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Multi-physics modelling for the safety assessment of complex structural systems under fire
No full textAmong all structures, high-rise buildings pose specific design challenges with respect of fire safety for a number of reasons, in particular the evaluation of both the fire development (fire action) and response of the structural system to fire (structural behaviour).
In relation to the fire action, large compartments and open hallways often present in modern high-rise buildings don’t let themselves to be designed within compliance to current codes and standards. A comprehensive analysis of the fire environment is required to understand the fire dynamics in these cases. A Computational Fluid Dynamic (CFD) model allows a quite accurate representation of realistic fire scenarios, because it takes into account the distribution of fuel, the geometry, the occupancy of individual compartments and the temperature rise in structural elements that are located outside the tributary area of fire scenario.
In relation to the structural behaviour under fire, the passive fire resistance of structural elements and the intrinsic robustness of the system are the only measures to rely on in order to maintain the structural integrity of the building during and after the fire and avoid major economic losses due to structural failures and prolonged inoperability of the premises. Disproportionate damages induced by fire can be avoided with a proper design of the structure, aimed at reducing the vulnerability of the elements to fire (i.e. their sensitivity to fire) or at increasing the robustness of the structural system (i.e. its sensitivity to local damages).
The topic of this thesis is the evaluation of the structural safety in case of fire by means of advanced multi-physics analyses with direct reference to the modern Performance-Based Fire Design (PBFD) framework. A fundamental aspect is how some basic failure mechanisms can be triggered or modified by the presence of fire on a part of a structural system, such as three hinge mechanism, bowing effects, catenary action, thermal buckling and snap-through, sway and non-sway collapse. High rise buildings, which are expected to be susceptible to fire-induced progressive collapse, will be investigated. Critical elements will be identified in the system and countermeasure for enhancement of structural integrity will be suggested. The investigation of the response of such a complex structures subjected to fire scenarios requires the use of CFD and Finite Element (FE) models for a realistic evaluation of the fire action and of the structural response respectively
Trattamento EVAR della patologia aneurismatica addominale: complicanze precoci e tardive
No full textDevelopment of a diffusive sampler for the simultaneous measurement of nitrogen dioxide, nitrous acid and nitric acid in indoor environments and in sites of interest for cultural heritage preservation
No full textIn indoor environments NO2 hydrolysis can take place on surfaces covered by a thin layer of
humidity leading to the formation of nitrous and nitric acid. The acidification, mainly caused by
nitric acid which has the tendency to remain on the surfaces rather than being released in the air,
can lead to damage to materials indoors. A correct speciation of compounds such as nitrous acid
and nitrogen dioxide, intertwined through this hydrolysis mechanism and with a mutual interference
on the measurements, could only be achieved by the subsequent collection of the two species on
selective substrates. To overcome these problems a novel “multipollutant” diffusive sampler was
designed for the collection of three different pollutants (nitric acid, nitrous acid and nitrogen
dioxide) at separate sampling stages. The diffusive sampler was tested against reference techniques
showing a good agreement and fulfilling the basic requirements of a measurement method
(linearity, selectivity and reproducibility of the measurement provided).
A survey aimed at a preventive conservation activity was performed inside two archives (Swiss
National Library and Biblioteque de Geneve) using the new selective sampling method. Laboratory
development, field validation and some results collected in indoor environments are reported and
discussed
Analysis, design and optimization of broadband microwave filters for high-power applications
No full textIndirect Optimization of Bang-Bang Control Problems and Applications to Formation Flying Missions
No full textThis thesis is focused on indirect optimization methods for the design of space missions, and, in particular, to a specific class of optimal control problems whose solution exhibits a discontinuous control law: the so called bang-bang optimal control.
Any attempt to solving such problems by using an indirect method without any specific treatment of the bang-bang control inevitably results into a failure, except for trivial problems.
The thesis compares two techniques, conceptually quite different, that aim to handle (or just to reduce) issues related to the discontinuous profile of the optimal control: the Multi-Bound Approach and the Continuation-Smoothing Technique.
These two approaches are first tried out/tested on a very simple case (the rocket-sled problem) and then applied to obtain the solution of two rather complex problems: the cooperative rendezvous and the deployment of a two-spacecraft formation that flies in a High Eccentricity Orbit (referring to the Simbol-X project).
The general philosophy that stands behind either approach is outlined, as well as relative strength and weakness. Range of applicability, effort required to the user, computational time, and convergence radius are analyzed and discussed.This work was supported by the Centre National d’Etudes Spatiales (CNES), [Contract Number 93333/00]
A gas-surface interaction model for the numerical study of rocket nozzle flows over pyrolyzing ablative materials
No full textAblative materials provide a widespread, reliable, and relatively low–cost way to manage the extremely high heat fluxes that are normally encountered in a wide variety of aerospace applications. Typically, both non–pyrolyzing carbon–based and pyrolyzing carbon– and silica–based materials are used with this intent in rocket nozzles. Unfortunately, during the rocket firing these materials undergo a consumption that modifies the nozzle internal contour increasing the nozzle throat area and causing a drop down of the chamber pressure that, ultimately, results in an overall rocket performance reduction. For this reason, it is important to advance the fundamental understanding of the nozzle erosion processes and to develop useful scientific tools in this subject area. To this aim, a comprehensive model that would allow the study of the behavior of different ablative materials in rocket nozzle environment accounting for surface ablation, pyrolysis gas in- jection and resin decomposition has been developed, tested and validated. The model relies on surface mass and energy balances and deals with the gas–surface interaction erosive phenomena, accurately solving the gas side, using a CFD ap- proach. Two different ablation models have been implemented to simulate both the erosion of carbon– and silica–based materials. The steady–state ablation approximation is used in order to estimate the solid conductive heat flux, as well as the pyrolysis gas mass flow rate, in a closed way and without requiring the accurate resolution of the material heating by means of a thermal response code. Firstly, the talk will address a thorough description of the theoretical/numerical model. Then, several simulations, from sub–scale to full–scale nozzles, will be presented and the results will be compared with the experimental results.AVIO Group Sp
Nearly identical, yet very different: comparing the folding of proteins with increasing degree of sequence identities but different structure and function
No full textMIU
