Università degli Studi di Padova
Civil, Architectural and Environmental Engineering
The overall thermo-hygro-mechanical behavior of concrete is to be investigated, because its bearing capacity is required together with its shielding properties, specifically when concrete structures are exposed to highenergy neutron... more
The overall thermo-hygro-mechanical behavior of concrete is to be investigated, because its bearing capacity is required together with its shielding properties, specifically when concrete structures are exposed to highenergy neutron fluxes, which represent the next generation facilities designed for the production of high energy radioactive ion beams in physics research. Irradiation in the form of either fast and thermal neutrons, primary gamma rays or gamma rays produced as a result of neutron capture, are learnt to affect concrete as well as neutron fluences of the order of 10 19 n/cm 2 and gamma radiation doses of 10 10 rad seem to become critical for concrete strength. The collection of data on concrete samples, variously exposed to neutron radiation, has allowed for defining a law for radiation damage within the FEM research code NEWCON3D, assessing the 3D coupled thermo-hygro-mechanical behavior of concrete, modeled as a multiphase porous medium, both at the macroscale and the mesoscale level. The required damage law is thought to be a function of the neutron flux impinging the concrete shielding wall, and a good estimate of this quantity has been provided by means of a Monte Carlo code developed by CERN and the National Institute of Nuclear Physics of Milan, Italy; this code handles radiation transport calculations and represents at this day one of the most reliable procedures for dealing with the interaction of radiation and matter. The suggested procedure for the radiation damage evaluation has allowed for discussing on differences between mesolevel and macrolevel approaches. Stochastic contour maps of the expected radiation field, properly interfaced with the numerical FE code, have allowed for obtaining a more precise evaluation of the radiation damage front as well as its evolution in time.
- by Carmelo Maiorana
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A recently initiated phase of experimentation and research in the online Distance Learning (DL) is here described. The project has been developed by the Department of Construction and Transportation Engineering of the Faculty of... more
A recently initiated phase of experimentation and research in the online Distance Learning (DL) is here described. The project has been developed by the Department of Construction and Transportation Engineering of the Faculty of Engineering at the University of Padua along with the well-established e-learning experience of the SSIS Veneto (Institute for the Formation of Secondary School's Teachers) of Cà Foscari-University of Venice, in collaboration with the webmaster management of TCN-EnginSoft of Padua. The work deals with teaching methodologies supported by the net, computer communication and information technologies, finalized to give both widespread access to useful resources and to create a more flexible exchange due to net communication. The experimentation of using web-based technologies to support traditional teaching for working students is described; in fact, Internet-based innovations offer opportunities for a curriculum improvement to those categories of students who could be considered at a disadvantage, like worker students or students with ear or motion deafness. ß
- by Carmelo Maiorana and +1
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- Engineering, Education, Structural mechanics
1] In this paper we present early results of laboratory experiments to investigate the transport and diffusion of floating particles (e.g., buoyant seeds) in open channel flow with emergent vegetation. The experiments are aimed at... more
1] In this paper we present early results of laboratory experiments to investigate the transport and diffusion of floating particles (e.g., buoyant seeds) in open channel flow with emergent vegetation. The experiments are aimed at providing a better understanding of the relevant particle-vegetation interaction mechanisms responsible for the observed diffusion processes. Qualitative observational data are then used to set up a stochastic model for floating particle transport and diffusion. Quantitative observations, such as the distribution of distances travelled by a particle before it is permanently captured by a plant and the arrival-time distributions at prescribed cross sections along the vegetated test section, are instead used to calibrate and validate the model. The comparison between theoretical predictions and experimental results is quite satisfactory and suggests that the observed relevant aspects of the particle-vegetation interaction processes are properly described in the model. Citation: Defina, A., and P. Peruzzo (2010), Floating particle trapping and diffusion in vegetated open channel flow, Water Resour. Res., 46, W11525,
Steady flow regimes in a free surface flow approaching an obstacle are described and extensively discussed. Attention is focused on the phenomenon of hydraulic hysteresis, and a simple one-dimensional theory to predict its occurrence in a... more
Steady flow regimes in a free surface flow approaching an obstacle are described and extensively discussed. Attention is focused on the phenomenon of hydraulic hysteresis, and a simple one-dimensional theory to predict its occurrence in a supercritical channel flow is proposed. It is shown that in many cases knowledge of the Froude number of the undisturbed approaching flow and of a geometric characteristic of the obstacle allows for a reliable prediction of the flow state. In the region of multiple regimes, however, the previous history of the flow must also be known.
