Thesis--Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution. / Includes bibliographical references (p. 181-186).

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

No description available.

Boundary layer ingesting (BLI) propulsion systems offer potential fuel burn reduction for civil aviation and synergize with new advanced airframe concepts. However, the distorted inlet flow for BLI systems can cause performance and stability margin loss. System level analyses generally size a single engine at a fixed design point which ignores the distributed nature of many BLI architectures. Furthermore, operability and performance during o design are generally not considered during the sizing process. In this thesis, a methodology is developed for multi-design point sizing of BLI propulsion systems for specific vehicle geometry including an operability constraint. The methodology is applied to a 300 passenger hybrid-wing body vehicle with embedded turbofan engines. The methodology required investigations into three main areas of research. The first was the modeling of BLI impacts over a range of flight conditions. A BLI analysis tool was developed which models the vehicle boundary layer, pre-entry region, inlet, and fan losses throughout the entire flight envelope. An experiment investigating the impact of the modeling approach is conducted, and results show that proper mapping of the fan, inlet, and BLI propulsive benefit is crucially important for making proper design decisions. The impact of BLI on the system was found to vary significantly during o ff design and especially with changes in vehicle angle of attack. The operability constraint is investigated using a parallel compressor model and was found to place a minimum limit on the propulsor height. The second area of investigation was the creation of a multi-propulsor sizing methodology which accounts for diff erences between propulsors during flight that is induced by their interaction with the vehicle. A modified multi-design point approach was used which employs a set of design and power management rules to relate the operation of the propulsors. A performance comparison of this methodology with the standard single propulsor approach showed a signicant difference. The final area of investigation was the determination of critical o ff-design conditions for the sizing procedure. A screening process is developed which tests all off -design conditions for a subset of the design space to find conditions which are stall margin or thrust deficient. The experiment showed that it is necessary to consider the high angle of attack take-off condition during sizing for the HWB vehicle and that a variable area nozzle is required to meet the operability constraint. A follow on experiment showed that the inclusion of this point reduced the achievable fuel burn benefit for more aggressive BLI designs.Boundary layer ingesting (BLI) propulsion systems offer potential fuel burn reduction for civil aviation and synergize with new advanced airframe concepts. However, the distorted inlet flow for BLI systems can cause performance and stability margin loss. System level analyses generally size a single engine at a fixed design point which ignores the distributed nature of many BLI architectures. Furthermore, operability and performance during o design are generally not considered during the sizing process. In this thesis, a methodology is developed for multi-design point sizing of BLI propulsion systems for specific vehicle geometry including an operability constraint. The methodology is applied to a 300 passenger hybrid-wing body vehicle with embedded turbofan engines. The methodology required investigations into three main areas of research. The first was the modeling of BLI impacts over a range of flight conditions. A BLI analysis tool was developed which models the vehicle boundary layer, pre-entry region, inlet, and fan losses throughout the entire flight envelope. An experiment investigating the impact of the modeling approach is conducted, and results show that proper mapping of the fan, inlet, and BLI propulsive benefit is crucially important for making proper design decisions. The impact of BLI on the system was found to vary significantly during o ff design and especially with changes in vehicle angle of attack. The operability constraint is investigated using a parallel compressor model and was found to place a minimum limit on the propulsor height. The second area of investigation was the creation of a multi-propulsor sizing methodology which accounts for diff erences between propulsors during flight that is induced by their interaction with the vehicle. A modified multi-design point approach was used which employs a set of design and power management rules to relate the operation of the propulsors. A performance comparison of this methodology with the standard single propulsor approach showed a signicant difference. The final area of investigation was the determination of critical o ff-design conditions for the sizing procedure. A screening process is developed which tests all off -design conditions for a subset of the design space to find conditions which are stall margin or thrust deficient. The experiment showed that it is necessary to consider the high angle of attack take-off condition during sizing for the HWB vehicle and that a variable area nozzle is required to meet the operability constraint. A follow on experiment showed that the inclusion of this point reduced the achievable fuel burn benefit for more aggressive BLI designs.

No description available.

Active contours are now a very popular technique for shape extraction, achieved by minimising a suitably formulated energy functional. Conventional active contour formulations suffer difficulty in appropriate choice of an initial contour and values of parameters. Recent approaches have aimed to resolve these problems, but can compromise other performance aspects. To relieve the problem in initialisation, an evolutionary dual active contour has been developed, which is combined with a local shape model to improve the parameterisation. One contour expands from inside the target feature, the other contracts from the outside. The two contours are inter-linked to provide a balanced technique with an ability to reject weak’local energy minima. Additionally a dual active contour configuration using dynamic programming has been developed to locate a global energy minimum and complements recent approaches via simulated annealing and genetic algorithms. These differ from conventional evolutionary approaches, where energy minimisation may not converge to extract the target shape, in contrast with the guaranteed convergence of a global approach. The new techniques are demonstrated to extract successfully target shapes in synthetic and real images, with superior performance to previous approaches. The new technique employing dynamic programming is deployed to extract the inner face boundary, along with a conventional normal-driven contour to extract the outer face boundary. Application to a database of 75 subjects showed that the outer contour was extracted successfully for 96% of the subjects and the inner contour was successful for 82%. This application highlights the advantages new dual active contour approaches for automatic shape extraction can confer.

