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City Gates. Proportional criteria and shape models for the design of Baroque gates in Turin
No full textBaroque Turin was the subject of three expansions, which involved the transformation of the city walls and the construction of new bastions and gates to access the city. The gate named Porta Nuova was designed by Carlo di Castellamonte and built in 1620; the Porta di Po since 1674, with the contributions of Amedeo di Castellamonte, designer of the guard-house, and Guarino Guarini, designer of the façade towards the river. Both gates were demolished in the early 19th century during the French occupation. There are numerous archival and iconographic documents representing them, testifying to the design phases and variants over time and, in the case of Porta di Po, the foundation remains, discovered in the late Ninety during the works in the area. Through graphical analyses and digital modeling will be proposed reconstructions, highlighted proportional criteria and set up comparisons with the different historical images
Investigation Into Advanced Architecture and Strategies For Turbocharged Compressed Natural Gas Heavy Duty SI-engine
No full textCNG is at present retaining a growing interest as a factual alternative to traditional fuel for SI engine thanks to its high potentials in reducing the engine-out emissions. Increasing thrust into the exploitation of NG in the transport field is in fact produced by the even more stringent emission regulations which are being introduced into the worldwide scenario. Specific attention is also to be devoted to heavy duty engines given the high impact they retain due to the diesel oil exploitation and to the PM emissions, the latter issue assessing for the need to shift towards alternative fuels such as natural gas. A thorough control of the air-to-fuel ratio appears to be mandatory in spark ignition CNG engines in order to meet the even more stringent thresholds set by the current regulations. The accuracy of the air/fuel mixture highly depends on the injection system dynamic behavior and to its coupling to the engine fluid-dynamic. The amount of injected fuel should in fact be properly targeted by the ECU basing on the estimation of the induced air and accounting for the embedded closed-loop strategies. Still, these latter are normally derived from engine-base routines and totally ignore the injection system dynamics. Thus, a sound investigation into the mixing process can only be achieved provided that a proper analysis of the injection rail and of the injectors is carried out. The first part of the present work carries out a numerical investigation into the fluid dynamic behavior of a commercial CNG injection system by means of a 0D-1D code. The research has been focused on defining the set of parameters to be precisely reproduced in the 0D-1D simulation so as to match the injection system experimental behavior. Specific attention has been paid to the one component which significantly contributes to fully defining its dynamic response, i.e. the pressure reducing valve. The pressure reducer is made up of various elements that retain diverse weights on the valve behavior and should consequently be differently addressed to. A refined model of the pressure reducer has hence been proposed and the model has been calibrated, tested and run under various operating conditions so as to assess for the set-up validity. Comparisons have been carried out on steady state points as well as through out a vehicle driving cycle and the model capability to properly reproduce the real system characteristic has been investigated into. The proposed valve model has proved to consistently replicate the injection system response for different speed and load conditions. A few methodological indications concerning modeling aspects of a pressure regulator can be drawn from the present study. The model has been run in a predictive mode so as to inquiry into the response of the system to fast transient operations, both in terms of speed and load. The model outputs have highlighted mismatches between the ECU target mass and the actually injected one and have hinted at the need for dedicated and refined control strategies capable of preventing anomalies in the mixture formation and hence in the engine functioning. The second part of the present work aims at deeply investigating into the potentials of a heavy duty engine running on CNG and equipped with two different injection systems, an advanced SP one and a prototype MP one. The considered 7.8 liter engine was designed and produced to implement a Sigle-Point (SP) strategy and has hence been modified to run with a dedicated Multi-Point (MP) system so as to take advantage of its flexibility in terms of control strategies. More specifically, a thorough comparison between the experimental performances of the engine equipped with the two injection systems has been carried out at steady state as well as at transient operations. Better performances in terms of cycle-to-cycle variability were proved for the MP system despite poorer mixture homogeneity. Attention has also been paid to the different engine control strategies to be eventually adopted in compliance with the constraints set by the two different layouts. A 0D-1D model has also been built and validated on the experimental data set to be hence exploited for investigating into different strategies both for the SP and for the MP layout. An extensive simulation has been carried out on the effects of the injection phasing on the SP system performance referring to the engine power output and to the air-to-fuel ratio homogeneity amongst the cylinders. Finally, as far as the MP injection system is concerned, the innovative fire-skipping (DSF) or cylinder deactivation has been considered and deployed by means of the numerical model, assessing for an overall decrease in the fuel consumption of 12% at part load operations
