Browsing by Author "Su, Weihua"
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Item Adaptive highly flexible multifunctional wings for active and passive control and energy harvesting with piezoelectric materials(University of Alabama Libraries, 2017) Tsushima, Natsuki; Su, Weihua; University of Alabama TuscaloosaThe purpose of this dissertation is to develop an analytical framework to analyze highly flexible multifunctional wings with integral active and passive control and energy harvesting using piezoelectric transduction. Such multifunctional wings can be designed to enhance aircraft flight performance, especially to support long-endurance flights and to be adaptive to various flight conditions. This work also demonstrates the feasibility of the concept of piezoelectric multifunctional wings for the concurrent active control and energy harvesting to improve the aeroelastic performance of high-altitude long-endurance unmanned air vehicles. Functions of flutter suppression, gust alleviation, energy generation, and energy storage are realized for the performance improvement. The multifunctional wings utilize active and passive piezoelectric effects for the efficient adaptive control and energy harvesting. An energy storage with thin-film lithium-ion battery cells is designed for harvested energy accumulation. Piezoelectric effects are included in a strain-based geometrically nonlinear beam formulation for the numerical studies. The resulting structural dynamic equations are coupled with a finite-state unsteady aerodynamic formulation, allowing for piezoelectric energy harvesting and active actuation with the nonlinear aeroelastic system. This development helps to provide an integral electro-aeroelastic solution of concurrent active piezoelectric control and energy harvesting for wing vibrations, with the consideration of the geometrical nonlinear effects of slender multifunctional wings. A multifunctional structure for active actuation is designed by introducing anisotropic piezoelectric laminates. Linear quadratic regulator and linear quadratic Gaussian controllers are implemented for the active control of wing vibrations including post-flutter limit-cycle oscillations and gust perturbation. An adaptive control algorithm for gust perturbation is then developed. In this research, the active piezoelectric actuation is applied as the primary approach for flutter suppression, with energy harvesting, as a secondary passive approach, concurrently working to provide an additional damping effect on the wing vibration. The multifunctional wing also generates extra energy from residual wing vibration. This research presents a comprehensive approach for an effective flutter suppression and gust alleviation of highly flexible piezoelectric wings, while allowing to harvest the residual vibration energy. Numerical results with the multifunctional wing concept show the potential to improve the aircraft performance from both aeroelastic stability and energy consumption aspects.Item Computational Study of Electron Transport in a Hall Effect Thruster with Magnetized Low Temperature Plasma(University of Alabama Libraries, 2025) Ahmed, Sajid; Olcmen, Semih; Volkov, Alexey N.Hall effect thruster (HET) is an electric space propulsion device providing higher specific impulse and smaller thrust requirements to satellites and interplanetary missions. Ionization and plasma generation are key to HET performance and efficiency and depend on the electron transport inside the channel of the HET. The proper understanding of the electron transport mechanism is very crucial in developing high fidelity computational models of the HET. In this study, a comprehensive investigation of electron dynamics in the ionization and acceleration zones of HET using a fully kinetic, three-dimensional particle-in-cell (PIC) simulation coupled with Monte Carlo collisions (MCC) was presented. The novelty of this work lies in the detailed analysis of electron transport mechanisms under varying anode voltages and analyzing the plasma instabilities, and their interactions, providing new insights into electron dynamics in the HET channel. Specifically, the influence of anode voltage variation from 100 V to 200 V on ion density was quantified, observing an increase of approximately 20% in ion production, directly impacting thruster efficiency. The ion velocity distribution functions (IVDF) have been characterized within both the channel and plume region offering a comprehensive evaluation of HET performance metrics. The simulation resolved the two key plasma instabilities--electron drift instability (EDI) and rotating spoke oscillations--and investigated their development and formation through the HET channel. Finally, the characterization of the EDI and rotating spokes were performed by means of the advanced spectral analysis technique--the power spectral density and spatial average mode diagrams. The speed of the rotating spoke was calculated and compared with existing literature. A bi-coherence quantification found a significant level of interaction with energy