Flexible Shell Research Articles

A coupled smoothed finite element method (S-FEM) for structural-acoustic analysis of shells

In this paper, a coupled smoothed finite element method (S-FEM) is developed to deal with the structural-acoustic problems consisting of a shell configuration interacting with the fluid medium. Three-node triangular elements and four-node tetrahedral elements that can be generated automatically for any complicated geometries are adopted to discretize the problem domain. A gradient smoothing technique (GST) is introduced to perform the strain smoothing operation. The discretized system equations are obtained using the smoothed Galerkin weakform, and the numerical integration is applied over the further formed edge-based and face-based smoothing domains, respectively. To extend the edge-based smoothing operation from plate structure to shell structure, an edge coordinate system is defined local on the edges of the triangular element. Numerical examples of a cylinder cavity attached to a flexible shell and an automobile passenger compartment have been conducted to illustrate the effectiveness and accuracy of the coupled S-FEM for structural-acoustic problems.

A numerical approach for simulating fluid structure interaction of flexible thin shells undergoing arbitrarily large deformations in complex domains

We present a new numerical methodology for simulating fluid–structure interaction (FSI) problems involving thin flexible bodies in an incompressible fluid. The FSI algorithm uses the Dirichlet–Neumann partitioning technique. The curvilinear immersed boundary method (CURVIB) is coupled with a rotation-free finite element (FE) model for thin shells enabling the efficient simulation of FSI problems with arbitrarily large deformation. Turbulent flow problems are handled using large-eddy simulation with the dynamic Smagorinsky model in conjunction with a wall model to reconstruct boundary conditions near immersed boundaries. The CURVIB and FE solvers are coupled together on the flexible solid–fluid interfaces where the structural nodal positions, displacements, velocities and loads are calculated and exchanged between the two solvers. Loose and strong coupling FSI schemes are employed enhanced by the Aitken acceleration technique to ensure robust coupling and fast convergence especially for low mass ratio problems. The coupled CURVIB-FE-FSI method is validated by applying it to simulate two FSI problems involving thin flexible structures: 1) vortex-induced vibrations of a cantilever mounted in the wake of a square cylinder at different mass ratios and at low Reynolds number; and 2) the more challenging high Reynolds number problem involving the oscillation of an inverted elastic flag. For both cases the computed results are in excellent agreement with previous numerical simulations and/or experiential measurements. Grid convergence tests/studies are carried out for both the cantilever and inverted flag problems, which show that the CURVIB-FE-FSI method provides their convergence. Finally, the capability of the new methodology in simulations of complex cardiovascular flows is demonstrated by applying it to simulate the FSI of a tri-leaflet, prosthetic heart valve in an anatomic aorta and under physiologic pulsatile conditions.

Stress–Strain State of Flexible Orthotropic Cylindrical Shells with a Reinforced Circular Hole

The stress–strain state of flexible orthotropic cylindrical shells with a reinforced circular hole under static loading is analyzed numerically. The incremental-loading procedure, modified Newton–Kantorovich method, and finite-element method are used. The effect of geometrical nonlinearity, the orthotropy of the material, and the stiffness of the reinforcement in a shell subject to uniform internal pressure on the distribution of stresses, strains, and displacements along the hole edge and in the zone of their concentration is studied

Axisymmetric Magnetoelastic Deformation of Flexible Orthotropic Shells of Revolutionwith Orthotropic Conductivity

An axisymmetric problem of magnetoelasticity for flexible orthotropic shells with orthotropic conductivity is solved. A governing system of nonlinear differential equations that describes the stress–strain state of flexible orthotropic shells of revolution in mechanical and magnetic fields is derived. Numerical examples are given. The dependence of the stress state of an orthotropic plate on the tangential component of magnetic-flux density and the dependence of the stress state of a spherical shell on the external current and mechanical load are analyzed

Experiments on the Dynamics of Flexible Cylindrical Shells Impacting on a Water Surface

