Assembly Of Elements Research Articles

Simplified method for real‐time seismic damage assessment of motorway bridges: Transverse direction—Accounting for abutment stoppers

SummaryIn the context of developing a real‐time seismic damage assessment technique, this paper proposes a simplified model that accounts for abutment stoppers, focusing on the transverse direction. Detailed 3D finite element models of 4 bridges of the Attiki Odos motorway are developed and used as benchmarks to assess its efficiency. The selected bridges vary in length, pier typologies, clearances, and pier‐deck connections. The simplified model entails a SDOF system of a pier, with assemblies of gap elements, lateral and rotational springs, and dashpots (top and bottom), representing the deck, the bearings, the abutment stoppers, and the foundation. The effect of stoppers is initially studied, focusing on the response of the abutment‐embankment system. To shed more light on the role of abutment stoppers, a parametric study is conducted, considering a wide range of clearances. Subsequently, the effect of variabilities in span length and pier height is examined. The simplified method is extended to nonideally symmetric systems and verified against the 3D benchmarks. Finally, the model is modified to account for multicolumn piers. The extended simplified model offers a reasonable prediction of the seismic damage state, reducing significantly the computational cost, and allowing detailed parametric studies. The latter are used to develop nonlinear regression model equations correlating a selected damage index with statistically significant intensity measures. Such equations offer a viable alternative for network‐wide seismic damage assessment as part of a real‐time emergency response framework. A pilot implementation is presented, illustrating the applicability of the proposed methodology.

Variation modeling and analysis with interval approach for the assembly of compliant aeronautical structures

Due to small production volume in aircraft industry, the available information of variation sources is often not enough to make assumptions on their probabilistic characteristics, especially in the stage of prototype manufacturing. To deal with the problem, an assembly variation modeling and analysis method based on the elasticity mechanics and interval approach is proposed for aircraft assembly. First, variation sources are modeled as bounded convex sets, which are defined as interval structural parameters in interval arithmetic. Then, variation modeling and analysis are successively implemented using the method of influence coefficient and interval arithmetic. After that, a uniform-splitting method is applied to achieve the refinement of the interval extension in variation analysis. To reduce the complexity of the finite element analysis and assembly variation computation, part deformation forms including warpage and torsion are concisely characterized with angle instead of the deviations of isolated key points on the part. The comparison of the assembly variations estimated with the proposed variation analysis method and actual experiment results verifies the effectiveness of the constructed assembly variation model and the proposed method. The interval approach–based assembly variation analysis method is a good complement to traditional probabilistic approach–based methods for compliant assembly systems, which is suited for linear and linearized nonlinear assembly systems. The proposed method provides an improved understanding of the application of compliant assembly variation analysis methods in aircraft manufacturing.

Antibiotic Resistance

Bacterial mechanisms of drug resistance operate at sequential lines of defense tackling drug at entry, accumulation, target binding, or downstream toxicity. These mechanisms are encoded by genomic changes ranging in scale from point mutations, through assembly of preexisting genetic elements, to horizontal import of genes from the environment. A many-to-many relationship prevails between resistance mechanisms and the spectrum of genetic changes encoding them.

Constructal Optimizations for Heat and Mass Transfers Based on the Entransy Dissipation Extremum Principle, Performed at the Naval University of Engineering: A Review.

Combining entransy theory with constructal theory, this mini-review paper summarizes the constructal optimization work of heat conduction, convective heat transfer, and mass transfer problems during the authors’ working time in the Naval University of Engineering. The entransy dissipation extremum principle (EDEP) is applied in constructal optimizations, and this paper is divided into three parts. The first part is constructal entransy dissipation rate minimizations of heat conduction and finned cooling problems. It includes constructal optimization for a “volume-to-point” heat-conduction assembly with a tapered element, constructal optimizations for “disc-to-point” heat-conduction assemblies with the premise of an optimized last-order construct and without this premise, and constructal optimizations for four kinds of fin assemblies: T-, Y-, umbrella-, and tree-shaped fins. The second part is constructal entransy dissipation rate minimizations of cooling channel and steam generator problems. It includes constructal optimizations for heat generating volumes with tree-shaped and parallel channels, constructal optimization for heat generating volume cooled by forced convection, and constructal optimization for a steam generator. The third part is constructal entransy dissipation rate minimizations of mass transfer problems. It includes constructal optimizations for “volume-to-point” rectangular assemblies with constant and tapered channels, and constructal optimizations for “disc-to-point” assemblies with the premise of an optimized last-order construct and without this premise. The results of the three parts show that the mean heat transfer temperature differences of the heat conduction assemblies are not always decreased when their internal complexity increases. The average heat transfer rate of the steam generator obtained by entransy dissipation rate maximization is increased by 58.7% compared with that obtained by heat transfer rate maximization. Compared with the rectangular mass transfer assembly with a constant high permeability pathway (HPP), the maximum pressure drops of the element and first-order assembly with tapered HPPs are decreased by 6% and 11%, respectively. The global transfer performances of the transfer bodies are improved after optimizations, and new design guidelines derived by EDEP, which are different from the conventional optimization objectives, are provided.

