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Ghods, MasoudEffect of Convection Associated with Cross-section Change during Directional Solidification of Binary Alloys on Dendritic Array Morphology and Macrosegregation
Doctor of Engineering, Cleveland State University, 2017, Washkewicz College of Engineering
This dissertation explores the role of different types of convection on macrosegregation and on dendritic array morphology of two aluminum alloys directionally solidified through cylindrical graphite molds having both cross-section decrease and increase. Al- 19 wt. % Cu and Al-7 wt. % Si alloys were directionally solidified at two growth speed of 10 and 29.1 µm s-1 and examined for longitudinal and radial macrosegregation, and for primary dendrite spacing and dendrite trunk diameter. Directional solidification of these alloys through constant cross-section showed clustering of primary dendrites and parabolic-shaped radial macrosegregation profile, indicative of “steepling convection” in the mushy-zone. The degree of radial macrosegregation increased with decreased growth speed. The Al- 19 wt. % Cu samples, grown under similar conditions as Al-7 wt. % Si, showed more radial macrosegregation because of more intense “stepling convection” caused by their one order of magnitude larger coefficient of solutal expansion. Positive macrosegregation right before, followed by negative macrosegregation right after an abrupt cross-section decrease (from 9.5 mm diameter to 3.2 mm diameter), were observed in both alloys; this is because of the combined effect of thermosolutal convection and area-change-driven shrinkage flow in the contraction region. The degree of macrosegregation was found to be higher in the Al- 19 wt. % Cu samples. Strong area-change-driven shrinkage flow changes the parabolic-shape radial macrosegregation in the larger diameter section before contraction to “S-shaped” profile. But in the smaller diameter section after the contraction very low degree of radial macrosegregation was found. The samples solidified through an abrupt cross-section increase (from 3.2 mm diameter to 9.5 mm diameter) showed negative macrosegregation right after the cross-section increase on the expansion platform. During the transition to steady-state after the expansion, radial macrosegregation profile in locations close to the expansion was found to be “S-shaped”. This is attributed to the redistribution of solute-rich liquid ahead of the mushy-zone as it transitions from the narrow portion below into the large diameter portion above. Solutal remelting and fragmentation of dendrite branches, and floating of these fragmented pieces appear to be responsible for spurious grains formation in Al- 19 wt. % Cu samples after the cross-section expansion. New grain formation was not observed in Al-7 wt. % Si in similar locations; it is believed that this is due to the sinking of the fragmented dendrite branches in this alloy. Experimentally observed radial and axial macrosegregations agree well with the results obtained from the numerical simulations carried out by Dr. Mark Lauer and Prof. David R. Poirier at the University of Arizona. Trunk Diameter (TD) of dendritic array appears to respond more readily to the changing growth conditions as compared to the Nearest Neighbor Spacing (NNS) of primary dendrites.

Committee:

Surendra Tewari, Ph.D. (Advisor); Jorge Gatica, Ph.D. (Committee Member); Orhan Talu, Ph.D. (Committee Member); Rolf Lustig, Ph.D. (Committee Member); Kiril Streletzky, Ph.D. (Committee Member)

Subjects:

Aerospace Materials; Automotive Materials; Chemical Engineering; Condensed Matter Physics; Engineering; Fluid Dynamics; High Temperature Physics; Materials Science; Metallurgy

Keywords:

Directional Solidification; Natural Convection; Fluid Flow; Binary Alloys; Macrosegregation; Dendritic Array; Dendrite Morphology; Solutal Remelting; Thermosolutal Convection; Aluminum Alloy; Cross section Change

Williams, Charles PLow Pressure Turbine Flow Control with Vortex Generator Jets
MS, University of Cincinnati, 2016, Engineering and Applied Science: Aerospace Engineering
In an aircraft engine at high altitude, the low-pressure turbine (LPT) section can experience low-Reynolds number (Re) flows making the turbine blades susceptible to large separation losses. These losses are detrimental to the performance of the turbine and lead to a roadblock for “higher-lift” blade designs. Accurate prediction of the separation characteristics and an understanding of mitigation techniques are of the utmost importance. The current study conducts simulations of flow control techniques for the Air Force Research Laboratory (AFRL) L2A turbine blade at low-Re of 10,000 based on inlet velocity and blade axial chord. This blade was selected for its “high-lift” characteristics coupled with massive separation on the blade at low-Re which provides an excellent test blade for flow control techniques. Flow control techniques involved various configurations of vortex generator jets (VGJs) using momentum injection (i.e. jet blowing). All computations were executed on dual-topology, multi-block, structured meshes and incorporated the use of a parallel computing platform using the message passing interface (MPI) communications. A high-order implicit large eddy simulation (ILES) approach was used in the simulations allowing for a seamless transition between laminar, transitional, and turbulent flow without changing flow solver parameters. A validation study was conducted involving an AFRL L1A turbine blade which showed good agreement with experimental trends for cases which controlled separation in the experiments. The same cases showed good agreement between different grid sizes. The differences between experimental and numerical results are largely attributed to differences in the setup. That is, the simulation did not include freestream turbulence or wind-tunnel wall effects. The flow control study conducted for the L2A blade showed a small degree of separation control for jets placed just downstream (DS) of the separation point. A limited study was conducted with jets moved upstream (US) of the natural separation point which showed an increase in effectiveness for one of the VGJs. This indicates a sensitivity of VGJ location relative to the point of separation. For the DS VGJs, separation control, increased as blowing ratio (BR) was increased and jet blowing frequency (F+) decreased. The increase in jet efficacy with decreasing F+ was unexpected and is mostly attributed to the jets being downstream of the separation location and having a low duty cycle (10%). Turbulent kinetic energy frequency spectra also show the presence of jet harmonics in the flow downstream of the best performing VGJs which dramatically increased in power when the VGJ was moved upstream. The most effective jet found in this study had BR=3.0, F+=3.02, and was located at x/Cx=0.53. This VGJ provided a 42.1% reduction in normalized integrated wake loss. One follow-on simulation was conducted taking the most effective VGJ and increasing the blowing ratio from BR=3.0 to 8.0. This provided a decrease in the amount of separation, nearly eliminating separation with only a small separation bubble remaining. This VGJ was able to provide a 42.8% reduction in normalized integrated wake loss. This work was conducted in coordination with the AFRL and has been approved for public release, case number: 88ABW-2016-1657.

