Masters Theses

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3D Simulator for Wind Interferometer Data-Model Comparison
Huda, Md Nurul (Virginia Tech, 2019-09-27)
The connection between earth and space weather has numerous impacts on spacecraft, radio communications and GPS signals. Thus, predicted & modeling this region is important, yet models (both empirical and first principles) do a poor job of characterizing the variability of this region. One of the main objectives of the NASA ICON mission is to measure the variability of the ionosphere and thermosphere at low-mid latitudes. The MIGHTI instrument on ICON is a Doppler Interferometer that measures the horizontal wind speed and direction with 2 discrete MIGHTI units, separated by 90˚, mounted on the ICON Payload Interface Plate. This work focuses on building a simulation of wind interferometer data, similar to MIGHTI, using a first-principles model as the input dataset, which will be used for early validation and comparison to the MIGHTI data. Using a ray-tracing approach, parameters like O, O2, O+, O2+, T, wind, solar F10.7 index will be read for every point along every ray from the model and brightness and Line of Sight (LOS) wind will be calculated as functions of altitude and time. These data will be compared to the MIGHTI observations to both to establish the limitation of such models, and to validate the ICON data. ICON will help determine the physics of our space environment and pave the way for mitigating its effects on our technology, communications systems and society. However, ICON is yet to launch and due to the unavailability of MIGHTI data, we have selected another instrument called WINDII (Wind Imaging Interferometer) from a different mission UARS (Upper Atmosphere Research Satellite) to demonstrate the utility of this data-model comparison. Similar to MIGHTI, WINDII measures Doppler shifts from a suite of visible region airglow and measures zonal and meridian winds, temperature, and VER (Volume Emission rate) in the upper mesosphere and lower thermosphere (80 to 300 km) from observations of the Earth's airglow. We will use a similar approach discussed for MIGHTI to calculate vertical profile of Redline airglow, Wind velocity, emission rate and compare them with our simulated results to validate our algorithm. We initially thought asymmetry calculation along the Line of Sight (LOS) would be the limiting factor. We believe there are other things going on such as variability in the winds associated with natural fluctuations in the thermosphere, atmospheric waves, inputs from the sun and the atmosphere below etc., appear to be bigger factor than just asymmetry along the line of sight.
A* Node Search and Nonlinear Optimization for Satellite Relative Motion Path Planning
Connerney, Ian Edward (Virginia Tech, 2021-11-03)
The capability to perform rendezvous and proximity operations about space objects is central to the next generation of space situational awareness. The ability to diagnose and respond to spacecraft anomalies is often hampered by the lack of capability to perform inspection or testing on the target vehicle in flight. While some limited ability to perform inspection can be provided by an extensible boom, such as the robotic arms deployed on the space shuttle and space station, a free-flying companion vehicle provides maximum flexibility of movement about the target. Safe and efficient utilization of a companion vehicle requires trajectories capable of minimizing spacecraft resources, e.g., time or fuel, while adhering to complex path and state constraints. This paper develops an efficient solution method capable of handling complex constraints based on a grid search A* algorithm and compares solution results against a state-of-the-art nonlinear optimization method. Trajectories are investigated that include nonlinear constraints, such as complex keep-out-regions and thruster plume impingement, that may be required for inspection of a specific target area in a complex environment. This work is widely applicable and can be expanded to apply to a variety of satellite relative motion trajectory planning problems.