Timber robotic fabrication: testing for an integral manufacturing

Going beyond sustainability and with the great development of technology, timber has a great potential to be explored as a building material. Its physical-mechanical properties such as lightness and elasticity allow the designing of complex structures and the growing trend in research in robotic fabrication has accelerated the development of dimensional design concepts that demonstrate that wood is absolutely contemporary and at the height of other innovative materials. This paper investigates on computer aided integrated architectural design and production of timber using advanced automated tools, aiming to provide integral solutions for the design and production of geometrically complex free-form architecture. Investigations on computer aided geometric design and integrated manufacturing are carried out with equal importance. This research is considering an integral and interdisciplinary approach, including computer science, robotics and architecture. The studies for translation of the geometrical into constructional elements consider integrated manufacturing. Addressing and numbering of the elements by iterative geometric design are investigated and compared to lexicographically ordered addressing systems, in order to provide an adequate data structure for the design, production and assembly of the constructional elements. The integrated digital design methods studied are tested and verified by the realization of one to one scale prototypes. The main aim of the research is to find ways of shifting the perspective of adventurous high quality architecture robotically produced with correspondingly reduced costs and minimized environmental impact.

Use of independent volume parameters in the development of new large displacement ANCF triangular plate/shell elements

In this paper, a new unified kinematic description, obtained from Bezier geometry using linear mapping and position vector gradients associated with three independent parameters, is used to develop large displacement plate/shell finite elements (FE). Contrary to the conventional FE method, in the approach developed in this paper based on the absolute nodal coordinate formulation (ANCF), no distinction is made between plate and shell structures. The proposed ANCF triangular plate/shell elements have 12 coordinates per node: three position coordinates and nine position gradient coordinates that define vectors tangent to coordinate lines at the nodes. The fundamental differences between the conventional FE and the new ANCF parameterizations are highlighted. In this investigation, two different parameterizations, each of which employs independent coordinates, are used. In the first parameterization, called volume parameterization, coordinate lines along the sides of the triangular element in the straight (un-deformed) configuration are used in order to facilitate the development of closed-form cubic shape functions. In the second parameterization, called Cartesian parameterization, coordinate lines along the global axes of the structure (body) coordinate system are used to facilitate the element assembly. The element transformation between the volume and the Cartesian parameterizations is developed and used to define the structure inertia and elastic forces. Three new fully parameterized ANCF triangular plate/shell elements are developed in this investigation: a four-node mixed-coordinate element (FNMC) and two three-node elements (TN1 and TN2). All the elements developed in this investigation lead to a constant mass matrix and zero Coriolis and centrifugal forces. A non-incremental total Lagrangian procedure is used for the numerical solution of the nonlinear equations of motion. The performance of the proposed ANCF triangular plate/shell elements is analyzed by comparison with the ANCF rectangular plate element and conventional three-node linear (TNL) and six-node quadratic (SNQ) triangular plate elements.

Development and testing of the reinforced wooden windows

Oversized window systems with extreme heights are becoming increasingly popular at European and global market. Such sizes can cause problems of bending of wooden elements which results in the decrease of main window properties and structural integrity. Double casement wooden windows of the 2 m height, with and without reinforcement, were tested at the pressure load of 2000 Pa in order to define its behaviour and develop numerical simulation. Numerical models were defined as an assembly of individual wooden elements with mutual contact, orthotropic behaviour, simulated dowels constrain and insulated triple glass unit. Simulations have provided insight in to mutual behaviour of all individual elements and have proven that contact between window and the wall represents weak point rather than the integrity of the wooden frame elements as initially assumed. During the next phase special reinforcements used to restrain moments at the contact points were tested both numerically and psychically.