Committee:

Kirti Ghia, Ph.D. (Committee Chair); Rolf Sondergaard, Ph.D. (Committee Member); Shaaban Abdallah, Ph.D. (Committee Member); Urmila Ghia, Ph.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Low Pressure Turbine;Vortex Generator Jet;Active Flow Control;Implicit Large Eddy Simulation;L2A;Low Reynolds Number Flow

Han, Jun HeeExperimental Investigation of Plasma-Assisted Combustion of Heavy Hydrocarbons Using Gliding/Rotating Arc
MS, University of Cincinnati, 2016, Engineering and Applied Science: Aerospace Engineering
Rotating/Gliding arc gas discharge is known as a suitable application for plasma aided combustion (PAC). In this study, effects of rotating arc discharge on combustion of diesel and biodiesel fuel are investigated. The main focus of the experiment is to determine the effectiveness of rotating-arc in enhancing combustion performance. The first stage of the burner is designed for the fuel-air mixture to interact with the rotating arc at fuel-rich condition. The second stage of the burner is the main combustion section to make the mixture at overall fuel-lean condition and properly hold the flame inside the combustion chamber. As a result, lean flammability limit determined by equivalence ratio at lean blowout is found to be extended quite a bit when the arc is on. FTIR (Fourier Transform Infrared Spectroscopy) measurements of exhaust gas show that both CO and CO2 concentration become higher and O 2 concentration lower for overall fuel-lean combustion with plasma on. Based on the results of level of total carbon oxidation, combustion efficiency is slightly higher with plasma than without plasma. Slightly more NO is produced when the arc is at present for a fixed equivalence ratio. However, with the extension of lean flammability condition achieved by plasma-assisted combustion the minimum NO is produced for PAC case. The increase of reactant temperature due to direct heat transfer from the arc to the surrounding and partial oxidation (exothermal) can mainly account for the observed enhancement of combustion for the PAC.

Committee:

Jongguen Lee, Ph.D. (Committee Chair); Shaaban Abdallah, Ph.D. (Committee Member); Mingming Lu, Ph.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Plasma;Rotating Arc;Fuel Reforming;Combustion;Diesel

Michaels, Simone ColetteDevelopment and Assessment of Artificial Manduca sexta Forewings: How Wing Structure Affects Performance
Master of Sciences (Engineering), Case Western Reserve University, 2016, EMC - Aerospace Engineering
This research presents novel fabrication and testing techniques for artificial insect wings. A series of static and dynamic assessments are designed which allow consistent comparison of small, flexible wings in terms of structure and performance. Locally harvested hawk moths are tested and compared to engineered wings. Data from these experiments shows that the implemented replication method results in artificial wings with comparable properties to that of M. sexta. Flexural stiffness (EI) data shows a considerable difference between the left and right M. sexta wings. Furthermore, EI values on the ventral wing side are found to be consistently higher than the dorsal side. Based on dynamic results, variations in venation structure have the largest impact on lift generation. Lift tests on individual wings and wing sets indicate detrimental effects as a result of wing-wake interaction.

Committee:

Roger Quinn (Advisor); Mark Willis (Committee Member); Richard Bachmann (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Biology; Engineering; Entomology; Mechanical Engineering

Keywords:

Manduca sexta; artificial wings; wing fabrication; biomimicry

Mahmoudi, BehzadInvestigation the Effect of Tribological Coatings: WC/a-C:H and Black Oxide on Micropitting Behavior of SAE52100 Bearing Steel
Doctor of Philosophy, University of Akron, 2015, Civil Engineering
Spherical roller bearings (SRBs) utilized in the gearboxes of wind turbine generators are known to be especially susceptible to premature failure due to low cycle micropitting of the raceways. Micropitting in rolling element bearings is believed to arise from significant roller/raceway sliding in thin film lubrication conditions. Roller/raceway sliding occurs in SRBs as a consequence of their geometry, and almost all the bearings in wind turbine gearboxes operate in thin film (or low lambda) lubrication conditions. There is currently no accepted solution to mitigate micropitting in wind turbine gearboxes that are equipped with SRBs. Since WC/a-C:H coatings on rolling elements have been effectively used to solve wear issues encountered by SRBs in other industrial applications, these coatings have been offered as a solution to low cycle micropitting in wind turbine gearbox SRBs. This research plan has been developed to test the hypothesis that a WC/a-C:H coating will mitigate or eliminate micropitting such as that experienced by SRBs in wind turbine gearboxes. The laboratory tool that is used to create micropitting on test specimens is the PCS Instruments Micropitting Rig (PCS MPR). The MPR is a three-contact disc machine in which there are three rings of equal diameter positioned at 120 degrees apart with a smaller diameter roller located in the middle and in contact with all the rings. This arrangement allows the test roller to be subjected to a large number of rolling contact cycles in a short period of time and hence significantly reduces testing time. At a typical entrainment speed of 3.5m/s, the central test roller will experience approximately one million contact cycles per hour. Since the controls of the PCS MPR allow the speed, slide-roll ratio, temperature, and load to be automatically and independently controlled, the thin film lubrication and slide/roll ratio conditions that generate micropitting on SRBs can be reproduced in the laboratory. Most wind turbine gearboxes operate with a synthetic ISO-320 lubricating oil with anti-wear and extreme pressure additives. However, to ensure thin film lubrication conditions necessary for micropitting experiments were performed on the MPR using an ISO-10 base oil. Baseline tribological testing were performed using untreated SAE 52100 rings and the roller. The targeted surface finish on the rings and the rollers varied from about 0.2 to about 0.6 micrometer Ra, and the entire surface topography was quantified using a Zygo 7300 3D optical profilometer. The sets of roller and rings were tested on the MPR using a range of slide/roll ratios from 0.0 to +/- 10% at contact stresses up to about 3 GPa. The number of cycles needed to generate the onset of micropitting was recorded and some tests were repeated up to three times. Results of micropitting tests on steel/steel, steel/WC/a-C:H and WC/a-C:H/steel contacts were compared with a tribological conversion coating; black oxide. Black oxide is a surface treatment that converts the surface of ferrous alloys to magnetite (Fe3O4). It has been utilized to reduce wear and corrosion of rolling element bearings and gears, and its use has become especially widespread on roller bearings used in the gearboxes of modular wind turbines. It has been reported that black oxide might have a lower friction coefficient than steel, which may reduce shear stresses due to friction, dampen vibrations, or possibly prevent the diffusion of hydrogen.

