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

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

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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

On continuation of inviscid vortex patches

This investigation concerns solutions of the steady-state Euler equations in two dimensions featuring finite area regions with constant vorticity embedded in a potential flow. Using elementary methods of the functional analysis we derive precise conditions under which such solutions can be uniquely continued with respect to their parameters, valid also in the presence of the Kutta condition concerning a fixed separation point. Our approach is based on the Implicit Function Theorem and perturbation equations derived using shape-differentiation methods. These theoretical results are illustrated with careful numerical computations carried out using the Steklov-Poincaré method which show the existence of a global manifold of solutions connecting the point vortex and the Prandtl-Batchelor solution, each of which satisfies the Kutta conditio