, even in the presence of a soft-core. A general expression, which is able to combine different kinds of variations (such as linear, parabolic, exponential, sine-wave, Gaussian and elliptic shapes), is introduced to define the thickness profiles. In addition, the same formulation can be employed to localize such variations and to define, consequently, ribbed structures. Since the adopted structural model is two-dimensional, the shell reference surface represents the physical domain in which the governing equations are written. Thus, the differential geometry is necessary to define accurately the doubly-curved surfaces at issue. The fundamental system is solved numerically by means of a local approach of the well-known Generalized Differential Quadrature (GDQ) method. The matrices that allow to solve the problem in hand are banded, since only a part of the discrete grid points is considered. As a consequence, the computational effort is lower, if compared to the corresponding global version. The accuracy, reliability and stability of the present approach are proved by the comparison with the results available in the literature and the solutions obtained through three-dimensional FEM models.

The role of shell evolution in shape coexistence

Abstract: We first review the shell evolution in exotic nuclei driven by nuclear forces. We then demonstrate that the underlying mechanism played by the balance of the tensor and central components in the effective nucleon–nucleon interaction is crucial when describing shape coexistence. This effect will be referred to as type II shell evolution, while the shell evolution passing through a series of isotopes or isotones is denoted as type I. We describe type II shell evolution in some detail for the case of the Ni nucleus as an example. We present how the fission dynamics can be related to enhanced deformation triggered by type II shell evolution, at its initial stage. It is suggested that the island of stability may be related to the suppression of this mechanism.

Hierarchical DSSC structures based on single walled TiO2 nanotube arrays reach back-side illumination solar light conversion efficiency of 8%

Abstract: In the present work we introduce a path to the controlled construction of DSSCs based on hierarchically structured single walled, self-organized TiO2 layers. In a first step we describe a simple approach to selectively remove the inner detrimental shell of anodic TiO2 nanotubes (NTs). This then allows controlled well-defined layer-by-layer decoration of these TiO2-NT walls with TiO2 nanoparticles (this in contrast to conventional TiO2 nanotubes). We show that such defined multiple layered decoration can be optimized to build dye sensitized solar cells that (under back-side illumination conditions) can yield solar light conversion efficiencies in the range of 8 %. The beneficial effects observed can be ascribed to a combination of three factors : 1) improved electronic properties of the single walled tubes themselves, 2) a further improvement of the electronic properties by the defined TiCl4 treatment, and 3) a higher specific dye loading that becomes possible for the layer-by-layer decorated single walled tubes.

Visualization of Bacterial Microcompartment Facet Assembly Using High-Speed Atomic Force Microscopy.

Abstract: Bacterial microcompartments (BMCs) are proteinaceous organelles widespread among bacterial phyla. They compartmentalize enzymes within a selectively permeable shell and play important roles in CO2 fixation, pathogenesis, and microbial ecology. Here, we combine X-ray crystallography and high-speed atomic force microscopy to characterize, at molecular resolution, the structure and dynamics of BMC shell facet assembly. Our results show that preformed hexamers assemble into uniformly oriented shell layers, a single hexamer thick. We also observe the dynamic process of shell facet assembly. Shell hexamers can dissociate from and incorporate into assembled sheets, indicating a flexible intermolecular interaction. Furthermore, we demonstrate that the self-assembly and dynamics of shell proteins are governed by specific contacts at the interfaces of shell proteins. Our study provides novel insights into the formation, interactions, and dynamics of BMC shell facets, which are essential for the design and engineering of self-assembled biological nanoreactors and scaffolds based on BMC architectures.

General higher-order layer-wise theory for free vibrations of doubly-curved laminated composite shells and panels

Abstract: The present article illustrates a general formulation for a higher-order layer-wise theory related to the analysis of the free vibrations of thick doubly-curved laminated composite shells and panels. The theoretical framework relates to the dynamic analysis of shell structures by using a general displacement field based on the Carrera Unified Formulation (CUF), including the stretching effect for each layer. The order of the expansion along the thickness direction is taken as a free parameter. The starting point of the present general higher-order layer-wise formulation is to propose a kinematic assumption, with an arbitrary number of degrees of freedom. The main aim of this work is to determine the explicit fundamental operators that can be used for the layer-wise (LW) approach. These fundamental operators are obtained for the first time by the author and are related to motion equations of doubly-curved shells described in an orthogonal curvilinear co-ordinate system. The free vibration shell and...