1] Shallow microtidal basins are characterized by extensive areas of tidal flats that lie within specific ranges of elevation. These landforms are inherently flat and their evolution strongly depends on the balance between sedimentary and... more
1] Shallow microtidal basins are characterized by extensive areas of tidal flats that lie within specific ranges of elevation. These landforms are inherently flat and their evolution strongly depends on the balance between sedimentary and erosive processes. Here we present a stochastic point model for tidal flat evolution to study the influence of tidal currents and wind waves on tidal flat equilibrium. The model accounts for sediment deposition and sediment resuspension by wind waves and is applied to the Venice lagoon, Italy. Model results show that the equilibrium elevation of tidal flats depends on the relationship between shear stress caused by wind waves and depth. It is found that wind wave shear stresses peak for a specific water depth which is a function of the local wave climate and fetch distance. Above this critical depth, tidal flats are unstable, since an increase in elevation reduces wave height and therefore erosion, preventing the system from recovering equilibrium conditions. The critical depth for equilibrium depends on fetch distance but not on substrate characteristics and, for the Venice lagoon, varies from À1.5 m for unlimited fetch (>3000 m) to À0.6 m for a fetch of 1000 m. The sediment characteristics determine instead the sediment input necessary to maintain the tidal flat in equilibrium at a specific elevation. Sediment inputs for tidal flats composed of fine sand need to be much higher than those required for tidal flats composed of cohesive material. Finally, we show that the spring-neap modulation of the tide is critical for tidal flat equilibrium, with erosive events occurring mostly during spring conditions that equilibrate the sediment deposition during neap tide. Citation: Fagherazzi, S., C. Palermo, M. C. Rulli, L. Carniello, and A. Defina (2007), Wind waves in shallow microtidal basins and the dynamic equilibrium of tidal flats,
1] A two-dimensional numerical model is used to study tidal hydrodynamics and distribution of bed shear stresses in the Fly River delta, Papua New Guinea. The model describes the propagation of the tidal wave within the delta and along... more
1] A two-dimensional numerical model is used to study tidal hydrodynamics and distribution of bed shear stresses in the Fly River delta, Papua New Guinea. The model describes the propagation of the tidal wave within the delta and along the river. Model results indicate that tidal discharge at the mouths of the distributary channels is between 10 and 30 times larger than the river discharge, and that the upstream part of the delta is flood-dominated, whereas near the mouth, the delta is ebb-dominated. Numerical simulations allow us to investigate the sensitivity of fluxes and bottom stresses with respect to the variations of sea level and the area of delta islands. The results suggest that a decrease in the total area of the delta occupied by islands increases the tidal prism and, therefore, the bed shear stresses. Similarly, an increase in sea level reduces the dissipation of the tidal signal and speeds up the propagation of the tidal wave within the delta, thus yielding higher discharges and increased bed shear stresses.
1] A numerical model that combines wind waves with tidal fluxes in a tidal basin is presented and validated. The model couples a hydrodynamic finite element module based on the shallow water equations with a finite volume module that... more
1] A numerical model that combines wind waves with tidal fluxes in a tidal basin is presented and validated. The model couples a hydrodynamic finite element module based on the shallow water equations with a finite volume module that accounts for the generation and propagation of wind waves. The wave module solves the wave action conservation on the same triangular mesh used in the hydrodynamic module, thus efficiently reproducing the physical relationships between waves and tide propagation. The combined wind wave-tidal model is applied to the Venice lagoon, Italy. The highly irregular bathymetry of this tidal environment, characterized by deep channels, emergent salt marshes, and extensive tidal flats, suggests the introduction of specific hypotheses that simplify the governing equations with a noteworthy increase in efficiency and robustness of the algorithm. Particular attention is devoted to the dissipation of wave energy at the steep boundaries between channels, tidal flats, and salt marshes. Simulations of wave fields generated under specific wind conditions are presented and discussed. The model results are compared, with good agreement, to field data collected in different stations inside the lagoon of Venice. Finally, evidence of the complementary effect of tidal currents and wind waves on bottom shear stresses is presented using the results of different simulations.
