Assembly Of Elements Research Articles

Semi-analytical buckling analysis of omega stiffened panels under multi-axial loads

This paper presents a semi-analytical method for the buckling analysis of composite panels reinforced with omega stiffeners and subjected to combined loading conditions of biaxial loads and shear. The approach is based on the representation of the panel as an assembly of plate elements, allowing to capture local buckling modes involving skin and stiffener deflections. The panel model includes also the possibility of accounting for the stiffener foot. Trigonometric shape functions are introduced to describe the buckling patterns, while the buckling equations are derived through the application of the minimum potential energy principle. The comparison with Abaqus finite element analyses is presented, demonstrating, for a wide variety of test cases, percent differences below 9% and a good accuracy of the computed buckling modes. The computational speed up is of the order of 100, suggesting the use of the formulation in the context of preliminary design loops, sensitivity analyses or design optimizations.

EFESTS: Educational finite element software for truss structure. Part II: Linear static analysis

This article presents a complete guide from the linear static finite element theory to the software development of the educational finite element software for truss structure (EFESTS). First, linear static formulations of truss structure are summarized, including the element formulation, element assembly and solution. Object-oriented programming is introduced to design the software architecture. Furthermore, the relations between the classes and their instances are clearly described using the static class diagram and the dynamic sequence diagram, respectively. Finally, the linear static solver is intuitively verified by the deformable configuration and stress contour of a 50-bar truss structure. More importantly, a visualization of graphical user interfaces is developed to dynamically assemble the element matrix into the truss matrix, which used to be one of the most difficult skills for students to master. Finally, this software is free for educational research and can be downloaded from the website: http://www.zuowenjie.net/efests.html . In the future, we will develop the geometric nonlinear static analysis solver for the truss structure.

Exfoliation of organic montmorillonite in iPP free of compatibilizer through the multistage stretching extrusion

Polypropylene (PP)/organic montmorillonite (OMMT) nanocomposites were first prepared through twin-screw extruder and then subjected to multistage stretching extrusion with an assembly of laminating-multiplying elements (LMEs, which divide and recombine polymer melts). The exfoliated efficiency of LMEs on OMMT dispersed in PP matrix was investigated by optical microscopy, scanning electron microscope, transmission electron microscopy and X-ray diffraction. Because of the absence of compatibilizer, molecular chains of PP were not intercalated into the galleries of OMMT during the multistage stretching extrusion. The exfoliation of OMMT was induced by the strong force occurred in LMEs, which can destruct van der Waal’s interaction between the laminate OMMT platelets. The exfoliation degree of OMMT has been improved with the increase of number of LMEs used. The dispersion morphology of OMMT was thermodynamically stable after secondary melt processing. As a result, the mechanical properties of composites have been enhanced with increasing LME number. We realized the exfoliation of OMMT by the function of strong shear field without the incorporation of compatibilizer.

Simultaneous ultrasonication‐assisted internal mixing to prepare MWCNTs‐filled epoxy composites with increased strength and thermal conductivity

The uniform dispersion of carbon nanotubes in epoxy resin is one of the key factors to achieve the composites with desirable mechanical and physical property enforcement. However, the widely used dispersion methods have their own respective limitations in pursuing satisfactory nanotube dispersion. Herein, a new dispersion approach, based on the synergetic effect of combining high speed internal mixing with running simultaneously continuous ultrasonication treatment, has been proposed. The dispersion of nanotubes was carried out in a high speed internal mixer, consisting of twin kneading block structured rotors and an integrated ultrasonic horn, which was intercalated into the central position between the twin rotors. At first, the FEM simulation was conducted to optimize the kneading element assembly and illuminate the geometry influence of the ultrasonic horn intercalation on the mixing flow. Afterwards, to confirm the feasibility of the approach, pristine MWCNTs (P‐CNTs), oxidation modified MWCNTs (M‐CNTs) and M‐CNTs/multilayer graphene nanoplatelets (MGPs) hybrid are dispersed into epoxy resin. The dispersion of each sample in its liquid epoxy state is investigated under transparent optical microscopy. More characterizations, including SEM, TG/DTA, tensile test, and thermal conductivity measurements, were conducted on the cured composites. Competitive reinforcements on mechanical tensile property and thermal conductivity were observed. Especially, at a 1.5 wt% M‐CNTs/MGPs hybrid content, the composite mechanical tensile strength and thermal conductivity were 47% and 30% higher than those of neat epoxy. This preliminary study demonstrates the feasibility and practicability of the proposed approach to achieving good MWCNTs dispersion and distribution in epoxy resin. POLYM. COMPOS., 37:870–880, 2016. © 2014 Society of Plastics Engineers

Protein structure prediction: assembly of secondary structure elements by basin-hopping.

