Dans toutes sortes de milieux industriels comme l'aéronautique, l'industrie spatiale, l'industrie pétrolière et tant d'autres, il est indispensable d'effectuer des calculs numériques pour simuler des phénomènes intervenant dans des systèmes naturels ou artificiels modélisables par la mécanique des milieux continus. Nous nous sommes intéressés à la question scientifique suivante: Comment, pour une simulation donnée et des moyens de calcul donnés, obtenir la plus grande précision de prédiction ? Le but de cette thèse est de faire le lien entre deux techniques de simulation numérique : les méthodes multigrilles et les nouvelles méthodes adaptatives anisotropes récemment développées. On résout une équation aux dérivées partielles elliptique. L'adaptation des maillages au problème donné repose sur une minimisation d'une grandeur donnée suivant la méthode d'adaptation employée: l'erreur d'interpolation pour l'adaptation basée-hessiens, une pondération de l'erreur d'approximation pour la méthode goal-oriented et la norme de l'erreur d'approximation pour la méthode norm-oriented. La méthode multigrille permet d'accelérer la convergence sur chaque maillage. Plusieurs cas tests ont été effectués pour s'assurer de l'efficacité des différentes méthodes. / In many industrial activities such as aeronautics, space industry, oil industry and many others, it is essential to carry out numerical computations to simulate phenomena occurring in natural or artificial systems modelisable by mechanical Continuum. This thesis focuses on the following scientific question: how, for a given simulation and computing means given, obtain the highest prediction accuracy? Our contribustion makes the link between two numerical simulation techniques: multigrid methods and new recently developed anisotropic adaptative methods. We solve an elliptic partial differential equation. The adaptation of the mesh to the given problem is based on minimization of a given magnitude following the adaptation method employed: the interpolation error for the Hessian-based adaptation, a weighting of the approximation error for goal-oriented method and the norm of the approximation error for the norm-oriented method. The multigrid method permits to accelerate convergence on each mesh. Several tests cases were carried out to ensure the effectiveness of the different methods.

This thesis is concerned with the channel assignment (CA) problem in multi-channel multi-interface wireless mesh networks (M2WNs). First, for M2WNs with general topologies, we rigorously demonstrate using the combinatorial principle of inclusion/exclusion that the CA solution space can be quantified, indicating that its cardinality is greatly influenced by the number of radio interfaces installed on each router. Based on this analysis, a novel scheme is developed to construct a new reduced search space, represented by a lattice structure, that is searched more efficiently for a CA solution. The elements in the reduced lattice-based space, labeled Solution Structures (SS), represent groupings of feasible CA solutions satisfying the radio constraints at each node. Two algorithms are presented for searching the lattice structure. The first is a greedy algorithm that finds a good SS in polynomial time, while the second provides a user-controlled depthfirst search for the optimal SS. The obtained SS is used to construct an unconstrained weighted graph coloring problem which is then solved to satisfy the soft interference constraints. For the special class of full M2WNs (fM2WNs), we show that an optimal CA solution can only be achieved with a certain number of channels; we denote this number as the characteristic channel number and derive upper and lower bounds for that number as a function of the number of radios per router. Furthermore, exact values for the required channels for minimum interference are obtained when certain relations between the number of routers and the radio interfaces in a given fM2WN are satisfied. These bounds are then employed to develop closed-form expressions for the minimum channel interference that achieves the maximum throughput for uniform traffic on all communication links. Accordingly, a polynomial-time algorithm to find a near-optimal solution for the channel assignment problem in fM2WN is developed. Experimental results confirm the obtained theoretical results and demonstrate the performance of the proposed schemes.

