Extended theory of hydraulic hysteresis in open channel flow

The occurrence of hysteresis in a supercritical, open-channel flow approaching an obstacle has been recognized and investigated both experimentally and theoretically over the last few decades. However, the available theory and experimental investigations in the literature do not include the case when subcritical flow, controlled from downstream, can establish across the obstacle. The present work fills this gap by proposing a new theory that includes this occurrence and shows that two different steady flow states can establish for the same obstacle geometry and flow conditions\u2014one with supercritical to subcritical transition far downstream from the obstacle, and the other with supercritical to subcritical transition far upstream from the obstacle. The proposed, more general theory includes the existing theory as a special case. Finally, two specific examples are illustrated and discussed, i.e., the case of flow over a raised bed hump, and the case of flow through a channel contraction

Multiple states in the flow through a sluice gate

This paper addresses the problem of hydraulic hysteresis for a supercritical open channel flow approaching a sluice gate when subcritical flow can establish downstream, against the gate. The possible flow configurations across the gate are classified on the basis of the Froude number of the incoming and downstream flows, and of the ratio of gate opening to the upstream supercritical flow depth. Within the above parameter space, two regions exist in which the problem admits a dual solution, that is, two different flow configurations can establish for the same gate opening and undisturbed flow conditions. In one of these regions, both smooth flow (i.e. the fluid flows under the gate without interacting with the gate) and free outflow conditions can establish; in the other region, both smooth flow and submerged flow can establish. For flow conditions in the above regions, the configuration that actually establishes depends on the previous history of the flow, thus implying the hysteretic character of the flow

A quantitative criterion to predict the occurrence of tidal bores

-Tidal bores are fascinating phenomena that occurs in the estuary of many tidal rivers worldwide. -Tidal bores have significant repercussions on ecology and morphodynamics of an estuary. -Despite the interest, a predictive criterion for tidal bore occurrence is still missing. -Tidal bore is assessed from a phenomenological standpoint, based on the results of a numerical study. -The predictive criterion for bore occurrence performs well against both numerical and real data

Positive Surge Propagation in Sloping Channels

A simplified model for the upstream propagation of a positive surge in a sloping, rectangular channel is presented. The model is based on the assumptions of a flat water surface and negligible energy dissipation downstream of the surge, which is generated by the instantaneous closure of a downstream gate. Under these hypotheses, a set of equations that depends only on time accurately describes the surge wave propagation. When the Froude number of the incoming flow is relatively small, an approximate analytical solution is also proposed. The predictive ability of the model is validated by comparing the model results with the results of an experimental investigation and with the results of a numerical model that solves the full shallow water equations

A quantitative criterion to predict the occurrence of tidal bores

-Tidal bores are fascinating phenomena that occurs in the estuary of many tidal rivers worldwide. -Tidal bores have significant repercussions on ecology and morphodynamics of an estuary. -Despite the interest, a predictive criterion for tidal bore occurrence is still missing. -Tidal bore is assessed from a phenomenological standpoint, based on the results of a numerical study. -The predictive criterion for bore occurrence performs well against both numerical and real data

Data of The double surge wave system that develops when a supercritical flow enters upstream of a pre-existing current

Data used in the paper titled "The double surge wave system that develops when a supercritical flow enters upstream of a pre-existing current

Free surface waves induced by vortex shedding in cylinder arrays

The paper presents and discusses the results of an accurate and extensive experimental investigation on the waves that originate when an array of cylinders is placed in an otherwise uniform open channel flow. The study was originally aimed at providing new and more accurate data to calibrate and validate a theoretical model recently proposed in the literature. However, two interesting characteristics of the phenomenon at hand, never reported in the literature, also emerged from the experimental study, i.e. (i) the wave produced by the cylinders is actually a metachronal wave rather than a pure transverse seiche; (ii) two different resonant conditions exist for each single wave mode, i.e. two typical Strouhal numbers characterize the resonance frequency of vortex shedding from the cylinders in an array. Evidence of the metachronal wave, as well as some preliminary data on the longitudinal component of this wave, are given in the paper. Also, the double resonance condition is experimentally demonstrated and discussed

Un modello 2D con porosit\ue0 per lo studio di allagamenti a larga scala in aree urbane

-Modello 2D con porosit\ue0 per lo studio a larga scala di allagamenti in aree urbane. -Introdotta una formulazione della porosit\ue0 di flusso anisotropa che evita la dipendenza dalla griglia. -Il modello \ue8 in grado di riprodurre la soluzione di riferimento sulla base di soli parametri geometrici. -L\u2019applicazione a casi studio con batimetrie reali \ue8 in fase di sviluppo

Floods, landscape modifications and population dynamics in anthropogenic coastal lowlands: the Polesine (northern Italy) case study

It is widely recognized that the complex relationship between humans, soil, and water has become increasingly complicated due to anthropogenic activities, and is further expected to worsen in the future as a result of population dynamics and climate change. The present study aims at shedding light on the multifaceted links between floods, landscape modifications, and population dynamics in anthropogenic coastal lowlands, using a large flood-prone area (the Polesine Region, northeastern Italy) as a significant case study. Based on the analysis of historical events and the results of hydraulic modeling, it is shown that human interventions on both the landscape and the subsoil have substantially altered the flooding dynamics, exacerbating hydraulic hazard. Furthermore, the combined analysis of people and assets exposure to inundation reveals that flood risk is not properly taken into account in land-use planning, nor it is properly understood by people living in areas subject to low-probability, high-impact flooding events

Flood inundation modeling in urbanized areas: A mesh-independent porosity approach with anisotropic friction

In the present work, a porosity-based numerical scheme for the Shallow Water Equations is presented. With the aim of accounting for the presence of storage areas, such as gardens, yards and dead zones, and for preferential flow pathways, both an isotropic storage porosity parameter and anisotropic friction are adopted. Particularly, the anisotropic effects due to the building alignments are evaluated defining conveyance porosities along principal directions and using them to express the friction losses in tensor form. The storage and conveyance porosities are evaluated from the geometry of the urban layout at a district scale and then assigned to computational cells rather than to cell sides, thus avoiding oversensitivity to the mesh design. The proposed formulation guarantees the C-property also in presence of wet-dry fronts. Model testing is performed analyzing schematic and idealized urban layouts, and against experimental data as well. The results obtained by the proposed anisotropic scheme are similar to a high-resolution model with resolved buildings, also in the presence of low-friction regimes, meanwhile with a remarkable reduction of the computational times