The prediction of protein tertiary structure from primary structure remains a challenging task. One possible approach to this problem is the application of basin-hopping global optimization combined with an all-atom force field. In this work, the efficiency of basin-hopping is improved by introducing an approach that derives tertiary structures from the secondary structure assignments of individual residues. This approach is termed secondary-to-tertiary basin-hopping and benchmarked for three miniproteins: trpzip, trp-cage and ER-10. For each of the three miniproteins, the secondary-to-tertiary basin-hopping approach successfully and reliably predicts their three-dimensional structure. When it is applied to larger proteins, correctly folded structures are obtained. It can be concluded that the assembly of secondary structure elements using basin-hopping is a promising tool for de novo protein structure prediction.

Identification and assembly of genomes and genetic elements in complex metagenomic samples without using reference genomes.

Most current approaches for analyzing metagenomic data rely on comparisons to reference genomes, but the microbial diversity of many environments extends far beyond what is covered by reference databases. De novo segregation of complex metagenomic data into specific biological entities, such as particular bacterial strains or viruses, remains a largely unsolved problem. Here we present a method, based on binning co-abundant genes across a series of metagenomic samples, that enables comprehensive discovery of new microbial organisms, viruses and co-inherited genetic entities and aids assembly of microbial genomes without the need for reference sequences. We demonstrate the method on data from 396 human gut microbiome samples and identify 7,381 co-abundance gene groups (CAGs), including 741 metagenomic species (MGS). We use these to assemble 238 high-quality microbial genomes and identify affiliations between MGS and hundreds of viruses or genetic entities. Our method provides the means for comprehensive profiling of the diversity within complex metagenomic samples.

Surveillant Assemblages of Governance in Massively Multiplayer Online Games: A Comparative Analysis

This paper explores governance in Massively Multiplayer Online Games (MMOGs), one sub-sector of the digital games industry. Informed by media governance studies, Surveillance Studies, and game studies, this paper identifies five elements which form part of the system of governance in MMOGs. These elements are: game code and rules; game policies; company community management practices; player participatory practices; and paratexts. Together these governance elements function as a surveillant assemblage, which relies to varying degrees on lateral and hierarchical forms of surveillance, and the assembly of human and non-human elements. Using qualitative mixed methods we examine and compare how these elements operate in three commercial MMOGs: Eve Online, World of Warcraft and Tibia. While peer and participatory surveillance elements are important, we identified two major trends in the governance of disruptive behaviours by the game companies in our case studies. Firstly, an increasing reliance on automated forms of dataveillance to control and punish game players, and secondly, increasing recourse to contract law and diminishing user privacy rights. Game players found it difficult to appeal the changing terms and conditions and they turned to creating paratexts outside of the game in an attempt to negotiate the boundaries of the surveillant assemblage. In the wider context of self-regulated governance systems these trends highlight the relevance of consumer rights, privacy, and data protection legislation to online games and the usefulness of bringing game studies and Surveillance Studies into dialogue.

One-way glass for microwaves using nonreciprocal metamaterials.

We introduce a class of nonreciprocal metamaterials based on composite assemblies of metallic and biased ferrimagnetic elements. We show that such structures act as ultrathin one-way glasses due to the competition between two modes at the surface of the ferrimagnetic elements--a low-loss surface wave that transmits the signal on the other side of the structure and a surface spin-wave resonance that produces strong isolation levels. These findings can be adapted to existing metamaterial geometries, offering a blueprint to achieve unidirectional propagation in a variety of artificial media at radio, microwave, and millimeter wave frequencies.

