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Proton therapy is an advanced cancer treatment modality that demands precise dosimetry for effective and safe patient outcomes. This thesis investigates the ionization chamber (IC) within the IBA proton therapy machine, which is crucial for measuring the proton dosage administered to patients. However, vibration disturbances can cause significant measurement variations and saturation problems
in the IC, potentially compromising treatment accuracy.
The study is structured into three parts. The first part involves the numerical modeling the IC, focusing on the geometry and tension of the electrodes, which are configured as sheets. This model aims to understand the baseline behavior of the IC electrodes under pre-tension. The second part investigates the actual dynamic behavior of the IC through Experimental Modal Analysis (EMA). The third part correlates the numerical and experimental results by optimizing the numerical model using a surrogate-assisted genetic algorithm. 
Results indicate that the tension applied to the sheets significantly influences the modal analysis outcomes. Optimization of the numerical model determined optimal tensions of 77.2 N vertically and 40.1 N horizontally, achieving a global variation of 3.7% between the numerical and experimental natural frequencies. The dynamic analysis also reveals a significant vibratory influence of the IC casing on the measurement sheets, leading to perturbations in electrometer readings.
This research contributes to medical physics by providing insights into the behavior of proton therapy dosimetry devices, with the aim of improving the performance and accuracy of proton therapy in clinical settings.

Modal analysis --- Ionization chamber --- Optimization --- Experimental testing --- Ingénierie, informatique & technologie > Ingénierie aérospatiale

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Nonlinearities are an important aspect to consider in the study of the vibrations of a structure, as they can influence the dynamics of the analysed system, resulting in unexpected behaviours. Nonlinear system identification aims at finding a mathematical model of the structure taking into account the nonlinear forces. One method used in the nonlinear system identification is the acceleration surface method, which helps at determining the functional form of these nonlinear forces by creating stiffness and damping curves. While the method has proven to work well in real-life applications, some artefacts sometimes appear in the stiffness and damping curves, making it more difficult to correctly interpret these curves. The aim of this work is thus to understand their origin and determine how the curves can be improved.

For this purpose, the acceleration surface method is applied to systems composed of 1, 2 and 10 degrees of freedom, whose response to sine sweep excitations is obtained through numerical integration. The nonlinearities consist of a cubic stiffness, a piecewise linear stiffness and Coulomb friction, which are all common types of nonlinearities encountered in real-life structures.

The analysis of the stiffness and damping curves obtained for the different systems reveals that the presence of harmonic components in the response of the system to the excitation can impact the curves, such that the curves can be composed of different lines, which can complicate the determination of the functional form of the nonlinear forces. Such phenomena particularly occur at superharmonic resonances and modal interactions. An effective way to improve the curves in such cases is the use of filters to remove the harmonic components from the response of the system to the excitation. Furthermore, in multiple degree of freedom systems, the linear forces that have been ignored in the equation of the acceleration surface method are responsible for the quality of the stiffness and damping curves. Applying the method to modes for which these forces are small thus yields better results. In particular, modes for which the neighbouring degrees of freedom of the linear connections oscillate in phase with the degree of freedom to which the acceleration surface method is applied have shown to produce better results. The position of the excitation and the extremity of the nonlinear connection to consider in the acceleration surface method also influence the quality of the stiffness and damping curves.

While the identification of the stiffness force can be done successfully in most cases, the functional form of the damping force remains difficult to determine with the acceleration surface method and it can only be found in some specific cases. The artefacts in the stiffness and damping curves can be explained by several phenomena, but are always due to the terms neglected in the equation of the acceleration surface method.

nonlinear vibrations --- acceleration surface method --- Ingénierie, informatique & technologie > Ingénierie aérospatiale

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Ce rapport présente une méthodologie stochastique pour la prédiction des jeux radiaux dans les compresseurs basse pression, visant à améliorer la fiabilité et les performances des moteurs aéronautiques. En utilisant une approche statistique basée sur la technique de Monte-Carlo, le modèle final permet de mieux estimer l'incertitude des jeux radiaux. L'analyse des facteurs influençant ces jeux, tels que les tolérances, l'ovalisation et les adders, aide à comprendre les variations possibles et propose des pistes pour l'optimisation des processus de conception et de maintenance des moteurs. Cette étude fournit une base pour la gestion des phénomènes aléatoires liés aux jeux radiaux et ouvre des perspectives pour des améliorations futures.

Jeu --- Prédiction --- Monte-Carlo --- Safran --- booster --- compresseur basse pression --- stochastique --- Ingénierie, informatique & technologie > Ingénierie mécanique

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Pretension, the intentional application of preload to bolted joints before they are subjected to external loads, is vital for the functionality and reliability of bolts in aeronautical assemblies. This preload is achieved by tightening the bolt to a specified torque or stretching it to a predetermined length, ensuring the joint remains secure and stable under operational loads. Pretension creates a compressive load within the joint, eliminating gaps and enhancing load transfer, reducing the likelihood of fretting or fatigue failure. It also prevents bolt self-loosening during flight-induced vibrations and dynamic loads, maintaining bolt clamp load and resisting relaxation.
In the aerospace industry, the significance of pretension on bolts is often overlooked, leading to designs without preload, which is considered conservative. This thesis investigates the influence of prestressing in bolted assemblies under shear conditions. It compares cases with and without preload, examining loosely assembled configurations and those with only enough torque to bring parts into contact. The study evaluates the physical behavior of a slat track assembly under different preload levels, focusing on the axial load in the bolt, as well as the shear load and bending moment.
The research involves evaluating an analytical method developed by Sonaca, which analyzes the behavior of bolted joints under shear forces without considering prestressing, providing a foundational understanding of bolted joint principles. To incorporate prestressing effects, a finite element model (FEM) is developed and compared with the analytical method to validate or challenge initial hypotheses. Additionally, the study explores the influence of various materials and geometric configurations on bolted joint performance through a parametric study, aiming to identify key factors that affect behavior and performance. Finally, the results are discussed in detail, highlighting their implications, limitations, and future research directions, offering valuable insights into the significance of prestressing in bolted assemblies.
Overall, pretension optimizes the performance and reliability of bolts within aeronautical assemblies, ensuring secure fastening, resistance to self-loosening, and enhanced load-bearing capacity, crucial for maintaining aircraft safety and the longevity of critical components.

Ingénierie, informatique & technologie > Ingénierie aérospatiale

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Ce travail de fin d'étude fut réalisé au sein de l'entreprise Safran Aero Boosters. L'objectif de ce stage était de développer une méthode permettant de mesurer les contraintes dans les filets des écrous de palier employés par Safran Aero Booster. De fait, ces écrous diffèrent de la visserie standardisée et nécessitent donc une méthodologie customisée. Ce document permis de mettre en évidence un comportement de l'écrou s'éloignant la littérature, car il subit une flexion modifiant la distribution des contraintes dans le filet.

Ecrou --- Filet --- Contraintes --- Méthodologie --- Ingénierie, informatique & technologie > Ingénierie mécanique