1,721,008 research outputs found
Dip Phenomenon in High-Curved Turbulent Flows and Application of Entropy Theory
No full textThe estimation of velocity profile in turbulent open channels is a difficult task due to the significant effects of the secondary flow. The present paper investigates the mechanism of the velocity-dip phenomenon, whereby the location of the maximum velocity appears to be below the free surface. Previous studies conducted in straight channels relate the mechanism of the velocity-dip phenomenon to secondary flow induced by anisotropy of turbulence. This work focuses on high-curved channels where the secondary motion, which is also induced by the channel’s curvature, evolves along the bend. The width-to-depth ratio, B/h, is one of the most important parameters that are affecting the secondary motion entity. In particular, the present study aims to investigatetheevolutionofthevelocity-dipalongthebendfortwovaluesofthewidth-to-depthratio andtheapplicabilityoftheentropicmodelforthedip-phenomenonestimation. Theresultsshowthat the velocity-dip is more accentuated for low values of the width-to-depth ratio, where the secondary motion plays a fundamental role in the distribution of the downstream flow velocity, although the velocity-dip is also present when the aspect ratio is higher than 10. Furthermore, the velocity profiles that were estimated by applying the entropic model are in good agreement with the measured ones, especially for B/h < 10
Studio delle variazioni granulometriche del pavimento a valle della diga sul torrente Camastra
No full textIn questo lavoro è presentato lo studio degli effetti indotti dalla diga di Ponte Fontanelle (Torrente Camastra, Potenza, Italia) sul tronco fluviale immediatamente a valle. Sono state analizzate e confrontate alcune tecniche di campionamento, utili all'individuazione dell'assortimento granulometrico del pavimento, evidenziando anche i limiti della loro applicabilità. Attraverso la tecnica di Wolman, si sono individuate le curve granulometriche relative a tre sezioni del tronco in esame. Sono state simulate le evoluzioni granulometriche, per le tre sezioni investigate, a partire dal 1988 fino al 1994. individuando la variazione temporale del D50. Le prime analisi evidenziano un processo di degradazione d'alveo che tende a stabilizzarsi nel tempo. Il confronto del profilo longitudinale del tronco in esame, rilevato in tempi successivi, sembra confermare sia la fase di degradazione (1988-1991) sia la fase di stabilizzazione del fondo (1991-1994)
A grey-based methodology for representing uncertainty in discharge measurements at a gauged river site
No full textThe velocity-area method and entropy method for assessing with uncertainty discharge measurements at a gauged river site are analysed and compared; uncertainty is represented through the grey number technique. Two different approaches for greyfication of both the methods are presented. In the first approach, the uncertainty affecting each measurement used to estimate the discharge is characterized by a grey number: all the grey uncertainty components are then combined through the grey mathematics. In the second approach, greyfication is applied to the relationship expressing the total uncertainty on the discharge measurement, provided by the EN ISO 748 guidelines.
Results of the application of the proposed methods to measurement data pertaining to a gauged Tiber river section show that the first greyfication approach leads to a larger discharge uncertainty estimate with respect to the latter. Furthermore, being the greyfication approach and the flow area quantification the same, the velocity-area and entropy methods provide nearly the same estimate of the uncertainty affecting the discharge measurements, i.e. the grey discharges they provide are fairly similar
Modello per la stima della scala di deflusso in siti fluviali con sole registrazioni di livello
No full textLa stima della portata in una sezione dotata di misure di livello richiede la conoscenza della scala di deflusso che però può essere sconosciuta o affetta da notevole incertezza. Tra gli approcci proposti in letteratura per superare questi inconvenienti, vi è il modello RCM (Moramarco et al., 2005) che può essere impiegato quando la scala di deflusso è nota in una sezione a monte, anche a notevole distanza dalla sezione di interesse, tanto da dover considerare l’afflusso laterale presente nel tratto intermedio. In questo studio il modello RCM viene esteso al caso in cui la scala di deflusso è nota in una sezione posta a valle. Anche nella nuova formulazione il modello RCM risulta affidabile nella riproduzione degli idrogrammi di portata e nella ricostruzione della scala di deflusso in sezioni idrometriche poste in corsi d’acqua con caratteristiche morfologiche differenti fra loro
Developing and testing a long-term soil moisture dataset at the catchment scale
No full textInferring long-term soil moisture time series with dense temporal resolution and representative of large areas is a challenging task. However, its accurate estimation over large areas might be essential for improving our knowledge of the mass and energy balance between the land surface and atmosphere,and also for many others practical applications. In this study,a long-term (1989–2011)simulated soil moisture dataset is developed by using 1-year in situ observations collected at 92 sites over an area of ~400 km2 in central Italy. Specifically, a soil water balance model is calibrated for reproducing the soil moisture temporal variability at each site and,then,is tested for representing also the spatial variability of in situ measurements. The good temporal and spatial agreement between modelled and observed data gives confidence about the use of the modelled data in the study area for reconstructing a long-term soil moisture dataset with hourly temporal resolution (in accordance with the availability of hydrometeorological observations). The developed soil water balance model and procedure can be applied also in other climatic regions to obtain a similar dataset. Indeed,the obtained dataset and the model code are made freely available from the authors and can be used for hydrological and satellite soil moisture products validation studies
Enhancement and comprehensive evaluation of the Rating Curve Model for different river sites
No full textThis study presents an enhancement of the Rating Curve Model (RCM) proposed by Moramarco et al. (2005) which was initially formulated to assess discharge at a downstream river site where only stage is monitored while the flow is recorded at an upstream section and significant lateral inflow can occur along the river branch. The original model formulation is here of fact extended for upstream discharge estimate by assuming the flow known at a downstream site and stages measured at both ends. In this
new configuration, the model can be applied to river reaches with negligible lateral inflow or to river reaches with significant lateral contribution but where a kinematic flow regime holds. The new model formulation is tested by considering two case studies, both selected in the Upper-Middle Tiber River basin, in central Italy. For the first case study, the model is applied to 22 flood events observed along three branches of the Tiber River with accurate rating curves at ends and having the same upstream river site.
RCM successfully simulates the discharge hydrographs observed at the upstream section closely capturing both the peak rate and the time to peak, with average absolute errors less than 5% and 0.36 h, respectively. The model accuracy is found independent of the intermediate basin area and, hence, of the lateral inflow contribution. The rating curve computed in this upstream section by using the shortest reach is slightly overestimated whereas the ones derived by applying the model to the other two reaches are
almost coincident and slightly underestimated, but for all of them the errors are less than 5%. The second case study concerns the estimation of the upstream rating curve at a river site, where discharge measurements are available for very low stages alone, starting from the flow known at two different downstream equipped sections. The RCM application to recorded flood events provides two very similar stage–discharge relationships with a maximum difference, between the reproduced rating curves,
of about 5 m3/s for the higher stage values. Moreover, the RCM accuracy is shown to be satisfactory for river reaches located in physiographic regions (northern Italy and Slovak Republic) different from the one used for the model development and testing and considered in the two case studies mentioned above.
Finally, the model capability to take implicitly account of the unsteady effects (i.e. rating loop) is shown through experimental data recorded by an ultrasonic flowmeter at a gauged site of the Tiber River as well as by considering a numerical test
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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