Acoustic Analysis of Spacecraft Cavities using the Boundary Element Method
Marshall, Peter Johannes (Virginia Tech, 2018-06-05)
Spacecraft structures are subject to a series of load environments during their service life, with the most severe of these occurring during the spacecraft's launch and ascension through the atmosphere. In particular, acoustic loads imposed on stowed satellites within the launch vehicle fairing can result in high mechanical loads on sensitive spacecraft hardware. These acoustic loads have the potential to damage important components and as such it is necessary to accurately characterize and predict the acoustic launch environment for a given mission. This research investigates the Sound Pressure Level (SPL) that can be measured in and around spacecraft cavities resulting from a known excitation and the resultant structural responses. Linear finite element analysis (FEA) is coupled with the Boundary Element method (BEM) to analyze spacecraft acoustic environments and corresponding structural responses at low frequencies on the order of the structural modes. Analytical capability for predicting acoustic environments inside the launch vehicle has improved significantly in recent years; however, while it is easy to perform an analysis and obtain results, the modeling effort can become unnecessarily complicated and analytical data can be hard to interpret. This work seeks to alleviate unnecessary complexity in the low-frequency regime of acoustic modeling by examining the fundamentals of coupled BEM-FEM analysis and applying simplification to a spacecraft model where possible to achieve results verified against direct field acoustic testing (DFAT) methods.
Active and Passive Flow Control over the Flight Deck of Small Naval Vessels
Shafer, Daniel Manfred (Virginia Tech, 2005-04-27)
Helicopter operations in the vicinity of small naval surface vessels often require excessive pilot workload. Because of the unsteady flow field and large mean velocity gradients, the envelope for flight operations is limited. This experimental investigation uses a 1:144 scale model of the U.S. Navy destroyer DDG-81 to explore the problem. Both active and passive flow control techniques were used to improve the flow field in the helicopter's final decent onto the flight deck. Wind tunnel data was collected at a set of grid points over the ship's flight deck using a single component hotwire. Results show that the use of porous surfaces decreases the unsteadiness of the flow field. Further improvements are found by injecting air through these porous surfaces, causing a reduction in unsteadiness in the landing region of 6.6% at 0 degrees wind-over-deck (WOD) and 8.3% at 20 degrees WOD. Other passive configurations tested include fences placed around the hangar deck edges which move the unsteady shear layer away from the flight deck. Although these devices cause an increase in unsteadiness downstream of the edge of the fence when compared to the baseline, the reticulated foam fence caused an overall decrease in unsteadiness in the landing region of 12.1% at 20 degrees WOD.
Active Flow Control of a Boundary Layer Ingesting Serpentine Diffuser
Harrison, Neal A. (Virginia Tech, 2005-07-13)
The use of serpentine boundary layer ingesting (BLI) diffusers offers a significant benefit to the performance of Blended Wing Body aircraft. However, the inherent diffuser geometry combined with a thick ingested boundary layer creates strong secondary flows that lead to severe flow distortion at the engine face, increasing the possibility of engine surge. This study investigated the use of enabling active flow control methods to reduce engine-face distortion. An ejector-pump based system of fluidic actuators was used to directly manage the diffuser secondary flows. This system was modeled computationally using a boundary condition jet modeling method, and tested in an ejector-driven wind tunnel facility. This facility is capable of simulating the high-altitude, high subsonic Mach number conditions representative of BWB cruise conditions, specifically a cruise Mach number of 0.85 at an altitude of 39,000 ft. The tunnel test section used for this experiment was designed, built, and tested as a validation tool for the computational methods. This process resulted in the creation of a system capable of efficiently investigating and testing the fundamental mechanisms of flow control in BLI serpentine diffusers at a minimum of time and expense. Results of the computational and wind tunnel analysis confirmed the large potential benefit of adopting fluidic actuators to control flow distortion in serpentine BLI inlets. Computational analysis showed a maximum 71% reduction in flow distortion at the engine face through the use of the Pyramid 1 ejector scheme, and a 68% reduction using the Circumferential ejector scheme. However, the flow control systems were also found to have a significant impact on flow swirl. The Pyramid 1 ejector scheme was found to increase AIP flow swirl by 64%, while the Circumferential ejector scheme reduced flow swirl by 30%. Computational analyses showed that this difference was the result of jet interaction. By keeping the jet flows separate and distinct, the diffuser secondary flows could be more efficiently managed. For this reason, the most practically effective flow control scheme was the Circumferential ejector scheme. Experimental results showed that the computational analysis slightly over-predicted flow distortion. However, the trends are accurately predicted despite slight variances in freestream Mach number between runs and a slightly lower tested altitude.
