Dipartimento di Ingegneria Civile - Tesi di Dottorato

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Questa collezione raccoglie le Tesi di Dottorato Dipartimento di Ingegneria Civile dell'Università della Calabria.

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Author: search.filters.author.Furgiuele, FrancoEnd date: 2019

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    Lo sviluppo dei sistemi di trasporto collettivo: studio di un indice per la determinazione del comfort a bordo.
    (2017-06-16) Tassitani, Antonio; Furgiuele, Franco; Astarita, Vittorio
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    Soluzioni innovative per lo sviluppo della mobilità sostenibile: aspetti metodologici e sperimentali
    (2017-06-16) Rogano, Daniele; Furgiuele, Franco; Guido, Giuseppe
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    Turbulence characteristics in open-­‐channel flows with highly rough beds.
    (2017-10-27) Ferraro, Domenico; Furgiuele, Franco; Gaudio, Roberto
    River motion is one of the most attractive and fascinating phenomena in nature. Since ancient times many scientists have been drawn into a vortex of confusion observing river motion. Flow observation is often simplified, running tests in a laboratory under controlled conditions, in order to test a specific phenomenon of a much more complex issue. A great number of these phenomena has been collected by researchers throughout the history of science, and other researchers have tried to merge the available knowledge to clarify the tangled phenomena. This work is focused on the turbulent characteristics of Open-Channel Flows (OCFs) over a highly rough bed. The use of coarse sediments is an attractive technique to solve many problems in rivers as well as to safeguard aquatic life. Issues like sediment transport phenomena or erosion and local scour, e.g. at bridge piers and abutments, can be counteracted by introducing coarse sediments. In this work the bed roughness effect on the turbulence characteristics of the flow is investigated through the relative submergence parameter Δ, which is the ratio between the roughness characteristic dimension and the water depth. Most of the theories and literature works has been developed for smooth-wall flows and rough-bed flows at very high relative submergence, whereas its applicability in OCFs with low relative submergence remains questionable; the simplest example is the velocity distribution (i.e., the universal logarithmic law). This thesis aims at improving the knowledge of turbulence structure developed over a highly rough bed in OCFs by varying the relative submergence. According to the relative submergence definition given before, it can be changed by modifying the water depth for a fixed roughness or varying the roughness keeping the water depth constant. The choice settled on the second strategy, because of the measurement instrument configuration. It will be described in detail in the chapter “Experimental equipment and procedures”. The relative submergence varied in the range from 3.13 to 10.07. Three long-duration experiments (each one with a given coarse sediment size) were performed in uniform flow conditions by using a 100 Hz ADV down-looking probe, in order to record the 3D velocity vector in each point of a given grid of measurements. The contribution of the Reynolds stress, the viscous and the form-induced shear stress was analysed, as well as the averaged velocity profiles, second- and third-order moments . A statistical tool will be proposed to verify the frozen-in Taylor hypothesis by comparing two typical time-scales, namely the large scale advection time and the characteristic nonlinear time. The proposed method based on the characteristic eddies timescales is more restrictive with respect to the classic frozen-in Taylor hypothesis, in which a simple comparison of the flow velocity and the fluctuation magnitude is made. Furthermore, one-point temporal correlations analysis will be performed in order to give a first indication of the integral scales lengths along the channel varying the relative submergence. Spectral analysis is introduced both in the frequency and in wavenumber domain. In experimental practice it is quite hard to obtain direct measures, which can allow computing directly a wavenumber spectrum. Temporal velocity signals are commonly recorded in a single point, and they are used to compute the frequency spectrum and then converted to wavenumber spectrum through the Taylor frozen-in hypothesis. Hence, the k−5/3 slope is investigated in the longitudinal velocity spectra. k is the wavenumber. Spectral analysis will be introduced in order to test the observed k−5/3 slope, in order to confirm that the inertial subrange is well visible at the investigated Re numbers. Furthermore, the validity of the −5/3 scaling region will be also tested by using the third-order longitudinal velocity structure function, which is expressed as a function of the turbulent kinetic energy (TKE) dissipation rate. The third-order longitudinal velocity structure function will be also used to provide an estimate of the magnitude of the TKE dissipation rate. In addition, in order to quantify the energy contribution of different eddyscales, premultiplied spectra will be employed. Thanks to this analysis, the Large Scales (LSs) and the Very Large Scale (VLSs) will be investigated. These scales will be associated with a characteristic wavenumber and intensity. ADV velocity measurement also allows exploring the longitudinal-vertical velocity co-spectra. In order to locate the normalized wavenumber associated with the peak in the premultiplied spectra, a systematic procedure to find the correct position of the peaks based on the center of mass concept will be proposed. Moreover, the peak distribution over the water depth will be plotted in inner and outer coordinates.