transfers between the EDI and rotating spoke with different anode voltage configurations. These findings provide critical insights into the mechanisms of electron transport and instability interactions in HETs, thereby offering a pathway to optimize magnetic field configurations, operating voltages, and propellant conditions for improved discharge stability, higher efficiency, and enhanced propulsion performance.Item Coupled Flexural-Torsional Vibration Analysis of a Double-Cantilever Structure for Nanomaching Application(University of Alabama Libraries, 2021) Zargarani, Anahita; Mahmoodi, Nima; University of Alabama TuscaloosaThis dissertation aims to investigate the coupled flexural-torsional vibrations of a piezoelectrically-actuated double-cantilever structure for nanomachining applications. The structure of interest consists of two identical Euler-Bernoulli cantilever beams connected by a rigid tip connection at their free ends. The double-cantilever structure in this study vibrates in two distinct modes: flexural mode or coupled flexural-torsional mode. The flexural mode refers to the in-phase flexural vibrations of the two cantilever beams resulting in transverse motion of the tip connection, while the coupled flexural-torsional mode refers to the coupled flexural-torsional vibrations of the cantilever beams resulting in the rotational motion of the tip connection. The latter is the main interest of this research. The governing equations of motion and boundary conditions are developed using Hamilton’s principle. Two uncoupled equations are found for each beam: one corresponding to the flexural vibrations and the other one corresponding to the torsional vibrations of the cantilever beam. The characteristic equations for both the flexural and the coupled flexural-torsional vibration modes are derived and solved to find the corresponding natural frequencies. The orthogonality condition among the mode shapes is derived and utilized to determine the modal coefficients corresponding to each mode of vibration. The time response to the forced vibrations of the structure is found using the Galerkin approximation method. The effects of the dimensional parameters, including the length of the cantilever beams and the length of the tip connection, and the piezoelectric input voltage on the natural frequencies and the amplitude of vibrations of the structure are analyzed. An experimental setup consisting of a piezoelectric double-cantilever structure is designed and utilized to verify the analytical results. First, the coupled flexural-torsional fundamental frequencies of the structure with various configurations are obtained experimentally, which are in good agreement with the analytically-determined values. Moreover, the experimental results verify the analytical results stating that the natural frequencies of the structure decrease as either the length of the cantilever beams or the length of the tip connection is increased. Next, the amplitudes of the coupled flexural-torsional vibrations of different configurations of the structure excited at their natural frequencies with a range of input voltages are obtained. The results of the effect of the dimensional parameters and the piezoelectric input voltage on the angle of rotation of the tip connection are presented.Item Development of multi-fidelity aeroelastic optimization framework for flexible wing conceptual design(University of Alabama Libraries, 2021) Huang, Yanxin; Su, Weihua; University of Alabama TuscaloosaThis dissertation introduces a framework to carry out the aeroelastic optimization around the steady-state for flexible fixed wings. Such a framework captures geometrical nonlinearities and aerodynamic unsteadiness, which are the challenges in modern aircraft design. This also takes full advantage of structural geometry by integrating multi-fidelity structures with vortex-lattice method (UVLM), allowing effective and accurate multi-stage aircraft design with a variety of aspect ratios. Functions of structural consistency are used to close the gap between multi-stage designs at different fidelity levels. A model update tool is used to ensure structural consistency and allow communications between stages and fidelity levels. In addition, this framework shows its potential to involve more disciplinaries, such as control and stability, by revealing sensitivities with respect to UVLM vorticities and grids.The lower-fidelity aeroelastic model integrates nonlinear strain-based beam elements with UVLM, while the higher-fidelity model integrates nonlinear displacement-based shell elements with UVLM. The resulting aeroelastic models are coupled with a gradient-based method, focusing on overall performance and detailed analysis, respectively. An artificial neural network (ANN) is established for the model update from the lower- to the higher-fidelity structure. It builds a database and performs a statistical approach to address the parameter inequality. Aerodynamic equations are linearized by performing small perturbations and assuming a frozen aerodynamic geometry. The