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2004 Conference object Unknown

Steady-state thermal mapping of electronic devices and circuits with multi-layer stack assembly by analytical relationships
Montesi M., Bagnoli P. E., Casarosa C., Pasquinelli G.
This paper deals with an analytical model for the steady-state temperature mapping of electronic devices and system boards. It is devoted to solid structures which can be schematically modelled as a stack of several homogeneous layers of different materials and different sizes, also with various degree of asymmetry, and with two-dimensionally distributed heat generations. This mathematical model was implemented to replace conventional finite-elements (FEM) thermal simulators for fast thermal mappings, accurate within 1% and able to run in interaction with electrical and electro-thermal automatic design tools. His convenience in terms of speed and calculation amounts is due to the required 2-D meshing grids only at the interfaces instead of 3-D. The implemented thermal simulation program was validated by comparing the results of some virtual samples with the corresponding temperature and heat flux maps obtained with the FEM analysis. The amount and the origin of the error percentages with respect to the FEM analysis were also investigated as a functions of the free input parameters of the model.Source: International Thermal Science Seminar, ITSS II, ASME-ZSIS, Grand Hotel Toplice, Bled, Slovenia, 13-16 June 2004

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2001 Report Unknown

Meccanica dei materiali e delle strutture
Lucchesi M., Padovani C., Pagni A., Pasquinelli G., Zani N.

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2013 Conference object Unknown

The NOSA-ITACA code for modelling and assessing the structural behaviour of ancient constructions
Girardi M., Padovani C., Pasquinelli G.
Recent studies have led to the implementation of the finite element code NOSA, in which masonry is described as a nonlinear elastic material with zero tensile strength and bounded compressive strength. The code has been successfully applied to a number of studies on important historic buildings, such as the Medici Arsenal and the church of San Pietro in Vinculis in Pisa, the bell tower of Buti, the church of Santa Maria Maddalena in Morano Calabro and the Rognosa tower in San Gimignano. With the aim of improving the performance of the NOSA code and equipping it with an interactive graphic tool for pre- and post-processing, the project "Tools for the modelling and assessment of the structural behaviour of ancient constructions" has been conducted by the laboratory of Mechanics of Materials and Structures of ISTI-CNR and a research team from the Department of Civil and Environmental Engineering of the University of Florence. The project, funded by the Region of Tuscany (2011-2013), has led to the development of the NOSA-ITACA code, resulting from integration of the NOSA code and the open source graphic platform SALOME. The NOSA-ITACA code has been used to study the church of San Francesco in Lucca, Italy. The church has been studied under two different conditions: in its actual state and in the presence of reinforcement structures. This case study highlights the important role of mathematical models and numerical tools in assessing the mechanical behaviour of historical masonry buildings in the presence of earthquakes, as well as in planning strengthening operations on such structures.Source: Problemi attuali e prospettive nell'ingegneria delle strutture - convegno in onore di Franco Maceri, Maratea (PZ), 26-27 settembre 2013

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2009 Report Unknown

Analisi strutturale della Chiesa Abbaziale di Santa Maria della Roccella
Girardi M., Lucchesi M., Pasquinelli G., Zani N.
Structural analysis of the Church of Santa Maria della Roccella.

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2014 Conference object Unknown

Structural analysis of the Dome of San Cerbone Cathedral in Massa Marittima (Italy)
Angelini G., De Falco A., Pellegrini D.
In this paper the assessment of the dome of the medieval cathedral of Massa Marittima (Italy) is carried out in order to evaluate the causes of its heavy damage. The deformation and the crack patterns on the vault and on the surface of the masonry drum are particularly complex and seem at first glance incomprehensible. In the context of the safety assessment of ancient masonry constructions, structural modeling can provide an important contribution to diagnose the damage while representing at the same time a valuable instrument to predict the effectiveness of consolidation interventions. This paper shows how the finite element numerical approach can be successfully employed as an assessment tool, provided that it is driven by the empirical intuitive method based on kinematic evaluations. The analysis has been conducted via the NOSA-ITACA code, developed in the framework of the project "NOSA-ITACA - Tools for modelling and assessing the structural behavior of ancient constructions" (2011-2013) promoted by the Tuscany Region (Italy). The code models masonry as a nonlinear elastic material, known as masonry-like (or no-tension) material, and is a code suitable to assess the structural behavior of masonry constructions. Initially, the different structural elements composing the dome were investigated to analyze their specific role and their typical pathology. The structure safety factor was successfully evaluated thanks to a detailed three-dimensional model of the dome with its substructure. Once validated the model in the light of the surveyed crack patterns, was also employed to design adequate strengthening interventions. For the sake of comparison, a commercial code was also used to perform the same analysis with a different constitutive equation for material thus offering the opportunity to highlight the peculiarity of NOSA-ITACA code.Source: SAHC 2014 - 9th International Conference on Structural Analysis of Historical Constructions, Mexico City, 14-17 October 2014

