88,109 research outputs found
Nonlinear Warping and Torsional Elongation in the Response of channel section beam
No full textIn last years, many paper have been devoted to nonlinear dynamics of 3D beams. In a previous paper [1] the Authors studied a nonlinear one-dimensional model of inextensional, shear undeformable, thin-walled beam with an open cross-section. Nonlinear in-plane and out-of-plane warping and torsional elongation effects were included in the model. By using a generalization of the Vlasov kinematical hypotheses, the nonlinear warping was described in terms of the flexural and torsional curvatures. The displacement field depends on three components only, two transversal translations of the shear center and the torsional rotation. By taking into account the order of magnitude of the various terms, the equations were simplified and the effect of symmetry properties has been also outlined. A discrete form of the equations was derived to study dynamic coupling phenomena in conditions of internal resonance. The results showed that warping and torsional elongation produce notable modifications in the response of the beam to harmonic excitation [2]. Unfortunately this model is very complex and the interpretation of the mechanical behavior of the system is very difficult.
Aim of the present paper is to study more in detail the effects of nonlinear warping and torsional elongation that has been shown to play an important role in the nonlinear response.
A preliminary study is developed to determine the different order of the kinematical quantities in a realistic beam, that will be a prototype for an experimental investigation, loaded by a static force at the free end in the direction orthogonal to the symmetry axis. A beam is considered characterized by the following nondimensional parameters : t/h=0.02, b/h=0.5, h/l=0.05, where t is the thickness of the section, b and h are the dimensions of the C cross section, being h orthogonal to the symmetry axis, and l the length of the cantilever beam. For this beam the ratio between torsional and flexural curvatures is about forty; this circumstance makes it possible to introduce a great simplification in the model developed in [1].
Through Hamilton principle, under the hypothesis of large torsional curvature and small flexural curvatures, three equations of motion are derived describing dynamics of inextensional and shear undeformable nonlinear 3D beam. An harmonic load is considered acting in the direction orthogonal to the symmetry axis and applied to the free end of the cantilever beam. A Galerkin discretization is performed by introducing the first three eigenfunctions and, by using multiple scale method and amplitude-modulation equations are obtained. Frequency-response and amplitude-load curves are evaluated to characterize the behaviour of the beam and highlight the nonlinear warping and torsional elongation contributions. A numerical investigation using a finite element model including geometrical nonlinearities, is performed to validate the mechanical model and an experimental test is also expected in the next future.
1. A. Di Egidio, A. Luongo, F. Vestroni, A nonlinear model for open cross-section thin-walled beams, Part I: Formulation, Int. J. of Non-Linear Mechanics, 2003, 38(7), 1067-1081
2. A. Di Egidio, A. Luongo, F. Vestroni, A nonlinear model for open cross-section thin-walled beams, Part II: Forced motion, Int. Journal of Non-Linear Mechanics, 2003, 38(7), 1083-109
Rendiconto online della Soc.Geol.Ital.
No full textIn this study we provide a general structural picture of Ischia
island shallow crust to model the processes occurring at shallow
depth, by using geological, geophysical, historical seismicity data
and analytical structural models of the island (PENTA &
CONFORTO, 1951; CUBELLIS & LUONGO, 1998; CUBELLIS et alii,
2004; CARLINO et alii, 2006; PAOLETTI et alii, 2009; VEZZOLI et
alii., 2009; SBRANA et alii, 2009). These studies support the
hypothesis of the presence of a shallow laccolith, which is
responsible of the resurgence of Mt. Epomeo, following the
Green Tuff eruption, volcanic activity and seismicity...PublishedPisa3.5. Geologia e storia dei vulcani ed evoluzione dei magmi3.6. Fisica del vulcanismoope
Modeling the linear dynamics of continuous viscoelastic systems on their infinite-dimensional central subspace
No full textA metamodel of linear viscoelastic continuum is formulated. Internal variables, of arbitrary number, are introduced to describe the viscous part of the strain, and a wide class of constitutive laws, suggested by rheological models, is considered. The spectral properties of the system are discussed. Based on the separation of the eigenvalues occurring when the viscous moduli are small, the system is reduced to its infinite-dimensional central subspace, on which the steady dynamics takes place. Both the center manifold method and the multiple scales method are used to build the reduced model, which is formulated in terms of the only observable variables. Examples relevant to one-, two-, and three-dimensional continua are worked out to illustrate the theory, in conjunction with the standard three-parameter model and the five-parameter model
Alberto Luongo – Paolo Nanni, Prato, i pratesi e gli enti assistenziali. Ricerche sugli ospedali e sui ceppi tra XIII e XV secolo, Pisa, Pacini, 2020 (Ospedali medievali tra carità e servizio, vol. 7), pp. 230
No full textRecensione del volume Alberto Luongo – Paolo Nanni, Prato, i pratesi e gli enti assistenziali. Ricerche
sugli ospedali e sui ceppi tra XIII e XV secolo, Pisa, Pacini, 202
Né migliore, né peggiore, ma diversa: dialogo sul libro Una città dopo la peste. Impresa e mobilità sociale ad Arezzo nella seconda metà del Trecento
No full text
Invariant representation of propagation propekties for bi-coupled periodic structures
No full textGeneral bi-coupled periodic systems are dealt with by means of transfer matrices of single units. The solutions of the associated characteristic equation are discussed in terms of invariant quantities by exploiting the well-known reversibility of its coefficients. An exhaustive description of the free wave propagation patterns is given on the invariant plane where propagation domains with qualitatively different character are identified. The asymptotic behavior of the roots of the characteristic equation when the invariants tend to infinity is analyzed. The contour plot of the real part of the propagation constants, responsible for the amount of attenuation of the characteristic waves, is illustrated on the invariants' plane. Next, several models of bi-coupled periodic structures made up of beams resting on elastic supports are considered. A non-linear mapping from the invariants' plane to the physical parameters plane provides a concise representation of the pattern of the propagation domains. A mechanical interpretation associated with the boundaries of these regions is given. Finally, the proper selection of the physical parameters governing the propagation modes is discussed. (C) 2002 Elsevier Science Ltd. All rights reserved
Pathogenesis of Fusarium oxysporum f. sp. melonis: a transcriptomic approach.
No full textTranscriptomic analysis of different races of Fusarium oxysporum f. sp. melonis, grown on different melon genotypes or in vitro
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