Robust Shell Research Articles

Koiter–Newton analysis of thick and thin laminated composite plates using a robust shell element

The Koiter–Newton method is a novel reduced-order modeling technique to efficiently trace the geometrically nonlinear equilibrium path of the structure in the presence of buckling. In this paper, the existing method is extended for nonlinear buckling analysis of thick and thin laminated composite plates. A 4-node quadrilateral element S4AT is developed as a geometric linear element in the co-rotational formulation of the Koiter–Newton method. The developed element S4AT is a combination of the membrane part and the plate-bending part. The quadrilateral area coordinate method is applied to make the element insensitive to the mesh distortion. The Reissner–Mindlin laminated composite plate theory is used to consider the transverse shear deformation effect, and the shear-locking phenomenon is eliminated using the Timoshenko laminated composite beam theory. The performance of the method in terms of reliability, accuracy and computational effort is demonstrated with several examples.

Porous hollow manganites with robust composite shells for oxidation of CO at low temperature

Hollow-type manganite-coated silica microspheres were synthesized via the thermal hydrolysis of urea. The Mn2O3/SiO2_3T microspheres with robust shells exhibit best catalytic performance for CO oxidation even at temperatures below 200 °C.

Fabrication of compositionally and topographically complex robust tissue forms by 3D-electrochemical compaction of collagen

Collagen solutions are phase-transformed to mechanically robust shell structures with curviplanar topographies using electrochemically-induced pH gradients. The process enables rapid layer-by-layer deposition of collagen-rich mixtures over the entire field simultaneously to obtain compositionally diverse multilayered structures. The in-plane tensile strength and modulus of the electrocompacted collagen sheet samples were 5200-fold and 2300-fold greater than those of the uncompacted collagen samples. Out-of-plane compression tests showed a 27-fold increase in compressive stress and a 46-fold increase in compressive modulus compared to uncompacted collagen sheets. Cells proliferated 4.9 times faster, and the cellular area spread was 2.7 times greater on compacted collagen sheets. Electrocompaction also resulted in a 2.9 times greater focal adhesion area than on regular collagen hydrogel. The reported improvements in the cell-matrix interactions with electrocompaction would serve to expedite the population of electrocompacted collagen scaffolds by cells. The capacity of the method to fabricate nonlinear curved topographies with compositional heterogeneous layers is demonstrated by sequential deposition of a collagen-hydroxyapatite layer over a collagen layer. The complex curved topography of the nasal structure is replicated by the electrochemical compaction method. The presented electrochemical compaction process is an enabling modality which holds significant promise for reconstruction of a wide spectrum of topographically complex systems such as joint surfaces, craniofacial defects, ears, nose, and urogenital forms.

Beyond diving depths: deepwater macroalgae in the New Zealand region

Recent research voyages in the New Zealand region have resulted in new macroalgal specimens and underwater imagery from a range of deepwater habitats in coastal and offshore areas. In addition, targeted surveys have enabled the investigation of the biodiversity of specific island and shelf regions of New Zealand, and assemblages in biogenic habitats, as well as the quantification of biodiversity of offshore areas where the potential for resource utilisation/extraction has been identified. Macroalgal records based on vouchered herbarium specimens were compiled for the New Zealand region, summarising their distribution by depth and region from 29.233° S to 52.55° S. A total of 275 taxa were recorded, with 249 identified to species level from depths greater than 19 m, and 179 species from depths greater than 29 m. Of the 249 species, 8 % were collected solely at depths greater than 29 m, and 6 % were found exclusively at levels deeper than 44 m. Around 17 % of species were found to be recorded across a very wide range of depths (e.g., habitat-forming kelp Ecklonia radiata from shallow subtidal habitats to depths in excess of 90 m). A study off the southwest North Island provided both presence and absence data for macroalgae, and, through sampling and imagery of the seabed, enabled the distribution and habitat associations of macroalgae in offshore benthic habitats dominated by soft sediments at depths of 14 to 97 m to be quantified and documented for the first time. The greatest proportion of sites where macroalgae were recorded (particularly non-geniculate coralline algae) were at depths of 45–59 m where there were either rocky outcrops or robust shell debris. This is the first collation and summary of data on the occurrence of deepwater macroalgae around New Zealand, and serve to identify gaps in sampling and to highlight issues around sampling methods and the different data that they provide. These data now serve as a baseline for subsequent work in New Zealand and for comparison with other deepwater ecosystems