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2012 Conference object Unknown

Innovative multilevel techniques for structural optimization
Porcelli M., Colson B., Toint P. L.
We address the structural optimization problem of sizing an aircraft fuselage. The problem consists in computing the dimensions of the dierent elements constituting a fuselage mini- mizing the total mass subject to some mechanical constraints. Mathematically, the problem may be formulated as a very large nonlinear optimization problem subjected to several non- linear inequality constraints. We show that this problem possesses a natural hierarchical structure that can be exploited by a multilevel approach. This approach is innovative in the industrial sector and represents a promising alternative to the commonly employed decom- position strategies. Hence, we propose a multilevel procedure which embeds the Recursive Multilevel Trust Region method [1] into an Augmented Lagrangian framework. Some results on both academic and industrial test cases are presented.Source: Congresso Biennale SIMAI MiniSimposio: MSP - Large-Scale Numerical Linear Algebra And Optimization, Torino, 25-28 June 2012

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2001 Report Unknown

Relaxed energy for transversely isotropic two-phase materials
Padovani C., Miroslav S.

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2005 Conference object Unknown

DJOSER : verifica teorica e sperimentale dell'accuratezza del simulatore termico stazionario per l'elettronica di potenza
Bagnoli P. E., Bartoli C., Pasquinelli G., Stefani F.
Nel presente lavoro, elaborato in connessione con quello precedente [1], vengono illustrati alcuni esempi di simulazioni termiche di strutture multistrato progettate in modo da replicare i tipici assemblaggi dei dispositivi elettronici di potenza. Tali esempi illustrano come il simulatore DJOSER sia pienamente sensibile alla configurazione geometrica del package sottostante alla superficie di dissipazione di potenza (incremento di spessori o asimmetria degli strati) ed alle condizioni al contorno di tipo convettivo. Il confronto tra i dati ottenuti dal simulatore analitico e da un programma basato sulla tecnica di calcolo agli elementi finiti hanno mostrato un'accuratezza della temperatura contenuta entro l'1 %. Le fonti di inaccuratezza nella procedura di calcolo di DJOSER sono il troncamento delle serie armoniche infinite, connesse con le funzioni di Green, e le dimensioni delle griglie bidimensionali con cui vengono descritte le funzioni di temperatura e flusso. Rispetto a questi due fattori sono state compiute numerose prove in modo da valutare l'errore percentuale medio e massimo anche in relazione al tempo di calcolo necessario, in modo da poter individuare dei valori di compromesso per il numero massimo di autovalori utilizzati e per le dimensioni delle griglie. In ultimo vengono presentati i risultati degli esperimenti effettuati su campioni reali atti a validare le mappe termiche con quelle ottenute con la termografia a raggi infrarossi.Source: XXIII Congresso Nazionale UIT sulla Trasmissione del Calore, Parma, 20-22 Giugno 2005

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2013 Report Unknown

Aircraft fuselage sizing with multilevel optimization
Colson B., Porcelli M., Toint P.
In this technical report we describe the activity research carried out in the years 2010-2012 at Department of Mathematics, University of Namur, Namur (Belgium) in collaboration with LMS Samtech, Angleur (Belgium), in the framework of the project "Méthodes de résolution de problèmes d'optimisation de grande taille pour les structures en matériaux composites" (Acronym LARGO "LARge-scale Optimization problems"). LARGO was granted by the Walloon Region and LMS Samtech in the context of the First Program (convention number 916981).