Actuator-Work Concepts Applied to Morphing and Conventional Aerodynamic Control Devices
Johnston, Christopher Owen (Virginia Tech, 2003-11-14)
The research presented in this thesis examines the use of an estimated "actuator work" value as a performance parameter for the comparison of various aerodynamic control device configurations. This estimated "actuator work," or practical work as it will be referred to as in this thesis, is based on the aerodynamic and structural resistance to a control surface deflection. It is meant to represent the actuator energy cost required to deflect a general configuration of conventional or unconventional control surface. Thin airfoil theory is used to predict the aerodynamic load distribution required for this work calculation. The details of applying thin airfoil theory to many different types of control surface arrangements are presented. Convenient equations for the aerodynamic load distributions and aerodynamic coefficients are obtained. Using the developed practical work equations, and considering only the aerodynamic load component, the practical work required for a given change in lift is compared between different control surface arrangements. For single control surface cases, it is found that a quadratic (morphing) trailing edge flap requires less practical work than a linear flap of the same size. As the angle of attack at which the change in lift occurs increases, the benefit of the quadratic flap becomes greater. For multiple control surface cases, it is necessary to determine the set of control deflections that require the minimum practical work for a given change in lift. For small values of the initial angle of attack, it is found that a two-segment quadratic trailing edge flap (MTE) requires more work than a two-segment linear flap (TETAB). But, above a small value of angle of attack, the MTE case becomes superior to the TETAB case. Similar results are found when a 1-DOF static aeroelastic model is included in the calculation. The minimum work control deflections for the aeroelastic cases are shown to be strongly dependent on the dynamic pressure.
Adaptive Control of Nonaffine Systems with Applications to Flight Control
Young, Amanda (Virginia Tech, 2006-05-05)
Traditional flight control design is based on linearization of the equations of motion around a set of trim points and scheduling gains of linear (optimal) controllers around each of these points to meet performance specifications. For high angle of attack maneuvers and other aggressive flight regimes (required for fighter aircraft for example), the dynamic nonlinearities are dependent not only on the states of the system, but also on the control inputs. Hence, the conventional linearization-based logic cannot be straightforwardly extended to these flight regimes, and non-conventional approaches are required to extend the flight envelope beyond the one achievable by gain-scheduled controllers. Due to the nonlinear-in-control nature of the dynamical system in aggressive flight maneuvers, well-known dynamic inversion methods cannot be applied to determine the explicit form of the control law. Additionally, the aerodynamic uncertainties, typical for such regimes, are poorly modelled, and therefore there is a great need for adaptive control methods to compensate for dynamic instabilities. In this thesis, we present an adaptive control design method for both short-period and lateral/directional control of a fighter aircraft. The approach uses a specialized set of radial basis function approximators and Lyapunov-based adaptive laws to estimate the unknown nonlinearities. The adaptive controller is defined as a solution of fast dynamics, which verifies the assumptions of Tikhonov's theorem from singular perturbations theory. Simulations illustrate the theoretical findings.
Adaptive Flight Control in the Presence of Input Constraints
Ajami, Amir Farrokh (Virginia Tech, 2005-12-02)
Aerospace systems such as aircraft or missiles are subject to environmental and dynamical uncertainties. These uncertainties can alter the performance and stability of these systems. Adaptive control offers a useful means for controlling systems in the presence of uncertainties. However, very often adaptive controllers require more control effort than the actuator limits allow. In this thesis the original work of others on single input single output adaptive control in the presence of actuator amplitude limits is extended to multi-input systems. The Lyapunov based stability analysis is presented. Finally, the resultant technique is applied to aircraft and missile longitudinal motion. Simulation results show satisfactory tracking of the states of modified reference system.
