268 research outputs found
On the effectiveness of higher-order terms in layer-wise shell models
No full textRefined layer-wise theories for shell and plate models are presented and discussed in this paper. Higher-order models are obtained through the Unified Formulation (UF) developed by the first author over the last decade. The effectiveness of each higher-order term is evaluated through the so-called mixed axiomatic/asympthotic approach (MAAA). MAAA has been recently developed and can be seen as a tool to build reduced refined models against full expansion theories. The development of reduced models is carried out through the investigation of the effectiveness of each unknown variable on the solution for a given problem. Reduced models are then built for various structural cases, such as thin and thick shells, layered shells and sandwiches. Results show the enhanced capabilities of MAAA and UF to develop refined layer-wise models with reduced computational costs
Classical, refined and component-wise analysis of reinforced-shell structures
No full textThis paper compares early and very recent approaches to the static analysis of reinforced-shell wing structures. Early approaches were those based on the pure semimonocoque theory along with the beam assumptions of the Euler Bernoulli and Timoshenko type. The recent approaches are based on a hierarchical, one-dimensional formulation. These are obtained by adopting various polynomial expansions of the displacement field above the cross-section of the structure according to the unified formulation which was recently proposed by the first author. Two classes were developed in the unified formulation framework. In the first class, Taylor expansion models were developed by exploiting N-order Taylor-like polynomials; classical beam theories (Euler-Bernoulli and Timoshenko) were obtained as special cases of Taylor expansion. In the second class, Lagrange expansion models were built by means of four- and nine-point Lagrange-type polynomials over the cross-section of the wing. The component-wise approach was obtained by using different four- and nine-point Langrangian descriptions for different wing components including panels, ribs, spar caps, stringers, and transverse ribs. The finite element method was used to develop numerical applications in the weak form. Finite element matrices and vectors are expressed in terms of fundamental nuclei whose forms do not formally depend on the order and the expansion. A number of typical aeronautical structures were analyzed, and semimonocoque results were compared to classical (Euler-Bernoulli and Timoshenko), refined (Taylor expansion), and component-wise (Lagrange expansion) models. Stress and displacement fields of simple statically determinate, redundant, and open-section wing-box structures were analyzed. Finite element models by a commercial software that make use of solid and shell elements were used for comparison purposes. Results have highlighted the enhanced capabilities of the present refined and component-wise formulations. The present component-wise approach appears to be the natural tool to analyze wing structures because it leads to results that can only be obtained by the use of three-dimensional elasticity (solid) elements whose costs are at least one order of magnitude higher than component-wise cases. Component-wise models in conjunction with finite elements could be seen as a modern way of analyzing reinforced-shell structures by removing classical assumptions of constant shear in the spar webs and panels
Classical, Refined, Zig-Zag, Layer-Wise Models and Best Theory Diagrams for Laminated Structures
No full textThis chapter overviews classical and advanced theories for laminated plates and shell structures. Findings from existing historical reviews are used to confirm that the advanced theories can be grouped and referred to as Lekhnitskii multilayered theories, Ambartsumian multilayered theories, and Reissner multilayered theories. The unified formulation proposed by the first author, which is known as CUF (Carrera Unified Formulation), is used to make numerical assessments of various laminated plate/shell theories. The~chapter ends by giving details of a recent reliable finite element formulation for laminated shell analysis. It is embedded in the CUF framework, and it leads to the classical, zig-zag, and layer-wise models as particular cases. Numerical mechanisms such as shear and membrane locking are contrasted by developing an appropriate choice of shape functions and mixed assumed shear strain techniques. Furthermore, the Best Theory Diagram (BTD) is introduced as a tool to evaluate the accuracy of any structural model against a reference solution. The BTD is obtained through an axiomatic/asymptotic method (AAM) developed by the authors and using genetic algorithms. BTDs for plate and shell Equivalent Single Layer models (ESL) are presented, and guidelines and recommendations are provided for the proper development of refined structural theories
Applying Mining Techniques to Analyze Vestibular Data
No full textThe vestibular apparatus allows to perform audiological and equilibrium human functions and to capture movements with respect to gravity. Damages to the vestibular system causes diseases that can be measured by using Vestibular Evoked Myogenic Potentials (VEMPs) test. The test produces a lot of data that has to be collected and analyzed to allow a disease study and classification. We propose a framework that includes algorithms able to perform pathology distribution and classification. It has been tested on electronic patient records loaded from the University Hospital database. The software allows to manage the structure and framework and a blind application of one of the available classification techniques shows a relation among gender and vestibular apparatus disease
LOOKING FOR THE HIGGS BOSON AND NEW PARTICLES: THE NECESSITY OF NEW DETECTOR TECHNOLOGIES
No full textATLAS Front-end Read-out Link Requirements
No full textThe purpose of this document is summarise ATLAS front-end read-out link architectures. Read-out links are used to transfer data from front-end electronics systems placed on detector to off-detector read-out drivers. The detector-specific information presented in this document has been obtained from the following set of `link contacts'. \begin{center} \begin{tabular}{rr} {\bf SCT} & Tony Weidberg \\ {\bf Pixels} & Martin Holder \\ {\bf TRT} & Peter Lichard \\ {\bf LArg} & Mark Pearce \\ {\bf Tiles} & Christian Bohm \\ {\bf Muon trigger} & Emilio Petrolo \\ \end{tabular} \end{ center} The dynamic nature of the opto-electronics industry and the different time-scales for the implementation of optical read-out links between ATLAS subdetectors means that the contents of this document are liable to change. As this document is intended to be a useful reference, such changes will be added to the document as appropriate and documented in full on the following page
Near-Optimal Feedback Guidance for Low-Thrust Earth Orbit Transfers