Conjugate heat transfer simulations of advanced research reactor fuel

The current work presents numerical simulations of coupled fluid flow and heat transfer of advanced U–Mo/Al and U–Mo/Mg research reactor fuels in support of performance and safety analyses. The objective of this study is to enhance predictions of the flow regime and fuel temperatures through high fidelity simulations that better capture various heat transfer pathways and with a more realistic geometric representation of the fuel assembly in comparison to previous efforts. Specifically, thermal conduction, convection and radiation mechanisms are conjugated between the solid and fluid regions. Also, a complete fuel element assembly is represented in three dimensional space, permitting fluid flow and heat transfer to be simulated across the entire domain. Seven case studies are examined that vary the coolant inlet conditions, specific power, and burnup to investigate the predicted changes in the pressure drop in the coolant and the fuel, clad and coolant temperatures. In addition, an alternate fuel geometry is considered with helical fins (replacing straight fins in the existing design) to investigate the relative changes in predicted fluid and solid temperatures. Numerical simulations predict that the clad temperature is sensitive to changes in the thermal boundary layer in the coolant, particularly in simultaneously developing flow regions, while the temperature in the fuel is anticipated to be unaffected. Finally, heat transfer between fluid and solid regions is enhanced with helical fins, which may be an attractive consideration in future designs to enhance performance and/or safety.

Effect of multistage tensile extrusion induced fiber orientation on fracture characteristics of high density polyethylene/short glass fiber composites

Abstract The high density polyethylene (HDPE)/short glass fiber (SGF) composites were prepared by multistage tensile extrusion with an assembly of laminating-multiplying elements (LMEs) connecting with an extruder. The strong shear and elongational force field in LME could make the fibers orientated along the melt flow direction. The degree of fiber orientation could be controlled by the number of LMEs. The SEM morphological observations illustrated that the fiber orientation degree was gradually increased by increasing the number of LMEs. However, the fiber length distribution and crystallinity of composites did not change much with increasing the LMEs, and would not affect the mechanical properties. The essential work of fracture (EWF) analysis at quasi-static rate of loading showed that the fracture toughness along the melt flow direction increased with the number of LMEs increasing because of the change of the fiber related damage mechanism. An opposite trend was found if samples were stretched perpendicular to the melt flow direction.

Subtelomeric CTCF and cohesin binding site organization using improved subtelomere assemblies and a novel annotation pipeline

Mapping genome-wide data to human subtelomeres has been problematic due to the incomplete assembly and challenges of low-copy repetitive DNA elements. Here, we provide updated human subtelomere sequence assemblies that were extended by filling telomere-adjacent gaps using clone-based resources. A bioinformatic pipeline incorporating multiread mapping for annotation of the updated assemblies using short-read data sets was developed and implemented. Annotation of subtelomeric sequence features as well as mapping of CTCF and cohesin binding sites using ChIP-seq data sets from multiple human cell types confirmed that CTCF and cohesin bind within 3 kb of the start of terminal repeat tracts at many, but not all, subtelomeres. CTCF and cohesin co-occupancy were also enriched near internal telomere-like sequence (ITS) islands and the nonterminal boundaries of subtelomere repeat elements (SREs) in transformed lymphoblastoid cell lines (LCLs) and human embryonic stem cell (ES) lines, but were not significantly enriched in the primary fibroblast IMR90 cell line. Subtelomeric CTCF and cohesin sites predicted by ChIP-seq using our bioinformatics pipeline (but not predicted when only uniquely mapping reads were considered) were consistently validated by ChIP-qPCR. The colocalized CTCF and cohesin sites in SRE regions are candidates for mediating long-range chromatin interactions in the transcript-rich SRE region. A public browser for the integrated display of short-read sequence–based annotations relative to key subtelomere features such as the start of each terminal repeat tract, SRE identity and organization, and subtelomeric gene models was established.

Morphological evolution of thermotropic liquid crystalline copolyester and its effects on rheological, thermal and flame-retarding behaviors of polycarbonate

Polycarbonate (PC)/phosphorus-containing thermotropic liquid crystalline copolyester (PHDDT) composites were prepared through a novel multistage stretching extrusion. The morphology of the PHDDT phase was controlled by combining an assembly of force-assembling elements (FAEs) with an extruder. SEM observation revealed that morphological evolution of PHDDT from platelets to microfibrils occurred by applying different number of FAEs. The dynamic rheological and thermogravimetric results showed that the increased interfacial area between PHDDT and PC led to a drastic reduction of the complex viscosity and a lower temperature of the maximum loss. Accompanied with the elongation of the PHDDT along flowing direction, the storage modulus and glass transition temperature of the composite were enhanced. However, compared with the system dispersed with the platelet-like phase, the micro-fibrillation of the flame-retarding PHDDT resulted in the decrease of the temperature of the heat release rate curve starting to rise up and the value of the limiting oxygen index. The confined space formed between the platelet-like PHDDT phase was considered to effectively retard the combustion of the whole material.