This work presents a comprehensive set of experimental results on the water entry of compliant cylindrical shells. Free fall experiments are conducted on a flexible thin cylinder varying the drop height. The problem studied here is not representative of a free cylinder as this is hold by a sledge, which acts as a concentrated mass. The impact dynamics is analyzed from accelerometers, linear position sensors, and through the analysis of high speed images. Further, an experimental methodology based on the modal decomposition method is developed and utilized to reconstruct the overall structural deformation and the distributed strain field on the base of local strain measurements. Fiber Bragg gratings are utilized for this purpose. Results show that the flexibility of the structure plays an important role on the impact dynamics, which is found to completely differ from the impact of rigid structures. The overall deformation of the shell follows the first mode shape of vibration of a free ring, while the stresses are influenced by the superposition of the higher mode shapes that are excited during the impact.

Advances and Recent Patents about Cracking Walnut and Fetching Kernel Device

In recent years, many patents have been devoted to develop the walnut mechanical cracking and kernel fetching, kernel shell separation and walnut classification techniques that can significantly improve the walnut shell cracking rate and decrease the walnut kernel breaking rate. However, those machines adjust poorly to different sizes of walnuts, requiring size grading by human with high kernel breaking rate, low efficiency. This paper analyzes the patent on new walnut cracking, kernel fetching and shell kernel separation equipment in recent years. Based on the sphere walnut models and the advantages of variety of walnut shell machine, the walnut shearing, pressing and cracking device is designed by the author. Different sizes of walnuts are adjusted to these machines, including the conveyor belt shear extrusion flexible shell system, flexible blade hammer kernel fetching system and the air-flexible screw blade coupling walnut kernel shell roller two-way separation system, realizing the function of walnut crashing, kernel fetching and shell kernel separation, with the walnut shell cracking rate being 98%, the kernel breaking rate 2.9% and the kernel revealing rate 70%, improving the walnut shell cracking rate and reducing the kernel breaking rate. Keywords: Air-flexible screw blade, cracking the shell, flexible blade hammer, roller two-way separation, walnut, walnut classification screening.

Investigation of supersonic flutter of thick doubly curved sandwich panels with CNT reinforced facesheets using higher-order structural theory

In this paper, the supersonic flutter characteristics of doubly curved sandwich shell panels, viz., cylindrical and spherical shells, with carbon nanotube (CNT) reinforced facesheets are investigated using QUAD-8 shear flexible shell element developed based on higher-order structural theory. The formulation accounts for the nonlinear variation of the in-plane and transverse displacements through the thickness, and abrupt discontinuity in slope of the in-plane displacement at the interface. The strain–displacement relation is accurately introduced in the formulation. The first-order high Mach number approximation to linear potential flow theory is employed for evaluating the aerodynamic pressure. The solutions of the complex eigenvalue problem, developed based on Lagrange’s equation of motion, are obtained by QR algorithm. The accuracy of the present formulation is validated considering the problems for which solutions are available in the literature. A detailed numerical study is conducted to highlight the significance of the higher-order model over the first-order theory and also to examine the influence of the volume fraction of the CNT, core-to-face sheet thickness, the shell thickness and the aspect ratio, radius-to-thickness ratio, and temperature on the flutter boundaries.

Discrete action micro-actuator optimization

Micro-electro-mechanical systems (MEMS) devices are widely used in industry. The micro-actuator is an important component of such devices, transforming external influence into mechanical displacement. The development of a design technique to derive the optimal design parameters for a micro-actuator is a problem of current interest. The present paper describes a technique for determining geometric parameters for a simplified micro-actuator structure (a hemispherical shell), such that under a prescribed critical pressure it will undergo a specified discrete deflection. Such a deflection is commonly referred to as "snap-through". A mathematical model and a Finite Element procedure for the mechanical analysis of a flexible thin-walled shell under large deformation are proposed. Initially the snap-through is modelled as a quasi-static effect, but subsequently, the influence of the inertia is also considered. The optimization procedure was performed using the PSE/MACROS optimization program. The results for an example model numerical optimization are shown.

