On the defect tolerance by fatigue spectral methods based on full-field dynamic testing

In real life production of dynamically loaded components, we might accept the risk of defects only if we can assess their position by NDT techniques, their effect by proper cumulative damage theory, the dynamic signature of the excitation and the structural dynamics of our structures in service. This work addresses the latter topic by means of experimental full-field optical techniques, which can provide accurate surface displacement distribution in a broad frequency band directly from real components, while recording the excitation, thus, with advanced numerical derivations, coming to an experiment-based full-field strain FRF characterisation, here applied on an aluminium plate. The knowledge of the material constitutive parameters is used to obtain the Von Mises equivalent stress FRFs. The signature of the excitation permits the evaluation of the Von Mises stress PSDs, which can be used in a spectral fatigue method (here the one from Dirlik), coming to a frequency-to-failure distribution. The same distribution can be scaled to a risk index and compared to the defect locations from NDT, in order to build a defect tolerance map and discriminate the product acceptance for dynamically loaded components. The smart exploitation of full-field optical techniques play a relevant role in measuring, with high spatial resolution, the manufactured components in their effective broad structural dynamics and give defect tolerance experiment-based maps, without the need of a highly tuned FE model

Exploiting Global Constraints for Search and Propagation

Résumé Cette thèse se concentre sur la Programmation par contraintes (PPC), qui est un paradigme émergent pour résoudre des problèmes complexes d’optimisation combinatoire. Les principales contributions tournent autour du filtrage des contraintes et de la recherche; les deux sont des composantes cl´e dans la résolution de problèmes complexes à travers la PPC. D’un côté, le filtrage des contraintes permet de réduire la taille de l’espace de recherche, d’autre part, la recherche définit la manière dont cet espace sera exploré. Les progrès sur ces sujets sont essentiels pour élargir l’applicabilité de CP à des problèmes réels. En ce qui concerne le filtrage des contraintes, les contributions sont les suivantes: premièrement, on propose une amélioration sur un algorithme existant de la version relaxée d’une contrainte commune qui apparaît souvent dans les problèmes d’affectation (soft gcc). L’algorithme proposé améliore en termes de complexité soit pour la cohérence, soit pour le filtrage et en termes de facilité d’implémentation. Deuxièmement, on introduit une nouvelle contrainte (soit dure soit relaxée) et les algorithmes de filtrage pour une sous-structure récurrente qui se produit dans les problèmes d’affectation des ressources hétérogènes (hierarchical gcc). Nous montrons des résultats encourageants par rapport à une d´écomposition équivalente basée sur gcc. En ce qui concerne la recherche, nous présentons tout d’abord les algorithmes pour compter le nombre de solutions pour deux importantes familles de contraintes: les contraintes sur les occurrences, par exemple, alldifferent, symmetric alldifferent et gcc, et les contraintes de séquence admissible, telles que regular. Ces algorithmes sont à la base d’une nouvelle famille d’heuristiques de recherche, centrées sur les contraintes et basées sur le d´énombrement. Ces heuristiques extraient des informations sur le nombre de solutions des contraintes, pour guider la recherche vers des parties de l’espace de recherche qui contiennent probablement un grand nombre de solutions. Les résultats expérimentaux sur huit différents problèmes montrent une performance impressionnante par rapport à l’état de l’art des heuristiques génériques. Enfin, nous expérimentons une forme forte, déjà connue, de filtrage qui est guidée par la recherche (quick shaving). Cette technique donne des résultats soit encourageants soit mauvais lorsqu’elle est appliquée aveuglément à tous les problèmes. Nous avons introduit un estimateur simple mais très efficace pour activer ou désactiver dynamiquement le quick shaving; de tests expérimentaux ont montré des résultats très prometteurs.----------Abstract This thesis focuses on Constraint Programming (CP), that is an emergent paradigm to solve complex combinatorial optimization problems. The main contributions revolve around constraint filtering and search that are two main components of CP. On one side, constraint filtering allows to reduce the size of the search space, on the other, search defines how this space will be explored. Advances on these topics are crucial to broaden the applicability of CP to real-life problems. For what concerns constraint filtering, the contribution is twofold: we firstly propose an improvement on an existing algorithm of the relaxed version of a constraint that frequently appears in assignment problems (soft gcc). The algorithm proposed outperforms the previously known in terms of time-complexity both for the consistency check and for the filtering and in term of ease of implementiation. Secondly, we introduce a new constraint (both hard and soft version) and associated filtering algorithms for a recurrent sub-structure that occurs in assignment problems with heterogeneous resources (hierarchical gcc). We show promising results when compared to an equivalent decomposition based on gcc. For what concerns search, we introduce algorithms to count the number of solutions for two important families of constraints: occurrence counting constraints, such as alldifferent, symmetric alldifferent and gcc, and sequencing constraints, such as regular. These algorithms are the building blocks of a new family of search heuristics, called constraint-centered counting-based heuristics. They extract information about the number of solutions the individual constraints admit, to guide search towards parts of the search space that are likely to contain a high number of solutions. Experimental results on eight different problems show an impressive performance compared to other generic state-of-the-art heuristics. Finally, we experiment on an already known strong form of constraint filtering that is heuristically guided by the search (quick shaving). This technique gives mixed results when applied blindly to any problem. We introduced a simple yet very effective estimator to dynamically disable quick shaving and showed experimentally very promising results

