Some numerical simulations of multi-scale physical phenomena consume a significant amount of computational resources, since their domains are discretized on high resolution meshes. An enormous wastage of these resources occurs in refinement of sections of the domain where computation of the solution does not require high resolutions. This problem is effectively addressed by adaptive mesh refinement (AMR), a technique of local refinement of a mesh only in sections where needed, thus allowing concentration of effort where it is required. Sections of the domain needing high resolution are generally determined by means of a criterion which may vary depending on the nature of the problem. Fairly straightforward criteria could include comparing the solution to a threshold or the gradient of a solution, that is, its local rate of change to a threshold. While the former criterion is not particularly rigorous and hardly ever represents a physical phenomenon of interest, it is simple to implement. However, the gradient criterion is not as simple to implement as a direct comparison of values, but it is still quick and a good indicator of the effectiveness of the AMR technique. The objective of this thesis is to arrive at an adaptive mesh refinement algorithm for a finite difference scheme using a quadtree decomposition approach. In the AMR algorithm developed, a mesh of increasingly fine resolution permits high resolution computation in sub-domains of interest and low resolution in others. In this thesis work, the gradient of the solution has been considered as the criterion determining the regions of the domain needing refinement. Initial tests using the AMR algorithm demonstrate that the paradigm adopted has considerable promise for a variety of research problems. The tests performed thus far depict that the quantity of computational resources consumed is significantly less while maintaining the quality of the solution. Analysis included comparison of results obtained with analytical solutions for four test problems, as well as a thorough study of a contemporary problem in solid mechanics.

Wire mesh dampers are under investigation because they are seen as replacements for squeeze film dampers as a source of direct stiffness and damping at bearing locations. There are several advantages of wire mesh dampers over squeeze film dampers, including: temperature insensitivity, oil-free operation, and the ability to contain large amplitude vibrations. Furthermore, due to their direct damping and lack of cross-coupled stiffness, the wire mesh reduces the response to imbalance and increases the stability of the system. The objective of this research was to determine the properties of wire mesh dampers under large amplitude vibrations. Impact testing was first conducted on the wire mesh as a means of obtaining the large amplitudes that were of interest. Next, to verify the results, a second methodology was employed using shaker testing. It was found that both the stiffness and hysteretic damping decrease with increasing displacement. However, they both approached asymptotes around 2 mils of displacement, and further increases in displacement had significantly less effect on the properties. Once the results were verified to be consistent, equations were obtained to describe the response of the wire mesh dampers. These equations were then used to create a new design workbook, which would allow an engineer to determine the properties of wire mesh dampers under conditions that they might experience.

Abstract In large-scale distributed multiprocessor systems, communication delay becomes the bottleneck of system performance. A main factor which affects communication delay is the adopted routing method and the router design light traffic, the queuing delay can be increased drastically due to message congestion. We have developed a hierarchical globally adaptive routing method. The method can poll global traffic status. According to the traffic status, it can select a routing path congestion which can alleviate. Therefore, the queuing delay due to congestion can be reduces significantly non-light traffic globally. We also developed two detail routing methods applied at different hierarchical routing levels¡Gthe look around routing method and the parallel approximate maze routing method. They can avoid selecting a routing path via congested regions as much as possible. In this research, we designed a performance simulator of the globally adaptive mesh router. We also provided a traffic with the different levels of non-uniform traffic distribution. We utilized the performance simulator to exercise minimal routing, adaptive routing and our globally adaptive routing methods. The experiment results show that our globally adaptive method obtains significant performance improvement in non-light traffic.

Land surface models (LSMs) simulate vertical fluxes, including evapotranspiration, in a rigorous manner, and are included in atmospheric models, including Regional and Global Circulation Models (RCMs and GCMs). Large-scale hydrological models on the other hand simulate the lateral processes that generate streamflow. Coupling of the two models (referred to as a hydrological land surface model) has the potential to combine the strengths of each. The MESH model developed at Environment Canada is such model that combines the Canadian Land Surface Scheme (CLASS) with a distributed hydrological model called WATFLOOD. In this thesis, the performance of the MESH model was explored using two different runoff generation schemes (i.e., elementary and enhanced runoff generation) and with a priori parameter values and with parameter calibration. The model was tested in the White Gull creek Basin located in the boreal forest, central Saskatchewan using meteorology and flux data recorded at two monitoring stations within the basin for driving and validation. Application of the model with a priori parameter values without calibration resulted in poor performance in simulating both streamflow and evapotranspiration while optimization to calibrate the model to the observed streamflow resulted in a good performance. Streamflow simulation with enhanced runoff generation included performed even better. The optimal model configuration was taken forward for a detailed parameter sensitivity analysis. Univariate analysis was used for pre-screening the parameter space to eliminate insensitive parameters, and subsequently multivariate analysis was performed for a subset of parameters. Vegetation parameters were more identifiable when an objective function measuring the fit to observed latent heat flux was used than when measuring the fit to streamflow. Physiographic and topographic parameters were more identifiable when a streamflow objective function was used. Streamflow was more sensitive to parameter variability than latent heat flux. The use of multiple objective functions to simultaneously constrain the model was explored. Selection of objective function had no significant effect on the simulated evapotranspiration but had some influence on streamflow. Using NSE objective function with streamflow was found to be the most effective way of identifying the best model runs. The additional constraints imposed by evapotranspiration had no impact on the results.

