Fuel cells represent a promising energy alternative to the traditional combustion of fossil fuels. In particular, solid oxide fuel cells (SOFCs) have been of interest due to their high energy densities and potential for stationary power applications. One of the key obstacles precluding the maturation and commercialization of planar SOFCs has been the absence of a robust sealant. A leakage computational model has been developed and refined in conjunction with leakage experiments and material characterization tests at Oak Ridge National Laboratory to predict leakage in a single interface metal-metal compressive seal assembly as well as multi-interface mica compressive seal assemblies. The composite model is applied as a predictive tool for assessing how certain parameters (i.e., temperature, applied compressive stress, surface finish, and elastic thermo physical properties) affect seal leakage rates.

The surface quality is identified by surface roughness parameters. The average surface roughness (Ra) is used in this study, as it is the most commonly used roughness parameter in the industry. A particular curved cavity of a forging die is selected for the experimental study. Different milling methods are tested. The comparison studies are conducted between 3-axes and 5-axes milling, linear and circular tool path strategies and down and up milling. According to the experimental study, appropriate method is determined for the milling of a particular curved cavity of a forging die. The experimental analysis based on design of experiments (DOE) has been employed by considering cutting speed, feed per tooth and stepover parameters. Multiple linear regression technique is used by which a mathematical formula has been developed to predict the Ra values for milling parameters. The results of the mathematical formula are controlled by conducting test experiments and good correlations are observed between the results of the formula and the results of test experiments.

Soil moisture condition of a watershed plays a significant role in separation of rainfall into infiltration and surface runoff, and hence is a key parameter for the majority of physical hydrological models. Due to the large difference in dielectric constants of dry soil and water, microwave remote sensing and particularly the commonly available synthetic aperture radar is a potential tool for such studies. The main aim of this study is to produce the distributed soil moisture maps of a catchment from active microwave imagery. For this purpose, nine field trips are performed within a small basin in western Anatolia and point surface soil moisture values are collected with a Time Domain Reflectometer. The field studies are planned to match radar image acquisitions and accomplished over the water year of 2004 - 2005. In this context, first, the Dubois Model, a semi-empirical backscatter model is utilized in the reverse order to develop radar backscatter &amp / #8211 / soil roughness relationship and soil roughness maps of the study area are obtained. Then another relationship is built between radar backscatter and the three governing surface parameters: local incidence angle, soil moisture and soil roughness, which is later used in the soil moisture estimation methods. Depending on land use and vegetation cover condition, surface soil moisture maps of the catchment are produced by Backscatter Correction Factors, Water Cloud Model and Basin Indexes methods. In the last part of the study, the soil moisture maps of the basin are input to a semi-distributed hydrological model, HEC-HMS, as the initial soil moisture condition of a flood event simulation. In order to investigate the contribution of distributed initial soil moisture data on model outputs, simulation of the same flood event is also performed with the lumped initial soil moisture condition. Finally, a comparison between both the distributed and lumped model simulation outputs and with the observed data is carried out.

Radial lip seals are used to prevent leakage between machine elements in many industrial applications. During operation, fluid film between seal lip and shaft surface generates a pressure distribution on the lip which is elastically deformed due to hydrodynamic pressure. Surface roughness parameters in terms of moments of height profile distribution (rms roughness, skewness and kurtosis) affect the rate of oil leakage. A computer program is developed for elastohydrodynamic analysis of radial lip seals. Both the fluid mechanics of the lubricating film and the elastic deformation of the lip are taken into consideration to determine the hydrodynamic pressure distribution and the oil flow through the seal lip. The effect of shaft surface roughness on hydrodynamic analysis is taken into account by using average Reynolds equation with flow factors. For non-Gaussian surfaces, the modified flow factors are used to investigate the effects of skewness and kurtosis on the oil leakage. Numerical tests are performed for different skewness, kurtosis and initial seal tightness values. Results show that when a seal is mounted with a high initial tightness, the hydrodynamic pressure developed is not enough to deform the lip to form a fluid film between the shaft and the seal lip. It is observed that for the same rms roughness and skewness, the side flow rate increases as the kurtosis value increases. However, for the same rms roughness and kurtosis values, the side flow rate decreases for all skewness values.

