Inertial granular flows lie in a region of parameter space between quasi-static and collisional regimes. In each of these phases the mechanisms of energy dissipation are often taken to be the defining features. Frictional contacts between grains and the transmission of energy through co-operative force chains dominate slowly sheared flows. In the opposite extreme infrequent high-energy collisions are responsible for dissipation in so-called gaseous granular flows. Borrowing from each of these extremes, it is postulated that during liquid-like flow, grain energy is transferred through frequent frictional interactions as the particles rearrange. This thesis focuses on the μ(I)-rheology which generalises the simple Coulomb picture, where greater normal forces lead to greater tangential friction, by including dependence on the inertial number I, which reflects the frequency of grain rearrangements. The equations resulting from this rheology, assuming that the material is incompressible, are first examined with a maximal-order linear stability analysis. It is found that the equations are linearly well-posed when the inertial number is not too high or too low. For inertial numbers in which the equations are instead ill-posed numerical solutions are found to be grid-dependent with perturbations growing unboundedly as their wavelength is decreased. Interestingly, experimental results also diverge away from the original μ(I) curve in the ill-posed regions. A generalised well-posedness analysis is used alongside the experimental findings to suggest a new functional form for the curve. This is shown to regularise numerical computations for a selection of inclined plane flows. As the incompressibility assumption is known to break down more drastically in the high-I and low-I limits, compressible μ(I) equations are also considered. When the closure of these equations takes the form suggested by critical state soil mechanics, it is found that the resultant system is well-posed regardless of the details of the deformation. Well-posed equations can also be formed by depth-averaging the μ(I)-rheology. For three-dimensional chute flows experimental measurements are captured well by the depth-averaged model when the flows are shallow. Furthermore, numerical computations are much less expensive than those with the full μ(I) system.

Thesis (Ph. D.)--University of Washington, 1988. / Vita. Bibliography: leaves [182]-187.

Fat bloom in chocolates is the gray-white discoloration and dullness that can occur on the surface of the confectionery. Fat bloom is a common quality defect that can result from temperature fluctuations during storage. Chocolates candies with peanuts or other nut fillings are more prone to fat bloom compared to plain chocolates, due to a release of incompatible nut oils into the chocolate matrix. The overall goal of this study was to determine if differences in triacylglycerol (TAG) composition and rheological properties of high, medium, and normal oleic peanuts influence fat bloom formation. All three peanut varieties showed high concentrations of triolein. Normal oleic peanuts had a slightly higher trilinolein than high and medium oleic peanuts, which contained trilinolein in trace amounts. Peanut pastes from the three peanut varieties all had a minimum apparent yield stress, and all pastes showed varying degrees of shear thinning. The apparent yield stress of high and normal oleic pastes was higher than the apparent yield stress of medium oleic paste. The absolute value of the flow index behavior was 1 for the high oleic peanut paste, suggesting friction in the experimental apparatus, even with use of Teflon plates. The peanut chocolate candies took around 45 days for significant dulling of the chocolates with temperature cycling between 26-29 °C approximately every 26 hours. Optical microscopy scans showed differences in glossiness and surface textural attributes of the unbloomed and bloomed peanut chocolate confectionery. Consumer evaluation showed some differences in the glossiness and significant differences in surface texture of unbloomed and bloomed chocolates. A majority (62%) of the survey respondents had seen whitish discoloration in chocolates and 40% of the respondents thought this is because the chocolate had grown old. / Ph. D.