Addition of Features to an Existing MDO Model for Containerships
Dasgupta, Amlan (Virginia Tech, 2001-05-10)
Traditionally, the "Design Spiral" is used for the design of ships. The design spiral endorses the concept that the design process is sequential and iterative. Though this procedure was very effective over the years, the current trend of engineering demands that more stress be put on the exploration of optimum design. With the advancement of computing technologies, the onus has shifted from finding better calculation schemes to formulating an economically viable design scheme. One of the objects of the FIRST project funded by MARITECH was to develop a computer tool to give the best ship design using optimization techniques. This was entrusted to the Department of Aerospace and Ocean Engineering at Virginia Polytechnic Institute and State University in Blacksburg, Virginia. A container ship was chosen as the test case. The problem was tackled from an owner's point of view. Hence, the required freight rate was chosen as the objective. To achieve that goal, the team developed a package that consists of three modules: optimization, geometric and a performance evaluation module. Though these modules are essentially independent, the user has control over an overall manager. He can change the initial value of design parameters, set bounds and vary constraint bounds as per his needs. Though he does not know what goes on behind the user interface, he still feels secure with the design process because he has overall control. This sense of security breaks down when he has access to limited variables and constraints. A prototype MDO tool is developed based on Microsoft's COM framework using ATL. With this design, the modules can be modified with minimum programming effort. The user interface gives the user flexibility to manipulate relevant parameters that affect the design. A geometric shape manipulation scheme is developed in which the hull form was generated by blending two hull forms. This MDO tool is used to design a container ship with the required freight rate as the objective to be minimized. It is noticed that without a structural constraint, the design tends towards one with maximum length and beam. This led to unreasonably large ratios of B/D and L/D. A B/D constraint is applied to the design to get a better structural design. Results with this constraint enabled have pointed in the direction of adding two other design variables. This constraint increases the depth of the ship. With the increase in depth, the center of gravity of the ship also rises decreasing the GM of the ship. This lowering of GM adversely affects the GM constraint. The number of tiers on deck (NTd) is made a design variable to enable the optimizer to have the flexibility of manipulating the cargo carrying capacity. It was noticed that the ship is unable to have a high NTd because of the violation of the GM constraint. Hence, ballast has also been added as a design variable to reduce the center of gravity of the ship increasing the GM of the ship. This feature enables the optimizer to carry greater cargo on deck improving the objective function. An effort is made to analyze the efficacy of the MDO tool by varying various parameters that affect the design. Technology factors have been introduced which give an insight on effect of key parameters. They also reflect on future design trends. Three evaluation tools: sensitivity analysis, alpha plots and restart option have been incorporated in the design process to gauge the results of optimization. The effect of another structural constraint L/D was also investigated. This constraint tends to bring down the overall length and is inconclusive in its results. Further analysis of this constraint is needed to draw usable conclusions. The linear response surface approximation was eliminated and the original stepwise discontinuous TEU capacity function is employed in the later examples. It was found that the minimum of the required fright rate occurred at the lower limits of length and beam on each TEU capacity platform. A systematic search of TEU plateaus in the vicinity of the primary optimum was necessary to define the secondary optimum
Advancements in the Design and Development of CubeSat Attitude Determination and Control Testing at the Virginia Tech Space Systems Simulation Laboratory
Wolosik, Anthony Thomas (Virginia Tech, 2018-09-07)
Among the various challenges involved in the development of CubeSats lies the attitude determination and control of the satellite. The importance of a properly functioning attitude determination and control system (ADCS) on any satellite is vital to the satisfaction of its mission objectives. Due to this importance, three-axis attitude control simulators are commonly used to test and validate spacecraft attitude control systems before flight. However, these systems are generally too large to successfully test the attitude control systems on-board CubeSat-class satellites. Due to their low cost and rapid development time, CubeSats have become an increasingly popular platform used in the study of space science and engineering research. As an increasing number of universities and industries take part in this new approach to small-satellite development, the demand to properly test, verify, and validate their attitude control systems will continue to increase. An approach to CubeSat attitude determination and control simulation is in development at the Virginia Tech Space Systems Simulation Laboratory. The final test setup will consist of an air bearing platform placed inside a square Helmholtz cage. The Helmholtz cage will provide an adjustable magnetic field to simulate that of a low earth orbit (LEO), and the spherical air bearing will simulate the frictionless environment of space. In conjunction, the two simulators will provide an inexpensive and adjustable system for testing any current, and future, CubeSat ADCS prior to flight. Using commercial off the shelf (COTS) components, the Virginia Tech CubeSat Attitude Control Simulator (CSACS), which is a low cost, lightweight air bearing testing platform, will be coupled with a 1.5-m-long square Helmholtz cage design in order to provide a simulated LEO environment for CubeSat ADCS validation.
