Thermo-mechanical delamination analysis by a plate model with "adaptive" representation of displacements and temperature

Progressive delamination under thermo-mechanical loading can lead either to a premature failure or a consistent loss of strength and stiffness of laminated and sandwich composites in service. Customary, three-dimensional finite element models are used to predict the stress fields with the highest accuracy, yet the behavior of the delamination crack is simulated by fracture mechanics or cohesive interface models, but these models may overwhelm the computational capacity. Refined plate models that accurately capture the stress fields with a lower computational effort are to date available, which may overcome the problem. Here a recently developed multilayered zig-zag model is applied to the analysis of delamination under impact and thermal loading. This model, which a priori fulfills the equilibrium of out-of-plane stresses and the heat conduction equation at the interfaces, has a hierarchic representation of displacements and temperature across the thickness, but just five displacement d.o.f. and two temperature d.o.f., in order to limit the memory storage occupation. The onset of delamination is predicted using stress based criteria, as customary, while a mesoscale model is used to accurately and efficiently accounts for the evolving damage. So, instead of guessing suited multiplication factors, the degraded properties of the failed regions are computed at each time step. The strain energy updating technique by the author is used to develop an efficient C finite element model. The numerical results show the good accuracy of the present modelling approac

Si-SiC based materials obtained by infiltration of silicon: study and applications

Many efforts and investments have been made in the last decades in order to obtain materials able to withstand extreme conditions in several technological fields such as future military, industrial and space based projects. The present PhD thesis addresses this problem dealing Ultra High Temperature Ceramics (UHTCs) and in particular focusing on Si-SiC-ZrB2 composites obtained with a technique named silicon reactive infiltration (SRI). Each major chapter of the present thesis relates to an article either published or in press on the journals indicated at the end in the seventh chapter (List of author's publications). The sequence of these chapters is obviously not random, but trying to follow the streamline that leads from the physico-chemical and technological properties of the material to its applications, in my case this is meant its use in industrial burners within an european project: CEREXPRO, that was financially supported by the European Commission in the FP7 (7th Framework Programme). The reader is introduced to the current state of the art of UHTC (Chapter 1) having a historical review of UHTC research carried out thus far. Since the most comprehensive research has been focused on compositions containing HfB2 or ZrB2, they are the primary materials discussed. The chapter concludes by illustrating a particular type of UHTC: the siliconized silicon carbide (Si-SiC) and the infiltration method used to obtain it. In the second chapter a methodology to produce Si-SiC-ZrB2 bulk ceramics, taking advantage of the reactive infiltration technique, is proposed. Preforms with different contents of SiC and ZrB2 were compacted with phenolic resin, pyrolysed and finally infiltrated with molten silicon at temperature above its melting point. A detailed study of the mutual interactions between the Si-SiC-ZrB2 constituent materials during their processing and of their chemical activity with oxygen at high temperatures in the prospect of using this material as a matrix of a continuous fiber reinforced composite is addressed in Chapter 3. The study of the early stage of oxidation is the first part of this chapter, while the second part is focused on the long-term oxidation of some selected samples at a high temperature. The aim of chapter four is to give an overview of the processing routes currently available for the preparation of macro-porous ceramics, with particular emphasis on the processing-microstructure-property relations inherent to each process. At the end, the chapter presents several high temperature applications in which Si-SiC foams are currently applied because of their superior thermo-mechanical properties. The Chapter 5, in fact, aims to track the changes of Si-SiC foam properties during the first part of a long time aging condition, typical of industrial burner applications. The project "CEREXPRO" (CERamic heat EXchangers with enhanced materials PROperties), discussed in the Chapter 6, was aimed to develop a new generation of ceramic heat exchangers for high temperature heat recovery with the target of significantly reducing the size and weight as well as also the price of such components by simplifying the manufacturing process and allowing a higher flexibility in the heat exchanger geometry. The use of precursors/template materials taken from the textile industries and a subsequent ceramic conversion, via liquid silicon infiltration, is proposed as the main technological path for reaching the above objectives. The main role of the Polytechnic within this project was the characterization process of material

Physical Inspection metering and evaluation of HVAC systems efficiency in tertiary buildings

