Department: Engineering and Applied Science: Aerospace Engineering ![[clear]](close-x.png "Remove this limiter")
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1.
Ahuja, Mohit.
Fuzzy counter Ant Algorithm for Maze Problem.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2011, University of Cincinnati
► AUTONOMOUS intelligent multi-agents have a widespread application in different fields including homeland…
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▼ AUTONOMOUS intelligent multi-agents have a widespread application in different fields including homeland security. Several applications of such autonomous robots include exploration, mine detection, border patrol, ISR missions etc. It is desired that the autonomous robot should have some adaptive and intelligent decision making capability for navigation in unknown obstacle rich terrains. Researchers in the field of AI and neural networks have considered the generalized maze problem an interesting test bed. Over the last couple of years, scientists and researchers have done a lot of work in this area. Using a cooperative multi agent robot system reduces the convergence time considerably as compared to using a single agent. Many algorithms, till date, have been proposed to develop a common decision support system among multi agents. However, most of the decision support systems are either time consuming or unscalable. Presented here is a fuzzy inference system used along with counter ant algorithm (modified ant colony optimization algorithm) that aids the agents in choosing paths along the unexplored regions, and hence, solves the maze problem in reduced time. MATLAB simulations results have been presented to demonstrate the effectiveness and scalability of the proposed algorithm. Application of the developed algorithm onto an actual mobile robot has also been shown to solve a lab based maze without the repetition of the already explored paths.
Advisors/Committee Members: Cohen, Kelly.
Subjects: Aerospace Materials
Keywords: Fuzzy Logic; Ant; Maze; Khepera; Carrot or Stick
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2.
Aull, Mark J.
Comparison of Fault Detection Strategies on a Low Bypass Turbofan Engine Model.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2011, University of Cincinnati
► Current diagnostics on most gas turbine engines involve off-line processing only. Since…
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▼ Current diagnostics on most gas turbine engines involve off-line processing only. Since failures can cause serious safety and efficiency problems, such as elevated turbine temperatures or compressor stall, it is desirable to diagnose problems in as close to real-time as possible. This project applies some of the methodology of Rausch, et. al. to a simulation of a low bypass turbofan. The model uses 9 health parameters to simulate faults or degradation of engine components. Sensor residuals from an extended Kalman filter were used with a non-linear engine model to estimate the engine health parameters. Other methods for generating health parameter estimates were also implemented and compared, including a tracking filter based on Newton's method and a back-propagation neural network. An implementation of a Bayesian network to engine fault diagnostics is demonstrated and a fuzzy diagnostic system is developed using a similar method, avoiding many of the difficulties traditionally encountered while developing fuzzy systems (the effectively infinite design degrees of freedom available while designing the system). Finally, the results of the diagnostic systems are compared in terms of accuracy of fault diagnosed, accuracy of the health parameter estimates produced, (simulation) time taken to produce a correct diagnosis, and time needed for the computation. The Bayesian network and fuzzy system have the best overall performance: both systems correctly diagnose each component fault, while the LKF and tracking filter fail for some cases and the neural network fails under some conditions. The Bayesian network diagnoses faults in about half the time from the introduction of the fault, while the fuzzy system estimates the health parameters more accurately and is less computationally intensive.
Advisors/Committee Members: Walker, Bruce.
Subjects: Aerospace Materials
Keywords: Fault Diagnostics; Gas Turbine; Kalman Filter; Bayesian Network; Fuzzy Logic
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3.
Bunnag, Shane.
Bleed Rate Model Based on Prandtl-Meyer Expansion for a Bleed Hole Normal to a Supersonic Freestream.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2010, University of Cincinnati
► The presented work shows that Prandtl-Meyer expansion can be used as a…
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▼ The presented work shows that Prandtl-Meyer expansion can be used as a foundation to predict bleed rate for a single bleed hole oriented normal to a supersonic freestream. A CFD study was used to explore flowfield phenomena that can be used in conjunction with Prandtl-Meyer expansion theory to improve model accuracy. Of these phenomena, the shear layer and barrier shock were the best defined and their geometric placement within the bleed hole were the basis for the bleed rate model. Coefficients of variation of the root mean square error between data and predictions were between 0.10 and 0.15 for all but the highest of freestream Mach numbers evaluated. Development of an analytical bleed rate model and recommendations for follow-on activity are presented.
Advisors/Committee Members: Hamed, Awatef.
Subjects: Aerospace materials
Keywords: boundary layer bleed; Prandtl-Meyer expansion; bleed rate model; shockwave boundary layer interaction; first principles; supersonic inlet
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4.
Charvat, Robert C.
Surveillance for Intelligent Emergency Response Robotic Aircraft (SIERRA Project).
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2012, University of Cincinnati
► Unmanned Aerial Systems (UASs) have proven their potential in wartime environments by…
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▼ Unmanned Aerial Systems (UASs) have proven their potential in wartime environments by providing an alternative to manned technologies that risk human life. UASs are able to perform in situations that are dangerous or undesirable to humans. Also, UASs allow for miniaturization of technologies previously used for these tasks, which provides higher task performance at a lower cost. By combining miniaturized technology platforms with already existing technologies from the public domain, this technology has proved to be beneficial to emergency management operations. Wildland fires are a source of concern to emergency management organizations and, as a natural occurrence, will continue to be concern in the future. As the world's population continues to grow, and people continue to spread into more rural environments, wildland fires are an increasing risk to life and infrastructure. For many locations, these risks can be managed with prevention programs and risk mitigation strategies. Such methods of prevention and mitigation include pre-existing fire lines and management of flammable materials near infrastructure. However, in many locations the primary form of risk reduction is a proper response to fires. As fire size tends to grows in an exponential manner with time, a quick response is essential to combating disaster. Rapid action requires significant surveillance to support situational awareness. Technology that can provide this situational awareness would be a significant advancement over current manned aerial platforms. The Surveillance for Intelligent Emergency Response Robotic Aircraft (SIERRA) Project is aimed at partnering government, manufacturing, emergency response, and academic expertise to develop unmanned aerial systems for use in emergency management environments. The SIERRA Project focuses on three areas of this development: Potential application of this technology with current fire tactics at the operational level, current technology capabilities and systems engineering requirements for this type of system, and analysis of flight data of the Zephyr (a tactical UAS platform weighing less than 10 pounds). After this research is completed, it will allow for the introduction of research into the concept of a wildland fire agency air force. This allows wildland fire forces to have full fleet capability, which will revolutionize wildland fire response and the recommended requirements for the next generation of tactical UAS platforms.
Advisors/Committee Members: Cohen, Kelly.
Subjects: Aerospace Materials
Keywords: SIERRA; UAS; Systems Engineering; Unmanned Aerial System; Drone; UAV
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5.
Clark, Adam W.
Characterization of Fluidic Instabilities in Vortex-Dominated Flows Using Time-Accurate Open Source CFD.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2012, University of Cincinnati
► The CFD software market of today has become saturated with two very…
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▼ The CFD software market of today has become saturated with two very different approaches; single purpose software codes written to model a specific type of flow, or jack-of-all-trades 'universal' commercial packages. Academics often argue that the commercial packages offer too little control over the details of the simulations, and companies frequently rail against the excessive cost and time commitments to develop their own specific-built CFD codes. The present study attempts to bridge this gap by examining the capabilities of OpenFOAM, an open source numerical solver, in a highly turbulent, vortex-dominated flow. The highly complex flowfield in the region immediately downstream of the backward facing step has provided a benchmark for numerical simulations since turbulence modeling began. A range of turbulence models within OpenFOAM are considered and compared against experimental data and literature. Two-equation models resulted in steady flow, albeit with reasonable average flowfield properties. The more advanced Reynolds Stress Transport Model resulted in an unsteady simulation with free shear layer properties in general agreement with both experimental and published data. This behavior mirrors other publications and codes, where it has been hypothesized that numerical perturbations caused by the discretization scheme excite the primary mode of instability of the free shear layer for the Reynolds Stress Models, but the overly dissipative nature of the two-equation models is sufficiently high to damp these stochastic fluctuations. With attention to the proper settings and turbulence model, OpenFOAM appears to perform relatively well in this complex and unsteady flowfield. The extreme level of control afforded by OpenFOAM would appear to meet the needs of academics and researchers while also satisfying corporate clients searching for a readily available package exhibiting a wide range of off-the-shelf capabilities.
