1,721,044 research outputs found
Gestione sostenibile dei deflussi urbani
No full textNegli ultimi decenni l’elevata intensità degli eventi meteorici e i processi di urbanizzazione hanno determinato l’aumento del deflusso superficiale in ambito urbano nel corso degli eventi di pioggia, con un notevole incremento delle portate, dei volumi idrici
e degli inquinanti da smaltire attraverso le reti fognarie e da riversare nei corpi idrici ricettori.
Da un punto di vista generale, per il controllo quantitativo e qualitativo delle crescenti portate meteoriche, possono essere utilizzate due diverse tipologie di rimedi: strutturali e non strutturali. Nella presente memoria vengono inizialmente descritti alcuni rimedi strutturali, facendo particolare riferimento alle tecniche di “Best Management Practices”, che utilizzano un approccio di tipo sostenibile basato principalmente sull’aumento
della capacità di invaso e di infiltrazione delle superfici del bacino e che sono utilmente da integrare e, ove possibile da sostituire, agli interventi di adeguamento delle vecchie reti di drenaggio urbano e alla realizzazione di nuove reti. Si fa successivamente
cenno ai rimedi non strutturali che sono rimedi non fisici, generalmente miranti all’abbattimento delle vulnerabilità del territorio, ovvero alla riduzione dell’esposizione dello stesso al rischio di danni conseguenti a eventi calamitosi. Nell’ultima parte della presente memoria viene presentata una metodologia per il dimensionamento delle trincee di infiltrazione
Nondimensional simulation-based regression formulas for slit dam design in mountain rivers
No full textCompact regression formulas were developed through one-dimensional (1D) unsteady flow numerical model simulations for the analysis of slit dam (SD) hydraulic behavior in torrents. The formulas allow an easy evaluation of the sediment-trapping efficiency and of the depth of the sediment deposit upstream from SDs at the peak time of flood. The use of the developed formulas also provides a first estimation of the dam self-cleaning effects at the end of the event associated with the receding stage of the hydrograph. Compared to the approaches available in the literature, the results of this work allow the extension of the analysis of the trapping processes behind SDs to conditions of unsteady flow. The developed formulas may represent a simple and reliable tool for SD design in mountain gravel bed rivers characterized by relatively steep slopes (1-5%)
Le paratoie mobili Hydrass per le cacciate nei canali fognari. Esperienze di laboratorio e confronti numerici
No full textCome è noto, all’interno delle reti di fognatura risultano necessarie periodiche operazioni di pulizia al fine di evitare o ridurre i problemi idraulici conseguenti alla presenza di sedimenti depositati sul fondo dei canali. A tale scopo, negli ultimi anni, sono stati messi a punto e adottati nuovi ed efficienti dispo-sitivi idraulici basati sulla generazione di onde di cacciata. Nella presente memoria, è presentata un’indagine sperimentale e numerica sul funzionamento idraulico della paratoia “Hydrass”, un particolare dispositivo mobile di cacciata in fognatura. L’indagine sperimentale è stata condotta in laboratorio utilizzando un modello in scala ridotta del dispositivo, al fine di caratterizzare le onde di cacciata determinate dalla paratoia mobile. L’indagine numerica è stata successivamente condotta mediante un modello matematico specificamente sviluppato per la simulazione della propagazione di onde di cacciata all’interno di canali fognari. Il confronto dei risultati numerici con le misure sperimentali ha consentito di valutare l’applicabilità in condizioni di moto vario delle leggi di efflusso del dispositivo determinate in una indagine precedente
Testing behavior and effects of PRVs and RTC valves during hydrant activation scenarios
No full textThis paper provides an insight into behavior and effects of pressure reducing valves (PRVs) and of valves controlled in real time (RTC) during hydrant activation scenarios, which determine high-flow conditions in water distribution networks (WDNs). The analysis is carried out through the pressure-driven unsteady flow modeling of an Italian WDN, in which a pressure control device is assumed to be installed in the pipe outgoing from the source. Scenarios are constructed considering alternatively a PRV or an RTC valve, as pressure control device, and two different sites for hydrant activation. The results highlight that, thanks to its capability of controlling the service pressure at the critical node, the RTC valve performs better than the PRV, which is regulated based on its outlet pressure. In fact, the adoption of the RTC valve attenuates pressure deficits in the network, above all when the control time step is suitably small to attenuate pressure head oscillations at the controlled node. An additional benefit of RTC lies in increased outflows from the hydrant. The benefits of the RTC valve are smaller when the hydrant is activated in more redundant parts of the network, where pipe water discharge variations put the system to a less severe test
P controller calibration for the real time control of moveable weirs in sewer channels
No full textIn this paper, a detailed study on the local real time control of moveable sharp-crested weirs in sewer channels is presented.
