1,721,295 research outputs found
CFD modelling of breakwaters embedding wave energy converters
Full text linkIn recent years the raising supply and environmental problems related to traditional fossil fuel exploitation for energy production have pushed the research on renewable sources. Among these, sea waves have a high potential, but still poorly used. Different technologies have been developed in order to harness wave energy, and the Oscillating Water Column (OWC) devices are the most accredited for an actual diffusion. This work is focused on the performance analysis of particular OWC-type devices, namely the REWECs (REsonant sea
Wave Energy Converter). Two different versions have been considered, the REWEC1 and the REWEC3, constituting a submerged and an emerged breakwater, respectively. The most interesting aspect of REWECs is the possibility to operate them under resonant conditions with that sea state which is the one that gives the highest yearly energy contribution. Both REWEC1 and REWEC3 dynamic behavior can be approximated by
means of a mass-spring-damper system. According to this approximation, a criterion for evaluating the oscillating natural frequency of the REWECs has been derived. A CFD model has been developed in order to verify the resonance behaviour of a scaled REWEC1 device. The water-air interaction has been taken into account by means of the Volume Of Fluid (VOF) model implemented in the commercial code Ansys Fluent. Both air and water fow felds have been assumed to be unsteady. The CFD model has been validated against
both analytical and experimental results. Simulation results showed a good agreement with both measurements and predictions, particularly when the Standard k-ω turbulence model is implemented inside the REWEC.
The CFD model has been applied also to the simulation of both conventional and REWEC1 submerged breakwater placed into a two-dimensional wave fume, obtaining a novel method for the valuation of the REWEC1 absorption coefcient. In fact, when considering the interaction of waves with a conventional submerged breakwater, the incident wave energy is shared into: a refected fractiona a dissipated fraction, due to the wave breaking and the friction losses on ita and a transmitted fraction to the shore. If the
submerged breakwater embeds a REWEC1, a further reduction of the transmitted energy can be achieved due to device absorption, improving the coast protection performance of the structure. Actually, a scaled REWEC1 breakwater without PTO-system (Power Take-Off) has been considered. Then, the simulation results showed only a small difference between the transmission coefcients of the two breakwaters, allowing however to calculate
the absorption coefcient of the REWEC1 due to the water losses inside the device. Finally, a full-scale REWEC3 breakwater has been simulated by means of CFD, taking into account the characteristics of the air turbine adopted as power take-off device. The breakwater replicated the one installed in the Civitavecchia harbour (Italy). A typical sea state has been reproduced by means of regular waves generated by a piston-type wave-maker. As in the case of the scaled REWEC1, CFD unsteady simulation have been carried out in a two dimensional (2D) reference frame, reducing the huge need of computational resources. In order to simulate the oscillating fow across the air turbine, a new method has been also proposed here. The zone of the domain corresponding to the duct where the air turbine is embedded has been modelled as a porous zone. Analytical equations able to model the exchange of mass and energy across the air duct and the turbine have been
implemented. The simulation results are in good agreement with the ones registered during the operation of the Civitavecchia plant. A further outcome of the work has been a deep insight into the fuid-dynamic behaviour of the water fow inside the REWEC3, highlighting the design improvements needed to reduce friction losses
Bambini, robot: esperienze educative di gioco e relazione
No full textThis paper presents an experience about the use of robotics in education, carried out in some kindergartens in Liguria (Italy). The proposed activities with robots (IROMEC, the Construction kits Lego ® MindStorms TM, Bee-bot and Lego WeDo are the most common) aim to support and complement the usual ludic activities: to promote in all children, including those with severe disabilities, the achievement of social and communica5on skills, as well as to share a natural predilection for playing.
This type of activity requires a structuring of the educational environment, technologically and socially oriented, as a result of an educational project based on a narrative background (accessible and transferable into several languages while playing (in all its forms and possibilities) and in cognitive exercise. The inclusive perspective of the narrative and the play allows children with physical disabili5es and autism to play with companions and to share special moments through the mediation and the relationship with the robot. The experience highlighted the possible affinity with paths of inclusion and use of ICF-CY (WHO, 2007). Our experience has allowed us to evaluate the potential and the limitations of the use of a robot both in a structured environment as well as in rela5on to the instructional design in kindergarten. The robotics allows teachers to get over a commonplace vision of technology deeply related to the computer and consider possible new educational frontiers
Figure di Merito e Metodologia di Confronto per Modelli Non Lineari di Dispositivi Elettronici a Microonde
No full textDiversi approcci di modellistica non lineare per dispositivi elettronici sono stati proposti negli ultimi anni e spesso i progettisti di circuiti elettronici denunciano la mancanza di criteri di confronto attendibili sulla base dei quali identificare quale modello potrebbe essere il più adatto per la loro specifica applicazione. Inoltre simili strategie di confronto risulterebbero necessarie anche per i gruppi di ricerca dediti all’identificazione ed all’estrazione di modelli, al fine di quantificare il grado di accuratezza ottenibile con l’approccio di modelling considerato. In questo lavoro viene presentato un nuovo criterio di confronto per la stima dell’accuratezza dei modelli in condizioni di grande segnale, basato sul confronto, in funzione della polarizzazione, tra misure e modello dei parametri ammettenza a piccolo segnale alle porte intrinseche del dispositivo
Caratterizzazione e Modellistica Degli Effetti Dispersivi Nei Dispositivi Elettronici a Microonde ed Onde Millimetriche
No full textLa modellistica a grande segnale di dispositivi FET III-V, qualora siano richiesti elevati livelli di accuratezza, non può servirsi della misura delle caratteristiche i/v del transistore effettuata semplicemente in regime statico. In generale, infatti, devono essere presi in considerazione tutti quei fenomeni dispersivi, dovuti all’autoriscaldamento e\o alla presenza di trappole (stati energetici spuri superficiali e livelli profondi), che sono causa di importanti deviazioni nelle caratteristiche dinamiche della corrente di drain in regime di bassa frequenza. Per tale motivo risulta necessario sostituire alle caratteristiche statiche convenzionali una quota di modello più raffinata, che descriva le leggi algebriche imposte dalla fisica del dispositivo alle grandezze elettriche alle porte tenendo conto della presenza di tali effetti di dispersione in bassa frequenza.
Diversi approcci al problema sono stati proposti dalla comunità scientifica e, spesso, la caratterizzazione tramite sistemi di misura i/v di tipo “impulsato” è stata indicata come la più appropriata per l’identificazione dei modelli del comportamento elettrico del dispositivo a grande segnale ed a bassa frequenza. Quale possibile alternativa a tali sistemi di misura viene proposto in questo lavoro un nuovo sistema di misura a grande segnale, basato su semplici eccitazioni sinusoidali a bassa frequenza, facilmente riproducibile con strumentazione convenzionale e di tipo “general-purpose”. Le potenzialità del banco sono state investigate utilizzando i dati sperimentali raccolti attraverso di esso per estrarre due modelli per la descrizione delle caratteristiche i/v dinamiche a bassa frequenza di dispositivi in tecnologia PHEMT (Pseudomorphic High Electron Mobility Transistor, di largo impiego per applicazioni nel campo delle microonde ed onde millimetriche)
L’idea di competenza degli insegnanti e degli alunni
No full textTante idee di competenza per una definizione di competenza; Le competenze situate; Le competenze generano soddisfazione; Partecipare e collaborare per diventare competent
Progettazione, azione e valutazione
No full texthttp://lascuola.it/nuovadidattica/it/home/mappe/1382696387986/138718555843
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Use of Genetic Algorithms in Propeller Foil Design.
No full textProgettazione di profili alari mediante algoritmi genetic
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