Since twenty years European Union produces Directive to decrease energy consumption. The building sector is one of the most affected, since the buildings we live and work are responsible of about one third of global European energy consumption. Heating, Ventilation and air conditioning systems (HVAC systems) are often unknown by end-users. Also building owner and manager do not know deeply how the systems is composed. In the present work the writer found numerous specific diagnosis and intervention on HVAC system to dramatically decrease energy consumption. Incredible energy savings are possible by simply check and set up the right schedule and set up of HVAC system. Numerous European funded project demonstrated the effectiveness of such approach. Two European project results are described: Harmonac and iSERVcmb. Harmonac set up standards for HVAC systems inspections, the main findings are related to: general lack of information about system/components effectively installed in a building, HVAC inspections needing of a specific knowledge, not available in the market, lack of knowledge on control system by maintenance service companies, general over sizing of Heating power, Cooling power and water flow, scarce availability of logged data concerning energy consumption. BMS (Building Management System), if properly designed and installed could decrease inspection time and increase energy efficiency. Nevertheless, the inspections carried out in those years show that few BMS were able to log energy data. With a correctly installed BMS data of consumption the strategy and schedule of HVAC system should be understand, and also pointed the major energy savings opportunities. Buildings long term metering shown that HVAC inspection is fundamental to ensure efficiency of systems and, as a result, the best performance in terms of energy savings and comfort. BMS system should help in this issue, but they have to be originally designed for this purpose. Short term metering demonstrated that such approach could be a low cost solution to understand system behaviour and potential improvement. Building owner approach to system inspection shown clearly that there is a common under estimation of energy savings that could be reached by simply control strategy management. Since is necessary to demonstrate to building owner how much energy (and money) is possible to save with metering and operation control, the writer believe that the next step is to provide robust benchmark for the most common activities. With benchmark data will be easier to understand the potential of energy savings that is possible to achieve in buildings. That will convince building owner and/or financial bodies and ESCO to invest in big refurbishment of existent building stock, that are just operated "as usual.

New Techniques for Reliability Characterization of Electronic Circuits

Integrated electronic systems are increasingly used in an wide number of applications and environments, ranging from critical missions to low cost consumer products. Information processing has been thoroughly integrated into everyday objects and activities, in the so-called ubiquitous computing paradigm. This wide distribution is caused mainly by the miniaturization of semiconductor devices (transistor channel length scaling from 180 nm in 1999 to 22 nm in 2012), which allows integrating a complete system on a single chip (SoC). However, there are many difficult challenges associated with continued cost reduction, size reduction, improved performance and improved power efficiency. One of these challenges is the reliability of these electronic systems. Important research efforts are aimed at improving the reliability of semiconductors. Manufacturing processes, intrinsic aging phenomena of components and environmental stress may cause internal defects and damages during the lifetime of a system, possibly causing misbehaviours or failures. In order to guarantee product quality and consumer satisfaction, it is necessary not only to discover faults as soon as possible in the manufacturing process, but also to continuously check for their absence throughout a product lifetime. Today's modern systems have become increasingly complex to design and build, while the demand for reliability and cost effective development continues. Reliability is one of the most important attributes in all these systems, including aerospace applications, real-time control, medical care, defence equipment, transportation, communication, entertainment products, agriculture, energy and environmental systems. Growing international competition has increased the need for all designers, managers, practitioners, scientists and engineers to ensure a high level of reliability of their product before release and during mission time, at the lowest cost. The interest in reliability has been growing in recent years and this trend will continue during the next decade and beyond. With testers being expensive pieces of equipment and the cost of transistors continuously decreasing, it make sense to use some of these low-cost transistors to replace the costly test tools, whenever possible. The first low cost approach we can think about is using the devices themselves to implement their own test. This is the underlying motivation of functional Software-Based Self-Test (SBST): a fast, powerful microprocessor, which has lots of resources, could certainty help in its testing procedure. Having the outstanding advantages of enabling at-speed testing, zero area overhead and actually testing the device's operation, this approach also has some drawbacks. Even if SBST is essentially suitable for online testing (and sometimes it is the only possible approach), it requires some dedicated system memory for the functional testing data, which can reach very big sizes. Also some faults happen to be functionally untestable; i.e., you cannot detect them exclusively by running proper software routines. For this reason a combination of both functional and structural test approaches is common practise. A second natural approach to low cost testing is design for test (DfT). Add some extra (cheap) area on-chip specifically in charge of performing and managing tests. The DfT path started long ago, but it is still a key element in 2012 International Technology Roadmap for Semiconductors (ITRS)[1] test roadmap. Different sorts of DfT enable the use of low cost testers, contributing to the full checking of a device, and may also be reused for online testing purposes. Logic and Memory Built-In Self Test (BIST) schemas are usual practises. Analogue DfT, even if it is not as advances as digital one, is also an interesting strategy, especially when the analogue or mixed-signal device is integrated in a wider digital system like a SoC Finally, there ar

Design of Algorithms and Protocols for Peer-To-Peer Streaming Systems

Peer-to-Peer Streaming (P2P-TV) systems have been studied in the literature for some time and they are becoming popular among users as well. P2P-TV systems target the real time delivery of a video stream, therefore posing different challenges compared to more traditional peer-to-peer applications such as file sharing (BitTor-rent) or VoIP (Skype). This document focuses on mesh based P2P-TV systems in which the peers form a generic overlay topology at application level upon which peers exchange small "chunks" of video. In particular, we study two problems related with this kind of systems: i) how to induce peers to share their available resources - such as their available upload bandwidth - in a totally automatic and distributed way; ii) how to localize P2P-TV traffic in order to lower the load on the underlying transport network without impairing the quality of experience (QoE) perceived by users. Goal i) can be achieved playing on two key aspects of P2P-TV systems that are: • the design of the trading phase needed to exchange chunks among neighbors; • the strategy adopted by peers to choose the neighbors to connect with, i.e., the policy employed to build and maintain the overlay topology at application level. The former task has been successfully accomplished with the development of algorithms that aim at adapting the rate at which peers offer chunks to their neighbors to both peer's available upload bandwidth and to the system demand. The results presented in this document show that the automatic adjustment of transmission rate to available upload capacity reduce delivery delays of chunks, thus improving the experience of users. Focusing on the latter problem, we prove that the topological properties of the overlay have a deep effect on both users' QoE and network impact. We developed a smart, flexible and fully distributed algorithm for neighbors selection and implemented it in a real P2P-TV client. This let us compare several different strategies for overlay construction in a large campaign of test-bed experiments. Results show that we can actually achieve the goal of leading peers to efficiently share their available resources - goal i) - while keeping a good degree of traffic localization, hence lowering the load on the underlying network - goal ii). Furthermore, our experimental results show that a proper selection of the neighborhood leads to a win-win situation where the performance of the application and QoE are both improved, while the network stress is nicely reduce