Aerodynamic Analysis of Variable Geometry Raked Wingtips for Mid-Range Transonic Transport Aircraft
Jingeleski, David John (Virginia Tech, 2012-12-21)
Previous applications have shown that a wingtip treatment on a commercial airliner will reduce drag and increase fuel efficiency and the most common types of treatment are blended winglets and raked wingtips. With Boeing currently investigating novel designs for its next generation of airliners, a variable geometry raked wingtip novel control effector (VGRWT/NCE) was studied to determine the aerodynamic performance benefits over an untreated wingtip. The Boeing SUGAR design employing a truss-braced wing was selected as the baseline. Vortex lattice method (VLM) and computational fluid dynamics (CFD) software was implemented to analyze the aerodynamic performance of such a configuration applied to a next-generation, transonic, mid-range transport aircraft. Several models were created to simulate various sweep positions for the VGRWT/NCE tip, as well as a baseline model with an untreated wingtip. The majority of investigation was conducted using the VLM software, with CFD used largely as a validation of the VLM analysis. The VGRWT/NCE tip was shown to increase the lift of the wing while also decreasing the drag. As expected, the unswept VGRWT/NCE tip increases the amount of lift available over the untreated wingtip, which will be very beneficial for take-off and landing. Similarly, the swept VGRWT/NCE tip reduced the drag of the wing during cruise compared to the unmodified tip, which will favorably impact the fuel efficiency of the aircraft. Also, the swept VGRWT/NCE tip showed an increase in moment compared to the unmodified wingtip, implying an increase in stability, as well providing an avenue for roll control and gust alleviation for flexible wings. CFD analysis validated VLM as a useful low fidelity tool that yielded quite accurate results. The main results of this study are tabulated "deltas" in the forces and moments on the VGRWT/NCE tip as a function of sweep angle and aileron deflection compared to the baseline wing. A side study of the effects of the joint between the main wing and the movable tip showed that the drag impact can be kept small by careful design.
An Aerodynamic Model for Use in the High Angle of Attack Regime
Stagg, Gregory A. (Virginia Tech, 1998-12-02)
Harmonic oscillatory tests for a fighter aircraft using the Dynamic Plunge--Pitch--Roll model mount at Virginia Tech Stability Wind Tunnel are described. Corresponding data reduction methods are developed on the basis of multirate digital signal processing. Since the model is sting mounted, the frequencies associated with sting vibration are included in balance readings thus a linear filter must be used to extract out the aerodynamic responses. To achieve this, a Finite Impulse Response (FIR) is designed using the Remez exchange algorithm. Based on the reduced data, a state–space model is developed to describe the unsteady aerodynamic characteristics of the aircraft during roll oscillations. For this model, we chose to separate the aircraft into panels and model the local forces and moments. Included in this technique is the introduction of a new state variable, a separation state variable which characterizes the separation for each panel. This new variable is governed by a first order differential equation. Taylor series expansions in terms of the input variables were performed to obtain the aerodynamic coefficients of the model. These derivatives, a form of the stability derivative approach, are not constant but rather quadratic functions of the new state variable. Finally, the concept of the model was expanded to allow for the addition of longitudinal motions. Thus, pitching moments will be identified at the same time as rolling moments. The results show that the goal of modeling coupled longitudinal and lateral–directional characteristics at the same time using the same inputs is feasible.