- by Andrea Defina and +1
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- Wave Energy, Finite Element, Multidisciplinary, Shear Stress
1] The finite-element model WWTM is applied to a system of lagoons at the Virginia Coast Reserve, USA. The model solves the shallow water equations to compute tidal fluxes, and is equipped with a wave propagation module to calculate wave... more
1] The finite-element model WWTM is applied to a system of lagoons at the Virginia Coast Reserve, USA. The model solves the shallow water equations to compute tidal fluxes, and is equipped with a wave propagation module to calculate wave height during local wind events. The model is validated using measured water elevations, wave heights, and periods at five locations within the lagoon system. Scenarios with different wind conditions, storm surges, and relative sea level are simulated. Results are analyzed in terms of bottom shear stresses on the tidal flats, a measure of sediment resuspension potential, and total wave energy impacting the marsh boundaries, which is the chief process driving lateral marsh erosion. Results indicate that wave energy at the marsh boundaries is more sensitive to wind direction than are bottom shear stresses. Wave energy on marsh boundaries and bottom shear stresses on the tidal flats increase with sea level elevation, with the former increasing almost ten times more than the latter. Both positive and negative feedbacks between wave energy at the boundaries and bottom shear stresses are predicted, depending on the fate of the sediments eroded from the salt marsh boundaries.
- by Andrea Defina and +1
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- Wave Energy, Sea Level, Multidisciplinary, Sea level rise
1] The drainage density of a network is conventionally defined as (proportional to) the ratio of its total channelized length divided by the watershed area, and in practice, it is defined by the statistical distribution and correlation... more
1] The drainage density of a network is conventionally defined as (proportional to) the ratio of its total channelized length divided by the watershed area, and in practice, it is defined by the statistical distribution and correlation structure of the lengths of unchanneled pathways. In tidal networks this requires the definition of suitable drainage directions defined by hydrodynamic (as opposed to topographic) gradients. In this paper we refine theoretically and observationally previous analyses on the drainage density of tidal networks developed within tidal marshes. The issue is quite relevant for predictions of the morphological evolution of lagoons and coastal wetlands, especially if undergoing rapid changes owing, say, to combined effects of subsidence and sea level rise. We analyze 136 watersheds within 20 salt marshes from the northern lagoon of Venice using accurate aerial photographs and field surveys taken in different years in order to study both their space and time variability. Remarkably, the tidal landforms studied show quite different physical and ecological characteristics. We find a clear tendency to develop characteristic watersheds described by exponential decays of the probability distributions of unchanneled lengths, and thereby a pointed absence of scale-free distributions which instead usually characterize fluvial settings. We further find that total channel length relates well to watershed area rather than to tidal prism, a somewhat counterintuitive result on the basis of dynamical considerations. Finally, we show that in spite of the apparent site-specific features of morphological variability, conventional measures of drainage density appear to be quite constant in space and time, indicating a similarity of form. We show that such similarity is an artifact of the Hortonian measure. Indeed, important morphological differences, most notably in stream (or link) frequency reflecting the true extent of branching innervating the marshes and the sinuosity of tidal meandering, may only be captured by introducing measures of the extent of unchanneled flow paths based on hydrodynamics rather than topography and geometry.