Two-Scale Homogenization of the Nonlinear Eddy Current Problem With FEM

An efficient and accurate computation of the eddy current losses in laminated iron cores of electric devices is of great interest. Modeling each laminate individually by the finite element method requires many elements and leads to large systems of equations. Homogenization represents a promising method to overcome this problem. A two-scale finite element method is proposed to efficiently compute the eddy current losses in laminated media with nonlinear material properties. A rather coarse finite element grid suffices to approximate the losses accurately. The method based on the magnetic vector potential is described. The laminates are basically considered individually in the finite element assembly taking account of the nonlinearity. This is computationally very intensive. Some adapted integration rules are introduced and studied to accelerate the finite element assembly. The accuracy and the computational costs of the proposed method are shown by a numerical example.

Environmental tests of embedded thin- and thick-film resistors in comparison to chip resistors

Purpose – The purpose of this paper is to investigate the influence of parameters of embedded resistive elements manufacturing process as well as the influence of environmental factors on their electrical resistance. The investigations were made in comparison to the similar constructions of discrete chip resistors assembled to standard printed circuit boards (PCBs). Design/methodology/approach – The investigations were based on the thin-film resistors made of NiP alloy, thick-film resistors made of carbon or carbon-silver inks as well as chip resistors in 0402 and 0603 packages. The polymer thick-film resistive films were screen-printed on the several types finishing materials of contact terminations such as copper, silver, and gold. To determine the sensitivity of embedded resistors versus standard assembled chip resistors on environmental exposure, the climatic chamber was used. The measurements of resistance were carried out periodically during the tests, and after the exposure cycles. Findings – The results show that the change of electrical resistance of embedded resistors, in dependence of construction and base material, is different and mainly not exceed the range of 3 per cent. The achieved results in reference to thin-film resistors are comparable with results for standard chip resistors. However, the results that were obtained for thick-film resistors with Ag and Ni/Au contacts are similar. It was not found the big differences between resistors with and without conformal coating. Research limitations/implications – The studies show that embedded resistors can be used interchangeably with chip resistors. It allows to save the area on the surface of PCB, occupied by these passive elements, for assembly of active elements (ICs) and thus enable to miniaturization of electronic devices. But embedding of passive elements into PCB requires to tackle the effect of each forming process steps on the operational properties. Originality/value – The technique of passive elements embedding into PCB is generally known; however, there are no detailed reports on the impact of individual process steps and environmental conditions on the stability of their electrical resistance. The studies allow to understand the importance of each factor process and the mechanisms of operational properties changes depending on the used materials.

Theoretical Analysis of Mechanical Vibration for Offshore Platform Structures

A new class of support structures, called Periodic Structures, is introduced in this paper as a viable means for isolating the vibration transmitted from the sea waves to offshore platform structures through its legs. A passive approach to reduce transmitted vibration generated by waves is presented. The approach utilizes the property of periodic structural components that create stop and pass bands. The stop band regions can be tailored to correspond to regions of the frequency spectra that contain harmonics of the wave frequency, attenuating the response in those regions. A periodic structural component is comprised of a repeating array of cells, which are themselves an assembly of elements. The elements may have differing material properties as well as geometric variations. For the purpose of this research, only geometric and material variations are considered and each cell is assumed to be identical. A periodic leg is designed in order to reduce transmitted vibration of sea waves. The effectiveness of the periodicity on the vibration levels of platform will be demonstrated theoretically. The theory governing the operation of this class of periodic structures is introduced using the transfer matrix method. The unique filtering characteristics of periodic structures are demonstrated as functions of their design parameters for structures with geometrical and material discontinuities, and determine the propagation factor by using the spectral finite element analysis and the effectiveness of design on the leg structure by changing the ratio of step length and area interface between the materials is demonstrated in order to find the propagation factor and frequency response.