Cryptic phenotypic plasticity in populations of the North American freshwater gastropod, Pleurocera semicarinata

BackgroundPhenotypic plasticity is termed ‘cryptic’ when it becomes so extreme as to prompt an (erroneous) hypothesis of speciation. Populations of pleurocerid snails nominally identified as Pleurocera (‘Goniobasis’ or ‘Elimia’) livescens are common elements of the macrobenthos in rivers and on lakeshores from Vermont through northern Ohio and northern Indiana to Wisconsin, USA. Small streams in southern Ohio, southern Indiana, and Kentucky are inhabited by Pleurocera semicarinata, and larger rivers by Lithasia obovata. The three nominal species differ only in qualitative aspects of shell morphology - P. semicarinata demonstrating a slender shell with a small body whorl, L. obovata a robust shell with a large body whorl, and P. livescens intermediate.ResultsHere I use allozyme electrophoresis to estimate genetic divergence over 11 enzyme loci among three populations of P. livescens, two populations of P. semicarinata, and one population of L. obovata sampled across 650 km of their combined range. With each of these six populations I sample a control population of Pleurocera canaliculata, demonstrating that the genetic divergence among the six known conspecific populations is comparable to that observed among the six study populations.ConclusionsThe specific nomina L. obovata and P. livescens would appear to be junior synonyms of P. semicarinata. The shell morphological differences by which these taxa have heretofore been distinguished would appear to result from ecophenotypic plasticity, driven perhaps by predation, substrate, or current.

Core–Shell Structured Silicon Nanoparticles@TiO2–x/Carbon Mesoporous Microfiber Composite as a Safe and High-Performance Lithium-Ion Battery Anode

A core-shell structured Si nanoparticles@TiO2-x/C mesoporous microfiber composite has been synthesized by an electrospinning method. The core-shell composite exhibits high reversible capacity, excellent rate capability, and improved cycle performance as an anode material for Li-ion batteries. Furthermore, it shows remarkable suppression of exothermic behavior, which can prevent possible thermal runaway and safety problems of the cells. The improved electrochemical and thermal properties are ascribed to the mechanically, electrically, and thermally robust shell structure of the TiO2-x/C nanocomposite encapsulating the Si nanoparticles, which is suggested as a promising material architecture for a safe and reliable Si-based Li-ion battery of high energy density.

Synthesis of Hollow Zinc Oxide Nanoparticles by Templating Micelles of Poly(styrene-b-acrylic acid-b-ethylene oxide) in Aqueous Solutions

Abstract Spherical hollow zinc oxide (ZnO) nanoparticles have been successfully synthesized by templating micelles of poly(styrene-b-acrylic acid-b-ethylene oxide) (PS-b-PAA-b-PEO). This polymer forms a micelle with a PS core, a PAA shell, and a PEO corona in aqueous solutions. Zinc chloride (ZnCl2) and sodium hydrogen carbonate (NaHCO3) were used as precursors of ZnO. In the synthesis, the PS core acts as a template for cavities of the hollow particles, the PAA shell is beneficial for arresting zinc ions for further mineralizing, and the PEG corona stabilizes the zinc hydrogen carbonate (Zn(HCO3)2)/polymer nanocomposite to prevent secondary aggregate formation. Hollow ZnO nanoparticles were obtained after the calcination of the separated (Zn(HCO3)2)/polymer nanocomposite at 500 °C for 4 h. The hollow ZnO nanoparticles were characterized by various techniques including transmission electron microscopy and X-ray diffraction analysis. The hollow ZnO particles have a spherical shape, a narrowly distributed size of 24.7 ± 1.3 nm, and a shell thickness of 6.9 ± 0.7 nm. Compared with other methods, the present method gives hollow ZnO nanoparticles with smaller size (ca. 25 nm), narrow size distribution, controlled shape, and robust shell. This result strongly demonstrates the advantages of the present synthesis route.

A robust shell element in meshfree SPH method

With the incorporation of total Lagrangian smoothed particle hydrodynamics (SPH) method equation and moving least square (MLS) function, the traditional SPH method is improved regarding the stability and consistency. Based on Mindlin-Ressiner plate theory, the SPH method simulating dynamic behavior via one layer of particles is applied to plate’s mid-plane, i.e., a SPH shell model is constructed. Finally, through comparative analyses on the dynamic response of square, stiffened shells and cylindrical shells under various strong impact loads with common finite element software, the feasibility, validity and numerical accuracy of the SPH shell method are verified. Consequently, further researches on SPH shell may well pave the way towards solving problems involving dynamic plastic damage, tearing or even crushing.