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    <> modello di gestione delle reti idriche in condizioni di emergenza
    (2017-06-16) Caruso, Olga; Furgiuele, Franco; Fiorini Morosini, Attilio
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    On the use of mechanistic modeling for the numerical analysis of low impact developments techniques
    (2017-06-16) Brunetti, Giuseppe; Furgiuele, Franco; Piro, Patrizia
    The increasing frequency of flooding events in urban catchments related to an increase in impervious surfaces highlights the inadequacy of traditional urban drainage systems. Low-impact developments (LIDs) techniques have proven to be valuable alternatives for stormwater management and hydrological restoration, by reducing stormwater runoff and increasing the infiltration and evapotranspiration capacity of urban areas. However, the lack of diffusion of adequate modelling tools represents a barrier in designing and constructing such systems. Mechanistic models are reliable and accurate tools for analysis of the hydrologic behaviour of LIDs, yet only a few studies provide a comprehensive numerical analysis of the hydrological processes involved and test their model predictions against field-scale data. Moreover, their widespread use among urban hydrologists suffers from some limitations, namely: complexity, model calibration and computational cost. This suggest that more research is needed to address these issues and examine the applicability of this kind of models. Thus, the main aim of this thesis was to investigate the benefits and the limitations in the use of mechanistic modelling for LIDs analysis. In this view, the mechanistic modelling approach has been used to simulate the hydraulic/hydrologic behaviour of three different LIDs installed at the University of Calabria: an extensive green roof, a permeable pavement and a stormwater filter. Each case study was used to examine a particular modelling aspect. The morphological and hydrological complexity of the green roof required the use of a three-dimensional mechanistic model, which was validated against experimental data with satisfactory results. The measured soil hydraulic properties of the soil substrate highlighted important characteristics, accounted in the simulation. The validated model was used to carry out a hydrological analysis of the green roof and its hydrological performance during the entire simulated period as well as during single precipitation events. Conversely, a one-dimensional mechanistic model was used to simulate the hydraulic behaviour of a permeable pavement, whose parameters were calibrated against experimental data. A Global Sensitivity Analysis (GSA) followed by a Monte Carlo filtering highlighted the influence of the wear layer on the hydraulic behaviour of the pavement and identified the ranges of parameters generating behavioural solutions in the optimization framework. Reduced ranges were then used in the calibration procedure conducted with the metaheuristic Particle swarm optimization (PSO) algorithm for the estimation of hydraulic parameters. The calibrated model was then validated against an independent set of data with good results. Finally, to address the issue of computational cost, the surrogate-based modelling technique has been applied to calibrate a two-dimensional mechanistic model used to simulate the hydraulic behaviour of a stormwater filter. The kriging technique was utilized to approximate the deterministic response of the mechanistic model. The validated kriging model was first used to carry out a Global Sensitivity Analysis of the unknown soil hydraulic parameters of the filter layer. Next, the Particle Swarm Optimization algorithm was used to estimate their values. Finally, the calibrated model was validated against an independent set of measured outflows with optimal results. Results of the present thesis confirmed the reliability of mechanistic models for LIDs analysis, and gave a new contribution towards a much broader diffusion of such modelling tools.
