▼ This thesis presents experimental and numerical investigations of flows around a circular cylinder with different ventilation hole shapes and ventilation holes arrangement. Ten models with different ventilation configurations are tested at ReD 55000, and data were acquired for each case at flow angles ranging from 0° to 180° at increment of 2.5°. It has been found that the best results in terms of drag force reduction are models where the holes are located on the sides (shoulders). With the best hole-configuration, the mean drag coefficient is reduced by 33.5% compared to the smooth surface case. Numerical investigations were conducted using FLUENT on a smooth cylinder and the cylinder with the experimentally-determined best hole-configuration. The CFD results show that the flow through the holes fixes the local separation locations on the cylinder, thereby reduce the flow induced force oscillation. The Strouhal number associated with vortex shedding is reduced from the smooth cylinder. Advisors/Committee Members: Ng, Terry.

▼ Numerical simulation of the Enthalpy formulation, for the Stefan problems, is known to be limited by two difficulties: 1) non-physical waviness in the temperature distribution, as well as unwanted oscillations close to the phase interface, for isothermal phase change, and 2) convergence and stability problems, as well as inaccuracies due to overwhelming dissipation of the numerical schemes, at the limit of small Stefan numbers. The method of space-time conservation element and solution element is known for its low dissipation and dispersion errors, as well as its distinguishingly high capability of capturing discontinuities accurately. Therefore, this numerical method, mainly applied to the fluid flow problems, represents an alternative for numerical modeling of moving boundary (Stefan) problems such as solid/liquid phase change. In this dissertation, space-time CE/SE schemes are developed, for the solid/liquid phase change problems, in one-, two-, and three- spatial dimensions. A separate formulation is also presented and programmed for the axisymmetric problems. The von Neumann stability analysis is applied to the one-dimensional scheme. The results of this analysis lead to a necessary stability condition. Each scheme is then validated, numerically, using benchmark problems without and with phase change. Both analytical and experimental results are used in the validation process. The results reveal that using the space-time CE/SE method, the first problem associated with the numerical modeling of the enthalpy method is eliminated. No non-physical waviness or unwanted oscillation is detected in the results. The second problem, however, still existed. Although accurate results can be obtained for small Stefan numbers using the CE/SE method, a case-dependent adjustment in dissipation was needed. This presents the potential for a modification in the original schemes. Numerical experiments are then conducted, in order to reveal the dissipative / dispersive behavior of the numerical scheme and its variation with the Stefan number. The results of this analysis lead to the development of a CE/SE scheme that is, to a considerable degree, insensitive to the value of the Stefan number. Finally, space-time CE/SE method is established as an alternative for the numerical simulation of the enthalpy method for the Stefan problems. Advisors/Committee Members: Keith, Theo G.

