Modellazione numerica, attraverso la tecnica dei volumi finiti, dei fenomeni di evoluzione d'alveo

The following paper deals with the mathematical modeling of the river-bed evolution processes. More particularly, point have been put to two different kinds of numerical models, the first one based on a classical "three equations approach" that applies, as a closure condition, a generic sediment transport formula, and, the second, based on a more physically-based "four equations approach ". The equations at the base of both the models are written for rivers of any cross-section; then, they are integrated by using the Finite Volume Method (FVM), very often used, in the last years, for the simulation of free surface flows. Both the models are explicit; at this time, they are first order precise both in the space and time. They are based, respectively, on a technique of resolution "decoupled" and one "coupled", depending on the techniques used to solve the set of governing equations (continuity equations for both the liquid and solid phases and momentum equations for the mixture water+sediments). Both the models have been applied, to the purpose to compare their results, to the case of a channel with assigned geometric and grain characteristics. The coupled model has been used besides for the simulation of dam-break phenomena interesting river-beds initially dry or wet, comparing the results obtained with experimental measures taken from the literature and results obtained by other similar numerical models