1,721,057 research outputs found
Analisi delle fasi di scavo e stabilizzazione di una grande caverna in calcari fratturati
No full textEvaluation of rock bolts effectiveness in reducing tunnel convergence in squeezing rocks
No full textAn analytical study of the rock bolt interaction in tunnels by using the equivalent material approach
No full textMethods and tools for the optimization of renewable technologies and hybrid energy systems. Metodi e strumenti per l'ottimizzazione di tecnologie rinnovabili e sistemi energetici ibridi
Full text linkThe United Nations (UN) project "Sustainable energy for all" sets three ambitious objectives to favor a sustainable development and to limit climate change:
- Universal access to modern energy services. Electricity is currently not available for 1.3 billion people and the global energy demand is expected to grow of about 35% within 2040, due to the increasing world population and the expanding economies
- Double the global rate of improvement in energy efficiency
- Double the share of renewable energy sources (RESs) in the global energy mix
In addition, according to the climate scenario assessed in the fifth assessment report (AR5) of the International Panel on Climate Change (IPCC), the prevention of undesirable climate effects requires a 40-70% reduction of greenhouse gas (GHG) emissions, compared with 2010 levels, by mid-century, and to near-zero by the end of this century (IPCC, 2014).
The achievement of such objectives requires and encourages the spread of RESs in the global energy mix, gradually replacing depleting and polluting energy sources based on fossil fuels, which still have the main incidence on the energy sector. RESs already play a major role in several countries, due to the technological development and the increasing market competitiveness, and the world renewable power capacity reached 22.1% in 2013, showing an increasing trend in 2014 (REN, 2014). However, supporting policies, robust investments from the private sector and efforts from the scientific community are still crucial to demonstrate the technical and economic sustainability and effectiveness of RESs, helping their large-scale diffusion.
Starting from such a background, this Ph.D dissertation focuses on the study, design and development of methods and tools for the optimization and enhancement of renewable energy technologies and their effective integration with energy storage solutions and traditional energy sources powered by fossil fuels (hybrid energy systems).
The analysis of the major literature and the different scenarios and perspectives of RESs in the national and international contexts have shown that their economic sustainability, and then their diffusion, is closely connected to a number of technical, economic/financial and geographical parameters. Such parameters are the input of the analytic models developed for the techno-economic design of photovoltaic (PV) plants and small wind turbines (SWTs) and applied to the economic feasibility study, through multi-scenario analysis, of such systems in some of the main European Union (EU) Countries. Among the obtained results, the self-consumption of the produced energy plays a crucial role in the economic viability of SWTs and PV plants and, particularly, after the partial or total cut of incentives and uncertainties related to supporting policies within the EU context. The study of the energy demand profile of a specific user and the adoption of battery energy storage (BES) systems have been identified as effective strategies to increase the energy self-consumption contribution. Such aspects have led to the development of an analytic model for the techno-economic design of a grid connected hybrid energy system (HES), integrating a PV plant and a BES system (grid connected PV-BES HES). The economic profitability of the grid connected PV-BES HES, evaluated for a real case study, is comparable with PV plants without storage in case of a significant gap between the cost of energy purchased from the grid and the price of energy sold to the grid, but high BES system costs due to the initial investment and the maintenance activities and the eventual presence of incentives for the energy sold to the grid can make the investment not particularly attractive. Thus, the focus has shifted to the techno-economic analysis of off-grid HES to meet the energy demand of users in remote areas. In this context, BES systems have a significant role in the operation and management of the system, in addition to the storage of exceeding energy produced by the intermittent and variable RESs. The analysis has also been strengthened by an industrial application with the aim to configure, test and install two off-grid HESs to meet the energy demand of a remote village and a telecommunication system.
In parallel, two experimental activities in the context of solar concentrating technology, a promising and not fully developed technology, have been carried out. The former activity deals with the design, development and field test of a Fresnel lens pilot-scale solar concentrating prototype for the PV energy distributed generation, through multi-junction solar cells, and the parallel low temperature heat recovery (micro-cogeneration CPV/T system). The latter activity deals with the development of a low cost thermal energy (TES) storage prototype for concentrating solar power (CSP) plants. TES systems show a great potential in the CSP plants profitability since they can overcome the intermittent nature of sunlight and increase the capacity factor of the solar thermal power plant.
Concluding, the present Ph.D dissertation describes effective methods and tools for the optimization and enhancement of RESs. The obtained results, showing their critical issues and potential, aim to contribute to their diffusion and favor a sustainable developmen
Short and long-term load conditions for tunnels in low permeability ground in the framework of the convergence-confinement method
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Stabilità del fronte di gallerie scavate con EPB in terreni sciolti stratificati di diversa permeabilità
No full textLa ricerca trae origine dall'analisi geotecnica di gallerie con fronte misto, che possono presentare particolari difficoltà nella valutazione della pressione di stabilizzazione richiesta e nella condotta dello scavo con scudi EPB. In particolare, vengono illustrati i risultati di alcune modellazioni idro-meccaniche tridimensionali, sviluppate per il caso tipico di un fronte attraversato da uno strato di terreno più sciolto e permeabile rispetto alle caratteristiche medie della formazione. Una situazione di questo tipo è stata incontrata nel corso dello scavo delle gallerie per una nuova linea metropolitana nella città di Vancouver, in depositi limosi di origine glaciale, con un battente idraulico di circa 20m. Fattori critici per la stabilità del fronte e il regolare avanzamento della TBM sono stati individuati nell'omogeneità e nella permeabilità sufficientemente ridotta del materiale all'interno della camera di scavo. La ricerca ha fornito indicazioni utili sul tipo di condizionamento applicabile nella pratica per ottenere le condizioni richieste nella camera di scavo e sui modelli ingegneristici in grado di rappresentarne il comportamento. Le prove in sito sul materiale estratto dalla coclea (misure di permeabilità e indici di lavorabilità) messe a punto nel cantiere di Vancouver presentano aspetti di interesse generale e sono applicabili anche in altre situazioni
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