developed UVLM and aeroelastic models are validated by reference models. Analytical aerodynamic sensitivities are verified by the results of finite-difference. In addition, the feasibility of the model update tool is demonstrated by generating a two-dimensional shell and a three-dimensional wing box from original one-dimensional beams. The feasibility of this framework is demonstrated by optimizing a fixed wing under a large upward bending deflection. The impact of different design variables is also observed and discussed. This research illustrates a comprehensive process for an early design of flexible wings. Although the current framework is limited to the incompressible flow and isotropic shell elements, it has the potential to involve more applications with compressibility corrections of UVLM and composite materials.Item Envisioning Urban Air Mobility in Small and Medium-Sized Urban Areas in the United States(University of Alabama Libraries, 2023) Yang, Chenxuan; Liu, JunUrban Air Mobility (UAM) represents a revolutionary innovation that utilizes low-altitude urban space to provide air transportation. While UAM offers numerous advantages and holds promise as a solution to traffic congestion, it faces various constraints, including public acceptance, economic considerations, and management challenges. While extensive research has explored the integration of UAM into mobility systems for large metropolitan areas, the potential benefits it could bring to smaller urban areas with populations under 350,000 have been under-discussed. This dissertation research aims to assess the feasibility and viability of implementing UAM in small and medium-sized urban areas. The first major study in this dissertation involves a national survey to investigate Americans' willingness to pay for URAM services and their preferences when faced with commutes that exceed a certain duration. The second study evaluates the impact of UAM on over 300 small and medium-sized urban areas by comparing the travel accessibility of existing road-based regional transportation systems with hypothetical UAM-integrated systems. These hypothetical UAM networks interconnect vertiports within regions, enabling travelers to reach their destinations via Vertical Take-Off and Landing (VTOL) aircrafts after reaching the nearest vertiport by ground transportation. The third study explores an innovative intermodal mobility system that integrates Shared Autonomous Vehicles (SAVs) and VTOLs within the UAM framework. Agent-based simulations are employed to assess the feasibility and viability of this system in small and medium-sized urban areas. This dissertation sheds light on the benefits and trade-offs associated with UAM in small and medium-sized urban areas. It serves as a valuable resource for evaluating the practicality of intermodal UAM services and informs policies related to the planning and implementation of UAM services in the United States.Item Estimation of morphing airfoil shapes and aerodynamic loads using artificial hair sensors(University of Alabama Libraries, 2015) Butler, Nathan Scott; Su, Weihua; University of Alabama TuscaloosaAn active area of research in adaptive structures focuses on the use of continuous wing shape changing methods as a means of replacing conventional discrete control surfaces and increasing aerodynamic efficiency. Although many shape-changing methods have been used since the beginning of heavier-than-air flight, the concept of performing camber actuation on a fully-deformable airfoil has not been widely applied. A fundamental problem of applying this concept to real-world scenarios is the fact that camber actuation is a continuous, time-dependent process. Therefore, if camber actuation is to be used in a closed-loop feedback system, one must be able to determine the instantaneous airfoil shape, as well as the aerodynamic loads, in real time. One approach is to utilize a new type of artificial hair sensors (AHS) developed at the Air Force Research Laboratory (AFRL) to determine the flow conditions surrounding deformable airfoils. In this study, AHS measurement data will be simulated by using the flow solver XFoil, with the assumption that perfect data with no noise can be collected from the AHS measurements. Such measurements will then be used in an artificial neural network (ANN) based process to approximate the instantaneous airfoil camber shape, lift coefficient, and moment coefficient at a given angle of attack. Additionally, an aerodynamic formulation based on the finite-state inflow theory has been developed to calculate the aerodynamic loads on thin airfoils with arbitrary camber deformations. Various aerodynamic properties approximated from the AHS/ANN system will be compared with the results of the finite-state inflow aerodynamic formulation in order to validate the approximation approach.Item Full Waveform Inversion-Based Ultrasound Computed Tomography for Material Characterization(University of Alabama Libraries, 2024) Aktharuzzaman, Md; Su, WeihuaThis dissertation presents a comprehensive investigation into