1,721,029 research outputs found
Schippa L., 1993; Meccanica dei fluidi - Temi d'esame svolti e commentati
No full textVengono riproposti, risolti e commentati i temi relativi alle verifiche informali tenute nell'a.a. 1991-1992 durante il corso di Meccanica dei Fluidi per allievi meccanici ed elettrotecnici svolto presso la Facoltà di Ingegneria dell'Università di Bologna. L'obiettivo perseguito è quello di dotare gli studenti di uno strumento didattico aggiuntivo a completamento delle esercitazioni condotte in aula, che permetta una rivisitazione del programma svolto durante le lezioni alla luce delle applicazioni più caratteristiche
Two-phase model for plane shear of dense granular flow
No full textThe authors have recently studied the reology of a mixture of small glass spheres and a glycerol solution in water. Strarting from a set of experiments, carried out at the University of Bologna as accurately as possible, they have proposed a light adjustment of the Bagnold's model that seems to bring a satisfactory agreement between theory and the experimental data.
The proposed model belongs anyway to the group of models that do not distinguish between the two phases (liquid and solid), presenting the above mentioned problems for the limit cases.
The same authors present here a possible further adjustment of the rheological model that takes into account the two different phases and that seems to work at least reasonably for the above mentioned limit cases
La rotta del reno a Galliera ed il ruolo dello scolmatore
No full textE’ stata simulata la piena relativa all’evento alluvionale del Novembre 1990 nel tratto di Reno compreso tra Casalecchio e la Bastia, ed è analizzata la rotta presso Galliera (Bologna), al fine di valutare il ruolo dello Scolmatore. Malgrado la consistenza dell’evento meteorico associato e malgrado l’occorrenza di un vizio arginale manifestatosi non appena i livelli in alveo hanno raggiunto il piano golenale nella fase crescente della piena lungo il Cavo Napoleonico, sbarrando il corso d’acqua attraverso manovre condotte sulle paratoie di Opera Reno. La simulazione della piena condotta nell’ipotesi che tale provvedimento non fosse stato adottato, mette in luce come si sarebbero verificati danni di un altro ordine di grandezza
Alluvial channel cross-section evolution. A physically based numerical model and experiments
No full textA physically-based numerical model is described aiming to represent cross-section evolution and bed-profile modification in a straight channel carrying non-cohesive sediments with any initial channel geometry. The model represents a 1-D gradually varied flow and 2DH vertically integrated sediment transport, taking into account sediment dispersion processes. The cross section evolution is simulated by treating suspended and bed-load transport in a unified sediment mass-balance scheme, including bank stability criteria as boundary condition. Experiments on a straight alluvial channel with sand bed and banks have been carried out in order to investigate cross-section evolution and regime conditions; our experimental results are compared with other results available in literature. The model is checked with experiments performed by ourselves and by other authors. Results are satisfactory in terms of regime values and cross section time evolution
Embankment overtopping and breach evolution modelling
No full textAn extended reach of the major Italian river, the river Po, is suitable for navigation. Regulation works are however needed to ensure good navigation conditions also during low water periods. Designing has been supported by hydraulic mathematical modeling in order to evaluate long term and middle term effects. Mobile bed simulations have been performed using a mathematical model based on one-dimensional shallow water equations and on Exner equation. The model has been numerically implemented with an implicit finite difference algorithm based on the four points Preissman scheme. Both actual and designed river configurations have been modeled in order to evaluate effects on design navigation channel, on sediment balance and bottom evolution, on hydraulic risk and on solid mass fluxes to the river delta
Modello fisicamente basato per la formazione di brecce negli sbarramenti in terra.
No full textViene presentato un modello numerico a fondo mobile applicabile allo studio dell’erosione per tracimazione degli sbarramenti in materiale sciolto. Le equazioni di iblancio per la fase liquida fanno ricorso ad un’originale formulazione delle equazioni alle acque basse per correnti monodimensionali scritte in forma conservativa. Il bilancio di massa per la fase solida è trattato in maniera disaccoppiata tramite l’equazione di Exner modificata. L’implementazione numerica è stata eseguita per mezzo dello schema alle differenze finite esplicito di MacCormack. In questo contributo il modello è applicato alla simulazione di due storici eventi La tracimazione dello sbarramento naturale formatosi sul fiume Mantaro a seguito di una frana, ed il collasso della diga in terra costruita sul fiume Teton. Nel primo caso la rottura avviene per progressiva erosione del rilevato in seguito a tracimazione, mentre nel secondo caso il fenomeno ha inizio con il sifonamento del corpo diga ,per poi concludersi con il sormonto della restante porzione di rilevato. I risultati delle simulazioni numeriche sono confrontati con i rilievi storici e con le ricostruzioni degli eventi fornite da altri modelli
Numerical modelling of catastrophic events produced by mud or debris flows
No full textMud and debris fl ows are natural phenomena representing serious hazard for population and structures in mountain zones, because of their rapid occurrence and the diffi culty in forecasting the phenomena initiation. Numerical models can however be useful in predicting the peak discharge and the strength of fl owing mass, helping administrations in preparing risk mitigation measures. In this work, a numerical model for hyperconcentrated fl ows is presented. It is based on shallow water equations, with a particular source terms treatment which translates into an increased numerical stability and makes the model highly versatile. The test case applications focus on some fundamental characteristics necessary for debris- and mud-fl ow representation. In particular, classic dam-break problems have been used to test wave celerity and wet-dry fronts propagation, while a mud-fl ow dam-break problem has been chosen to investigate model sensibility to different rheological schemes. Then, the model has been applied to two real events that occurred in Northern Italy. The fi rst one is a debris fl ow which took place at Acquabona, near Cortina d'Ampezzo. This event is extensively documented, since it has been observed by a monitoring station prepared by the University of Padua. The second one is a tragic event, during which the little town of Stava has been stricken by a destructive mud fl ow caused by the collapse of two earth dams. © 2011 WIT Press
Indagine sperimentale e verifica su modello del processo di evoluzione della sezione trasversale in alveo alluvionale
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