Committee:

Gary Doll, Professor (Advisor); Evans Ryan, Doctor (Committee Member); Binienda Wieslaw, Doctor (Committee Member); Dong Yalin, Doctor (Committee Member); Menzemer Craig, Doctor (Committee Member); Sancaktar Erol , Doctor (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Materials Science; Mechanical Engineering

Keywords:

DLC coating, Tribology, Bearing, Micropitting, Black Oxide, Surface Fatigue, Frictional Heat, Flash Temprature, Hertzian Contact

Hagerty, PhillipPhysical Vapor Deposition of Materials for Flexible Two Dimensional Electronic Devices
Master of Science (M.S.), University of Dayton, 2016, Chemical Engineering
Molybdenum Disulfide (MoS2) and Tungsten Disulfide (WS2) are two materials in a larger class of materials known as Transition Metal Dichalcogenides (TMDs) that have begun emerge as semiconducting materials. When their horizontal length scale is reduced from bulk to monolayer they demonstrate surprising combinations of properties including a direct electronic band gap and mechanical flexibility. Two dimensional (2D) materials have the potential to revolutionize performance and tailorability of electro-optical devices fabricated entirely from molecularly thin materials. In a departure from traditional exfoliation or high temperature chemical vapor deposition approaches for 2D materials synthesis, novel plasma-based physical vapor (PVD) techniques were used to fabricate uniform films over large areas. This experimental approach allowed unique studies. For example, vapor phase growth allowed systematically variation of the sulfur vacancy concentration in MoS2 and WS2 and subsequent correlation to electronic properties. This effort leads to controlled bottom-up assembly of 2D devices on flexible and standard substrates to experimentally couple the remarkable intrinsic mechanical and electronic properties of ultrathin materials, which are particularly appealing for molecular sensing. The pursuit of an all physical vapor deposited field effect transistor (FET) is the main priority for the 2D materials community as definitive demonstration of the feasibility of physical vapor deposition as a scalable technique for consumer electronics. PVD sputtered Titanium Nitride (TiN) and Tungsten (W) were experimentally characterized as potential back gated materials, Plasma Vapor Deposited (PLD) a-BN was electrically characterized as a uniform ultra-thin low temperature dielectric, and sputtered MoS2 and WS2 were electrically characterized as a semiconductor material. Tungsten deposition methods were previously researched and mimicked for smooth and conductive back gate material depositions. TiN was parameterized and the best room temperature deposition conditions were 70V applied to the sputtering gun with 25 sccm gas flow of 90% N2 and 10% Ar for 60 minutes. The best high temperature depositions were done at 500oC, 70V applied to the sputtering gun with 25 sccm gas flow of 90% N2 and 10% Ar for 30 minutes. Dielectric a-BN electrical characterization began to occur after 6nm which equated to 100 pulses, while 200 pulses equated to 16.5nm thickness. A dielectric constant of 5.90 ± .65 is reported for a-BN for under 20nm thickness. Soft probing techniques by conductively pasted gold wires on the probe tips were required to obtain true electrical measurements of 2D materials in a stacked structure, otherwise scratching would occur and uniformity would cease to exist in the film. Chemical Vapor Deposition (CVD) and mechanical exfoliation have provided the only working TMD semiconductor 2D materials in MOSFET structure to date with lithographic electrical connections. PVD sputtering as a new synthesis method for crystalline TMD with a stoichiometric ratio is achievable over large areas. Though, reduced area depositions are required for doped Silicon and Silicon Oxide (SiO2) based FET structures to limit the chance of encountering a pinhole. With reduced area and stoichiometric enhancement control, sputtered TMD films exhibit high sensitivity to oxygen and are electrically conductive even when exposed to a field effect. Increasing the grain size of the sputtered materials is the next driving force towards a fully recognizable TMD thin film transistor.

Committee:

Christopher Muratore, PhD (Committee Chair); Terrence Murray, PhD (Committee Member); Kevin Myers, DSc (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Electrical Engineering; Engineering; Materials Science

Keywords:

PVD; materials; 2D materials; Nanoelectronics; TMDs; 2D Transistors; Molybdenum Disulfide; MoS2; WS2; Tungsten Disulfide

Thompson, John RyanRELATING MICROSTRUCTURE TO PROCESS VARIABLES IN BEAM-BASED ADDITIVE MANUFACTURING OF INCONEL 718
Master of Science (MS), Wright State University, 2014, Mechanical Engineering
The advancement of laser or electron beam-based additive manufacturing requires the ability to control solidification microstructure. Previous work combined analytical point source solutions and nonlinear thermal finite element analysis (FEA) to explore the effects of deposition process variables on Ti-6Al-4V solidification microstructure. The current work seeks to extend the approach to Inconel 718, with the addition of Cellular Automaton-Finite Element (CAFE) models. Numerical data from finite element results are extracted in order to calculate accurate melt pool geometry, thus leading to corresponding cooling rates and thermal gradients. The CAFE models are used to simulate grain grown and nucleation, providing a link between additive manufacturing process variables (beam power/velocity) and solidification microstructure. Ultimately, a comparison of results between Ti-6Al-4V and Inconel 718 is expected to lay the ground work for the integrated control of melt pool geometry and microstructure in other alloys.