Advisors/Committee Members: Abdallah, Shaaban.
Subjects: Aerospace Materials
Keywords: OpenFOAM; open source; CFD; backstep; backward facing step; turbulence modeling
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6.
Cornwell, Michael.
Causes of Combustion Instabilities with Passive and Active Methods of Control for practical application to Gas Turbine Engines.
Degree: PhD, Engineering and Applied Science: Aerospace Engineering, 2011, University of Cincinnati
► Combustion at high pressure in applications such as rocket engines and gas…
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▼ Combustion at high pressure in applications such as rocket engines and gas turbine engines commonly experience destructive combustion instabilities. These instabilities results from interactions between combustion heat release, fluid mechanics and acoustics. This research explores the significant affect of unstable fluid mechanics processes in augmenting unstable periodic combustion heat release. The frequency of the unstable heat release may shift to match one of the combustors natural acoustic frequencies which then can result in significant energy exchange from chemical to acoustic energy resulting in thermoacoustic instability. The mechanisms of the fluid mechanics in coupling combustion to acoustics are very broad with many varying mechanisms explained in detail in the first chapter. Significant effort is made in understanding these mechanisms in this research in order to find commonalities, useful for mitigating multiple instability mechanisms. The complexity of combustion instabilities makes mitigation of combustion instabilities very difficult as few mitigation methods have historically proven to be very effective for broad ranges of combustion instabilities. This research identifies turbulence intensity near the forward stagnation point and movement of the forward stagnation point as a common link in what would otherwise appear to be very different instabilities. The most common method of stabilization of both premixed and diffusion flame combustion is through the introduction of swirl. Reverse flow along the centerline is introduced to transport heat and chemically active combustion products back upstream to sustain combustion. This research develops methods to suppress the movement of the forward stagnation point without suppressing the development of the vortex breakdown process which is critical to the transport of heat and reactive species necessary for flame stabilization. These methods are useful in suppressing the local turbulence at the forward stagnation point, limiting dissipation of heat and reactive species significantly improving stability. Combustion hardware is developed and tested to demonstrate the stability principles developed as part of this research. In order to more completely understand combustion instability a very unique method of combustion was researched where there are no discrete points of combustion initiation such as the forward stagnation point typical in many combustion systems including swirl and jet wake stabilized combustion. This class of combustion which has empirical evidence of great stability and efficient combustion with low CO, NOx and UHC emissions is described as high oxidization temperature distributed combustion. This mechanism of combustion is shown to be stable largely because there are no stagnations points susceptible to fluid mechanic perturbations. The final topic of research is active combustion control by fuel modulation. This may be the only practical method of controlling most instabilities with a single technique. As there are many papers reporting active combustion control algorithms this research focused on the complexities of the physics of fuel modulation at frequencies up to 1000 Hz with proportionally controlled flow amplitude. This research into the physics of high speed fluid movement, oscillation mechanical mechanisms and electromagnetics are demonstrated by development and testing of a High Speed Latching Oscillator Valve.
Advisors/Committee Members: Gutmark, Ephraim.
Subjects: Aerospace Materials
Keywords: Combustion Instability; Thermoacoustic Instability; Active Combustion Control; Flameless Combustion; Swirl Stabilized Combustion; Vortex Breakdown
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7.
Ernest, Nicholas D.
UAV Swarm Cooperative Control Based on a Genetic-Fuzzy Approach.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2012, University of Cincinnati
► The ever-increasing applications of UAV’s have shown the great capabilities of these…
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▼ The ever-increasing applications of UAV’s have shown the great capabilities of these technologies. However, for many cases where one UAV is a powerful tool, an autonomous swarm all working cooperatively to the same goal presents amazing potential. Environment that are dangerous for humans, are either too small or too large for safe or reasonable exploration, and even those tasks that are simply boring or unpleasant are excellent areas for UAV swarm applications. In order to work cooperatively, the swarm must allocate tasks and have adequate path planning capability. This paper presents a methodology for two-dimensional target allocation and path planning of a UAV swarm using a hybridization of control techniques. Genetic algorithms, fuzzy logic, and to an extent, dynamic programming are utilized in this research to develop a code known as “UNCLE SCROOGE” (UNburdening through CLustering Effectively and Self-CROssover GEnetic algorithm). While initially examining the Traveling Salesman Problem, where an agent must visit each waypoint in a set once and then return home in the most efficient path, the work’s end goal was a variant on this problem that more closely resembled the issues a UAV swarm would encounter. As an extension to Dr. Obenmeyer’s “Polygon-Visiting Dubins Traveling Salesman Problem”, the Multi-Depot Polygon-Visiting Dubins Multiple Traveling Salesman Problem consists of a set number of visibility areas, or polygons that a number of UAV’s, based in different or similar depot must visit. While this case is constant altitude and constant velocity, minimum turning radii are considered through the use of Dubins curves. UNCLE SCROOGE was found to be adaptable to the PVDTSP, where it competed well against the methods proposed by Obenmeyer. Due to limited benchmarking ability, as these are newly formed problems, Obenmeyer’s work served as the only basis for comparison for the PVDTSP. UNCLE SCROOGE brought a 9.8% increase in accuracy, and a run-time reduction of more than a factor of ten for a 20 polygonal case with strict turning requirements. This increase in performance came with a 99% certainty of receiving the best found solution over the course of 100 runs. With only a 1% chance for error in this particular case, the hybridized method has been shown to be quite powerful. While no comparison is currently possible for MDPVDMTSP solutions, UNCLE SCROOGE was found to develop promising results. On average, it takes the code 25.62 seconds to approximately solve a 200 polygon, 4 depot, 5 UAV’s per depot problem. This polygon count was increased even up to 2,500, with a solution taking 9.8 hours. It has been shown that UNCLE SCROOGE performs well in solving the MDPVDMTSP and has acceptable scalability.
Advisors/Committee Members: Cohen, Kelly.
Subjects: Aerospace Materials
Keywords: UAV Swarm; Cooperative Control; Genetic Algorithm; Fuzzy Logic; Traveling Salesman Problem
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8.
Galbraith, Daniel S.
Computational Fluid Dynamics Investigation into Shock Boundary Layer Interactions in the “Glass Inlet” Wind Tunnel.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2011, University of Cincinnati
► Mixed compression inlets offer a potential increase in pressure recovery compared to…
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▼ Mixed compression inlets offer a potential increase in pressure recovery compared to conventional external compression inlets at Mach numbers above two. However, these inlets suffer from problems with shock boundary layer interactions which cause flow instabilities and severe performance reductions. Previous experiments conducted at the University of Michigan used a wind tunnel with glass side walls and an extensive test section to measure the shock boundary layer interaction associated with a single oblique shock. This work presents an investigation of possible improvements to the current single shock experiment. A 10° oblique shock generator was designed by researchers at the University of Michigan and simulated at the University of Cincinnati. The 10° design did not start in the actual wind tunnel, but was successfully simulated by bypassing the transients from quiescent flow with the help of an initial solution generated from one dimensional inviscid nozzle theory. The residuals from the simulation leveled off at higher levels than expected in some mesh blocks, which indicates unsteadiness. The same case was then simulated in a time accurate manner, and showed very small variations in the solution over time. The magnitude of these variations were large enough to prevent the residuals in the steady simulation from dropping, but small enough that an averaged solution could be used for analysis. A grid dependency study was conducted and found that the 24 million node grid is very close to being grid independent. A new design was desired that would allow the actual tunnel to start, and this resulted in a 6° oblique shock generator. This geometry allows the tunnel to start, and produces a more benign shock boundary layer interaction than the 10° oblique shock generator. A follow up experiment has been designed where the oblique shock is followed by a normal shock and a subsonic diffuser. This new configuration will provide insights into the effects that combined oblique and normal shock boundary layer interactions have on the health of the boundary layer in the diffuser section of a mixed compression inlet. The extensive glass walls of the wind tunnel will allow direct access for optical measurements of the shock boundary layer interactions and the diffuser section. Corner separations in a tunnel affect the flow in the center of the tunnel. The oblique shock causes the low momentum flow in the tunnel corners to separate. This in turn creates shocks at the separation bubble leading edge that propagates into the flow-field. Depending on the size of the tunnel and the Reynolds number, these shocks can meet at the tunnel centerline and cause a pressure rise. This pressure rise can help to keep the boundary layer attached by smearing the pressure gradient, or intensify separations by adding an additional region of adverse pressure gradients, depending on where the corner shocks interact relative to the main shock boundary layer interaction.
