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Lakes play an important role in providing various ecosystem services. However, stressors such as climate change, land use, or land-cover change threaten the ecological functions of lakes. National and international legislations address these threats and establish consistent, long-term monitoring schemes. Remote sensing techniques based on the use of Unmanned Aerial Vehicles (UAV) have recently been demonstrated to provide accurate and low-cost spatio-temporal views for the assessment of the ecological status of aquatic ecosystems and the identification of areas at risk of contamination. Few studies have been carried out so far on the employment of these tools in the monitoring of lakes. Therefore, high-resolution UAV surveys were used to analyse and evaluate natural and anthropogenic impacts on the habitat status of a volcanic lake in a protected area. Five UAV flights took place during a year-long cycle (November 2020 to November 2021) in a volcanic lake located in southern Italy. For each flight performance, an orthomosaic of georeferenced RGB images was obtained, and the different features of interest were monitored and quantified using automated processing in a GIS environment. The UAV images made it possible not only to estimate the flooded shores but also to detect the impact of human-made structures and infrastructures on the lagoon environment. It has been possible to observe how the rapid changes in lake-water level have led to the submersion of about 90.000 m2 of terrain in winter, causing the fragmentation and degradation of habitats, while the connectivity of the natural ecosystem has been threatened by the presence of the road around the lake. The proposed methodology is rather simple and easily replicable by decision makers and local administrators and can be useful for choosing the best restoration interventions.

Vortex-induced vibrations (VIV) in systems with more than one degree of freedom often present complex synchronization among the motion components, also hidden by the randomness that characterizes the motion itself. A phase average method has been here developed and applied to the displacements of a tethered sphere, at low mass and damping, to analyze its xy trajectories over a wide range of reduced velocities, 5 ≤ U* ≤ 25 (Reynolds numbers, 5.1 × 103 ≤ Re ≤ 2.67 × 104). This method has allowed the identification of both the periodic and chaotic contribution of each motion component, accurately reconstructing the underlying trajectory periodic pattern. The two classical vibration modes, I and II, have been also observed. The method developed here was able to better rebuild the experimental data compared to other methods found in the relevant literature, providing useful insights into the study of the dynamic response of a freely-oscillating tethered sphere immersed in a steady flow.

Modelling and evaluating the resilience of environmental systems has recently raised significant interest among both practitioners and researchers. However, it has not yet been used to measure the absorption and recovery capacities of a river subject to varying levels of pollution due to natural and anthropic sources of contamination within the basin. Fast worldwide population growth and climate change are contributing to an increased degradation status in surface water bodies and to a decreased efficiency of their natural self-purification processes. Decision-makers are, therefore, more and more encouraged to implement alternative management strategies focussed on improving the system resilience to current and future perturbations. To this end, a novel Water Resilience Index (WRI), based on different quality parameters, was developed,and it is here proposed to estimate the ability of the river Bacchiglione, located in Northeast Italy, absorb continuous and unpredictable changes due to potential effects of point sources of pollution, that is,urban and industrial wastewater, and still maintain its vital functions. This new index is integrated in a mathematical model, which represents the river as an influence diagram where the nodes are the gauged stations and the arcs are the fluvial reaches among the stations, to identify the river reaches in need of resilience improvement. In addition, in order to simplify the analytical procedure and lower the costs and times of the monitoring activities, aprincipalcomponentanalysis is also used, as it is able to reduce the number of the water quality parameters to be collected from the sampling stations, distributed along the main river, and thus to calculate a minimum WRI. The good agreement between the results obtained by both the original and minimum WRI shows the effectiveness of the proposed methodology. This approach could be applied to all basins with the same issues, and not just in the Italian case study here analysed, as it might be a valid tool to plan interventions and mitigation actions, protecting the resource from pollution risks and achieving environmental quality and Sustainable Development Goals both in the water bodies and their surrounding territories. In addition, this strategy could be integrated in the existing models supporting local decision-makers and administrators, aiming at increasing the resilience of urban and rural areas to pollution phenomena and facilitating the development of effective policies to reduce the impacts of global change on water quality.