▼ This project focused on modifying membrane surfaces to increase fouling control while improving permeability and selectivity, resulting in membranes with longer operational lives, lower cleaning frequencies, and higher efficiencies. The modifications involved the attachment of a temperature sensitive polymer to keep the membrane from fouling. The membrane modifications, which produced a self-cleaning cellulose acetate membrane, involved grafting the surface with a thermally responsive film layer of hydroxypropyl cellulose (HPC). HPC possesses a lower critical solution temperature (LCST) of approximately 43C. When attached to a surface, HPC forms a film, which collapses at temperatures above the LCST and expands when cooled to below the LCST. By keeping the film in a non-equilibrium state, via oscillating the temperature of the membrane surface, (as was observed by flux decline), fouling was reduced. Two surface modification techniques were tested and compared to the unmodified membrane - Method 1 and Method 2. Method 1 involved the attachment of a gel layer whereas Method 2 was the attachment of polymer structures on the surface of the membrane. Roughness measurements, using a wet atomic force microscopy (AFM) cell, and filtration experiments (to monitor flux declines) were performed at cold temperatures (25C), at hot temperatures (60C) and with temperature oscillations. The unmodified membrane had roughness values that were higher when hot and lower when cold, and it displayed flux declines under all temperature conditions when a humic solution was filtered. Since the humic solution was acting as a fouling agent, the decrease in flux indicated the membrane was fouling. When Method 1 was used, both roughness values and filtration experiments supported temperature activation. Wet Method 1 membranes at cold temperatures displayed an average roughness of 8.40 nm while at hot temperatures, the roughness decreased to 0.92 nm, supporting the hypothesis of the film being expanded at cold temperatures and collapsed at hot temperatures. Filtration experiments using the Method 1 membrane showed that flux measurements remained nearly constant at all temperature test conditions; however, initial flux values were significantly lower than the unmodified membrane due to the potential film formation within pores. On the other hand, the Method 2 showed higher initial flux values (not significantly different from the unmodified membrane) since the film was formed in solution then attached to the membrane, which was believed to be farther away from the membrane surface. Membrane roughness values for Method 2 were on average 6.80 nm and 5.02 nm for cold and hot temperatures. As with Method 1, Method 2 membranes displayed nearly no flux decline irrespective of temperature condition when a humic solution was filtered through. Even though temperature responses were more pronounced when Method 1 membranes were used as compared to the Method 2 membranes, the loss in initial fluxes due to pore blockage with Method 1 made Method 2 more advantageous. A Method 2 modified membrane would produce a self-cleaning membrane. The use of harsh chemicals during normal membrane cleaning would be avoided with the Method 2 modified membrane as a constant flux operation could be achieved using temperature oscillations only. Advisors/Committee Members: Escobar, Isabel.

▼ This thesis presents a crack detection and classification algorithm and describes the procedure of pavement image compression for efficient storage. The algorithm is built upon wavelet transform. The application of wavelets to images yields different frequency sub-bands. Also, this algorithm is based on the fact that crack pixels are darker than their surroundings. The crack detection algorithm decomposes a pavement image into four sub-bands: one low frequency sub-band called approximation and three high frequency sub-bands called detail. Cracks appear clearly in the low frequency subband at the first level through extended pseudo color matrix scaling. The algorithm of classification first revises and re-computes the horizontal, vertical and diagonal details at the first level through the energy conservation function, and then forms a new image through adding corresponding points in the four new sub-bands; finally it applies Radon transform to this new image. For images compressed for storage, the algorithm combining noise reduction and compression through wavelet transform is used. Advisors/Committee Members: Salari, Ezzatollah.

▼ Maintenance of pavements is a very important aspect for the Departments of Transportation in any country. The first step towards maintenance is the identification of faulty pavement areas and their documentation for further action. Many methods have been devised to identify the cracks on pavements apart from the crude process of manual inspection. Image processing, ultrasonic detection and infrared detection have been the most common methods of automated inspection. For the use of images, external factors such as shadows and improper lighting might result in noise. Localized thresholding is implemented by dividing the image into smaller blocks and identifying a local threshold and finding the crack pixels using the threshold of each block. Correlating the intensity and the relative values of the RGB components of the image, the region of interest is obtained from the original image. The image is converted into a black and white image in the end to identify the existing cracks, recreate the lost crack image, identifying the type of cracks based on the orientation of the cracks and thereby rating the pavement accordingly. Advisors/Committee Members: Salari, Ezzatollah.