TSFC: A Structure-Preserving Form Compiler

A form compiler takes a high-level description of the weak form of partial differential equations and produces low-level code that carries out the finite element assembly. In this paper we present the Two-Stage Form Compiler (TSFC), a new form compiler with the main motivation to maintain the structure of the input expression as long as possible. This facilitates the application of optimizations at the highest possible level of abstraction. TSFC features a novel, structure-preserving method for separating the contributions of a form to the subblocks of the local tensor in discontinuous Galerkin problems. This enables us to preserve the tensor structure of expressions longer through the compilation process than other form compilers. This is also achieved in part by a two-stage approach that cleanly separates the lowering of finite element constructs to tensor algebra in the first stage, from the scheduling of those tensor operations in the second stage. TSFC also efficiently traverses complicated expressions, and experimental evaluation demonstrates good compile-time performance even for highly complex forms.

A Stencil Scaling Approach for Accelerating Matrix-Free Finite Element Implementations

We present a novel approach to fast on-the-fly low order finite element assembly for scalar elliptic partial differential equations of Darcy type with variable coefficients optimized for matrix-free implementations. Our approach introduces a new operator that is obtained by appropriately scaling the reference stiffness matrix from the constant coefficient case. Assuming sufficient regularity, an a priori analysis shows that solutions obtained by this approach are unique and have asymptotically optimal order convergence in the $H^1$- and the $L^2$-norms on hierarchical hybrid grids. For the preasymptotic regime, we present a local modification that guarantees uniform ellipticity of the operator. Cost considerations show that our novel approach requires roughly one-third of the floating-point operations compared to a classical finite element assembly scheme employing nodal integration. Our theoretical considerations are illustrated by numerical tests that confirm the expectations with respect to accuracy and run-time. A large scale application with more than a hundred billion ($1.6\cdot10^{11}$) degrees of freedom executed on 14310 compute cores demonstrates the efficiency of the new scaling approach.

CONV-3D Code Application for CFD-Modeling of Lead-Bismuth Coolant

The results of testing the three-dimensional CFD-code on problems very close to real processes for lead–bismuth eutectic are presented: flow in a 19-fuel element assembly with three spacing lattices and convection in the ‘tumbler’ model. The results of convergence on a sequence of grids permit drawing the conclusion that for a 19-fuel element assembly the error in the calculation of the friction coefficient on a more finely divided grid does not exceed 10% with two-fold smaller grid step in each direction. Similar arguments are valid for the calculation of the hydraulic resistance coefficient.

Stability analysis forn-periodic arrays of fluid systems

Many fluid systems consisting of an assembly of multiple but identical elements exhibit collective and synchronized motion involving groups of locked-in units. A computational framework for this type of fluid system with examples from hydrodynamic stability and turbomachinery is presented.

A Rayleigh-Ritz approach for postbuckling analysis of variable angle tow composite stiffened panels

A Rayleigh-Ritz solution approach for generally restrained multilayered variable angle tow stiffened plates in postbuckling regime is presented. The plate model is based on the first order shear deformation theory and accounts for geometrical nonlinearity through the von Kármán’s assumptions. Stiffened plates are modelled as assembly of plate-like elements and penalty techniques are used to join the elements in the assembled structure and to apply the kinematical boundary conditions. General symmetric and unsymmetric stacking sequences are considered and Legendre orthogonal polynomials are employed to build the trial functions. A computer code was developed to implement the proposed approach and to establish its applicability and its features for investigating variable angle tow structures. The proposed solution is validated by comparison with literature and finite elements results. Original results are presented for postbuckling of variable angle tow stiffened plates showing the potentialities of the method.

Heat conduction constructal optimization for nonuniform heat generating area based on triangular element

A nonuniform heat generating model in a triangular area is built in this paper. Constructal optimizations of the models with constant and discrete variable cross-sectional high conductivity channels (HCCs) are performed by choosing minimum maximum temperature difference (MTD) as optimization objective. Optimal constructs of the triangular element and triangular first order assembly (TFOA) are obtained, respectively. The results indicate that for the TFOA with constant cross-sectional HCCs, the minimum MTD is reduced by increasing the nonuniform heat generating (NUHG) coefficient p, namely the heat conduction performance (HCP) is better when more heat generation is generated near the heat sink. The HCP of TFOA is also improved by increasing its complexity of internal structure. Furthermore, the minimum MTD of TFOA with discrete variable cross-sectional HCCs is reduced by 12.57% than that with constant cross-section. Therefore, the HCP of TFOA can be further improved by adopting discrete variable cross-sectional structures for the HCCs. The optimization results obtained from numerical calculations can provide some theoretical guidelines for the optimal heat dissipation designs of electronic devices.

