1,721,146 research outputs found
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
Experimental analysis and 2DH numerical simulations fo waves and current flows around low-crested rubble-moud structures
No full textObjective of this paper is to analyse flow patterns and velocity fields around rubble mound low-crested structures based on wave basin experiments and 2DH numerical simulations.
Experiments were performed in the 12.5x9.7 m2 wave basin at Aalborg University, DK, within the framework of the EU-funded project DELOS. Two different layouts were designed: two detached breakwaters with a gap in between and an oblique breakwater forming a rip channel with the basin side wall. Both cases of narrow and wide berm were tested under 2D and 3D, regular and irregular wave attacks.
Fluxes around and through the structures are examined by means of image analysis and measurements of free surface elevation and velocity at fixed locations.
An original scheme for evaluating the overtopping discharge through a wave by wave analysis of wave gauge records over the barrier is described. Overtopping discharges are reconstructed and related to existing wave run-up models for emerged and zero-freeboard structures.
Since no measurement was performed in the rubble mound, a ‘scale’ model to estimate filtration flux based on other available datasets containing filtration velocity and set-up is proposed and verified. The analysis of the datasets allows also to enlighten different filtration mechanisms depending on structure submergence.
The approach for evaluating separately the different flux terms is then globally checked for zero freeboard and emerged structures through experimental mass balance.
For deeply submerged structures, for which this approach fails, numerical simulations are carried out and the accuracy of the commercial 2DH model MIKE 21 is tested in predicting parameters relevant to the design process as set-up, overtopping and returning flows. Simulations are also presented for a sample emerged case in order to show how some limitations in the tool can be surpassed to allow general applications. The numerical model furthermore allows to describe the physical processes over the whole area of interest, whereas extensive measurements cannot be performed due to the test imperfect repeatability in presence of irregular waves and thus the impossibility of moving the limited number of available instruments
Geosintetici nel controllo dell'erosione: un'introduzione
No full textIn particolare nelle opere di sistemazione dei corsi d’acqua le tecniche di ingegneria naturalistica hanno subito negli ultimi anni un notevole impulso, anche per la rinnovata ed accresciuta attenzione nei confronti delle problematiche ambientali. gli interventi di ingegneria naturalistica sui corsi d’acqua perseguono il duplice obiettivo da una parte di limitare i processi erosivi e stabilizzare il letto, dall’altra di favorire la rinaturazione del corpo idrico facilitando il ritorno delle specie riparie caratteristiche dell’ambiente in cui si opera. Su questo fronte è perarltro necessario puntare ad un elevato grado di complessità della cenosi, che permette al biotopo una maggiore stabilità insediativa ed una più elevata autoregolazione. Non vanno inoltre sottostimati altri aspetti a latere dell’intervento pure essi importanti, quali il maggiore valore ecologico garantito dalla presenza di un numero rilevante di microambienti che offrono ricetto a numerosi organismi viventi, la più marcata capacità autodepurativa raggiunta dal corpo idrico a fronte della presenza della vegetazione ed infine la rivalutazione degli ambiti fluviali a fini ricreativ
Constitutive relation for dense granular flow
No full textWe propose an experimentally derived constitutive equation for dense granular-fluid mixture (e. g. debris-flow). It is based on frictional (quasi-static) and collisional (dynamic) stress component. The model has been compared with experiments carried out in an annular rheometer (Angeloni, Lamberti, Schippa 19971) using glass spheres and natural sand shearing in air and in newtonian viscous fluids (i. e. water and water-glycerol solution) having different viscosity. The measures of the velocity distribution inside the channel leads to the a characterization of the actual shearing layer and to the evaluation of the related parameters (e. g. concentration, shear rate, etc). Dynamic stress component is consistent with that originally proposed by Bagnold (1954) in the asymptotic grain-inertia regime, but in the macro-viscous regime the value of the constant scatter from the original one, because of the presence of the quasi static stress component. The weighted function related to the quasi-static and dynamic stress seems to be slightly dependent on the grain characteristics (i. e. mainly the shape) in the range of the experiments. The constitutive model herein proposed compare satisfactorily with our experiments
Studio dell'abbassamento dell'alveo del fiume Po: previsioni trentennali di abbassamento a Cremona
No full textViene descritto lo studio relativo alle previsioni trentennali (1993-2023) di abbassamento dell’alveo del Po in corrispondenza del porto di Cremona, basato sull’impiego di un modello matematico di evoluzione del letto esteso all’asta di Po compresa tra la Becca e Pontelagoscuro. Le simulazioni sono state condotte sulla scorta di scenari verosimili individuati anche attraverso la consultazione di diversi testimoni dalla quale sono emerse informazioni di diverso dettaglio che sono qui riassunte. Il modello numerico alle differenze finite applica una serie di bilanci a tronchi elementari individuati da sezioni trasversali adiacenti, impiegando stime degli apporti di sedimenti e degli scambi di essi con l’esterno. Il bilancio di massa nell’ambito della sezione è valutato secondo due differenti approcci: il primo assume che l’effetto di ridistribuzione dei sedimenti nell’ambito della sezione bagnata sia massimo, causando quindi una traslazione verticale uniforme dell’intero contorno bagnato; il secondo pone che la variazione locale del fondo sia proporzionale alla tensione di attrito agente sulle particelle. assumendo che gli eventuali effetti di trasporto diffusivo trasversale siano bilanciati e trascurando l’influenza dell’inclinazione trasversale del fondo. La ricostruzione della recente vicenda storica passata (1964-84) attraverso l’impiego di entrambi i modelli di bilancio sedimentario proposti, ha permesso di calibrare un modello meglio rappresentante il reale comportamento dell’alveo. Ad integrazione di questo studio specifico, sono state riconsiderate differenti stime relative all’evoluzione del profilo del fondo, per evidenziare l’importanza reciproca di cause diverse agli effetti dell’abbassamento dell’alveo
Shear flow of a liquid-grain mixture: the quasi-static component of the stress. Part 1: experiments
No full textAn integrated approach to beach management in Lido di Dante, Italy.
No full textThe aim of the paper is to present an integrated approach to coastal zone management and the benefits derived from the synergy of different monitoring methodologies. Lido di Dante, Italy, was selected for this purpose because suffers of great erosion and is well documented under engineering, socio-economic and ecological aspects (it is one of DELOS Project case studies).
The paper presents the relation among the most relevant results obtained in the site. First, effects of shore protection works and wave climate on beach morphology are examined by analysing field measurements of waves and currents together with hydrodynamic simulations and bathymetry surveys in the area.
Then, socio-economic impact of coastal defence is documented by the statistics derived from face-to-face interviews that provided beach valuation and user preferences.
Finally, abundance and type of organisms on the rocky structures, based on results from ecological surveys, are related to the intensity distribution of wave and current flows around and over the structure.
The complex interaction among the beach, the structures, the hydrodynamics, the eco-system and the society is discussed and the necessity of multi-disciplinary guidelines for constructing beach defences is enhanced
- …