No full textThis research proposes a near-optimal feedback guidance based on nonlinear control for low-thrust Earth orbit transfers. For the numerical simulations, two flight conditions are defined: (i) nominal conditions and (ii) nonnominal conditions that account for the orbit injection errors and the stochastic failures of the propulsion system. Condition (ii) is studied through an extensive Monte Carlo Analysis, to demonstrate the nonlinear feedback guidance’s numerical stability andconvergence properties. To illustrate the performance under both conditions, an orbit transfer from low Earth orbit to geostationary orbit is considered. Near-optimality of the feedback guidance comes from carefully selecting the nonlinear control gains. Comparison of the transfer with an existing study that uses optimal control reveals that orbit transfers based on feedback orbit control are very close to the optimal solution.Control & Simulatio
Social impact measurement on social enterprises : systematic review and recommendations
No full textThe purpose of this dissertation is to build forma mentis for practitioners and academics in choosing or analyzing social impact measurement models. Although the lack of definitional clarity around the expression ‘social impact’ and the barriers to social performance measurement, many recognize the relevance of these practices for organizations within the social economy, especially social enterprises, characterized by the dilemmas emerging from their hybrid nature. With this regard, if academics suggest the development of a common, globally accepted methodology, this sounds as the quest for the ‘Holy Grail’. Instead, several models raised during the years, each tailored to the distinct aspects of given organizations or interventions. This study employs a systematic review based on secondary data contributed to the identification of 27 models. The study classified the methods by representative variables, selected by the author to fulfill the purpose of this dissertation and resulting into a conceptual scheme. Moreover, by investigating the most up-to-date models, positive and negative trends were as well identified as outcomes of a thematic analysis: if a multi-stakeholder engagement is required, these practices try also to involve a fit of social measurement findings onto the strategic planning of the organization. On the contrary, some methods were noticed to be still time consuming and resource intensive, confirming main concerns among scholars. Last, a blended approach employing both quantitative and qualitative information seems preferred. Based on the findings, the author finally proposes a typical path to perform social performance measurement.O objetivo desta dissertação é construir uma forma mentis para profissionais e acadêmicos na escolha ou análise de modelos de mensuração do impacto social. Embora a falta de clareza de definição em torno da expressão ‘impacto social’ e as barreiras à medição do desempenho social, muitos reconhecem a relevância dessas práticas para organizações dentro da economia social, especialmente para empresas sociais, caracterizadas pelos dilemas emergentes da sua natureza híbrida. Com relação a isso, se os acadêmicos sugerirem o desenvolvimento de uma metodologia comum e globalmente aceita, parece uma busca pelo "Santo Graal". Em vez disso, vários modelos foram criados durante os anos, cada um adaptado aos aspectos distintos de determinadas organizações ou intervenções. Este estudo usa uma revisão sistemática baseada em dados secundários que contribuiu para a identificação de 27 modelos. O estudo classificou os métodos por variáveis representativas, selecionadas pelo autor para cumprir o objetivo desta dissertação e, que resultou num quadro conceptual. Além disso, ao investigar os modelos mais atualizados, as tendências positivas e negativas foram também identificadas,como resultadosde uma análise temática: se um compromisso de múltiplas stakeholders é necessário, essas práticas também envolvem um ajustedo planeamente estratégico da organização. Pelo contrário, alguns métodos ainda consomem muito tempo e são intensivos em recursos, confirmando as principais preocupações entre os estudiosos. Por fim, uma abordagem combinada, empregando informações quantitativas e qualitativas, parece preferida. Com base nos resultados, o autor finalmente propõe um caminho típico para realizar a medição do desempenho social
Use of Lagrange multipliers to combine 1D variable kinematic finite elements
No full textThis paper deals with finite element problems that require different formulations in different subregions of the problem domain. Attention is focused on a variable kinematic, one-dimensional, finite element formulation which was recently introduced by the first author. Finite elements with different order of expansion over the cross-section plane are employed in different regions of the 1D domain. Lagrange multipliers are used to "mix" different elements. Constraints are imposed on displacement variables at a number of points whose location over the cross-section is a parameter of the method. The number and the location of the connection points can be modified until convergence is reached. The method is first assessed by encompassing sample problems and then it is applied to analyze a number of structures which requires different formulations in different regions. Compact, thin-walled and bridge-like sections are considered to show the effectiveness of the methodology proposed as well as its advantages to solve practical problems
Guidelines and recommendations on the use of higher order finite elements for bending analysis of plates
No full textThis paper compares and evaluates various plate finite elements to analyse the static response of thick and thin plates subjected to different loading and boundary conditions. Plate elements are based on different assumptions for the displacement distribution along the thickness direction. Classical (Kirchhoff and Reissner-Mindlin), refined (Reddy and Kant), and other higher-order displacement fields are implemented up to fourth-order expansion. The Unified Formulation UF by the first author is used to derive finite element matrices in terms of fundamental nuclei which consist of 3 × 3 arrays. The MITC4 shear-locking free type formulation is used for the FE approximation. Accuracy of a given plate element is established in terms of the error vs. thickness-to-length parameter. A significant number of finite elements for plates are implemented and compared using displacement and stress variables for various plate problems. Reduced models that are able to detect the 3D solution are built and a Best Plate Diagram (BPD) is introduced to give guidelines for the construction of plate theories based on a given accuracy and number of terms. It is concluded that the UF is a valuable tool to establish, for a given plate problem, the most accurate FE able to furnish results within a certain accuracy range. This allows us to obtain guidelines and recommendations in building refined elements in the bending analysis of plates for various geometries, loadings, and boundary conditions
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