La gestione e l'impatto dei siti UNESCO:monitoraggio e valutazione dei siti italiani nel dibattito internazionale

La tesi analizza il mutamento nello scenario dei siti UNESCO e nella loro gestione, osservando in particolar modo quale sia la realtà italiana all'interno di tale contesto. Negli ultimi anni, infatti, la realtà della Lista del patrimonio mondiale UNESCO è notevolmente mutata, sono emerse nuove forme di valore e tipologie di patrimonio iscritto nella lista. Questi nuovi scenari richiedono nuove forme di amministrazione, sia dal punto legislativo che da quello socioeconomico. Nel primo capitolo viene descritto il quadro teorico e pratico di tali mutamenti negli anni e sono analizzati gli strumenti messi in atto in ambito internazionale per governare tali realtà complesse ed eterogenee e la loro interazione e impatto sul contesto locale di riferimento. In base al quadro fornito, nel secondo capitolo l'analisi si concentra sulla candidatura del paesaggio culturale dell'area vitivinicola delle Langhe, Monferrato e Roero visto come esempio di nuova tipologia di sito patrimonio dell'umanità e attualizzazione del dibattito teorico descritto. La larga diffusione sul territorio e la molteplicità di attori coinvolti nel processo, o dagli effetti dello stesso, hanno fatto sì che la candidatura stessa rappresentasse un fenomeno pubblico con rilevanti impatti anche di carattere sociale ed economico. Le strategie e metodologie di governance, analizzate nella teoria e nella pratica nei capitoli precedenti, necessitano di un processo di monitoraggio e valutazione, che viene approfondita all'interno della terza parte della tesi, esaminando preferibilmente le tematiche dell'efficacia della gestione e dell'impatto provocato dall'iscrizione alla lista de patrimonio mondiale e gli strumenti di studio e controllo attualmente in atto. Da tale analisi si sintetizza un modello che valuti la gestione del sito UNESCO descrivendo l'impatto generato sul territorio principalmente in termini qualitativi di rapporto con il territorio. Lo scopo è di studiare quanto le attività dei siti UNESCO, in particolare negli ambiti della conoscenza, conservazione valorizzazione e comunicazione abbiano ricadute significative sul territorio. Tale modello viene applicato ai casi studio di: Napoli, Genova, Firenze, Val d'Orcia, Pienza, Residenze Reali, Val Camonica, Alberobello. La conclusione del lavoro di ricerca riassume le considerazioni dei capitoli precedenti cercando di sintetizzare i casi analizzati in un modello per la comprensione della gestione di un sito UNESCO dalla fase di creazione dello stesso al mantenimento di tali risultati nel tempo, anche espandendo la discussione verso altre forme di patrimonio, come quello intangibile, o politiche pubbliche, come quelle rivolte all'innovazione e la creativit

Energy aware control algorithms for computer networks

The main motivation of this work is to investigate techniques to reduce the power consumption inside a network element. It is enough to consider the high energy demand associated to the telecommunication networks field. As practical consequence the power consumption has become a relevant parameter and it represents a critical constraint for the network designers looking both the whole network infrastructure and the network elements like switches, routers and servers. The PhD has been focused mainly on two research areas of interest, the first one was the power consumption inside the switching fabric of an high speed router. The target was to analyze the effect of the dynamic power inside a switching fabric, to evaluate a set of optimization strategies in order to minimize the power consumption and to achieve the best trade-off between power, high performances and packet delays; the crossbar was used as reference switching architecture for this study. Looking at the consumption side, generally speaking, it is possible to define two families of switching fabrics: �1)Bit-rate independent switching fabric, in which the consumption does not depend on the number of transported bits; this family is typical of optical switching fabrics �2)Bit-rate dependent switching fabric, where the total consumption is proportional to the data transmission bit-rate, this family is typical of electronic switching fabrics The second research activity was carried at the Alcatel-Lucent Bell Laboratories, based in New Jersey (USA) and over a period of 9 months. The study of the power consumption across several network elements that are commercially available for the "corporate" market. We started from a set of collected larger number of power measurements over these network elements and thanks to them we were able to develop a linear mathematical model to describe the power consumption of a generic network elemen