Advisors/Committee Members: Turner, Mark.
Subjects: Aerospace Materials
Keywords: shock; shockwave; boundary; layer; interaction
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9.
Grage, Danielle L.
Study of jet exhaust noise sources and their mitigation through lobed mixers and chevrons.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2011, University of Cincinnati
► As regulations to reduce noise pollution become more stringent, understanding the noise…
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▼ As regulations to reduce noise pollution become more stringent, understanding the noise sources within jet exhaust and how they can be mitigated is important as jet noise is one of the dominant contributors to the overall acoustic signature of an engine. The objective of this study is to understand the effects two exhaust mixing devises, lobed mixers and chevrons. To this end, three basic configurations were studied: a confluent mixer and nozzle (Confluent), a buried lobed mixer with a circular nozzle (MixerA), and a buried lobed mixer with a chevron nozzle (Chevron+MixerB). The hardware was tested at GE Aviation’s Cell-41 – Anechoic free jet facility. Acoustic data was acquired, as well as flowfield data using Particle Image Velocimetry (PIV). RANS-based (Reynolds Averaged Navier-Stokes) Computational Fluid Dynamics (CFD) analyses were also conducted to complement the test data. Three operating conditions were considered, defined by their shear level, which is a function of the average mixed velocity of the core flow: low shear (80%), nominal shear (100%), and high shear (112%). The results from the PIV and CFD were used for mutual validation and very good correlation was observed for the MixerA configuration with good correlation overall. The acoustic results were consistent with the flowfield analysis, as well as previous studies, and showed that the presence of mixing devices can provide a low frequency acoustic benefit with some modest increase in high frequency noise, due to increasing mixing near the nozzle and reduced turbulence downstream. An additional high frequency noise source was also identified for MixerA at the high shear condition, which was not present for other configurations. This source showed similar features to the High Mach Lift (HML) previously reported by Tester et al and Garrison et al in 2005. It is thought to be the result of shear layer interaction with a normal shock, resulting from localized pockets of supersonic flow that form near the nozzle exit plane. This source was absent for the Chevron+MixerB configuration and more work must be done to better understand the phenomenon.
Advisors/Committee Members: Gutmark, Ephraim.
Subjects: Aerospace Materials
Keywords: jet exhaust; lobed mixer; acoustic; chevron; PIV; CFD
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10.
Guillou, Erwann.
Flow Characterization and Dynamic Analysis of a Radial Compressor with Passive Method of Surge Control.
Degree: PhD, Engineering and Applied Science: Aerospace Engineering, 2011, University of Cincinnati
► Due to recent emission regulations, the use of turbochargers for force induction…
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▼ Due to recent emission regulations, the use of turbochargers for force induction of internal combustion engines has increased. Actually, the trend in diesel engines is to downsize the engine by use of turbochargers that operate at higher pressure ratio. Unfortunately, increasing the rotational speed tends to reduce the turbocharger radial compressor range of operation which is limited at low mass flow rate by the occurrence of surge. In order to extent the operability of turbochargers, compressor housings can be equipped with a passive surge control device also known as ported shroud. This specific casing treatment has been demonstrated to enhance surge margin with minor negative impact on the compressor efficiency. However, the actual working mechanisms of the bypass system remain not well understood. In order to optimize the design of the ported shroud, it is then crucial to identify the dynamic flow changes induced by the implementation of the device to control instabilities. Experimental methods were used to assess the development of instabilities from stable, stall and eventually surge regimes of a ported shroud centrifugal compressor. Systematic comparison was conducted with the same compressor design without ported shroud. Hence, the full pressure dynamic survey of both compressors’ performance characteristics converged toward two different and probably interrelated driving mechanisms to the development and/or propagation of unsteadiness within each compressor. One related the pressure disturbances at the compressor inlet, and notably the more apparent development of perturbations in the non-ported compressor impeller, whereas the other was attributed to the pressure distortions induced by the presence of the tongue in the asymmetric design of the compressor volute. Specific points of operation were selected to carry out planar flow measurements. At normal working, both standard and stereoscopic particle imaging velocimetry (PIV) measurements were performed to calculate the instantaneous and mean velocity fields at the inlet of the compressor. At incipient and full surge, phase-locked PIV measurements were added. In this work, satisfying characterization of the compressor inlet flow instabilities was obtained at different operational speeds. Combining transient pressure data and PIV measurements, the time evolution of the complex flow patterns occurring at surge was reconstructed and a better insight into the bypass mechanisms was achieved.
Advisors/Committee Members: Gutmark, Ephraim.
Subjects: Aerospace Materials
Keywords: Radial Compressor; Surge; Passive Control; Ported Shroud; Particle Image Velocimetry; PIV
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11.
Hanlon, Nicholas P.
Neuro-Fuzzy Dynamic Programming for Decision-Making and Resource Allocation during Wildland Fires.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2011, University of Cincinnati
► Fire is a natural agent of change for our planet’s survival and…
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▼ Fire is a natural agent of change for our planet’s survival and has the capability to cause devastating effects (economical, societal, environmental, etc) when it encroaches into our daily lives. In the midst of a wildland fire, incident commanders are bombarded with massive amounts of data, accurate or not, and must make real-time decisions on how to allocate available resources to extinguish the fire with minimal damage. The scenario is modeled as an attacker-defender style game, such that the defender (resources with fire retardants) is protecting its assets (homes, businesses, power plants, etc) while the attacker (wildland fires) is attempting to deliver maximum destruction to those assets. The problem can be formulated in terms of optimal control theory, utilizing the gold standard of optimization, Dynamic Programming (DP), to exhaustively search the solution space for the minimized cost. However, its drawback is directly related to its method of finding the optimal solution: the exhaustive search. The amount of processing time to compute the minimum cost exponentially increases with the complexity of the system. For this reason, the DP approach is generally executed offline for real-world applications. Due to the large solution space of a wildland fire scenario, execution of DP offline is problematic as resource allocation decisions must be made in real-time. The current research effort seeks to show a new and unique control algorithm, based on Neuro-Fuzzy Dynamic Programming (NFDP), that can nearly replicate the DP algorithm results but can execute in real-time and remain robust to uncertainties. An artificial neural network provides the approximate cost-to-go function for the DP, fulfilling the need for real-time execution. The neural network is trained by approximate policy iteration using Monte Carlo simulations. Since our sensors may provide inaccurate or incomplete data of the environment, a fuzzy logic component is integrated to provide robustness in the system. The problem is also extended to include multiple layers of defense as opposed to a one layer attempt to eliminate the incoming threat. The multi-layered defense requires a unique approach in the NFDP algorithm that calculates future expected costs since a fire must successfully elude three layers of defense to constitute an attack on an asset. Four control methodologies are examined in the research: a greedy-based heuristic, DP, NDP (Neuro-Dynamic Programming), and NFDP. DP and the heuristic are used as benchmark cases; the premise of the heuristic approach is to protect the highest valued assets at all costs. The control methodologies are compared based on three parameters: processing time, remaining asset health, and scalability. The processing time quantifies the requirement of real-time decisions. The asset health is a measure of how well the defender protected its assets from the attacker. Scalability is how well the algorithm scales with increased complexity. With proper adjustments to the architecture and training techniques of the artificial neural network and fine-tuning of the fuzzy controller parameters, NFDP illustrates its ability to perform real-time decision-making, obtaining near optimal results in the presence of uncertainty in the sensor data, and scales well with increased complexity.
