1,720,982 research outputs found
3-D Underflow of a Sluice Gate at a Channel Inlet; Experimental Results and CFD Simulations
No full textThe underflow of a sluice gate is well known when the gate is set into a channel of the same
width (2-D underflow), while no studies are found in the literature when the gate is flush with the wall of the
tank or reservoir upstream to the channel (3-D underflow). Experimental and numerical investigations were
carried out to study the flow in this case, in a small range of relative openings, considering three wall slopes,
and obtaining an equation for the discharge coefficient. Afterwards, numerical simulations were performed
by means of a CFD (Computational Fluid Dynamics) model, following the RANS approach and based on a
finite-volume computational code. Comparison of experimental and numerical results showed that the
simulations predict accurately the flow behaviour; thereafter discharge coefficients in a more extended range
of relative openings were computed for use in the practice
Flow Resistance in Open Channel Due to Vegetation at Reach Scale: A Review
Full text linkVegetation on the banks and flooding areas of watercourses significantly affects energy losses. To take the latter into account, computational models make use of resistance coefficients based on the evaluation of bed and walls roughness besides the resistance to flow offered by vegetation. This paper, after summarizing the classical approaches based on descriptions and pictures, considers the recent advancements related to the analytical methods relative both to rigid and flexible vegetation. In particular, emergent rigid vegetation is first analyzed by focusing on the methods for determining the drag coefficient, then submerged rigid vegetation is analyzed, highlighting briefly the principles on which the different models are based and recalling the comparisons made in the literature. Then, the models used in the case of both emergent and submerged rigid vegetation are highlighted. As to flexible vegetation, the paper reminds first the flow conditions that cause the vegetation to lay on the channel bed, and then the classical resistance laws that were developed for the design of irrigation canals. The most recent developments in the case of submerged and emergent flexible vegetation are then presented. Since turbulence studies should be considered as the basis of flow resistance, even though the path toward practical use is still long, the new developments in the field of 3D numerical methods are briefly reviewed, presently used to assess the characteristics of turbulence and the transport of sediments and pollutants. The use of remote sensing to map riparian vegetation and estimating biomechanical parameters is briefly analyzed. Finally, some applications are presented, aimed at highlighting, in real cases, the influence exerted by vegetation on water depth and maintenance interventions
Uso dei GIS a supporto di un modello di simulazione di eventi di piena nei bacini urbani,
No full textÈ ormai noto che i Sistemi Informativi Geografici (GIS) ed i Modelli Digitali del Terreno ad alta definizione sono un supporto ideale per la modellistica idrologica distribuita, pur presentando, nelle applicazioni all’idrologia urbana, diverse difficoltà dovute alla complessità dell’ambiente urbanizzato e alla scarsa disponibilità di dati plano-altimetrici di precisione adeguata all’applicazione di modelli di drenaggio a tale scala. Scopo del presente lavoro è quello di utilizzare i suddetti strumenti per l’applicazione e la taratura di un modello idrologico distribuito a scala urbana, valutandone l’efficacia rispetto alla metodologia tradizionale. Sono stati pertanto sviluppati ed elaborati i dati geografici del bacino sperimentale del Canale Liguori (Cosenza) e della sua rete di drenaggio, e si è realizzato un Modello Digitale del Terreno (DTM) per la determinazione dei parametri morfologici necessari alla modellistica. Il DTM ha consentito di generare, attraverso opportune procedure, i sottobacini afferenti a ciascun tronco di rete e di determinare le relative caratteristiche topografiche (area, lunghezza dei percorsi superficiali, pendenza, ecc.), dati che, integrati con quelli contenuti nel GIS, permettono di ottenere, attraverso la sovrapposizione di attributi spazialmente distribuiti con la rete di fognatura, le informazioni necessarie a formare la base dati che rappresenta l’input per il modello idrologico utilizzato, il MOUSE. La taratura del modello rispetto a una serie di eventi registrati ha permesso di evidenziare come la procedura seguita dia risultati del tutto confrontabili con quelli ottenuti attraverso la ben più onerosa procedura manuale tradizionalmente seguita
Investigation of flow resistance exerted by rigid emergent vegetation in open channel
No full textThe issue of the resistance to flow in open channels with vegetation has been considered by several researchers mainly experimentally, but the case of rigid emergent vegetation with linear stem arrangement is scarcely investigated. In the present work, the results are presented of an experimental investigation related to the case of rigid emergent vegetation that has been modeled by placing small rods on the bottom of a laboratory flume in aligned configuration. Tests have been executed by varying the flow rate, the bottom slope and the number and the diameter of the rods, by directly measuring the drag force exerted by the flow on a given number of rods, and the water-level profiles. A new expression has been devised for the drag coefficient as a function of the vegetation density, weakly dependent on the stem Reynolds number that allows the use of the former also in large-scale cases. The experimentally measured forces exerted by the flow on the rods have been also compared with the results obtained by applying the momentum equation in integral form to given control volumes, exhibiting a general agreement, but also showing that the use of this technique for the evaluation of the drag coefficients can give rise to not negligible errors. One of the experimental tests has been numerically simulated with the RANS technique (Reynolds-Averaged Navier–Stokes equations), and it is found that the results, mainly in terms of water-level profiles, confirm the ability of such a numerical technique in investigating this complex category of flow cases. © 2019, Institute of Geophysics, Polish Academy of Sciences & Polish Academy of Sciences
Discharge Coefficient Analysis for Sluice Gates Set in Weirs
No full textExperimental tests and computational tests were performed to analyse discharge coefficients when gates are
placed into weir walls. Gate slope and side contraction effect have been considered. A great number of
experiments were conducted by considering three angles of inclination of the weir, three shape ratio and three
values of the relative opening. Two mathematical equations were obtained, relating the discharge coefficient
to the parameters that characterize the phenomenon. Furthermore, computational tests were performed
following the Reynolds-Averaged Navier-Stokes (RANS) approach in conjunction with a turbulence closure
model. In order to track the fluid surface, the Volume of Fluid algorithm being used. Numerical results have
been validated against the experimental showing a good agreement. The validated numerical fluid flow can
help to better understand the phenomenon not caught by the experiments
Drag coefficient of in-line emergent vegetation in open channel flow
No full textAlong the banks of rivers, trees and bushes are often planted in a single line. In the case of trees, the trunks are simulated in hydraulic laboratories by a set of cylinders, and the drag coefficient can be estimated with the use of various different methodologies, including by direct measurement, using the momentum equation, equating turbulence intensity and drag force, numerical modeling, and genetic programming. However, for the sake of simplicity, many equations have been proposed in the scientific literature that allows its immediate estimation. Some of these equations are used in this work to verify their ability to reproduce experimental data obtained for in-line cylinders by Mulahasan and Stoesser ([2017]. Flow resistance of in-line vegetation in open channel flow. International Journal of River Basin Management, 15(3), 329–334. https://doi.org/10.1080/15715124.2017.1307847), who obtained the drag force by applying the momentum equation. Several statistical descriptors have been used for this purpose. We found that the equations derived from staggered and random arrangements generally overestimate by a large amount the CD values; instead, a few relationships and in particular one derived from a squared arrangement provide much better results
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