In narrow open channels, the three-dimensional nature of the flow and the transport momentum from the sidewalls to the central region cause the maximum longitudinal velocity to occur below the water surface. The entropy model is unable to accurately describe the velocities near the free surface when the dip phenomenon exists. The present paper proposes a new dip-modified entropy law for steady open channel flows, which consists of three additional terms: the first one similar to Coles&rsquo, function, the second one linearly proportional to the logarithmic distance from the free surface, and the third one depending on the cubic correction near the maximum velocity. The validity of the new model was tested on a set of laboratory measurements carried out in a straight rectangular flume with smooth boundaries and for different values of water discharge, bottom slope, and aspect ratio. A detailed error analysis showed good agreement with the data measured through the present research and a more accurate prediction of the velocity-dip-position compared with the one evaluated through the original entropy model. In addition, the modified entropy wake law matched very well with other literature data collected in rectangular cross-sections with different flow conditions.

To simulate the dynamics of two-dimensional dam-break flow on a dry horizontal bed, we use a smoothed particle hydrodynamics model implementing two advanced boundary treatment techniques: (i) a semi-analytical approach, based on the computation of volume integrals within the truncated portions of the kernel supports at boundaries and (ii) an extension of the ghost-particle boundary method for mobile boundaries, adapted to free-slip conditions. The trends of the free surface along the channel, and of the impact wave pressures on the downstream vertical wall, were first validated against an experimental case study and then compared with other numerical solutions. The two boundary treatment schemes accurately predicted the overall shape of the primary wave front advancing along the dry bed until its impact with the downstream vertical wall. Compared to data from numerical models in the literature, the present results showed a closer fit to an experimental secondary wave, reflected by the downstream wall and characterized by complex vortex structures. The results showed the reliability of both the proposed boundary condition schemes in resolving violent wave breaking and impact events of a practical dam-break application, producing smooth pressure fields and accurately predicting pressure and water level peaks.

The estimated population growth in the next decades will create severe scarcity of water and will have a tremendous impact on the natural environment. Both the developed and developing countries will have to face increasing challenges to match the greater demand of clean and safe water, looking for supplies far from the residential area. This situation will be furtherly exasperated by the effects of climate change which, increasing the frequency and intensity of extreme events, will reduce the availability and the quality of water resources and will subject the population to serious and ongoing hazards. In such context, an accurate and continuous monitoring of surface waters represents a fundamental step to reduce the contamination status and plan actions for a sustainable management of this resource. In the last years, the development of advanced methodologies and high-tech equipment able to lower the times and costs of the field surveys has not been associated with an appropriate training of the technical staff of public and private bodies responsible for the control of the territory. In most cases, unable to outsource highly qualified personnel due to lack of funding, such bodies tend to reduce the monitoring activities, leaving the areas even more subject to the risk of disastrous events. The present paper proposes an innovative educational tool based on the virtual reality in support to technical and non-technical workforces in field activities. The tool represents a Virtual Laboratory able to train on the standard techniques for the accurate monitoring of the water discharge in open-channel flows and was successfully tested on a sample of people from the private and public water sector. According to the results, its use increased the fieldworkers&rsquo, ability to quickly move within the river as well as to easily and correctly manage the measurement equipment and methodology, so reducing the costs and times of surveys in situ.

In this paper, vortex-induced vibrations (VIV) of an elastically mounted sphere with two linear degrees of freedom have been experimentally studied. The dynamic response analysis shows that, for the range of reduced velocity from 2 to 14 here investigated, the sphere exhibits similar amplitudes and frequencies compared to the tethered sphere, and Modes I and II are detected. A new application of the phase average approach allowed extrapolating the periodic trajectory pattern from the experimental trajectories. In particular, more than one dominant harmonic component is observed in the streamwise oscillation, so the sphere trajectories are significantly different from the traditional figure-of-eight shape. The main difference is that these trajectories are not self-intersecting. Based on the experimental observations, an analytical model of the trajectory is built and discussed.