the development and application of a Full Waveform Inversion (FWI)-based ultrasound computed tomography (USCT) for characterizing both elastic and acoustic materials. The focus of this work is on enhancing imaging accuracy, analyzing image resolution, and exploring the potential of this method for characterizing additively manufactured components and soft-tissue-like structures. The core contribution of this dissertation is the introduction of an innovative FWI-based imaging algorithm tailored for USCT. This algorithm addresses several critical aspects of ultrasonic imaging. One of the main challenges in implementing FWI is the necessity of accurate source signature information, which is often proprietary and unavailable to end users. To overcome this, the dissertation proposes a linear inversion-based source estimation approach, allowing the source signature to be extracted from experimental data. The pro- posed transducer modeling approach is validated using USCT data from an aluminum 6061 specimen. The FWI results, incorporating the inverted source time functions, demonstrated promising wave speed reconstructions even with a 0.5 MHz transducer, despite its limited resolution capability for elastic applications. Furthermore, the dissertation explores the application of the FWI-based USCT in characterizing the effects of post-processing conditions of additively manufactured (AM) components. The study focused on Nickel-based super alloy (Inconel 718) specimens, examining the effects of stress-relief heat treatment and heat treatment combined with isostatic pressing. The reconstructed wave speed models revealed significant differences between as-built and post-processed specimens. However, distinguishing between the two post-processed specimens was challenging due to their close wave speed ranges. To this point, elastic wave equation was incorporated while modeling the wave propagation to characterize elastic materials. Additionally, the feasibility of the FWI-based USCT to characterize soft-tissue-like structures was investigated applying the acoustic wave equation within the spectral element method. A cylindrical rat phantom is a widely recognized tool for testing and calibrating various medical imaging devices. This small phantom is compatible with USCT and can be customized in both size and shape. In this research, a cylindrical rat phantom with regions of varying wave speeds was considered as soft structure. This phantom was employed to study and validate the imaging performance of the proposed FWI-based USCT frame- work. Initially, a numerical model which had a wave speed regions similar to the physical in-house rat phantom in the spectral element based solver, i.e., SPECFEM2D. An in-house water-immersed USCT with limited array coverage with two linear phased array transducers was used to acquire data. The resolution of the reconstructed images validated the effectiveness of this approach for complex soft-tissue-like structures. Experimental data from an in-house water-immersed USCT system were then used to estimate the source time function, employing the proposed method. A comparative analysis between the estimated source time function and the synthetically generated Ricker wavelet showed that while the Ricker wavelet provided superior resolution, the estimated source signature successfully captured internal tissue features, highlighting the potential of the proposed approach. In conclusion, this dissertation advances the field of USCT by developing a robust FWI- based imaging algorithm. The work demonstrates the potential applicability and capability of FWI-based USCT in diverse non-destructive testing applications across various engineering domains, including additive manufacturing components and soft-tissue-like structures. This work lays a solid foundation for future research and practical applications in non- destructive evaluation and medical imaging.Item LPV modeling of a flexible wing aircraft using modal alignment and adaptive gridding methods(Elsevier, 2017) Al-Jiboory, Ali Khudhair; Zhu, Guoming; Swei, Sean Shan-Min; Su, Weihua; Nguyen, Nhan T.; Michigan State University; University of Diyala; National Aeronautics & Space Administration (NASA); NASA Ames Research Center; University of Alabama TuscaloosaOne of the earliest approaches in gain-scheduling control is the gridding based approach, in which a set of local linear time-invariant models are obtained at various gridded points corresponding to the varying parameters within the flight envelop. In order to ensure smooth and effective Linear Parameter Varying control, aligning all the flexible modes within each local model and maintaining small number of representative local models over the gridded parameter space are crucial. In addition, since the flexible structural models tend to have large dimensions, a tractable model reduction process is necessary. In this paper, the notion of sigma-shifted H-2- and H-infinity-norm are introduced and used as a metric to measure the model mismatch. A new modal alignment algorithm is developed which utilizes