Navigation, Guidance, Control and Dynamics Commons^™

Computer Based Modeling For Small E-Vtol Propeller Performance, Ege Konuk

Mechanical & Aerospace Engineering Theses & Dissertations

The emerging field of urban air mobility (UAM) offers a novel transportation method for civil, commercial, and military applications. Vertical take-off and landing (VTOL) configurations present challenges for performance prediction during crucial flight operations. An advanced computational framework for predicting propeller performance in electric vertical takeoff and landing (eVTOL) aircraft during transition flight is essential for future concept designs. This research extends the Blade Element Momentum Theory (BEMT) to model propeller behavior at high incidence angles, crucial for eVTOL operation.

The study begins with a review of tilt-wing/rotor configurations for eVTOLs and tackles the complex aerodynamic phenomena associated with rotors …

Design And Implementation Of A Launching Method For Free To Oscillate Dynamic Stability Testing, Kristen M. Carey

Mechanical & Aerospace Engineering Theses & Dissertations

Magnetic Suspension and Balance Systems (MSBS) allow for static, forced oscillation and free to oscillate dynamic stability testing in a wind tunnel without the need for a physical support. The objectives of study are to assist in the application of the free to oscillate testing method in an MSBS to determine dynamic stability characteristics for various re-entry capsule designs.

This thesis discusses the development and testing of a launching method called the grabber for use in the MSBS Subsonic Wind Tunnel at NASA Langley Research Center. Aerodynamic tests were run to support the use of this method and compare the …

Nonlinear Flight Control Design Using Backstepping Methodology, Thanh Trung Tran

Mechanical & Aerospace Engineering Theses & Dissertations

The subject of nonlinear flight control design using backstepping control methodology is investigated in the dissertation research presented here. Control design methods based on nonlinear models of the dynamic system provide higher utility and versatility because the design model more closely matches the physical system behavior. Obtaining requisite model fidelity is only half of the overall design process, however. Design of the nonlinear control loops can lessen the effects of nonlinearity, or even exploit nonlinearity, to achieve higher levels of closed-loop stability, performance, and robustness. The goal of the research is to improve control quality for a general class of …

Flight Dynamics Nonlinearity Assessment Across A New Aerodynamic Attitude Flight Envelope, Ayman Muhammad Abdallah

Mechanical & Aerospace Engineering Theses & Dissertations

A new asymmetric level aerodynamic attitude flight envelope is introduced in this dissertation. The aerodynamic attitude envelope is an angle of attack vs. sideslip angle region which describes the extent of where an aircraft can sustain a steady slipping horizontal flight condition. The new envelope is thus an extension of the more common speed-altitude symmetric level flight envelope. This new envelope can be used for design requirements, dynamic analysis, control synthesis, or performance comparison. Moreover, this envelope provides enhanced insight into trimability-controllability limitations within the aircraft design model. The aerodynamic attitude flight envelope is constructed for a six degree of …

Guidance And Navigation For A Spinning Projectile Using A Strapdown Seeker, Timothy J. Josey

Mechanical & Aerospace Engineering Theses & Dissertations

This thesis describes the derivation and implementation of an Extended Kalman Filter for the purpose of estimating the line of sight rates between a non-thrusting, guided projectile and a ground target. Line of sight rates are required signals to implement the proportional navigation guidance scheme. Using low-cost strapdown sensors, the line of sight rate is not directly measurable but is observable as shown in this thesis. The line of sight signal generated by strapdown seekers inherently includes projectile body motion, but with the use of a global positioning system and a strapdown inertial sensor suite, the seeker signal is transformed …

System Identification Of An Autonomous Surface Vehicle, Christopher John Cook

Mechanical & Aerospace Engineering Theses & Dissertations

The modeling and system identification of a small pontoon based marine craft, without rudder control, in a controlled environment. Old Dominion University's autonomous surface vehicle was modeled using the Observer/Kalman System Identification method. The experimental position data was collected using a laser positioning system along with Arduino based sensors on board the boat to collect the motor speeds of the dual outboard motors. The data was then compiled using the System/ Observer/Controller Identification Toolbox to derive a dynamic model that is capable of providing path estimation and prediction information to the autonomous robotic system.

A Multi-Objective Differential Evolution Algorithm For Engineering Design Optimization, Shantanu S. Muluk

Mechanical & Aerospace Engineering Theses & Dissertations

The current research investigation focuses on the development of a multi-objective global optimizer based on the differential evolution algorithm. A rotationally invariant version of the original differential evolution algorithm is adopted as the core component of the optimization procedure. The optimizer is applied to a number of multi-objective problems: constrained problems, problems of high dimensionality, and problems with non-convex Pareto fronts.

