Fractures can profoundly affect the capacity of carbonate reservoirs to store and permeate fluids, depending on the properties and abundance of fractures. Fractures exist abundantly in carbonate outcrops; however, their abundance in subsurface carbonates is obscure because of the data shortages and uncertainties about the factors that drive fracturing in sedimentary basins. The objective of this research is twofold. The first is to study abundance of fractures in gently deformed carbonates, which were generally overlooked. The second is to address measuring fracture abundance using electrical borehole imaging, which is the mostly used method to describe reservoir fractures. Fractures were studied from areas in the gently folded and shallowly (less than 2 km depth) buried interiors of the Arabian Platform. The study areas include outcrops and reservoirs of the Late Jurassic Arab carbonates in the sprawling homocline of Central Arabia and a low-relief dome in Eastern Arabia. The Cenozoic Rus carbonates in the dome outcrops were also studied. Fracture abundance was measured from the outcrops using scanlines and from the reservoirs using core and borehole images of extended-reach drilling. Many systematic properties were drawn on mineralization, orientation, and abundance of fractures. The fractures were found to be opening mode, mostly barren, and exist with subvertical dips, and some regional trends. The fractures display significantly differing ranges of abundance that were controlled by the subtle structural bending of the dome and homocline, carbonate lithofacies, and paucity of fracture mineralization. The borehole imaging was found to significantly lower fracture abundance. The detection of fractures was subject to several factors including size of fracture widths, nature of fracture roughness, and present-day stress field. The results have implications for modeling of fracture systems and tectonic regimes. For example, finding that fracture abundance varies drastically in such gently deformed regions indicates that carbonates are very sensitive to fracturing processes. Moreover, the borehole imaging limitations influence the models of fracture abundance and orientations, which are often used to deduce paleo tectonic regimes and present-day geodynamics in carbonate reservoirs.

This thesis deals with a theoretical and an experimental exploration of squeeze film levitation (SFL) of light objects. The investigations aimed to find the important design parameters controlling this levitation mechanism and also to suggest an alternative way to implement SFL. The study, through computer modelling and experimental validation, focused on Poisson's contraction effect for generating SFL. A finite element model (ANSYS) was verified by experimental testing of five different plate designs. Each plate was subjected to a uniaxial plain stress by an arrangement of two hard piezoelectric actuators (PZT) bonded to the bottom of the plate and driven with DC or AC voltages. It was observed that pulsation of a dimple or crest shaped elastic deformation along the longitudinal axis in the central area of the plate was created because of Poisson's contraction. This Poisson's effect generated the squeeze-film between the plate and the levitated object. The separation distance between a floating lightweight object and the plate was analysed using computational fluid dynamics (ANSYS CFX) through creation of a modelling model for the air-film entrapped between the two interacting surfaces - a typical three-dimensional fluid-solid interaction system (FSI). Additionally, the levitation distance has been experimentally measured by a Laser Sensor. A satisfactory agreement has been found between model predictions and experimental results. Two levitation systems, one based on a horn transducer (Langevin type) and the other one in the form of a plain rectangular plate made of Aluminium and firmly fastened at both ends with a surface-mounted piezoelectric actuator, were compared in this thesis. Both devices were based on SFL mechanism. Evidently, the performances of both designs were greatly influenced by the design structure and in particular by the driving plate characteristics such as plate size and geometry as well as the driving boundary conditions. To this end, physical experiments were carried out and it was found that the device utilising horn-type transducer yields better levitation performance. Ultimately, the research explained the confusion between three approaches to non-contact levitation through literature review and also pointed out some essential parameters like piezoelectric actuators location, material of the driving structure, coupled-field between the actuators and the driving structure and the fluid-solid interface that was existed between the excited plate and the levitated object.

