Multi-disciplinary shape optimization of an entry capsule integrated with custom neural network approximation and multi-delity approach

This paper describes a new integrated approach for the multi-disciplinary optimization of a entry capsule’s shape. Aerothermodynamics, Flight Mechanics and Thermal Protection System behaviour of a reference spaceship when crossing Martian atmosphere are considered, and several analytical, semi-empirical and numerical models are used. The multi-objective and multi-disciplinary optimization process implemented in Isight software environment allows finding a Pareto front of best shapes. The optimization process is integrated with a set of artificial neural networks, trained and updated by a multi-fidelity evolution control approach, to approximate the objective and constraint functions. Results obtained by means of the integrated approach with neural networks approximators are described and compared to the results obtained by a different optimization process, not using the approximators. The comparison highlights advantages and possible drawbacks of the proposed method, mainly in terms of calls to the true model and precision of the obtained Pareto front

Hollow vortices and wakes past Chaplygin cusps

By using analytic tools for 2D rotational inviscid flow, the stagnation points of Pocklington hollow vortices are replaced by Chaplygin cusps, that is, by regions of fluid at rest. By solidifying the bounding free streamlines, solid bodies are obtained along whose walls adverse pressure gradients are avoided. These results are relevant to the theory and practice of control of separated flow at high Reynolds number. Examples are presented pertinent to single bodies and cascade of bodies which trap hollow vortices or generate open hollow wake

Propagation of boundary and geometrical uncertainties for the aeroacoustics analysis of a side mirror

Uncertainty in the design and operation of engineering systems may arise from various sources. The uncertainties in physical properties of materials and inevitable randomness in boundary conditions and geometries, as well as physical models uncertainties, are a few examples of such uncertainties that can significantly restrict the reliability of deterministic analyses and designs. For a reliable analysis and design process based on computational fluid dynamics (CFD) simulations, including computational aeroacoustics (CAA), all sources of uncertainty must be considered in the analysis and design process. However, CAA analyses requires exceptionally fine 3D computational meshes, very small time-step, and (usually) high-dimensional stochastic space, bringing to very high, and up to now prohibitive, computational costs. In the literature, various techniques have been proposed for uncertainty quantification (UQ). The Monte Carlo (MC) approach is widely used for UQ given its conceptual simplicity, but, unfortunately, the conventional MC methods converge slowly and often require a large number of samples to achieve reasonable accuracy and thus are impractical for problems with a large number of uncertainties, and/or very high computational costs. During the last decades, some other more efficient UQ approaches have been developed, with some of them being intrusive and others non-intrusive. The intrusive approaches involve some modifications of the implemented code, while non-intrusive methods consider the models as black-box and sample it through the use of meta-modelling techniques. Aeroacoustics has received great attention in the last years, due to the ever stricter noise regulations, and increased computational capabilities. However, despite the stochastic nature of most aeroacoustics systems and models, non-deterministic investigations in regards to computational aeroacoustics are limited. In this contribution, some non-intrusive approaches for probabilistic propagation of uncertainties are presented through the use a simple automotive test case, considering boundary and geometrical uncertainties for the aeroacoustics analysis of a side mirror. Obtained results are then used to detail some approaches giving statistical similitude between uncertain numerical performance and (synthetic) uncertain experimental data

Un progetto per Porta Genova

LAUREA MAGISTRALEE’ prevista la dismissione a breve di ben sette degli scali ferroviari presenti sul territorio milanese; aree di vaste dimensioni ed inserite nel tessuto urbano, spazi che sono rimasti preclusi alla città per anni e possono oggi venire restituiti ad essa. Lo strumento urbanistico vigente, il PGT di Milano, riconosce l’importanza degli scali definendoli come Ambiti di Trasformazione, ovvero aree che andranno a costituire i nuclei per il rinnovamento dell’intero tessuto comunale. Questa tesi di laurea affronta il tema della riqualificazione dello scalo ferroviario di Milano Porta Genova. Lo scalo è inserito nel tessuto urbano ottocentesco, ed affaccia in parte sull’alzaia del Naviglio Grande. Rispondendo alle indicazioni del PGT, il progetto prevede il trattamento di gran parte della superficie dello scalo a spazi aperti e pubblici, e la realizzazione di nuovi edifici a destinazione residenziale, commerciale e pubblica. L’intero progetto segue la peculiare forma dell’area, dovuta alla curva dei binari; il disegno dello spazio pubblico e del parco riprendono le linee della vecchia ferrovia. E’prevista una fascia di verde pubblico, che parte dalla testata dello scalo, in continuità con il sistema di Via Dezza-Parco Solari, per poi arrivare sul percorso ciclopedonale dell’alzaia del Naviglio Grande. La S.L.P. prevista verrà concentrata in due punti: su Via Valenza e nella parte di scalo prospiciente al Naviglio. L’edificio realizzato su via Valenza, a destinazione residenziale e commerciale, insiste sull’attuale muro di confine dello scalo, e ne riprende la forma e la matericità. Il suo ruolo è anche quello di definire lo spazio pubblico ponendosi come un nuovo limite, non più invalicabile ma permeabile. Gli edifici realizzati sul Naviglio Grande, a destinazione residenziale e commerciale, sono pensati come un sistema a pettine, che si relaziona con i retri di Via Tortona con un fronte continuo e si inserisce perpendicolarmente al Naviglio creando un rapporto più movimentato. Nell’ottica del progetto risulta fondamentale il rapporto tra edifici e spazi aperti, che sono in relazione e continuo dialogo

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Le problème de la mécanique des fluides, concernant les écoulements décollés derrière des obstacles immobiles ou en mouvement, est traité par l’étude de deux sujets: a) recherches sur l’existence de solutions stationnaires des equations d’Euler et Navier-Stokes pour grands nombres de Reynolds, au-delà des corps caractérisés par pointes ou singularités géométriques; b) analyse du sillage non stationnaire derrière une turbine à axe vertical (VAT). L’étude de ces deux différents régimes d’écoulements, concernant le phénomène du détachement derrière corps émoussés ou profils alaires à haut angle d’incidence, a permis la mise au point de plusieurs techniques analytiques et numériques basées sur le champ de vorticité.The problem of the separated flows dynamics past obstacles at rest or moving bodies is addressed by means of the study of two topics a) investigation on the existence of some steady solutions of the Euler equations and of the Navier-Stokes equations at large Reynolds number, past bodies characterized by a cusp; b) analysis of the unsteady wake behind a Vertical Axis Turbine (VAT). The survey of such different flow regimes related to the separation phenomenon past bluff bodies or bodies at incidence allowed to devise several numerical and analytical techniques based on the evaluation of the vorticity field

Simulation of ice shedding around an airfoil

In this work we propose to model ice shedding by an innovative paradigm that is based on cartesian grids, penalization and level sets. The use of cartesian grids bypass the meshing issue in complex geometries and moreover allows extensions to higher order accuracy in a natural and simple way. Penalization is an efficient alternative to explicitly impose boundary conditions so that the body fitted meshes can be avoided, making multi fluid/multi physics flows easy to set up and simulate. Level sets describe the geometry in a non-parametric way so that geometrical and topological changes due to physics and in particular ice-shedding are straight forward to follow.Grilles cartésiennes, pénalisation et suivi d'interface pour la simulation et l'optimisation d'écoulements complexe