Quick -witted damping device is glued to full -automatic system

Abstract: The utility model discloses a quick -witted damping device is glued to full -automatic system, including mounting panel and bottom plate, the both sides of bottom plate are provided with fixing bolt, are provided with the fastening rubber pad on the lower surface of bottom plate, be equipped with vibration -isolating rubber pad on the upper surface of bottom plate, be equipped with magnetism shock attenuation unit on vibration -isolating rubber pad, magnetism shock attenuation unit removes end and stiff end and all sets up in the shell including shell, removal end, stiff end and bracing piece, and remove end and stiff end and be the permanent magnet, and the magnetic pole syntropy, a fixed support bar is served in the removal, vibration -isolating rubber pad's both sides still are equipped with the spring respectively. The utility model discloses a fix pneumatic diaphragm pump on the mounting panel, its vibrations that produce at the operation in -process are absorbed by magnetism shock attenuation unit and spring, can not produce the striking to ground, and the interelectrode interact of magnetism can not take place deformation because of long -time the use, and the shock attenuation effect remains unchanged, reduces and safeguards the frequency, keeps good shock attenuation effect.

A unified solution for the vibration analysis of FGM doubly-curved shells of revolution with arbitrary boundary conditions

Abstract: This paper describes a unified solution for the vibration analysis of functionally graded material (FGM) doubly-curved shells of revolution with arbitrary boundary conditions. The solution is derived by means of the modified Fourier series method on the basis of the first order shear deformation shell theory considering the effects of the deepness terms. The material properties of the shells are assumed to vary continuously and smoothly along the normal direction according to general three-parameter power-law volume fraction functions. In summary, the energy functional of the shells is expressed as a function of five displacement components firstly. Then, each of the displacement components is expanded as a modified Fourier series. Finally, the solutions are obtained by using the variational operation. The convergence and accuracy of the solution are validated by comparing its results with those available in the literature. A variety of new vibration results for the circular toroidal, paraboloidal, hyperbolical, catenary, cycloidal and elliptical shells with classical and elastic boundary conditions as well as different geometric and material parameters are presented, which may serve as benchmark solution for future researches. Furthermore, the effects of the boundary conditions, shell geometric and material parameters on the frequencies are carried out.

Vibrational analysis of functionally graded carbon nanotube-reinforced composite spherical shells resting on elastic foundation using the variational differential quadrature method

Abstract: In this paper, the free vibration characteristics of embedded functionally graded carbon nanotube-reinforced composite (FG-CNTRC) spherical shells are studied based on a numerical approach. The elastic foundation is considered to be Pasternak-type. Moreover, the extended rule of mixture is used so as to obtain the material properties of FG-CNTRC. The shell is also modeled according to the first-order shear deformation shell theory. The energy functional of the structure is obtained first. Using differential operators, the discretized form of the energy functional is derived. By means of the variational differential quadrature (VDQ) method, the reduced forms of mass and stiffness matrices are then obtained. Selected numerical results are given to investigate the effects of different parameters such as elastic foundation coefficients, boundary conditions, CNT volume fraction, thickness-to-radius ratio and type of distribution of CNT on the vibrations of FG-CNTRC spherical shells.

The modified couple stress functionally graded cylindrical thin shell formulation

Abstract: In this article, the functionally graded (FG) cylindrical thin shell formulation is developed by using modified couple stress theory. The equations of motion and classical and nonclassical boundary conditions are extracted based on Hamilton's principle. As a special case, the equations of motion in conjunction with the boundary conditions for simply supported FG cylindrical shell are obtained, and then Navier solution procedure is used for analysis free vibration of nano shell. Afterwards, the influences of different parameters like length scale parameter, distribution of FG properties, and length to radius ratio on dimensionless natural frequency are investigated and compared with classical theory.

Size-dependent torsional buckling analysis of functionally graded cylindrical shell

Abstract: The size-dependent torsional buckling behavior of functionally graded (FG) cylindrical shell is investigated on the basis of modified couple stress theory using the shell model. The material properties of FG nanoshell are considered change through thickness direction according to power law distribution. The modified couple stress shell theory with the von Karman geometrical nonlinearity is utilized to establish theoretical formulations. The governing equations and boundary conditions are derived using the minimum potential energy principle. As a special case, the torsional buckling of simply supported and clamped FG cylindrical shell is examined using the GDQ method. Afterwards, the influences of geometrical parameters, such as length scale parameter, length, and thickness, as well as material property gradient index of the FG cylindrical shell on the critical torsional buckling moment are studied.