Ischaemic heart disease remains the single leading cause of death throughout the world. Rupture of an advanced atheromatous coronary plaque precipitates the majority of these clinical events, resulting in thrombosis and myocardial infarction. Post-mortem studies have identified thin-cap fibroatheroma (TCFA) as the plaque subtype most prone to rupture with prospective virtual-histology intravascular ultrasound (VH-IVUS) studies linking VH-TCFA to future adverse clinical events. VH-TCFA are however common along the coronary tree with the majority remaining clinically silent, suggesting that factors other than plaque phenotype play an important role in determining rupture and future plaque behaviour. Rupture is thought to occur when the structural stress within the plaque exceeds the material strength of the overlying fibrous cap. Previous histological work has demonstrated that ruptured plaques are associated with higher stress compared to non-ruptured controls, with in vivo VH-IVUS studies linking higher plaque structural stress (PSS) with the presentation of acute coronary syndrome. Wall shear stress (WSS) on the other hand has been implicated in early plaque development and plaque growth suggesting that both PSS and WSS can influence future plaque behaviour. The work presented in this thesis is associated with a number of novel findings. First, it is the only work to demonstrate that in vivo PSS is higher in coronary atherosclerotic plaques with rupture vs. no rupture across a range of plaque subtypes and irrespective of whether analysis of the entire plaque or of regions close to the minimal luminal area is performed. Second, it shows that the pattern and extent of plaque progression and regression defined as an increase and decrease in plaque area, respectively, are associated with specific biomechanical environments at baseline, in the only study that examines the role of both PSS and WSS in this process. More specifically, high PSS is associated with changes consistent with increased vulnerability both in areas of progression and regression. On the other hand, lower WSS at baseline is associated with greater increases in plaque area and burden in areas that progress and with smaller decreases in areas that regress largely due to changes in fibrous tissue. Although the role of WSS in determining future plaque behaviour has been previously examined, this is the first time that this is assessed specifically in areas of progression and regression, particularly important in view of the dynamic nature of atherosclerotic plaques. More importantly, the work presented in this thesis demonstrates that the interplay of these biomechanical forces is associated with specific patterns of plaque progression and regression despite the fact that PSS and WSS are independent of each other. This has never been previously demonstrated and further suggests that incorporation of biomechanical analysis can play role in the identification of plaques that lead to future clinical events. Finally, the ability of PSS to identify plaques that lead to adverse clinical events was assessed through a propensity core matched analysis of the PROSPECT (A Prospective Natural-History Study of Coronary Atherosclerosis) study. The analysis presented here is the largest, most extensive and thus most significant work to ever examine this with results suggesting that incorporation of PSS and associated parameters can improve the capability of VH-IVUS to identify plaques that lead to such events. In summary, the results of this thesis suggest that coronary PSS plays an important role in the pathophysiology of plaque rupture, and that its incorporation in routine plaque assessment may improve our current ability to identifying coronary plaques that lead to future adverse clinical events. The interplay between PSS and WSS may also affect future plaque behaviour and in particular progression and regression. Prospective studies are now required to fully evaluate the role of these biomechanical forces in plaque development, and whether their incorporation in plaque evaluation can be of clinical significance.

Um modelo de elementos finitos de casca capaz de representar estruturas soldadas, sem adicionar erros significativos em termos da rigidez estrutural, poderia ser amplamente empregado em problemas dinâmicos em que o método da tensão estrutural (hot spot) é aplicado para análises de vida em fadiga. O âmbito deste trabalho é formular uma técnica de modelagem capaz de fazê-lo. Para alcançar esse objetivo, uma otimização paramétrica para a representação de estruturas soldadas através de elementos de casca foi realizada. As variáveis de projeto propostas na formulação empregada foram definidas como o comprimento do tamanho de perna e a espessura do elemento de casca representando o filete de solda. O foco da otimização foi encontrar uma faixa de espessura/tamanho de perna que não modificasse significativamente as primeiras frequências naturais e conseguisse entregar resultados similares aos obtidos por um modelo sólido. Programação linear sequencial foi empregada na otimização. A estrutura analisada foi do tipo T, com seção constante e espessura e profundidade diversas, sob diferentes modos de carregamento. Uma vez que os parâmetros ótimos foram encontrados, duas diferentes metodologias de modelagem foram propostas e comparadas com outras três bem estabelecidas e apresentadas em normas e na literatura. Os resultados foram comparados quanto às primeiras frequências naturais, massa total, tensão estrutural e vida em fadiga. / A finite element shell model capable of representing a welded structure without any significantly error on its stiffness could be widely applied to dynamic problems in which the structural stress method (hot-spot approach) is employed for fatigue analysis. The scope of the present work is to formulate a modeling technique capable of doing so. In order to accomplish it, a parametric optimization for simulating welded structures using shell elements is made, the design variables in the proposed formulation are defined as the weld leg length and thickness of the shell element representing the weld fillet. The main goal of the optimization was to find a range of thickness/leg length which would not change significantly the first natural frequencies, and still deliver results similar to the ones obtained by a solid model. Sequential linear programming optimizations are performed in a T-shaped structure under different loading scenarios, with constant section and different plate thicknesses and depths. Once the optimal parameters are found, two different modeling techniques are presented and compared with three well established methodologies presented in standards and the literature. The differences in the results are compared for first natural frequencies, total mass, hot spot stress and fatigue life.