Mesh simplification is an important task in Computer Graphics due to the ever increasing complexity of polygonal geometric models. Specifically in real-time rendering, there is a necessity that these models, which can be acquired through 3D scanning or through artistic conception, have to be simplified or optimized to be rendered on today's hardware while losing as little detail as possible. This thesis proposes a mesh simplification algorithm that works by identifying and simplifying features. Then it simplifies the remaining mesh with the simplified features frozen. The algorithm is called Quadric Error with Feature Curves (QEFC). Quadric Error with Feature Curves works as a tool that allows the user to interactively select a percentage of the most important points of the feature curves to be preserved along with the points determined by the Quadric Error Metric algorithm.

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L'objectif de cette thèse est la simulation numérique de la propagation d'une décharge électrique dans un champ électrique à haute tension. Un modèle minimal est utilisé pour la description de la physique. Le modèle consiste en un modèle d'équations de convection-diffusion-réaction de particules électrique couplé à l'équation de Poisson pour le potentiel électrique. Nous simulons la propagation d'une décharge en 3D, qui présente des ramifications causées par des perturbations locales dans le champ électrique. Nous avons mis en oeuvre une méthode basée sur l'adaptation dynamique de maillages pour la simulation numérique. Les propriétés de la méthode sont testées d'abord sur un simple problème analogue en 2D. Cette approche a été suffisante pour le développement de la méthode, même si en 2D le problème est d'un type différent (décharge plane), et cela a permis une transition simple au vrai problème 3D. / The aim of this thesis is a numerical simulation of a streamer propagation (electric discharge in a high voltage electric field). The minimal model is used for the streamer description. The model consists of a system of convection-diffusion-reaction equations for electric particles coupled with Poisson’s equation for an electric potential. We simulate a general streamer motion in 3D which is presented by streamer branching. It is caused by local disturbances in the electric field. We have developed a method based on a dynamically adaptation of grids for the simulation. The properties of the method are tested on simpler problems in 2D (less time consuming). This approach is sufficient for the development of the method even if it is different type of problem (planar discharge) and it allows a simple transition to 3D. / Tato dizertační práce se zabývá numerickou simulací propagace streameru (elektrický výbojve vysokonapět'ovém elektrickém poli). Pro popis streameru je použit minimální model, který se skládá ze soustavy transportních rovnic pro elektricky nabité částice spárovaných s Poissonovou rovnicí pro elektrický potenciál. V práci simulujeme obecný pohyb streameru ve 3D. Tento obecný pohyb je prezentován rozvětvením streameru, kterého se dosáhne pomocí lokálních poruch v elektrickem poli. Pro numerickou simulaci streameru jsme vyvinuli meto du založenou na dynamické adaptaci síte, jejíž vlastnosti byly otestováný na jednodušších problé-mech ve 2D (menší časová náročnost). I když jde o jiný typ problému (rovinný výboj), pro vývoj metody je dostatečný a umožňuje snadný přechod do 3D.

Im Bereich der Zugangsnetze werden zukünftig drahtlose Multihop-Erweiterungen des Internets durch mobile Ad-hoc-Netze sowie durch drahtlose vermaschte Netze (sog. Wireless Mesh Networks) Verbreitung finden, da diese Netztechnologien den Datentransfer einfacher und schneller, womöglich auch deutlich kostengünstiger, durchführen können als zellulare Mobilfunknetze.