Advisors/Committee Members: Cohen, Kelly.
Subjects: Aerospace Materials
Keywords: Resource Allocation; Decision Making; Optimal Control; Artifical Intelligence; Fuzzy Logic
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12.
Ichihashi, Fumitaka.
Investigation of Combustion Instability in a Single Annular Combustor.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2011, University of Cincinnati
► The well known criterion for combustion instability is called the Rayleigh’s criterion.…
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▼ The well known criterion for combustion instability is called the Rayleigh’s criterion. It indicates that, for combustion instability to occur, the heat release rate (q’) and pressure oscillation (p’) must be in phase. This thesis describes measurement techniques and study methods for combustion instabilities that occurred in the prototype single annular sector Rich-Burn Quick-Mix Lean-Burn (RQL) combustor on the original (short) and new (long) experimental rig configuration with a focus on q’ and p’ measurements. A change in the configuration of the combustor rig was necessary in order to acquire more precise measurements of forward- and backward-moving acoustic pressure waves within the rig by mounting pressure transducers on preselected locations of the upstream duct, downstream duct and combustion area. Pressure transducers provided such local pressure behaviors as amplitude and frequency per location, also in addition to transfer functions that allow for the calculation of the acoustic impedance at any location within the combustor rig. A high-speed camera was capable of filming a chemiluminescene image, i.e., the rate of heat release through a quartz window that is mounted on the side of the combustor. Two imaging analysis techniques, Proper Orthogonal Decomposition and Fourier Transformation, were applied to the chemiluminescene image obtained by a high-speed video device. Two different test cases were investigated. Both a high and low fuel-to-air ratio were used for the investigation of the Rayleigh’s criterion, which was confirmed by the corresponding q’ and p’ data sets. Finally, the resonance frequency that agrees with combustion instability was well predicted by utilizing the one-dimensional wave propagation theory and the known geometry of the combustor rig, temperature of fluid, and boundary conditions.
Advisors/Committee Members: Jeng, San-Mou.
Subjects: Aerospace Materials
Keywords: Combustion Instability; POD; RQL; Proper Orthogonal Decomposition; Combustion Acoustic; Rayleigh's Criterion
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13.
Kivelevitch, Elad H.
Robust, Real Time, and Scalable Multi-Agent Task Allocation.
Degree: PhD, Engineering and Applied Science: Aerospace Engineering, 2012, University of Cincinnati
► Assigning a group of mobile agents to perform certain tasks defined by…
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▼ Assigning a group of mobile agents to perform certain tasks defined by their locations and priorities is a major research problem in optimization in general and particularly in multi-robot systems. This problem can be formulated as variants of the well-known Multiple-Depots, Multiple Traveling Salesmen Problem (MDMTSP), in which the agents start their travel from an initial location (a depot), and the goal is to obtain a solution that either minimizes the total of all tour lengths (the classical case), minimizes the length of the longest tour (the min-max case), or maximizes a profit of performing tasks taking into account the cost of travel to these tasks (the profitable case). It should be noted that while these problems are variants of the same problem, they are usually solved by specialized algorithms tailored for each specific variant. In this work, agents interact in a virtual economic market that can be used to solve all three variants of the problem with minor changes to the algorithm. The motivation behind using a market-based approach is mostly because of the ability of economic markets to get good results, in a short span of time, for large-scale problems, and in complex and dynamic situations. The market-based solution developed in this work demonstrates near-optimal results for all three variants, compared to state-of-the-art algorithms, each tailored for a specific variant. Moreover, the ability to obtain near-optimal results in the face of changes is demonstrated in scenarios that include the appearance and disappearance of tasks and the addition and removal of agents. The approach is further enhanced by introducing hierarchies into the market, where tasks are geographically clustered to expedite the search in large problems. Finally, the market-based approach is also enhanced using fuzzy logic to reduce the sensitivity of the cost of travel to tasks, whose location is uncertain. This work makes several new contributions to the field. First, while market-based solutions to the MTSP have been proposed in the past, this approach is the first one to include hierarchical markets and presents better and faster results with fewer constraints than previous approaches. Second, this is the first algorithm that is both as near-optimal as algorithms tailored for each specific MTSP variant and that can handle all three variants of the MDMTSP like other meta-heuristic algorithms. In particular, this solution obtains results that are very close, in terms of optimality, to the results obtained by linear programming for the classical case and the MTSP with constant profits case, but at a significantly reduced calculation time. For the min-max case, the current solution improves over the best known solution in terms of cost, by as much as 75%, albeit at a longer runtime. Finally, this solution is scalable to large problem instances and can be used as an online algorithm that handles changes in the scenario during runtime. As a whole, this novel approach is everything required from an algorithm for assigning mobile agents to tasks: near-optimal, versatile, robust to scenario changes, and fast.
Advisors/Committee Members: Cohen, Kelly.
Subjects: Aerospace Materials
Keywords: Traveling Salesmen Problem; Market-based optimization; Multi-agent systems
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14.
Knapke, Robert D.
Unsteady Analysis of a Counter-Rotating Aspirated Compressor Using Phase-Lag and Non-Linear Harmonic Methods.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2011, University of Cincinnati
► An analysis of the MIT counter-rotating aspirated compressor (CRAC) has been conducted…
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▼ An analysis of the MIT counter-rotating aspirated compressor (CRAC) has been conducted using two different 3D viscid turbulent unsteady solvers. The Turbo phase-lag time accurate and the Numeca FineTurbo Non-Linear Harmonic (NLH) methods were utilized to gain an understanding of the flow field. Grid dependency studies and comparisons with experimental data were conducted where appropriate. Speedline simulations were conducted to better understand the off-design performance of this compressor stage. Both simulation methods show good agreement with the experimental data. The best agreement is found between the FineTurbo simulation when using iso-thermal boundary conditions. Comparisons of simulations with and without aspiration illustrate the importance of aspiration on the stage performance. Unsteady analysis of the flow field is presented to show the details of the blade row interactions. A detailed analysis of the aspiration slot and plenum was also performed.
Advisors/Committee Members: Turner, Mark.
Subjects: Aerospace Materials
Keywords: counter-rotation; aspiration; compressor; CFD; suction; unsteady
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15.
Korte, Christopher M.
A Comparison of Two-Dimensional Pose Estimation Algorithms Based on Natural Features.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2011, University of Cincinnati
► Pose-estimation is a vital part of any semi-autonomous or autonomous system. Pose-estimation…
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▼ Pose-estimation is a vital part of any semi-autonomous or autonomous system. Pose-estimation allows the system to determine the position and orientation of specific objects located in three-dimensional space. This information then can be used for obstacle avoidance or for rendezvous and docking. The primary motivation for this research is to address one of the key program risks for the NASA Crew Exploration Vehicle (CEV) program, more specifically, the low technology readiness levels of relative navigation sensors. The two dimensional pose estimation algorithms usually use a single calibrated camera and a model in order to generate the pose estimate. This thesis will explore two of those algorithms: the POSIT algorithm and the Pose from an Ellipse algorithm. The POSIT algorithm found the pose of a simulated spacecraft target within three degrees of rotational accuracy and four percent of the total distance to the target, which is comparable to sensors developed specifically for relative navigation. The Pose from an Ellipse algorithm was accurate within eight degrees of rotational accuracy with a few outliers and was good within four and a half percent of the total target distance.
Advisors/Committee Members: Walker, Bruce.
Subjects: Aerospace Materials
Keywords: Pose-Estimation; Image Processing; Model Matching
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16.
Lakhamraju, Raghava Raju.
Characterization of the jet emanating from a self-exciting flexible membrane nozzle.