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    Multi-level assessment of the environmental benefits of a permeable pavement: numerical analysis and experimental investigations
    (2018-05-09) Turco, Michele; Furgiuele, Franco; Piro, Patrizia
    The increasing frequency of flooding events in urban catchments related to an increase in impervious surfaces highlights the inadequacy of traditional urban drainage systems whose aim is to rapidly collect and convey overland flows to the treatment plants. Recently, scientific community has focused its attention on Low-impact developments (LIDs) techniques that have proven to be valuable alternatives for stormwater management and hydrological restoration, by reducing stormwater runoff by reproducing natural hydrological processes in urban areas. However, the lack of diffusion of adequate modelling tools represents a barrier in designing and constructing such systems. In general, Permeable Pavement (PP) represents a good solution to solve stormwater management problems both in quantitative and qualitative way. This thesis focused on assessing the hydraulic behaviour and water quality performance of permeable pavements based on laboratory experiments and developing a modelling approach for the water flow in order to assisting engineers and researchers in the design of these systems. In this way, an adequate hydrological description of water flow in the pavement system relies heavily on the knowledge of the unsaturated hydraulic properties of the construction materials. Although several modelling tools and many laboratory methods already exist in the literature to determine the hydraulic properties of soils, the importance of an accurate description of hydraulic properties of materials used in the permeable pavement, is increasingly recognized in the fields of urban hydrology. Thus, the aim of this study is to propose techniques/procedures on how to interpret water flow through the structural system using the HYDRUS model. The overall analysis includes experimental and mathematical procedures for model calibration and validation to assess the suitability of the HYDRUS-2D model to interpret the hydraulic behaviour of a lab-scale permeable pavement system. The system consists of three porous materials: a wear layer of porous concrete blocks, a bedding layers of fine gravel, and a sub-base layer of coarse gravel. The water regime in this system, i.e. outflow at the bottom and water contents in the middle of the bedding layer, was monitored during ten irrigation events of various durations and intensities. The hydraulic properties of porous concrete blocks and fine gravel described by the van Genuchten functions were measured using the clay tank and the multistep outflow experiments, respectively. Coarse gravel properties were set at literature values. In addition, some of the parameters (Ks of the concrete blocks layer, and α, n and Ks of the bedding layer) were optimized with the HYDRUS-2D model from water fluxes and soil water contents measured during irrigation events. The measured and modelled hydrographs were compared using the Nash-Sutcliffe efficiency (NSE) index (varied between 0.95 and 0.99) while the coefficient of determination R2 was used to assess the measured water content versus the modelled water content in the bedding layer (R2= 0.81÷0.87). The parameters were validated using the remaining sets of measurements resulting in NSE values greater than 0.90 (0.91÷0.99) and R2 between 0.63 and 0.91. Results have confirmed the applicability of HYDRUS-2D to describe correctly the hydraulic behaviour of the lab-scale system. Water quality performance aimed to improve the knowledge of the system to remove heavy metals (Copper and Zinc) from stormwater runoff. It was assessed by using batch and contaminant flow experiments. Batch experiments were conducted on each construction material of the PP and highlighted that, among the pavement materials tested, only concrete blocks had the potential to adsorb the heavy metals investigated. Results shown that the adsorption capacity of the porous concrete is higher in adsorbing Cu (70% ÷ 90%) than Zn (69% ÷ 75%). Flow contaminant experiment were performed under different inflow concentrations. Results show that removal rates of Cu and Zn of the lab-scale pavements range from 85% to 92% and from 65% to 82%, respectively
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    Interpretation of local scouring at bridge piers and abutments with the phenomenological theory of turbulence
    (2019-03-04) Coscarella, Francesco; Furgiuele, Franco; Gaudio, Roberto; Manes, Costantino
    The phenomenological theory of turbulence is here applied to the scouring phenomenon at bridge piers and abutments. In the last ve decades many researches have been devoted to the development of predictive formulae able to quantify the maximum scour depth for both design and risk assessment needs of hydraulic structures. Owing to the complexity of the problem, most of the proposed formulae were developed on an empirical basis, which made them susceptible to scale issues and not fully consistent with the physics underpinning the scouring phenomenon. Recently, some studies of Gioia & Bombardelli (2005), Bombardelli & Gioia (2006), Manes & Brocchini (2015) and Ali & Dey (2018) have proposed a di erent approach, which exploits a theory to derive scaling relations between the equilibrium scour depth and non-dimensional parameters. Their work presented the phenomenological theory of turbulence and the paradigms of the sediment incipient motion theory assuming rough ow conditions, meaning that the momentum transport near the sediment-water interface was dominated by eddies belonging to the turbulent energy spectrum inertial range and scaling with the sediment diameter. In order to provide more general models and on the basis of the ndings of Bonetti et al. (2017), the present work relaxes this as sumption by exploring the scaling of the equilibrium scour depth in cases where momentum transport is a ected by eddies belonging to the dissipation and production range. This improvements were applied to the scouring phenomenon at bridge piers, to derive a predictive formula for the maximum scour depth, and to the scouring phenomenon at bridge abutments, to derive a scaling law that does not allow a directly assessment of the maximum scour depth, but provides new avenues for the development of general predictive formulae that are founded more on physical than empirical bases. In both cases, the proposed theory includes the relevant non-dimensional parameters controlling the scouring process and, contrary to commonly employed empirical formulae, it is free from scale issues.