This work addresses Channel Assignment in a multi-radio multi-channel (MRMC) Wireless Mesh Network (WMN) using both Wi-Fi and Dynamic Spectrum Access (DSA) spectrum bands and standards. This scenario poses new challenges because nodes are spread out geographically so may have differing allowed channels and experience different levels of external interference in different channels. A solution must meet two conflicting requirements simultaneously: 1) avoid or minimise interference within the network and from external interference sources, and 2) maintain connectivity within the network. These two requirements must be met while staying within the link constraints and the radio interface constraints, such as only assigning as many channels to a node as it has radios. This work's original contribution to the field is a unified framework for channel optimisation and assignment in a WMN that uses both DSA and traditional Wi-Fi channels for interconnectivity. This contribution is realised by providing and analysing the performance of near-optimal Channel Assignment (CA) solutions using metaheuristic algorithms for the MRMC WMNs using DSA bands. We have created a simulation framework for evaluating the algorithms. The performance of Simulated Annealing, Genetic Algorithm, Differential Evolution, and Particle Swarm Optimisation algorithms have been analysed and compared for the CA optimisation problem. We introduce a novel algorithm, used alongside the metaheuristic optimisation algorithms, to generate feasible candidate CA solutions. Unlike previous studies, this sensing and CA work takes into account the requirement to use a Geolocation Spectrum Database (GLSD) to get the allowed channels, in addition to using spectrum sensing to identify and estimate the cumulative severity of both internal and external interference sources. External interference may be caused by other secondary users (SUs) in the vicinity or by primary transmitters of the DSA band whose emissions leak into adjacent channels, next-toadjacent, or even into further channels. We use signal-to-interference-plus-noise ratio (SINR) as the optimisation objective. This incorporates any possible source or type of interference and makes our method agnostic to the protocol or technology of the interfering devices while ensuring that the received signal level is high enough for connectivity to be maintained on as many links as possible. To support our assertion that SINR is a reasonable criterion on which to base the optimisation, we have carried out extensive outdoor measurements in both line-of-sight and wooded conditions in the television white space (TVWS) DSA band and the 5 GHz Wi-Fi band. These measurements show that SINR is useful as a performance measure, especially when the interference experienced on a link is high. Our statistical analysis shows that SINR effectively differentiates the performance of different channels and that SINR is well correlated with throughput and is thus a good predictor of end-user experience, despite varying conditions. We also identify and analyse the idle times created by Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) contention-based Medium Access Control (MAC) operations and propose the use of these idle times for spectrum sensing to measure the SINR on possible channels. This means we can perform spectrum sensing with zero spectrum sensing delay experienced by the end user. Unlike previous work, this spectrum sensing is transparent and can be performed without causing any disruption to the normal data transmission of the network. We conduct Markov chain analysis to find the expected length of time of a sensing window. We also derive an efficient minimum variance unbiased estimator of the interference plus noise and show how the SINR can be found using this estimate. Our estimation is more granular, accurate, and appropriate to the problem of Secondary User (SU)-SU coexistence than the binary hypothesis testing methods that are most common in the literature. Furthermore, we construct confidence intervals based on the probability density function derived for the observations. This leads to finding and showing the relationships between the number of sampling windows and sampling time, the interference power, and the achievable confidence interval width. While our results coincide with (and thus are confirmed by) some key previous recommendations, ours are more precise, granular, and accurate and allow for application to a wider range of operating conditions. Finally, we present alterations to the IEEE 802.11k protocol to enable the reporting of spectrum sensing results to the fusion or gateway node and algorithms for distributing the Channel Assignment once computed. We analyse the convergence rate of the proposed procedures and find that high network availability can be maintained despite the temporary loss of connectivity caused by the channel switching procedure. This dissertation consolidates the different activities required to improve the channel parameter settings of a multi-radio multi-channel DSA-WMN. The work facilitates the extension of Internet connectivity to the unconnected or unreliably connected in rural or peri-urban areas in a more cost-effective way, enabling more meaningful and affordable access technologies. It also empowers smaller players to construct better community networks for sharing local content. This technology can have knock-on effects of improved socio-economic conditions for the communities that use it.

Two refinement techniques to generate solution adaptive meshes have been developed. Both techniques utilize arbitrary polyhedra (general elements) to constrain the propagation of refinement. A face-based approach that produces isotropic refinement and a combined element- and edge-based approach that produces anisotropic refinement are presented. Refinement is triggered through sensors that use a shock detection algorithm or error estimation based on the smoothness of the reconstructed solution variables. The basic algorithms as well as specific implementation issues are presented. The advantages and disadvantages of the different methods are discussed and illustrated through a set of synthetic and realistic test cases. It is shown that general elements can be employed effectively in solution adaptive meshes generated using refinement.