The communication range between a civilian Unmanned Aerial Vehicle (UAV) and a Ground Control Station (GCS) is affected by the government regulations that determine the use of frequency bands and constrain the amount of power in those frequencies. The application of multiple UAVs in search and rescue operations for example demands a reliable, long-range inter-UAV communication. The inter-UAV communication is the ability of UAVs to exchange data among themselves, thus forming a network in the air. This ability could be used to extend the range of communication by using a decentralized routing technique in the network. To provide this ability to a fleet of autonomous dirigible UAVs being developed at the University of Ottawa, a new communication framework was introduced and implemented. Providing a true mesh networking based on a novel routing protocol, the framework combines long-range radios at 900 MHz Industrial, Scientific and Medical (ISM) band with the software integrated into the electronics platform of each dirigible. With one radio module per dirigible the implemented software provides core functionalities to each UAV, such as exchanging flight control commands, telemetry data, and photos with any other UAV in a decentralized network or with the GCS. We made use of the advanced networking tools of the radio modules to build capabilities into the software for route tracing, traffic prioritization, and minimizing self-interference. Initial test results showed that without acknowledgements, packets can be received in the wrong order and cause errors in the transmission of photos. In addition, a transmission in a presence of a third broadcasting node slows down by 4-6 times. Based on these results our software was improved to control to flow of transmit data making the fragmentation, packetization, and reassembly of photos more reliable. Currently, using radios with half-wavelength dipole antennas we can achieve a one-hop communication range of up to 5 km with the radio frequency line-of-sight (RF LOS). This can be extended further by adding as many radio nodes as needed to act as intermediate hops.

This thesis is concerned with the performance and measurement uncertainty of wire-mesh sensors in different air-water flow regimes in horizontal pipes. It also presents measurements of void fraction and interfacial velocity in such flows. It was found that the interfacial velocity measurements of the wire-mesh sensors were in good agreement with those taken with a high-speed camera and estimates of the uncertainties of these measurements are presented. Drift-flux models were fitted to the measurements and it was found that the parameters of these models were not only sensitive to the flow regime, but also to the liquid superficial velocity.

Les modèles 3D sont des contenus précieux très utilisés dans l'industrie, et donc la cible potentielle de piratages. Le tatouage robuste pour les maillages 3D apporte une réponse au problème du traçage de traître. Dans l'état de l'art du domaine, la couche d'adaptation du contenu en particulier est testée face des attaques standards. Une approche robuste à la pose est alors étudiée. Elle utilise une estimation robuste de l'épaisseur, définie comme la distance un nuage de points construits à partir de mesures du diamètre. Les performances expérimentales montrent qu'elle forme un point de départ prometteur pour le tatouage robuste de maillages 3D posés. Pour les maillages statiques, la modulation des distances radiales est une approche efficace du tatouage. Elle a été formulée comme un problème d'optimisation quadratique sous contrainte, dont nous proposons plusieurs extensions : une transformée par étalement, des primitives de référence calculées de manière intégrale, des directions de déplacement arbitraires, et de nouvelles métriques pour minimiser la distorsion perçue par un utilisateur. Des expériences illustrent leurs bénéfices pour le compromis entre la robustesse et la fidélité du tatouage. La sécurité est analysée par l'intermédiaire de deux mécanismes de protection et par une série d'attaques et de contre-Mesures. Un système de resynchronisation est intégré afin d'améliorer la résistance au rognage. Des points de recalage sont insérés dans une configuration spécifique qui porte les informations habituellement éliminées par l'attaque. Au décodage, elles sont récupérées de manière aveugle. Un gain significatif des performances est mesuré expérimentalement. / 3D models are valuable assets widely used in the industry and likely to face piracy issues. This dissertation deals with robust mesh watermarking that is used for traitor-Tracing. Following a review of state-Of-The-Art 3D watermarking systems, the robustness of several content adaptation transforms are benchmarked. An embedding domain robust against pose is investigated, with a thickness estimation based on a robust distance function to a point cloud constructed from some mesh diameters. A benchmark showcases the performance of this domain that provides a basis for robust watermarking in 3D animations. For static meshes, modulating the radial distances is an efficient approach to watermarking. It has been formulated as a quadratic programming problem minimizing the geometric distortion while embedding the payload in the radial distances. This formulation is leveraged to create a robust watermarking framework, with the integration of the spread-Transform, integral reference primitives, arbitrarily selected relocation directions and alternate metrics to minimize the distortion perceived. Benchmarking results showcase the benefits of these add-Ons w.r.t the fidelity vs. robustness watermarking trade-Off. The watermark security is then investigated with two obfuscation mechanisms and a series of attacks that highlight the remaining limitations. A resynchronization approach is finally integrated to deal with cropping attacks. The resynchronization embeds land-Marks in a configuration that conveys synchronization information that will be lost after cropping. During the decoding, this information is blindly retrieved and significant robustness improvements are achieved.