The past three decades have seen a fast expanding interest in thermal problems exhibiting a change of phase, more commonly known as Stefan problems. With the rapid advance in computer technology the use and expansion of numerical simulation schemes has been responsible for large advances in this field. The increasing size of computers has led to more sophisticated and complex numerical solutions becoming feasible from a computational point of view. On the other hand, part of this interest has developed from industrial quarters where a knowledge of the location of a melting/freezing boundary may be of critical importance for certain processes. Much experimental work has been completed in this field. However, it is still useful to be able to obtain quick, accurate numerical solutions to such problems and it is with this in mind that this thesis is presented. Ideas from both of the above areas of interest are treated. In the first case a simple to program and computationally efficient numerical scheme is proposed for solving one dimensional Stefan problems and its merits are discussed in relation to several of the more common existing solution schemes. This scheme is then modified to cater for a two dimensional problem which crudely imitates a possible heating configuration in some industrial processes. The problem, with its attendant difficulties, is first approximated by a 'test' problem which is constructed so as to admit an analytic solution. This allows assessment of the numerical procedure in two dimensions. In the course of this work a pseudo-analytic solution was obtained for the original two dimensional problem. Finally, in collaboration with the British Gas Corporation, a complex industrial freezing problem is discussed concerning the flow of liquid through an enclosed channel. Some simplifying assumptions are proposed to reduce the problem to a form for which a relatively simple numerical scheme may be adopted. Several simulations are completed to examine the effect of varying physical parameters on the solution and in particular to test for situations of blockage or steady-state.

Test sections in laboratory studies should be fully developed and uniform if they are to be generalized. The objective of this study is to develop a model for predicting the uniform flow development length (Lunif) in a rough laboratory flume as a function of hydraulic parameters and bed particle roughness height (ks). Using an ADV time-averaged point velocity was measured in developing and fully developed turbulent subcritical rough open-channel flows. A series of laboratory tests were carried out in a 6.1-m-long and 0.46-m-wide rectangular channel. Tests were conducted with fine gravel (d50 = 5.8 mm, ks = 3.1d90 = 0.026 m), medium gravel (d50 = 14 mm, ks = 0.068 m), and with fine /medium gravel (d50 = 11 mm, ks = 0.04 m). For each test, longitudinal point velocity measurements were made along the center of the channel at five elevations, and at thirteen longitudinal stations. The study concluded that for flow to be uniform, the flow depth and mean cross-sectional velocity must be constant. In addition, root mean square of the fluctuating component of the velocity, RMS(u'), which is the measure of the turbulence intensity, should be uniform in order for a flow to consider uniform. Thus, RMS(u') is one of the indicative measures for determining the location where the developing flow is fully developed and uniform. The results showed that increasing the bed roughness height decreases the uniform flow development length. Using the dimensional and statistical analyses Lunif was estimated as a linear function of Reynold's particle number and Froude number.

No description available.

Transition of the attachment fine boundary layer was investigated using a large swept cylinder. Results for natural transition and transition tripping with two-dimensional trip wires were simila to those obtained by Poll using a similar, but smaller, model. ]Lower displacement thickness Reynolds numbers but larger trip sizes, than for the flat-plate boundary layer, were required for transition. The investigation of transition tripping was then extended to involve three-dimensional trips. The attachment line boundary layer was less susceptible to three-dimensional trips than to two-dimensional trips but upper and lower bounds of attachment line Reynolds number for transition were identical. It was also found that the roughness Reynolds numbers for fully effective three-dimensional trips were similar for the attachment line and flat-plate boundary layers. Another common feature was the more abrupt upstream movement of the transition front with increasing Reynolds number for three-dimensional trips than for two-dimensional trips. Turbulence spreading downstream of a three-dimensional trip was also examined and, as in the flat-plate boundary layer, was found to be heavily dependent on Reynolds number (varying from 3° at low Reynolds number to a value approaching 10° as Reynolds number exceeded the value for natural transition), but was also dependent on either the trip size or the initial conditions at which the trip first introduced turbulent spots. The effects of higher levels of freestrearn turbulence were then investigated for both two-dimensional and three-dimensional trips. With a small increase in freestrea turbulence the conditions for transition with twodimensional trips were affected far more than those for three-dimensional trips, for which only the transition completion conditions were affected signfficantly, resulting in a reduced extent ofthe transition region. Larger levels of turbulence appeared to have similar effects on the two trip types. Restrictions in model length and windspeed for the higher turbulence tests prevented an accurate investigation of the effects of turbulence,on the upper and lower bounds for transition tripping and on the influence of spanwise distance at higher levels of turbulence. Finally, the interaction between two trips positioned on the attachment line was examined. The effect of the second trip on the transition Reynolds number was found to a function of the streamwise separation distance between the two trips.