Degree: PhD, Engineering and Applied Science: Aerospace Engineering, 2012, University of Cincinnati
► The present research investigates the development and characterization of a novel self-exciting…
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▼ The present research investigates the development and characterization of a novel self-exciting flexible membrane nozzle. Upon excitation (oscillations that are produced by exerting tension at the nozzle exit and passing air through it), the flexible nozzle is capable of producing time-dependent flow that is fairly consistent at a flow condition (a particular tension and volume flow rate of air). The fluidic device is a passive means of enhancing mixing as there is no external excitation mechanism. The resultant flow is self-excited over a range of conditions and produces pulsatile flow that is excited by the motion of the flexible membrane. The baseline configuration of the flexible membrane nozzle involves symmetrical placement of the edges at the nozzle exit. The exit of the nozzle offers variable area geometry, with the shape approximately resembling a variable aspect ratio ellipse. Particle Image Velocimetry (PIV) is employed to illustrate and characterize the large-scale flow structures of the jet motion and the eduction of coherent structures was performed using Proper Orthogonal Decomposition (POD). For a particular nozzle diameter, the flow conditions are controlled by the tension applied to the flexible nozzle and volume flowrate of air through it. PIV measurements have been conducted mainly along the mid-minor axis plane since the crucial flow structure interactions occur in this plane due to the nozzle operation. Based on a set of experiments conducted within the physical limitations of the nozzle, the near field of the nozzle exit was found to be governed by the interactions of two sets of large-scale vortical structures - starting vortices and entrainment vortices (features of pulsatile flows) and the exact nature of their evolution is dependent on the operating conditions. As in elliptic jets, the near field of the nozzle is found to be extremely sensitive to the initial conditions (nozzle configuration). A cross-spectral analysis is also performed in the near field of the jet using two hot-wire anemometers to characterize the evolution of large-scale flow structures for the various flow conditions. For a baseline nozzle in fully closed configuration, for a given tension at the nozzle exit, increase in volume flow tends to produce higher jet spread (more prominent at lower tensions) and increased range of turbulence production. For a particular flow rate, increase in tension results in a more symmetric jet along the centerline and high turbulence production in the near field. Under certain flow conditions, the dynamic flapping of the jet generated half-width spreading rates that exceeded that of slot nozzles. The flow characteristics are compared to that of existing nozzles that generate high mixing rates at the exit. The application of POD on the PIV information shows that the reconstructed images from few modes provide decent illustrations of the flow structures with filtered effect on the turbulent flow field. In essence, this analysis separates the oscillation of the jet from the velocity fluctuations due to the turbulent flow behavior. In the current study, with certain operating conditions, increased half-width spreading rates and enhanced centerline velocity decay can be generated. A predominant flapping jet or highly turbulent jet at the nozzle exit can be achieved by modifying the flow conditions.
Advisors/Committee Members: Gutmark, Ephraim.
Subjects: Aerospace Materials
Keywords: flow control; flexible nozzle; self-excitation; pulsatile jet; noncircular jet; starting and entrainment vortices
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17.
Li, Zhisong.
Advanced Computational Modeling for Marine Tidal Turbine Farm.
Degree: PhD, Engineering and Applied Science: Aerospace Engineering, 2012, University of Cincinnati
► In the global effort of exploring low-cost renewable energy and reducing greenhouse…
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▼ In the global effort of exploring low-cost renewable energy and reducing greenhouse gas emissions, energy sources in the ocean are receiving more and more attentions. The kinetic energy from ocean currents is enormous and virtually inexhaustible. Among the different kinds of ocean currents, the tidal flow is most predictable and sufficiently rapid for power generation to many well-chosen sites. To convert the stream momentum into electrical power, a device called marine tidal turbine, predominantly horizontal-axis, is used. Working like a windmill underwater, the tidal turbine operates in a unique environment constrained by water-free surfaces and seabeds. The present study will concentrate on the numerical modeling of tidal turbine operations in standalone and array configurations. Dedicated computational fluid dynamics (CFD) models are first created for this particular research application. Based on the solutions obtained from simulations, comparative investigations are then taken to assess the wake characteristics in a turbine farm scenario in order to minimize any unfavorable wake/turbine interactions. The effects of free surface waves and uneven bed terrains are also studied. To establish the simulations, one steady and one time-transient code are developed using modular programming and parallel processing design. The core solver uses a classic projection method to solve the three-dimensional incompressible flow problem and an efficient s-coordinate method to model the free surface, both of which are well verified with analytical solutions. An actuator disc model and an actuator line model are numerically implemented for the steady and unsteady codes respectively, validated by experimental data. To include the natural water waves and ambient turbulence unsteadiness, the inflow boundary condition in time-transient code incorporates a fifth-order Stokes wave generator and artificial velocity fluctuations. Foreseeing the rotational movements and anisotropic turbulence from turbine spinning, a second-moment closure or nonlinear eddy viscosity assumption is needed for turbulence modeling. The project adopts an explicit algebraic Reynolds stress model, balancing the demand for solution accuracy and computational economy. Extensive tests and case running have been performed using the simulation codes with parametric modifications for different evaluation purposes. In scalability tests, both codes can give acceptable speedup up to 30 nodes and the steady state code achieves better performance due to its highly explicit formulations. The steady and unsteady codes are compared as baselines cases and they agree well in predicting wake velocity deficits. In steady state modeling of a single turbine, the study appraises the influence on turbine wake from rotor size, inflow profiles, and three different simple bed terrains. In unsteady modeling, turbine wake under long waves exhibits some velocity superposition behavior. Turbine array simulations first probe the steady state flow features in a number of rotor configurations: side-by-side, transverse, streamwise, co-rotating, and contra-rotating. They are examined for their wake restoration rates and turbulence intensities. Then the time-averaged wake activities in the staggering and tilted line layout are inspected and compared to settle a fluid dynamic preference. Finally an unsteady modeling is carried out for a pair of upstream-downstream and contra-rotating rotors, enabling a dynamic analysis on the turbine interactions.
Advisors/Committee Members: Ghia, Kirti.
Subjects: Energy
Keywords: Computational Fluid Dynamics; Marine Tidal Turbine Farm; Actuator Disc; Actuator Line; Free Surface Wave; Parallel Computation
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18.
Madhi, Elhoucine.
In-Situ Creep Monitoring Using Directional Potential Drop Sensors.
Degree: PhD, Engineering and Applied Science: Aerospace Engineering, 2010, University of Cincinnati
► Recent research effort indicates that potential drop (PD) methods can be exploited…
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▼ Recent research effort indicates that potential drop (PD) methods can be exploited for nondestructive evaluation (NDE) of creep degradation in low-alloy steels especially during early stages of creep which remains a big challenge for most other NDE methods. For this purpose, a highly directional low-frequency Alternating Current Potential Drop (ACPD) sensor was developed for in-situ monitoring of creep in metals. The sensor relies on a modified ACPD technique that measures both values of resistance in the axial and lateral directions using a square-electrode configuration. The technique essentially monitors the variation in the ratio of the measured axial and lateral resistances, therefore can efficiently separate the mostly isotropic common part of the resistivity variation caused by reversible temperature variations from the mostly anisotropic differential part caused by direct geometrical (size and shape) and indirect material (resistivity) effects of creep. As compared to the more commonly used in-line electrode configuration, the square arrangement used in this sensor has a much higher geometrical sensitivity and is much more directional and thus allows higher sensitivity to detect creep-induced anisotropy and texture. Similarly to ordinary strain gauges, the relative sensitivity of the sensor is defined as a gauge factor that can be approximated as a sum of geometrical and material parts. Initially, subtle material changes produce weak electric anisotropy via reversible and irreversible piezoresistivity due to elastic and plastic strains, respectively. So for an important part of creep life, the sensor is more sensitive to geometrical variations than material effects and acts as a strain gauge with a geometrical gauge factor as high as 4 to 5. At high temperature, much stronger irreversible resistivity changes also occur with time due to preferentially aligned clusters of cavities developing along grain boundaries approximately perpendicular to the applied stress and subsequent cracks forming between these cavities. The ensuing electric anisotropy is detected by the directional sensor. Results from a 2D Finite element analysis indicate however that the resulting anisotropy only starts to have a significant effect on the resistance ratio when the size of the creep-induced microcracks is comparable to the electrode separation (4 mm in this case), i.e., at later stages of creep degradation. A few thermo-mechanical creep tests were undertaken on stainless steel 304 and on 25% Cr - 1% Mo low-alloy steel typically used in the power plant industry. Despite the short time-span of most of these tests, the results show that the sensor is capable of monitoring material degradation from its onset in the elastic regime to ultimate rupture. These tests also show that, although the sensitivity to material effects remain smaller than to the geometrical ones up to the initiation of preferentially oriented microcracks, later the material gauge factor sharply increases and close to rupture can reach a value of more than 10.