RAS: a robotic assembly system for steel structure erection and assembly

This research focuses on a long-standing, yet critical problem in the erection of steel structures. In the current state of practice, steel workers must stand on an unfinished structure to assist with the assembly of structural elements manually. They must pull on the wire hanging under the rigging elements to align the bolting holes of the moving and fixed elements. This work is often performed in high places, which can be very risky. Therefore, we have developed a robotic assembly system (RAS) for steel beam erection and assembly to prevent workers from having to work in a high place. The RAS consists of four methods: rotation, alignment, bolting, and unloading. The rotation method involves a flywheel installed on top of the rigging beam, which aims to rotate the beam to the assembly angle. The alignment method includes both vertical and horizontal alignment. The vertical alignment relies on a camera and a marker on the column to align the beam altitude. The horizontal alignment relies on a specially-designed beam, which allows for it to be smoothly guided into the right position. The bolting method is used to connect the beam to a fixed element. We designed an additional guide hole above each bolt hole. The bolt can be inserted in the guide hole and slid to the bolt hole. The unloading method is used to unload the crane cable and the RAS. We use a pin mechanism for the beam-hook connection so it can easily be unplugged by a motor. The system is built in a scaled experimental construction site to validate its feasibility. The results show that the RAS can operate the assembly process without humans working at risky heights, and can complete faster than the traditional method. In conclusion, we have developed a robotics assembly system that can help reduce the frequency of accidental falls during the steel beam assembly process. The RAS adheres to the process of the current erection method and can be broadly introduced to existing construction sites.

Simplified load follow schemes to simulate long-term daily load follow operation

Simulation of Daily Load Follow Operation (DLFO) for a whole cycle has long computation time as well as tedious lengthy input files. The purpose of this study is to reduce the computation burden associated with long-term DLFO simulation by developing a Simplified Load Follow Scheme (SLFS) simulation that can reproduce the core characteristics of long-term DLFO simulation (reference scheme) at End of Cycle (EOC). To achieve this aim, the SLFS employs two constraints: energy production and cycle length must equal those of the reference scheme. The solution variables in a SLFS then becomes operation time and power level satisfying the two constraints. In this paper, low power levels of 50%, 63%, 75%, and a maximum power level of 100% are employed for the SLFSs. Operation times are determined to satisfy the two constraints for the given power level. The reference scheme in this paper employs OPR1000 Mode-K daily load follow scheme for the Small Modular Reactor (SMR).The results show the SLFSs can predict Core Radial Plane Burnup (CRPB) and Core Radial Plane Power (CRPP) distributions of a long-term DLFO with errors lower than 6% across the core height. Axial Offset (AO) and Control Element Assembly (CEA) critical height of the SLFSs are also comparable with the reference scheme with low errors of 1.5% and 4.5% respectivelyat EOC. The computational time of the simplified schemes is reduced by more than 29 times than that of the reference scheme. Single Control Element Assembly (SCEA) Ejection is simulated to validate the applicability of the simplified schemes. The SCEA ejection simulations also show CRPP distribution errors less than 6%. In conclusion, the SLFSs can be used to simulate long-term DLFO with marginal errors of less than 6%.

Discrete least-squares finite element methods

A finite element methodology for large classes of variational boundary value problems is defined which involves discretizing two linear operators: (1) the differential operator defining the spatial boundary value problem; and (2) a Riesz map on the test space. The resulting linear system is overdetermined. Two different approaches for solving the system are suggested (although others are discussed): (1) solving the associated normal equation with linear solvers for symmetric positive-definite systems (e.g. Cholesky factorization); and (2) solving the overdetermined system with orthogonalization algorithms (e.g. QR factorization). The finite element assembly algorithm for each of these approaches is described in detail. The normal equation approach is usually faster for direct solvers and requires less storage. The second approach reduces the condition number of the system by a power of two and is less sensitive to round-off error. The rectangular stiffness matrix of second approach is demonstrated to have condition number O(h−1) for a variety of formulations of Poisson’s equation. The stiffness matrix from the normal equation approach is demonstrated to be related to the monolithic stiffness matrices of least-squares finite element methods and it is proved that the two are identical in some cases. An example with Poisson’s equation indicates that the solutions of these two different linear systems can be nearly indistinguishable (if round-off error is not an issue) and rapidly converge to each other. The orthogonalization approach is suggested to be beneficial for problems which induce poorly conditioned linear systems. Experiments with Poisson’s equation in single-precision arithmetic as well as the linear acoustics problem near resonance in double-precision arithmetic verify this conclusion. The methodology described here is an outgrowth of the discontinuous Petrov–Galerkin (DPG) methodology of Demkowicz and Gopalakrishnan (2015). The strength of DPG is highlighted throughout, however, the majority of theory presented is more general. Extensions to constrained minimization principles are also considered throughout but are not analyzed in experiments.