The effectiveness of the proposed optimization framework in real engineering design problems is demonstrated by carrying out an aerodynamic shape optimization of wind turbine airfoils. The investigation focuses on both thin and thick airfoils. The produced Pareto-optimal airfoil shapes …

Modeling And Analysis Of Low Earth Orbit Satellite And Ground Station Data Exchange Topology, Ersin Kocoglu

Mechanical & Aerospace Engineering Theses & Dissertations

In order to utilize space effectively, the primary function of satellite control in orbit around the Earth must be accomplished. This controlling process includes two main segments, ground stations serving as the controller units and orbiting satellites as the units to be controlled. This thesis explores a topological data exchange model that contains one satellite and multiple ground stations. The model is implemented in digital computer software. This model has multiple purposes and can be used to simulate satellite passes over ground stations and can also be used to predict communication time and the amount of transferred data. The model …

Multivariable Flight Control Design Tool Incorporating Gain And Phase Root Locus, Yong Ki Yoon

Mechanical & Aerospace Engineering Theses & Dissertations

A challenging problem in flight control system design for highly maneuverable aircraft is the coordinated control of the lateral-directional axes. Design goals are based on desired flying qualities giving an indication of whether the response to pilot inputs will be acceptable. Satisfying these closed-loop design objectives employing a computerized flight control system requires multiple feedback and crossfeed paths which operate in a well coordinated fashion. Contemporary control design tools, which close all loops simultaneously, have addressed this problem for several decades. Concerns associated with these strategies are the complicated mathematical relationships between the designer inputs and resulting closed-loop properties, and …

Experimental Investigation Of Active Control Of Bluff Body Vortex Shedding, Ilteris Koc

Mechanical & Aerospace Engineering Theses & Dissertations

Mean and fluctuating forces acting on a body are strongly related to vortex shedding generated behind it. Therefore, it is possible to obtain substantial reductions of at least the unsteady forces if vortex shedding is controlled or its regularity is reduced. While conventional active flow control methods are mainly concerned with direct interaction with, and alteration of, the mean flow about a body, modern techniques involve altering existing flow instabilities using relatively small inputs to obtain large-scale changes of mean flows. Aerodynamic flow control may be intended to delay or suppress boundary layer separation through creation of a boundary layer …

Assessment Of Preliminary Design Approaches For Metallic Stiffened Cylindrical Shell Instability Problems, Vicki Owen Britt

Mechanical & Aerospace Engineering Theses & Dissertations

A preliminary design tool for metallic stiffened fuselage cylindrical panels subjected to longitudinal compression has been developed and validated by comparison to test results. Several methodologies for stiffened panel buckling and failure predictions were examined and evaluated. An appropriate level of analysis fidelity was determined for different failure modes and design details. Results from panel tests conducted to verify analytical methods used to design the Gulfstream V aircraft were presented. The panels were representative of four general skin/stringer configurations on the aircraft. Finite Element analyses and standard analytical methods were used to predict panel failure loads. The accuracy of the …

Micron-Level Actuator For Thermal-Fluid Control In Microchannels, Nurhak Erbas

Mechanical & Aerospace Engineering Theses & Dissertations

Effectiveness of an actuator is investigated for thermal-flow control in microchannels. First, simulations of a single actuator in a quiescent external medium are performed in order to study the parameters characterizing the synthetic jet flow from the actuator. For this purpose, a simplified, two-dimensional configuration is considered. The membrane motion is modeled in a realistic manner as a moving boundary in order to accurately compute the flow inside the actuator cavity. The geometric and actuation parameters of the actuator are investigated to define the effectiveness of the jet flow. The study is done initially at macro scales. Then, the flow …

Contemporary-Classical Sequential Loop Design With Parameter Uncertainty, Donghyuk Jeong

Mechanical & Aerospace Engineering Theses & Dissertations

Standard sequential loop closure design based on Evans root migration concepts is a well accepted, insightful and effective technique for meeting nominal performance objectives and traditional gain-phase stability margin requirements. Unfortunately, assessment of closed-loop variations resulting from parameter error is a post-process, implying an undesirable design-assess-redesign procedure is necessary if variations are found unacceptable. Further, the modem parameter uncertainty assessment framework is often inconsistent, both quantitatively and qualitatively, with the redesign task. Specifically, the parameter uncertainty assessment variables are not readily apparent in the sequential loop design framework, and these variables provide little guidance for the redesign strategy. Therefore, enhancing …

New Methodology For Robust Control System Design And Analysis For Single Parameter Uncertain Systems, Charles J. Player

Mechanical & Aerospace Engineering Theses & Dissertations

Due to the conservative nature of the standard singular value robustness tests there is ambiguity in the results that they provide. The tests only establish a sufficient condition and therefore provide little insight to the stability robustness of a system that fails the test. However, for a single parameter uncertain system that is modeled using structured uncertainty, an Evans root locus can be derived that shows how system closed-loop poles change with the magnitude of the single parameter uncertainty. This technique provides clear stability robustness insight. Further, another Evans root locus can be derived that shows how system closed-loop zeros …

Numerical Integration Strategy For Generating Root Migration Diagrams, Deepak H. Panduranga

Mechanical & Aerospace Engineering Theses & Dissertations

Evans root locus is a graphical method for analyzing or designing the stability and performance of a single channel closed-loop system. The method consists of plotting the locus of closed-loop characteristic equation roots in the complex plane as the loop gain parameter is varied over a wide range of values. Several methods for plotting the root locus graph exist and can be mainly classified into two types: analytical methods and numerical methods. The most common numerical method is based on polynomial factoring or root solving. A less common, alternative method for generating the root locus graph is based on numerical …