Clinal variation in the shell morphology of intertidal snail Acanthina monodon in the Southeastern Pacific Ocean

In this study we determine clinal variation of Acanthina monodon shell morphology along the southeastern Pacific coast. Our goals were to describe the clinal variation between biogeographical areas, and between localities along the latitudinal gradient between 30° and 54°S. Specimens were collected from 12 localities throughout the entire geographical distribution range of the species. Geometric morphometric analyses were used to evaluate the morphological variation of A. monodon along the Chilean coast. Relative warps and centroid size scores were used to compare the shape and size and their morphological variation and similarity was evaluated through multivariate analyses between all populations. The first two relative warps explained 78% variance. Size and shape scores decreased southward showing high biogeographical and latitudinal variation, principally due to both the thickness of the lip and the spire length. Multivariate analyses showed two main morphotypes: northern populations with short spires, thick and smooth lips and robust shells; the other with longer spires, thinner ornamented lips and weak shells associated with southern populations. However, three southern populations showed a merging of characteristics from both morphotypes, which could correspond to an intermediate morphotype or a morphological transitional zone. The results suggest the existence of clinal variation along the southeastern Pacific coast showing two morphotypes to north and south of 41°S, with a feature merging zone that probably extends to 45°S, related to biogeographical areas proposed for the Chilean coast. We suggest that the morphotypes reported are the result of site-specific eco-phenotypes responding to local variation.

Functionalizing organic dye with cross-linked electrolyte-blocking shell as a new strategy for improving DSSC efficiency

A simple method used to reduce the electron recombination in dye-sensitized solar cells (DSSCs) is demonstrated. The new dye molecule VTPCA equipped with a thermally cross-linkable styryl group can undergo polymerization during the annealing step of device fabrication to generate an electrolyte-blocking shell, which can impede undesirable electron recombination with the electrolyte. The Jsc, Voc, FF of the solar cell sensitized with VTPCA are 9.83 mA cm−2, 0.74 V, and 0.73, respectively, yielding an overall conversion efficiency of 5.31%. The result acquires 31.4% improvement on device efficiency compared to the unmodified device. In addition, with the incorporation of co-adsorbent chenodeoxycholic acid (CDCA) and cross-linkable repair additive 4,4′-divinyltriphenylamine (DVTP), the optimized device with a robust shell shows an overall 46.8% enhancement over the basic model device.

Robust Shell Phenotype is a Local Response to Stream Size in the GenusPleurocera(Rafinesque, 1818)

Although local correlations between shell phenotype and stream size have often been documented in freshwater mollusks, the species- and even genus-level taxonomy of pleurocerid snails has historically been based almost entirely on aspects of the shell. Here I test the hypothesis that lightly shelled pleurocerid populations inhabiting smaller rivers in east Tennessee and north Georgia, variously assigned to the genus Goniobasis or Elimia, may be local variants of heavily shelled Pleurocera populations downstream. Populations of the nominal species Goniobasis (“Elimia”) acutocarinata, G. clavaeformis, and Pleurocera unciale were sampled from the Powell, Little, and Hiwassee subdrainages of the Tennessee River, and populations nominally Goniobasis carinifera and Pleurocera vestita sampled from the Coahulla subdrainage of the Mobile Basin. A population of Goniobasis simplex was sampled from each of the four subdrainages to calibrate expected levels of genetic divergence. Gene frequencies at ten polymorphic allozyme-encoding loci (15 populations, 30 individuals per population) revealed that each population of Pleurocera was more closely related to its local populations of Goniobasis (or “Elimia”) than to any other population of Pleurocera. All nine populations identified as G. acutocarinata, G. clavaeformis, and P. unciale appear to be conspecific, their minimum genetic identity of 0.771 much greater than the 0.356 minimum identity among the four G. simplex controls. The specific relationship between the nine Tennessee populations and populations of G. carinifera and P. vestita from the Mobile Basin is ambiguous, with identities ranging down to 0.284. This larger set of 11 populations is here referred to as the carinifera group. Evidence that intraspecific variation in shell morphology has risen to the level of the genus suggests that Goniobasis, Elimia, and several other generic nomina be subsumed under Pleurocera (Rafinesque, 1818).

