System Architecture Optimization Using Hidden Genes Genetic Algorithms with Applications in Space Trajectory Optimization

In this dissertation, the concept of hidden genes genetic algorithms is developed. In system architecture optimization problems, the topology of the solution is unknown and hence, the number of design variables is variable. Hidden genes genetic algorithms are genetic algorithm based methods that are developed to handle such problems by hiding some genes in the chromosomes. The genes in the hidden genes genetic algorithms evolve through selection, mutation, and crossover operations. To determine if a gene is hidden or not, binary tags are assigned to them. The value of the tags determine the status of the genes. Different mechanisms are proposed for the evolution of the tags. Some mechanisms utilize stochastic operations while others are based on deterministic operations. All the proposed mechanisms are tested on mathematical and space trajectory optimization problems. Moreover, Markov chain models of the mechanisms are derived and their convergence is investigated analytically. The results show that the proposed concept are capable to search for the optimal solution by autonomously enabling the algorithms to assign the hidden genes

Experimental and modeling study of foam flow in pipes with two foam-flow regimes

The use of foams can be found abundantly in many applications in a wide range of industries, including oil and gas industry. Although understanding foam flow behavior is crucial for the optimization of such applications, the complex flow behavior of foams has been a major challenge. Recent experimental studies with surfactant foams presented a new way to characterize foam flow characteristics by using two flow regimes: the low-quality regime showing either plug-flow or segregated-flow pattern, and the high-quality regime showing slug-flow pattern. This study consists of three main components: (1) experimental investigation of foam rheology in pipes; (2) building up of a new foam model consistent with lab-measured experimental data; and (3) use of the model in petroleum drilling hydraulics modeling and simulation. The major outcome of this study can be summarized as follows. First (Part 1), by conducting foam flow experiments in pipes, this study shows the concept of two foam-flow regimes is still valid and effective not only with surfactant foams but also with foams in the presence of additives such as polymers and oils. This finding is important because many field applications of foam flow involve some levels of additives. Second (Part 2), this study for the first time presents how to build a foam model which is consistent with two foam-flow regimes evidenced by experimental data. The model requires four model parameters – two parameters to capture rheological properties (e.g. consistency index and flow behavior index, if power-law rheology is applied) and two parameters to define the dependence of foam rheology to gas and liquid flow rates in both foam flow regimes. Third and last (Part 3), the significance of this model is verified by implementing it into existing foam drilling hydraulics calculations in a 10,000 ft vertical well in which foams are injected down into the drill pipe, through the drill bit and circulated up to the surface along the annulus. The results show that this new foam model equipped with two flow regimes is advantageous over the conventional foam model especially when foams become dry and unstable in the well, improving the accuracy

Mechanical modeling of Intraneural Ganglion Cyst

Intraneural Ganglion Cyst is a 200 year old mystery related to nerve injury which is yet to be solved. Current treatments for the above problem are relatively simple procedures related to removal of cystic contents from the nerve. However, these treatments may result into neuropathic pain and recurrence of the cyst. The articular theory proposed by Spinner et al., (Spinner et al. 2003) takes into consideration the neurological deficit in Common Peroneal Nerve (CPN) branch of the sciatic nerve and affirms that in addition to the above treatments, ligation of articular branch results into foolproof eradication of the deficit. Mechanical Modeling of the Affected Nerve Cross Section will reinforce the articular theory (Spinner et al. 2003). As the cyst propagates, it compresses the neighboring fascicles and the nerve cross section appears like a signet ring. Hence, in order to mechanically model the affected nerve cross section; computational methods capable of modeling excessively large deformations are required. Traditional FEM produces distorted elements while modeling such deformations, resulting into inaccuracies and premature termination of the analysis. The methods described in this Master’s Thesis are effective enough to be able to simulate such deformations. The results obtained from the model adequately resemble the MRI image obtained at the same location and shows an appearance of a signet ring. This Master’s Thesis describes the neurological deficit in brief followed by detail explanation of the advanced computational methods used to simulate this problem. Finally, qualitative results show the resemblance of mechanical model to MRI images of the Nerve Cross Section at the same location validating the capability of these methods to study this neurological deficit

Advanced mechanics of materials with microstructure

The study of advanced materials aimed at improving human life has been performed since time immemorial. Such studies have created everlasting and greatly revered monuments and have helped revolutionize transportation by ushering the age of lighter–than–air flying machines. Hence a study of the mechanical behavior of advanced materials can pave way for their use for mankind’s benefit. In this school of thought, the aim of this dissertation is to broadly perform two investigations. First, an efficient modeling approach is established to predict the elastic response of cellular materials with distributions of cell geometries. Cellular materials find important applications in structural engineering. The approach does not require complex and time-consuming computational techniques usually associated with modeling such materials. Unlike most current analytical techniques, the modeling approach directly accounts for the cellular material microstructure. The approach combines micropolar elasticity theory and elastic mixture theory to predict the elastic response of cellular materials. The modeling approach is applied to the two dimensional balsa wood material. Predicted properties are in good agreement with experimentally determined properties, which emphasizes the model’s potential to predict the elastic response of other cellular solids, such as open cell and closed cell foams. The second topic concerns intraneural ganglion cysts which are a set of medical conditions that result in denervation of the muscles innervated by the cystic nerve leading to pain and loss of function. Current treatment approaches only temporarily alleviate pain and denervation which, however, does not prevent cyst recurrence. Hence, a mechanistic understanding of the pathogenesis of intraneural ganglion cysts can help clinicians understand them better and therefore devise more effective treatment options. In this study, an analysis methodology using finite element analysis is established to investigate the pathogenesis of intraneural ganglion cysts. Using this methodology, the propagation of these cysts is analyzed in their most common site of occurrence in the human body i.e. the common peroneal nerve. Results obtained using finite element analysis show good correlation with clinical imaging patterns thereby validating the promise of the method to study cyst pathogenesis

