La simulation numérique des écoulements (CFD) est largement utilisée aujourd'hui dans l'industrie aéronautique, de l'avant-projet à la conception des appareils. En parallèle, la puissance des calculateurs s'est accrue, permettant d'effectuer des simulations résolvant les équations de Navier-Stokes moyennées (RANS) dans un délai de restitution acceptable du point de vue industriel. Cependant, les configurations simulées sont de plus en plus complexes géométriquement, rendant la réalisation du maillage très coûteuse en temps humain. Notre objectif est de proposer une méthode permettant de simplifier la génération de maillages autour de géométries complexes, en exploitant les avantages de la méthode Chimère, tout en levant les difficultés principales rencontrées par cette méthode dans le calcul des connectivités. Dans notre approche, le domaine de calcul est découpé en régions proches et en régions éloignées des corps. Des grilles curvilignes de faible extension décrivent les régions autour des corps. Le maillage de fond est défini par un ensemble de grilles cartésiennes superposées aux grilles de corps, qui sont engendrées et adaptées automatiquement selon les caractéristiques de l'écoulement. Afin de traiter des maillages recouvrants autour de géométries complexes sans surcoût humain, les différentes grilles sont regroupées par composant Chimère. Des relations d'assemblage sont alors définies entre composants, en s'inspirant de la Géométrie de Construction des Solides (CSG), où un solide peut être construit par opérations booléennes successives entre solides primitifs. Le calcul des connectivités Chimère est alors réalisé de manière simplifiée. Des simulations RANS sont effectuées autour d'un fuselage d'hélicoptère avec mât de soufflerie et autour d'une aile NACA0015 en incidence, afin de mettre en oeuvre la méthode. / Computational fluid dynamics (CFD) is widely used today in aeronautics, while the computing power has increased, enabling to perform simulations solving Reynolds-averaged Navier-Stokes equations (RANS) within an acceptable time frame from the industrial point of view. However, the configurations are more and more geometrically complex, making the mesh generation step prohibitive. Our aim is here to propose a method enabling a simplification of the mesh generation over complex geometries, taking advantage of the Chimera method and overcoming the major difficulties arising when performing overset grid connectivity. In our approach, the computational domain is partitioned into near-body regions and off-body regions. Near-body regions are meshed by curvilinear grids of short extension describing the obstacles involved in the simulation. Off-body mesh is defined by a set of adaptive Cartesian grids, overlapping near-body grids. In order to consider overset grids over complex geometries with no additional cost, grids are gathered by Chimera component, and assembly relations are defined between them, inspired by Constructive Solid Geometry, where a solid can result from boolean operations between primitive solids. The overset grid connectivity is thus simplified. RANS simulations are performed over a helicopter fuselage with a strut, and over a NACA0015 wing.

In the process of engineering design of structural shapes, the flat plate analysis results can be generalized to predict behaviors of complete structural shapes. In this case, the purpose of this project is to analyze a thin flat plate under conductive heat transfer and to simulate the temperature distribution, thermal stresses, total displacements, and buckling deformations. The current approach in these cases has been using the Finite Element Method (FEM), whose basis is the construction of a conforming mesh. In contrast, this project uses the mesh-free Scan Solve Method. This method eliminates the meshing limitation using a non-conforming mesh. I implemented this modeling process developing numerical algorithms and software tools to model thermally induced buckling. In addition, convergence analysis was achieved, and the results were compared with FEM. In conclusion, the results demonstrate that the method gives similar solutions to FEM in quality, but it is computationally less time consuming.