Aerodynamic Properties of the Inboard Wing Concept
Orr, Matthew William (Virginia Tech, 2003-12-19)
This investigation examines a new concept in airliner configurations from an experimental aerodynamics point of view. The concept proposes mounting the fuselages at the tips of a low aspect ratio wing. The motivation for this configuration is to provide an increase in the number of passengers carried with no increase in span over conventional designs. An additional motivation is the change in the wake flow of the wing, due to the fuselages and vertical tails, which may reduce the effect of the trailing vortex on trailing aircraft. During this investigation, two models of different scales were used to measure the aerodynamic forces and moments of the inboard wing configuration. The tests were conducted in the Virginia Tech 6X6 ft. wind tunnel using a six-component strain gauge balance. The Reynolds number based on chord for the small model was 465,000 and for the large model was 1,225,000. For reference, tests were also conducted with a plain wing having the same span as the full configuration. The L/D values found for this non-optimized configuration were modest compared to those for conventional transports. The vertical tails were shown to act as winglets, reducing drag and increasing L/D. These results suggest areas for substantial improvement in aerodynamic performance of the configuration.
Aerodynamics and Acoustics of the Virginia Tech Stability Tunnel Anechoic System
Crede, Erin Dawne (Virginia Tech, 2008-06-11)
The acoustic treatment and calibration of a new anechoic system for the Virginia Tech Stability Wind Tunnel has been performed. This novel design utilizes Kevlar cloth to provide a stable flow boundary, which eliminates the need for a free jet and jet catcher. To test this concept a series of measurements were performed both to validate the reduction in overall test section noise levels and to ascertain the effect of these modifications on the test section aerodynamics. An extensive program of experiments has been conducted to examine the performance of this new hardware under a range of conditions. These include baseline experiments that reveal the aerodynamic and aeroacoustic performance of the tunnel in its original configuration, treatment of the tunnel circuit with validation of in-flow noise reduction, wind tunnel tests to examine the effect of the test section acoustic treatment, and measurements of the aerodynamic and aeroacoustic characteristics of a NACA 0012 airfoil model over a range of angles of attack and Reynolds numbers. These measurements show that acoustically treating the walls of the circuit both upstream and downstream of the test section, as well as the fan, result in an overall reduction of 5 dB depending on frequency, of the in-flow noise level. These measurements also show that the complete system provides a reduction of between 15 to 20dB depending on frequency, in the in-flow background noise level. Measurements taken both within the test section and in the adjacent chambers also show that large Kevlar windows can be used to quietly and stably contain the flow, eliminating the need for an open-jet and jet catcher system, as well as overall noise levels competitive with many other facilities. Measurements on several airfoils at various angles of attack and Reynolds number show that the interference correction for the fully anechoic configuration is approximately -22% for model with a chord length equal to half the test section height. Aerodynamic measurements with the NACA 0012 airfoil show its lift, drag and boundary layer characteristics at high Reynolds numbers are consistent with theoretical expectations. Measurements of the window deflection as well as examination of flow transpiration through the Kevlar windows were accomplished, both with and without the NACA 0012 model. These measurements, along with the interference correction data, confirm that the Kevlar windows are a stable flow boundary.