Committee:

Nathan Klingbeil, Ph.D. (Advisor); Raghavan Srinivasan, Ph.D., P.E. (Committee Member); Jaimie Tiley, Ph.D. (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Engineering; Materials Science; Mechanical Engineering

Keywords:

Additive Manufacturing Beam Laser FEA CAFE ProCAST Inconel 718 Ti-6Al-4V melt pool process variables microstructure power velocity gamma prime 3D printing Rosenthal

Liutkus, Timothy JamesDigital Image Correlation in Dynamic Punch Testing and Plastic Deformation Behavior of Inconel 718
Master of Science, The Ohio State University, 2014, Mechanical Engineering
A custom punch-die fixture allowing full field three-dimensional Digital Image Correlation (DIC) measurements on the rear surface of the specimen is introduced for dynamic and quasi-static punch experiments. The punch fixture design methodology is described. Results from punch experiments on 5.08 mm Ti-6Al-4V disk specimens using three different punch geometries in both dynamic and quasi-static conditions are presented and discussed. These experiments can be used to generate material failure data under complex stress states. Such data is essential in developing and calibrating complex material models, like those developed for precipitate hardened Inconel 718. The plastic behavior of precipitate hardened Inconel 718 under various strain rates, orientations, and temperatures is examined; and a punch experiment that uses 3D-DIC measurements of the punch specimen is presented. The research presented herein is part of an ongoing project to develop and calibrate a material model in a finite element code, LS-DYNA. Such models are valuable for the simulation of dynamic events, such as blade off failure in aircraft engines. The equipment, theory, and methodologies used to complete experiments in tension and compression at different strain rates and temperatures are presented. Quasi-static experiments are conducted using a biaxial servo-hydraulic load frame and dynamic experiments using two split Hopkinson bars. A specially designed furnace and adapters are used to complete experiments at elevated temperatures. DIC is an optical method for measuring full field deformations and strains on the specimen surface that is utilized extensively in this work. Experimental results for precipitate hardened Inconel 718 are presented and discussed. The material shows significant strain hardening and some strain rate sensitivity in tension. Data from experiments at elevated temperature show complex temperature dependence. The material shows decreasing flow stress with increasing temperature and decreasing ductility between 21°C and 600°C. Between 600° and 800°C the ductility increases significantly. Compression experiments at various strain rates show similar strain hardening and less rate sensitivity than in tension. The material is anisotropic in the ±45° from rolling directions and shows anisotropy between tension and compression loadings in the transverse direction. These data are used to determine parameters for a Johnson-Cook plasticity model, and yield criteria are discussed. Additional work is presented for the design of plane stress, plane strain, and axisymmetric fracture specimens. These specimens will be used in future work in the generation of a failure surface based on stress triaxiality and lode parameter – two stress-state parameters which govern material failure.

Committee:

Amos Gilat (Advisor); Mark Walter (Committee Member)

Subjects:

Aerospace Materials; Engineering; Mechanical Engineering

Keywords:

Experimental Mechanics, Plasticity, High Rate Testing, Inconel 718, Punch Testing

Rose, David HarryA Cumulative Damage Approach to Modeling Atmospheric Corrosion of Steel
Doctor of Philosophy (Ph.D.), University of Dayton, 2014, Materials Engineering
Past attempts to develop models that predict atmospheric corrosion rates used statistical regression, “power-law”, or other approaches that result in linear or simple nonlinear corrosion rate predictions. Such models were calibrated by statistically comparing corrosion test results to predictions based upon long-term (e.g., annual) deposition measurements of chloride aerosols and/or SO2. Relative humidity, if explicitly considered, was only used to define the amount of time during the year when conditions were thought to be favorable for corrosion. Most models ignored temperature effects but those that do only consider annual averages. A new approach was constructed to predict corrosion rates using the concept of cumulative damage. This new model is analogous to some types of fatigue models and is based upon the Eyring equation, which was originally developed to predict the dependence of chemical reaction rates on levels of the presumed acceleration factors. The model makes hourly weight loss predictions, which when added together makes longer-term “cumulative” predictions. Principal advantage of using hourly predictions is that the effects of diurnal and seasonal temperature cycles and related changes to relative humidity are explicitly considered. The stochastic nature of atmospheric contaminants is considered as well. An inverse modeling approach using Monte Carlo simulations was used to fit various candidate models to proxy environmental characterization data representing conditions at corrosion test sites. Proxy data (measured elsewhere and for other purposes) was used to infer the stochastic environmental severity at sites where corrosion tests were conducted. Such data included hourly SO2 and ozone data obtained from the Environmental Protection Agency’s Air Quality System database, longer-term chloride deposition data from the National Atmospheric Deposition Program’s on-line database, and hourly weather data from the U.S. Air Force’s 14th Weather Squadron. Proxy data was used so that if this current research proved successful, follow-on work could lead to a practical methodology that design engineers could employ to make realistic predictions without having to explicitly characterize the environment at a location of interest. Cumulative predictions made using such data were statistically compared to quarterly corrosion test results that came from a DoD Strategic Environmental Research and Development Program (SERDP) funded effort and other related programs that used the same testing protocols. Billions of simulations were conducted whereby coefficients employed by the candidate model were randomly varied and the individual predictions statistically compared to test measurements in order to identify the most accurate model. Each candidate model was calibrated by considering hourly data for an entire year at multiple locations in order to quantify interactions between acceleration factors. The degree of fit between the model results and test measurements at the calibration sites was very high (R2=~ 0.99). When the optimum model was applied to locations where corrosion tests were conducted but not used for calibration, the fit was not quite as good, but was still quite high (R2=~0.86). Analyses were conducted to identify ways to further improve accuracy, thus laying the framework for future efforts.

Committee:

Douglas Hansen, Ph.D. (Advisor)

Subjects:

Aerospace Materials; Automotive Materials; Materials Science

Keywords:

atmospheric corrosion; cumulative damage; mass loss; modeling; predictions; environmental severity; climate zones; surf zones; urban pollution; Monte Carlo simulations

Meeboon, NonDesign and Development of a Porous Injector for Gaseous Fuels Injection in Gas Turbine Combustor
MS, University of Cincinnati, 2015, Engineering and Applied Science: Aerospace Engineering
A novel porous injector is designed for injection of gaseous fuel in land based gas turbine combustors. The injector is tested at atmospheric conditions at Combustion Research Laboratory, University of Cincinnati. In the present study, seven injector configurations are tested for mixing quality, LBO limits and emissions. For mixing studies, the CO2 technique is adopted to evaluate the fuel-air mixing under atmospheric conditions of the porous injector. The experiments are carried out at 4% pressure drop condition across the injector. The CO2 concentrations are converted to fuel mass fractions for the comparison. A comparison between the top/bottom injections, center/no center injection and 7/30 micron porous tubes show that these configurations do not impact the fuel-air mixing distribution. PIV measurements are carried out in non-reacting as well reacting conditions. Velocity profiles are obtained at a 1%-4% pressure drop condition. The experiments are carried out with and without combustor. A weak outer recirculation zone is observed downstream of the injector in the combustor. The velocity profiles are same at the exit plane of the injector with and without combustor. The velocity decreases gradually along the combustor. The ignition and lean blow out limit are observed to increase as the pressure drop increases. The flame liftoff distance is found to increase as the pressure drop increases. The NO, CO, and O2 emissions are evaluated at the downstream of the porous injector at 6" from the entrance of the combustor. The results show that the NOx emissions are ~ 7 ppm @ 15% O2.

