1,720,958 research outputs found
A model reduction procedure based on the ps-FEM for postbuckling analysis of composite shells
No full textThis paper presents a new computational framework for the efficient postbuckling analysis of laminated shell-like structures. The proposed approach is a two-step model reduction procedure that integrates the global/local refinement capabilities of the ps-Finite Element Method (ps-FEM) with a Ritz-based projection technique. First, the ps-FEM is used with a perturbation procedure to generate Ritz vectors with global/local representation capabilities. Then, the finite element equations are projected onto the reduced subspace spanned by these vectors, yielding a low-dimensional yet high-fidelity reduced-order model. The resulting reduced-order nonlinear equations are solved via the Asymptotic Numerical Method to ensure robustness and performance, even in the presence of strong nonlinearities. To further enhance the level of fidelity of the reduced solution, a subspace updating strategy is activated during the nonlinear solution process. The effectiveness of the proposed framework is demonstrated through a series of numerical benchmarks featuring bifurcation behavior, mode interaction, and unstable postbuckling responses. The results highlight the ability of the method to accurately capture both global and localized nonlinear structural phenomena, while requiring limited computational resources
Application of the ps−Version of the Finite Element Method to the Analysis of Laminated Shells
Full text linkThe development of accurate and efficient numerical methods is of crucial importance for the analysis and design of composite structures. This is even more true in the presence of variable stiffness (VS) configurations, where intricate load paths can be responsible for complex and localized stress profiles. In this work, we present the ps−version of the finite elements method (ps−FEM), a novel FE approach which can perform global/local analysis through different refinement strategies efficiently and easily. Within this framework, the global behavior is captured through a p−refinement by increasing the polynomial order of the elements. For the local one, a mesh−superposition technique, called s−refinement, is used to improve locally the solution by defining a local/fine mesh overlaid to the global/coarse one. The combination of p− and s−refinements enables us to achieve excellent accuracy−to−cost ratios. This paper aims to present the numerical formulation and the implementation aspects of this novel approach to VS composite shell analysis. Numerical tests are reported to illustrate the potential of the method. The results provide a clear insight of its potential to guarantee fast convergence and easy mesh refinement where needed
Strong- and Weak-Form Physics Informed Neural Networks for the Analysis of Composite Plates and Shells
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Analysis of composite laminates using physics informed neural networks and extreme learning machine
Full text linkLAUREA MAGISTRALEL'analisi delle strutture composite multistrato rappresenta una sfida sempre più grande con la comparsa di nuovi livelli di complessità nella scienza dei materiali. Strumenti adeguati sono in costante sviluppo per dare ai ricercatori le capacità di comprendere meglio la natura dei materiali e come utilizzarli. È stata implementata una nuova metodologia nel campo del Machine Learning (ML), conosciuta come Physics Informed Neural Networks (PINN). Questa architettura è impiegata per approssimare la soluzione di problemi di collocazione dei valori limite formulati in conformità con la Formulazione Unificata Generalizzata del Sublaminato (S-GUF). La novità dell'approssimazione risiede nell'applicazione congiunta di PINN e dell'algoritmo Extreme Learning Machine (ELM), che si basa sulla soluzione di un sistema lineare dei minimi quadrati a norma minima per soddisfare i vincoli fisici imposti dal problema. Un ulteriore livello di novità lo rende il primo tentativo di utilizzare queste tecniche in modo combinato a una formulazione di cinematica variabile, senza precedenti lavori riportati nell'area. Lo scopo di questo approccio è quello di ottenere l'accesso a un nuovo strumento che permetta l'analisi di piastre complesse multistrato con diversi modelli di cinematica variabile in modo efficiente, permettendo il confronto di metodi e modelli.
Un'attenzione speciale è data al confronto e alla stabilità delle formulazioni forti e deboli in questo quadro. Un approccio forte è sviluppato estraendo un sistema di equazioni differenziali parziali dall'espressione del Principio dei Lavori Virtuali, che sono imposte attraverso tutti i punti in una griglia di collocazione per imporre condizioni di equilibrio e compatibilità. Alcuni problemi numerici sono riportati lungo il lavoro, motivando lo sviluppo di nuovi modi per superarli. L'influenza accoppiata dei parametri di rete e di altri fattori dati dalla geometria o dall'approssimazione è studiata grazie a una dettagliata analisi di sensibilità. Infine, l'implementazione iniziale fatta per piastre rettangolari è estesa a gusci e piastre di forme arbitrarie, il che lo rende uno strumento versatile che supera i limiti di altre metodologie adatte solo a risolvere problemi semplici.The analysis of multilayered composite structures presents an ever increasing challenge with the appearance of new levels of complexity within material science. Proper tools are in constant development to give researchers the capabilities to better understand the nature of materials and how to use them. A novel methodology in the field of Machine Learning (ML), known as Physics Informed Neural Networks (PINN) has been implemented. This architecture is employed to approximate the solution of boundary-value collocation problems formulated in compliance with the Sublaminate Generalized Unified Formulation (S-GUF). The novelty of the approximation resides in the joint application of PINN and the Extreme Learning Machine (ELM) algorithm, which is based on the solution of a minimum-norm least squares linear system to fulfill the physical constraints imposed by the problem. An additional layer of novelty makes it the first attempt to use these techniques in a combined fashion to a variable-kinematics formulation, without previous work reported in the area. The aim of this approach is to gain access to a new tool that allows the analysis of complex multilayered plates with different variable kinematics models in an efficient way, allowing the comparison of methods and models.
A special attention is given to the comparison and stability of strong and weak-form formulations within this framework. A strong approach is developed by extracting a system of partial differential equations from the expression of the Principle of Virtual Works, that are imposed across all points in a collocation grid to enforce equilibrium and compatibility conditions. Certain numerical issues are reported along the work, motivating the development of new ways to overcome them. The coupled influence of network parameters and other factors given by the geometry or the approximation is studied thanks to a detailed sensitivity analysis. Finally, the initial implementation made for rectangular plates is extended to shells, and plates of arbitrary shapes, what makes it a versatile tool that overcomes the limitations of other methodologies only suited to solve simple problems
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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