Effect of Sample Preparation on the Microstructural Evaluation of Al-GNPs Nanocomposites
No full textMetallography is a key characterization method which can be affected by different variables. In aluminum-graphene nanoplatelet nanocomposites, mechanical interlocking is the main interfacial bonding. During the standard polishing, graphene nanoplatelets are removed leaving microvoids, and consequently in the microstructure of samples after sintering, two types of microvoids are revealed: one corresponding to the lack of sintering and another to the location of graphene which is removed during the polishing step. Thus, in this work a different polishing route is recommended to avoid the formation of the polishing related microvoids
Living in a flexible space
No full textHow long does a space or an object have to last? If in the past an object or a building manufacturing was designed to last as much as possible, nowadays it is designed to have a life related to the time in which it will be used. Flexibility is what characterizes a space, it's the ability to be variable and adaptable to changes in the lives of users or in relation to the use which these will make over time. The evolution of the labour market, the difficulty of inserting within it and the need to push more and more frequent move today in the trial of living space models increasingly flexible: people, especially young people, are forced to move on territory outlining a new condition to which the flexible nomadic dwellings offer an adequate response, ensuring high functional performance in confined space
Balancing Heritage Conservation and Sustainable Development - The Case of Bordeaux
No full textOver the past few decades sustainability concerns have positioned themselves with a central importance to the contemporary debate on the future development of cities, due to fast urbanization, increasing pollution, intensity of climate change and resource consumption. In this worldwide context, the historic city is suffering from pressures never seen before. For this reason, in the historic urban landscape urban conservation strategies have to be integrated within the large goals of sustainable development, as affirmed by the recent UNESCO's Recommendation on the Historic Urban Landscape adopted in 2011. The Recommendation reflects the actual international attention given in order to find a holistic approach, which integrates urban conservation and development in balance with social, environmental, economic and cultural sustainable considerations. Through this framework, certain questions emerge: how can urban conservation open up to sustainability whilst keeping intact tangible and intangible values and heritage? What are the strategies and policies implemented? Recognizing that sustainability is a primary challenge that urban conservation faces, this paper aims to present the case study of Bordeaux, a port city in south-western France. Since 2007, Bordeaux has been inscribed as an inhabited historic city on the World Heritage List on the basis of an outstanding urban and architectural ensemble. Yet at the same time, it has developed a series of interesting policies in order to avoid a "museification" of the inner city with the aim of ensuring a "historic living city", able to evolve and develop itself in a sustainable way over time in accordance with its heritage. For these reasons the case of Bordeaux is emblematic to demonstrate the possible adaptation of urban conservation tools in order to take into account sustainability aims and shows a great step forward in wedding heritage preservation and sustainable development, currently still far from being a common practice
Robustness assessment of rc framed structures against progressive collapse
No full textThe structural behaviour of buildings under overloading or extraordinary events like impacts, explosions or human errors is extensively admitted to be an influential feature of structural design. Structural robustness is a requirement provided by many current design codes. However, the problem is often recognized in a qualitative manner without referring to a specific process for the evaluation or the achievement of the robustness of constructions. In this paper, a novel procedure derived from dynamic and non-linear static analyses is provided for evaluating and comparing the relative robustness of reinforced concrete (RC) frame buildings against progressive collapse. The developed methodology offers a formal way to compute "robustness curves" following the sudden loss of one or more vertical load carrying member/s. This method suggests a strategy for the definition of the robustness indices, which are applied to two RC frame buildings. The first building was designed for gravity load and earthquake resistance in accordance with Eurocode 8 and the second was the same structure, modified according to the tie force (TF) method. The TF method is one of the major design quantitative procedures for enhancing resistance to progressive collapse and it is currently recommended by the codes of practice. In an attempt to demonstrate the suitability of the procedure, the structural robustness and resistance to progressive collapse of the two schemes is compared