Committee:

San-Mou Jeng, Ph.D. (Committee Chair); Umesh Bhayaraju, Ph.D. (Committee Member); Samir Tambe, Ph.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Porous;Injector;Gaseous fuel;Gas turbine;Combustor;Fuel-air mixing

Walker, Alex RFuzzy Attitude Control of a Magnetically Actuated CubeSat
MS, University of Cincinnati, 2013, Engineering and Applied Science: Aerospace Engineering
The problem of magnetic attitude control of a CubeSat is analyzed. Three controller types are examined: a Constant-Gain Simple PD controller, a Linear Constant-Gain Optimal PD controller (i.e. an LQR), and a Fuzzy Gain-Scheduled PD controller. Each subsequent controller type utilizes a more-complex design algorithm. The Simple PD controller is tuned by hand iteration, the LQR is tuned using rule-of-thumb algorithms, and the Fuzzy Gain-Scheduled PD controller is designed using a Genetic Algorithm operating on two Fuzzy Inference Systems. Though the basic structures of these three controllers are identical, the differing design processes lead to different controller performance. The use of a Genetic-Fuzzy System is of particular interest, because this demonstrates the use of an intelligent algorithm to automate the controller design process. The techniques presented herein are directly applicable to any magnetically actuated satellite that can be modeled as a rigid body, although the mass distribution, geometry, and orbit of the satellite will determine controller-specific constants.

Committee:

Kelly Cohen, Ph.D. (Committee Chair); Elad Kivelevitch, Ph.D. (Committee Member); Phil Putman, Ph.D. (Committee Member); Grant Schaffner, Ph.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Attitude Control;CubeSat;Magnetic;Fuzzy Logic;Genetic Algorithm

Perrino, MichaelAn Experimental Study into Pylon, Wing, and Flap Installation Effects on Jet Noise Generated by Commercial Aircraft
PhD, University of Cincinnati, 2014, Engineering and Applied Science: Aerospace Engineering
A pylon bottom bifurcation and a wing with variable flaps were designed and built to attach to a scaled model of a coaxial exhaust nozzle system. The presence of the pylon bifurcation, wing, and flaps modify the characteristics of the exhaust flow forc- ing asymmetric flow and acoustics. A parametric study was carried out for assessing and relating the flow field characteristics to the near-field pressure and far-field acous- tic spectra. The flow field was investigated experimentally using both stream-wise and cross-stream PIV techniques where the near-field pressure and far-field acoustic spectra were measured using microphone arrays. Contour mapping of the flow field characteristics (e.g. mean velocity and turbulence kinetic energy levels) and near-field acoustics with and without installation effects were used to explain the changes in the far-field acoustics.

Committee:

Ephraim Gutmark, Ph.D. D.Sc. (Committee Chair); Asif Syed, Ph.D. (Committee Member); Jeffrey Kastner, Ph.D. (Committee Member); Paul Orkwis, Ph.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Aeroacoustics;Aircraft Engine;Pylon;Noise;Nozzle

Notaro, VincentMixing Analysis of Like Doublet Injectors in High Pressure Environments for Gelled Propellant Simulants
MS, University of Cincinnati, 2014, Engineering and Applied Science: Aerospace Engineering
Impinging doublet injectors offer rocket designers an effective way to atomize and mix opposing jets of fuel and oxidizer. The adaptability of the injector designs and ease of manufacturing make them attractive choices for designers. The adaptability of injector designs introduces many variables to the system like orifice diameter, nozzle orifice pairings, and working fluid to name a few. This expanse of variables requires characterization of phenomenon produced and measurement of performance. The characterization of phenomenon can be used to help explain performance. The atomization and spray characteristics of impinging jets are well understood. The studies in this field cover a multitude of design variables. While mixing quantification is well understood for liquid working fluids and similar orifice pairings, data are still lacking on non-Newtonian working fluids, specifically gelled simulants, and dissimilar orifice pairings. In addition, like mixing data exists for sprays in elevated ambient pressure conditions. Gelling of propellants provides advantages of easier handling and less vapor issues as compared to liquid propellants. Dissimilar orifice pairs offer the opportunity to achieve desired mixture ratios without largely varying operating conditions. A review of mixing studies for liquid working fluids is conducted. The studies focus on defining mixing efficiencies changes based on the injector design variables. In addition, some mixing mechanisms are established and discussed phenomenologically. A review of atomization studies is also conducted. These studies help shed light on mixing characteristics as well as help progress diagnostics in the mixing study field. These studies also focus injector design variables but cover more variables in greater depth than the mixing studies. A combination of a pressure chamber, two flow systems for the two different working fluids, and two pairings of nozzles is used to characterize mixing over different injection velocities and ambient conditions. In addition, the two working fluids and two different nozzle pairings allow comparisons to be made between the different cases. The injection velocity conditions range from 8 m/s to 20 m/s in ambient pressure conditions from atmospheric to 500 psi. Mixing efficiency is calculated using spray mass distributions acquired by PLIF technique. The data processing procedure is defined and is applicable to similar data acquisition systems. The mixing data acquired show that for similar orifice diameter impingement, the ambient pressure increase above atmospheric enhances mixing for both gelled and non-gelled fluid due to reduced break-up lengths. However, the mixing efficiency stops increasing and remains constant above a certain ambient pressure. Gelled simulant generally results in poorer mixing efficiencies than the non-gelled simulant, suggesting momentum carried and pre-impingement jet conditions are the determining factors in mixing. For dissimilar orifice diameter impingement, mixing is generally constant over all the ambient pressures including atmospheric. This may be due to the far downstream distance collection location. For optimized operating conditions, the dissimilar orifice-diameter impingement case can produce better mixing than the similar orifice diameter impingement case.