Anomalous assembly of ill-fitting elements

Anomalous assembly of ill-fitting elements

Hydrodynamics of pulsed columns: The effect of new parameters affecting the pressure drop

In industrial solvent extraction units, minimizing the energy input of liquid–liquid contactors is essential. Knowledge of the pressure drop evolution with both geometry and operating conditions is therefore required in order to achieve optimal sizing of the column. In this paper, yet unexplored parameters possibly affecting pressure drop in pulsed columns are investigated, namely the packing mounting clearance and the pulsation features. Their effect on pressure drop is addressed based on an experimental study, otherwise complemented by CFD simulations.The three possible types of flow (permanent flow, oscillating flow, and their combinations) have been actually investigated and compared, for both a disk and doughnut column (DDC) and a perforated plate column (PPC). Our experiments categorically confirm that the pressure drop along the column depends only on the mean fluid velocity, and is independent of the flow-type. This was moreover evidenced regardless of the pulsing device used (mechanical or pneumatical).Additionally, the influence of the mounting clearance required for the assembly of packing elements in industrial columns has been investigated and quantified for the first time. Thanks to an original DDC set-up, we measured the effect of a controlled non-zero gap between the rings and the wall on the pressure drop, hence completing the list and the analysis of parameters influencing the energy consumption in a pulsed column.

Multi-physics simulation of nuclear reactor core by coupled simulation using CUPID/MASTER

In order to visualize a realistic nuclear reactor behavior for abnormal control rod operation accident scenario, a multi-physics approach was performed. Multi-dimensional thermal hydraulics in the reactor core was calculated by coupling the reactor kinetics code. The reactor core for thermal hydraulic analysis is obtained by the CUPID which is aimed for the analysis of transient two-phase flows in nuclear reactor components by Korea Atomic Energy Research Institute (KAERI). In the present paper, a multi-physics simulation was performed by coupling CUPID with a three dimensional neutron kinetics code, MASTER which is a two-group, three-dimensional neutron diffusion code for microscopic depletion, xenon dynamics, on-line Departure of Nucleate Boiling (DNB) analysis and kinetics calculation. The MASTER code is merged into the CUPID code as a dynamic link library (DLL). The OPR1000 reactor core was taken into account by adopting porous media approach. Two hypothetical accident scenarios for malfunction of control element assembly (CEA) were numerically reproduced; (i) CEA drop and (ii) ejection accident. The coupled simulation shows a reasonable and consistent thermal hydraulic behavior. The multi-dimensional thermal hydraulics results show asymmetric temperature distribution which was not obtained by the best-estimated thermal hydraulics code before.

Reduced dosage of the chromosome axis factor Red1 selectively disrupts the meiotic recombination checkpoint in Saccharomyces cerevisiae.

Meiotic chromosomes assemble characteristic “axial element” structures that are essential for fertility and provide the chromosomal context for meiotic recombination, synapsis and checkpoint signaling. Whether these meiotic processes are equally dependent on axial element integrity has remained unclear. Here, we investigated this question in S. cerevisiae using the putative condensin allele ycs4S. We show that the severe axial element assembly defects of this allele are explained by a linked mutation in the promoter of the major axial element gene RED1 that reduces Red1 protein levels to 20–25% of wild type. Intriguingly, the Red1 levels of ycs4S mutants support meiotic processes linked to axis integrity, including DNA double-strand break formation and deposition of the synapsis protein Zip1, at levels that permit 70% gamete survival. By contrast, the ability to elicit a meiotic checkpoint arrest is completely eliminated. This selective loss of checkpoint function is supported by a RED1 dosage series and is associated with the loss of most of the cytologically detectable Red1 from the axial element. Our results indicate separable roles for Red1 in building the structural axis of meiotic chromosomes and mounting a sustained recombination checkpoint response.