1,720,999 research outputs found
Gusci ribassati multistabili. Un modello per la selezione della forma ottimale in presenza di vincoli al bordo
Full text linkEnhanced models for the nonlinear bending of planar rods: localization phenomena and multistability
No full textWe deduce a one-dimensional model of elastic planar rods starting from the Föppl–von Kármán model of thin shells. Such model is enhanced by additional kinematical descriptors that keep explicit track of the compatibility condition requested in the two-dimensional parent continuum, that in the standard rods models are identically satisfied after the dimensional reduction. An inextensible model is also proposed, starting from the nonlinear Koiter model of inextensible shells. These enhanced models describe the nonlinear planar bending of rods and allow to account for some phenomena of preeminent importance even in one-dimensional bodies, such as formation of singularities and localization (d-cones), otherwise inaccessible by the classical one-dimensional models. Moreover, the effects of the compatibility translate into the possibility to obtain multiple stable equilibrium configurations
L'influenza dell’ingobbamento nella dinamica di travi in parete sottile
No full textSi mostra l’influenza dell’ingobbamento sulla dinamica lineare di travi con sezione aperta e sottile. Il modello è monodimensionale diretto, con cinematica finita e un descrittore sommario d’ingobbamento. La dinamica deriva dal bilancio di potenza, le relazioni costitutive sono iperelastiche non lineari per cogliere gli accoppiamenti noti. La dinamica è arricchita da azioni d’inerzia d’ingobbamento rappresentate secondo una proposta di letteratura. Con una procedura alle differenze finite si trovano le pulsazioni naturali per un esempio e si confrontano con la letteratura e codici commerciali, evidenziando l’influenza dell’ingobbamento e del descrittore d’inerzia relativo
A class of morphing shell structures satisfying clamped boundary conditions
No full textMany examples of multi-stable shell structures have been recently proposed with the underlying hypothesis of the shell being completely free on its boundary. We describe a class of shallow shells which are bistable after one of their sides is completely clamped. This result, which has relevant technological implications, is achieved by a suitable design of the initial, stress-free, shape
Enhanced models for the nonlinear bending of planar rods: localization phenomena and multistability
No full textWe deduce a one-dimensional model of elastic planar rods starting from the Föppl-von Kármán model of thin shells. Such model is enhanced by additional kinematical descriptors that keep explicit track of the compatibility condition requested in the two-dimensional parent continuum, that in the standard rods models are identically satisfied after the dimensional reduction. An inextensible model is also proposed, starting from the nonlinear Koiter model of inextensible shells. These enhanced models describe the nonlinear planar bending of rods and allow to account for some phenomena of preeminent importance even in one-dimensional bodies, such as formation of singularities and localization (d-cones), otherwise inaccessible by the classical one-dimensional models. Moreover, the effects of the compatibility translate into the possibility to obtain multiple stable equilibrium configurations
Prevention and control of OQDS (olive quick decline syndrome) outbreaks caused by Xylella fastidiosa
No full textIn Southern Italy, since 2013, there has been an ongoing Olive Quick Decline Syndrome (OQDS) outbreak, due to the bacterium Xylella fastidiosa, which has caused a dramatic impact from both socio-economic and environmental points of view. The main players involved in OQDS are represented by the insect vector, Philaenus spumarius, its host plants (olive trees and weeds) and the bacterium, X. fastidiosa. Current agronomic practices are mainly based on uprooting the sick olive trees and their surrounding ones, with later installment of olive cultivars more resistant to the bacterium infection. Unfortunately, both of these practices are having an undesirable impact on the environment (most of these olive trees were monumental ones) and on the economy. Based on a mathematical model expressed in terms of a nontrivial system of ordinary differential equations, our analysis has provided a clear picture of all possible steady states (feasible equilibria) and their stability properties, corresponding to a variety of different parameter scenarios; all of this has been illustrated by a set of computational experiments. A significant original contribution of this paper is the proof of the global asymptotic stability of each of the feasible equilibria under its existence assumptions, a fact that excludes multiple equilibria under the given conditions. It has emerged that the removal of a suitable amount of weed biomass (host plants of the juvenile stages of the insect vector of X. fastidiosa) from olive orchards and surrounding areas leads to the eradication of the epidemic, without requiring neither the removal nor the substitution of the existing olive trees
Warping and Ljapounov stability of non-trivial equilibria of non-symmetric open thin-walled beams
No full textWe investigate the eects of warping on the dynamic stability of non-trivial equilibrium congurations for non-symmetric open thin-walled beams. We use a direct one-dimensional model coarsely describing warping; the rest of the kinematics is exact. Dynamic derives from the balance of power; constitutive relations are nonlinear, hyper-elastic, and distinguish the roles of the centroids and shear centres; inertial actions account for warping, too. By centred nite dierences, the warping inertial action is found ineective on the natural angular frequencies. Then, we follow non-trivial equilibrium paths and investigate their Ljapounov stability,
by examining the small superposed oscillations. Results for generic, non-symmetric cross-sections are presented
and discussed, showing the eects of warping and of coupling constitutive coecients
Sulle condizioni di vincolo interno per un modello diretto di trave con ingobbamento
No full textSi studiano in maniera sistematica gli effetti dei vincoli interni di scorrimento nullo rispetto ai due posti significativi delle sezioni trasversali di travi aperte di spessore sottile. In particolare, si scrivono le equazioni di campo linearizzate per il problema di biforcazione statica e se ne studiano le variazioni rispetto a quelle note in letteratura. Si propongono interpretazioni meccaniche e si avanzano ipotesi su possibili raffinamenti di un modello monodimensionale diretto
A numerical approach for the stability analysis of thin-walled beams
No full textIn this contribution we implement a suitably adapted version of the finite differences technique to solve the field equations for a thin-walled beam, as obtained by means of a direct one-dimensional model. This technique lets us find non trivial equilibrium paths and study their stability under both conservative and non conservative actions. Some results are presented and discussed
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