1,720,998 research outputs found
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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Modeling the deterioration of the stiffness and of the collagen fibril distribution in a discrete model of the cornea microstructure
No full textWe present a stochastic approach to model the mechanical deterioration of the reinforcing microstructure of the human cornea. The fundamental structural micro-components of the stroma, collagen and crosslinks, are assembled deterministically into an elementary trusswork cell, multiply repeated and distorted to form a three-dimensional shell with the shape of a cornea. The spatial orientation of the collagen -like elements of each cell is thus characterized stochastically with a non correlated random angle field, obeying an assigned probability density function, leading to a non-deterministic structural stiffness. It follows that the mechanical response of the model to the action of deterministic forces equivalent to the intraocular pressure is stochastic due to the random spatial orientation of collagen fibers. The deterioration of the mechanical stiffness of the collagen components is described through a scalar variable field, evolving in space and in time, representative of a progressive damage which causes heterogeneity and asymmetric behavior. The damage variable acts in two ways on the global stiffness: (i) by reducing the stiffness of the collagen components; (ii) by modifying the dispersion coefficient of the probability density function. The equilibrium equations of the damaging model are solved at discrete time steps, with a fully explicit solution scheme, by means of the stochastic finite element improved perturbation method. The results show that when the collagen fibril stiffness reduces to 10% of the healthy value, as expected in the case of the vision-impairing condition known as keratoconus, the displacement field due to intraocular pressure is significantly affected in terms of both average and variance distributions. This effect confers a typical conical shape to the cornea. In particular, the analysis shows that high values of the response variances are confined in the keratoconus area, which agrees with a high level of uncertainties due to loss of fibril organization and thickness reduction under pathologic conditions
An enriched 2D multi-scale model based on a Cosserat continuum for the analysis of regular masonry
No full textA multi-scale nonlinear homogenization procedure is presented for the analysis of the inplane structural response of masonry panels characterized by a regular texture. A Cosserat continuum model is adopted at the macroscopic level, while a classical Cauchy model is employed at the microscopic scale; proper bridging conditions are stated to connect the two scales. The constitutive behaviour of bricks and mortar at the microscopic level is based on a scalar damage model, non symmetric in tension and compression. As for the regularization of the strain softening response, the standard fracture energy method is used at micro-level, while at the macro-level the inner capabilities of Cosserat continuum are exploited. A numerical example is presented and a comparison with an experimental test is performe
Influence of a Wieghardt foundation on the dynamic stability of a fluid conveying pipe
No full textThis article considers the behaviour of a fluid conveying pipe on a partial elastic foundation. The model of the pipe is that of a Timoshenko beam; the foundation response is of Wieghardt type. Both material and environmental damping are taken into account. The critical value of the velocity of the fluid inducing dynamical instability of the system is evaluated as a function of the attachment ratio of the foundation for various values of the physical quantities involved. It is shown that this dependance is not always monotonic
Homogenization procedure for the 2D Cosserat continuum
No full textThis work presents a contribution to the development of computational
homogenization procedures, in which a Cosserat continuum at the macroscopic level and an elastic heterogeneous Cauchy medium with periodic texture at the microscopic level are coupled. A new polynomial kinematic map is formulated, taking into account
all the Cosserat deformation components and satisfying all the governing equations at the micro-level in case of a homogeneous
elastic material. In addition, the distribution of the perturbation field, arising when the actual heterogeneous nature of the material is taken into account, is analyzed. Contrary to the case of first-order homogenization, it emerges that the periodicity conditions are no longer appropriate. A micromechanical method is finally addressed to solve this microstructural boundary value problem
A contribution to the stability of an overhanging pipe conveying fluid
No full textWe investigate the dynamic stability of a pipe that conveys fluid, clamped or pinned at one end and with an intermediate support, thus exhibiting an overhang. The model of the pipe incorporates both Euler–Bernoulli and Bresse–Timoshenko schemes as well as transverse inertia. Material and external damping mechanisms are taken into account, while the conveyed fluid is supposed to be in fully turbulent flow. The pipe can rest on a linear elastic Winkler soil. The influence of all the physical quantities and of the overhang length on the critical velocity of the fluid front is investigated. Some numerical results are presented and discussed
Analisi multi-scala dei pannelli in muratura basata su formulazioni agli elementi finiti miste
No full textA first order multi-scale model for regular masonry based on a periodic homogenization technique is presented. In particular, a two-field mixed finite element formulation is proposed for the solution of the boundary value problem at the macroscopic level, aiming at improving the accuracy of the macroscopic field evaluation. Some applications on simple 2D structures are shown both in the field of linear elastic and elastic-plastic behavior
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