This paper describes an innovative virtual laboratory for students of Hydraulic Engineering at an Italian university that shows water discharge measurement techniques applied in open-channel flows. Such new technology, which supports traditional practical classes, has the potential to increase students&rsquo, motivation and improve their skills, as well as simultaneously reducing the costs, time, and possible dangers that continuous field experiments would involve. Thanks to this immersive and interactive experience that is carried out indoors, students learn to move around a fluvial environment, as well as work more safely and with reduced risks of accidents. Besides, the virtual lab can boost learners&rsquo, interest by combining education with pleasure and making knowledge more fun. Collaboration with a group of students enrolled in the Master&rsquo, s degree course of the Civil and Environmental Engineering program at Basilicata University at the early stages of developing the educational tool led to improvements in its performance and features. Also, a preliminary testing procedure carried out on a student sample, verified the achievement of the students&rsquo, learning objectives in terms of knowledge and skills. Such analysis indicated that students took more active role in the teaching/learning process and they showed greater interest in the topic dealt with through the new technology compared to the involvement of students observed during traditional lessons in previous years. The architecture and operational modes of the virtual laboratory as well as the results of the preliminary analysis are discussed.

Summary Large debris, including vehicles parked along floodplains, can cause severe damage and significant loss of life during urban area flash-floods. In this study, the authors validated and applied the Smoothed Particle Hydrodynamics (SPH) model, developed in Amicarelli et al. (2015), which reproduces in 3D the dynamics of rigid bodies driven by free surface flows, to the design of flood mitigation measures. To validate the model, the authors compared the model’s predictions to the results of an experimental setup, involving a dam breach that strikes two fixed obstacles and three transportable floating bodies. Given the accuracy of the results, in terms of water depth over time and the time history of the bodies’ movements, the SPH model explored in this study was used to analyse the mitigation efficiency of a proposed structural intervention – the use of small barriers (groynes) to prevent the transport of floating bodies. Different groynes configurations were examined to identify the most appropriate design and layout for urban area flash-flood damage mitigation. The authors found that groynes positioned upstream and downstream of each floating body can be effective as a risk mitigation measure for damage resulting from their movement.

