Department: Aerospace Engineering ![[clear]](close-x.png "Remove this limiter")
13 matches in the database.
These are records: 1 - 13.
1.
Alford, Lionel Devon Jr.
Aerodynamic Analysis of Natural Flapping Flight Using a Lift Model Based on Spanwise Flow.
Degree: PhD, Aerospace Engineering, 2010, University of Dayton
► This study successfully described the mechanics of flapping hovering flight within the…
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▼ This study successfully described the mechanics of flapping hovering flight within the framework of conventional aerodynamics. Additionally, the theory proposed and supported by this research provides an entirely new way of looking at animal flapping flight. The mechanisms of biological flight are not well understood, and researchers have not been able to describe them using conventional aerodynamic forces. This study proposed that natural flapping flight can be broken down into a simplest model, that this model can then be used to develop a mathematical representation of flapping hovering flight, and finally, that the model can be successfully refined and compared to biological flapping data. This paper proposed a unique theory that the lift of a flapping animal is primarily the result of velocity across the cambered span of the wing. A force analysis was developed using centripetal acceleration to define an acceleration profile that would lead to a spanwise velocity profile. The force produced by the spanwise velocity profile was determined using a computational fluid dynamics analysis of flow on the simplified wing model. The overall forces on the model were found to produce more than twice the lift required for hovering flight. In addition, spanwise lift was shown to generate induceddrag on the wing. Induced drag increased both the model wing’s lift and drag. The model allowed the development of a mathematical representation that could be refined to account for insect hovering characteristics and that could predict expected physical attributes of the fluid flow. This computational representation resulted in a profile of lift and drag production that corresponds to known force profiles for insect flight. The model of flapping flight was shown to produce results similar to biological observation and experiment, and these results can potentially be applied to the study of other flapping animals. This work provides a foundation on which to base further exploration and hypotheses regarding flapping flight.
Advisors/Committee Members: Altman, Aaron.
Subjects: Animals; Biology; Engineering; Fluid dynamics; Mechanical engineering; Zoology
Keywords: flapping, insect, bird, aerodynamic, spanwise, spanwise flow, wing length, wing, hovering, hover, flight, biological flight, model of flapping flight
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2.
Atkinson, Michael D.
Control of Hypersonic High Angle-Of-Attack Re-Entry Flow Using a Semi-Empirical Plasma Actuator Model.
Degree: PhD, Aerospace Engineering, 2012, University of Dayton
► The aim of this dissertation was to explore the possibility of using…
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▼ The aim of this dissertation was to explore the possibility of using flow control to stabilize re-entry flight at very high angle-of-attack. This was carried out in three steps: 1) study the structure of representative high angle-of-attack re-entry flows; 2) develop a semi-empirical plasma actuator model that can be applied to control high angle-of-attack re-entry flows; 3) application of the plasma actuator model to study the control of representative re-entry flows. The calculations include viscous and thermochemical non-equilibrium effects, and a high-fidelity physical model to resolve complex flow structure. The contribution of this dissertation was to provide a detailed description of hypersonic viscous flow around blunt-nosed elliptical cone at very high angle-of-attack. High-fidelity, thermochemical non-equilibrium numerical solutions of high angle-of-attack re-entry flows were not published prior to this research, and thus this research can provide a foundation to calculate, analyze, and describe very high angle-of-attack hypersonic re-entry flows. Paramount to this dissertation was the development of a new phenomenological MHD plasma actuator model. A semi-empirical actuator model was developed by adding source terms to the momentum equation, vibrational energy equation, and total energy equation, employing an exponential decay function based on the formulations of Kalra et al. and Poggie. This new plasma actuator model was extended from Poggie's model to include thermochemical non-equilibrium effects and expanded from Kalra's et al. two-dimensional model to include three-dimensional effects. Development, validation, and calibration of the plasma actuator model was based on a qualitative comparison to the experiment of Kalra et al. on manipulating turbulent shock-wave/bounday layer interaction using plasma actuators. The effect of the plasma actuators on turbulent shock-wave/boundary-layer interaction was simulated numerically and a detailed description of the complex flow structure with and without actuation was provided. Finally, application of the plasma actuators to control the complex flow structure of high angle-of-attack re-entry flight vehicles was investigated. To the best of the author's knowledge, no prior research on high angle-of-attack re-entry vehicle control using plasma actuators has been published. Lastly, this dissertation serves as a foundation to compute, analyze, and control complex flow generated around re-entry vehicles at high angle-of-attack.
Advisors/Committee Members: Camberos, José A.