Vibration Analysis of Functionally Graded Carbon Nanotubes Reinforced Composite Shell Structures

Abstract: Carbon fiber reinforced polymer composites shell structures have been extensively used in the diverse fields of engineering. These structures always possess load carrying capacity due to the special geometrical shapes, and they are also subjected to dynamic loads which cause vibrations. Hence, the study of vibration problems of such shell structures is of great importance. In the recent past, nanostructured materials have gained significant importance from a technological point of view for the wide range of engineering applications that involve high levels of performance and multi functionality. Particularly, carbon nanotubes (CNTs) have shown extraordinary potentials to become the new generation material. The addition of CNT with functionally Graded Materials not only provides enriched mechanical, electrical and thermal properties but that may eliminate the interlaminar stresses which usually exist in the traditional laminated composites due to mismatch of elastic modulus. The present work deals with the vibration and damping analysis of two distinct types of structures. First type of structure is functionally graded carbon nanotubes reinforced composite (FG-CNTRC) shell structure which consists of carbon nanotube as reinforcing phase and polymer as matrix phase. Another type is functionally graded carbon nanotubes reinforced hybrid composite (FG-CNTRHC) shell structure which consists of conventional carbon fiber as reinforcing phase and single-walled carbon nanotubes (SWCNTs) based polymer as matrix phase. The material properties of FG-CNTRC shell structure are graded smoothly through the thickness direction of shell according to uniform distribution (UD) and some other functionally graded (FG) distributions (such as FG-Χ, FG-V and FG- ) of the volume fraction of CNTs and the effective material properties are estimated by employing Eshelby–Mori–Tanaka approach considering the randomly oriented agglomerated CNTs. The Eshelby–Mori–Tanaka approach in conjunction with strength of material approach is implemented to obtain the material properties of FG-CNTRHC materials. The material properties of FG-CNTRHCs are assumed to be graded through the thickness direction according to power law distributions of the volume fraction of carbon fibers and fiber orientations. After determining the effective material properties of both structures an eight node shell element considering transverse shear effect according to Mindlin’s hypothesis has been formulated for finite element (FE) modelling and analysis of such functionally graded composite shell structures. The formulation of shell mid-surface in an arbitrary curvilinear coordinate system based on the tensorial notation has been presented. The Rayleigh damping model has been implemented in order to study the effects of carbon nanotubes (CNTs) on damping capacity of such shell structures. Different types of spherical shell panels have been analyzed in order to study the impulse and frequency responses. The influences of CNT volume fraction, CNT distribution, geometry of the shell, CNT agglomeration and material distributions on the dynamic behaviour of FG-CNTRC shell structures and the effects of CNT volume fraction, carbon fiber, geometry of the shell, power law index, CNT agglomeration and material distributions on the vibration damping characteristics of FG-CNTRHC shell structures have also been presented and discussed. Various types of FG-CNTRC and FG-CNTRHC shell structures (such as spherical, ellipsoidal, doubly curved and cylindrical) have been analyzed and discussed in order to present the comparative studies in terms of settling time, first resonant frequency and absolute amplitude corresponding to first resonant frequency and considering without and with agglomeration effects of CNTs on vibrations responses of such shell structures are presented. The results show that the CNT agglomeration, CNT distribution and volume fraction of CNT have a significant effect on vibration and damping characteristics of the structures. It is also observed that the FG-CNTRHC shell structures have better dynamic responses compared to FG-CNTRC shell structure.

High-Performance Heterostructured Cathodes for Lithium-Ion Batteries with a Ni-Rich Layered Oxide Core and a Li-Rich Layered Oxide Shell.

Abstract: The Ni-rich layered oxides with a Ni content of >0.5 are drawing much attention recently to increase the energy density of lithium-ion batteries. However, the Ni-rich layered oxides suffer from aggressive reaction of the cathode surface with the organic electrolyte at the higher operating voltages, resulting in consequent impedance rise and capacity fade. To overcome this difficulty, we present here a heterostructure composed of a Ni-rich LiNi0.7Co0.15Mn0.15O2 core and a Li-rich Li1.2-x Ni0.2Mn0.6O2 shell, incorporating the advantageous features of the structural stability of the core and chemical stability of the shell. With a unique chemical treatment for the activation of the Li2MnO3 phase of the shell, a high capacity is realized with the Li-rich shell material. Aberration-corrected scanning transmission electron microscopy (STEM) provides direct evidence for the formation of surface Li-rich shell layer. As a result, the heterostructure exhibits a high capacity retention of 98% and a discharge-voltage retention of 97% during 100 cycles with a discharge capacity of 190 mA h g-1 (at 2.0-4.5 V under C/3 rate, 1C = 200 mA g-1).