SPHERA v.9.0.0 (RSE SpA) is a FOSS CFD-SPH research code validated on the following application fields: floods with transport of solid bodies and bed-load transport; fast landslides and their interactions with water reservoirs; sediment removal from water bodies; fuel sloshing tanks; hydrodynamic lubrication for energy efficiency actions in the industrial sector. SPHERA is featured by several numerical schemes dealing with: transport of solid bodies in fluid flows; treatment of fixed and mobile solid boundaries; dense granular flows and an erosion criterion. The source and executable codes, the input files and the free numerical chain of SPHERA v.9.0.0 are presented. Some reference validations and applications are also provided. SPHERA is developed and distributed on a GitHub public repository. Program summary Program title: SPHERA v.9.0.0 Program files doi: http://dx.doi.org/10.17632/pwv9rsf3w8.1 Code Ocean capsule: https://doi.org/10.24433/CO.7457751.v1 Licensing provisions: GNU General Public License 3 Programming language: Fortran 95 Supplementary material: software documentation/guide, 34 tutorials Nature of problem: SPHERA v.9.0.0 has been applied to free-surface and multi-phase flows involving the following application fields: floods (with transport of solid bodies, bed-load transport and a domain spatial coverage up to some hundreds of squared kilometres), fast landslides and wave motion, sediment removal from water reservoirs, fuel sloshing tanks, hydrodynamic lubrication. Solution method: SPHERA v.9.0.0 is a research FOSS (“Free/Libre and Open-Source Software”) code based on the SPH (“Smoothed Particle Hydrodynamics”) technique, a mesh-less Computational Fluid Dynamics numerical method for free surface and multi-phase flows. The five numerical schemes featuring SPHERA v.9.0.0 deal with: dense granular flows; transport of solid bodies in free surface flows; boundary treatment for both mobile and fixed frontiers; 2D erosion criterion. Additional comments including restrictions and unusual features: SPHERA v.9.0.0 is a 3D research FOSS (“Free/Libre and Open-Source Software”) code (developed under the subversion control system Git) with peculiar features for: floods (with transport of solid bodies, bed-load transport and a domain spatial coverage up to some hundreds of squared kilometres), fast landslides and wave motion, sediment removal from water reservoirs, fuel sloshing tanks, hydrodynamic lubrication. The whole numerical chain of SPHERA is made of FOSS, freeware and Open Data numerical tools. References: SPHERA (RSE SpA), https://github.com/AndreaAmicarelliRSE/SPHERA , last access on 28May2019 Amicarelli A., G. Agate, R. Guandalini; 2013; A 3D Fully Lagrangian Smoothed Particle Hydrodynamics model with both volume and surface discrete elements; International Journal for Numerical Methods in Engineering, 95: 419–450, DOI: 10.1002/nme.4514 Amicarelli A., R. Albano, D. Mirauda, G. Agate, A. Sole, R. Guandalini; 2015; A Smoothed Particle Hydrodynamics model for 3D solid body transport in free surface flows; Computers & Fluids, 116:205–228. DOI 10.1016/j.compfluid.2015.04.018 Amicarelli A., B. Kocak, S. Sibilla, J. Grabe; 2017; A 3D Smoothed Particle Hydrodynamics model for erosional dam-break floods; International Journal of Computational Fluid Dynamics, 31(10):413-434; DOI 10.1080/10618562.2017.1422731 Manenti S., S. Sibilla, M. Gallati, G. Agate, R. Guandalini; 2012; SPH Simulation of Sediment Flushing Induced by a Rapid Water Flow; Journal of Hydraulic Engineering ASCE 138(3): 227–311. Di Monaco A., S. Manenti, M. Gallati, S. Sibilla, G. Agate, R. Guandalini; 2011; SPH modelling of solid boundaries through a semi-analytic approach. Engineering Applications of Computational Fluid Mechanics, 5(1):1-15.

Surface water quality has a vital role when defining the sustainability of the ecological environment, public health, and the social and economic development of whole countries. Unfortunately, the rapid growth of the worldwide population together with the current climate change have mostly determined fluvial pollution. Therefore, the employment of effective methodologies, able to rapidly and easily obtain reliable information on the quality of rivers, is becoming fundamental for an efficient use of the resource and for the implementation of mitigation measures and actions. The Water Quality Index (WQI) is among the most widely used methods to provide a clear and complete picture of the contamination status of a river stressed by point and diffuse sources of natural and anthropic origin, leading the policy makers and end-users towards a more and more correct and sustainable management of the water resource. The parameter choice is one of the most important and complex phases and recent statistical techniques do not seem to show great objectivity and accuracy in the identification of the real water quality status. The present paper offers a new approach, based on entropy theory and known as the Maximum Information Minimum Redundancy (MIMR) criterion, to define the optimal subset of chemical, physical, and biological parameters, describing the variation of the river quality level in space and time and thus identifying its pollution sources. An algorithm was implemented for the MIMR criterion and applied to a sample basin of Northeast Italy in order to verify its reliability and accuracy. A comparison with the Principal Component Analysis (PCA) showed how the MIMR is more suitable and objective to obtain the optimal quality parameters set, especially when the amount of investigated variables is small, and can thus be a useful tool for fast and low-cost water quality assessment in rivers.

