1,720,967 research outputs found
An efficient physics-based modeling strategy for pluvial floods in urban areas with a subgrid scheme for the stormwater drainage network
Full text linkThis study presents an efficient physics-based modeling strategy for simulating urban pluvial floods, which uses a subgrid approach to account for the contribution of (part of) underground drainage pipes. Coupled with a two-dimensional (2D) hydrodynamic model solving the porous version of the shallow water equations for the free-surface flow, the subgrid formulation allows running rain-on-grid (RoG) simulations while avoiding the time-consuming inclusion of the many small-scale components forming the stormwater network, such as one-dimensional (1D) pipes and storm drains. The proposed model accounts for the anisotropic additional conveyance provided by the stormwater drainage networks, assuming that the water level represents both the local free-surface elevation and the piezometric head for flow in pipes. Model parameters such as pipe direction, diameter, roughness, and spacing, can be derived from aerial images and limited surveys, thus reducing the data requirement and allowing for an easier model implementation than with classical dual-drainage models. Different applicative tests demonstrate that the use of the subgrid model ensures reasonable accuracy with low modelling effort and computational cost. The proposed approach offers an efficient and practical solution for pluvial flood assessment, particularly in data-limited and/or large-scale urban areas, providing support for flood management and mitigation strategies
Assessing 40 years of flood risk evolution at the micro-scale using an innovative modeling approach: the effects of urbanization and land planning
Full text linkThe present work is aimed at assessing the change in time of flood risk as a consequence of landscape modifications. The town of San Donà di Piave (Italy) is taken as a representative case study because, as most parts of the North Italy floodplains, it was strongly urbanized and anthropized in the last several decades. As a proxy for flood risk, we use flood damage to residential buildings. The analysis is carried out at the local scale, accounting for changes to single buildings; GIS data such as high-resolution topography, technical maps, and aerial images taken over time are used to track how the landscape evolves over time, both in terms of urbanized areas and of hydraulically relevant structures (e.g., embankments). Flood hazard is determined using a physics-based, finite element hydrodynamic code that models in a coupled way the flood routing within the Piave River, the formation of levee failures, and the flooding of adjacent areas. The expected flood damage to residential buildings is estimated using an innovative method, recently proposed in the literature, which allows estimating how the damage evolves during a single flood event. The decade-scale change in the expected flood damage reveals the detrimental effect of urbanization, with flood risk growing at the pace of a fraction of urbanized areas. The within-event time evolution of the flood damage, i.e., how it progresses in the course of past or recent flood events, reflects changes in the hydrodynamic process of flooding. The general methodology used in the present work can be viewed as a promising technique to analyze the effects on the flood risk of past landscape evolution and, more importantly, a valuable tool toward an improved, well-informed, and sustainable land planning
Flow under vertical sluice gates: Flow stability at large gate opening and disambiguation of partial dam-break multiple solutions
No full textThe present paper deals with two open issues concerning the free orifice flow under vertical sluice gates, namely, the flow stability at large gate openings and the disambiguation of multiple solutions in the case of partial dam-break. The study of these problems, which are mutually connected, is based on ad hoc laboratory experiments and numerical simulations with a computational fluid dynamics model tracking the free surface with the two-phase volume of fluid method. A series of quasi-steady states is used to assess the threshold of relative gate openings that determines the passage from orifice flow to non-interacting flow; in addition, a set of dam-break experiments with partial gate opening (i.e., lower than the initial upstream water level) is performed to find reliable criteria to disambiguate multiple exact solutions supplied by the one-dimensional shallow water theory. It is found that the dependence of contraction and discharge coefficients on the relative gate opening has a dramatic impact on the stability of orifice flow at large gate openings
Fully Developed Open Channel Flow Over Clusters of Freshwater Mussels Partially Buried in a Gravel Bed