Subjects: Aerospace Engineering
Keywords: Hypersonic, Reentry; CFD; Plasma actuators; Flow Control; High angle of attack
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3.
Bani Younes, Ahmad Hani.
Investigation of the Flowfield Surrounding Small Photodriven Flapping Wings.
Degree: MS, Aerospace Engineering, 2009, University of Dayton
► The flowfield surrounding wings with a pure flapping motion was studied in…
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▼ The flowfield surrounding wings with a pure flapping motion was studied in quiescent air at a Reynolds number of approximately 200 using particle image velocimetry (PIV) in unusually thin illuminated planes (~0.3 mm). Typical wing semi-spans were on the order of a few millimeters. The polymer cantilever wings consisting of monodomain liquid crystal polymers made from azobenzene (azo-LCN) were flapped at 30 Hz at a large amplitude (>170°). Chordwise and spanwise planar slices of the flow across the wings were obtained and used to estimate the unsteady aerodynamic forces generated by the flapping wings. This study focuses on the flapping flight of small-scale wings in order to visualize the flowfield characteristics. The small-scale wings were, indeed, able to induce the surrounding flowfield and generate aerodynamic contribution, which was clearly observed in spanwise plane. Images at various spanwise and chordwise locations were acquired and processed. In terms of results, the spanwise flow was the dominant. The chordwise results were not conclusive useful due to the poor light filtering. The PIV displacement and velocity uncertainties were small quantitatives compared to the vorticity and circulation uncertainties.
Advisors/Committee Members: Altman, Aaron.
Subjects: Aerospace materials
Keywords: Particle Image velocimetry (PIV); Flapping Wing; Photodriven flapper; Liquid Crystal Polymer; Flow visualization; Spanwise Flow; Vortex Flow
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4.
Geyman, Matthew Kenneth.
Wing/Wall Aerodynamic Interactions in Free Flying, Maneuvering MAVs.
Degree: MS, Aerospace Engineering, 2012, University of Dayton
► Micro Air Vehicles (MAVs) are small remotely piloted air vehicles that can…
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▼ Micro Air Vehicles (MAVs) are small remotely piloted air vehicles that can be flown between or inside of buildings for military or surveillance purposes. This type of flight in the urban environment involves many aerodynamic hazards. The research in this thesis investigates how the aerodynamic interactions between a maneuvering MAV’s wingtip vortex and its distance away from a building wall could affect the MAV’s flight controls. Free flight particle image velocimetry (PIV) testing and wind tunnel testing are used to investigate the aerodynamic interactions between a MAV wingtip vortex and a wall. Elliptical instabilities and a vortex rebound off of the wall are discovered in the PIV testing while the wind tunnel results show a higher aircraft coefficient of lift near the wall. All of these results force the aircraft to experience a rolling motion while flying along a wall. It is imperative that a MAV anticipate this motion and adjust its flight controls in order to accurately fly along a wall and successfully complete its mission in an urban environment.
Advisors/Committee Members: Altman, Aaron.
Subjects: Aerospace Engineering
Keywords: MAV; UAV; aerodynamics; wall effect; wingtip vortex; PIV; wind tunnel; micro air vehicle; vicon
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5.
Hammer, Patrick Richard.
A Discrete Vortex Method Application to Low Reynolds Number Aerodynamic Flows.
Degree: MS, Aerospace Engineering, 2011, University of Dayton
► Although experiments and CFD are very powerful tools in analyzing a niche…
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▼ Although experiments and CFD are very powerful tools in analyzing a niche of fluid dynamics problems relevant to developing Micro Aerial Vehicles (MAVs), reduced order methods have shown to be very capable in helping researchers achieve a basic understanding of flow physics with application to highly iterative design processes due to the less computationally expensive nature of the low order models. The current study used one low order method, the Discrete Vortex Method, to model the aerodynamic flow fields and forces around a thin airfoil undergoing a variety of flows, as well as parametric studies to determine the important factors that had to be adjusted to make the results more representative of the physical phenomenon being modeled. Initial investigations validated the code’s use in steady flow and low amplitude unsteady flow cases by comparing it with circulation distributions of various airfoil shapes, the Wagner function, and Theodorsen’s function. The results showed a strong dependency on bound vortex number and time step size. The code was then used to capture the flow behavior around the airfoil for various AIAA Fluid Dynamics Technical Committee Low Reynolds iv Number Working Group (FDTC-LRWG) canonical cases. Implementing the Uhlman method in the Discrete Vortex Method allowed for the calculation of the pressure at the airfoil surface and in the flow field during high angle attack maneuvers. This method proved very capable in calculating the pressures, forces, and force coefficients around the airfoil post-flow separation in the canonical cases where other methods (such as the Unsteady Bernoulli Method) fall short. The code was also tuned with respect to the results with respect to vortex size, leading edge separation strength factor, desingularization function, wake radius size factor, and in the Uhlman method itself to yield an optimal comparison with experimental and CFD results. The study found a bound vortex number of 30, a leading edge separation strength factor of 1.0, the planetary desingularization function, a wake radius size factor of 1.0, and using just the volume integral term on the RHS of the Uhlman method gave the best results for the geometry analyzed. An investigation then determined the dependency of reduced frequency on the lift and drag coefficients for the canonical cases. Finally, the code was used to model a “true perch” by implementing a curve fit function which caused the horizontal free stream velocity to decrease to zero. In this context, the forces were of more interest than the force coefficients since the coefficients experienced anomalous behavior as the free stream velocity approached zero. It was also interesting to find that the code modeled behavior very similar to shear layer instabilities in the LE and TE shear layers, caused by a rippling effect as the bound circulation changed in strength and sign as the LEV and TEV interacting with it. Recommendations were then made to apply the code to airfoils with either fixed or variable camber since camber acts as a high lift device and could prove very beneficial in the design and development of MAVs
Advisors/Committee Members: Altman, Aaron.