A first-order analytical solution is proposed for the actual depth-averaged concentration of tracers in shallow river flows in the presence of large Peclet numbers (defined as the ratio of section-averaged velocity times channel width to turbulent diffusion coefficient). The solution shows how complete transverse mixing is never achieved due to the typical shape of the velocity and diffusion coefficient profile, which alternatively tend—depending on the downstream location of the cross-section—to concentrate the mass at the centre or at the boundaries of the cross-section itself. The first-order analytical solution proves to be consistent with the results of Lagrangian numerical simulations based on real-field input data, which show how the solute mass breakthrough curves always exhibit anomalous behaviour and a considerable and persistent delay when compared with those that are analytically obtained by assuming a truly one-dimensional process.

The present study develops an integrated methodology combining the results of the water-quality classification, according to the Water Framework Directive 2000/60/EC—WFD, with those of a mathematical integrity model. It is able to analyse the potential anthropogenic impacts on the receiving water body and to help municipal decision-makers when selecting short/medium/long-term strategic mitigation actions to be performed in a territory. Among the most important causes of water-quality degradation in a river, the focus is placed on pollutants from urban wastewater. In particular, the proposed approach evaluates the efficiency and the accurate localisation of treatment plants in a basin, as well as the capacity of its river to bear the residual pollution loads after the treatment phase. The methodology is applied to a sample catchment area, located in northern Italy, where water quality is strongly affected by high population density and by the presence of agricultural and industrial activities. Nearly 10 years of water-quality data collected through official monitoring are considered for the implementation of the system. The sample basin shows different real and potential pollution conditions, according to the resilience of the river and surroundings, together with the point and diffuse pressure sources acting on the receiving body.

Landslides and debris flows can strongly interact with the river network and its mass transport processes, determining modifications of the river pattern with consequent effects on the hydrodynamic phenomena, alterations of the existing morphologies and possible interferences with anthropic works. Modifications of the cross section geometry and channel slope may produce changes in the sediment budget, with consequent repercussions on the stream evolutionary dynamics and its equilibrium configuration, leading to a new river branch arrangement. In this paper, investigations were carried out on a gravel-bed reach in the middle valley of the Noce River in Basilicata (Italy), which in 2007 suffered a progressive morpho-hydrodynamic change caused by a landslide. Because of the phenomenon complexity, mainly due to the mutual interaction between the landslide and the river transport dynamics, an integrated approach that combines field observations and numerical modelling in a spatial scale and natural environment, rarely available in literature, is suggested. The results highlight a satisfying correspondence between the altimetric profiles obtained through the numerical models and those deriving from the field surveys.

This study has developed a 3D Smoothed Particle Hydrodynamics (SPH) numerical scheme to reproduce the transport of rigid bodies in free surface flows (e.g. floods, surface waves). It is based on the Euler–Newton equations for body dynamics, implemented through the SPH formalism. This scheme has been coupled to a Weakly Compressible (WC)-SPH model for the main flow, based on the semi-analytic approach (Di Monaco et al. 2011). The SPH boundary treatment of Adami et al. (2012) has been implemented and adapted to free-slip conditions to model the “fluid–solid body” coupling terms. On the other hand, the “solid–solid” (“body–body” and “body–frontier”) interactions are represented by the “boundary force particles” of Monaghan (2005). This technique has been implemented by introducing some modifications to represent the impingements of entire bodies (not only isolated particles), even at low velocities. The new model has been validated on a sequence of 2D and 3D test cases. They involve preliminary tests both with single and multiple bodies and frontiers, four water entries of falling solid wedges, and the propagation of a 3D dam break front. This is driven by the regular lift of a mobile gate, transports a floating body (6 degrees of freedom) and impacts two fixed obstacles and several solid frontiers. This last phenomenon has also been experimentally realized during this study. Validation refers to comparisons vs. measurements, Unsteady Reynolds-Averaged Navier–Stokes (URANS) results, other SPH models, analytical and theoretical solutions.