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    Experimental and numerical modeling of solitary wave loads on horizontal circular cylinders
    (2019-03-04) Tripepi, Giuseppe; Furgiuele, Franco; Aristodemo, Francesco
    The present thesis deals with an experimental and numerical study on the horizontal and vertical hydrodynamic forces induced by solitary waves on submerged horizontal circular cylinders. Laboratory tests were performed in the wave flume of the University of Calabria. A battery of pressure transducers was mounted along the external contour of a cylinder while four wave gauges were located close to the cylinder. The correct displacement of the wavemaker was checked by an ultrasonic sensor located behind the paddle. A number of 134 experimental tests were conducted in the wave channel taking into account different wave attacks and five depths of the cylinder location ranging between half water depth and the bottom of the flume. From the numerical viewpoint, two different numerical models were adopted. The first one is the diffusive weakly-compressible Smoothed Particle Hydrodynamics (SPH) model. To improve the results and prevent spurious flows near the cylindrical contour, a packing algorithm has been applied to initialize the SPH fluid particles. The acoustic components occurring in the numerical pressure field were filtered through the application of Wavelet Transform. The numerical simulations provided to investigate in detail the flow field near the cylinder not modeled by the laboratory investigation. This Lagrangian model was used only in the case where the cylinder was placed at half water depth. The high time consuming of the SPH simulations led to adopt another numerical approach. In this context, the Eulerian OlaFlow model was used to investigate the other four depths of the cylinder. With respect to the experimental tests, additional numerical simulations were performed to extend the range of the analysis. Considering all the five positions of the cylinder, a total of 176 numerical simulations were carried out. The good agreement between experimental and numerical forces and kinematics at the cylinder has allowed the calibration of the hydrodynamic coefficients in the Morison and transverse semi-empirical equations by different time-domain methods. The present thesis has showed an alternative method (Gurnari and Filianoti, 2017) to assess the horizontal forces. Based on the concept that a solitary wave is subjected to a slowdown passing over the cylinder, this formulation was used after the experimental calibration of the speed drop factor. In this work, an extension of the transverse for-mulation which considered a new form of the lift force was also presented. For two specific depths, this formulation resulted necessary to model correctly the peaks and the phase shifts of the vertical forces. The experimental and numerical analysis were presented comparing the time variation of the experimental and numerical simulations for two test cases at each depth. The overall analysis of the peaks forces was evaluated as a function of the wave amplitude. In addition, the weight of the different force components, i.e. drag, lift and horizontal and vertical inertia, was evaluated and analyzed with respect to the maximum values of the horizontal and vertical force. The time variation of the horizontal forces calculated by the Gurnari and Filianoti (2017) solution was compared with the experimental ones for the two vertical extreme positions of the cylinder. The comparison between the experimental and the Gurnari and Filianoti (2017) equation was performed in relation to the horizontal force peaks.