Committee:

Jongguen Lee, Ph.D. (Committee Chair); San-Mou Jeng, Ph.D. (Committee Member); Milind Jog, Ph.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

doublet injector;impinging jet;mixing efficiency;hypergolic;gelled simulant;ambient pressure

Foster, DanielMechanical and Thermal Characterization of Ultrasonic Additive Manufacturing
Doctor of Philosophy, The Ohio State University, 2014, Welding Engineering
Additive manufacturing is an emerging production technology used to create net shaped 3-D objects from a digital model. Ultrasonic Additive Manufacturing (UAM) is a relatively new type of additive manufacturing that uses ultrasonic energy to sequentially bond layers of metal foils at temperatures much lower than the melting temperature of the material. Constructing metal structures without melting allows UAM to have distinct advantages over beam based additive manufacturing and other traditional manufacturing processes. This is because solidification defects can be avoided, structures can be composed of dissimilar material and secondary materials (both metallic and non-metallic) can be successfully embedded into the metal matrix. These advantages allow UAM to have tremendous potential to create metal matrix composite structures that cannot be built using any other manufacturing technique. Although UAM has tremendous engineering potential, the effect of interfacial bonding defects on the mechanical and thermal properties have not be characterized. Incomplete interfacial bonding at the laminar surfaces due to insufficient welding energy can result in interfacial voids. Voids create discontinuities in the structure which change the mechanical and thermal properties of the component, resulting in a structure that has different properties than the monolithic material used to create it. In-situ thermal experiments and thermal modeling demonstrates that voids at partially bonded interfaces significantly affected heat generation and thermal conductivity in UAM parts during consolidation as well as in the final components. Using ultrasonic testing, elastic properties of UAM structures were found to be significantly reduced due to the presence of voids, with the reduction being the most severe in the transverse (foil staking) direction. Elastic constants in all three material directions decreased linearly with a reduction in the interfacial bonded area. The linear trend permits the ability to predict bonded interfacial area in the manufacturing environment without the need for destructive mechanical or metallurgical tests. The feasibility of two process monitoring techniques for UAM were also evaluated. A method to test resonance frequency using a Photonic Doppler Velocimeter to detect vibrational motion was developed and tested. Preliminary testing revealed that resonance testing could be used to determine average interfacial bonded area in a UAM sample. In-situ vibration velocity of the sonotrode, welding foil and substrate were measured using the Photonic Doppler Velocimeter system. Analysis of the velocity data revealed that by analyzing absolute velocity, relative velocity and phase angles of the three structures a bonding vs. non-bonding conditions could be determined in-situ using the Photonic Doppler Velocimeter system.

Committee:

Wei Zhang, PhD (Advisor); Sudarsanam Suresh Babu, PhD (Committee Member); Glenn Daehn, PhD (Committee Member); Stanislav Rokhlin, PhD (Committee Member)

Subjects:

Aerospace Materials; Materials Science; Mechanical Engineering

Keywords:

Welding, Additive Manufacturing, Ultrasonic Additive Manufacturing, Photonic Doppler Velocimeter

Ichihashi, FumitakaInvestigation of Combustion Instability in a Single Annular Combustor
MS, University of Cincinnati, 2011, Engineering and Applied Science: Aerospace Engineering
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.

Committee:

San-Mou Jeng, PhD (Committee Chair); Shanwu Wang, PhD (Committee Member); Kelly Cohen, PhD (Committee Member); Asif Syed, PhD (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Combustion Instability;POD;RQL;Proper Orthogonal Decomposition;Combustion Acoustic;Rayleigh's Criterion

Driscoll, Robert BEXPERIMENTAL INVESTIGATION OF SHOCK TRANSFER AND SHOCK INITIATED DETONATION IN A DUAL PULSE DETONATION ENGINE CROSSOVER SYSTEM
MS, University of Cincinnati, 2013, Engineering and Applied Science: Aerospace Engineering
An experimental investigation was carried out to study the travel of a shockwave through a crossover tube and analyze the ability to cause shock initiated detonation. This concept involved using a pulse detonation engine (PDE) as a driver to produce a shockwave. This shockwave travelled to a second, adjacent detonation tube. In this driven PDE, the shockwave would reflect off of the inner, concaved wall causing shock initiated detonation. A preliminary study using a dual PDE crossover tube system yielded experimental results that have shown successful cases where reflected shockwaves are used to cause direct detonation initiation. For that study, two reactant-filled PDEs were connected through an air-filled crossover tube, with the driver PDE ignited. High speed pressure sensors were used to verify combustion wave speeds. Preliminary results showed shock initiated detonation to be possible when using a dual PDE crossover system. Additionally, a parametric study was carried out to investigate shock initiated detonation within a dual PDE crossover system. Shockwaves produced by a driver PDE were carried through crossover tubes of varying lengths and bends to the driven PDE. The driving PDE was ignited using a traditional spark plug. From burning wave speeds measured by high speed pressure sensors, results have shown a transferred shockwave reflecting off the wall of the driven PDE will achieve shock initiated detonation. However, the results have also yielded cases where the initial shockwave reflection does not directly initiate a detonation in the driven PDE, but rather causes ignition leading to accelerated deflagration to detonation transition (DDT). Overall results have shown that for specific tube geometries, there is a maximum effective crossover tube length in which shock initiated detonation is possible. Furthermore, shadowgraph techniques were used to capture and study the propagation of a transferred shockwave produced by a driving detonation tube. To accomplish this, a single PDE was used to drive a shockwave through a clear, composite, transfer tube. Shock attenuation data was gathered during this study. This information created a relation between shock strength and crossover tube length. Also, regardless of the filling conditions of the transfer tube, all shock waves reach similar attenuation rates at relatively the same transfer tube length. Moreover, a vortex plume study was carried out to capture and study shock Mach number decay as a planar shockwave transitions to a spherical shockwave at the exit of a transfer tube. Transfer tubes of varying lengths and bends were used in the study. General Attenuation Law was used to further understand the relation between spherical shock strength and propagation distance. Results showed that a bend placed at the end of the transfer tube enhances the strength of a planar shockwave. Finally, with the aid of the two shadowgraph experiments, a correlation between maximum effective crossover tube length and shock strength was created. Performance in the driven PDE begins to decrease when the incident shock strength decreases below M = 2.0.