The landslide phenomenon interfering with river processes is a complex topic and its interpretation through models is still being studied and tested. In this work, the authors describe the investigations carried out on a single-thread gravel-bed reach of the Noce River in Basilicata (Italy), which underwent a progressive morphodynamic change caused by a landslide, mobilized from the right-side slope of the basin, in July 2007. Riverbed dynamics and morphological alterations were analysed by field observations, topographic surveys, and numerical modelling. These methodologies allowed us to provide information on the future morphological variations in the river reach, useful also to the choice of protection interventions of vulnerable works, and civil infrastructures subject to erosion phenomena.

Entropy model application to river presents relevant aspects for theoretical and practical issues useful for cross section velocity distribution. The ratio between mean and maximum velocities is dependent on local branch morphology and remains quite uniform among similar location sections. Recent studies propose the formulation of Manning's roughness, n, based on such ratio and the ratio between the positions where the velocity is zero and maximum, y0/ymax, but falling for low depth. Basing on steady flows experiences, the paper analyses the dependence of n on entropy parameter, M, for low depths, proposing an equation for y0/ymax knowing slope and submergence.

Braided rivers quickly vary their geometry, modifying their boundaries and floodplains. Therefore, flooding of a braided stream is typically associated with high hydrologic risk in the surrounding areas or alluvial valleys. A forecast of these morpho-hydrodynamic processes is therefore essential when managing the environmental and economic impact of flood events. A few studies in the past demonstrated that open channels spontaneously tend to establish and maintain an equilibrium state that corresponds to a specific level of cross-sectional velocity entropy. The present study analyses for the first time the relationship between bank-full flow (described by measures of velocity entropy and second-order spatial statistics) and bed topography (described in terms of bed elevation second-order spatial statistics) in gravel-bed braided rivers at cross-sectional scale, in both equilibrium and pre-equilibrium conditions. Based on the outcome of suitable laboratory experiments, we found that, in gravel bed braided rivers, longitudinal equilibrium during floods is associated with a periodic-like spatial minimization of normalized cross-sectional velocity entropy. This periodic-like minimization of cross-sectional velocity entropy (and statistical variance) corresponds to a periodic-like maximization of normalized bed elevation variance, according to general theories on longitudinal river profile evolution. Additionally, bed evolution occurs by both entropy minima/maxima appearance and growth and entropy minima/maxima longitudinal migration.

The knowledge of the fluid discharge in free surface flows requires a great number of velocity measurements along the whole cross-section, taking up a large amount of time, using expensive equipment, and employing specialized labor. To overcome these obstacles, various models have been developed thus far that show how to estimate the mean velocity through the maximum velocity. In three-dimensional open channels, the maximum velocity can be located below the free surface because of the presence of secondary flows mainly originating by the sidewalls, an occurrence known as dip-phenomenon. In this condition, predicting the maximum velocity position is quite difficult and has always represented a challenge to most hydraulic engineers and researchers. In the present study, a mathematical model derived from the information entropy theory is proposed to evaluate the velocity-dip-position over the entire cross-section of both wide and narrow open channels, thus overcoming the limitations of the existing methods. Large literature measurement sets, collected in uniform and non-uniform flows, were used to test the validity of the model, showing good agreement with the experimental data and providing an accurate estimation of the dip-position.

The implementation of the Water Framework Directive (WFD) 2000/60/EC, aimed at achieving a “Good” Ecological Status of surface water bodies by 2015, indicates the adoption of a River Basin Management approach by using a model which works as a support for decision making. This work has applied the suggestions put forward by the WFD by means of a mathematical model called the Integrity Model. This represents valid support when assessing the efficiency of planned interventions which may directly or indirectly play a role in enhancing the quality of surface waters at the basin scale. Herein the results of a preliminary application limited to just two indexes on the Bacchiglione river basin, located in Northern Italy, are both presented and compared with the results of institutional monitoring activities in compliance with set technical regulations. The proposed model appears to be useful when carrying out Strategic Environmental Assessment (SEA) procedures in accordance with Directive 2001/42/EC concerning water management and protection plans as well as for the Environmental Impact Assessment (EIA) procedure to be carried out on the interventions identified.