Provision of Ancillary Services utilizing a Network of Fast-Charging Stations for Electrical Buses

We demonstrate how charging infrastructure for electrical vehicles can be utilized for the provision of Ancillary Services to the Power Grid. Fast- charging stations that supply energy to vehicles at high power rates in- corporate energy storage to prevent high currents to the grid and to avoid peak-demand price charges. A network of charging stations with storage has also the potential to generate Ancillary Services. The main challenge is in the synchronization between the stochastic demand for control energy and the requirements for fast-charging services from arriving electrical ve- hicles. The method presented first calculates the maximum capacity of control-energy the system can provide and during operation delivers it to the grid upon request, while it continuously provides fast-charging ser- vices to the vehicles. To showcase our concept we utilize the ABB TOSA electrical bus charging network and the Ancillary Services requirements of Swissgrid, the Transmission System Operator of Switzerland. We show, through our simulation studies, using realistic models and energy prices, that the method is technically feasible, can deliver a considerable level of control energy and has a minor impact on the lifetime of the storage system, while generating substantial economic advantages

RESULTS OF THE TEFFMA EUROPEAN FP7 PROJECT: TOWARDS EXPERIMENTAL FULL FIELD MODAL ANALYSIS

The improvements in the electronics of modern cameras have raised the attention on image based technologies also for the measurement of complex vibration patterns for dynamic analyses in a broad extent beyond Holography. The advent of digital cameras has brought ESPI techniques to a recent success. Besides, the production of hi-speed digital cameras has recently raised DIC technique as another competitive technology in the full field domain; the SLDV, thanks to its ability to scan discrete locations over the surface, can also be considered close to the full field technologies. Present dynamic testing and analysis approaches, based on traditional transducers, do not take full advantage of the growing optical measurements, while full field techniques have proved to be increasingly effective in complex dynamic analysis. The potential of three completely different technologies was benchmarked in the TEFFMA project. SLDV, dynamic ESPI and hi-speed DIC were here first deployed in a complex and unique test on the estimation of FRFs with high spatial accuracy from a thin vibrating plate. A peculiar pointwise comparison was addressed by means of discrete geometry transforms to put all the three technologies on trial at each physical point of the surface. These researches numerically evaluated and compared also rotational and dynamic strain FRFs. Thereafter, dynamic stress FRFs can be modelled directly, by means of a constitutive model: spectral fatigue approaches can try to predict the life of a component in many excitation conditions, highlighting benefits and drawbacks of a direct experimental approach to failure & risk assessment. The identification of EMA models highlighted the increasing quality of shapes that can be obtained nowadays from native full field high resolution gears, against that of a scanning system like the SLDV tested. Model updating results were compared between scanning and native full field technologies, with comments and details on the test rig, on the advantages and drawbacks of the approaches

Analisi cinetostatica grafica di meccanismi piani. Applicazioni per la Meccanica delle Macchine

Esso si propone come ausilio allo studio applicativo delle nozioni teoriche dei corsi fondamentali e di base per la Meccanica delle Macchine. La trattazione \ue8 stata volutamente resa via via pi\uf9 articolata, con il crescendo degli strumenti a disposizione del lettore, che potr\ue0 quindi trovare soluzione ai problemi pi\uf9 semplici propri della didattica ma anche a quelli pi\uf9 complessi ed aderenti ai casi reali ed industriali. Inoltre, si propone come uno strumento di comprensione e verifica dei metodi di modellazione numerica pi\uf9 avanzati