The integrated Network Enhanced Telemetry (iNET) radios provide a two-way telemetry link that interconnects the airborne instrumentation system with ground-based systems. This capability brings the flight test telemetry domain into the realm of the more classic mesh networks in a mobile ad-hoc environment. The underlying radio frequency (RF) communication protocols defined in the iNET standards support a variety of classic networking protocols. The scheduling algorithms between Link Managers and radios can operate as a collision network, like classic Ethernet. This paper describes the communication protocols and scheduling algorithms of the iNET radios, and it provides results of their use in a self-scheduling algorithm such as a classical token ring network.

In this thesis a methodology is presented to optimise non–linear mathematical models in numerical engineering applications. The method is based on biological evolution and uses known concepts of genetic algorithms and evolutionary compu- tation. The working principle is explained in detail, the implementation is outlined and alternative approaches are mentioned. The optimisation is then tested on a series of benchmark cases to prove its validity. It is then applied to two different types of problems in computational engineering. The first application is the mathematical modeling of turbulence. An overview of existing turbulence models is followed by a series of tests of different models applied to various types of flows. In this thesis the optimisation method is used to find improved coefficient values for the k–ε, the k–ω-SST and the Spalart–Allmaras models. In a second application optimisation is used to improve the quality of a computational mesh automatically generated by a third party software tool. This generation can be controlled by a set of parameters, which are subject to the optimisation. The results obtained in this work show an improvement when compared to non–optimised results. While computationally expensive, the genetic optimisation method can still be used in engineering applications to tune predefined settings with the aim to produce results of higher quality. The implementation is modular and allows for further extensions and modifications for future applications.

>Magister Scientiae - MSc / Wi-Fi authentication mechanisms include central authentication, dynamic and distributed authentication and some encryption methods. Most of the existing authentication methods were designed for single-hop networks, as opposed to multihop Wi-Fi mesh networks. This research endeavors to characterize and compare existing Wi-Fi authentication mechanisms to find the best secure connection mechanism associated with Wi-Fi mesh network fragmentation and distributed authentication. The methodology is experimental and empirical, based on actual network testing. This thesis characterizes five different types of Wrt54gl firmware, three types of Wi-Fi routing protocols, and besides the eight Wi-Fi mesh network authentication protocols related to this research, it also characterizes and compares 14 existing authentication protocols. Most existing authentication protocols are not applicable to Wi-Fi mesh networks since they are based on Layer 2 of the OSI model and are not designed for Wi-Fi mesh networks. We propose using TincVPN which provides distributed authentication, fragmentation, and can provide secure connections for backbone Wi-Fi mesh networks.