Suspended sediment concentration is a key aspect in the forecasting of river evolution dynamics, as well as in water quality assessment, evaluation of reservoir impacts, and management of water resources. The estimation of suspended load often relies on empirical models, of which efficiency is limited by their analytic structure or by the need for calibration parameters. The present work deals with a simplified fully-analytical formulation of the so-called entropic model in order to reproduce the vertical distribution of sediment concentration. The simplification consists in the leading order expansion of the generalized spatial coordinate of the entropic velocity profile that, strictly speaking, applies to the near-bed region, but that provides acceptable results also near the free surface. The proposed closed-form solution, which highlights the interplay among channel morphology, stream power, secondary flows, and suspended transport features, allows reducing the needed number of field measurements and, therefore, the time of field activities. Its accuracy and robustness were successfully tested based on the comparison with laboratory data reported in literature.

The design of submerged structures in sea currents presents certain problems that are not only connected to the shape of the obstacle but also to the number of acting forces as well as the correct modelling of the structures dynamic response. Currently, the common approach is that of integrated numerical modelling, which considers the contribution of both current and structure. The reliability of such an approach is better verified with experimental tests performed on models of simple geometry. On the basis of these considerations, the present work analyses the hydrodynamic forces acting on a sphere, which is characterised by a low mass ratio and damping. The sphere is immersed in a free surface flow and can oscillate along the streamwise and transverse flow direction. It is located at three different positions inside the current: close to the channel bottom, near the free surface and in the middle, and equally distant from both the bottom and free surface. The obtained results for different boundaries and flow kinematic conditions show a relevant influence of the free surface on the hydrodynamic forces along both the streamwise and transverse flow directions.

The entropy model allows estimating, in an expeditive way, both water discharge and flow velocity field in open channels. In fact, such a model presents an almost simple analytical structure based on the evaluation of a single parameter calculated through the ratio between the mean and maximum flow velocities in the cross section. Recent studies have demonstrated that for large-scale roughness, the evaluation of the entropy parameter seems to be affected by the local conditions near the bed. In order to investigate such influence, this paper proposes an explicit relationship between the entropy parameter and the relative submergence. This relation was validated using data collected in a rectangular tilting flume of laboratory in which the bed roughness was composed of elements of regular shape such as spheres. Several tests were performed in conditions of large-scale roughness (1.9

In the present work, an entropy based velocity profile model is proposed to describe the velocity field in open channels in case of large-scale roughness. In particular, the model considers the relationship between the entropy parameter and the relative submergence along with the depth where maximum flow velocity occurs. The proposed approach was validated by means of laboratory tests, carried out in a flume under steady flow conditions and homogeneous roughness. The comparison between the calculated velocity profiles and the observed ones seems to demonstrate the validity and reliability of the proposed method.

This work analyzes the dynamic response of a sphere located close to the floor of a hydraulic channel within steady free-surface current flows. The sphere is free to move in transverse (y) and streamwise (x) directions, and it is characterized by a mass ratio m* equal to 1.34. The oscillation amplitudes and the frequencies of the sphere have been measured by means of the image analysis of a charge coupled device (CCD) camera. The experimental data show a significant influence of the free surface on the sphere movement and highlight a different behavior of the dynamic response to the increasing of the water level on the upper part of the body.