Subjects: Aerospace Engineering; Fluid Dynamics; Mechanical Engineering
Keywords: Unsteady Aerodynamics; High Angle of Attack; Discrete Vortex Method; Vortex Particle Method; Perching
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6.
Johnson, Douglas James.
Carbon Foam Infused with Pentaglycerine for Thermal Energy Storage Applications.
Degree: MS, Aerospace Engineering, 2011, University of Dayton
► A thermal energy storage device that uses pentaglycerine as a phase change…
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▼ A thermal energy storage device that uses pentaglycerine as a phase change material was developed. This solid-state phase change material was embedded in a carbon foam thermal conduction enhancer. This device and others identically constructed but using a paraffin phase change material were tested by imposing different input fluxes, 2.3 or 6.0 W/cm2 on one end, while the opposite end was either insulated or actively cooled with an output flux that varied from 3.1 to 5.4 W/cm2. The resulting temperature distributions within the devices were recorded at five locations; this information was used to determine the specific energy storage capacity, heating rate and the cycling performance of each device. It was found that the pentaglycerine/foam combination is capable of a specific storage capacity of 67 J/g; it demonstrated a storage capacity 174% of the paraffin/foam device, by eliminating the volume change and leakage problems associated with solid-liquid phase change materials.
Advisors/Committee Members: Ervin, Jamie S.
Subjects: Aerospace Engineering; Aerospace Materials; Engineering; Materials Science
Keywords: carbon foam; pentaglycerine; solid-solid; phase change; thermal energy storage
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7.
Landolfo, Giuseppe.
Aerodynamic and Structural Design of a Small Nonplanar Wing UAV.
Degree: MS, Aerospace Engineering, 2008, University of Dayton
► The overall air vehicle performance of a multiple lifting surface configuration has…
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▼ The overall air vehicle performance of a multiple lifting surface configuration has been studied with respect to both structural and aerodynamic considerations for a candidate mission similar to that of the AeroVironment Raven. The configuration studied is a biplane joined at the tips with endplates. More specifically, this study aims to determine if this particular nonplanar wing concept can meet the requirements of the mission for a small Reconnaissance, Surveillance and Target Acquisition UAV. The mission capabilities of small UAVs are constantly growing by implementing recent developments in miniature computers and peripherals, electronic sensors, and optical sensing equipment at affordable cost. The requirements for the mission profile of a small UAV using the aforementioned equipment are defined with an emphasis on the potential advantages that can be offered by the nonplanar concept wing under investigation. A structural analysis using the finite element software ADINA and an aerodynamic analysis based on wind tunnel experimental data and vortex panel code results are performed. The results, compared under varying assumptions specific to an equivalent monoplane and a biplane, suggest potential efficiency gains for the new configuration may be possible using the nonplanar wing configuration under explicit conditions. The results also show structural characteristics and not aerodynamics alone are critical in determining the utility of this nonplanar concept.
Advisors/Committee Members: Altman, Aaron.
Subjects: Engineering
Keywords: Aerospace; aircraft design; aerodynamics; structural analysis; UAV; unmanned aircraft; biplane
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8.
Memon, Muhammad Omar.
Carbon Nanostructures As Thermal Interface Materials: Processing And Properties.