Modeling of Foam Flow in Porous Media for Subsurface Environmental Remediation

Among numerous foam applications in a wide range of disciplines, foam flow in porous media has been spotlighted for improved/enhanced oil recovery processes in petroleum-bearing geological formations and shallow subsurface in-situ NAPL (non-aqueous phase liquid) environmental remediation in contaminated soils and aquifers. In those applications, foams are known to reduce the mobility of gas phase by increasing effective gas viscosity and improve sweep efficiency by mitigating subsurface heterogeneity. This study investigates how surfactant/foam process works fundamentally for environmental remediation purpose by using MoC (Method of Characteristics) based foam modeling and simulation techniques. It consists of two main parts: Part 1, developing foam model using three-phase fractional flow theory accounting for foam flow rheology such as foam strength and stability at different phase saturations; and Part 2, extending the model to investigate the mechanisms of surfactant/foam displacement in multi-layer systems. Part 1 investigates six scenarios such as different levels of foam strength (i.e., gas mobility reduction factors), different initial conditions (i.e., initially oil/water or oil/water/gas present), foam stability affected by water saturation (Sw), oil saturation (So), and both together, and uniform vs. non-uniform initial saturations. The process is analyzed by using ternary diagrams, fractional flow curves, effluent histories, saturation profiles, time-distance diagrams, and pressure and recovery histories. The results show that the three-phase fractional flow analysis presented in this study is robust enough to analyze foam-oil displacements in various conditions, as validated by an in-house numerical simulator built in this study. The use of numerical simulation seems crucial when the foam modeling becomes complicated and faces multiple possible solutions. Part 2 first shows how to interpret theoretically the injection of surfactant preflush and following foams into a single-layer system at pre-specified rock and fluid properties, and then extends the knowledge gained into multi-layer systems where the properties vary in different layers. The results in general show that the mechanisms of foam displacement strongly depend on foam properties such as gas-phase mobility reduction factors (MRF), limiting water saturation (Sw*), critical oil saturation (So*), and so on as well as petrophysical properties of individual layers such as porosity (φ), permeability (k), relative permeability and so on. The overall sweep efficiency in a multi-layer system is very difficult to predict because of the complexity, but the mathematical framework presented in this study is shown to be still reliable. The in-house foam simulator is also extended to compare with modeling results

Characterization and Performance of Algal Biofilms for Wastewater Treatment and Industrial Applications

This study was carried out on algal biofilms grown using rotating algal biofilm reactors (RABRs) with the aim of: i) characterizing their growth in terms of photosynthetic activity and morphology ii) evaluating their performance as a wastewater treatment option and a feedstock for biofuels production, and iii) examining the algal-bacteria interactions. A review of algal biofilm technologies currently employed in wastewater treatment processes was made to compare nutrient removal efficiencies, factors that influenced algal biofilm growth, and the different bioproducts generated from algal biomass. Consequently, research efforts were directed towards addressing pertinent issues identified in literature in order to optimize these systems for wastewater treatment and bioproducts production. Successful growth of algal biofilms in municipal wastewater and subsequent removal of nutrients from the wastewater was demonstrated. Photosynthetic and respiration rates observed with depth of the biofilm were influenced by the biofilm composition (single vs. mixed species), culturing conditions (laboratory vs. outdoor), orientation to the light, nitrogen availability (N-replete vs. N-deplete), and dissolved inorganic carbon availability (presence or absence of bicarbonate). Slight enhancement in lipid production was also observed as a result of nitrogen stress and bicarbonate addition. However, the accumulated lipids were not as much as expected or as reported in suspended cultures. Presence of bacteria positively influenced microalgae growth in the mixed cultures but the reverse was not true. In conclusion, photosynthetic activity and biofilm structure were characterized with methods developed for the algal biofilms in this study. For now, productivity of the algal biofilms needs to be maximized in order to fully utilize its potential as a biofuel feedstock and nutrient removal option. Further research on algae-bacteria interactions using species native to the wastewater grown algal biofilms is recommended

The Left Atrial Appendage (LAA): Proximity of the Circumflex Artery and Evaluation of a Novel Method of Closure

The left atrial appendage (LAA) is an area of interest because of its thrombogenic potential in patients with atrial fibrillation. The current standard for LAA removal is epicardial excision, which may leave residual volume thereby undermining its effectiveness. Also, LAA surgery may injure the nearby circumflex artery. This investigation aims to measure the proximity of the circumflex artery to the LAA at various points, and evaluate pericardial patch exclusion as a novel method of LAA closure in a cadaveric model. After performing both procedures in all (n=27) hearts, epicardial excision left 24% of the original volume while pericardial patch exclusion left 4%. The circumflex artery was closest to the LAA at the 4 o’clock position. These results suggest that physicians should beware of the injuring the circumflex artery at 4 o’clock and that pericardial patch exclusion may be a viable alternative for surgical LAA closure in patients with atrial fibrillation

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