A 3‐node flat triangular shell element with corner drilling freedoms and transverse shear correction

AbstractThe formulation, implementation and testing of simple, efficient and robust shell finite elements have challenged investigators over the past four decades. A new 3‐node flat triangular shell element is developed by combination of a membrane component and a plate bending component. The ANDES‐based membrane component includes rotational degrees of freedom, and the refined nonconforming element method‐based bending component involves a transverse shear correction. Numerical examples are carried out for benchmark tests. The results show that compared with some popular shell elements, the present one is simple but exhibits excellent all‐around properties (for both membrane‐and bending‐dominated situations), such as free of aspect ratio locking, passing the patch test, free of shear locking, good convergence and high suitability for thin to moderately thick plates. The developed element has already been adopted in a warpage simulation package for injection molding. Copyright © 2011 John Wiley & Sons, Ltd.

NUMERICAL TREATMENT OF DAMAGE PROPAGATION IN AXIALLY COMPRESSED COMPOSITE AIRFRAME PANELS

In the design phase of stringer-stiffened composite airframe panels, it is a key issue to exploit material reserves as far as possible to create lighter and safer aircraft. A recent approach is to apply postbuckling design — standard for metallic panels — also to composite parts. This work focusses on the development of a simulation procedure which accurately predicts the postbuckling response of composite panels while accounting for damage propagation. For this purpose we employ a robust shell element formulation which allows for arbitrary stacking sequences as well as a variable location of the reference plane. A ply discount model is incorporated to account for intralaminar damage growth. The cohesive zone approach is implemented in a so-called interface element to predict interlaminar damage growth, respective skin–stringer separation. The numerical model is validated via a numerical example with experimental evidence.

Effects of past, present, and future ocean carbon dioxide concentrations on the growth and survival of larval shellfish.

The combustion of fossil fuels has enriched levels of CO(2) in the world's oceans and decreased ocean pH. Although the continuation of these processes may alter the growth, survival, and diversity of marine organisms that synthesize CaCO(3) shells, the effects of ocean acidification since the dawn of the industrial revolution are not clear. Here we present experiments that examined the effects of the ocean's past, present, and future (21st and 22nd centuries) CO(2) concentrations on the growth, survival, and condition of larvae of two species of commercially and ecologically valuable bivalve shellfish (Mercenaria mercenaria and Argopecten irradians). Larvae grown under near preindustrial CO(2) concentrations (250 ppm) displayed significantly faster growth and metamorphosis as well as higher survival and lipid accumulation rates compared with individuals reared under modern day CO(2) levels. Bivalves grown under near preindustrial CO(2) levels displayed thicker, more robust shells than individuals grown at present CO(2) concentrations, whereas bivalves exposed to CO(2) levels expected later this century had shells that were malformed and eroded. These results suggest that the ocean acidification that has occurred during the past two centuries may be inhibiting the development and survival of larval shellfish and contributing to global declines of some bivalve populations.

Geometrically nonlinear analysis of thin shell by a quadrilateral finite element with in-plane rotational degrees of freedom

We present in this research article, the improvements that we made to create a four nodes flat quadrilateral shell element for geometrically nonlinear analysis, based on corotational updated lagrangian formulation. These improvements are initially related to the improvement of the in-plane behaviour by incorporation of the in-plane rotational degrees of freedom known as “drilling degrees of freedom” in the membrane displacements field formulation. In the second phase, a co-rotational spatial local system of axes which adapts well to the problems of quadrilateral elements is adopted, while ensuring simplicity and effectiveness at numerical level. The required goal being mainly to have a robust thin shell element associated with a simplified formulation. The obtained element remains economic, and showing a robust behaviour in delicate situations of tests.

The Sonochemical and Biological Effects of Three Clinically-Used Contrast Agents

The encapsulation of gas bubbles has resulted in improved stability and added a binding capacity to shells for ultrasound-guided targeted delivery. However, this has also changed the physical and acoustical properties of the final formulation. In this study, we have evaluated three clinically-used contrast agents of different compositions, namely, Levovist, Sonazoid, and SonoVue, with respect to their sonochemical and biological effects at different concentrations. The results showed that both shell elasticity and reactivity played a role in modulating both effects influencing the extent of ultrasound-induced free-radical formation. Microbubbles with elastic shells were found to be more capable of inducing delayed symptoms of cell killing, whereas the combined use of chemically reactive robust shells and high-density gases, such as perfluorocarbons, could exert a protective effect on cells. These conclusions offer new perspectives on how microbubbles interact with biological systems and might be useful in tailoring novel microbubbles in the future.

