Entropy parameter estimation in large-scale roughness open channel

The entropy model allows estimating, in an expeditive way, both water discharge and flow velocity field in open channels. In fact, such model presents an almost simple analytical structure, based on the evaluation of a single parameter calculated through the ratio between the mean and maximum flow velocities in the cross section. Recent studies have demonstrated that, for large-scale roughness, the evaluation of the entropy parameter seems to be affected by the local conditions near the bed. In order to investigate such influence, the present work proposes an explicit relationship between the entropy parameter and the relative submergence. This relation was validated using data collected in a rectangular tilting flume of laboratory, where the bed roughness was composed by elements of regular shape such as spheres. Several tests were performed in conditions of large-scale roughness (1.9<D/d<6.4) and for different values of slope (0.05%<i<1%) and water discharge (7l/s<Q<76l/s). The method shows a good agreement between the observed and calculated data for both the velocity profiles and water discharges

Information Entropy Theory Applied to the Dip Phenomenon Analysis in Open Channel Flows

The knowledge of the fluid discharge in free surface flows requires a great number of velocity measurements along the whole cross-section, taking up a large amount of time, using expensive equipment, and employing specialized labor. To overcome these obstacles, various models have been developed thus far that show how to estimate the mean velocity through the maximum velocity. In three-dimensional open channels, the maximum velocity can be located below the free surface because of the presence of secondary flows mainly originating by the sidewalls, an occurrence known as dip-phenomenon. In this condition, predicting the maximum velocity position is quite difficult and has always represented a challenge to most hydraulic engineers and researchers. In the present study, a mathematical model derived from the information entropy theory is proposed to evaluate the velocity-dip-position over the entire cross-section of both wide and narrow open channels, thus overcoming the limitations of the existing methods. Large literature measurement sets, collected in uniform and non-uniform flows, were used to test the validity of the model, showing good agreement with the experimental data and providing an accurate estimation of the dip-position

An analysis method of the vortex-induced vibrations of a tethered sphere

AbstractVortex-induced vibrations (VIV) in systems with more than one degree of freedom often present complex synchronization among the motion components, also hidden by the randomness that characterizes the motion itself. A phase average method has been here developed and applied to the displacements of a tethered sphere, at low mass and damping, to analyze its xy trajectories over a wide range of reduced velocities, 5 ≤ U* ≤ 25 (Reynolds numbers, 5.1 × 103 ≤ Re ≤ 2.67 × 104). This method has allowed the identification of both the periodic and chaotic contribution of each motion component, accurately reconstructing the underlying trajectory periodic pattern. The two classical vibration modes, I and II, have been also observed. The method developed here was able to better rebuild the experimental data compared to other methods found in the relevant literature, providing useful insights into the study of the dynamic response of a freely-oscillating tethered sphere immersed in a steady flow

Statistical characterization of flow field structure in evolving braided gravel beds

Braided rivers quickly vary their geometry, modifying their boundaries and floodplains. Therefore, flooding of a braided stream is typically associated with high hydrologic risk in the surrounding areas or alluvial valleys. A forecast of these morpho-hydrodynamic processes is therefore essential when managing the environmental and economic impact of flood events. A few studies in the past demonstrated that open channels spontaneously tend to establish and maintain an equilibrium state that corresponds to a specific level of cross-sectional velocity entropy. The present study analyses for the first time the relationship between bank-full flow (described by measures of velocity entropy and second-order spatial statistics) and bed topography (described in terms of bed elevation second-order spatial statistics) in gravel-bed braided rivers at cross-sectional scale, in both equilibrium and pre-equilibrium conditions. Based on the outcome of suitable laboratory experiments, we found that, in gravel bed braided rivers, longitudinal equilibrium during floods is associated with a periodic-like spatial minimization of normalized cross-sectional velocity entropy. This periodic-like minimization of cross-sectional velocity entropy (and statistical variance) corresponds to a periodic-like maximization of normalized bed elevation variance, according to general theories on longitudinal river profile evolution. Additionally, bed evolution occurs by both entropy minima/maxima appearance and growth and entropy minima/maxima longitudinal migration

Modelling large floating bodies in urban area flash-floods via a Smoothed Particle Hydrodynamics model

Large debris, including vehicles parked along floodplains, can cause severe damage and significant loss of life during urban area flash-floods. In this study, the authors validated and applied the Smoothed Particle Hydrodynamics (SPH) model, developed in Amicarelli et al. (2015), which reproduces in 3D the dynamics of rigid bodies driven by free surface flows, to the design of flood mitigation measures. To validate the model, the authors compared the model's predictions to the results of an experimental setup, involving a dam breach that strikes two fixed obstacles and three transportable floating bodies. Given the accuracy of the results, in terms of water depth over time and the time history of the bodies' movements, the SPH model explored in this study was used to analyse the mitigation efficiency of a proposed structural intervention - the use of small barriers (groynes) to prevent the transport of floating bodies. Different groynes configurations were examined to identify the most appropriate design and layout for urban area flash flood damage mitigation. The authors found that groynes positioned upstream and downstream of each floating body can be effective as a risk mitigation measure for damage resulting from their movement. (C) 2016 Elsevier B.V. All rights reserved