This work analyzes the effects of the interaction between an oscillating sphere and free surface flows through the reconstruction of the flow field around the body and the analysis of the displacements. The experiments were performed in an open water channel, where the sphere had three different boundary conditions in respect to the flow, defined as h* (the ratio between the distance of the sphere upper surface from the free surface and the sphere diameter). A quasi-symmetric condition at h* = 2, with the sphere equally distant from the free surface and the channel bottom, and two conditions of asymmetric bounded flow, one with the sphere located at a distance of 0.003m from the bottom at h* = 3.97 and the other with the sphere close to the free surface at h* = 0, were considered. The sphere was free to move in two directions, streamwise (x) and transverse to the flow (y), and was characterized by values of mass ratio, m* = 1.34 (ratio between the system mass and the displaced fluid mass), and damping ratio, ζ = 0.004. The comparison between the results of the analyzed boundary conditions has shown the strong influence of the free surface on the evolution of the vortex structures downstream the obstacle.

The submerged and semi-submerged structures (off-shore platforms, wind farms, floating buildings, marine turbines, oil conduits, buoys) in sea currents are often subjected to strong vibrations that condition the structural stability and also give rise to serious damage to the mechanical parts of the structures, with consequent efficiency loss of the system and above all, repercussions in the environment in which they are located. These vibrations increase when the structures are immersed in bounded flows (presence of the bed and/or the free surface). In order to attenuate and eliminate these problems, analytical and experimental means are used to describe the dynamic behaviour of structures for different flow field configurations and boundary conditions. Recent research has demonstrated that integrated numerical modelling (considering both structure and fluid characteristics) is the more suitable way to value the dynamic response of a system. To check on the reliability of the resolution methods experimental controls are needed that, for the complexity of structures, requires models with simplified geometries (spheres, cylinders, rectangles). In this context, the present work aims to provide some experimental results obtained analyzing both the oscillations and the forces acting on a structure to simple geometry (sphere) characterized by low values of mass and damping and invested by a free surface steady flow.

This work analyzes the influence of boundary conditions on the movements of a sphere immersed in a steady free surface flow. The sphere is free to move both in the transverse and streamwise directions and it is characterized by the values of the mass ratio m∗ equal to 1.34 and of the damping ratio ζ equal to 0.004. In all the experiments the blockage coefficient is kept constant, while the sphere is located at different distances from the free surface and from the bottom wall of the channel. The movements of the sphere have been measured by means of the image analysis of a charge coupled device camera which provides the 2D (streamwise and transverse) displacements of the sphere with a temporal resolution of 0.02 s. The experimental data show a significant influence of the boundaries on the sphere movement and highlight a different behavior of the amplitude response between the three different experimental setups considered.

The study of flow-induced excitation on structures and obstacles is one of the main topics of fluid dynamics related to the practical interests in a large number of engineering applications e.g. aerodynamic, mechanical, civil, naval, etc. New design and project techniques have offered hazardous solutions, resulting in structures that are even more slender and flexible. This has led to a number of situations of self-excited vibration due to the interaction between flow fields and structures. Forces coming from this mechanism depend upon both the incoming flow and the structure motion, giving rise to a strong non-conservative force field, which may eventually lead to a growing structure motion. The aim of this chapter is to offer an overture about the phenomenon of the fluid–structure interaction. Because of the importance that the cylindrical and spherical shapes have in the practical applications and the generalizations that these shapes allow, in this chapter the fluid–structure interaction is mainly referred to these basic shapes.

The paper deals some important aspects concerning the study of desertification phenomenon that has significantly interested all European countries of the Mediterranean basin in the last decades. The territorial sensibility, qualitatively and/or quantitatively, of the risk related to the desertification processes has been valued as grade of susceptibility to the phenomenon in the study area, with respect to the hydraulic and hydrologic conditioning factors. The methodological approach followed is based on the classification of desertification indicators by means of a suitable conceptual model applied to the study area in Basilicata region. The classical desertification indexes have been evaluate referring to the study area generating temporal informative map. To achieve such objective, the historical series of temperatures and rainfall of several gauge-stations have been analysed, and the first results show an increasing trend for the temperature in last years, according to the global scale. An increase of aridity and erosion index values is, also, outlined by the collected data with slight reductions at higher altitudes.