Swing-Up And Balancing Nonlinear Control For A Rotational Inverted Pendulum, Jiang Wang

Mechanical & Aerospace Engineering Theses & Dissertations

In this thesis, nonlinear controllers are designed for the swing-up and balance modes of a rotational inverted pendulum, which is a pendulum hinged on a horizontally rotating link. The proposed control algorithms are designed by partial feedback linearization and sliding mode control techniques, for swing-up and balancing respectively. First a mathematical model of the pendulum dynamics is derived, followed by experimental verification. Then the system model is partially linearized, which makes it possible for the system to track a simple desired trajectory with "pump energy" function. Then a swing-up controller is designed. For an under-actuated mechanical system, like the inverted …

Optimal Aeroelastic Vehicle Sensor Placement For Root Migration Flight Control Applications, Abdul Ghafoor Al-Shenhabi

Mechanical & Aerospace Engineering Theses & Dissertations

An important step in control design for elastic systems is the determination of the number and location of control system components, namely sensors. The number and placement of sensors can be critical to the robust functioning of active control systems, especially when the system of interest is a large high-speed aeroelastic vehicle. The position of the sensors affects not only system stability, but also the performance of the closed-loop system. In this dissertation, a new approach for sensor placement in the integrated rigid and vibrational control of flexible aircraft structures is developed. Traditional rigid-body augmentation objectives are addressed indirectly through …

Long-Term Aircraft Structural Integrity Prediction Under The Influence Of Feedback Control, Si-Bok Yu

Mechanical & Aerospace Engineering Theses & Dissertations

This thesis investigates the influence of feedback control, and other factors associated with loading characteristics, on fatigue damage reduction and long-term integrity of aircraft structural components. An actively controlled flexible aircraft model and a new state space modeling procedure for crack growth are utilized to uncover important factors which influence airframe crack growth. A matrix of simulation test cases is constructed to cover such variables as open-loop operation, nominal closed-loop operation, perturbed closed-loop operation (i.e., feedback gain variation), nominal maneuver profile, perturbed maneuver profile (including overload strength and frequency), atmospheric gust, and mean stress level. Simulation output data including crack …

Investigation Of An Alternative Technique For Measuring Turbulence In The Upper Atmosphere, Charles Patrick Leonard

Mechanical & Aerospace Engineering Theses & Dissertations

The capability of the Global Positioning System (GPS) as a tool for measuring turbulence in the upper atmosphere is presented. By studying experimental ground and flight test data, a methodology for extracting macroscale turbulence data from in situ measurements was developed.

A description of the GPS using a single nonprecision receiver is followed by data from ground and flight testing. Ground testing focused on determining the smallest turbulent scales discernible by the GPS receiver. Testing was also undertaken to compare turbulence data from the GPS with that of a simultaneously operating constant-temperature hot-wire anemometer, the conventional tool for making turbulence …

Dynamics And Control Of Two Suspension Mechanisms For Ground-Based Testing Of Space Structures, Joseph E. Wilson

Mechanical & Aerospace Engineering Theses & Dissertations

Two suspension systems which effectively simulate a gravity-free environment are presented. A single degree-of-freedom suspension system utilizing a specially profiled band mechanism in conjunction with a torsional spring is presented to show its feasibility and applicability for use as a ground-based testing device for flexible space structures. The second device, a two degree-of-freedom suspension system consisting of two springs and a folding linkage is presented to show the feasibility as a testing device for suspending space structures on earth.

Problems resulting in unwanted dynamic behavior due to deviations from the design parameters for both systems are addressed. A nonlinear controller …

An Approach For Including Reliability In Control System Designs, Ime Isaac Akpan

Mechanical & Aerospace Engineering Theses & Dissertations

An approach is developed for non-catastrophic control component failure accommodation for large space structures. Reliability is considered for both the control configuration (i.e., selecting actuator locations over an admissible set) and the ultimate operation of the system. The approach presented is to construct a measure of performance that indicates the absolute goal of the system, and for a given structural design, to determine the lowest achievable cost conditional upon the failure states of the system (i.e., which actuators are operational). These costs are then weighted and summed to provide an overall system performance measure. This expected performance measure is then …

Low Speed Handling Characteristics Of A Supersonic Transport By Eigenstructure Assignment, Michael Peter Lazar

Mechanical & Aerospace Engineering Theses & Dissertations

A synthesis procedure, based upon optimal regulator theory and eigenvalue/eigenvector assignment technique, was used in the design of a low-speed lateral control system for the SCAT-15F supersonic transport. Emphasis was placed on reducing the lateral acceleration at the pilot's station. Control laws were designed to make the aircraft handling characteristics acceptable with the exception of the lateral acceleration. It was found that a compromise between the roll performance requirements and the peak lateral acceleration requirement is needed for a successful SCAT-15F design.