Firstly, an experimental analysis aimed at determining the hydraulic behaviour of the regulator under both free flow and submerged flow conditions was carried out.
Then, a numerical investigation into the calibration of proportional (P) controllers for the weir control was performed. In particular, suitable values were evaluated for the controller proportional parameter in order to obtain quick regulations and avoid the occurrence of permanent water level oscillations behind the weir. A dimensionless approach was adopted for the generalisation of the results
A simplified approach for the design of infiltration trenches
No full textThe use of infiltration trenches has proven to be useful to reduce runoff in urban surfaces. The design of these structures is based on the continuity equation taking into account inflow, outflow and detention water volumes. Basic procedures evaluate entering flow rates and relative volumes directly as a function of rain event characteristics, without taking into account rain-runoff processes occurring in the watershed. An improved simplified procedure, based on the kinematic model for the description of rain-runoff processes, has been developed here using a dimensionless approach. The procedure and the relative applicative design graphs are presented and discussed
Application of Real-Time Control Techniques to Reduce Water Volume Discharges from Quality-Oriented CSO Devices
No full textThis paper shows the extent to which the application of real-time control techniques can help in reducing the flows discharged from quality oriented combined sewer overflow (CSO) devices in sewer systems. To this end, a quality oriented CSO device, namely the highcrested side-weir (HCSW) with downstream gate, was taken into account for the analysis. A numerical model able to simulate routing of flows in proximity to CSO devices was specifically used to evaluate the benefits of the HCSW with downstream gate, in comparison with the more traditional low-crested side-weir (LCSW), and the coupled use of HCSWs and in-sewer mobile gates controlled in real time. The model was applied by considering four different modeling scenarios to the case study of a sewer catchment in Italy, in which real storm-water events had been recorded during previous experimental investigations. Results of the simulations prove the HCSW with downstream gate always considerably reduces CSO volumes in comparison with LCSW overflow devices. Significant additional benefits are obtained by the implementation of underflow gates controlled by real-time control (RTC), even if the presence of such mobile devices may sporadically lead to a local increase in the overflow discharge
A model for non-uniform sediment transport induced by flushing in sewer channels
No full textA novel unsteady flow numerical model for the simulation of the transport of non-uniform non-cohesive sediment mixtures (SM) during flushing operation in sewers is presented in this paper. The model was applied to the case of a flush experimental test that was recently carried out in a combined sewer channel of the sewer system of Paris city that exhibits depositional problems due to relatively coarse sediments. The model output was compared to the results of the field experiments as well as to those obtained with a model for the transport of uniform sediments (US). The model for SM provided a reliable interpretation of the selective transport of the sediments deposited in the channel bed as induced by the flush. The comparison showed the model for SM to provide an enhanced description of the erosional effects of the flush on the deposits, including improved evaluation of the volume of sediments flushed out of the experimental channel in the field
Controller calibration for moveable weirs in sewer systems
No full textOne of the main objectives of real time control (RTC) application in combined sewer systems is the reduction of overflow discharges during rain events. For this purpose, adequately controlled moveable regulators, such as gates or weirs, can be placed inside the main trunk sewers for activating the available in-line storage capacity.
In this paper, a detailed study on the local control of a moveable sharp-crested weir in sewer collectors is presented.
Firstly, an experimental analysis has been carried out for determining the hydraulic behaviour of the regulator, considering both free flow and submerged flow conditions and taking into account the different weir heights occurring during the regulation processes.
Secondly, a numerical investigation on the calibration of proportional units for the local control of the weirs has been performed. In particular, a detailed model based on the De Saint Venant equations has been used to describe the hydrodynamic phenomena connected with the RTC of moveable regulators in sewer collectors. A dimensionless approach has also been adopted for the generalisation of the results of the analysis.
Finally, a comparison with previous results concerning the control of moveable gate regulators is presented
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