1,721,003 research outputs found
Experimental investigation of 2-D free convection in a differentially heated trapezoidal cavity
No full textNew developments in frontier models for objective assessments
Full text linkThis dissertation is the result of some innovative proposals, in the wide framework of production efficiency frontier models, that have the common goal of reducing subjective choices of the researcher by using, as far as possible, objective methods.
In particular, the first proposal links the economic efficiency theory to the spatial econometrics with the aim of taking into account - in the efficiency evaluation of a productive unit - the neighborhood effects in a global way avoiding the subjective selection of a set of variables identifying territorial effects. The method called Spatial Stochastic Frontier Analysis (SSFA) has been published in Fusco and Vidoli (2013) for the production efficiency analysis and generalized in this thesis to be able to also analyze the cost efficiency.
The second proposal, instead aims to introduce enhancements in the methods using frontier techniques to aggregate simple indicators in a composite indicator. Subjectivity is avoided in the identification of the set of aggregation weights necessary for constructing the composite indicator, in the definition of a preference structure among simple indicators and in the extreme values and outliers influence
removal. The two methods proposed, called respectively Directional Benefit of the Doubt (D-BoD) and Robust Directional Benefit of the Doubt (RD-BoD), have been published in Fusco (2015) and Vidoli, Fusco and Mazziotta (2015). The dissertation consists of four parts: the first one introduces the foundations of the economic efficiency analysis and gives key economic concepts and definitions needed for a proper understanding of the following parts, focusing both on parametric and on nonparametric methods for cross-sectional and panel data and for mono-output and multi-output production processes; the second one discusses the fundamentals of the spatial econometrics, on the main connection proposals with the efficiency theory and shows in detail the SSFA method and the related R package called SSFA implemented to allow other researchers to use it; in the third part the concept of composite indicator and the required steps for its construction are discussed and D-BoD and RD-BoD are shown, moreover the related R package Compind is presented; all proposed methods have been tested both on simulated data and on real
data and the results are shown in the fourth part. In the last part, two innovative applications, respectively on the estimation of non performing loans of commercial banks (Fusco and Maggi, 2016) and on the estimation of the local governments’ expenditure needs (Vidoli and Fusco, 2017) by using the efficiency and spatial theories, are also included
Free surface perturbation induced by a vertical 2-D liquid jet introduced from the bottom of a rectangular tank: numerical study by SPH method
No full textHydro-morphological alteration and related effects on fish habitat induced by sediment management in a regulated Alpine river
No full textStudio sperimentale e numerico di getti bidimensionali entro vasche a pelo libero costante
No full textSediment transport below a small alpine reservoir desilted by controlled flushing: field assessment and one-dimensional numerical simulation
No full textPurpose: Sediment transport and riverbed sedimentation were investigated in an alpine stream below a small hydropower reservoir desilted by a controlled sediment flushing (CSF) operation. The term “controlled” refers to the operational tasks implemented to mitigate the downstream environmental impact of the operation. The experimental dataset acquired before, during, and after the CSF was also used to carry out and calibrate a one-dimensional sediment transport model of the monitored event. Materials and methods: The investigated reservoir is located in the central Italian Alps, and its original storage was 160,000 m3, about 30% filled by a mixture of sand and silt/clay before the CSF. Downstream sediment concentration was controlled by releasing clear water from upstream reservoirs and regulating the work of earth-moving equipment in the emptied reservoir. A 3.6-km-long reach with average slope of 0.015 was monitored: concentration and grain size of suspended sediment were measured during the CSF and the riverbed alteration was evaluated by volumetric sampling and measurements of the deposits’ thickness. Sedimentation and River Hydraulics—One Dimensional (SRH-1D) was used to simulate sediment transport during the monitored CSF. Model parameters were calibrated by comparing the computed and the observed amount of sediment deposited along the study reach. Results and discussion: Sediment flushing was carried out in October 2010 for 3 days. Ca. 16,000 m3 of sediment were evacuated, representing approximately 30% silt/clay and 70% sand. 2.4 Mm3 of clear water was released to reduce sediment concentration and increase transport capacity downstream. About 3000 m3 of sand was deposited in the study reach after the CSF, with maximum height up to 0.2 m. Although the riverbed before the CSF was simply set as mono-granular, after calibrating the parameters, good agreement was achieved between the depositional pattern computed by SRH-1D and the one observed, both in terms of deposit thickness and grain size of deposited sediment. The sensitivity analysis revealed a major role of the parameters controlling bed mixing processes in affecting the simulated deposition after the CSF. Conclusions: Sediment below 0.1 mm in diameter was not detected in river deposits after the flushing: the effects on river biota associated with substrate clogging by very fine sediment were therefore minimized. After proper calibration, 1-D sediment transport modeling can effectively support the planning of CSF operations: to minimize the downstream environmental effects, concurrently achieving acceptable flushing efficiency, the analyzed scenarios as well as the model outputs need to be carefully evaluated from a multidisciplinary perspective
Experimental Study of the Scour Regimes Downstream of an Apron for Intermediate Tailwater Depth Conditions
No full textThe local scour of a non-cohesive bed due to a 2-D submerged horizontal jet is investigated experimentally in presence of a protection apron. Previous researches conducted without protection apron demonstrate that, when the tailwater depth is either deep or shallow, the equilibrium state characteristics of the scoured bed profile are mainly a function of the densimetric Froude number. However, when the submergence is between these two extremes, at fixed Froude number, three different scour regimes are possible. For relatively shallow tailwater depths, the jet mainstream directs towards the free surface (surface jet scouring regime), determining shallow and elongated scour profiles. For relatively large tailwater depths, the jet remains attached to the channel bottom (bed jet scouring regime), leading to deeper and shorter scour profiles. For intermediate conditions, the flicking of the jet between the erodible bed and the water free-surface is possible. When this instability occurs, the shape of the scour hole rapidly changes as a response of the jet mainstream position (bed-surface jet scouring regime). This paper aims to give an experimental description of the three mentioned regimes when a protection apron partly reduces the action of the flow on the loose bed. Scour hole profile evolution and velocity profile measurements obtained by LDA and ADV velocimetry are discussed
Experimental investigation of 3D separation in a cylinder rough flat plate junction
No full textIn this paper the results of an experimental study concerning the separated flow region which develops upstream from a cylindrical obstacle vertically placed on a rough surface and subjected to a fully developed turbulent boundary layer, will be analyzed. This region is characterized by a strongly time-variant vortex system, whose main features were described by a great number of authors through velocity and pressure measurements and flow visualizations, for a wide range of Reynolds number. The experimental results were interpreted using the topological approach by Hunt et al. (1978), Baker (1980), Dargahai (1989). However for a turbulent inlet boundary layer the number of vortices observed is still a controversial issue. This type of flow occurs in several technical applications, e.g. local scouring at bridge piers. To this avail bed roughness could play an important role in defining the vortex system structure and stability. In this paper, the instantaneous characteristics of the vortical structure were highlighted by the flow visualizations. LDV measurements of the longitudinal and vertical velocity components were carried out for three different Reynolds numbers. In one of these conditions, the crosswise mean velocity component was computed and a statistical analysis of the instantaneous velocity signals was performed. Furthermore by applying the topological concepts of critical point and sectional streamline the main features of the separated flow were identified
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