1,721,000 research outputs found
Modellazione agli elementi discreti di reti metalliche per applicazioni di rinforzo corticale
No full textSecured drapery systems are extensively used to mitigate the risk connected with shallow instabilities and rockfall in both soil and rock slopes. Despite the wide application of these systems, various features of their mechanical behaviour in field conditions remain unknown. This lack of knowledge is related to the fact that the standard laboratory configurations adopted for mesh mechanical characterisation are poorly representative of the field conditions. In this thesis, the Discrete Element Method is used in order to analyse the mechanical behaviour of wire meshes in secured drapery applications. Experimental results, obtained from several test configurations, are used to validate the mesh model. This has permitted to prove the effectiveness of the adopted numerical approach in simulating the mechanical response of a wire mesh from simple laboratory conditions to complex configurations in which the mesh interacts with multiple external bodies. The mesh model is adopted to address the problem of the punching behaviour of an anchored mesh. This represents the most likely condition in secured drapery installation aimed to retain potentially unstable blocks along rock slopes. A parametric study is conducted, leading to the definition of simple analytical relations that can enable practitioners to account for the effect of the problem’s variables on the mechanical response of the mesh system. A simple procedure allowing for the extension of the standard laboratory mechanical characterisation (i.e. standard UNI punch test) to a general field condition is also provided. A large-scale model of a secured drapery system in soil retaining applications is implemented. The obtained results have permitted to characterized the force transmission mechanism inside the mesh system, thus highlighting the role of the different system components. A parametric analysis is performed to investigate the role of several variables on the mechanical response of the mesh system. Particular attention is devoted to the evolution of the unstable process in the retained material. This has permitted to identify a failure mechanism that may be considered as typical in such kind of applications.Secured drapery systems are extensively used to mitigate the risk connected with shallow instabilities and rockfall in both soil and rock slopes. Despite the wide application of these systems, various features of their mechanical behaviour in field conditions remain unknown. This lack of knowledge is related to the fact that the standard laboratory configurations adopted for mesh mechanical characterisation are poorly representative of the field conditions. In this thesis, the Discrete Element Method is used in order to analyse the mechanical behaviour of wire meshes in secured drapery applications. Experimental results, obtained from several test configurations, are used to validate the mesh model. This has permitted to prove the effectiveness of the adopted numerical approach in simulating the mechanical response of a wire mesh from simple laboratory conditions to complex configurations in which the mesh interacts with multiple external bodies. The mesh model is adopted to address the problem of the punching behaviour of an anchored mesh. This represents the most likely condition in secured drapery installation aimed to retain potentially unstable blocks along rock slopes. A parametric study is conducted, leading to the definition of simple analytical relations that can enable practitioners to account for the effect of the problem’s variables on the mechanical response of the mesh system. A simple procedure allowing for the extension of the standard laboratory mechanical characterisation (i.e. standard UNI punch test) to a general field condition is also provided. A large-scale model of a secured drapery system in soil retaining applications is implemented. The obtained results have permitted to characterized the force transmission mechanism inside the mesh system, thus highlighting the role of the different system components. A parametric analysis is performed to investigate the role of several variables on the mechanical response of the mesh system. Particular attention is devoted to the evolution of the unstable process in the retained material. This has permitted to identify a failure mechanism that may be considered as typical in such kind of applications
STUDIO DI UN FLUSSO GRANULARE SECCO SU CANALETTA INCLINATA ATTRAVERSO IL METODO AGLI ELEMENTI DISCRETI
Full text linkLe colate detritiche sono eventi calamitosi che possono verificarsi in aree acclivi una volta che il materiale instabile viene messo in movimento, innescato da eventi come forti piogge o lo scioglimento della neve. La velocità del flusso e l'energia che accumulano lungo i ripidi pendii e i canali naturali sono tali che questi eventi possono mettere in pericolo sia le persone che le costruzioni, sottolineando quindi l’importanza di un attento monitoraggio. Al fine di comprendere meglio come poter attrezzare una sezione di monitoraggio trasversale al flusso, attraverso un approccio numerico agli elementi discreti, viene simulato un flusso granulare non stazionario su uno scivolo inclinato. Il materiale granulare secco viene discretizzato attraverso aggregati di sfere con parametri al contatto calibrati sulla base di semplici prove di laboratorio. L’analisi è condotta misurando le forze su una piastra di base e le caratteristiche del flusso su un volume di controllo al di sopra di quest’ultima
Micro-poromechanical simulation of the collapse of a granular column in a viscous fluids
Full text linkIn this work a numerical study of a granular collapse in a viscous fluid is presented. Using a DEM - PFV (Pore Finite Volume) coupled model, the influence of the initial solid fraction is investigated. The time evolution of the collapse and the dependency of the deposit morphology (triangular or trapezoidal) on the initial solid fraction and aspect ratio are analyzed. Furthermore, the influence of the initial state of the granular material on the time evolution of the pore pressure is studied. The numerical results are consistent with experimental observation (Rondon et. al, 2011) showing the capability of the DEM - PFV coupled model to simulate saturated granular media
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
Comparison of two dem strategies for modelling cortical meshes
Full text linkThis work deals with the particle-based modelling of cortical wire meshes. Such meshes are being used in many engineering applications but their modelling is particularly complex because of the common large displacement serviceability conditions, the chance of localized failures, and the intrinsic geometrical and mechanical anisotropies. The discrete element method has proved to be an excellent numerical tool for the investigation of such structures. Here, two modelling strategies are compared using a wire-node description and a wire-cylinder description: In the first the wire mesh is described by a collection of spheres at nodes linked by long-range interaction forces, in the second the wires are represented by means of interconnected cylinders. The force-displacement constitutive model of the interactions is calibrated based on specific tensile tests. The comparison is performed on results of tensile tests and punch tests on a reference mesh panel
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
Modellazione agli elementi discreti di prove di punzonamento di una rete corticale doppio torta a maglia esagonale
Full text linkLe reti metalliche sono comunemente usate per la protezione su pendio e la prevenzione del rischio di crolli e distacchi. La loro progettazione è principalmente basata su considerazioni di carattere empirico, legate all’esperienza del progettista; data l’importanza di tali interventi, e al fine di ottimizzare il progetto, stanno entrando in uso nuovi metodi numerici. In questo lavoro verrà impiegato il metodo agli elementi discreti (DEM), particolarmente adatto per lo studio di problemi a grande deformazioni, fino alla rottura degli elementi. L’obiettivo è quello di validare un modello di rete doppio torta a maglia esagonale durante una prova di punzonamento attraverso il raffronto con i risultati sperimentali. In particolare verranno analizzati tre diversi modelli costitutivi e l’influenza delle curve tensione-deformazione relative al filo singolo e a quello doppio torto
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
- …