the defined metric for aligning all the local models over the entire gridded parameter space. Furthermore, an Adaptive Grid Step Size Determination algorithm is developed to minimize the number of local models required to represent the gridded parameter space. For model reduction, we propose to utilize the concept of Composite Modal Cost Analysis, through which the collective contribution of each flexible mode is computed and ranked. Therefore, a reduced-order model is constructed by retaining only those modes with significant contribution. The NASA Generic Transport Model operating at various flight speeds is studied for verification purpose, and the analysis and simulation results demonstrate the effectiveness of the proposed modeling approach. (C) 2017 Elsevier Masson SAS. All rights reserved.Item Multidisciplinary Design Optimization and Analysis Using a Hybrid Augmented Lagrangian Genetic Algorithm(University of Alabama Libraries, 2020) Benabbou, Adam; Su, Weihua; University of Alabama TuscaloosaA major challenge in the aerospace design process is the balance between simulation fidelity and various types of resource constraints such as financial and computational. To develop new data analytical capabilities and improve the reliability of medium fidelity projects using well selected algorithms and methods, a multidisciplinary simulation and optimization tool is developed using MATLAB. In the process, several key areas of research are identified, investigated and methods of analyses are discussed. Primarily, a novel method for implementing a hybrid augmented Lagrangian genetic algorithm is developed and thoroughly tested using a variety of benchmark problems. The algorithm is then implemented to optimize surrogate models for an MDO case study. This test case is a wing model of size comparable to a Cessna 172, flying at cruising speed. However, the methodology presented in this thesis could be extended beyond subsonic aircraft wing optimization and even outside the realm of aerospace engineering. The study allows for a better understanding of the methods used in multidisciplinary design optimization for conceptual design. The proof-of-concept successfully demonstrates the versatility of the MDO framework and opens the project up to several future avenues of research.Item Nonlinear Model Predictive Control of Tiltrotor Urban Air Mobility Aircraft(University of Alabama Libraries, 2024) Santos Martins Nunes, Jessica; Su, WeihuaThis dissertation presents the development and simulation of the Nonlinear Model Predictive Controller (NMPC) of a tiltrotor urban air mobility (UAM) aircraft. The aircraft's free flight is governed by nonlinear rigid-body dynamic equations involving multiple tiltrotors, considering gyroscopic and inertial effects. Control variables include rotor spin acceleration, tilt rate, and deflections of the elevator, aileron, and rudder. NMPC performance is evaluated in vibration suppression during level flight and lateral and longitudinal path tracking. NMPC is compared with a Linear Quadratic Regulator (LQR) and linear Model Predictive Controller (MPC). While NMPC and LQR achieve similar vibration suppression, NMPC outperforms all in path tracking by accounting for the aircraft's nonlinear dynamics and predicting future responses for optimal control inputs.This work also investigated stabilizing the aircraft during control effector malfunctions in level flight. With rotor spin acceleration and tilt rate as inputs, two failure modes were examined: elevator failure and asymmetric push tiltrotor failure. Results show that NMPC can maintain trajectory control, even with disturbances from asymmetric tiltrotor failure, by using back rotors as backup push thrusters. NMPC also mitigates phugoid vibrations from elevator failure by using the back rotors for pitch control. Improved stability was noted when back rotors spun after reaching the desired tilt. Lastly, NMPC's gust control was tested with continuous turbulent and discrete "1-cosine" gusts, successfully maintaining level flight, though effectiveness declined with stronger gusts. The discrete gust caused more pitch deviations, even at low intensities.In summary, the study found NMPC suitable for eVTOL applications due to its effectiveness in vibration suppression, path tracking, control under failure, and gust handling. However, its high computational cost limits real-time use, which could be improved with neural-network-based NMPC. Integrating path planning and trajectory algorithms is also recommended to enhance NMPC's capabilities. Additionally, incorporating lifting surface-to-rotor and rotor-to-rotor wake interactions and platform flexibility in the eVTOL model is suggested to improve accuracy and support NMPC's viability for eVTOL application.Item Optimal discrete-time compensation design for real-time hybrid simulation(University of Alabama Libraries, 2017) Hayati, Saeid; Song, Wei; University of Alabama TuscaloosaReal-Time Hybrid Simulation (RTHS) is a powerful and cost-effective dynamic experimental technique. In civil engineering, RTHS has the