Between geometry and craft: the setting‐out of the NiGRES Tower

AbstractIn 1899 Vladimir Shuchov (1853–1939), the polymath Russian engineer, was awarded a patent covering the principles he had devised for hyperbolic lattice towers. These hyperbolic towers are constructed from an assembly of straight elements connected together with complex three‐dimensional joints. However, their full geometry is difficult to discern from the (orthogonal) drawings still available. Until now, little was known about the technological advances that made these complex designs feasible. This paper presents an investigation into the mathematical principles and operational practices that may have been used for determining the actual geometry of individual elements for setting out and constructing the metal lattices, thus illuminating the conjunction of geometry and craft.

Metrology Assisted Assembly of Airplane Structure Elements

Geometric deformations in large components like airplane shells caused by e.g. gravitation influences have to be compensated before assembly. The research objective is to develop a metrology assisted robot based assembly system that detects deformations and compensate them through force controlled movements of the robots. The determination of robot compensation movements uses a model of the components deformation behaviour. For the determination of the model parameters an identification process is developed, which uses samples of the real component deformation behaviour caused by defined external forces to approximate the parameters (e.g. stiffness) of the component.

A strategy for prediction of the elastic properties of epoxy-cellulose nanocrystal-reinforced fiber networks

SUMMARY: The reinforcement potential of cellulose nanocrystal (CNC) additions on an idealized 2-dirmensional (2-D) fiber network structure consisting of micron sized fiber elements was investigated. The reinforcement mechanism considered in this study was through the stiffening of the micron sized fiber elements via a CNC-epoxy coating. A hierarchical analytical modeling approach was used to estimate the elastic properties spanning three different structural features; i) micromechanics for CNC-epoxy properties, ii) laminate theory for fiber elements coated with CNCepoxy, and iii) a 2-D network model for an assembly of interconnected fiber elements. The extent to which CNCepoxy coating can stiffen a fiber element was dependent on the CNC volume fraction, CNC-epoxy layer thickness, CNC alignment, CNC aspect ratio, and the original stiffness of the fiber element. Calculations suggest there is a potential for CNC additions to stiffen network structures, the extent to which is strongly depending on the initial fiber element stiffness. Incorporation of limited experimental observations into the model and fiber element properties typical of fibers used in paper products, however, suggests that the enhancement of CNCs on a wood fiber element and thus on the network structure, may be limited.

Automatic finite element formulation and assembly of hyperelastic higher order structural models

The formulation of higher order structural models and their discretization using the finite element method is difficult owing to their complexity, especially in the presence of nonlinearities. In this work a new algorithm for automating the formulation and assembly of hyperelastic higher-order structural finite elements is developed. A hierarchic series of kinematic models is proposed for modeling structures with special geometries and the algorithm is formulated to automate the study of this class of higher order structural models. The algorithm developed in this work sidesteps the need for an explicit derivation of the governing equations for the individual kinematic modes. Using a novel procedure involving a nodal degree-of-freedom based automatic assembly algorithm, automatic differentiation and higher dimensional quadrature, the relevant finite element matrices are directly computed from the variational statement of elasticity and the higher order kinematic model. Another significant feature of the proposed algorithm is that natural boundary conditions are implicitly handled for arbitrary higher order kinematic models. The validity algorithm is illustrated with examples involving linear elasticity and hyperelasticity.

Picking up speed: advances in the genetics of primary ciliary dyskinesia

Abnormal ciliary axonemal structure and function are linked to the growing class of genetic disorders collectively known as ciliopathies, and our understanding of the complex genetics and functional phenotypes of these conditions has rapidly expanded. While progress in genetics and biology has uncovered numerous cilia-related syndromes, primary ciliary dyskinesia (PCD) remains the sole genetic disorder of motile cilia dysfunction. The first disease-causing mutation was described just thirteen years ago, and since that time the pace of gene discovery has quickened. These mutations separate into genes that encode axonemal motor proteins, structural and regulatory elements, and cytoplasmic proteins that are involved in assembly and preassembly of ciliary elements. These findings have yielded novel insights into the processes involved in ciliary assembly, structure, and function, which will allow us to better understand the clinical manifestations of primary ciliary dyskinesia. Moreover, advances in techniques for genetic screening and sequencing are improving diagnostic approaches. In this manuscript, we will describe the structure, function, and emerging genetics of respiratory cilia, review the genotype-phenotype relationships of motor ciliopathies, and explore the implications of recent discoveries for diagnostic testing for primary ciliary dyskinesia.