1,721,042 research outputs found
RELAZIONE ENTROPICA TRA LA VELOCITÀ MEDIA E LA VELOCITÀ MASSIMA: verifica sperimentale in canali di laboratorio
No full textApplication of entropic approach to estimate the mean flow velocity and Manning roughness coefficient in a high-curvature flume
No full textThe entropy-based approach allows the estimation of the mean flow velocity in open channel flow by using the maximum flow velocity. The linear relationship between the mean velocity, umax, and the mean flow velocity um, through the dimensionless parameter Φ(M), has been verified both in natural rivers and in laboratory channels. Moramarco and Termini (2015) investigated the reliability of the entropy-based formula in a straight channel and under different bed and side-walls roughness conditions. The present study aims to furtherly validate the entropy-based approach and to explore the effectiveness of entropy-based formula in high curvature channels. Results show that as effect of the downstream variation of the channel’s curvature the value of the parameter (M) varies along the bend. When the bed deformation is evident the variation of the parameter (M) is strongly reduced compared to that obtained in absence of the bed deformation. Results also show that the Manning’s roughness coefficients determined through the entropy-based formula are in agreement with those estimated by applying other literature’s expressions but, unlike the latter, through the parameter (M) the entropy-based formula could account for the effects due to the advective momentum transport by cross-circulation along the strongly curved reaches of the channel
Analisi sperimentale di laboratorio sulla stima della velocità media del flusso mediante la teoria entropica
No full textEntropic model application to identify cross-sectional flow effect on velocity distribution in a large amplitude meandering channel
No full textLiterature shows the application of the entropy concept in open channels flow. No existing research has been addressed to the application of the entropy concept for evaluating the effect of secondary flow which especially develops in curved channels. The purpose of this paper is to explore the possibility to evaluate the effect of the secondary flow on the stream-wise velocity distribution starting only from the knowledge of the surface velocity and the entropic concept application. The analysis is conducted with the aid of data collected in a large-amplitude meandering laboratory flume for two different values of the width-to-depth ratio. Results show that the location of the maximum velocity varies not only along the bend but also along the water depth, depending on the relative entity of the cross-circulation and the convective flow acceleration. It has been also verified that the entropic parameter varies along the bend as a function of the width-to-depth ratio. The application of the entropic model to the examined cases has allowed the verification that not only the shape of the velocity profile but also the bed shear stress evolution along the bend could be estimated by the entropic model starting from the knowledge of the surface velocity only
Stima della velocità media tramite teoria entropica al variare della configurazioni planimetrica: verifica sperimentale in canali di laboratorio
No full textIl modello di entropia sviluppato da Chiu (1988) consente di correlare la velocità media, um, e umax mediante una relazione lineare, um,=Φ(M) umax, che dipende dal parametro entropico, M, caratteristico della sezione fluviale. Tale formulazione è stata verificata su diversi corsi d’acqua naturali con differenti caratteristiche idrauliche e geometriche (Ammari et al. 2010, Xia, 1997; Moramarco et al. , 2004). Nel presente lavoro, l’attenzione è rivolta alla verifica della relazione entropica tra la velocità media e la velocità massima al variare delle configurazioni planimetriche del canale (andamento rettilineo e andamento curvilineo) e in presenza di elementi forzanti come la curvatura del canale e la deformazione del fondo. L’analisi è condotta con l’ausilio di dati sperimentali raccolti in canali di laboratorio realizzati presso il Dipartimento DICAM dell’Università di Palermo
INFLUENCE OF BED ROUGHNESS AND CROSS SECTION GEOMETRY ON MEDIUM AND MAXIMUM VELOCITY RATIO IN OPEN CHANNEL FLOW
Full text linkThe paper deals with the analytic-theoretical derivation of the relationships between the entropic quantity Φ(M), representing the ratio between the mean and maximum flow velocity, and the relative submergence and aspect ratio, using classical open channel flow equations. Φ(M) is found to be highly dependent on the relative submergence when large or intermediate roughness scale occur, while it might be assumed almost constant for a small roughness scale. Furthermore, considering the hydraulic geometry relationships, it is attempted to relate the relative submergence to the aspect ratio of flow through a log-relationship whose coefficients depend on the local bed slope, with an important implication for hydrological practices. Then, a practical relation between Φ(M) and aspect ratio is proposed and validated in the operative chain for discharge assessment, showing high robustness and stability. The proposed model has been applied to a set of experimental velocity data collected in gaged river sites with different geometric and hydraulic characteristics as well as low, medium and high flows
Entropic approach to estimate the mean flow velocity:experimental investigation in laboratory flumes
No full textThe paper deals with the linear entropic relationship between the maximum velocity, u max , and the mean flow velocity, u m, through a dimensionless parameter
U (M), in open-channel flow. The analysis is conducted with the aid of experimental data collected in straight laboratory flumes under different bed and side-walls roughness conditions. In particular, rough/vegetated beds and smooth/rough side-walls conditions have been investigated. The results show that, in the investigated conditions (with exception of low-
submergence vegetated bed— h/k v \2), U (M) can be assumed equal to a value that is very close to that found in natural channels. This demonstrates that
U (M) is able to implicitly reflect the different hydraulic behavior which is determined in rough and submerged
vegetated beds. Thus, the entropy-based Manning’s roughness formula has been validated and the sensitivity analysis of Manning’s coefficient with the values of
y o (location of the zero-velocity plane) has been also performed. It is found that this formula is quite robust to represent the observed flow resistance also in the presence of vegetation
COMPARISON OF TWO SIMPLE REAL-TIME FLOOD FORECAST MODELS: THE CASE STUDY OF THE PO RIVER (ITALY)
No full textThe performance of two simple models for real-time flood forecasting is investigated and compared. The first approach, named as RCM-RT, is based on the Rating Curve Model (RCM) and provides, involving only two parameters, future estimates of both discharge and water level at a river site where only the stage is monitored while the flow is known at an upstream section.
The second model, named MHBA, is described by a linear stochastic formulation of flood wave propagation and is based only on stage data.
Both models require that the forecast lead-time and the parameters are identified a-priori through a calibration phase involving different observed flood events.
The two models are tested on a long reach of the Po River (northern Italy) for several flood events. The obtained results show that both models provide an accurate forecast water level 32 hours in advance
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