Cardanol-based oligomers with “hard core, flexible shell” structures: from synthesis to UV curing applications

UV cured polymers based on cardanol exhibit excellent mechanical properties due to the unique “hard core, flexible shell” structures of the hyperbranched renewable oligomers.

Design of Anchorage for Flexible Structures

The analytical calculation of hold-down loads for open-top tanks and other flexible structures relies on a fundamental assumption that the structure behaves rigidly. Consequently, the relevant design codes provide measures to achieve sufficient rigidity in order to validate this assumption. This paper examines the open-top tanks meeting recognised codes such as API650 [1] and AWWA D100 [2] and the actual hold-down loads through finite element analysis. The results show that the assumption that the tanks are rigid is not necessarily conservative and that higher than expected localised hold-down loads may arise for a given set of geometries. The paper considers possible changes to the ring stiffeners recommended by the design codes and the approach employed by other codes in the design of flexible shell structures.

The Effect of Wettability on the Dynamical Behaviors of Single-Walled Carbon Nanotube

The dynamical behaviors of single-walled carbon nanotube (SWCNT) with the internal and external wettability are studied based on a multiple flexible shell model in the paper. The SWCNT-water system comprises five constituent parts, that is, the SWCNT, the absorbed inner and outer layers of water molecules, the water in the center of the SWCNT, and the water surrounding the absorbed outer water layer. Here we consider the absorbed water layers as infinitesimally thin shells, which interact with the nanotube via a continuum Lennard-Jones potential, and the water in the center of the SWCNT and the counterpart surrounding the absorbed outer water layer as the potential flow. It is found that the interactions of SWCNT and the water layer are responsible for an upshift in the frequency of the SWCNT and the total upshift is approximately the sum of the two corresponding upshifts. The vdW interactions also cause the increase of the frequency of internal and external water shells. We hope that the paper can offer a new modeling approach to determine whether carbon nanotubes have adsorbed fluids inside their pores and could be used for detecting changes in their filling state.

A molecular dynamic model for analyzing concentrations of electrolytes: Fractional molar dependences of microstructure properties

Aqueous electrolyte solutions play an important role in many electrophysical and chemical processes in aerospace technology and industrial applications. As noncovalent interactions, the interactions between ions are crucially important for biomolecular structures as well (protein structure folding, molecular level processes followed by ionic pair correlations, the formation of flexible hydrate shells, and so on). Specifically, ions (cations and anions with the same valence charges) can form stable pairs if their sizes match. The formation of ionic pairs can substantially affect the thermodynamic stabilities of proteins in the alkali salts physiologically present in the human body. Research aims and problems impose severe demands on readjustments of the ionic force fields and potential parameters developed to describe aqueous solutions and electrolytic systems. Ionic solutions and their interaction with biomolecules have been observed for over 100 years [1], but the behavior of such solutions remains poorly studied today. New data obtained in this work deals with parameterization strategies and adjustments for the ionic force fields of the alkali cations and halide anions that should be helpful in biomolecular research. Using molecular dynamics (MD) models, four electrolytic systems (HCl-H2O, LiCl-H2O, NaCl-H2O, and KCl-H2O) are investigated as binary mixtures of water and cations and anions, respectively. The intermolecular interaction parameters are varied for two of the four model electrolytes (HCl-H2O and NaCl-H2O) to simulate the possibility of different ionic shells forming during interaction with water. It is found that varying the potential parameters strongly affects the dynamic and structural characteristics of electrolyte systems. MD simulations are performed in the temperature range of 300 to 600 K with a step of 50 K. MD simulations for all electrolyte models (HCl-H2O, LiCl-H2O, NaCl-H2O, KCl-H2O) are also conducted for different molar fractions of electrolyte concentration: 16, 8, and 1 mol/kg. Energies of diffusion activation are calculated using the Arrhenius equation, thereby constructing temperature dependence graphs of diffusion coefficients for all four electrolyte systems. The observed diffusion properties of the electrolyte systems are found to correlate well with the energy and structural radial distribution data.