Germanium is a brittle semi-metal, used for lenses and windows in Thermal Imaging Systems since it transmits infrared energy in the 2 &micro / m - 12 &micro / m wavelength range at peak. In this thesis study, polycrystalline diamond is used as cutting tool material to machine germanium. Diamond is the hardest, most abrasion-resistant material and polycrystalline diamond is produced by compacting small diamond particles under high pressure and temperature conditions, which results more homogeneous, improved strength and a durable material. However, slightly reduced hardness is obtained when compared with natural diamond. Different from finish cutting, rough cutting, performed before finishing, is used to remove most of the work-piece material. During rough cutting, surface roughness is still an important concern, since it affects the finishing operations. Roughness of the surface of product is affected by a number of factors such as cutting speed, depth of cut, feed rate as cutting parameters, and also rake angle as tool geometry parameter. In the thesis, the optimum cutting and tool geometry parameters are investigated by experimental studies for rough cutting of germanium with polycrystalline diamond tools. Single Point Diamond Turning Machine is used for rough cutting, and the roughness values of the optical surfaces are measured by White Light Interferometer. Experiments are designed by making use of &ldquo / Full Factorial&rdquo / and &ldquo / Box-Behnken&rdquo / design methods at different levels considering cutting parameters as cutting speed, depth of cut, feed rate and tool geometry parameter as rake angle.

A comprehensive understanding of the interactions between orthopaedic and dental implant surfaces with the surrounding host tissue is essential in the design of advanced biomaterials that better promote bone growth and osseointegration of implants. Dental implants with roughened surfaces and high surface energy are well known to promote osteoblast differentiation in vitro and promote increased bone-to-implant contact in vivo. In addition, increased surface roughness increases osteoblasts response to the vitamin D metabolite 1α,25(OH)2D3. However, the exact mechanisms mediating cell response to surface properties and 1α,25(OH)2D3 are still being elucidated. The central aim of the thesis is to investigate whether integrin signaling in response to rough surface microtopography enhances osteoblast differentiation and responsiveness to 1α,25(OH)2D3. The hypothesis is that the integrin α5β1 plays a role in osteoblast response to surface microtopography and that 1α,25(OH)2D3 acts through VDR-independent pathways involving caveolae to synergistically enhance osteoblast response to surface roughness and 1α,25(OH)2D3. To test this hypothesis the objectives of the studies performed in this thesis were: 1) to determine if α5β1 signaling is required for osteoblast response to surface microstructure; 2) to determine if increased responsiveness to 1α,25(OH)2D3 requires the vitamin D receptor, 3) to determine if rough titanium surfaces functionalized with the peptides targeting integrins (RGD) and transmembrane proteoglycans (KRSR) will enhance both osteoblast proliferation and differentiation, and 4) to determine whether caveolae, which are associated with integrin and 1α,25(OH)2D3 signaling, are required for enhance osteogenic response to surface microstructure and 1α,25(OH)2D3. The results demonstrate that integrins, VDR, and caveolae play important roles in mediating osteoblast response to surface properties and 1α,25(OH)2D3. Silencing of the β1 integrin in osteoblast-like MG63 cells significantly reduced osteogenic response to surface topography and 1α,25(OH)2D3. Silencing of the α5 subunit did not alter the response of MG63 cells to changing surface roughness or chemistry, although future work must confirm these results given similar cell surface α5 integrin expression observed in control and α5-silenced cells. Multifunctional RGD, KRSR, and KSSR coated surfaces show that RGD increased osteoblast proliferation and reduced differentiation, KRSR had no affect on osteoblast phenotype, and KSSR increased osteoblast differentiation. These results suggest that titanium surfaces can be modified to manipulate proliferation and differentiation and that RGD/KSSR functionalized surfaces could be further investigated for use as osteointegrative surfaces. The results using VDR deficient osteoblasts demonstrate that 1α,25(OH)2D3 acts via VDR-dependent mechanisms in cells cultured on titanium surfaces that support terminal differentiation. In caveolae deficient osteoblasts, 1α,25(OH)2D3 affected cell number, alkaline phosphatase activity, and TGF-β1 levels, although levels of osteocalcin and PGE2 were not affected. These results are consistent with the hypothesis that VDR is required for the actions of 1α,25(OH)2D3, but that caveolae-dependent membrane 1α,25(OH)2D3 signaling modulates traditional VDR signaling. The exact mechanisms for this interaction remain to be shown. Overall, these results are important in better understanding the role of β1 integrin partners in mediating osteoblast response to implant surfaces and in understanding how integrin signaling can alter osteoblast differentiation and responsiveness to 1α,25(OH)2D3 via genomic and non-genomic pathways.