Aerodynamics of a Transonic Turbine Vane with a 3D Contoured Endwall, Upstream Purge Flow, and a Backward-Facing Step
Gillespie, John Lawrie (Virginia Tech, 2017-08-09)
This experiment investigated the effects of a non-axisymmetric endwall contour and upstream purge flow on the secondary flow of an inlet guide vane. Three cases were tested in a transonic wind tunnel with an exit Mach number of 0.93-a flat endwall with no upstream purge flow, the same flat endwall with upstream purge flow, and a 3D contoured endwall with upstream purge flow. All cases had a backward-facing step upstream of the vanes. Five-hole probe measurements were taken 0.2, 0.4, and 0.6 Cx downstream of the vane row trailing edge, and were used to calculate loss coefficient, secondary velocity, and secondary kinetic energy. Additionally, surface static pressure measurements were taken to determine the vane loading at 4% spanwise position. Surface oil flow visualizations were performed to analyze the flow qualitatively. No statistically significant differences were found between the three cases in mass averaged downstream measurements. The contoured endwall redistributed losses, rather than making an improvement distinguishable beyond experimental uncertainty. Flow visualization found that the passage vortex penetrated further in the spanwise direction into the passage for the contoured endwall (compared to the flat endwall), and stayed closer to the endwall with a blowing ratio of 1.5 with a flat endwall (compared to no blowing with flat endwall). This was corroborated by the five hole probe results.
Aeroelastic Analysis of Membrane Wings
Banerjee, Soumitra Pinak (Virginia Tech, 2007-08-22)
The physics of flapping is very important in the design of MAVs. As MAVs cannot have an engine that produces the amount of thrust required for forward flight, and yet be light weight, harnessing thrust and lift from flapping is imperative for its design and development. In this thesis, aerodynamics of pitch and plunge are simulated using a 3-D, free wake, vortex lattice method (VLM), and structural characteristics of the wing are simulated as a membrane supported by a rigid frame. The aerodynamics is validated by comparing the results from the VLM model for constant angle of attack flight, pitching flight and plunging flight with analytical results, existing 2-D VLM and a doublet lattice method. The aeroelasticity is studied by varying parameters affecting the flow as well as parameters affecting the structure. The parametric studies are performed for cases of constant angle of attack, plunge and, pitch and plunge. The response of the aeroelastic model to the changes in the parameters are analyzed and documented. The results show that the aerodynamic loads increase for increased deformation, and vice-versa. For a wing with rigid boundaries supporting a membranous structure with a step change in angle of attack, the membrane oscillates about the steady state deformation and influence the loads. For prescribed oscillations in pitch and plunge, the membrane deformations and loads transition into a periodic steady state.
Aircraft agility
Thompson, Brian G. (Virginia Tech, 1992)
A definition of an aircraft agility vector is given as the time rate-of-change of the applied forces acting on an aircraft and agility is characterized as being representable by instantaneous and integral time-scales. A unified framework for evaluating instantaneous and integral agility is developed based on the notion of a new dynamic model for aircraft motions. This model may be viewed as intermediate between a point-mass model, in which the body attitude angles are control-like, and a rigid-body model, in which the body attitude angles evolve according to Newton's Laws. Specifically, we consider the case of symmetric flight and construct a model in which the body roll-rate and pitch-rate are the controls. Accordingly, we refer to this new dynamics model as the body-rate model, (BRM). Instantaneous agility is presented as the locus of achievable agility vectors and the construction of such agility sets is demonstrated from aerodynamic and propulsive data for a modern jet fighter. Figures depicting this locus are displayed with indications of the limiting control. An integral performance flight problem is presented and subsequently solved via the optimal control theory. Agility metrics are suggested for this problem based on the transients which exist between the dynamics of the BRM and those of the point-mass model. Suggestions are also provided on the use of instantaneous agility sets and integral agility metrics in the design of aircraft and in performance comparisons of competing aircraft.