1] This paper deals with hydrologic studies relevant to the works engineered for the protection of the city of Venice (Italy) from major flooding under significant climate change scenarios. Such works foresee the temporary closure of the... more
1] This paper deals with hydrologic studies relevant to the works engineered for the protection of the city of Venice (Italy) from major flooding under significant climate change scenarios. Such works foresee the temporary closure of the lagoon surrounding the city to tidal exchanges with the Adriatic Sea in times of sea storm surges via the operation of a set of mobile gates. A general hydrologic model of the $2000 km 2 mainland contributing runoff to the lagoon of Venice is coupled in time and space with a 2-D finite element model of the relevant tidal hydrodynamics to forecast maximum lagoonal surges in times of closure. We also study the impacts of run-through discharges bypassing the mobile gates and wind setups at time scales comparable to the foreseen closures (from a few to tens of hours). Climate change scenarios are recapitulated by up to +50 cm relative sea level rises by 2100 (the projected lifetime of the current protection works). Possible flooding of the city due to residual fluxes entering the lagoon during prolonged closures is examined. A probabilistic framework is also proposed for computing the statistics of maximum lagoon rises and stage-rise durations. Our studies suggest the adequacy of the design of temporary closures with respect to flooding and provide methods for general exercises in assessing the impact of regional climate change scenarios.
1] This paper deals with hydrologic studies relevant to the works engineered for the protection of the city of Venice (Italy) from major flooding under significant climate change scenarios. Such works foresee the temporary closure of the... more
1] This paper deals with hydrologic studies relevant to the works engineered for the protection of the city of Venice (Italy) from major flooding under significant climate change scenarios. Such works foresee the temporary closure of the lagoon surrounding the city to tidal exchanges with the Adriatic Sea in times of sea storm surges via the operation of a set of mobile gates. A general hydrologic model of the $2000 km 2 mainland contributing runoff to the lagoon of Venice is coupled in time and space with a 2-D finite element model of the relevant tidal hydrodynamics to forecast maximum lagoonal surges in times of closure. We also study the impacts of run-through discharges bypassing the mobile gates and wind setups at time scales comparable to the foreseen closures (from a few to tens of hours). Climate change scenarios are recapitulated by up to +50 cm relative sea level rises by 2100 (the projected lifetime of the current protection works). Possible flooding of the city due to residual fluxes entering the lagoon during prolonged closures is examined. A probabilistic framework is also proposed for computing the statistics of maximum lagoon rises and stage-rise durations. Our studies suggest the adequacy of the design of temporary closures with respect to flooding and provide methods for general exercises in assessing the impact of regional climate change scenarios.
1] The drainage density of a network is conventionally defined as (proportional to) the ratio of its total channelized length divided by the watershed area, and in practice, it is defined by the statistical distribution and correlation... more
1] The drainage density of a network is conventionally defined as (proportional to) the ratio of its total channelized length divided by the watershed area, and in practice, it is defined by the statistical distribution and correlation structure of the lengths of unchanneled pathways. In tidal networks this requires the definition of suitable drainage directions defined by hydrodynamic (as opposed to topographic) gradients. In this paper we refine theoretically and observationally previous analyses on the drainage density of tidal networks developed within tidal marshes. The issue is quite relevant for predictions of the morphological evolution of lagoons and coastal wetlands, especially if undergoing rapid changes owing, say, to combined effects of subsidence and sea level rise. We analyze 136 watersheds within 20 salt marshes from the northern lagoon of Venice using accurate aerial photographs and field surveys taken in different years in order to study both their space and time variability. Remarkably, the tidal landforms studied show quite different physical and ecological characteristics. We find a clear tendency to develop characteristic watersheds described by exponential decays of the probability distributions of unchanneled lengths, and thereby a pointed absence of scale-free distributions which instead usually characterize fluvial settings. We further find that total channel length relates well to watershed area rather than to tidal prism, a somewhat counterintuitive result on the basis of dynamical considerations. Finally, we show that in spite of the apparent site-specific features of morphological variability, conventional measures of drainage density appear to be quite constant in space and time, indicating a similarity of form. We show that such similarity is an artifact of the Hortonian measure. Indeed, important morphological differences, most notably in stream (or link) frequency reflecting the true extent of branching innervating the marshes and the sinuosity of tidal meandering, may only be captured by introducing measures of the extent of unchanneled flow paths based on hydrodynamics rather than topography and geometry.