1,720,969 research outputs found
CONFRONTO FRA DIFFERENTI TECNICHE DI MODELLAZIONE DELLA DISPERSIONE DI INQUINANTI IN ATMOSFERA GENERATA DA UNA PICCOLA CENTRALE A BIOMASSE.
No full textNonostante i notevoli pregi, lo sfruttamento dell’energia da biomassa implica in ogni caso emissioni di fumi in atmosfera
che spesso, specialmente in caso di cogenerazione, avviene in prossimità di abitazioni o di attività lavorative. La pericolosità
delle emissioni è fortemente correlata alle caratteristiche di ventosità locali; per questo motivo la dispersione degli inquinanti è
usualmente studiata attraverso modelli di calcolo che, oltre alle caratteristiche della sorgente, utilizzano come input dati storici
sul vento.
La famiglia di modelli più diffusamente utilizzata per questo tipo di indagini è quella dei codici gaussiani (Gaussian Plume
Model - GPM); tale tipologia di modelli tuttavia non è in grado di interpretare gli effetti di singolarità del campo di moto del
vento indotte da complessità orografiche.
Nel presente lavoro viene proposta una nuova tecnica di modellazione della dispersione di inquinanti quali particolato ed
emissioni gassose che utilizza il modello CFD (Computational Fluid Dynamics) Phoenics; le potenzialità del codice e
l’accuratezza dei risultati sono stati verificati attraverso il confronto dei risultati ottenuti con il modello gaussiano Windimula
sullo stesso dominio di calcolo. Il confronto è stato dunque effettuato considerando le emissioni prodotte da una piccola
centrale a biomassa inserita in una località caratterizzata da orografia fortemente complessa
An optimized method to evaluate the performance of trench isolation for railway-induced vibration
No full textData mining techniques for performance analysis of onshore wind farms
No full textWind turbines are an energy conversion system having a low density on the territory, and therefore needing accurate condition monitoring in the operative phase. Supervisory Control And Data Acquisition (SCADA) control systems have become ubiquitous in wind energy technology and they pose the challenge of extracting from them simple and explanatory information on goodness of operation and performance. In the present work, post processing methods are applied on the SCADA measurements of two onshore wind farms sited in southern Italy. Innovative and meaningful indicators of goodness of performance are formulated. The philosophy is a climax in the granularity of the analysis: first, Malfunctioning Indexes are proposed, which quantify goodness of merely operational behavior of the machine, irrespective of the quality of output. Subsequently the focus is shifted to the analysis of the farms in the productive phase: dependency of farm efficiency on wind direction is investigated through the polar plot, which is revisited in a novel way in order to make it consistent for onshore wind farms. Finally, the inability of the nacelle to optimally follow meandering wind due to wakes is analysed through a Stationarity Index and a Misalignment Index, which are shown to capture the relation between mechanical behavior of the turbine and degradation of the power output
Valutazione sperimentale dell’efficacia di barriere assorbenti per l’attenuazione delle vibrazioni prodotte dal traffico ferroviario
No full textIl presente lavoro intende fornire un contributo alla comprensione dei meccanismi di
funzionamento dei dispositivi noti come “barriere assorbenti” – realizzate mediante trincee a
sezione rettangolare, di profondità compresa tra 1 e 4 m, scavate direttamente nel terreno
parallelamente al tracciato dei binari – per l’attenuazione delle vibrazioni prodotte dal traffico
ferroviario, con particolare riferimento ai convogli ad Alta Velocità. Una serie di prove in sito
in vera grandezza è stata condotta in località Campegina (RE), in corrispondenza della nuova
linea AV Bologna-Milano, per testare l’efficacia di barriere assorbenti, realizzate
rispettivamente mediante: i) trincee non sostenute di diversa profondità; e, ii) trincee
sostenute con pannelli modulari in c.a. prefabbricato. Nella sperimentazione sono stati
utilizzati una sorgente di vibrazione artificiale ed un convoglio reale, modello ETR 500,
circolante alla velocità di 120 km/h
Dynamic effects of wind loads on a gravity damper
No full textThe gravity damper is safety device used for the air treatment that prevent overpressure inside the unit through the opening. It is a normally closed valve under the effect of the gravity force, which, under the action of the incident air flow, allows to manage any excess mass. Clearly, although the device is rather simple and therefore reliable, the operating conditions may prove burdensome, especially if the gravity dampers are applied to installations of energy transformation, such as the gas turbines; this is mainly due to the need to develop large masses of air at speeds rather incurred. This article describes an experiment carried out on a gravity damper designed to be installed in a gas turbine. The characterization has been performed in numerical (CFD-FEM), considering both the mode shapes and the natural frequencies of the device in working condition as well as any phenomenon of detachment of the fluid that can trigger vortex shedding and subsequently validated in the wind tunnel facilities of the University of Perugia. In particular, what is wanted to be highlighted is the fact that, after a preliminary analysis, it has been clearly evident that, under the operating conditions, the structure would be affected by phenomena of vortex shedding. The shedding frequency is next to some natural frequencies of the structure, with obvious repercussions on the integrity of the structure. An experimental vibration analysis performed in the wind tunnel at flow regime has in fact allowed to identify the phenomenon of lock-in