Algorithmic Modifications to a Multidisciplinary Design Optimization Model of Containerships
Ganguly, Sandipan (Virginia Tech, 2004-05-06)
When designing a ship, a designer often begins with "an idea" of what the ship might look like and what specifications the ship should meet. The multidisciplinary design optimization model is a tool that combines an analysis and an optimization process and uses a measure of merit to obtain what it infers to be the best design. All that the designer has to know is the range of values of certain design variables that confine the design within a lower and an upper bound. The designer then feeds the MDO model with any arbitrary design within the bounds and the model searches for the best design that minimizes or maximizes a measure of merit and also meets a set of structural and stability requirements. The model is multidisciplinary because the analysis process, which calculates the measure of merit and other performance parameters, can be a combination of sub-processes used in various fields of engineering. The optimization process can also be a variety of mathematical programming techniques depending on the type of the design problem. The container ship design problem is a combination of discreet and continuous sub-problems. But to avail the advantages of gradient-based optimization algorithms, the design problem is molded into a fully continuous problem. The efficiency and effectiveness with which an optimization process achieves the best design depends on how well the design problem is posed for the optimizer and how well that particular optimization algorithm tackles the type of design problems posed before it. This led the author to investigate the details of the analysis and the optimization process within the MDO model and make modifications to each of the processes, so that the two become more compatible towards achieving a better final design. Modifications made within the optimization algorithm were then used to develop a generalized modification method that can be used to improve any gradient-based optimization algorithm.
Analysis and Design of a Morphing Wing Tip using Multicellular Flexible Matrix Composite Adaptive Skins
Hinshaw, Tyler (Virginia Tech, 2009-07-01)
The material presented in this thesis uses concepts of the finite element and doublet panel methods to develop a structural-aerodynamic coupled mathematical model for the analysis of a morphing wing tip composed of smart materials. Much research is currently being performed within many facets of engineering on the use of smart or intelligent materials. Examples of the beneficial characteristics of smart materials might include altering a structure's mechanical properties, controlling its dynamic response(s) and sensing flaws that might progressively become detrimental to the structure. This thesis describes a bio-inspired adaptive structure that will be used in morphing an aircraft's wing tip. The actuation system is derived from individual flexible matrix composite tube actuators embedded in a matrix medium that when pressurized, radical structural shape change is possible. A driving force behind this research, as with any morphing wing related studies, is to expand the limitations of an aircraft's mission, usually constrained by the wing design. Rather than deploying current methods of achieving certain flight characteristics, changing the shape of a wing greatly increases the flight envelope. This thesis gives some insight as to the structural capability and limitations using current numerical methods to model a morphing wing in a flow.
The Analysis and Prediction of Jet Flow and Jet Noise about Airframe Surfaces
Smith, Matthew James (Virginia Tech, 2013-10-15)
Aircraft noise mitigation has been an ongoing challenge for the aeronautics research community. In response to this challenge, aircraft concepts have been developed in which the propulsion system is integrated with the airframe to shield the noise from the observer. These concepts exhibit situations where the jet exhaust interacts with an airframe surface. Jet flows interacting with nearby surfaces exhibit a complex behavior in which acoustic and aerodynamic characteristics are altered. The physical understanding and accurate modeling of these characteristics are essential to designing future low-noise aircraft. In this thesis, an alternative approach is created for predicting jet mixing noise that utilizes an acoustic analogy and the solution of the steady Reynolds-Averaged Navier-Stokes (RANS) equations using a two equation turbulence model. A tailored Green's function is used in conjunction with the acoustic analogy to account for the propagation effects of mixing noise due to a nearby airframe surface. The tailored Green's function is found numerically using a newly developed ray tracing method. The variation of the aerodynamics, acoustic source, and far- field acoustic intensity are examined as a large flat plate is moved relative to the nozzle exit. Steady RANS solutions are used to study the aerodynamic changes in the field-variables and turbulence statistics. To quantify the propulsion airframe aeroacoustic (PAA) installation effects on the aerodynamic source, a non-dimensional number is formed that can be used as a basic guide to determine if the aerodynamic source is affected by the airframe and if additional noise produced by the airframe surface is present. The aerodynamic and noise prediction models are validated by comparing results with Particle Image Velocimetry (PIV) and far-field acoustic data respectively. The developed jet noise scattering methodology is then used to demonstrate the shielding effects of the Hybrid Wing Body (HWB) aircraft. The validation assessment shows that the acoustic analogy and tailored Green's function provided by the ray tracing method are capable of capturing jet shielding characteristics for multiple configurations and jet exit conditions.

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Browsing Masters Theses by Department "Aerospace and Ocean Engineering"

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