Um modelo de elementos finitos de casca capaz de representar estruturas soldadas, sem adicionar erros significativos em termos da rigidez estrutural, poderia ser amplamente empregado em problemas dinâmicos em que o método da tensão estrutural (hot spot) é aplicado para análises de vida em fadiga. O âmbito deste trabalho é formular uma técnica de modelagem capaz de fazê-lo. Para alcançar esse objetivo, uma otimização paramétrica para a representação de estruturas soldadas através de elementos de casca foi realizada. As variáveis de projeto propostas na formulação empregada foram definidas como o comprimento do tamanho de perna e a espessura do elemento de casca representando o filete de solda. O foco da otimização foi encontrar uma faixa de espessura/tamanho de perna que não modificasse significativamente as primeiras frequências naturais e conseguisse entregar resultados similares aos obtidos por um modelo sólido. Programação linear sequencial foi empregada na otimização. A estrutura analisada foi do tipo T, com seção constante e espessura e profundidade diversas, sob diferentes modos de carregamento. Uma vez que os parâmetros ótimos foram encontrados, duas diferentes metodologias de modelagem foram propostas e comparadas com outras três bem estabelecidas e apresentadas em normas e na literatura. Os resultados foram comparados quanto às primeiras frequências naturais, massa total, tensão estrutural e vida em fadiga. / A finite element shell model capable of representing a welded structure without any significantly error on its stiffness could be widely applied to dynamic problems in which the structural stress method (hot-spot approach) is employed for fatigue analysis. The scope of the present work is to formulate a modeling technique capable of doing so. In order to accomplish it, a parametric optimization for simulating welded structures using shell elements is made, the design variables in the proposed formulation are defined as the weld leg length and thickness of the shell element representing the weld fillet. The main goal of the optimization was to find a range of thickness/leg length which would not change significantly the first natural frequencies, and still deliver results similar to the ones obtained by a solid model. Sequential linear programming optimizations are performed in a T-shaped structure under different loading scenarios, with constant section and different plate thicknesses and depths. Once the optimal parameters are found, two different modeling techniques are presented and compared with three well established methodologies presented in standards and the literature. The differences in the results are compared for first natural frequencies, total mass, hot spot stress and fatigue life.

Um modelo de elementos finitos de casca capaz de representar estruturas soldadas, sem adicionar erros significativos em termos da rigidez estrutural, poderia ser amplamente empregado em problemas dinâmicos em que o método da tensão estrutural (hot spot) é aplicado para análises de vida em fadiga. O âmbito deste trabalho é formular uma técnica de modelagem capaz de fazê-lo. Para alcançar esse objetivo, uma otimização paramétrica para a representação de estruturas soldadas através de elementos de casca foi realizada. As variáveis de projeto propostas na formulação empregada foram definidas como o comprimento do tamanho de perna e a espessura do elemento de casca representando o filete de solda. O foco da otimização foi encontrar uma faixa de espessura/tamanho de perna que não modificasse significativamente as primeiras frequências naturais e conseguisse entregar resultados similares aos obtidos por um modelo sólido. Programação linear sequencial foi empregada na otimização. A estrutura analisada foi do tipo T, com seção constante e espessura e profundidade diversas, sob diferentes modos de carregamento. Uma vez que os parâmetros ótimos foram encontrados, duas diferentes metodologias de modelagem foram propostas e comparadas com outras três bem estabelecidas e apresentadas em normas e na literatura. Os resultados foram comparados quanto às primeiras frequências naturais, massa total, tensão estrutural e vida em fadiga. / A finite element shell model capable of representing a welded structure without any significantly error on its stiffness could be widely applied to dynamic problems in which the structural stress method (hot-spot approach) is employed for fatigue analysis. The scope of the present work is to formulate a modeling technique capable of doing so. In order to accomplish it, a parametric optimization for simulating welded structures using shell elements is made, the design variables in the proposed formulation are defined as the weld leg length and thickness of the shell element representing the weld fillet. The main goal of the optimization was to find a range of thickness/leg length which would not change significantly the first natural frequencies, and still deliver results similar to the ones obtained by a solid model. Sequential linear programming optimizations are performed in a T-shaped structure under different loading scenarios, with constant section and different plate thicknesses and depths. Once the optimal parameters are found, two different modeling techniques are presented and compared with three well established methodologies presented in standards and the literature. The differences in the results are compared for first natural frequencies, total mass, hot spot stress and fatigue life.