The Knocking Noise on Twin Tube Shock Absorbers: Individuation and Analysis of the Phenomenon
No full textRivers’ Water Level Assessment Using UAV Photogrammetry and RANSAC Method and the Analysis of Sensitivity to Uncertainty Sources
Full text linkWater-level monitoring systems are fundamental for flood warnings, disaster risk assessment and the periodical analysis of the state of reservoirs. Many advantages can be obtained by performing such investigations without the need for field measurements. In this paper, a specific method for the evaluation of the water level was developed using photogrammetry that is derived from images that were recorded by unmanned aerial vehicles (UAVs). A dense point cloud was retrieved and the plane that better fits the river water surface was found by the use of the random sample consensus (RANSAC) method. A reference point of a known altitude within the image was then exploited in order to compute the distance between it and the fitted plane, in order to monitor the altitude of the free surface of the river. This paper further aims to perform a critical analysis of the sensitivity of these photogrammetric techniques for river water level determination, starting from the effects that are highlighted by the state of the art, such as random noise that is related to the image data quality, reflections and process parameters. In this work, the influences of the plane depth and number of iterations have been investigated, showing that in correspondence to the optimal plane depth (0.5 m) the error is not affected by the number of iterations
On the Possible Wind Energy Contribution for Feeding a High Altitude Smart Mini Grid
Full text linkThe use of renewable energy sources to increase electricity access, especially in remote areas as high mountains, is a possible contribution to poverty reduction, climate change mitigation and improved resilience. In this paper an evaluation of the wind potential of a remote area in Nepal is performed, using CFD methods and the simulation of a micro wind turbine projected by Perugia University. With an accurate analysis of wind data and air density effects it is possible to test energy production potential in areas with high average wind speed. The overall estimated production for each turbine is an interesting result and an easily exportable contribution to the perspective of sustainable development at very high altitudes and remote areas
How Wind Turbines Alignment to Wind Direction Affects Efficiency? A Case Study through SCADA Data Mining
Full text linkSCADA control systems are the keystone for reliable performance optimization of wind farms. Processing into knowledge the amount of information they spread is a challenging task, involving engineering, physics, statistics and computer science skills. The present work deals with the effects on the efficiency of turbine inability of optimal aligning to the wind direction, due to meandering wind caused by wakes. The approach is tested on a judiciously chosen cluster of turbines of a wind farm sited in southern Italy. By a post-processing method based on discretization of nacelle position measurements, a set of dominant patterns of the cluster is identified. The patterns associated to best performances are individuated and it is shown that they correspond to non-trivial alignment to wind direction
Large Amplitude Oscillatory Shear From Viscoelastic Model With Stress Relaxation
No full textThe analytic response for the Cauchy extra stress in large amplitude oscillatory shear (LAOS) is computed from a constitutive model for isotropic incompressible materials, including viscoelastic contributions, and relaxation time. Three cases of frame invariant derivatives are considered: lower, upper, and Jaumann. In the first two cases, the shear stress at steady-state includes the first and third harmonics, and the difference of normal stresses includes the zeroth, second, and fourth harmonics. In the Jaumann case, the stress components are obtained in integral form and are approximated with a Fourier series. The behavior of the coefficients is studied parametrically, as a function of relaxation time and constitutive parameters. Further, the shear stress and the difference of normal stresses are studied as functions of shear strain and shear rate, and are visualized by means of the elastic and viscous Lissajous–Bowditch (LB) plots. Sample results in the Pipkin plane are reported, and the influence of the constitutive parameters in each case is discussed.</jats:p
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