Abstract. This paper presents numerical simulations of free surface flows induced by a dam break comparing the shallow water approach to fully three-dimensional simulations. The latter are based on the solution of the complete set of Reynolds-Averaged Navier-Stokes (RANS) equations coupled to the Volume of Fluid (VOF) method.The methods assessment and comparison are carried out on a dam break over a flat bed without friction, a dam break over a triangular bottom sill and a dam break flow over a 90 • bend. Experimental and numerical literature data are compared to present results.The results demonstrate that the shallow water approach, even if able to sufficiently reproduce the main aspects of the fluid flows, loses some three-dimensional phenomena, due to the incorrect shallow water idealization that neglects the three-dimensional aspects related to the gravity force.

The simulation of multiphase flows is an outstanding challenge, due to the inherent complexity of the underlying physical phenomena and to the fact that multiphase flows are very diverse in nature, and so are the laws governing their dynamics. In the last two decades, a new class of mesoscopic methods, based on minimal lattice formulation of Boltzmann kinetic equation, has gained significant interest as an efficient alternative to continuum methods based on the discretisation of the NS equations for non ideal fluids. In this paper, three different multiphase models based on the lattice Boltzmann method (LBM) are discussed, in order to assess the capability of the method to deal with multiphase flows on a wide spectrum of operating conditions and multiphase phenomena. In particular, the range of application of each method is highlighted and its effectiveness is qualitatively assessed through comparison with numerical and experimental literature data.

A large-scale floodplain delineation algorithm is applied to identify potentially inundated areas at the basin scale. The model, which mainly uses a digital elevation model (DEM) and design flood peak discharge at the outlet as input data, is implemented within a geographic information system (GIS). It implements a preliminary GIS-based terrain analysis framework for estimating the stream network, surface flow direction and drainage grids, while the core algorithm implements an automated fluvial cross-section extraction for discharge and flow height estimation. The delineation is then implemented by filtering the floodplain cells as those cells whose elevation is lower than the corresponding channel flow height. The proposed 'hydrogeomorphic floodplain', obtained on the Tiber River basin (approx. 17 000 km ) avec la reconnaissance topographique à 90 m de résolution mondiale par le radar de la navette spatiale de la NASA (SRTM) est comparée aux cartes officielles des inondations de l'Autorité du bassin du fleuve Tibre. L'étude de cas présentée montre la possibilité d'utiliser un algorithme de SIG automatisé et les données de télédétection largement disponibles pour l'identification préalable de l'empreinte des plaines inondables à l'échelle mondiale.

The 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.

This paper describes the application of detailed computational fluid dynamics (CFD) to simulate the formation and propagation of waves generated by the impact of landslide material with water. The problem is schematised as a multiphase-multicomponent fluid flow: compressible air, water and transported alluvial material. The landslide simulation is performed by means of a hybrid approach: as a rigid solid body slipping down along an inclined slope until it starts penetrating the water body. The CFD model solves the Navier-Stokes equations with the RNG k-ɛ turbulence closure scheme and the volume of fluid multiphase method, which maintains the interface as a sharp front. The governing equations are solved using the commercial CFD code, FLUENT. The computed results are compared with experimental data reported in the literature. The model is then applied to simulate the 1958 Lituya bay Tsunami event with a 2D a simplified geometry and the results are compared to others found in literature.

Abstract:In 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.

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Various mechanical, ocean, aerospace and civil engineering problems involve solid bodies impacting the water surface and often result in complex coupled dynamics, characterized by impulsive loading conditions, high amplitude vibrations and large local deformations. Monitoring in such problems for purposes such as remaining fatigue life estimation and real time damage detection is a technical and scientific challenge of primary concern in this context. Open issues include the need for developing distributed sensing systems able to operate at very high acquisition frequencies, to be utilized to study rapidly varying strain fields, with high resolution and very low noise, while scientific challenges mostly relate to the definition of appropriate signal processing and modeling tools enabling the extraction of useful information from distributed sensing signals. Building on previous work by some of the authors, we propose an enhanced method for real time deformed shape reconstruction using distributed FBG strain measurements in curved bodies subjected to impulsive loading and we establish a new framework for applying this method for structural health monitoring purposes, as the main focus of the work. Experiments are carried out on a cylinder impacting the water at various speeds, proving improved performance in displacement reconstruction of the enhanced method compared to its previous version. A numerical study is then carried out considering the same physical problem with different delamination damages affecting the body. The potential for detecting, localizing and quantifying this damage using the reconstruction algorithm is thoroughly investigated. Overall, the results presented in the paper show the potential of distributed FBG strain measurements for real time structural health monitoring of curved bodies under impulsive hydrodynamic loading, defining damage sensitive features in terms of strain or displacement reconstruction errors at selected locations along the structure.