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Bounded-input-bounded-state stabilization of switched processes and periodic asymptotic controllability
No full textThe main result of this paper is a sufficient condition for the existence of periodic switching signals which render asymptotically stable at the origin a linear switched process defined by a pair of real matrices. The interest of this result is motivated by the application to the problem of bounded-input-bounded-state (with respect to an external input) stabilization of linear switched processes
Proper Orthogonal Decomposition for Surrogate Models in Aerodynamics
No full textThis study describes the design and implementation of surrogate models for aerodynamic optimization or database generations. Two different methods are presented: the first one follows the classical methodology: a parametric POD is applied to a set of initial solutions or snapshots obtained with an high fidelity CFD model. With respect to approaches presented in literature, in this research work no truncation of the POD modes is performed and they are all used to construct the surrogate model. Several applications are presented: a backward facing step case, the analysis of the flow around a NACA 0012 airfoil and a RAE 2822 supercritical airfoil, the optimization of an automotive external shape and a database generation of a three-dimensional aircraft
Experimental and numerical approaches for the quantification of tumble intensity in high-performance SI engines
No full textThe activity presented in the paper is focused on the development of a high-performance engine specifically dedicated to CNG fueling. The engine features a variable valve actuation system as well as different possible compression ratios ranging between 12 and 14. More specifically, the present work carries out an experimental and numerical characterization of the steady-state tumble flow from the engine head and deals with the development and assessment of a numerical model for the engine-cycle transient simulation. Experimental tests were carried out at Fiat Research Center (CRF) on a flow test rig equipped with two different devices for the tumble measurement, based on the Ricardo method and on the two-dimensional HWA acquisition of the axial velocity, respectively. It is worth highlighting that the HWA technique was purposely developed by CRF for the tumble characterization. The experimental results were also used for the calibration of a ‘virtual flow box' numerical model, which was in turn exploited to gain complimentary information about the characteristics of the tumbling flow and to define the requirements for the transient CFD model of the real engine, both in terms of discretization mesh and turbulence modeling. The results showed that the HWA technique represents a factual alternative to the integral techniques for tumble characterization. It also provides additional information about the unevenness of the flow distribution generated by the intake system. The ‘virtual flow box' simulations pointed out that good results can be obtained by using the Realizable k- model, whereas both the Realizable and the RNG k- models proved to be appropriate for the engine transient simulations. Finally, the CFD models showed to be fairly accurate and reliable, especially when the relative changes from one engine geometry and/or valve actuation to another need to be accounted for
Improvement of Agilent 3458A Performances in Wideband Complex Transfer Function Measurement
No full textDigital multimeters (DMMs) Agilent 3458A are valuable devices in accurate characterization of voltage transducers. Five selectable ranges, from 100 mV to 1 kV, high input impedance and accuracy make this device the state of the art. The paper focuses on the correction of the multimeter frequency response when used in Direct Current digitising mode (DCV), to allow post-correction of the errors introduced by the digitizers. To this end, two different approaches for the identification of the multimeter input complex filter function up to about 100 kHz are proposed. They are, respectively, based on the identification of the complex filter transfer function considering the input stage of the DMM as a black box and on the estimation of the parameter of the DMM input stage. The two methods are validated in a test case and equivalence of the results obtained is found. As a further verification, a deep investigation of DCV and direct sampling mode is performed when the zero level trigger mode is set
Blunt notch failure behavior of low alloy steels, as quenched from high or conventional austenitizing temperatures: An investigation through FFM
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Teoria del progetto architettonico. Dai disegni agli effetti
No full textDopo gli anni fortunati dell'impegno dell'architettura italiana, e dopo più di tre decenni di silenzio, il libro riapre la discussione sulla teoria e propone, a partire da categorie completamente rinnovate, una riflessione sistematica sul potere del progetto. Grazie allo spostamento dell'attenzione dal soggetto (le sue buone intenzioni, insegnate all'università) all'oggetto (i prodotti progettuali, in azione nel sistema sociale che li contiene), il volume si impegna in una trattazione analitica e verificabile delle pratiche progettuali. Che cos'è un progetto architettonico? A chi e a che cosa deve il proprio potere? Quali fatti deve considerare? Quali valori può incarnare? Invece di rivolgersi alle teorie dell'architettura e alla loro implicita normatività, il libro risponde a queste domande concentrandosi sulle forme della prassi progettuale. In un confronto continuo con altri saperi - quali l'ontologia sociale, l'Actor-Network Theory, la semiologia, la sociologia della tecnica, le scienze cognitive, la geografia - la "teoria del progetto" ambisce a ricomporre un campo di competenza, altrimenti misconosciuto o ridotto ad altro: l'arte, le tecniche edilizie, la burocrazia, l'attivismo politico e sociale. Se concepita come sapere positivo, l'azione progettuale può invece essere intesa come uno specifico insieme di competenze e poteri, a cavallo fra tecnica e politica, dimensione burocratica e simbolica, previsione e narrazione. Con una prefazione di Maurizio Ferraris
Data Distribution and Control in Modern Networks
No full textData Distribution and control over the Internet and modern networks is a very hot issue these days. The aim of this thesis is to address, on one hand, data dissemination in terms of energy consumption over Content Delivery Networks (CDNs) and, on the other hand, network control and scalability issues regarding Software Defined Networking (SDN). Data dissemination via CDNs is a leading energy-consuming sector in the ICT area. A CDN system can be abstracted as a main server hosting the entire data set and several surrogate servers, each one housing a portion of the whole data set. In order to design the architecture of a CDN system and to plan network policies, having a clear idea about energy consumption of the network can play an important role. Thus, a realistic model is needed to compute energy consumption of a system according to network characteristics. This model can guide network architects to design an energy efficient network while keeping performance in the desired level. In this dissertation, a new model to compute energy consumption of CDNs is presented. Two major aspects distinguish this model from the existing ones. Firstly, the Internet topology considered in the model, despite existing models exploiting a flat graph, is a three-tier map which is close to the real Internet topology. The three-tier topology represents the three levels of ISPs forming the Internet. The second novelty of the model is that total energy consumption also comprises synchronization energy consumption, which is the energy consumed to keep all surrogate servers up to date and synchronized. In order to validate the model, a CDN simulator is designed to simulate the hierarchical network and to consider synchronization energy consumption. Results show the importance of synchronization and reveal how synchronization can affect the total energy consumption. Various caching strategies are compared and the impact of caching policies, content popularity, network topology and number of surrogates is discussed. In all mentioned scenarios, various content request and modification ranges are compared
The Web, the Users, and the MOS: Influence of HTTP/2 on User Experience
No full textThis work focuses on the evaluation of Web quality of experience as perceived by actual users and in particular on the impact of HTTP/1 vs HTTP/2. We adopt an experimental methodology that uses real web pages served through a realistic testbed where we control network, protocol, and application configuration. Users are asked to browse such pages and provide their subjective feedback, which we leverage to obtain the Mean Opinion Score (MOS), while the testbed records objective metrics. The collected dataset comprises over 4,000 grades that we explore to tackle the question whether HTTP/2 improves users experience, to what extent, and in which conditions. Findings show that users report marginal differences, with 22%, 52%, 26% of HTTP/2 MOS being better, identical, or worse than HTTP/1, respectively. Even in scenarios that favor HTTP/2, results are not as sharp as expected. This is in contrast with objective metrics, which instead record a positive impact with HTTP/2 usage. This shows the complexity of understanding the web experience and the need to involve actual users in the quality assessment process