Advisors/Committee Members: Nagy, Peter.
Subjects: Mechanical engineering
Keywords: creep monitoring; directional sensor; potential drop; ACPD; material gauge factor; geometrical gauge factor
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19.
Meckstroth, Christopher.
Receding Horizon Robot Control for Autonomous Spacecraft Capture.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2010, University of Cincinnati
► A large portion of desired future space missions require spacecraft having the…
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▼ A large portion of desired future space missions require spacecraft having the ability to autonomously rendezvous and grapple one another. This thesis investigates the second portion of this task, namely the real-time path planning of a 7 degree of freedom robotic arm for the purpose of autonomously grappling satellites using a method based on Receding Horizon Control (RHC). RHC was chosen for the algorithm’s ability to perform in real-time by calculating the path over a future time interval while traversing the previously calculated path. A successful grapple requires the dexterous arm to maneuver an end effector into the cylindrical hole provided by one of the four fixtures used to attach the satellite to the launch vehicle which placed it into orbit. This must be accomplished while maintaining constraints and limitations imposed by the robot arm kinematics and joint limitations and at the same time avoiding interference with other portions of the satellite such as the thruster nozzle. A 3-D Visualization Software Toolkit was developed for the simulation and validation of the path planner developed in this thesis. Using this software, a fully simulated experiment was developed in which the robot arm attempted to grapple each of the attachment fixtures from a total of 8,000 different random initial arm poses. The results showed goals were achieved in both planning of the path in real-time with average calculation times of the entire path less than 20 seconds and success in grappling the target satellite with without ever failing when grappling the nearest attachment fixture to the robot end effector for joint angles separately varying uniformly by ±30 degrees from nominal positions.
Advisors/Committee Members: Cohen, Kelly.
Subjects: Aerospace materials
Keywords: Receding Horizon; Path Planner; Autonomous; Robotic
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20.
Mignee, Juliette L.
Proper Orthogonal Decomposition Applied to a Supersonic Single Flow Jet.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2012, University of Cincinnati
► Proper Orthogonal Decomposition (POD) is used in order to better understand the…
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▼ Proper Orthogonal Decomposition (POD) is used in order to better understand the coherent structure of a non-ideally expanded supersonic single flow jet. The method has been performed using numerical results obtained from Large Eddy Simulation (LES) obtained by Junhui Liu and Dr. K. Kailasanath from Naval Research Laboratory and from Particle Image Velocimetry (PIV) performed by Nick Heeb and Dr. D. Munday from the Propulsion and Gas Dynamics Laboratory at the University of Cincinnati. Experimental techniques, such as Particle Image Velocimetry (PIV) are available to visualize the structure of supersonic flow. The flow domain which can be observed by these experimental techniques is a plane embedded in the entire flow. The LES flow domain is a 3D domain. A numerical grid is created to match the PIV domain size. Comparison between PIV and LES showed that the flow domain size acts as a spatial filter. The largest scale structure that can be observed is limited by the domain size, which is dictated by the PIV technologies features, such as laser energy, Charge-Coupled Device (CCD) camera resolution. The numerical results for their part are very sensitive to the grid employed. Proper Orthogonal Decomposition was performed on two different grids for the baseline nozzle. It is seen that the grid size is a very sensitive parameter when educing the coherent structure of a supersonic non-ideally expanded jet. It acts as a spatial filter of turbulent scales. iii The POD analysis is used to compare baseline and chevrons nozzles flows and how chevrons impact the baseline coherent structure. It is observed that the chevrons increase the Turbulent Kinetic Energy near the nozzle exit and reduce it downstream. By studying the POD modes, energy, and Modal Amplifications Coefficients, it can be concluded that the chevrons break down large stream wise oriented energy containing structures near the nozzle exit and transfer this energy to smaller radial oriented structures and therefore decrease the energy further downstream.
Advisors/Committee Members: Gutmark, Ephraim.
Subjects: Aerospace Materials
Keywords: Supersonic; Jet; Decomposition; Turbulence; Structure; Flow
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21.
Miller, Adam.
Mitigation of Occupant Acceleration in a Mine-Resistant Ambush-Protected Vehicle Blast Event Using an Optimized Dual-Hull Approach.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2012, University of Cincinnati
► With casualties mounting overseas due to Improvised Explosive Devices (IEDs) and other…
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▼ With casualties mounting overseas due to Improvised Explosive Devices (IEDs) and other roadside bombs, improving the safety of armored vehicles for service personnel overseas is of paramount importance. Accurate numerical simulations of the blast event provide a means to quickly and economically evaluate the blast-protection performance of armored vehicles, and to develop improved blast countermeasures. The goal of the work described in this thesis is to provide a system that can mitigate blast accelerations to a level where the acceleration is no longer a lethal threat to the occupants of an armored vehicle. The hypothesis is that through the manipulation of the mass ratio, stiffness and damping properties of a dual-hull system, the safety of current Mine Resistant Ambush Protected (MRAP) vehicles can be greatly improved. The results show that, in comparison to the standard single-hull vehicle, the dual-hull vehicle reduces head injury criteria by 95.7%, neck compression by 78.3%, chest acceleration by 97.5% and leg forces by an average of 97%. Further work should focus on developing a realistic structural interface between the hulls and evaluating it using simulation, followed by fabrication and testing of limited test articles and full-vehicle systems.
Advisors/Committee Members: Schaffner, Grant.
Subjects: Aerospace Materials
Keywords: Blast Mitigation; Human Injury; IED; Armored vehicles; Finite Element; Optimization
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22.
Mindel, Scott A.
Design of Experimental Facility to Simulate Pulsating Flow Through a Blockage.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2011, University of Cincinnati
► In order to investigate the feasibility of noninvasively detecting blockages in pipelines,…
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▼ In order to investigate the feasibility of noninvasively detecting blockages in pipelines, experimental research was by designing a facility at the University of Cincinnati to carry out the work. The goal of the work is to ultimately design a facility that can noninvasively detect blockages in arteries, while being able to simultaneously taking flow visualization and pressure measurements. The research primarily dealt with understanding the capabilities of the facility, as well as taking wall pressure and microphone measurements, as well as flow visualization, in order to study the effects of blockages, pulsation frequencies, and pressure head on flow through the pipeline, in hopes of understanding how to improve the facility in the future to achieve the goal of the facility. The main experimental studies performed on the facility deal with steady flow, which simulates the diastole part of the cardiac cycle, and pulsating flow. These measurements of the steady flow resulted in determining that as the blockage size increases, as well the flow velocity, the pressure drop across the blockage increases. It was also determined that the spectra can be collapsed by the Strouhal number, a non-dimensional parameter based on the blockage, or in case of the largest blockage, the effective blockage, properties. Another way to try and collapse the blockages is to study blockages that have similar flow properties, such as Re or flow rate. It was determined that the most comparable flows come from having both the similar flow properties. For pulsating flows, it was concluded that due to the fact the pressure wave generated from rotating wheel is downstream of the blockage, the wave moves in the opposite direction of the flow, which causes the fundamental pulsation amplitude to be higher downstream of the blockage due to wave energy being reflected back towards the source. Flow visualization was shown to be an invaluable tool to help visually verify many of the results from the steady and pulsating flow results. Many of the results, such as the fact that the largest blockage (96%) has different fluid dynamic properties than the smaller blockages were confirmed from flow visualization. Flow visualization also helps determine the length of a jet that forms downstream of a blockage. It was shown that as in previous studies as the severity of the blockage increases, the jet length decreases. Also, for pulsating flows, the high the pulsating frequency, the shorter the jet length is due to the decreased amount of time the flow has to travel before the subsequent pressure wave. Microphone measurements were also investigated however due to the transmission loss through the pipe, no conclusive results could be found. Finally, recommendations for future work to improve the current facility were discussed.