Degree: MS, Aerospace Engineering, 2011, University of Dayton
► The power density of electronic packages has substantially increased. The thermal interface…
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▼ 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.
Advisors/Committee Members: Lafdi, Khalid.
Subjects: Aerospace Materials
Keywords: Carbon Nanofibers; Thermal Resistance; Power Spike
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9.
Morris, Seth Henderson.
Quasi-Transient Calculation of Surface Temperatures on a Reusable Booster System with High Angles of Attack.
Degree: MS, Aerospace Engineering, 2011, University of Dayton
► The calculation of a recovery temperature based heat transfer coefficient proves to…
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▼ The calculation of a recovery temperature based heat transfer coefficient proves to be sufficiently independent of wall temperature to use in a three dimensional, transient temperature model of a thermal protection system of a reusable booster concept. After a derivation of recovery temperature from the 1st law of thermodynamics, the weak dependence of the recovery temperature based heat transfer coefficient is investigated by 72 Computational Fluid Dynamics (CFD) models at angles of attack ranging from 0° to 90° over a range of Mach numbers, from Mach 2 to 5, and a variety of thermal boundary conditions at the wall, from isothermal to a conductive wall. Then, the heat transfer coefficient is calculated at many steady state CFD solutions for a reusable booster system concept on a given trajectory and applied to a transient Finite Element Analysis (FEA) model of a thermal protection system. Results are presented graphically.
Advisors/Committee Members: Fry, Timothy J.
Subjects: Aerospace Engineering; Atmosphere; Computer Science; Fluid Dynamics; High Temperature Physics; Mechanical Engineering
Keywords: quasi; transient; heat; transfer; coefficient; hypersonic; CFD; computational; fluid; dynamics; thermodynamic; FEA; steady; state; recovery; temperature; reusable; booster; system; high; speed; computing; super; computer; kinetic; energy
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10.
O'Neil, Alanna R.
Chemiluminescence and High Speed Imaging of Reacting Film Cooling Layers.
Degree: MS, Aerospace Engineering, 2011, University of Dayton
► The demand for more efficient and compact gas turbine engines has resulted…
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▼ The demand for more efficient and compact gas turbine engines has resulted in an increase in the operating temperatures and pressures and a decrease in combustor weight and size. These advances may result in incomplete combustion products entering the turbine section. The products can react with the air intended to cool the turbine vanes, and the resulting flame can cause damage to the engine. This study reports chemiluminescence measurements of flames and correlates these to heat release rate and the measured heat flux to a surface. To accomplish this, fuel rich combustion products are generated in a well-stirred reactor. The flow of products is directed over a flat plate with cooling air jets normal to the flow. Chemiluminescence data of the flames is obtained, along with high speed images, and temperature measurements of the flow inside the test section. Three film cooling geometries are studied: normal holes, fan shaped holes, and slot. Measurements are acquired at three equivalence ratios (1.3, 1.4, and 1.5) at three different blowing ratios (M = 1, 4, and 7). It is found that the rate of heat release from the flame does not always trend the same as the heat transfer to the surface. It is also seen that a large reaction region does not always equate to high heat flux to the surface. If enough cooling air is present the surface is protected from the heat released from the flame.
Advisors/Committee Members: Ballal, Dilip.
Subjects: Aerospace Engineering
Keywords: Film Cooling; Chemiluminescence; Reacting Boundary Layers; Flames; Image Analysis
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11.
Ross, Ian Jonathan.
Wind Tunnel Blockage Corrections: An Application to Vertical-Axis Wind Turbines.
Degree: MS, Aerospace Engineering, 2010, University of Dayton
► An investigation into wake and solid blockage effects of Vertical-Axis Wind Turbines…
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▼ An investigation into wake and solid blockage effects of Vertical-Axis Wind Turbines (VAWTs) in closed test-section wind tunnel testing is described. Static wall pressures have been used to derive velocity increments along a wind tunnel test-section which in-turn are applied to provide evidence of wake interference characteristics of rotating bodies interacting within this spatially restricted domain. Vertical-axis wind turbines present a unique aerodynamic obstruction in wind tunnel testing whose blockage effects have not been extensively investigated.The flow-field surrounding these wind turbines is asymmetric, periodic, unsteady, separated and highly turbulent. Static pressure measurements are taken along a test-section sidewall to provide a pressure signature of the test models under varying rotor tip-speed ratios (freestream conditions and model RPM’s). To provide some guidance on the scaling of the combined effects of wake and solid blockage, wake characteristics and VAWT performance produced by the same vertical-axis wind turbine concept have been tested at different physical scales in two different wind tunnels. This investigation provides evidence of the effects of large wall interactions and wake propagation caused by these models at well below generally accepted standard blockage figures.