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2006 Conference object Unknown

Analisi termomeccanica non lineare del rivestimento refrattario di una siviera
Lucchesi M., Padovani C., Pagni A., Pasquinelli G., Zani N.
In questo lavoro si studia il comportamento termomeccanico di una siviera il cui rivestimento refrattario è modellato come un materiale non resistente a trazione. Dopo avere analizzato un ciclo termico rappresentativo del funzionamento della siviera, si sono considerate due distribuzioni di temperatura in corrispondenza delle quali sono state effettuate le verifiche meccaniche. Queste hanno fornito, oltre ai valori di spostamenti, deformazioni e tensioni, anche indicazioni utili per determinare la distribuzione delle fratture nel refrattario.Source: convegno annuale dell'associazione italiana di metallurgia, Milano, 22-24/11/2017

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2013 Conference object Unknown

Numerical validation of a new energetic fracture criterion in elastic-plastic fracture mechanics for aluminium alloys
Binante V., Frediani A., Lavorini L.
The paper deals with numerical studies of two-dimensional quasi-static crack growth problems, for elastic-plastic materials with isotropic harening behaviour. In particular, the fem analyses regard centre-cracked panel, CCP, specimens, made of Al2024-T3 alloy, subjected to monotonic increasing load histories, without any constraint about the intensity of the deformation. The main result of these studies is a new fracture criterion, based on the fracture property of the Energy Momentum Tensor; during a quasi static crack propagation, the trace of the Energy Momentum Tensor, evaluated at the current crack tip, reaches a value independent of the crack length. Based on this property, the proposed fracture criterion allows us to describe the crack growth resistance curve (load versus crack extension) of aluminium alloys, in a good agreement with experimental tests.Source: AIDAA 2013 - XXII Conference Italian Association of Aeronautics and Astronautics, pp. 14–96, Naples, Italy, 9-12 September 2013

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2015 Article Unknown

Fatigue behavior of stiffener to cross beam joints in orthotropic steel decks
Croce P., Pellegrini D.
In the paper the possibility to evaluate the fatigue strength of stiffener to cross beam joints in orthotropic steel decks is discussed. The proposed methodology, based on Paris-Erdogan law, allows to derive a sound estimate of the stress intensity factor K combining the indirect approach, based on the Rice J-integral, with the direct one, based on the extrapolation of experimental or numerical data. The practical implementation of the proposed methodology allowed to predict correctly the actual fatigue life of a previously tested real scale specimen, so validating its potentialities.Source: Procedia engineering 101 (2015): 101–108. doi:10.1016/j.proeng.2015.02.014
DOI: 10.1016/j.proeng.2015.02.014

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2013 Report Unknown

A variable fixing version of the two-block nonlinear constrained Gauss-Seidel algorithm for l1-regularized least-squares
Porcelli M., Rinaldi F.
The problem of finding sparse solutions to underdetermined systems of linear equations is very common in many fields like e.g. signal/image processing and statistics. A standard tool for dealing with sparse recovery is the l1-regularized least-squares approach that has been recently attracting the attention of many researchers. In this paper, we describe a new version of the two-block nonlinear constrained Gauss- Seidel algorithm for solving l1-regularized least-squares that at each step of the iteration process fixes some variables to zero according to a simple rule. We prove the global convergence of the method and we report numerical results on some test problems showing the efficiency of the implemented algorithm.

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2005 Part of book or chapter of book Unknown

Singular equilibrated stress fields for no-tension panels
Lucchesi Massimiliano, Silhavy Miroslav, Zani Nicola
In this work we study the equilibrium problem for rectangular panels made of a no-tension material, clamped at the bottom, subjected to distributed vertical loads on the top, and to different types of lateral loads. Admissible and equilibrated stress fields are interpreted as vector-valued measures with zero divergence. Such stress fields are explicitly determined under the assumption that the measure is absolutely continuous outside a smooth curve which supports a delta type singularity of the stress.Source: Mechanical modelling and computational issues in civil engineering, edited by Michel Fremond; Franco Maceri, pp. 255–265. Berlin Heidelberg: Springer-Verlag, 2005
DOI: 10.1007/3-540-32399-6_12

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2009 Conference object Unknown