Committee:

Ephraim Gutmark, Ph.D., D.Sc. (Committee Chair); David Munday, Ph.D. (Committee Member); Mark Turner, Sc.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Pulse Detonation Engine;Detonation;Crossover

Memon, Muhammad OmarCarbon Nanostructures As Thermal Interface Materials: Processing And Properties
Master of Science (M.S.), University of Dayton, 2011, Aerospace Engineering
The power density of electronic packages has substantially increased. The thermal interface resistance involves more than 50% of the total thermal resistance in current high-power packages. The portion of the thermal budget spent on interface resistance is growing because die-level power dissipation densities are projected to exceed 100 W/cm2 in near future. There is an urgent need for advanced thermal interface materials (TIMs) that would achieve order-of-magnitude improvement in performance. Carbon nanotubes and nanofibers have received significant attention in the past because of its small diameter and high thermal conductivity. The present study is intended to overcome the shortcomings of commercially used thermal interface materials by introducing a compliant material which would conform to the mating surfaces and operate at higher temperatures. Thin film “labeled buckypaper” of CNF based Materials was processed and optimized. An experimental setup was designed to test processed materials in terms of thermal impedance as a function of load and materials density, thickness and thermal conductivity. Results show that the thermal impedance decreased in conjunction with the increasing heat-treatment temperature of CNFs. TIM using heat treated CNF showed a significant decrement of 54% in thermal impedance. Numerical simulations confirmed the validity of the experimental model. A parametric study was carried out which showed significant decrement in the thermal resistance with the decrease in TIM thickness. A transient spike power was carried out using two conditions; uniform heat pulse of 24 Watts, and power spikes of 24-96 Watts. The results show that heat treated CNF was 12% more temperature resistant than direct contact with more than 50% enhancement in heat transport across it.

Committee:

Khalid Lafdi (Committee Chair); Lawrance Flach (Committee Member); Kevin Hallinan (Committee Member); Don Klosterman (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Carbon Nanofibers; Thermal Resistance; Power Spike

Rose, Isaac D.Aerodynamic Modeling of an Unmanned Aerial Vehicle Using a Computational Fluid Dynamics Prediction Code
Master of Science (MS), Ohio University, 2009, Electrical Engineering (Engineering and Technology)
The process of creating a six degree-of-freedom model for an aerospace vehicle requires detailed knowledge of the aerodynamic characteristics. This thesis presents an implementation of a Computational Fluid Dynamics (CFD) predictioncomputer code to generate aerodynamic coefficients for the Brumby Mk. I Unmanned Aerial Vehicle (UAV). The aerodynamic coefficients include both the force and moment coefficients. These values are verified by creating a Matlab/Simulink six degree-of-freedom model.

Committee:

Douglas A. Lawrence, PhD (Advisor); Jerrel Mitchell, PhD (Committee Member); Jeffrey Dill, PhD (Committee Member); William Kaufman, PhD (Committee Member)

Subjects:

Aerospace Materials; Electrical Engineering; Engineering

Keywords:

Brumby; Computational Fluid Dynamics; DATCOM; Missile DATCOM; Aerodynamic Coefficients; Aircraft Model; six degree-of-freedom model

Balagurunathan, JayakishanInvestigation of Ignition Delay Times of Conventional (JP-8) and Synthetic (S-8) Jet Fuels: A Shock Tube Study
Master of Science (M.S.), University of Dayton, 2012, Mechanical Engineering
The global depletion of petroleum-based fuels has led the world to more closely examine alternate fuels. Therefore, alternate fuels produced from feedstocks such as coal, soybeans, palm oil or switch grass through methods such as coal liquefaction, biomass gasification, and Fischer-Tropsch synthesis have been tested. Among these techniques, fuels generated using Fischer-Tropsch technologies are of interest because they produce clean burning hydrocarbons similar to those found in commercial fuels. Therefore, in this study the Fischer-Tropsch derived S-8 fuel was evaluated as a drop-in replacement for the jet fuel JP-8. The jet fuel JP-8 is comprised of n-, iso- and cyclo- alkanes as well as aromatics while the S-8 fuel is primarily comprised of n- and iso- alkanes. The composition of the fuel affects its ignition characteristics chemically and physically by either advancement or delay of time to ignition. Since this study focused on the chemical effects, the fuels were completely pre-vaporized and pre-mixed. A high pressure, high temperature heated single pulse shock tube was used for this study. The shock tube is an established experimental tool used to obtain ignition delay data behind reflected shock waves under operating conditions relevant to modern engines. The experiments were conducted over a temperature range of 1000-1600 K, a pressure of 19±2 atm, equivalence ratios of 0.5, 1 and 3, within a dwell time of 7.6±0.2 ms and an argon dilution of 93% (v/v). Ignition delay times were measured using the signal from the pressure transducer on the end plate with guidance from the optical diagnostic signal. Along with JP-8 and S-8, the ignition delay of n-heptane was also studied. N-heptane was chosen to represent the n-alkanes in the fuels for this study since it was present in both fuels and also to prove the fact that the n-alkanes were rate controlling. The results indicate that both S-8 and JP-8 fuels have similar ignition delays at corresponding equivalence ratios. The fuel-rich mixtures ignited faster at lower temperatures (<1150 K) and the fuel-lean mixtures ignited faster at higher temperatures (>1150 K). In the transition period between lower to higher temperatures (~1100-1200 K), the equivalence ratio had no significant effect on the ignition delay time. The results also show that the ignition delay time measurements of S-8 and JP-8 fuels are similar to the ignition delay of n-heptane at the equivalence ratio of Φ=0.5 and thereby indicate that the n-alkanes present in these fuels controlled the ignition under these conditions. The ignition delay results of S-8 and JP-8 at Φ=3.0 from this study were also compared to prior work (Kahandawala et al., 2008) on 2-methylheptane and n-heptane/toluene (80/20 liquid vol.%), respectively and found to be indistinguishable. This data serves to extend the gas phase ignition delay database for both JP-8 and S-8 and is the first known data taken for both these fuels at higher temperatures (>1000 K) for an equivalence ratio of 3.0 with argon as the diluent gas.

