organizzazione scientifica dell'evento

organizzazione scientifica dell' evento con revisione dei sommari

We develop a numerical analysis of the buoyancy driven natural convection of a fluid in a three dimensional shallow cavity (4.1.1) with a horizontal gradient of temperature along the larger dimension. The fluid is a liquid metal (Prandtl number equal to 0.015) while the Grashof number (Gr) varies in the range 100,000-300,000. The Navier-Stokes equations in vorticity-velocity formulation have been integrated by means of a linearized fully implicit scheme. The evaluation of fractal dimension of the attractors in the phase space has allowed the detection of the chaotic regime. The Ruelle-Takens bifurcation sequence has been observed as mechanism for the transition to chaos: the quasi periodic regime with three incommensurate frequencies is the instability mechanism responsible for the transition to chaos. Physical experiments confirm the existence of this scenario.

We present an investigation of epsilon -entropy, h(epsilon), in dynamical systems, stochastic processes and turbulence, This tool allows for a suitable characterization of dynamical behaviours arising in systems with many different scales of motion. Particular emphasis is put on a recently proposed approach to the calculation of the epsilon -entropy based on the exit-time statistics. The advantages of this method are demonstrated in examples of deterministic diffusive maps, intermittent maps, stochastic self- and multi-affine signals and experimental turbulent data. Concerning turbulence, the multifractal formalism applied to the exit-time statistics allows us to predict that h(epsilon) similar to epsilon (-3) for velocity-time measurement. This power law is independent of the presence of intermittency and has been confirmed by the experimental data analysis. Moreover, we show that the epsilon -entropy density of a three-dimensional velocity field is affected by the correlations induced by the sweeping of large scales. (C) 2000 Elsevier Science B.V. All rights reserved.

An efficient approach to the calculation of the E-entropy is proposed. The method is based on the idea of looking at the information content of a string nf data hv annalyzing the signal only nt thp instants when the fluctuations are larger than a certain threshold is an element of, i.e., by looking at the exit-time statistics. The practical and theoretical advantages of our method with respect to the usual one are shown by the examples of a deterministic map and a self-affine stochastic process.

We review a recently proposed approach to the computation of the E-entropy of a given signal based on the exit-time statistics, i.e., one codes the signal by looking at the instants when the fluctuations are larger than a given threshold, epsilon. Moreover, we show how the exit-times statistics, when applied to experimental turbulent data, is able to highlight the intermediate-dissipative-range of turbulent fluctuations. (C) 2000 Elsevier Science B.V. All rights reserved.

We consider a Cauchy singular integral equation on the real line. A direct numerical mehod for solving this integral equation is given. We prove the convergence of the proposed method.

The numerical resolution of a Cauchy singular integral equation on the real line is stricly related with the good approximation of the Hilbert transform. In this paper we consider a numerical method besed on an approximation of the Hilbert transform and for this we prove the convergence in weighted uniform spaces.

We deal with the numerical evaluation of the Hilbert transform on the real line by a Gauss type quadrature rule. The convergence and the stability of the method are investigated.

Flood area detection from multipass Synthetic Aperture Radar (SAR) data can be performed via amplitude change detection techniques. These methods allow flooded zones to be discriminated only when they are flooded at the time of the second passage, and not at the time of the first one. Coherence derived from multipass SAR interferometry can be used instead, as an indicator of changes in the electromagnetic scattering behaviour of the surface, thus potentially revealing all the areas affected by the flood event at any time between the two passes. The paper presents a prototype application of such techniques, that is, a flood map obtained from ERS-1/2 data taken over Béziers (Southern France), through proper thresholding of a combination of amplitude and coherence information. Produced in the framework of an ESA project, the map consists of a DXF vector file which can be imported directly into most commercial GIS software. © 2000 Taylor & Francis Ltd.

In this paper we consider a class of strongly singular, nonlinear integral equations. A numerical method is proposed and its convergence is proved in weighted Sobolev spaces.

Collocation and quadrature methods for singular integro-differential equations of Prandtl's type are studied in weighted Sobolev spaces as well as in weighted spaces of continuous functions. A fast algorithm based on the quadrature method is proposed. Convergence results and error estimates are given.

We deal with the numerical evaluation of integrals of functions with strong singularities often used in applications. The convergence and the stability of the methods for the numerical computation of such integrals is investigated. The goodness of the numerical results for pratical applications are examined.