Triangle meshes have become an increasingly popular shape representation. Given the ease of standardization it allows and the proliferation of devices (scanners, range images ) that capture and output shape information as meshes, this representation is now used in applications such as virtual reality, medical imaging, rapid prototyping, digital art and entertainment, simulation and analysis, product design and development. In product development manipulation of mesh models is required in applications such as visualization, analysis, simulation and rapid prototyping. The nature of manipulation of the mesh includes annotation, interactive viewing, slicing, re-meshing, mesh optimization, mesh segmentation, simplification and editing. Of these editing has received the least attention. Mesh model often requires editing either locally or globally based on the application. With the increased use of meshes it is desirable to have formal reasoning tools that enable manipulation of mesh models in product development. The mesh model may contain artifacts like self-intersection, overlapping triangles, inconsistent normal’s of triangles and gaps or holes with or without islands. It is necessary to repair the mesh before further processing the mesh model. An automatic algorithm is proposed to repair and fill arbitrary holes while maintaining curvature continuity across the boundaries of the hole. The algorithm uses slices across the hole to first identify curves that bridge the hole. These curves are then used to find the surface patch that would fill the hole. The proposed algorithm works for arbitrary holes in any mesh model irrespective of the type of underlying surface and is able to preserve features in the mesh model that are missing in the input information. Since editing during product development is mostly feature based, an automatic algorithm to recognize shape features by directly clustering the triangles constituting a feature in a mesh model is proposed. Shape features addressed in the thesis are volumetric features that are associated with either addition or removal of a finite volume. The algorithm involves two steps – isolating features in 2D slices followed by a 3D traversal to cluster all the triangles in the feature. Editing a mesh model mainly implies editing local volumetric features in that model. An automatic algorithm is proposed for parametric editing of volumetric features in the mesh model. The proposed algorithm eliminates the need of original CAD model while manipulating any volumetric feature in the mesh model based on feature parameters. An automatic algorithm to manipulate global shape parameters of the object using the mesh model is developed. Global shape parameters include thickness, drafts and axes of symmetry. As the mesh models do not explicitly carry this information global editing of mesh models (other than for visualization) has not been attempted thus far. This thesis proposes the use of mid-surface to identify and manipulate global shape parameters for a class of objects that are classified as thin walled objects. Mid-curves are first identified on slices of the part and then the mid-surface is obtained from these mid-curves. Results of implementation are presented and discussed along with the scope for future work.

Com a popularização de equipamentos tradicionais de captura de imagens, como câmeras digitais, e o avanço tecnológico dos dispositivos não invasivos, como tomografia e ressonância, cresce também a necessidade e consequente uso de métodos numéricos para simulação de fenômenos físicos em domínios definidos por imagens. Um dos pré-requisitos para a aplicação de tais métodos numéricos consiste na discretização do domínio em questão, num processo denominado geração de malhas. Embora diversos métodos de geração de malha tenham sido propostos para discretizar domínios definidos por primitivas geométricas, pouco tem sido feito no sentido de gerar uma decomposição diretamente a partir de imagens. Neste trabalho, apresentamos uma abordagem de geração de malhas de qualidade a partir de domínios definidos por imagens com textura. Mais especificamente, a pesquisa descrita nesta tese contribui com a melhoria do algoritmo Imesh, ao sanar três de suas principais limitações: tratamento de imagens com texturas; controle do nível de refinamento da malha e suporte a outros tipos de elementos. Estas contribuições flexibilizam o processo de geração da malha, e ainda ampliam o domínio de aplicações do algoritmo Imesh, à medida que são considerados domínios definidos por imagens com textura e o uso de métodos numéricos para elementos não simpliciais torna-se possível. O algoritmo de melhoria da malha gerada utiliza uma abordagem inovadora de remalhamento baseada em templates e guiada por retalhos de Bézier / With the spreading of traditional image capturing devices, such as digital cameras, and the technological advancement of more specific imaging devices such as CT and MRI, also increased the need and the following use of numerical methods for simulation of physical phenomena in domains defined by images. One of the prerequisites for the application of such numerical methods is the discretization of the corresponding domain, in a process called mesh generation. Although several methods of mesh generation have been proposed to discretize domains defined by geometric primitives, little has been done to generate a decomposition directly from images. We present an approach to generate quality meshes from domains defined by images with texture. More specifically, the research described in this thesis contributes to the improvement of the Imesh algorithm, removing three of its main limitations: treatment textured images, control of the level of the mesh refinement and support for other types of non-simplicial elements. These contributions provide flexibility to the mesh generation process, and extend the range of applications of Imesh by both handling textured images and considering the use of numerical methods for non-simplicial elements. The mesh quality improvement algorithm uses a new approach based on mesh templates and it is guided by Bezier patches

