801 research outputs found
Population and Space in the Mediterranean: The Challenges of the 21st Century (Introduction)
No full textThe Mediterranean region features diverse and overlapping socioeconomic and demographic dynamics, with collateral effects that have become increasingly more significant and difficult to solve. The region’s demographic evolution has been uneven. Indeed, while natural population increase in the countries of the northern shore has been weak for several decades (when it did not turn negative, as it did in Italy), the southern and eastern shores continue to benefit from a still considerable natural surplus despite a sharp decline in fertility (Angeli & Salvini, 2018; Bellis, Carella, Léger, Parant, 2021a). Furthermore, the contrasting demographic regimes along the northern (European), eastern (Asian) and southern (African) shores have resulted in a major change in the distribution of the populations whose composition by age group is also very different (Parant & Léger, 2020). In 2020, the countries of the African shore represent the most populated area of the Mediterranean Basin (39% vs. 38% for the countries of the European shore), while in 1950 the northern shore grouped two-thirds of the total population. Moreover, 47% of individuals on the southern shore and 42% of those residing on the eastern shore are now under 25 years old; while the under 25s represent just over a quarter of the population (26%) on the northern shore (Bellis, Carella, Léger, Parant, 2021b). The population of the northern shore is inexorably aging, whereas those of the southern and eastern shores have remained young despite the increase in life expectancy
La popolazione del Mediterraneo all’orizzonte del 2050: le previsioni sollevano molti interrogativi
No full textL’area del Bacino Mediterraneo identifica da sempre un interessante aggregato geografico in cui si osservano ancora oggi profondi divari. Mostrando gli scenari previsivi delle Nazioni Unite, Gil Bellis, Maria Carella, Jean-François Léger e Alain Parant inducono a riflettere sulle implicazioni dei persistenti squilibri demografici tra le rive del Mediterraneo
NURBS-Based Collocation Methods for the Structural Analysis of Shells of Revolution
No full textIn this work we present a collocation method for the structural analysis of shells of revolution based on Non-Uniform Rational B-Spline (NURBS) interpolation. The method is based on the strong formulation of the equilibrium equations according to Reissner-Mindlin theory, with Fourier series expansion of dependent variables, which makes the problem 1D. Several numerical tests validate convergence, accuracy, and robustness of the proposed methodology, and its feasibility as a tool for the analysis and design of complex shell structures
Auxetic anti-tetrachiral materials: equivalent elastic properties and frequency band-gaps
No full textA comprehensive characterization of the novel class of anti-tetrachiral cellular solids, both considering the static and the dynamic response, is provided in the paper. The heterogeneous material is characterized by a periodic microstructure made of equi-spaced rings each interconnected by four ligaments. In the most general case, rings and ligaments are surrounded by a softer matrix and the rings can be filled by a different material. First, the first order linear elastic homogenized constitutive response is estimated resorting to two different microstructural models: a discrete model, in which the ligaments are modeled as beams and the presence of the matrix is neglected and the equivalent elastic properties are evaluated through a simplified analytical approach, and a more detailed continuous model, where the actual properties of matrix, ligaments and rings, varying in the 2D domain, are considered and the first order computational homogenization is adopted. Special attention is given to the dependence of the 2D overall Cauchy-type elastic constants on the mechanical and geometrical parameters characterizing the microstructure. The results, indeed, show the existence of large variations in the linear elastic constants and degree of anisotropy. A comparison with available experimental results confirms the validity of the analytical and numerical approaches adopted. Finally, the rigorous Floquet–Bloch approach is applied to the periodic cell of the cellular solid to evaluate the dispersion of propagation waves along the orthotropic axes in the framework of elasticity and to detect band gaps characterizing the material. A numerical approach, based on the first order computational homogenization, is also adopted and the rigorous and approximate solutions are compared
A COSSERAT BASED MULTI-SCALE MODEL FOR MASONRY STRUCTURES
No full textThis paper presents a multi-scale model for the analysis of the in-plane structural response of regular masonry. It is based on a computational periodic homogenization technique and is characterized by the adoption of the Cosserat continuum model at the macroscopic structural level, taking into account the influence of the microstructure on the global response and correctly describing the localization phenomena; at the microscopic representative volume element (RVE) level, where the nonlinear constitutive behavior, geometry, and arrangement of the masonry constituents are modeled in detail, a standard Cauchy model is employed. An isotropic nonsymmetric damage model is adopted for the bricks and mortar joints. The solution algorithm is based on a parallelization strategy and on the finite-element method. Some numerical applications on typical masonry structures are reported, showing both the global response curves and the stress and damage distributions on the RVEs
Recensione: Albino Pierro, Dieci poesie in dialetto tursitano, Lucca, Maria Pacini Fazzi editore, 1981.
No full textAuxetic behavior and acoustic properties of microstructured piezoelectric strain sensors
No full textThe use of multifunctional composite materials adopting piezo-electric periodic cellular lattice structures with auxetic elastic behavior is a recent and promising solution in the design of piezoelectric sensors. In the present work, periodic anti-tetrachiral auxetic lattice structures, characterized by different geometries, are taken into account and the mechanical and piezoelectrical response are investigated. The equivalent piezoelectric properties are obtained adopting a first order computational homogenization approach, generalized to the case of electro-mechanical coupling, and various polarization directions are adopted. Two examples of in-plane and out-of-plane strain sensors are proposed as design concepts. Moreover, a piezo-elasto-dynamic dispersion analysis adopting the Floquet–Bloch decomposition is performed. The acoustic behavior of the periodic piezoelectric material with auxetic topology is studied and possible band gaps are detected
A finite element formulation for dynamic systems with frequency-independent material damping
No full textTime domain dynamic analysis in presence of frequency-independent material damping: a finite element formulation
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