Flows around immersed boundaries exhibit many complex, well defined and active dynamical structures. In fact, features such as shock waves, strong vorticity concentrations in shear layers, wakes, or boundary layer regions are critical elements in representing the dynamics of a flow field. In order to capture the correct kinematic and dynamic quantities associated with the fluid flows, one must be able to efficiently refine the computational mesh around areas containing high gradients of pressure, density, velocity, or other suitable flowfield variables that characterize distinct structures. Although there are techniques which utilize simple gradient-based Local Mesh Refinement (LMR) to adapt resolution selectively to capture structures in the flow, such methods lack the ability to refine structures based on the relative strengths and scales of structures that are presented in the flow. The inability to adequately define the strength and scale of structures typically results in the mesh being over-refined in regions of little consequence to the physical definition of the problem, under-refined in certain regions resulting in the loss of important features, or even the emergence of false features due to perturbations in the flowfield caused by unnecessary mesh refinement. On the other hand, significant user judgment is required to develop a "good enough" mesh for a given flow problem, so that important structures in the flowfield can be resolved. In order to overcome this problem, multiresolution techniques based on the wavelet transform are explored for feature identification and refinement. Properties and current uses of these functional transforms in fluid flow computations will be briefly discussed. A Multiresolution Transform (MRT) scheme is chosen for identifying coherent structures because of its ability to capture the scale and relative intensity of a structure, and its easy application on non-uniform meshes. The procedure used for implementation of the MRT on an octree/quadtree LMR mesh is discussed in detail, and techniques used for the identification and capture of jump discontinuities and scale information are also presented. High speed compressible flow simulations are presented for a number of cases using the described MRT LMR scheme. MRT based mesh refinement performance is analyzed and further suggestions are made for refinement parameters based on resulting refinement. The key contribution of this thesis is the identification of methods that lead to a robust, general (i.e. not requiring user-defined parameters) methodology to identify structures in compressible flows (shocks, slip lines, vertical patterns) and to direct refinement to adequately refine these structures. The ENO-MRT LMR scheme is shown to be a robust, automatic, and relatively inexpensive way of gaining accurate refinement of the major features contained in the flowfield.

Cette thèse porte sur la prédiction haute-fidélité de phénomènes visqueux turbulents modélisés par les équations Reynolds-Averaged Navier-Stokes (RANS). Si l’adaptation de maillage a été appliquée avec succès aux simulations non-visqueuses comme la prédiction du bang sonique ou la propagation d’explosion, prouver que ces méthodes s’étendent et s’appliquent également aux simulations RANS avec le même succès reste un problème ouvert. Dans ce contexte, cette thèse traite des problématiques relatives aux méthodes numériques (solveur de mécanique des fluides) et aux stratégies d’adaptation de maillage. Pour les méthodes numériques, nous avons implémenté un modèle de turbulence dans notre solveur et nous avons conduit une étude de vérification et validation en deux et trois dimensions avec comparaisons à l’expérience. Des bons résultats ont été obtenus sur un ensemble de cas tests, notamment sur le calcul de la traînée pour des géométries complexes. Nous avons également amélioré la robustesse et la rapidité de convergence du solveur, grâce à une intégration en temps implicite, et grâce à une procédure d’accélération multigrille. En ce qui concerne les stratégies d’adaptation de maillage, nous avons couplé les méthodes multigrilles à la boucle d’adaptation dans le but de bénéficier des propriétés de convergence du multigrille, et ainsi, améliorer la robustesse du processus et le temps CPU des simulations. Nous avons également développé un algorithme de génération de maillage en parallèle. Celui-ci permet de générer des maillages anisotropes adaptés d’un milliard d’éléments en moins de 20 minutes sur 120 coeurs de calcul. Enfin, nous avons proposé une procédure pour générer automatiquement des maillages anisotropes adaptés quasi-structurés pour les couches limites. / This thesis deals with the high-fidelity prediction of viscous turbulent flows modelized by the Reynolds-Averaged Navier-Stokes (RANS) equations. If mesh adaptation has been successfully applied to inviscid simulations like the sonic boom prediction or the blast propagation, demonstrating that these methods are also well-suited for 3D RANS simulations remains a challenge. This thesis addresses research issues that arise in this context, which are related to both numerical methods (flow solver) and mesh adaptation strategies. For the numerical methods, we have implemented a turbulence model in our in-house flow solver and carried out its verification & validation study. Accurate results were obtained for a representative set of test cases, including the drag prediction workshop. Additional developments have been done to improve the robustness and the convergence speed of the flow solver. They include the implementation of an implicit time integration and of a multigrid acceleration procedure. As regards mesh adaptation, we have coupled the adaptive process to multigrid in order to benefit from its convergence properties and thus improve the robustness while preventing losses of computational effort. We also have devised a parallel mesh generation algorithm. We are able to generate anisotropic adapted meshes containing around one billion elements in less than 20min on 120 cores. Finally, we introduced a procedure to automatically generate anisotropic adapted quasi-structured meshes in boundary layer regions.