1,720,979 research outputs found
On the impact of urbanization on flood hydrology of small ungauged basins: the case study of the Tiber river tributary network within the city of Rome
No full textThe small ungauged basins of the highly urbanized area of the city of Rome are often the subject of critical flood conditions for the significant human-made transformations. In this work the EBA4SUB framework, implementing the hydrogeomorphic width function instantaneous unit hydrograph rainfall run-off model, and using digital elevation model, land use and synthetic precipitation as main input information, is applied for evaluating extreme hydrologic forcing conditions at the basic scale. The goal is to understand the rationale behind the observed increasing frequency of local urban inundations that are also observed in the uplands. Results present the impact of urbanization expressed by both the run-off coefficient, the artificial drainage, impacted by paved surfaces and a dramatic number of river–road intersections (i.e. culverts), and the upstream to downstream non-natural scaling behaviour of hydrologic parameters and in particular the peak discharge per unit drainage area
Live monitoring of the distributed strain field in impulsive events through fiber Bragg gratings
No full textIn this paper, we propose a measurement technique based on local strain measurements to perform real-time reconstruction of the overall structural deformation and the distributed stress field produced by the impact of a body on a water free surface. In particular, we seek establishing a measurement chain capable of acquiring and elaborating the signals at high frequency, so that it can be utilized to study rapidly varying strain fields, such as those occurring in impulsive events. Fiber Bragg gratings are utilized to sense the local structural deformation. Experiments are conducted on flexible plastic wedges with variable deadrise angles impacting on a quiescent fluid surface. The experimental tests are performed in free fall and we explore variations of the entry velocity by varying the drop height. The structural deformation is reconstructed from point-wise strain measurements utilizing a modal reconstruction methodology. The impact dynamics are analysed through accelerometers and linear position sensors. Results show that the impact behaviour of the flexible body is characterized by a main overall deformation where the structure is distorted in the direction of the loading, whereby marked vibrations, whose amplitude increase with the entry velocity, dominate the dynamic response. The influence of the mode shapes considered in the present analysis on the accuracy of the results is also observed. The proposed methodology allows for a fairly high acquisition frequency, which translates into a real-time structural reconstruction technique. Results show that the proposed methodology can be a valuable tool for the live monitoring of structures undergoing impact events
Multi-component Lattice Boltzmann simulation of the hydrodynamics in drip emitters
Full text linkIn this paper, we propose a fast and efficient numerical technique based on the Lattice Boltzmann method (LBM) to model the flow through a reference drip emitter geometry. The aim of the study is to demonstrate the applicability of the LBM as a reliable simulation tool for the hydraulic optimisation of irrigation systems. Results for the water flow through a rectangular drip emitter are in good agreement with literature numerical and experimental data. Furthermore, we demonstrate the feasibility of the proposed model to simulate a multi-component flow that could be used to simulate the presence of additives, contaminants, and suspended particles
On the investigation of the performances of a DEM-based hydrogeomorphic floodplain identification method in a large urbanized river basin: the Tiber river case study in Italy
No full textFloodplains are critical landscape features for their importance in both ecohydrological and socio-economic terms.
River valleys are, in fact, the domain where the interdependence of the complex human-environmental interface
is more significant. Riparian zones, along perennial channels, where the frequency of saturation is high and most
flooding occurs, are also the areas where urban areas and infrastructures (e.g. highways, bridges, railways, etc)
are more present. This is mainly due to geomorphologic conditions since those areas are predominantly flat and
easier to develop. One of the more challenging issues under changing climatic, environmental and human drivers
for implementing efficient current and future urban plans is to accurately and timely identify, map and characterize
the potential flooding scenarios of floodplains. This is currently achieved by implementing detailed topographic,
hydrologic and hydraulic studies for flood modeling and mapping for different frequencies (i.e. return time), but
those activities are rarely implemented at the large (river basin) scale for their economic cost and time of implementation.
In addition to that, flood map updating is not as frequent as needed for following the rapid changing
land use conditions. As a result, it is very often the case that urban plans are based on heterogeneous and discontinuous
flood map information. Nevertheless, several recent researches demonstrated the potential for the use of high
resolution digital elevation models (DEMs) to define the floodplain feature by means of automated hydrogeomorphic
methods. This means identifying the flood prone area by filtering potentially inundated cells by implementing
proper morphological and hydrological analyses. In this work we implemented the flooplain identification model
proposed by Nardi et al. (WRR, 2006) which automatically extract the river network and estimate flood water levels
according to a predefined scaling Leopold law. Inundated areas are consequently identified as those river buffers,
draining towards the channel, with an elevation that is less than the maximum flow depth of the corresponding outlet.
Keeping in mind that this hydrogeomorhic model performances are strictly related to the quality and properties
of the input DEM and that the intent of this kind of methodology is not to substitute standard flood modeling and
mapping methods, in this work the performances of this approach are qualitatively evaluated by comparing results
with standard flood maps. The Tiber river basin was selected as case study, one of the main river basins in Italy
covering a drainage area of approximately 17.000 km2. This comparison is interesting for understanding the performance
of the model in a large and complex domain where the impact of the urbanization matrix is significant.
