Taratura di un modello afflussi-deflussi su bacini sperimentali urbani italiani

Obiettivo della presente ricerca e’ quello di calibrare e verificare un modello di trasformazione afflussi-deflussi su alcuni bacini urbani sperimentali italiani. Il modello considerato utilizza, per la trasformazione in pioggia netta, la metodologia “Curve Number” in cui è introdotta la possibilita’ di considerare una percentuale di area priva di perdite iniziali e, per la trasformazione afflussi- deflussi, lo schema dell’onda cinematica. La calibrazione dei parametri viene effettuata per mezzo di un codice di calcolo che implementa l’algoritmo di Gauss-Mardquard-Levenberg per la minimizzazione di una opportuna funzione obiettivo

State of art in block ramp and downstream stilling basin design

Block ramps are hydraulic structures which are commonly used in river restoration projects. Especially in the last few decades, the use of this type of structures have become more and more popular. They furnish a correct balance between the hydraulic functioning and the environmental care, as they minimize the impact on the environment in which they are located. In addition, they can be considered flexible structures, i.e. they can easily adapt to the in situ conditions and they can be easily built to re-convert traditional concrete structures. They can be built either by loose or fixed blocks, arranged on a sloped bed. However, a correct design of this structural typology has to take into consideration several aspects. In particular, the hydraulic functioning of a block ramp is assured when the structure remains stable, i.e. when the blocks are not removed from their original position. Thus, the first step in designing block ramps has to be the structural stability. Furthermore, the analysis has to focus also on the dissipative process occurring on them, in particular it has to consider the different flow regimes that can take place and the effect of the bed roughness on the energy dissipation. Another important aspect is the stilling basin design. In fact, a block ramp has not to be considered as an isolated element in the contest in which it is located. It is part of that contest and it contributes to modify it. Thus, it is extremely important to consider the scour process occurring downstream of the structure. In particular, the maximum scour depth and length have to be carefully estimated in order to avoid structural collapse of the ramp. The scour process occurring downstream of the structure is also extremely important in terms of energy dissipation. In fact, the global dissipative process is the result of two distinct processes: one occurring on the ramp and the other in the downstream stilling basin. Finally, the analysis has to take into consideration which are the global sediment transport conditions of the river in which the structure is located. Thus, it has to be conducted in both clear water and live-bed conditions. It appears evident that a correct design of this type of structures is a complex operation which requires a particular attention in order to avoid functioning problems

Structural defence for plunge pool scour

Plunge pool scour is a major topic in presence of hydraulic structures that foresees the production of jets. The scour hole is a function of several variables including the tailwater, the densimetric Froude number, the sediment granulometry, the water discharge. The maximum scour depth is of great interest in the design process. Aim of the paper is to analyze the effect of structures, inserted in the scour hole, in order to mitigate the scour geometry. About 300 tests have been carried out in the Hydraulic laboratory of the University of Pisa (Italy) in order to assess the advantages and the problems connected with the insertion of a rigid structures in the river bed. In this paper a first description of the phenomena is presented

Analysis of scour characteristics in presence of aerated crossing jets

Jets scour is a major topic in hydraulic engineering. It has to be carefully analysed in order to understand the mechanism and predict its geometry. The jets configuration has a deep infuence on the scour features. In the present paper the analysis was conducted in presence of two symmetric crossing jets, varying the discharge, the air content, the tailwater level in the downstream stilling basin, the angle between the jets and the vertical distance of the jets crossing point from the water surface, for different vertical jets angle. It was proven that the presence of the air in the jets deeply affects the scour morphology. The scour geometry was analysed and compared with the respective obtained in black water conditions. Useful practical relationships are proposed to estimate the main scour hole dimensions. The analysis was also extended to non-dimensional prof les and it was proved that the effect of air content on them is negligible

Hydraulic jumps on rough and smooth beds: aggregate approach for horizontal and adverse-sloped beds

Hydraulic jumps, which frequently occur in hydraulic structures, have been extensively studied over the last century. However, only a few studies have evaluated hydraulic jumps in flows over rough beds and there are no studies that consider the air entrainment effect on conjugate depths. The current paper reports the results of an experimental investigation of hydraulic jump properties in flows over adverse-sloped rough beds, including the effect of air entrainment. Furthermore, a semi-theoretical predictive relationship is proposed to estimate jump characteristics for a wide range of hydraulic and geometric conditions covering both rough and smooth beds

D-jump in rough sloping channels at low Froude numbers

Hydraulic jump is a phenomenon which usually occurs in rivers and in correspondence with hydraulic structures. It is characterized by a rapid transition from a super- to sub-critical flow conditions, involving a huge energy dissipation. For its characteristics and its relevance in hydraulics, it has been studied since the early years of the last century. Nevertheless, many features still require a further investigation, e.g., scale effects, air entrainment process, effect of bed roughness on conjugate depths, etc. In particular, in the last few decades, the analysis of the main geometric parameters has been further developed. Nevertheless, no studies dealing with D-jump occurring on a rough sloping channel are present in literature. Therefore, the present paper reports the results of experimental investigations, which allowed to develop a semi-theoretical approach in order to evaluate the D-jump conjugate depth in a wide range of channel bed geometric and boundary configurations

A REVIEW OF HYDRAULIC JUMP PROPERTIES ON BOTH SMOOTH AND ROUGH BEDS IN SLOPING AND ADVERSE CHANNELS

Hydraulic jump is a phenomenon which has received significant attention in recent years and it is still studied because of its capacity to dissipate a considerable amount of the flow energy. Nevertheless, the importance of the topic still requires significant efforts from the scientific community. Namely, the prediction of the main lengths of the hydraulic jump are still an open question, as the actual knowledge on the topic does not cover all the possible configurations and boundary conditions which can usually be found in practical applications. In particular, the effects of bed roughness, bed slope, channel geometry, and air concentration on the conjugate depths ratio are still not fully understood. The present paper aims to furnish a synthetic picture of the state of art regarding the hydraulic jump properties in a wide range of both boundary conditions and geometric configurations. In particular, the analysis will be focused on the effect of both relative roughness and bed slope on the conjugate depth ratio, including the effect of air entrainment on the estimation of the effective depth. Furthermore, some predicting relationships proposed by different authors will be compared and discussed

Scour at Foundations of Rock Made Low-Head Structures

Experimental Studie