Thermo-mechanical solver for multi layer packages of power electronic devices and systems. Preliminary results
Bagnoli P. E., Girardi M., Padovani C., Pagni A., Pasquinelli G.
The DJOSER code has been tested as a useful and friendly tool for the thermal analysis of power electronic devices constituted by multilayer structures. The other problem connected with the packaging evaluation is the calculation of the thermally induced stresses and strains in the various layers of the assembling structures. This paper deals with the thermo-mechanical behaviour of 1-dimensional structures made up of layers with different geometrical and thermo-mechanical properties subjected to thermal loads. A first version of the thermo-mechanical solver connected with the DJOSER program has been implemented. The solver is able to calculate the stresses at the layer interfaces, using the same strategy of DJOSER, i.e. a semi-analytical mathematical approach, as well as the same structural models (stepped pyramidal structures, homogeneous layers). The basic theory is briefly exposed and the method is applied to a two-layers structure whose results are compared with those obtained using standard FEM analyses.Source: 27th UIT National Heat Transfer Conference. UIT09-041, pp. 225–230, Reggio Emilia, 22-24 June 2009

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2008 Conference object Unknown

Static analysis of masonry vaults and domes
Girardi M., Padovani C., Pagni A., Pasquinelli G.
We propose a method for studying masonry vaults and domes, with the aim of providing a computational tool that can be used to evaluate the safety of masonry structures, as well as to guide the choice of strengthening operationes. We briefly recall the constitutive equation and the numerical methods used for modeling the mechanical behavior of masonry vaults and domes and implemented in the finite element code NOSA. We then describe the study of an existing vault of historical and architectural importance.Source: International workshop IN SITU MONITORING OF MONUMENTAL SURFACES, pp. 335–340, Florence, Italy, 27-29 october 2008

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2017 Article Unknown

Fast Hessenberg reduction of some rank structured matrices
Gemignani L., Robol L
We develop two fast algorithms for Hessenberg reduction of a structured matrix $A = D + UV^H$, where $D$ is a real or unitary n x n diagonal matrix and $U, V in mathbb{C}^{n times k}$. The proposed algorithm for the real case exploits a two-stage approach by first reducing the matrix to a generalized Hessenberg form and then completing the reduction by annihilation of the unwanted subdiagonals. It is shown that the novel method requires O(n^2 k) arithmetic operations and is significantly faster than other reduction algorithms for rank structured matrices. The method is then extended to the unitary plus low rank case by using a block analogue of the CMV form of unitary matrices. It is shown that a block Lanczos-type procedure for the block tridiagonalization of Re(D) induces a structured reduction on A in a block staircase CMV-type shape. Then, we present a numerically stable method for performing this reduction using unitary transformations and show how to generalize the subdiagonal elimination to this shape, while still being able to provide a condensed representation for the reduced matrix. In this way the complexity still remains linear in k and, moreover, the resulting algorithm can be adapted to deal efficiently with block companion matrices.Source: SIAM journal on matrix analysis and applications (Print) 38 (2017): 574–598. doi:10.1137/16M1107851
DOI: 10.1137/16M1107851

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2009 Other Unknown

Elementi di calcolo tensoriale
Padovani C.
Lezioni del corso "Introduzione al calcolo tensoriale", Scuola di Dottorato in Ingegneria "Leonardo da Vinci", Universita' di Pisa, 2009.

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2012 Part of book or chapter of book Unknown

A criterion for ductile crack growth based on the energy momentum tensor
Binante V., Frediani A.
It is well known that in quasi-static crack propagation under growing external loads a Griffith-like energy balance predicts no energy surplus for fracture; this result is known as the paradox of Rice . The paradox is generally attributed to the assumptions of small scale yielding and perfect plasticity of material. In this paper we show that the paradox does not lie in the assumptions of infinitesimal strain conditions, neither in the work-hardening rules. Afterwards, we investigate the stress and strain fields, ahead of the crack front in the case of large scale yielding at the crack tip, and discover that the trace of the Energy-Momentum Tensor assumes a constant value during the whole process of crack extension. When this value is assumed as a critical condition for crack growth, we obtain a curve load versus crack extension in excellent agreement with available experimental data. The Rice's paradox is thus overcome, and a new criterion for ductile crack growth is introduced.Source: Variational Analysis and Aerospace Engineering II: Mathematical Challenges for Aerospace Design, edited by Buttazzo G., Frediani A., pp. 67–92. New York: Springer, 2012
DOI: 10.1007/978-1-4614-2435-2_4

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2002 Other Unknown

Appunti di analisi funzionale Parte I: Spazi metrici
Padovani C.
No abstract available

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