Structural shape optimisation is a field that has been studied since early on in the development of finite element methods. The sub-fields of shape and topology optimisation are continuously growing in industry and aim to leverage the benefits of technologies such as 3D printing and additive manufacturing. These fields are also being used to optimise designs to improve quality and reduce cost. Gradient-based optimisation is well understood as an efficient method of obtaining solutions. In order to implement gradient-based optimisation methods in the context of structural shape optimisation, sensitivities describing the change of the domain stiffness are required. To obtain the stiffness sensitivities, mesh deformation sensitivities are required. In this study, a mesh generating method is developed that provides mesh deformation sensitivities. For shape optimisation it is advantageous to employ an optimisation algorithm that allows for the manipulation of CAD geometry. This means that the CAD geometry is finalised upon completion of the optimisation process. This, however, necessitates the calculation of accurate sensitivities associated with non-linear geometries, such as NURBS (those present in CAD), by the mesher. The meshing method developed in this study is analogous to a linear truss system. The system is solved for static equilibrium through a geometrically non-linear finite element analysis using Newton’s method. Sensitivities are made available by Newton’s method for use in generating mesh sensitivities for the system. It is important for the mesher to be able to accurately describe the geometrical domain which approximates the geometry being modelled. To do so, nodes on the boundary may not depart from the boundary. Instead of prescribing all boundary nodes, this mesher frees the boundary nodes to move University of Pretoria ii Department of Mechanical and Aeronautical Engineering along, but not away from the boundary. This is achieved using multipoint constraints since they allow for an analytical relationship between boundary node movement and the boundary. Two multipoint constraint (MPC) methods are investigated for boundary discretisation, namely, the Lagrangian and master-slave elimination methods (MSEM). The MSEM presents several difficulties in obtaining convergence on non-linear boundaries in general when compared to the Lagrangian method. The MSEM has reduced computational requirements for a single Newton step, especially when direct solvers are used. However, when indirect solvers are implemented the time difference between the two MPC methods reduces significantly. For a “medium” curvature geometry the Lagrangian implementation has only a 6% time penalty. The Lagrangian method is selected as the preferred MPC method for implementation in the mesher to avoid the convergence problems associated with the MSEM. This is justified on the basis of reliability outweighing the 6% time penalty for what is intended to be a tool in the shape optimisation process. Analytical sensitivities are obtained for the truss system in order to account for the MPC boundaries. The analytical mesh sensitivities are proven to be accurate through comparison with numerical sensitivities. The method is demonstrated to be able to accurately described the mesh deformation throughout the domain for both uniform and non-uniform meshes in the presence of non-linear boundaries. / Dissertation (MEng)--University of Pretoria, 2020. / Mechanical and Aeronautical Engineering / MEng (Mech) / Unrestricted

No description available.

Background Parastomal hernia is a common stoma complication causing the patient considerable inconvenience. The patient becomes aware of a bulge around the stoma, but a bulge is not always a parastomal hernia and diagnostics must be performed to enable differential treatment. It is difficult to distinguish between a bulge and a hernia. Results based on clinical examination and computerised tomography (CT) in the supine position, have not been convincing. Three-dimensional intrastomal ultrasonography (3D US) is a novel technique shown to be promising in the assessment of stoma complaints. Two studies were performed to determine inter- and intra-observer reliability as well as the validity of 3D US as an alternative to CT when assessing stoma complaints. There are numerous options for the treatment of parastomal hernia, but none has been shown superior. In the recent decades the use of mesh in the repair of incisional and inguinal hernia has become routine. New materials must be evaluated as there are potential morbidity and even mortality risks with mesh repair. As recurrence of a parastomal hernia is an even greater challenge, the method of choice should have a low risk for recurrence. A prospective multicenter study was performed to evaluate safety and recurrence rate when using Parastomal Hernia Patch BARDTM (PHP), a mesh specially designed for parastomal hernia repair. A stoma has a profound impact on the patient´s daily life, both physical and psychological. A parastomal hernia with its associated risk for leakage and incarceration worsens the situation. Patient driven assessment of healthcare outcome is important if we are to improve medical care. A quality of life (QoL) survey was performed to assess the impact of parastomal bulging and hernia on the patient´s daily life. Methods Forty patients were investigated and the 3D US images were twice evaluated by two or three physicians to assess inter- and intra-observer reliability. Totally 20 patients with stoma complaints requiring surgery were examined with CT and 3D US prior to surgery. The findings were compared with the intraoperative findings – regarded as the true outcome. Fifty patients with parastomal hernia requiring surgery were enrolled from three hospitals. Patients were followed up one month and one year after repair using PHP. Patients still alive in 2008 who had been operated between1996 and 2004 for rectal cancer in Uppsala/Örebro-, Stockholm/Gotland-, and Northern Regions (986 patients) and registered in the Swedish Rectal Cancer Registry (SRCR) were invited to fill in four QoL questionnaires. Results Inter-observer agreement using 3D US reached 80% for the last 10 patients examined, with a kappa value of 0.70. Intra-observer agreement for two examiners was 80% and 95%. The learning curve levelled out at 30 patients. Both CT and 3D US showed high sensitivity and specificity when compared with intraoperative findings. After surgery for parastomal hernia with a PHP, the complication rate at one month was 30% and recurrence rate at one year was 22%. Twelve patients were reoperated within one year. In the QoL study, 31.5% of the patients with a stoma reported a bulging or a hernia. 11.7% had been operated for parastomal hernia. A hernia or a bulge gave rise to significantly more pain and impaired stoma function. Overall QoL was inferior in patients with a permanent stoma compared to a group without a stoma.