An ionic self-assembly approach towards sandwich-like graphene/SnO2/graphene nanosheets for enhanced lithium storage

Two-dimensional graphene/SnO2/graphene (G/SnO2/G) hybrids with SnO2 nanoparticles sandwiched in graphene sheets have been constructed by a facile ionic self-assembly process. The resulting G/SnO2/G hybrids possessed flexible and ultrathin graphene shells that effectively enwrapped the SnO2 nanoparticles. When the hybrids were used as the anode materials in lithium-ion batteries (LIBs), their unique core–shell architecture provided double protection against the aggregation and volume changes of SnO2 nanoparticles, and ensured favorable transport kinetics for charge carriers. As a result, the hybrids exhibited a superior cycling stability (600 mA h g−1 over 60 cycles) and excellent rate capability (120 mA h g−1 at 5.0 A g−1).

Dendrimer-type peptoid-decorated hexaphenylxylenes and tetraphenylmethanes: synthesis and structure in solution and in the gas phase.

Branched organic nanostructures are useful scaffolds that find multiple applications in a variety of fields. Here, we present a novel approach to dendrimer-like structures. Our design contains a rigid hydrocarbon-based core (hexaphenylxylylene/tetraethynylphenylmethane) combined with a library of N-substituted oligoglycines (so-called peptoids) providing a flexible shell. The use of click chemistry allows rapid assembly of the nanostructures. The possibility of tuning the size and the solubility of this new type of nanostructure will be advantageous for future applications such as heterogeneous catalysis.

Hollow zeolitic imidazolate framework nanospheres as highly efficient cooperative catalysts for [3+3] cycloaddition reactions.

Herein we describe a novel, hollow-structured zeolitic imidazolate framework (ZIF-8-H) nanosphere as a highly efficient catalyst for [3+3] cycloaddition reactions. The programmed installation of acidic Zn(2+) species and basic imidazolate moieties creates a synergistic catalytic system. Appropriate positioning of these functionalities in the catalytic system makes it possible to bring two substrates into close proximity and activate them cooperatively. Moreover, the flexible shell and the surface mesopores of ZIF-8-H provide the capacity for favorable binding of various sized substrates, stabilizing intermediates via their multiple force networks and the increased accessibility of the active sites. These features render ZIF-8-H a more highly active promoter than its homogeneous precursors, bulk ZIF-8 and ZIF-8-N nanoparticles. Finally, the robust catalyst can be easily recovered and reused 10 times without loss of catalytic activity.

Stress State of Flexible Composite Shells with Reinforced Holes

The nonlinear deformation of flexible composite shells with reinforced curved holes under static loading is studied. Problems of this class are formulated, and a numerical method for solving them with allowance for finite deflections is outlined. The distributions of stresses, strains, and displacements along the boundary of the hole and in the zone of stress concentration in an orthotropic cylindrical shell with a reinforced hole subjected to uniform internal pressure are examined. The results are analyzed and compared to the solutions of the corresponding linear elastic problems for a shell with a nonreinforced hole

Collecting high-order interactions in an effective pairwise intermolecular potential using the hydrated ion concept: the hydration of Cf³⁺.

This work proposes a new methodology to build interaction potentials between a highly charged metal cation and water molecules. These potentials, which can be used in classical computer simulations, have been fitted to reproduce quantum mechanical interaction energies (MP2 and BP86) for a wide range of [M(H2O)n](m+)(H2O)ℓ clusters (n going from 6 to 10 and ℓ from 0 to 18). A flexible and polarizable water shell model (Mobile Charge Density of Harmonic Oscillator) has been coupled to the cation-water potential. The simultaneous consideration of poly-hydrated clusters and the polarizability of the interacting particles allows the inclusion of the most important many-body effects in the new polarizable potential. Applications have been centered on the californium, Cf(III) the heaviest actinoid experimentally studied in solution. Two different strategies to select a set of about 2000 structures which are used for the potential building were checked. Monte Carlo simulations of Cf(III)+500 H2O for three of the intermolecular potentials predict an aquaion structure with coordination number close to 8 and average R(Cf-O) in the range 2.43-2.48 Å, whereas the fourth one is closer to 9 with R(Cf-O) = 2.54 Å. Simulated EXAFS spectra derived from the structural Monte Carlo distribution compares fairly well with the available experimental spectrum for the simulations bearing 8 water molecules. An angular distribution similar to that of a square antiprism is found for the octa-coordination.