Advisors/Committee Members: Gutmark, Ephraim.
Subjects: Aerospace Materials
Keywords: Coronary Artery Disease Detection; Pipe Flow; Blockages in Pipes; Pulsating Flow
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23.
Munday, David.
Flow and Acoustics of Jets from Practical Nozzles for High-Performance Military Aircraft.
Degree: PhD, Engineering and Applied Science: Aerospace Engineering, 2010, University of Cincinnati
► This research project examines supersonic jets from nozzles representative of the practical…
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▼ This research project examines supersonic jets from nozzles representative of the practical variable-geometry convergent-divergent nozzles used on high-performance military aircraft. The nozzles employed have conical convergent sections, sharp throats and conical divergent sections. Nozzles with design Mach numbers of 1.3, 1.5, 1.56 and 1.65 are tested and the flow and acoustics examined. Such nozzles are found to produce a double-diamond shock structure consisting of two overlapping sets of shock cells, one cast from the nozzle lip and one cast from the nozzle throat. These nozzles are found to produce no shock-free condition at or near the design condition. As a result they produce shock-associated noise at all supersonic conditions. The shock cell spacing, broad-band shock-associated noise peak frequency and screech frequency all match those of more traditional nearly isentropic convergent-divergent nozzles. A correlation is proposed which improves upon the Prandtl-Pack relation for shock cell spacing in that it accounts for differences in nozzle design Mach number which the Prandtl-Pack relation does not. This proposed relation reverts to the Prandtl-Pack equation for the case of a design Mach number of 1.0. Chevrons are applied to the nozzles with design Mach numbers of 1.5 and 1.56. The effective penetration of the chevrons is found to be a function of the jet Mach number. Increasing jet Mach number increases effective penetration of the chevrons and increases the magnitude of all chevron effects. Chevrons on supersonic jets are found to reduce shock cell length, increase mixing and spreading, decrease turbulent kinetic energy at the end of the potential core and increase it near the nozzle. Chevrons corrugate the shear layer but not the shock structures inside the jet which remain axisymmetric. Chevrons thicken the shear layer, reducing the sonic diameter and reducing the diameter of the shock cells. By reducing their diameter they also reduce the shock cell spacing. Chevrons reduce low-frequency mixing noise near the end of the potential core, increase high-frequency noise near the nozzle exit. They eliminate screech and reduce broad-band shock-associated noise and shift it to higher frequencies. Fluidic injection is applied to the nozzle with design Mach number of 1.5. Fluidic injection corrugates the shear layer, increases mixing and spreading, reduces low frequency mixing noise, increases high frequency noise, reduces broad-band shock-associated noise and shifts its peak to higher frequency.
Advisors/Committee Members: Gutmark, Ephraim.
Subjects: Aerospace Materials
Keywords: jet noise; chevrons; microjets; fluidics; Prantdl-Pack; supersonic jets
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24.
Nejman, Anthony J.
Kinematic Analysis and Joint Hysteresis Modeling for a Lower-Body, Exoskeleton-Style Space Suit Simulator.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2011, University of Cincinnati
► A mechanical exoskeleton has the capacity to replicate the properties of a…
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▼ A mechanical exoskeleton has the capacity to replicate the properties of a pressurized space suit with regards to motion resistance. Using such an exoskeleton for ground based mission training and research provides a lower-cost, less operationally-complex alternative to using a space suit. To that end, NASA is supporting the development of such a device, termed a Space Suit Simulator (S3). The S3 must be designed to allow the wearer the same range of motion allowed in a space suit, and the joints must be actuated to produce the experienced resistive torques. The challenge moving forward is to develop a lower limb (ankle, knee, hip) exoskeleton and then a whole-body exoskeleton that includes multiple interconnected joints with some joints having multiple degree-of-freedom, such as the hip and shoulder. A kinematic design of the lower-body exoskeleton was developed by using Denavit-Hartenberg notation and transformation matrices to derive the Jacobian matrix, which was in turn used to develop a method of testing for singular configurations along a given path of motion. The S3 was tested for singularities while operating through a standard walking gait cycle, and no singularities were uncovered. Translational manipulability of the S3 end effector was analyzed at near-singular configurations along the gait cycle to determine directions of motion which may result in increased joint torques or loss of freedom of motion. A graphical representation of the leg and S3 end effector workspace verified that the S3 allows the human leg to move within the operational envelope anticipated during space suit use. The four degree-of-freedom exoskeleton design eliminates constrictive singularities by aligning human and exoskeleton joint axes. A computational algorithm, based on the Preisach hysteresis model, was used to mimic space suit joint hysteresis behavior in knee flexion and hip abduction/adduction, and it was demonstrated that linear actuators may be used to produce the required joint torque resistance. The kinematic design and computational hysteresis algorithms will support the further development of a physical space suit simulator.
Advisors/Committee Members: Schaffner, Grant.
Subjects: Aerospace Materials
Keywords: space suit simulator; exoskeleton; kinematic analysis; joint hysteresis; manipulability; manipulator workspace
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25.
Niehaus, Justin.
Use of Computational Fluid Dynamics to Evaluate Energy Loss in Three Palliative Strategies of Hypoplastic Left Heart Syndrome.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2010, University of Cincinnati
► Hypoplastic Left Heart Syndrome is a congenital disease that affects neonates and…
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▼ Hypoplastic Left Heart Syndrome is a congenital disease that affects neonates and leaves them with an under developed left ventricle. There are three palliative strategies for correcting this disease, which all involve redirecting the blood flow of the heart. In this study, computational fluid dynamics will be used to determine the energy loss in each of the palliative strategies. The losses of the three strategies will be compared to each other, along with the shear stress on the walls. The volumetric flow rate of the systemic and pulmonary circulatory systems of each palliative strategy will also be evaluated. In addition, the differences in systemic and diastolic losses will be compared.
Advisors/Committee Members: Abdallah, Shaaban.
Subjects: Aerospace Materials
Keywords: Computational Fluid Dynamics; Hypoplastic Left Heart Syndrome
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26.
Prajapati, Seeran.
Potential drop detection of creep damage in the vicinity of welds.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2012, University of Cincinnati
► Recent research studies indicated that directional Alternating Current Potential Drop (ACPD) measurements…
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▼ Recent research studies indicated that directional Alternating Current Potential Drop (ACPD) measurements could be exploited for nondestructive evaluation (NDE) of creep damage. Unfortunately, creep damage is often concentrated in welded sections where the inspection is less straightforward. In this work, a directional square-electrode ACPD probe with spring-loaded contact pins was used to evaluate different levels of creep damage in the vicinity of weldments. The electric transfer resistance is measured in two orthogonal directions to detect creep-induced material damage. This is particularly difficult close to weld/base-metal interfaces because the electric conductivity might changes significantly from one side of the interface to the other and therefore exhibit an apparent anisotropy caused by the influence of the boundary. The feasibility of directional ACPD evaluation of creep damage in the vicinity of such transition regions was studied by experimental, analytical, and numerical means. FE simulations validated the analytical predictions and experimental observations and offered an opportunity to further investigate critical effects, such as the inclination angle of the interface relative to the surface.
Advisors/Committee Members: Nagy, Peter.
Subjects: Electromagnetism
Keywords: ACPD; Creep Damage; Weld
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27.
Sabo, Chelsea.
