1,721,008 research outputs found
Application of lattice gas techniques to the study of sediment erosion and transport caused by laminar sheet flow
No full textCoupling Flood Propagation Modeling and Building Collapse in Flash Flood Studies
No full textFlash flood events threaten the safety of people either because of the direct impact of the flow on people and car stability or because of structural damages to buildings. Traditionally, buildings stability is assessed with ex post analyses by vulnerability models applied to the results of hydraulic models where buildings are permanently present on the flooded domain. However, in the case of building collapse, the geometry of the computational domain should be adapted during the simulation and, accordingly, a more realistic approach would require the coupling of hydraulic modeling and structural analysis. This paper provides an example of a simple methodology implementing this procedure in HEC-RAS 2D using the results from a physically-based structural vulnerability model for masonry buildings. After positively testing the capabilities of the solver to model the flow field around isolated obstacles as well as the flow field in urban districts on complex bathymetries, the proposed procedure is applied to the reconstruction of the flood event in the Corna di Darfo village (Northern Italy) after the collapse of the Gleno dam in 1923
A conceptual model of vehicles stability in flood flows
No full textA large number of flood-related fatalities in urban areas are due to drowning of people in vehicles. Therefore, reliable models of the vulnerability of vehicles impacted by flow are necessary for risk assessment and emergency management. This paper includes the effect of the sloping terrain in a four-parameter dimensionless conceptual model of the stability of vehicles impacted by flow. A set of parameters was calibrated on the basis of experimental data from the literature in order to reproduce the average stability limits of a wide range of vehicles tested in laboratory conditions. These parameters can also be used to represent the average stability conditions of a wide variety of circulating vehicles as required in flood risk mapping
Horizontal Pressure Gradient Parameterization for One-Dimensional Lake Models
Full text linkThis work presents a new method for closure of horizontally averaged 1-D thermohydrodynamic equations in an enclosed reservoir by parameterizing the horizontal pressure gradient usually omitted in 1-D lake models. Horizontal pressure gradient is computed using an auxiliary multilayer model where horizontal structure of speed and pressure is given by 1-st Fourier mode. A major effect of new parameterization in 1-D lake model is the emergence of explicitly reproduced H1 seiche modes. The parameterization is implemented in the LAKE model, with minor (2–4%) extra computational cost imposed. The model is applied to Lake Iseo (Italy), and calculated temperature series are compared to measured ones in upper, middle, and deep portions of metalimnion. The amplitude of seiche-induced temperature oscillations well matched the observed amplitude by tuning the bottom friction coefficient only. The synoptic variability of thermocline vertical displacement caused by wind events is well reproduced by the model. The dominant peak of quasi-diurnal period in temperature power spectrum was captured in simulations as well. Using the new parameterization of horizontal pressure gradient extends the applicability of a 1-D lake model formulation to small lakes, which size is less than internal Rossby radius, and where pressure gradient dominates over Coriolis force
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
Dam-Break Wave Propagation in Alpine Valley with HEC-RAS 2D: Experimental Cancano Test Case
Full text linkFlood modeling by numerical solution of the two-dimensional (2D) shallow-water equations is ordinary practice. HEC-RAS 2D was recently released along with a suite of test cases showing the very good performance of the code in many practical situations. However, validation test cases aimed at demonstrating the capability of the software to deal with dam-break floods on very steep and irregular bathymetries are very limited. This paper tests HEC-RAS 2D against the discharge hydrographs measured in a historical physical model built in Froude similitude to analyze the consequences of the hypothetical collapse of the Cancano I dam (northern Italy) and the propagation of the resulting dam-break wave along the 15-km reach of the downstream alpine valley. The experimental hydrographs and the measured extent of the flooded areas are well reproduced by the numerical simulations. Moreover, the results obtained with HEC-RAS 2D are in very good agreement with those obtained using TELEMAC 2D, which confirms the suitability of the HEC-RAS 2D software for dam-break flood studies in steep alpine valleys. The data of the test case are made available to the scientific community for validation purposes
Intermittent meromixis controls the trophic state of warming deep lakes
Full text linkVertical mixing modulates nutrient dynamics in lakes. However, surface warming reduces the range of vertical mixing and the probability of full circulation events. Important consequences of reduced vertical mixing include the sequestration of phosphorus (P) within a stagnant zone and the promotion of oligotrophication. Nevertheless, warming-induced shifts from full to partial mixing (meromixis) are not permanent and are partially reversible during exceptionally cold or windy winters. In this study, we investigated how intermittent meromixis affects lake P budgets. We examined the P cycle of a perialpine lake with variable mixing depths by pairing sedimentation and release flux measurements with sedimentary archives. We found that the amount of dissolved P surpassed that of the potentially mobile P in the sediments by a 13:1 ratio. At least 55% of the settled P was rapidly released to bottom waters isolated from flushing, illustrating the general biogeochemical mechanism that promotes deep-water P storage when lakes undergo warming. This storage process is abruptly inverted when meromixis suddenly retreats, deeper mixing introduces P pulses to the surface waters, thereby promoting phytoplankton proliferation. Our estimates showed that lakes containing up to 40% of the global freshwater volume could shift towards intermittent meromixis if the atmospheric warming trend continues. Thus, these lakes might accumulate 0–83% of their P load in irregularly circulating waters and are prone to large P pulses
- …