3D multi-physics modelling and validation of the model of a Polymer Electrolyte Membrane Fuel
No full textThis Ph.D. thesis focuses on testing and modelling PEMFC single cell systems, to better understand internal phenomena and to find out operative solutions able to increase the overall cell performance. Thus, the first step is based on the creation and validation of a wide spectrum of multi-physics models of PEMFC fed with hydrogen or methanol, by using Comsol® Multi-physics platform coupled with Matlab®. All models are able to work under different operating conditions and with materials of different characteristics (membranes and catalysts). Moreover, the efforts were also focused on the creation of models of systems similar to fuel cell, as the gas diffusion electrode (GDE). The GDE is usually employed to analyze the electrochemical properties of the catalytic layer. Each single model was validated against a huge set of experimental data (partly obtained at POLITO, partly provided by the partners of two research projects: DURAMET and NAMEDPEM). After the model validation, these models were used to investigate the internal phenomena, and how materials, geometry and operative conditions affect the cell performance. Furthermore, particular problems affecting the entire FC system such as water flooding, methanol crossover, flow patterns design and current density distribution were deeply investigated to provide reasonable solutions. In general, the 3D multi-physics, multi-component, multi-phase and not-isothermal models developed in this Ph.D. include Maxwell-Stefan, Navier-Stokes-Brinckman, and extended two-phase Darcy-law to solve velocity, pressure, and mass transfer equations, and modified Butler-Volmer and Tafel equations to describe the electrochemical kinetics. All the equations are coupled to each other to simulate the performance of a single cell PEMFC (or GDE), reproducing the electrochemical, fluid-dynamics, and thermal phenomena. Each model was validated by comparing the simulated results, in terms of electric performance (polarization curves and power density curves), with experimental data obtained by changing several parameters: -Type of membranes: Nafion® (N112, N115, N117), Fumapem® (F1850) for the DMFC, Nafion® (N-HP and NR-212) for the hydrogen-fed PEMFC. -Dimensions of active area of the single cell: 5cm2 and 25cm2. -Catalyst: eight different catalysts for the DMFC, four for the hydrogen-fed PEMFC, three for the GDE (commercial Pt/C, PtRu/C and lab-made FeNC-based catalysts). -Operative conditions: pressure, methanol inlet concentration, air or oxygen at the cathode, cell and flow temperatures, anode and cathode flow rates, humidification and stoichiometric ratio (for the hydrogen-fed PEMFC). -Flow field designs: unique serpentine, four parallel serpentines and four inlet serpentine. After the validation, the models were used to reproduce and study the multi-dimensional trends of particular phenomena which produce system losses and/or affect the performance. In first istance, the multi-physics analysis was used to improve the way to deposit the catalyst, thus the catalytic layer distribution was investigated in order to have a better uniformity in the current density distribution at the membrane/anodic catalyst interface. The proposed solutions, the 3-Layers MEA, was modelled in Comsol® and tested in the lab. It should avoid hot-spots on the membrane as a consequence of the better uniformity in the current density distribution, with a consequent increase in the life-time of the MEA (chapter I) The second step was the analysis of the influence of water flooding and catalyst materials. The extended two-phase Darcy-law was used into the model to describe the mass transport inside the micro-porous structure of the noble/non-noble metal cathode catalyst, produced in our labs. The multi-physics analysis displays a direct relationship between the water saturation, the oxygen diffusion flow, and the oxygen consumption. Thus, water condensation inside the micro-pores may produce the flooding of micro and meso-porous, showing a consequent link between condensation and decreasing of cell performance (chapter II). The third step of the multi-physics analysis was the study of the influence of FF design (unique serpentine, four parallel serpentines, four inlet serpentines.) and types of membrane on system performance. A large amount of lab tests and simulation were performed for each FF, by changing the temperatures, the inlet flow rates, the inlet methanol concentrations and the type of cathode flow. Pulse Field Gradient (PFG) NMR spectroscopy was used to get a direct measurement of the diffusion coefficients of water and methanol through the membranes. Thus, the model was used as a tool to investigate anodic overpotentials, water and methanol crossover flow rates, current density distribution along the membrane, understanding the relationship between the shape of the FF and cell performance (i.e. pressure and methanol consumption).