<p>The ever increasing demand for video content directed the focus of researchfrom traditional server-based schemes to peer-to-peer systems for videodelivery. In such systems, video data is delivered to the users by utilizing theresources of the users themselves, leading to a potentially scalable solution.Users connect to each other, forming a p2p overlay network on top of theInternet and exchange the video segments among themselves. The performanceof a p2p system is characterized by its capability to deliver the videocontent to all peers without errors and with the smallest possible delay. Thisconstitutes a challenge since peers dynamically join and leave the overlay andalso contribute different amounts of resources to the system.The contribution of this thesis lies in two areas. The first area is theperformance evaluation of the most prominent p2p streaming architectures.We study the streaming quality in multiple-tree-based systems. We derivemodels to evaluate the stability of a multiple tree overlay in dynamic scenariosand the efficiency of the data distribution over the multiple trees. Then, westudy the data propagation in mesh-based overlays. We develop a generalframework for the evaluation of forwarding algorithms in such overlays anduse this framework to evaluate the performance of four different algorithms.The second area of the thesis is a study of streaming in heterogeneous p2poverlays. The streaming quality depends on the aggregate resources that peerscontribute to the system: low average contribution leads to low streamingquality. Therefore, maintaining high streaming quality requires mechanismsthat either prohibit non-contributing peers or encourage contribution. In thisthesis we investigate both approaches. For the former, we derive a model tocapture the evolution of available capacity in an overlay and propose simpleadmission control mechanisms to avoid capacity drainage. For the latter, inour last work, we propose a novel incentive mechanism that maximizes thestreaming quality in an overlay by encouraging highly contributing peers tooffer more of their resources.</p> / QC 20100506

A polygon mesh, or a 3D mesh, consisting of a collection of vertices, edges, and polygons in three-dimensional space, is the standard way of representing 3D objects. In practice, polygon meshes acquired from the 3D scanning process fail to meet the quality requirements for most practical applications. Mesh defects like holes, duplicate elements, non-manifold elements are introduced during the scanning process, which lowers the quality of the output meshes. In this thesis, we describe a complete mesh-repairing process that fixes all defects within a polygon mesh. This process is divided into two parts: the mesh-cleaning part and the hole-filling part. In the mesh-cleaning part, we describe the ways of repairing different types of mesh defects. In the hole-filling part, we discuss two main hole-filling approaches: the surface-based method and the volumetric. In addition, we present a hybrid algorithm by combining the surface-based approach and the volumetric approach. We compare the meshes created by different hole-filing algorithms and show that the new algorithm is a good alternative to the existing ones. / Thesis (Master, Computing) -- Queen's University, 2013-09-11 23:45:08.591

With the rapid development of wireless networks, mesh networks are evolving as a new important technology, presenting a high research and commercial interest. Additionally, wireless mesh networks have a wide variety of applications, offering the ability to provide network access in both rural and urban areas with low cost of maintenance. One of the main functionalities of a wireless mesh network is load balancing routing, which is the procedure of finding the best, according to some criteria, routes that data need to follow to transfer from one node to another. Routing is one of the state-of-the-art areas of research because the current algorithms and protocols are not efficient and effective due to the diversity of the characteristics of these networks. In this thesis, two new routing algorithms have been developed for No Intra-Cell Interference (NICI) and Limited Intra-Cell Interference (LICI) networks based on WiMAX, the most advanced wireless technology ready for deployment. The algorithms created are based on the classical Dijkstra and Ford-Fulkerson algorithms and can be implemented in the cases of unicast and multicast transmission respectively.