UAV Two-Dimensional Path Planning In Real-Time Using Fuzzy Logic.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2011, University of Cincinnati
► There are a variety of scenarios in which the mission objectives rely…
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▼ There are a variety of scenarios in which the mission objectives rely on a UAV being capable of maneuvering in an environment containing obstacles in which there is little prior knowledge of the surroundings. In these situations, not only can these obstacles be dynamic, but sometimes there is no way to plan ahead of the mission to avoid them. Additionally, there are many situations in which it is desirable to send in an exploratory robot where the environment is dangerous/ contaminated and there is a great deal of uncertainty. These scenarios could either be too risky to send people or not available to humans. With an appropriate dynamic motion planning algorithm in these situations, robots or UAVs would be able to maneuver in any unknown and/or dynamic environment towards a target in real-time. An autonomous system that can handle these varying conditions rapidly and efficiently without failure is imperative to the future of unmanned aerial vehicle (UAV). This paper presents a methodology for two-dimensional path planning of a UAV using fuzzy logic. This approach is selected due to its ability to emulate human decision making and relative ease of implementation. The fuzzy inference system takes information in real time about obstacles (if within the agent’s sensing range) and target location and outputs a change in heading angle and speed. The FL controller was validated for both simple (polygon obstacles in a sparse space) and complex environments (i.e. non-polygon obstacles, symmetrical/concave obstacles, dense environments, etc). Additionally, Monte Carlo testing was completed to evaluate the performance of the control method. Not only was the path traversed by the UAV often the exact path computed using an optimal method, the low failure rate makes the Fuzzy Logic Controller (FLC) feasible for exploration. The FLC showed only a total of 3% failure rate, whereas an Artificial Potential Field (APF) solution, a commonly used intelligent control method, had an average of 18% failure rate. Also, the APF method failed about 1/3 of the time for very dense environments (the FLC only had 5% failure rate). These results highlighted one of the advantages of the FLC method: its adaptability to additional rules while maintaining low control effort. Furthermore, the solutions showed superior results when compared to the APF solutions when compared to distance traversed. Overall, the FLC produced solutions that were on average only about 7.7% greater distance traveled (as opposed to 9.7% for the APF).
Advisors/Committee Members: Cohen, Kelly.
Subjects: Aerospace Materials
Keywords: UAV; Path Planning; Fuzzy Logic; Online; Real-Time; Motion Planning
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28.
Siddappaji, Kiran.
Parametric 3D Blade Geometry Modeling Tool for Turbomachinery Systems.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2012, University of Cincinnati
► Turbomachinery blades are an integral part of air breathing propulsion systems, gas…
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▼ Turbomachinery blades are an integral part of air breathing propulsion systems, gas and steam turbines and other energy conversion devices. The blade design is a very important process since it defines component performance. A parametric approach for the blade geometry design has been implemented. A variety of three dimensional blade shapes can be created using only a few basic parameters and limited interaction with a CAD system. Using a general approach for creating the blade geometries makes the process easy and robust for creating 3D blade shapes for various turbomachinery components. The geometry of the blade is defined by a very basic set of geometric and aerodynamic parameters. Parameters such as flow angles, axial chord, thickness to chord ratio and streamline meridional coordinates are defined. The leading edge and trailing edge are defined by curves as part of the input. Using these parameters, a specified number of 2D airfoils are created and are radially stacked on the desired stacking axis. The sweep and lean perturbations of the blade are defined by splines as a function of a few control points. The design tool generates a specified number of 3D blade sections and each section consists of a defined number of coordinates in the cartesian coordinate system. These sections can be lofted in a CAD package to obtain a solid 3D blade model, which has been demonstrated using Unigraphics-NX. Parametric update of the spline points defining the 3D blade sections creates new blade shapes without going back into the CAD interface. This approach for the design is very beneficial as the geometry can be modified quickly and easily as per the needs of the designer at any point of time. Using this tool, blade shapes of a 10 stage compressor similar to the GE/NASA EEE HPC, a 3 stage booster, a reverse engineered GE 1.5 MW wind turbine and a centrifugal compressor based on a NASA design are constructed as examples. The general capabilty of the design tool is demonstrated through these examples.
Advisors/Committee Members: Turner, Mark.
Subjects: Aerospace Materials
Keywords: parametric geometry; blade geometry generator
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29.
Soliman, Salah M.
Micro-Particles and Gas Dynamics in an Axi-Symmetric Supersonic Nozzle.
Degree: PhD, Engineering and Applied Science: Aerospace Engineering, 2011, University of Cincinnati
► A new biolistic gene gun for micromolecular drug delivery to human skin…
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▼ A new biolistic gene gun for micromolecular drug delivery to human skin has been developed and numerically tested. The device generates supersonic flow to accelerate the mediated microparticles to sufficient speeds to breach the outer human skin layer. The device is referred to as CDN-WPI and consists of; a high pressure gas tank, a convergent-divergent nozzle (C-D), and a constant area mixing duct. The mediated microparticles are entrained from a parallel inlet after the exit of the C-D nozzle. The gas from the high pressure tank accelerates through the C-D nozzle to supersonic speeds which in turn accelerate the powder microparticles through the constant area mixing duct to high speeds. A validated numerical procedure is used to study the two-phase flow dynamics inside the biolistic gun using different geometrical configurations. Different driver gas pressures, gas type (helium and air), adding gas swirl, microparticles types and size are considered in this study. The dimensions of the device C-D nozzle, mixing duct length, and the number of particles inlets are the geometrical configurations studied. It is found that using the CDN-WPI device requires reduced driver gas pressure by 50 % compared to the existing devices. The reduction in the gas driver pressure is a result of the elimination of the losses due to boundary layer separation found in all previous devices. The entrainment of the solid microparticles and gas from the parallel inlets precludes flow separation by energizing the boundary layer over the constant area duct walls. As a result, the CDN-WPI is more efficient and safer to use. Further validation is done using semi-empirical particle penetration calculations and the computed flow field which compare very well with the available experimental data. The axi-symmetric model has been used exclusively in all previous numerical solutions of biolistic guns. To check the validity of this assumption, the axi-symmetric results are compared with the results of 3-D model solutions with continuous particles inlet along periphery. The results compare very well which justify the axi-symmetric assumption solutions. We investigated the 3-D two-phase flow field with one, two, and four particle inlets. The 3-D simulations show that for practical and efficient gene gun device, more than one particle inlet is required.
Advisors/Committee Members: Abdallah, Shaaban.
Subjects: Aerospace Materials
Keywords: CFD; Supersonic nozzle; 3-D numerical study; Biolistic Gene gun; Particles-gas flows
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30.
Vick, Andrew W.
Genetic Fuzzy Controller for a Gas Turbine Fuel System.
Degree: MS, Engineering and Applied Science: Aerospace Engineering, 2010, University of Cincinnati
► In this study, a fuel system controller for a gas turbine engine…
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▼ In this study, a fuel system controller for a gas turbine engine was examined. Controller design in this application is challenging due to nonlinearities in the closed loop system, as well as uncertainties associated with hardware components from part variation or degradation. Current closed loop design methodologies are discussed, as are the limitations or challenges facing these systems. Details on fuzzy logic control and its benefits in this type of application are explored. Information on genetic algorithms is presented, along with a study on how this optimization approach can be utilized to enhance the fuzzy logic controller process. A fuzzy logic controller structure was developed for providing closed loop fuel control in the gas turbine application, using a genetic algorithm to tune the system to provide an accurate and fast response to changing input demands. With a genetic fuzzy controller in place, closed loop analysis was performed, along with a stochastic robustness analysis to assess controller performance in an uncertain environment. Results show that the genetic fuzzy system performed well in this application, resulting in a system with fast rise and settling times to stepping inputs, while also minimizing overshoot and steady state error. Robustness characteristics of the fuzzy controller were also demonstrated, as the stochastic robustness analysis yielded acceptable performance in each simulation of the closed loop system with uncertainties included.
Advisors/Committee Members: Cohen, Kelly.
Subjects: Aerospace Materials
Keywords: Genetic Algorithm; Fuzzy Logic; Gas Turbine; Fuel System
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