COLOMBINI , Marco Enrico

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The flow of an incompressible Newtonian fluid inside a torsionally oscillating spherical cavity is considered. The three-dimensional Navier-Stokes and continuity equations are solved by means of a Galerkin projection spectral method, based on a second-order incremental fractional-step approach. Legendre and Jacobi polynomial expansions are used...

This contribution is a remake of the one published under the same title by Reynolds (Nord. Hydrol., vol. 7, 1976, pp. 161–183). As in that paper, attention is given to the latest developments in the field of river morphodynamics and, in particular, on the formation of bed patterns. Stimulated by the work by Kidanemariam and Uhlmann (J. Fluid...

L'evento del 4 novembre 2011 ha colpito duramente la città di Genova. Lo ha fatto causando la perdita di sei vite umane e danni superiori ai 200 milioni di Euro. Avrebbe potuto causare altre vittime? La risposta, purtroppo, è sì. Avrebbe potuto concludersi senza perdite di vite umane? La risposta, purtroppo, potrebbe essere ancora sì. Il tema...

A linear stability theory for dune and antidune formation is presented that implements a rotational two-dimensional flow model. As in previous linear theories, the phaselag between sediment transport and bed elevation remains the main mechanism driving instability. However, it is shown that this phase-lag varies significantly in a neighbourhood...

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The bed instability leading to the formation of alternate and multiple bars in river has been deeply investigated in the past, starting from the linear analyses of Callander (1969) and Blondeaux and Seminara (1985), through the weakly nonlinear analyses of Colombini et al. (1987) and Schielen et al. (1993), up to the fully nonlinear solution of...

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The linear stability of a uniform flow in an infinitely wide erodible channel is investigated with respect to disturbances of the bed that are periodic in both the transverse and the longitudinal directions. A rotational flow and sediment transport model, originally developed to study the formation of two-dimensional dunes and antidunes, is...

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The effect of coupling or decoupling bed and flow dynamics is analyzed in the framework of a linear analysis of the stability of a uniform, rotational, two-dimensional flow in an infinitely wide channel with a bed composed by incoherent sediments. It is shown that results obtained with the coupled analysis in term of instability of...

The linear and weakly nonlinear stability of a uniform flow in an infinitely wide open channel with erodible bottom is studied. Under suitable conditions the flow is found to be unstable, leading to the formation of dunes and antidunes. At a linear level, the corresponding regions of existence are presented and compared with experimental data....

A linear stability analysis for dune and ripple formation is presented that implements a rotational two-dimensional flow model valid in the smooth as well as in the transitional and rough flow regimes. Sediment is assumed to be transported as bedload, disregarding the role of suspension. Therefore, the main mechanism driving instability, for...

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Nella memoria Federici & Seminara (2002) si è dimostrato come sia più adeguato utilizzare un'analisi di stabilità spaziale, piuttosto che temporale, per interpretare il meccanismo d'instabilità delle barre fluviali. La formazione delle barre appare infatti associata all'amplificazione nello spazio di perturbazioni forzate nella sezione...

Federici & Seminara (2003) have recently shown that the nature of bar instability is convective rather than absolute. This implies that bar evolution observed either in nature or in the laboratory is due to the spatial amplification of perturbations that are permanently present in the initial cross-section of the channel. In the present paper,...