Hypercholesterolemia is a dominant risk factor for a variety of cardiovascular diseases and involves a chronic inflammatory component in which neutrophil activity plays a critical role. Recently, fluid shear stress mechanotransduction has been established as a control mechanism that regulates the activity of neutrophils by reducing the formation of pseudopods and the surface expression of CD18 integrins, thereby rendering these cells rounded, deformable, and non-adhesive. This is critical for maintaining a healthy circulation, because chronically activated neutrophils not only release excess cytotoxic and degradative agents but also exhibit a reduced efficiency to pass through the small vessels of the microcirculation leading to increased microvascular resistance. We hypothesized that aberrant neutrophil mechanosensitivity to fluid shear stress due to the altered blood environment (i.e., excess plasma cholesterol) is a contributing factor for elevated hemodynamic resistance in the microcirculation associated with hypercholesterolemia. For this purpose, the present work firstly showed that the sensitivity of neutrophils to fluid shear stress depends on the cholesterol-dependent fluidity of the cell membrane, and that, in the face of hypercholesterolemia, the neutrophil mechanosensitivity highly correlated with the plasma levels of free cholesterol. The second part of this project demonstrated that, when subjected to shear stress fields, leukocyte suspensions exhibited transient (within 10 min of flow onset) time-dependent reductions in their apparent viscosity. Moreover, shear-induced changes in viscosity of cell suspensions were influenced by disturbances of membrane cholesterol and fluidity in a fashion similar to that for shear-induced pseudopod retraction. Finally, the third part of this work provided evidence that neutrophils played a role in hypercholesterolemia-related impairment of flow recovery response to transient ischemia. In conclusion, results of the current work provided the first evidence that cholesterol is an important component of the neutrophil mechanotransducing capacity and impaired neutrophil shear mechanotransduction may disturb the blood flow rheology, leading to elevations in the apparent viscosity as well as in the resistance. This cholesterol-linked perturbation may be a contributing factor for the pathologic microcirculation associated with hypercholesterolemia.

[pt] Para avaliação de movimentos de corridas de detritos em vertentes montanhosas, é necessária uma abordagem reológica através de modalegem consitutiva da massa de solo descendente. O modelo de Bingham é amplamente empregado na literatura de corridas, sendo seus parâmetros a viscosidade plástica e tensão de escoamento. Esta análise provê o entendimento da propagação do movimento dos detritos em campo, ao fornecer uma estimativa de sua velocidade, espessura e alcance. O presente trabalho apresenta uma proposta para determinação da tensão de escoamento e viscosidade de solos, através de ensaios de abatimento de tubo cilíndrico. A tensão de escoamento e a viscosidade foram determinadas em um reômetro rotaticonal, com base nas taxas de cisalhamento definidas nos ensaio de abatimento. Foram estudados dois solos naturais do Rio de Janeiro, com diferentes granulometrias e plasticidades. Os resultados experimentais obtidos são comparados com soluções analíticas da literatura, e mostram que deve-se ter cuidado na definição destes parametros reológicos com base apenas em dados relacionados a distribuição granulométrica dos solos. Como resultado, foi estabelecida uma relação entre teor de umidade, tensão de escoamento e viscosidade. Comparando os dados obtidos com resultados disponíveis na literatura, conclui-se que a metodologia desenvolvida pode fornecer uma maneira simples de avaliar parâmetros reológicos de solos para análises de corridas. / [en] To evaluate debris flow downhill movements, it is necessary a rheological approach through constitutive modelling the descendent moving mass. Bingham s model is widely employed in the debris flow literature, its input parameters being plastic viscosity and yield stress. Such analysis provides understandings of the propagation of the debris motion in the field, once it provides an estimate of its velocity, thickness and range area. The present study presents a proposal for the assessment of soil yield stress and plastic viscosity, by laboratorial testing on a cylindrical tube slump test. Through the definition of shearing rates in the slump tests, yield stress and viscosity were determined on a plate–plate rheometer. Two natural soils from Rio de Janeiro, Brazil, with differing grain size distribution and plasticity, were used in the investigation. The experimental results obtained are compared with analytical and semi empirical solutions from the literature, and show that care must be taken in defining viscosities based only on data related to grain size. Correlations were obtained concerning to soil moisture and shear rates, defined in the slump tests, and also between plastic viscosity and yield stress, defined in the rheometer tests. As a result, good relationships between water content and both yield stress and viscosity were established. Comparing the obtained data with other results available in the literature it is concluded that the developed experimental methodology may provide a simple way to evaluate rheological parameters of soils for debris flow analyses.