Oil reservoirs and soil can be homogeneously wet (water-wet, oil-wet, neutralwet) or heterogeneously wet (mixed wet or fractionally wet). The goal of this research is to model the detailed configuration of wetting and non-wetting phases within homogeneously and heterogeneously wet porous media. We use a dense random pack of equal spheres as a model porous medium. The geometry of the sphere pack is complex but it is known. In homogeneously wet porous media we quantify the effect of low saturations of the wetting phase on the non-wetting phase relative permeability by solving analytically the geometry of the wetting phase. At low saturations (at or near the drainage endpoint) the wetting phase exists largely in the form of pendular rings held at grain contacts. Pore throats correspond to the constriction between groups of three grains, each pair of which can be in contact. Thus the existence of these pendular rings decreases the void area available for the flowing non-wetting phase. Consequently, the existence of the pendular rings decreases the permeability of non-wetting phase. Our model explains the significant permeability reduction of the non-wetting phase with a small change in the wetting phase in a low permeability porous medium. To model heterogeneously wet porous medium, we assume that the porous medium is fractionally wet where each grain is either oil-wet or water-wet. These waterwet or oil-wet grains are distributed randomly within the porous medium. We calculate analytically the stable fluid configuration in individual pores and throats of a fractionally wet medium. The calculation is made tractable by idealizing the configurations as locally spherical (menisci) or toroidal (pendular rings.) Because the calculation of the interface position is entirely local and grain-based, it provides a single, generalized, geometric basis for computing pore-filling events during drainage as well as imbibition. This generality is essential for modeling displacements in fractionally wet media. Pore filling occurs when an interface becomes unstable in a pore throat (analogous to the Haines condition for drainage in a uniformly wet throat), when two or more interfaces come into contact and merge to form a single interface (analogous to the Melrose condition for imbibition in uniformly wet medium), or when a meniscus in a throat touches a nearby grain (a new stability criterion). The concept of tracking the fluid/fluid interfaces on each grain means that a traditional pore network is not used in the model. The calculation of phase saturation or other quantities that are conveniently computed in a network can be done with any approach for defining pore bodies and throats. The fluid/fluid interfaces are mapped from the grain-based model to the network as needed. Consequently, the model is robust as there is no difference in the model between drainage and imbibition, as all criteria are accounted for both increasing and decreasing capillary pressure. / text

The performance gap between processor and memory continues to remain a major performance bottleneck in both application specific and general purpose processors. This thesis strives to ease the above bottleneck by exploiting the characteristics of the application domain to improve the cache organization for two distinct processor architectures: (1) application specific processors for packet forwarding, (2) general purpose processors. Packet forwarding algorithms make use of a trie data structure to determine the forwarding route. We observe that the locality characteristics of the nodes at various levels of such a trie are different. Nodes that are closer to the root node, especially those that are immediate children of the root node (level-one nodes), exhibit higher temporal locality than nodes lower down the trie. Based on this observation we propose a novel Heterogeneously Segmented Cache Architecture (HSCA) that uses separate caches for level-one and lower-level nodes, each with carefully chosen sizes. We also propose a new replacement policy to enhance the performance of HSCA. Performance evaluation indicates that HSCA results in up to 32% reduction in average memory access time over a unified cache that shares the same cache space among all levels of the trie. HSCA also outperforms a previously proposed results cache. The use of a large root branching factor in a forwarding trie forcefully introduces a large number of nodes at level-one. Among these, only nodes that cover prefixes from the routing table are useful while the rest, are superfluous. We find that as many as 75% of the level-one nodes are superfluous. This leads to a skewed distribution of useful nodes among the cache sets of the level-one nodes cache. We propose a novel two-level mapping framework that achieves a better nodes to cache set mapping and hence incurs fewer conflict misses. Two-level mapping first aggregates nodes into Initial Partitions (IPs) using lower order bits and then remaps them from IPs into Refined Partitions (RPs), that form sets, based on some higher order bits. It provides flexibility in placement by allowing each IP to choose a different remap function. We propose three schemes conforming to the framework. A speedup in average memory access time of as much as 16% is gained over HSCA. In general purpose processor architectures, the design objectives of caches at various levels of the hierarchy are different. To ensure low access latencies, L1 caches are small and have low associativities, making them more susceptible to conflict misses. The extent of conflict misses incurred is governed by the placement function and the memory access patterns exhibited by the program. We propose a mechanism to learn the access characteristics of the program at runtime by analyzing the repetitive phases of program. We then make use of the two-level mapping framework to dynamically adapt the placement function. Further, we elegantly incorporate two-level mapping into the cache organization without increasing the cache access latency. Performance evaluation reveals that the proposed adaptive placement mechanism eliminates 32—36% of misses on average over a range of cache sizes. To prevent expensive off-chip accesses, L2 caches are larger and have higher associativities. Hence, the replacement policy plays a significant role in determining L2 cache performance. Further, as the inherent temporal locality in memory accesses is filtered out by the L1 cache, an L2 cache using the widely prevalent LRU replacement policy incurs significantly higher misses than the optimal replacement policy (OPT). We propose to bridge this gap through a novel replacement strategy that mimics the replacement decisions of OPT. The L2 cache is logically divided into two components, a Shepherd Cache (SC) with a simple FIFO replacement and a Main Cache (MC) with an emulation of optimal replacement. The SC plays the dual role of caching lines and shepherding the replacement decisions close to optimal for MC. Our proposed organization can cover 40% of the gap between LRU and OPT, resulting in 7% overall speedup.

[pt] Neste trabalho são analisadas junções entre guias coaxiais não homogêneos com perdas. A expansão modal dos campos eletromagnéticos em um guia coaxial com duas camadas radiais é detalhadamente deduzida, e posteriormente a formulação é generalizada para guias com multicamadas radiais. As constantes de propagação para guias com perdas são determinadas pelo método do winding number, garantindo que todos os autovalores possam ser encontrados. O método do casamento de modos é aplicado na análise e projeto de estruturas coaxiais. A formulação é aplicada na otimização de estruturas de acoplamento e cornetas radiantes com carregamento dielétrico não homogêneo. O preenchimento não homogêneo é empregado nas estruturas radiantes a fim de minimizar a perda de retorno, e principalmente controlar e melhorar o formato do diagrama de radiação para operação em banda larga. Adicionalmente, a formulação é utilizada para analisar a propagação eletromagnética em sistemas de telemetria sem fio para poços de petróleo. / [en] In this work, we analyzed junctions between coaxial waveguides heterogeneously filled with lossy dielectrics. The modal expansion of the electromagnetic fields in a coaxial waveguide with two radial layers is derived in detail, and afterward the formulation is generalized for a multilayer waveguide. The propagation constants for lossy waveguides are determined through the method of winding number, ensuring that all eigenvalues can be found. The mode matching technique is applied in the analysis and design of coaxial structures. The formulation is applied in the optimization of coupling structures and radiating horns with heterogeneous dielectric loading. The heterogeneous filling is used in radiating structures in order to reduce the return loss, and especially to control and improve the shape of the radiation pattern for broadband operation. Additionally, the formulation is used to analyze the electromagnetic propagation in wireless telemetry systems for oil wells.