Advisors/Committee Members: Altman, Aaron.
Subjects: Aerospace materials; Engineering; Experiments; Fluid dynamics; Mechanical engineering
Keywords: Low Speed Wind Tunnel; Wind Tunnel Blockage Corrections; Vertical-Axis Wind Turbine; Aerodynamics; Bluff-Body Aerodynamics; Savonius
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12.
Stanley, Daniel C.
Experiments in Vortex Formation of Plunging & Flapping Flat Plates.
Degree: MS, Aerospace Engineering, 2008, University of Dayton
► Reynolds number, Strouhal number, and formation number are insufficient to quantify the…
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▼ Reynolds number, Strouhal number, and formation number are insufficient to quantify the flow properties of a flapping wing system. These parameters do not take enough information from the input variables into account. As part of the current study, the velocity profile and angle of attack were varied during a single pure plunge flapping stroke using an infinite aspect ratio flat plate. Although the velocity profile was either a constant velocity or quarter-sine velocity, the average Reynolds number was held constant at 3000. Strong differences in the flow structure, both qualitatively and quantitatively, were obtained. A new metric is proposed that is able to take these differences in the input variables into account. This metric utilizes the theory of maximum work potential and statistical regressions of the experimental data in order to obtain a model of the experimental parameter space. With this model, estimates of the desired outputs can be made given values for the inputs.The main portion of this study focuses on the differences in flow structure, using qualitative and quantitative techniques, due to finite aspect ratio and flapping about a hinge point. Data at various spanwise and chordwise locations were taken in order to analyze the leading edge, trailing edge, and tip vortices. A small study was also conducted on the effects of changing Reynolds number. It was found that for the infinite aspect ratio plate, using a quarter-sine velocity profile, instead of a constant velocity profile, enhances the production of circulation. Operating at a slight angle of attack (85° instead of 90°) also enhances circulation production; however, operating at a large angle of attack (60° instead of 90°) has the opposite effect due to pinch-off of both the leading and trailing edge vortices. Hinging the wing at the root and using a finite aspect ratio causes the constant velocity profile to produce higher values of circulation than the quarter-sine velocity profile. This trend is the opposite of that seen for the infinite aspect ratio cases. It was also found that flapping in this highly three-dimensional manner greatly hinders the production of circulation as compared to the infinite aspect ratio, pure plunge experiments.
Advisors/Committee Members: Altman, Aaron.
Subjects: Fluid dynamics
Keywords: vortex formation; low Reynolds number fluid dynamics; formation parameter; formation time; formation number
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13.
Thompson, Ernest.
Incorporation of Computational Fluid Dynamics into Flight Vehicle Preliminary Design.
Degree: PhD, Aerospace Engineering, 2012, University of Dayton
► Nonlinear, high fidelity aerodynamic analysis methods are considered computationally expensive and impractical…
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▼ Nonlinear, high fidelity aerodynamic analysis methods are considered computationally expensive and impractical for use in the preliminary design environment. In lieu of nonlinear methods, linear aerodynamic methods are utilized in the execution of design tasks because of their computational efficiency. Linear codes are considered accurate in low Mach number flight regimes where aerodynamics is generally linear but are not accurate in transonic flight regime due to the simplified assumptions that are required by such codes. This investigation demonstrates that nonlinear aerodynamic analysis methods are necessary when performing design tasks in the presence of nonlinear phenomena. To reduce the cost of using nonlinear aerodynamic analysis, the velocity transpiration boundary condition was employed to simulate surface deformations and control surface deflections. Observations showed velocity transpiration offers significant computational savings when compared to mesh motion enabled codes. To improve turnaround, a distributed computing framework wasadopted to distribute workload and information storage across a network. A comparative design study was carried out comparing linear and nonlinear analysis tools in design. A rectangular wing's structural mass was optimized to perform both a roll and pull-up maneuver while subjected to rolleffectiveness and skin stress constraints. At a subsonic design point, the linear and nonlinear tools produced similar designs. However, at a transonic design point, the tools produced significantly different designs. The addition of aerodynamic shape variables to the design space at the transonic design point led to a further enhanced design. The results of this study reaffirm the notion that nonlinear high-fidelity aerodynamic analysis methods must be utilized when designing vehicles that will operate in nonlinear regimes. Further, several methods were demonstrated that could reduce the cost of using nonlinear analysis methods.
Advisors/Committee Members: Eastep, Franklin.
Subjects: Aerospace Engineering
Keywords: Air Vehicle Design
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