▼ In chemical processing industries, heating, cooling and other thermal processing of viscous fluids are an integral part of the unit operations. Consequences of improper mixing include non-reproducible processing conditions and lowered product quality. Static mixers economically promote the mixing of flowing fluid streams. One typical static mixer, the helical static mixer, consists of left- and right-twisting helical elements placed at right angles to each other. The range of Reynolds numbers of practical flows for helical static mixers in industry is usually from very small values to not very large values (e.g., Re = 5,000). This thesis describes how static mixing processes of single-phase Newtonian and also non-Newtonian liquids can be simulated numerically and provides useful information that can be extracted from the simulation results. The Turbulent flow case is solved using the most common Reynolds Averaged Navier-Stocks (RANS) models as well as Large-Eddy Simulation (LES) turbulent flow model. The numerical simulation of the mixing in the helical static mixer has been performed via a two-step procedure. In the first step, the flow velocity (and the pressure) is computed. These values are then used as input to the next step. In the second step the particle trajectory in the flow field is calculated. At the entry of the pipe inlet, a large number of marker particles are uniformly distributed over half of the flow field. This represents a simplified model for diametrical feeding of the mixer with two liquids. Using different measurement tools, such as Residence Time Distribution (RTD) and Particles Distribution Uniformity (PDU), the performance of a six-element helical static mixer is studied. It is shown that the Reynolds number has a major impact on the performance of a static mixer. It is also shown that the performance of a helical static mixer is different for Newtonian and non-Newtonian fluids in non-creeping flows. Finally, heat transfer within a helical static mixer is investigated. The effects of different flow conditions on the performance of the mixer are studied. It is shown that the helical static mixer is more effective for low Reynolds number laminar flows. Advisors/Committee Members: Keith, Theo G.

▼ In this thesis, a novel, fast and self-adaptive image processing method is proposed for the extraction and connection of break points of cracks in pavement images. The algorithm first finds the initial point of a crack and then determines the crack’s classification into transverse and longitudinal types. Different search algorithms are used for different types of cracks. Then the algorithm traces along the crack pixels to find the break point and then connect the identified crack point to the nearest break point in the particular search area. The nearest point then becomes the new initial point and the algorithm continues the process until reaching the end of the crack. The experimental results show that this connection algorithm is very effective in maximizing the accuracy of crack identification. Advisors/Committee Members: Salari, Ezzatollah.

▼ Numerous fatigue-critical parts could be found in ground vehicles, and time-varying loads have always challenged automotive designers. Fatigue design and life assessment of these components are essentially influenced by the material used and manufacturing processes chosen. Exploring the design criteria and optimization potentials with respect to manufacturing processes is vital to the industry. This study was aimed at developing general procedures for fatigue analysis and optimization of safety-critical automotive components with manufacturing considerations. A literature survey was conducted, specimen and component tests were performed, and finite element stress analysis and durability and optimization evaluations of similar components produced by different manufacturing technologies were made to achieve the objectives. The typical example component chosen was a vehicle steering knuckle made of three competing materials and manufacturing processes including forged steel, cast aluminum and cast iron. In the literature survey, manufacturing processes were studied and compared with focus on mechanical behavior. The methods used in the literature for fatigue life evaluation and prediction of automotive components, as well as for optimization studies with respect to geometry, material and manufacturing aspects were also reviewed. Specimen strain controlled tests were conducted to obtain material monotonic and cyclic deformation and fatigue properties. Components’ fatigue behaviors were investigated via constant-amplitude load-controlled fatigue tests. Comparisons of materials monotonic and fatigue properties, and components’ fatigue behaviors were made for competing material and manufacturing processes. In terms of structural performance and durability, based on both material testing and component evaluation, forged steel was found superior to cast iron which in turn was found superior to cast aluminum. Finite element models of the components were analyzed, using linear and nonlinear stress analyses. The nominal stress and local stress and strain approaches were employed to assess durability of the components. Experimental and analytical stress and fatigue life results were compared to evaluate the validity of the analytical approaches. The strength and shortages of the applied models and alternative analyses were also investigated. It was concluded that the local life prediction approaches in combination with either nonlinear finite element analysis results, or linear finite element analysis results corrected for local plasticity, yielded satisfactory predictions. A procedure was developed to optimize forged automotive components for weight reduction and cost savings with fatigue strength as the key performance indicator. By considering geometry variations, alternative materials and manufacturing process parameters as design variables, the example part was optimized. Guidelines were developed and limitations were identified for the optimization procedure. Although the optimization results showed limited changes for the particular example component, the approach that was followed is applicable to other forged components. It was emphasized that geometrical optimization of manufactured components could only be realistic and practical if other important parameters like material, manufacturability, and cost are taken into account. Advisors/Committee Members: Fatemi, Ali.