Results of this investigation confirm the potential of such DEM-based floodplain mapping models for providing
a fast timely homogeneous and continuous inundation scenario to urban planners and decision makers, but also
the drawbacks of using such methodology where the humans are significantly and rapidly modifying the surface
properties
On the simulation of floods in a narrow bending valley. The malpasset dam break case study
Full text linkIn this paper, we investigate the performance of three-dimensional (3D) hydraulic modeling when dealing with river sinuosity and meander bends. In river bends, the flow is dominated by a secondary current, which has a key role on the flow redistribution. The secondary flow induces transverse components of the bed shear stress and increases the velocity in outward direction, thus generating local erosion and riverbed modifications. When in river bends, the 3D processes prevail, and a 3D computational fluid dynamics (CFD) model is required to correctly predict the flow structure. An accurate description of the different hydrodynamic processes in mildly and sharply curved bends find a relevant application in meanders migration modeling. The mechanisms that drive the velocity redistribution in meandering channels depend on the river's roughness, the flow depth (H), the radius curvature (R), the width (B) and the bathymetric variations. Here, the hydro-geomorphic characterization of sharp and mild meanders is performed by means of the ratios R/B, B/H, and R/H, and of the sinuosity index. As a case study, we selected the Malpasset dam break on the Reyran River Valley (FR), as it is perfectly suited for investigating performances and issues of a 3D model in simulating the inundation dynamics in a river channel with a varying curvature radius
Perimetrazione delle aree inondabili
No full textSono discusse le più recenti innovazioni della ricerca sulla modellazione fluidodinamica (CFD) a confronto con i classici approcci riconducibili alle equazioni tipo shallow water e alle equazioni di Navier-Stokes. Vengono esposti i fondamenti del Lattice Boltzmann Method secondo le ipotesi di Bhatnagar–Gross–Krook. Il lavoro fornisce i risultati computazionali di alcuni casi di studio notevoli
Metodo lattice boltzmann per la simulazione di correnti rapidamente variate
No full textLa modellazione tridimensionale (3D) delle correnti superficiali è un argomento di notevole interesse per la crescente necessità di verifica numerica degli scenari di progettazione di strutture, infrastrutture civili nonché per la progettazione e protezione del territorio e dell’ambiente in genere. La caratterizzazione numerica 3D in ambito professionale ha da sempre incontrato difficoltà sia per quanto riguarda le ingenti risorse computazionali richieste che nella rappresentazione numerica dei complessi ed eterogenei processi fisici che intervengono. La simulazione di geometrie complesse è un altro fattore che ha impedito la rapida diffusione dei codici di calcolo 3D nella pratica ingegneristica. I modelli Navier-Stokes e SPH rappresentano esempi comuni di schemi numerici influenzati da queste problematiche. In questa memoria viene proposto ed implementato un modello 3D basato sullo schema del Lattice Boltzmann Method (LBM) ottimizzato per il trattamento di geometrie complesse ed applicato ai tipici esempi di flussi tridimensionali quali derivanti da rotture arginali o da onde a fronte ripido che si propagano in ambito urbano. Alcuni test numerici di verifica dell’adattabilità ed efficienza computazionale dimostrano le potenzialità del modello LBM in ambito ingegneristico
Enhanced energy dissipation through 3D printed bottom geometry in Tuned Sloshing Dampers
No full textThis paper presents an experimental investigation about the dissipation properties of Tuned Sloshing Dampers (TSDs) characterized by different bottom geometries. An experimental campaign on sloped and rounded shaped TSDs is carried out considering a uni-directional harmonic base motion, by varying the water level and the excitation characteristics, i.e. amplitude and frequency. Results are compared with those obtained on a rectangular flat bottom TSD and benchmarked against a classic Tuned Mass Damper (TMD). The present study demonstrates that a TSD with a suitably modified bottom shape can significantly outperform a traditional flat-bottom TSD in terms of maximum amount of dissipated energy and robustness against frequency mistuning
Sull’ottimizzazione di un metodo semplificato su base idrogeomorfologica per la caratterizzazione geometrica delle aree golenali su larga scala
No full textLa delimitazione preliminare delle aree potenzialmente allagabili con metodi semplificati alla scala del bacino idrografico è un argomento di attuale interesse. Tali metodi costituiscono, da un lato, un valido supporto per la necessaria attività di definizione preliminare del dominio di studio dei Piani di Assetto Idrogeologico (PAI) e, dall’altro, rappresentano uno strumento per la zonazione su larga scala del rischio idraulico di bacini non strumentati. Il presente lavoro illustra gli aspetti applicativi di una procedura di caratterizzazione idrogeomorfologica, ottimizzata in ambiente GIS, che consente l’analisi quantitativa della geometria e delle proprietà idrologico-idrauliche del’alveo e delle aree golenali basata principalmente sui modelli digitali delle elevazioni (DEM) e su alcune ipotesi di analisi semplificata della forzante idrologica. Nel metodo presentato, rispetto a (Nardi et al., 2004, 2006), sono implementati: i) un criterio più accurato di definizione della direzione media di propagazione delle piena; ii) alcuni algoritmi che consentono di ottenere risultati non condizionati dagli errori del DEM (i.e.: depressioni ed aree pianeggianti artificiali). Tali integrazioni del codice di calcolo originario (Nardi et al., 2006) permettono una più accurata stima, sia della geometria dell’area allagabile, sia dei relativi stati idrologico-idraulici. Ciò consente l’utilizzo della metodologia proposta come strumento di identificazione speditiva delle aree potenzialmente allagabili di qualsiasi tronco fluviale ricadente in piccoli bacini fluviali e costieri più o meno urbanizzati fino ai grandi bacini naturali dei paesi in via di svilupp
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