In this study, ABS Publication 115, “Guidance on Fatigue Assessment of Offshore Structures” is briefly reviewed. Emphasis is on the S-N curves based fatigue assessment approach of non-tubular joints, and both size and environment effects are also considered. Further, fatigue tests are performed to study the fatigue strength of load-carrying and non-load-carrying steel cruciform joints that represent typical joint types in marine structures. The experimental results are then compared against ABS fatigue assessment methods, based on nominal stress approach, which demonstrates a need for better fatigue evaluation parameter. A good fatigue parameter by definition should be consistent and should correlate the S-N data well. The equivalent structural stress parameter is introduced to investigate the fatigue behavior of welded joints using the traction based structural stress approach on finite element models of specimens, and representing the data as a single Master S-N curve.

Most of the water fed into a paper machine is removedmechanically in the forming and press sections. One of thefactor which has an important influence on mechanicaldewatering, i.e. in both forming and pressing, is thestress-strain behaviour of the fibre network. The focus of this thesis is on the development of improvedmathematical descriptions of the stress-strain behaviourexhibited by fibre networks in the forming and press sections.The first part of the thesis presents a physically based modelof the forming and densification of fibre mats in twin-wireformers. The model can calculate the ecect of the applicationof a varied load through the forming section. It was developedfrom mass and momentum balances of the fibre and liquid phases,the fibre mat stress-porosity relation and an expression forthe permeability as a function of the porosity. The fibre-matstress-porosity relation used is rate-independent and presentshysteresis. Simulations have been conducted to study theeffects of roll pressure, blade pulses, wire tension andbeating. The effect of sequential blade pressure pulses afterthe forming roll on the dewatering and the concentrationgradients could be characterised. The simulations alsoexhibited rewetting by expansion when the fibre mats left theforming roll. Increasing wire tension resulted in increaseddewatering, but the rate of increase diminished rapidly withincreasing tension. The simulation results also indicated thatbeating has a large influence on dewatering. The second part of the thesis presents two models of therate-dependent stress-strain behaviour of the fibre networkthat is observed in wet pressing. The first model was based onthe approach pioneered by Perzyna (1966) for strain-ratedependent plasticity and was quite satisfactory for calculatingthe stress-strain behaviour of the fibre network in singlepress nips. It was successfully applied for studyingdensification and dewatering in both normal wet pressing andhigh temperature wet pressing. However, the first model onlyincludes rate dependence in the compression phase of thecompressionexpansion cycle; the expansion phase is treated asbeing rate independent The second model of the stress-strain behaviour of the fibrenetwork treats both compression and expansion as being ratedependent, according to experimental observations. It is basedon the idea that the wet fibre web may be conceived as alayered network of restricted swelling gels. A swollen fibre isa restricted gel, the inner swelling pressure in a swollenfibre wall being balanced by the stresses in the fibre wallstructure. The observed rate dependence of wet webs in bothcompression and expansion phases was attributed to the flow ofwater out of and into the fibre walls. The second model gavepredictions that are in good agreement with results fromuniaxial experiments using pressure pulses of arbitrary shapefor both a single pulse and a sequence of pulses. It maytherefore be used as a general model for the rheologicalbehaviour of the wet fibre network in wet pressing, providedthe model parameters are estimated from experimental data withsmall experimental error. KEYWORDS:Paper, modelling, dewatering, forming, wetpressing, fibre network stress, rheology, hysteresis,intra-fibre water, compressibility, structural stress,stress-strain, restricted gels, swelling. / <p>QC 20161026</p>