Mobile Augmented Reality for flood events management

The frequency of flood events worldwide has increased significantly over the past decades, and with it so has the need to employ information technologies able to help mobile workforces, both technicians and volunteers, during surveys in the emergency phases. In view of this, a client-server framework for the development of a mobile application that uses Augmented Reality (AR) was implemented. This platform, which increases visual perception of the real world merging additional information with the natural scene in real time, allows mobile workforces to more easily reach the most critical areas subject to flooding and rapidly make a decision on the level of flood protection. The performance of the prototype was evaluated on the Bradano river, located in the south-eastern Basilicata region (Italy), both in a real case study and in a simulated one. The obtained results show how the application represents an innovative tool compared to the existing ones, being it able to show, timely and continuously up-to-date, augmented information on various vulnerability scenarios during the emergency phases, helping both technical and non-technical operators to quickly intervene, containing or preventing secondary disasters, thus reducing deaths and injuries, and limiting the resulting economic losses and social disruption

Stima del parametro entropico per correnti stazionarie in presenza di scabrezza intermedia

Nel presente lavoro, una metodologia speditiva, basata sulla distribuzione entropica di velocità, è proposta per ricostruire il campo di moto di correnti a pelo libero in presenza di scabrezza intermedia. Tale metodologia consente di determinare il parametro entropico nota che sia la sommergenza relativa. Un’ampia serie di misure sperimentali è stata acquisita da prove condotte su un canale rettangolare situato presso il Laboratorio di Idraulica dell’Università degli Studi della Basilicata, per differenti valori di pendenza e portata, in condizioni di moto stazionario, con valori intermedi di sommergenza relativa e rapporto di aspetto minore di 7.5

Analysis of river bed dynamic evolution following a landslide dam

Landslides and debris flows can strongly interact with the river network and its mass transport processes, determining modifications of the river pattern with consequent effects on the hydrodynamic phenomena, alterations of the existing morphologies and possible interferences with anthropic works. Modifications of the cross section geometry and channel slope may produce changes in the sediment budget, with consequent repercussions on the stream evolutionary dynamics and its equilibrium configuration, leading to a new river branch arrangement. In this paper, investigations were carried out on a gravel-bed reach in the middle valley of the Noce River in Basilicata (Italy), which in 2007 suffered a progressive morpho-hydrodynamic change caused by a landslide. Because of the phenomenon complexity, mainly due to the mutual interaction between the landslide and the river transport dynamics, an integrated approach that combines field observations and numerical modelling in a spatial scale and natural environment, rarely available in literature, is suggested. The results highlight a satisfying correspondence between the altimetric profiles obtained through the numerical models and those deriving from the field surveys.Peer ReviewedPostprint (published version

Assessment of pressure sources and water body resilience: An integrated approach for action planning in a polluted river basin

The present study develops an integrated methodology combining the results of the water-quality classification, according to the Water Framework Directive 2000/60/ECâ\u80\u94WFD, with those of a mathematical integrity model. It is able to analyse the potential anthropogenic impacts on the receiving water body and to help municipal decision-makers when selecting short/medium/long-term strategic mitigation actions to be performed in a territory. Among the most important causes of water-quality degradation in a river, the focus is placed on pollutants from urban wastewater. In particular, the proposed approach evaluates the efficiency and the accurate localisation of treatment plants in a basin, as well as the capacity of its river to bear the residual pollution loads after the treatment phase. The methodology is applied to a sample catchment area, located in northern Italy, where water quality is strongly affected by high population density and by the presence of agricultural and industrial activities. Nearly 10 years of water-quality data collected through official monitoring are considered for the implementation of the system. The sample basin shows different real and potential pollution conditions, according to the resilience of the river and surroundings, together with the point and diffuse pressure sources acting on the receiving body

Flow-induced vibration of an elastically sphere at high combined mass-damping parameter

The paper reports the results of the experimental analysis on the transverse flow-induced vibration of an elastically mounted rigid sphere in a free surface flow. Simultaneous displacement and velocity measurements have been used to describe the free vibrations. Experiments have been performed referring to low mass ratio value (m*), high combined massdamping parameter (m*ζ), small amplitude (A/D<1) and low values of relative submergence (ratio between water depth and sphere diameter). Preliminary results compared to the literature case studies suggest a different behaviour between the test case of the sphere and those referred to the cylinder mainly concerning the lock-in and hysteresis phenomena