Full text linkThe present study uses results of eddy‐resolving numerical simulations to investigate the open channel flow over large clusters of freshwater mussels (Unio elongatulus) partially buried in a rough, gravel bed. The density of the mussels forming the array varies from 26 to 500 mussels/m2. The flow structure is analyzed at large distances from the leading edge of the mussel bed, where the flow can be considered fully developed. The effects of changing the mussel bed density, the filtering discharge, the burial level and the roughness of the bed surface in which mussels are burrowed, are investigated in terms of flow field, turbulent structures, drag forces, and bed shear stresses. It is found that strong interactions occur between energetic eddies generated by the larger gravels on the exposed bed surface and by the mussel shells. Simulations results show that for a burial depth close to 50% and a ratio between the average gravel size and the mussel protruding height of 0.13, the shell induced turbulence becomes dominant for mussel bed densities around 50 mussels/m2. The influence of the bed roughness becomes less relevant with increasing mussel density, as the generation of energetic eddies is mostly controlled by mussel‐to‐mussel interactions. For fixed bed roughness, burial level and filtering velocity, the mean streamwise drag force and the associated drag coefficient for the exposed part of each mussel decrease with increasing mussel density, even if strong variations are observed for individual mussels. For constant mussel bed density and burial level, the mean streamwise drag force and the mean drag coefficient decrease slightly with increasing bed roughness. Increasing the burial level decreases not only the drag forces but also the drag coefficients because of the more streamlined shape of the top of the mussels. Strong active filtering acts toward decreasing the mean streamwise force and the mean drag coefficient. The spanwise drag forces contribute significantly to the total drag force, especially for high mussel bed densities. Based on smooth bed calculations, bed‐averaged shear stresses are reduced in highly dense clusters
Remote sensing for optimal estimation of water temperature dynamics in shallow tidal environments
Full text linkGiven the increasing anthropogenic pressures on lagoons, estuaries, and lakes and considering the highly dynamic behavior of these systems, methods for the continuous and spatially distributed retrieval of water quality are becoming vital for their correct monitoring and management. Water temperature is certainly one of the most important drivers that influence the overall state of coastal systems. Traditionally, lake, estuarine, and lagoon temperatures are observed through point measurements carried out during field campaigns or through a network of sensors. However, sporadic measuring campaigns or probe networks rarely attain a density sufficient for process understanding, model development/validation, or integrated assessment. Here, we develop and apply an integrated approach for water temperature monitoring in a shallow lagoon which incorporates satellite and in-situ data into a mathematical model. Specifically, we use remote sensing information to constrain large-scale patterns of water temperature and high-frequency in situ observations to provide proper time constraints. A coupled hydrodynamic circulation-heat transport model is then used to propagate the state of the system forward in time between subsequent remote sensing observations. Exploiting the satellite data high spatial resolution and the in situ measurements high temporal resolution, the model may act a physical interpolator filling the gap intrinsically characterizing the two monitoring techniques
Flood damage functions based on a single physics- and data-based impact parameter that jointly accounts for water depth and velocity
Full text linkDirect flood damage is commonly assessed using damage models (i.e., vulnerability functions and fragility curves), which describe the relationship between hazard, vulnerability, and the (probability of) damage for items exposed to floods. In this paper, we introduce a non-dimensional impact parameter that, according to the physics of damage mechanisms and/or tuned on field or lab data, combines water depth and flow velocity in a general and flexible form. We then suggest a general approach to assess relative damage functions for items of different nature, subject to either progressive or on–off damage processes. The proposed method enhances traditional tools that use inundation depth as the main (or only) explicative variable, and allows recasting the results from previous studies in an elegant, flexible and unique form. Compared to multivariate models that link flow variables to damage directly, the physics-based approach allows for an intelligible assessment of flood hazard and the associated damage, even in case of scarce or sparse data. The proposed impact parameter and the related procedure to assess the relative damage functions are applied to different kinds of exposed items (people, vehicles, and buildings), demonstrating the general applicability and validity of the proposed method
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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