Background: The Theory of Cultural Distress offers a framework for understanding the potential outcomes in patients who do not receive care that incorporates their cultural beliefs (DeWilde & Burton, 2017).This study represents initial steps in researching the theory byexploring the layering of stressors that place the patient at risk for Cultural Distress. Methods: Utilized aCross-sectional descriptive correlational analysis of intersecting identities (Structural Stressors), ethnicity-related stressors (Otherness) and ethnic-identity (Otherness) to develop understanding of the potential effects of these variables on psychological stress. Independent variables included intersecting identities, perceived ethnic discrimination, concern for stereotype confirmation, own group conformity pressure, and group membership. The dependent variable was perceived stress. Participants were also asked to define the word culture. Results: Stereotype confirmation concern, perceived ethnic discrimination, group membership, and own group conformity pressure were significantly associated with perceived stress. Intersectionality was not significantly associated with perceived stress but was significantly associated with perceived ethnic discrimination. Regression analysis revealed stereotype confirmation concern, own group conformity pressure, and group membership as significant predictors of perceived stress. Participant definitions of culture primarily fell under two themes, Collectiveness and Individualness, indicating that the way we live is highly influenced by our shared experiences, and also a product of individual choices. Discussion: Results indicated that structural stressors had no influence on psychological stress but were associated with perceptions of discrimination. The experience of otherness significantly influenced psychological stress. Additional research and tool development is needed to better understand how structural stressors may influence psychological stress.

<p>Most of the water fed into a paper machine is removedmechanically in the forming and press sections. One of thefactor which has an important influence on mechanicaldewatering, i.e. in both forming and pressing, is thestress-strain behaviour of the fibre network.</p><p>The focus of this thesis is on the development of improvedmathematical descriptions of the stress-strain behaviourexhibited by fibre networks in the forming and press sections.The first part of the thesis presents a physically based modelof the forming and densification of fibre mats in twin-wireformers. The model can calculate the ecect of the applicationof a varied load through the forming section. It was developedfrom mass and momentum balances of the fibre and liquid phases,the fibre mat stress-porosity relation and an expression forthe permeability as a function of the porosity. The fibre-matstress-porosity relation used is rate-independent and presentshysteresis. Simulations have been conducted to study theeffects of roll pressure, blade pulses, wire tension andbeating. The effect of sequential blade pressure pulses afterthe forming roll on the dewatering and the concentrationgradients could be characterised. The simulations alsoexhibited rewetting by expansion when the fibre mats left theforming roll. Increasing wire tension resulted in increaseddewatering, but the rate of increase diminished rapidly withincreasing tension. The simulation results also indicated thatbeating has a large influence on dewatering.</p><p>The second part of the thesis presents two models of therate-dependent stress-strain behaviour of the fibre networkthat is observed in wet pressing. The first model was based onthe approach pioneered by Perzyna (1966) for strain-ratedependent plasticity and was quite satisfactory for calculatingthe stress-strain behaviour of the fibre network in singlepress nips. It was successfully applied for studyingdensification and dewatering in both normal wet pressing andhigh temperature wet pressing. However, the first model onlyincludes rate dependence in the compression phase of thecompressionexpansion cycle; the expansion phase is treated asbeing rate independent</p><p>The second model of the stress-strain behaviour of the fibrenetwork treats both compression and expansion as being ratedependent, according to experimental observations. It is basedon the idea that the wet fibre web may be conceived as alayered network of restricted swelling gels. A swollen fibre isa restricted gel, the inner swelling pressure in a swollenfibre wall being balanced by the stresses in the fibre wallstructure. The observed rate dependence of wet webs in bothcompression and expansion phases was attributed to the flow ofwater out of and into the fibre walls. The second model gavepredictions that are in good agreement with results fromuniaxial experiments using pressure pulses of arbitrary shapefor both a single pulse and a sequence of pulses. It maytherefore be used as a general model for the rheologicalbehaviour of the wet fibre network in wet pressing, providedthe model parameters are estimated from experimental data withsmall experimental error.</p><p><b>KEYWORDS:</b>Paper, modelling, dewatering, forming, wetpressing, fibre network stress, rheology, hysteresis,intra-fibre water, compressibility, structural stress,stress-strain, restricted gels, swelling.</p>