Graphene-encapsulated SnO2 hollow spheres as high-performance anode materials for lithium ion batteries

Graphene-encapsulated SnO2 hollow spheres (GE-SnO2 HS) are synthesized by a simple electrostatic self-assembly process. The prepared composite consists of SnO2 hollow spheres (SnO2 HS) in the interior, which are encapsulated by flexible ultra-thin graphene shells at the exterior. This novel architecture is expected to buffer large volume changes and effectively prevent the detachment and agglomeration of SnO2 during the lithiation and delithiation processes. The GE-SnO2 HS composite exhibits much better electrochemical performance than bare SnO2 HS. In addition, the composite delivers a high reversible capacity of 422mAhg−1 after 100 cycles at a current density of 158mAg−1 and a capacity of 237mAhg−1 after 30 cycles at a higher current density of 1580mAg−1. These results suggest that the GE-SnO2 HS composite can provide new opportunities to enhance the properties of tin-based materials for use in high-capacity lithium ion batteries.

Конструктивные решения безбалочных безкапительных перекрытий с предварительно напряженной арматурой

In the article the authors present advanced constructions of prestressed reinforced concrete flat ceiling, where high-strength ropes in elastic shell are used as stressed reinforcement. The novelty of the solution lays in diagonal arrangement of hard valves and use of high-strength ropes in a flexible shell of Monostrand type. This type of prestress, in our opinion, is the most acceptable from technical point of view for selective reinforcement of separate tense rods or cables. The use of pre-stressed reinforcement in the form of individual rods or cables increases the rigidity and crack resistance of concrete beamless slabs. The use of high-strength ropes in the monostrand-type shell makes it possible to prestress in frames of single cell plate or floor in general and to reduce labour input for stressing armature. The paper presents original solution with diagonal position of the valve. The authors suggest the use of prestressed diagonal valves as in all cells of the floor with the cells of the same or only slightly different size and in separate cells of the floor (for roofs with different cells). The diagonal location of stressed reinforcement proposed in the work is an efficient solution for extending the range of dimensions and loads size.

Encapsulated within graphene shell silicon nanoparticles anchored on vertically aligned graphene trees as lithium ion battery anodes

Silicon has been regarded as one of the most promising anode material for the next generation lithium ion battery. Unfortunately, the structure damage caused by the volume change of silicon and the continual interfacial reaction due to the electrolyte remain two major challenges. Here, we design a novel kind of in-situ growth binder-free silicon-based anodes. The adaptable silicon nanoparticles were encapsulated in graphene nanosheets (SiNPs@GNS). Simultaneously, the SiNPs@GNS composites anchored on vertically aligned graphene trees with loose intersecting leaves (GrTr). In the resulting samples, the GNS shells, as adaptable sealed wraps, could synergistically accommodate the volume change of the wrapped SiNPs, thus effectively avoiding the direct contact between encapsulated silicon and the electrolyte and enabling the interfacial and structural stabilization of encapsulated SiNPs during cycling. The GrTrs directly grown on current collector act as supporters of SiNPs, which ensure their dispersion uniformity and supply three dimensional short transportation paths for both Li ions and electrons. The in-situ growth of SiNPs@GNS–GrTr composites were proximately used as anodes in LIBs without adhesives and other complex brushing processes of the active material. The composite material exhibits a high capacity (1528mAhg−1 at 150mA/g), relatively good cycle stability (88.6% after 50 cycles), and fast charge/discharge rate (412mAhg−1 at 8A/g). The uniquely designed structure of the composites, which provide an ultra-thin, flexible GNS shell to accommodate the changes in volume, introduces large efficient areas, good conductivity, three dimensional transportation paths for both Li ions and electrons, and contributes to its excellent performance.