Facile preparation of titania hollow spheres by combination of the mixed solvent method and the sol–gel process and post-calcination

Polystyrene (core)–titania (shell) composite spheres consisting were readily prepared by a sol–gel process of titanium tetrabutoxide (TBOT) in a mixed solvent of ethanol/acetonitrile (3:1, v/v). Smooth and homogeneous titania coatings formed when the mixed solvent was dehydrated by anhydrous sodium sulfate. The thickness and surface roughness of titania coating increase with increase of the TBOT concentration. By adjusting the TBOT concentration in the range of 5.8–29.0 mM, the size of titania-coated PS spheres could be varied from 990 to 1125 nm. Calcination at elevated temperature gave dense, homogeneous, robust shells of anatase titania. The sizes of titania hollow spheres are 11.3–16.9% smaller than those of the titania-coated PS spheres as a result of calcination-induced shrinkage. The composite and hollow spheres were characterized by scanning electron microscopy, transmission electron microscopy and electron diffraction measurements. These core–shell organic–inorganic spheres and hollow ceramic spheres may have wide applications in catalysts, adsorbents, lightweight fillers, capsules, etc.

Design optimization of a torpedo shell structure

An optimized methodology to design a more robust torpedo shell is proposed. The method has taken into account reliability requirements and controllable and uncontrollable factors such as geometry, load, material properties, manufacturing processes, installation, etc. as well as human and environmental factors. The result is a more realistic shell design. Our reliability optimization design model was developed based on sensitivity analysis. Details of the design model are given in this paper. An example of a torpedo shell design based on this model is given and demonstrates that the method produces designs that are more effective and reliable than traditional torpedo shell designs. This method can be used for other torpedo system designs.

Immobilizing Au-nanocolloids in co-branched polymer molecules in presence of gluconic acid in poly(vinyl alcohol) in hot water

It is explored that in hot water (50–70 °C) polymer molecules of poly(vinyl alcohol) (PVA) induce Au 3+ → Au reaction and serve as an Au-stabilizer by immobilizing the Au-particles capping in part of the polymer molecules. Adding gluconic acid (GA) inhibits Au 3+ coalescence in small groups in process to the reaction capping in surface stabilized PVA–GA polymer molecules. Tetrachloroauric acid HAuCl 4·3H 2O (supplies Au 3+) in reaction with PVA molecules (with as much GA as twice the PVA in molar ratio) demonstrates the experiments. A robust shell comprises Au-nanoparticles of a thin polymer surface layer characterized by light absorption (450–750 nm) in the Au-surface plasmon bands. In general, GA affects the formation of Au-nanoparticles, with a blue shift (smaller size) of the absorption, e.g., from 565 nm in 1.0 wt% Au in reaction in PVA to that of 540 nm in PVA–GA, with an order of improved value of absorbance. X-ray diffraction of the films or thin plates (2–5 mm thickness) has well-defined lattice reflections (1 1 1), (2 0 0), (2 2 0), (3 1 1), (2 2 2) and (4 0 0) in fcc-Au crystallites (∼25 nm average size). Microstructure reveals non-agglomerated particles of near cuboids or prismatic shapes of 35–70 nm widths.

Nanoparticle-Assembled Capsule Synthesis: Formation of Colloidal Polyamine−Salt Intermediates

There is current interest in developing new synthesis strategies for multifunctional hollow spheres with tunable structural properties that would be useful in encapsulation and controlled release applications. A new route was reported recently, in which the sequential reaction of polyamines, multivalent anions, and charged nanoparticles leads to the formation of polymer-filled and water-filled organic/inorganic micron-sized structures known as nanoparticle-assembled capsules. This technique is unique among other capsule preparation routes, as it allows the rapid and scalable formation of robust shells at room temperature, in near-neutral water, and with readily available precursors. This nanoparticle assembly synthesis route involves two steps: the formation of polymer aggregates and the subsequent deposition of particles around the aggregates. The purpose of this paper is to understand in greater detail the noncovalent chemistry of the polymer-salt aggregation step. With poly(allylamine hydrochloride) (PAH) as the model polymer, aggregate formation was investigated as a function of charge ratio, pH, and time through dynamic light scattering, electrophoretic mobility measurements, chloride ion measurements, and optical microscopy. PAH formed aggregates by the cross-linking action of divalent and higher-valent anions above a critical charge ratio and in a pH range defined by the pKa values of PAH and the anion. The aggregates grew in size through coalescence and with growth rates that depended on their surface charge. Controlling polymer aggregate growth provided a direct and simple means to adjust the size of the resultant capsule materials.