(chapter III) To improve the research on the area of catalyst properties, the study focused on the cathode using the gas diffusion electrode (GDE), trying to find out key parameters which influence the performance of catalysts for the oxygen reduction reaction. A commercial Pt-based catalysts and the non-noble metal Fe-N-C catalyst prepared in-house were tested and modelled, to carry out a sensitive analysis by varying the inlet oxygen flow rate, showing the influence of oxygen diffusive flow on the catalyst performance. The multi-physics analysis provides the way to increase the performance of the non-noble metal catalyst by changing some system properties as tortuosity, porosity and hydrophobicity (chapter IV) After the large analysis developed for DMFC, the PhD work continued with the modelling of hydrogen-fed PEMFC, to complete, in such way, the general sensitivity analysis on PEMFC systems. Obviously, some innovations and changings were introduced to adapt the model with the new inlet fuel, as new equations and parameters for the electrochemical behaviours, initial and boundary conditions, H2 crossover and controlled parameters, i.e., relative humidity. The multi-physics analysis and the lab tests show how the relative humidity influence the performance, in relation to the variation of pressure and temperature (chapter V) After the experimental and modelling studies, the PhD work was focused on several aspects, in order to improve the performance of the single cell with Fe-N-C catalyst on the cathode, related to material improvement and the single cell system: the active surface area, the percentage of micro-pores present in the catalytic layer, the membrane type, the procedure of catalyst deposition, the back pressure and the closing force. Thus, the modelling and lab work performed outcome in an excellent result: the system performance increases four times than the initial computed value, from about 10 mW cm-2 to 40.6 mW cm-2
Analysis of injection, mixture formation and combustion processes for innovative CNG Engines
No full textNatural gas is a promising alternative fuel for internal combustion engines application due to its low carbon content and high knock resistance. The work presented in this thesis deals with the fluid dynamics, experimental study and optimization of different technologies aimed at exploiting the potentials of such fuel at best. The first section of the work is aimed at the combustion chamber optimization with the focus on the combustion stability. The engine considered in the study is a prototype specifically dedicated to CNG. It features a variable valve actuation system and has been released with different and very high compression ratios ranging from 12 to 14. An innovative experimental methodology based on hot wire anemometry (HWA) purposely developed by Centro Ricerche Fiat (CRF) has been adopted for the characterization of the steady-state tumble. The HWA method has been validated against the well-known Ricardo method and is used as a basis for the development and validation of a numerical "virtual flow bench". The numerical model has been used to gain a deeper insight into the fluid dynamic phenomena and to replace the experimental campaign considering a head variant and quantifying its tumbling and volumetric performances. A transient 3D CFD analysis for the complete engine cycle has been performed in order to evaluate the effect on the combustion process of different compression ratios and head designs.The results showed that the HWA technique represents a factual alternative to the integral technique for the tumble characterization. The "Virtual flow box" model turned out to be accurate enough to evaluate the main flow motions induced by the head design and to be a valid tool complementary to the experimental method. Finally, the transient model used in combination with the ECFM-3z combustion model is fairly accurate for the comparative analysis between different engine designs and/or valve actuations. Despite the main findings of the flow model activity, importance should also be placed onto advanced technologies for natural gas engines such as direct injection. Thus, the second section is aimed at the numerical study of a natural gas direct injection engine. The numerical complexity caused by the high pressure ratio at nozzle exit has been faced using an accurate mesh procedure able to correctly capture the formation of shocks structures. Moreover, the actual needle geometry and the realistic needle movement has been taken into account in order to correctly simulate the opening and closing transient. The final mix and turbulence level has been evaluated comparing two engine prototypes and considering several injection strategies. Finally, a qualitative validation of the computational model has been performed comparing the simulation results with the available experimental data obtained through the PLIF procedure on an equivalent optical engine. The CFD model resulted to be accurate in the prediction of the mixing quality and it shows to be a reliable tool for the analysis of the main mixing mechanism and so for the assessment of the best injection strategy
Waring loci and the Strassen conjecture
No full textThe Waring locus of a form F is the collection of the degree one forms appearing in some minimal sum of powers decomposition of F. In this paper, we give a complete description of Waring loci for several family of forms, such as quadrics, monomials, binary forms and plane cubics. We also introduce a Waring loci version of Strassen's Conjecture, which implies the original conjecture, and we prove it in many cases