1,720,991 research outputs found
Real-time displacement monitoring of a composite stiffened panel subjected to mechanical and thermal loads
No full textReal-time reconstruction of the deformed structural shape using in situ strain measurements is an inverse problem, commonly called shape sensing. The knowledge of the deformed structural shape in real time has important implications for assessing strain, stress, and failure states, and thus constitutes a key component of structural health monitoring. In addition, shape sensing is required for control and actuation of smart structures. In this paper, shape sensing analyses are carried out for typical composite stiffened structures using the inverse Finite Element Method (iFEM). By using a limited set of discrete strain data, iFEM allows full-field reconstruction of displacements that can thus be monitored also far from sensor locations. First, the iFEM theoretical framework and the formulation of a triangular, inverse shell element are briefly discussed. Then, a general strain-sensor configuration amenable to stiffened shell structures is proposed. Several numerical results are presented for static, dynamic, and thermal loadings. The robustness of the method with respect to input errors is also investigated. It is shown that iFEM is a viable methodology for shape sensing of composite stiffened structures, having the desired computational efficiency, accuracy, and robustness with respect to strain-measurement errors. The iFEM shape-sensing methodology is particularly attractive because it does not require any information regarding applied loading, elastic material constants, inertial properties, or damping characteristic
Development of a locking-free quadrilateral element for laminated composite and sandwich plates based on refined zigzag theory
No full textA class of higher-order C0 composite and sandwich beam elements based on the Refined Zigzag Theory
No full textBased on the Refined Zigzag Theory (RZT), a class of efficient higher-order C0-continuous beam elements is formulated and numerically assessed. The attention is mainly on the choice of shape functions that allow for free shear locking effects in slender beams. For this purpose, interdependent/anisoparametric interpolations are adopted to approximate the four independent kinematic variables. To achieve simpler (with a reduced number of nodal dofs) elements, a constraint condition on the axial variation of the effective transverse shear strain is adopted, which consists in reducing the polynomial degree of the shear strain measure (or, equivalently, the shear force), by one order. The issues investigated for the assessment are (i) shear locking, i.e., strategies for formulating shear-locking free C0 refined zigzag beam elements, (ii) computational efficiency, and (iii) predictive capability and accuracy. Accuracy and predictive capabilities of the proposed class of higher-order beam elements are numerically assessed by analyzing cantilevered beams over a range of loading conditions, lamination sequences, heterogeneous material properties, and slenderness ratios. It is concluded that the constraint condition on the transverse shear strain gives rise to a remarkably accurate class of higher-order C0 constrained refined zigzag beam elements, which offer the best compromise between computational efficiency and accurac
Shape Sensing of Stiffened Plates Using Inverse FEM Aided by Virtual Strain Measurements
No full textThe inverse problem of structural deformation reconstruction using experimentally measured strains, known as ‘shape sensing’, is a topic with numerous applications in the field of Structural Health Monitoring (SHM). Existing shape sensing methods are influenced by the number and location of in-situ strain sensors used. A dense strainsensor array can produce accurate displacement predictions, whereas a sparse strain-sensor distribution leads to inaccurate predictions and possibly a breakdown of the method. In the latter cases, introducing virtual strain sensors can provide additional input strain data for the shape sensing method. This paper provides experimental validation of this coupled shape-sensing approach, using real and virtual strain data, for the displacement reconstruction of a stiffened aluminium plate instrumented with fibre optic sensors. The inverse Finite Element Method (iFEM) is the shape sensing technique employed, and two strategies are compared for producing virtual strain data: the Smoothing Element Analysis (SEA), and modal expansion. The experimental results presented demonstrate the effectiveness of the two strategies investigated
Refined Zigzag Theory for laminated composite and sandwich plates derived from Reissner's Mixed Variational Theorem
No full textA mixed-field Refined Zigzag Theory (RZT(m)) for laminated plates is presented. The theory is developed using Reissner's Mixed Variational Theorem (RMVT) and employs the kinematic assumptions of the displacement-based Refined Zigzag Theory (RZT). In addition, a robust set of assumed transverse-shear stresses is implemented. The stresses, initially derived by integration of the three-dimensional elasticity equations, satisfy a priori the continuity conditions along the layer interfaces and on the bounding surfaces. With the aid of the strain-compatibility variational statement of RMVT, the transverse-shear stresses are expressed in terms of first-order derivatives of the kinematic variables. The RZT(m)retains a fixed number of kinematic variables (seven) regardless of the number of material layers. To ascertain the importance of transverse-shear stress assumptions, the layer-wise polynomial approximation scheme is also implemented. Numerical results concerning the elasto-static and vibration problems of simply supported and clamped plates, demonstrate that RZT(m)is more accurate than RZT, both in terms of local and global responses. These results also reveal that the transverse-shear stresses achieved by a layer-wise polynomial scheme are considerably less accurate, particularly for highly heterogeneous laminates. Furthermore, the RZT (m) is well suited for developing C0-continuous finite elements, thus resulting attractive for large-scale analysis of laminated structure
Shape sensing of plate structures using the inverse Finite Element Method: investigation of efficient strain-sensor patterns
Full text linkMethods for real-time reconstruction of structural displacements using measured strain data is an area of active research due to its potential application for Structural Health Monitoring (SHM) and morphing structure control. The inverse Finite Element Method (iFEM) has been shown to be well suited for the full-field reconstruction of displacements, strains, and stresses of structures instrumented with discrete or continuous strain sensors. In practical applications, where the available number of sensors may be limited, the number and sensor positions constitute the key parameters. Understanding changes in the reconstruction quality with respect to sensor position is generally difficult and is the aim of the present work. This paper attempts to supplement the current iFEM modeling knowledge through a rigorous evaluation of several strain-sensor patterns for shape sensing of a rectangular plate. Line plots along various sections of the plate are used to assess the reconstruction quality near and far away from strain sensors, and the nodal displacements are studied as the sensor density increases. The numerical results clearly demonstrate the effectiveness of the strain sensors distributed along the plate boundary for reconstructing relatively simple displacement patterns, and highlight the potential of cross-diagonal strain-sensor patterns to improve the displacement reconstruction of more complex deformation patterns
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
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
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