<p>The general trend toward increased use of computer models and simulations during product development has led to a need for accurate and reliable product models. The function of many products relies on contact interfaces between interacting components. To simulate the behavior of such products, accurate models of both components and interfaces are required. Depending on the purpose of the simulation, interface models of different degrees of complexity are needed. In simulation of very large systems with many interfaces, it might be computationally expensive to integrate detailed models of each individual interface. Condensed models, or abstractions, that describe the interface properties with a minimum of degrees of freedom are therefore required.</p><p>This thesis deals with mechanical interfaces with an emphasis on friction. In the four appended papers friction models are discussed in terms of condensed models, as well as in terms of more detailed contact models. The aim is to study how friction can be modeled in behavioral simulation of products and to discuss the convenience and relevance of using different types of friction models as building blocks of a system model in behavioral simulations.</p><p>Paper<b> A </b>presents a review of existing condensed friction models for sliding contacts under different running conditions and discusses the models from both simulation and tribological points of view.</p><p>In papers<b> B </b>and <b>C</b> a simplified contact model, called the elastic foundation model, is used to model friction in a boundary-lubricated rolling and sliding contact. The model is integrated in a dynamic rigid body model of a mechanical system, the system behavior is simulated, and the result is compared with experimental results.</p><p>Paper <b>D</b> discusses the application of the elastic foundation model to rough surface contact problems and investigates how the error in the elastic foundation results depends on surface roughness.</p>

The hydrodynamic effects of long-line mussel farms are studied through a two-pronged approach. Large-scale hydrodynamic effects are investigated through the use of field measurements, primarily at a large mussel farm in Golden Bay, New Zealand (230 long-lines, covering an area of 2.45 km by 0.65 km). The research focuses on three areas: the effect of the farm on currents, mixing and stratification, and the dissipation of wave energy. Measurements are also made of the forces on long-line anchor ropes, and a limited investigation is made of phytoplankton depletion. The second approach is the use of laboratory drag measurements and Particle Tracking Velocimetry (PTV) to study the effect of mussel dropper (vertical lengths of mussel-encrusted crop rope) roughness and spacing on flow at small scales. These experiments provide data on very rough cylinders, and on cylinder arrays. The field measurements show that the local effects of mussel farms on currents are significant, but that magnitudes of the effects depend on dropper density, mussel sizes, orientation of the long-lines to the flow, and other parameters that are necessary to characterise the complex interactions between a farm and the flow. The drag on the submerged structures reduces water velocities within the Golden Bay farm by between 47% and 67%. Mussel farms present a porous obstacle to the flow, and flow that does not pass through the farm must be directed around or beneath it. The field measurements indicate that at the study site, most of the flow is diverted around the farm despite its large horizontal dimensions. The droppers at the study site extend over most of the water column (average dropper length ~ 8 m, average water depth ~ 11 m), providing a restriction to the flow beneath the farm. The strength of the density stratification may also favour a horizontal diversion. The flow around the farm is essentially two-dimensional. This suggests that two-dimensional numerical models should be sufficient to obtain reasonable predictions of the velocity drop within, and the diversion around, mussel farms. A simple two-dimensional pipe-network model gives reasonable estimates of the velocity within the farm, demonstrating that the drag of the farm may be adequately parameterised through local increases of bed friction. A wake in the form of reduced velocities extends downstream of the farm, and a mixing layer analogy suggests that this wake spreads slowly. The downstream extent of the wake cannot be determined, although it is likely to be limited by the tidal excursion. The degree of vertical mixing caused by the flow through a mussel farm cannot be quantified, although there are clear interactions between the stratification and the farm. Two mixing mechanisms are considered. A shear layer is generated beneath the farm due to the difference in velocities between the retarded flow within the farm and the flow beneath. Shear layers beneath mussel farms are likely to be weak unless the ambient currents are strong. It will be necessary for stratification to be weak or non-existent for this mechanism to generate significant mixing. The second mechanism is smaller-scale turbulence generated by the mussel droppers. Although the efficiency of this form of mixing is likely to be low, the large number of mussel droppers suggests that there will be some enhancement of vertical mixing. Frequency-dependent wave attenuation is recorded, and is predicted with some success by an analytical model. Both the model and the field data show that wave dissipation increases as the wave period decreases. Wave energy dissipation at the study site averages approximately 10%, although the measurements are made during a period of low wave heights (Hs < 0.25 m). Measurements of long-line anchor rope tension at two study sites indicate that the loadings are induced by the tide, currents, and waves. Dynamic wave loadings may be significant, and higher wave forces are measured at the offshore end of a long-line. The issue of seston or phytoplankton depletion is considered briefly through the examination of fluorescence, turbidity, and acoustic backscatter data. Although the results are consistent with a reduction of seston within the farm, differences between the inside and outside of the farm are not statistically significant. Mussel droppers resemble extremely rough circular cylinders, with the mussel shells forming the surface roughness elements. Drag measurements and PTV flow visualisation are used to investigate the importance of the large surface roughness, and the influence of dropper spacing and long-line orientation on flow. Drag measurements conducted with smooth and rough cylinders show that high surface roughness (ks/D ~ 0.092) has little effect on the drag coefficient of single cylinders in the range 4,000 < Re < 13,000, yet increases the drag coefficient of a row of cylinders normal to the flow. High surface roughness on single cylinders has the effect of shortening the near-wake region, increasing the peak turbulent kinetic energy (TKE) behind the cylinder, and decreasing the Strouhal number (St = 0.21, 0.19, 0.17 for ks/D = 0, 0.048, and 0.094 respectively). Arrays of rough cylinders (ks/D = 0.094) demonstrate similar flow characteristics to those of smooth cylinders. At cylinder spacings of S/D < 2.2, the surface roughness acts to favour the formation of a particular metastable wake pattern, whereas different metastable wake patterns are formed each run behind the smooth cylinders. The experiments show that the drag on single row arrays of cylinders are related to the cylinder spacing (increasing drag with decreasing spacing), and the drag also varies with the sine of the angle to the flow, except where the array is at low angles to the flow. The PTV measurements provide new data regarding the two-dimensional distributions of velocity, TKE, and turbulence statistics behind the cylinder arrays.