Committee:

Sukh Sidhu, Dr (Committee Chair); Philip Taylor, Dr (Committee Member); Moshan Kahandawala, Dr (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Alternative Energy; Automotive Engineering; Automotive Materials; Chemical Engineering; Chemistry; Energy; Engineering; Environmental Engineering; Mechanical Engineering; Petroleum Engineering; Technology

Keywords:

Ignition delay; shock tube; S-8; JP-8; Jet fuels; Fuel characteristics; heated shock tube; Fischer-Tropsch; Alternate fuels; alkanes; synthetic fuel; fuel; iso-alkanes; jayakishan balagurunathan

Vempati, Vamsi KrishnaISOTHERMAL DEFORMATION AND MODELING OF Ti-6Al-4V
Master of Science in Engineering (MSEgr), Wright State University, 2012, Materials Science and Engineering
Ti-6Al-4V has attractive properties such as high strength to weight ratio, good fatigue properties and excellent corrosion resistance and these properties have made this alloy an important material for the aerospace industry. In this thesis, the deformation behavior of Ti-6Al-4V with several processing histories, was studied by conducting isothermal constant strain rate compression tests over a temperature range of 829oC to 996oC (1525ºF to 1825ºF) and at strain rates of 10-2 s-1, 10-1 s-1 and 100 s-1. True stress versus true strain flow curves showed a peak stress followed by flow softening. The data was analyzed to obtain constitutive equations to describe the variation of flow stress as a function of strain, strain rate and temperature. The strain rate sensitivity values were found to increase as the temperature was increased, and the activation energy for deformation was found to be comparable to values reported in literature. Finite element simulations were carried out using the temperature corrected flow curves as input. The simulated and experimental results were found to be comparable to each other.

Committee:

Raghavan Srinivasan, PhD (Advisor); Raghavan Srinivasan, PhD (Committee Member); Sharmila Mukhopadhyay, PhD (Committee Member); Balakrishna Cherukuri, PhD (Committee Member)

Subjects:

Aerospace Materials; Materials Science

Keywords:

materials science

Ernest, Nicholas D.UAV Swarm Cooperative Control Based on a Genetic-Fuzzy Approach
MS, University of Cincinnati, 2012, Engineering and Applied Science: Aerospace Engineering

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.

Committee:

Kelly Cohen, PhD (Committee Chair); Manish Kumar, PhD (Committee Member); Bruce Walker, ScD (Committee Member)

Subjects:

Aerospace Materials

Keywords:

UAV Swarm;Cooperative Control;Genetic Algorithm;Fuzzy Logic;Traveling Salesman Problem;;

Mignee, Juliette L.Proper Orthogonal Decomposition Applied to a Supersonic Single Flow Jet
MS, University of Cincinnati, 2012, Engineering and Applied Science: Aerospace Engineering
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.

Committee:

Ephraim Gutmark, PhD DSc (Committee Chair); Mihai Mihaescu, PhD (Committee Member); Shaaban Abdallah, PhD (Committee Member); Jeffrey Kastner, PhD (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Supersonic;Jet;Decomposition;Turbulence;Structure;Flow;

Hanlon, Nicholas P.Neuro-Fuzzy Dynamic Programming for Decision-Making and Resource Allocation during Wildland Fires
MS, University of Cincinnati, 2011, Engineering and Applied Science: Aerospace Engineering

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.

Committee:

Kelly Cohen, PhD (Committee Chair); Manish Kumar, PhD (Committee Member); Grant Schaffner, PhD (Committee Member); Bruce Walker, ScD (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Resource Allocation;Decision Making;Optimal Control;Artifical Intelligence;Fuzzy Logic

Aull, Mark J.Comparison of Fault Detection Strategies on a Low Bypass Turbofan Engine Model
MS, University of Cincinnati, 2011, Engineering and Applied Science: Aerospace Engineering
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.

Committee:

Bruce Walker, ScD (Committee Chair); Kelly Cohen, PhD (Committee Member); Daniel Humpert, MS (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Fault Diagnostics;Gas Turbine;Kalman Filter;Bayesian Network;Fuzzy Logic

Kulkarni, Mandar MadhukarPrediction of Elastic Properties of a Carbon Nanotube Reinforced Fiber Polymeric Composite Material Using Cohesive Zone Modeling
MS, University of Cincinnati, 2009, Engineering : Aerospace Engineering
Fiber composite materials are ideal engineered materials to carry loads and stresses in the fiber direction due to their high in-plane specific mechanical properties. However, premature failure due to low transverse mechanical properties constitutes a fundamental weakness of composites. A solution to this problem is being addressed through the creation of a nano-reinforced laminated composite (NRLC) materials where carbon nanotubes (CNTs) are grown on the surface of the fiber filaments to improve the matrix-dominated properties. The carbon nanotubes increase the effective diameter of the fiber and provide a much larger interface area for the polymeric matrix to wet the fiber. The objective of this thesis work is to numerically predict the elastic properties of these nano-reinforced fiber composites. Finite Element Method (FEM) is used to evaluate the effective mechanical properties employing a 2D and 3D cylindrical representative volume element (RVE) based on multiscale modeling approach. In continuum mechanics, perfect bonding is assumed between the carbon fiber and the polymer matrix and between the carbon nanotubes and the polymer matrix. In the multiscale modeling approach in this work, cohesive zone approach is employed to model the interface between carbon fiber and polymer matrix and between the CNTs and the polymer matrix. Traction-displacement plots obtained from molecular dynamics simulations are used to derive the constitutive properties of the cohesive zone material model used for CNT-Polymer interface. For NRLC, the cohesive zone material model properties are assumed based on the information found in the literature. Effective material constants are extracted from the solutions of the RVE for different loading cases using theory of elasticity of isotropic and transversely isotropic materials. Experimental mechanical characterization data is used for correlation and validation of numerical results. It is observed that the cohesive zone material model is capable of capturing the interface behavioral details and provides more realistic results for the mechanical response of composite materials. Experimental results show that the potential improvement in matrix-dominated properties of the NRLC suggested by the numerical study can be realized only with the availability of improved and sophisticated NRLC fabrication techniques.

Committee:

Jandro Abot, PhD (Committee Chair); Ala Tabiei, PhD (Committee Member); Dong Qian, PhD (Committee Member)

Subjects:

Aerospace Materials; Engineering; Materials Science; Mechanics

Keywords:

Carbon Nanotubes; Composite Materials; Cohesive Zone Model; Delamination; Finite Element Method

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