In this thesis a study of the factors affecting virus and virus-sized particle transport in discrete fractured dolomite rocks is presented. Physical and chemical characteristics of two fractured rocks were determined, including fracture aperture distribution, rock matrix porosity, mineral composition, and surface charge. Hydraulic and transport tests were conducted in the fractures with a conservative solute (bromide) and carboxylate-modified latex (CML) microspheres of three sizes (20, 200, and 500 nm in diameter). The earlier arrival of larger microspheres as compared to bromide indicated the effects of pore-size exclusion and preferential flow paths in the fractures. The tailing of the bromide and the smaller microsphere (20 nm) in the breakthrough curves (BTC) indicated the diffusive mass transfer between the mobile water (flowing) and immobile water (stagnant water in the low aperture areas and porous rock matrix). The effects of ionic strength and cation type on the transport of viruses (bacteriophages MS2 and PR772) and virus-sized microspheres (20 and 200 nm) were determined from the transport tests in a fracture at three levels of ionic strength (3, 5, and 12 mM) and composition (containing Na+ and/or Ca2+ ions). Retention of the microspheres and bacteriophages increased with increasing ionic strength. The addition of divalent ions (Ca2+) influenced the retention to a greater extent than monovalent ions (Na+). The effects of the aperture distribution variability, matrix diffusion, and specific discharge on the solute and microsphere transport were determined from the transport tests conducted in two fractures. The higher variability in the aperture distribution contributed to higher solute dispersion, and flow channeling as evident from the breakthrough curves for individual spatially distributed outlets. A three-dimensional model simulation of the bromide transport with varying matrix porosity identified that the porous matrix influenced the solute transport. In the transport tests, retention of the microspheres decreased with increasing specific discharge in both fractures. The results of this research have helped in identifying the important factors and their effects on solute, virus, and virus-sized colloid transport in fractured dolomite rocks, which can be useful in determining the risk of pathogen contamination of water supplies in fractured dolomite rock aquifers.

Mémoire (M.Sc.A.)--Université du Québec à Chicoutimi, 2000. / Document électronique également accessible en format PDF. CaQCU