advantage of investigating the dynamic behavior of full-scale and complex structures by testing only the critical components. To implement a stable and accurate RTHS, the time delay in the experiment loop needs to be compensated. This delay is mostly introduced by servo-hydraulic actuator dynamics and can be reduced by applying appropriate compensators. Several existing compensators have demonstrated effective performance in reducing the actuator time delay. But most of them have been applied only in cases where the structure under investigation is subjected to inputs with relatively low-frequency content such as earthquake motion. To make RTHS an attractive technique for engineering applications with broader excitation frequency, a discrete-time feedforward compensator is developed via various optimization techniques to enhance the performance of RTHS. The effectiveness of the proposed compensator is demonstrated through both numerical and experimental studies. The proposed compensators are successfully applied to RTHS tests to study the seismic behavior of a linear-elastic reinforced concrete building equipped with a new type of tuned mass damper, known as the Disruptive Tuned Mass (DTM) damper designed by the National Aeronautics and Space Administration (NASA). The obtained results show that the proposed compensator reduces the time delay adequately and leads to a successful RTHS test. Results also suggest that the DTM damper can successfully reduce the response of the building subjected to the seismic loads. In addition, the dynamic properties of the DTM damper are fully investigated and a mathematical model is suggested for it.Item Optimization and uncertainty quantification of multi-dimensional functionally graded plates(University of Alabama Libraries, 2018) Hussein, Omar Shokry Ahmed; Mulani, Sameer B.; University of Alabama TuscaloosaFunctionally graded structures (FGS) are structures that have varying properties in one or more directions that yield better performance over homogenous structures. The grading is usually considered through the thickness of beams, plates, or shells with different grading profiles. In this work, the design and analysis of multi-dimensional functionally graded nanocomposite structures are of interest with a focus on the material grading in the in-plane directions of plates, and the effect of the uncertainties in the elastic properties on the mechanical performance. The dissertation consists of six chapters; chapter one provides a literature review of the recent developments in the area of functionally graded structures, a brief overview of the properties and modeling of nanocomposites, and the uncertainty quantification of nanocomposites. The second chapter proposes a method for the design of multi-dimensional functionally graded structures based on the polynomial expansion of the volume fraction of the reinforcement. The third chapter extends the proposed method to design complex non-rectangular domains via coordinates transformations, and study the effects of the boundary conditions, loading type, and grading direction. The fourth chapter studies the reliability of in-plane FG plates by considering multiple sources of uncertainties (e.g. reinforcement size, volume fraction, and distribution). The fifth chapter studies the nonlinear dynamic and static responses of the FG plates by considering the post-flutter and the post-buckling behaviors. The sixth and last chapter provides a summary of the work done and the proposed future work. Throughout the dissertation work, the in-plane grading is optimized such that the minimum amount of reinforcement is used to satisfy certain mechanical performance constraints. The in-plane FG clamped plates showed a 45% average saving in the reinforcement amount compared to homogenous plates, while for simply supported plates the saving strongly depends on the problem nature and varies from 4% to 45%. For stiffened plates, the in-plane grading of the stiffeners led to a saving that can reach up to 200%. The reliability analysis showed that both homogenous and FG plates have the same level of uncertainty in the global responses. Also, the non-linear analysis indicated that both plates will in general behave similarlyItem Optimum Wing Shape of Highly Flexible Morphing Aircraft for Improved Flight Performance(American Institute of Aeronautics and Astronautics, 2016) Su, Weihua; Swei, Sean Shan-Min; Zhu, Guoming G.; University of Alabama Tuscaloosa; National Aeronautics & Space Administration (NASA); NASA Ames Research Center; Michigan State UniversityIn this paper, optimum wing bending and torsion deformations are explored for a mission adaptive, highly flexible morphing aircraft. The complete highly flexible aircraft is modeled using a strain-based geometrically nonlinear beam formulation, coupled with unsteady aerodynamics and six-degree-of-freedom rigid-body motions. Since there are no conventional discrete control surfaces for trimming the flexible aircraft, the design space for searching the optimum wing geometries is enlarged. To achieve high-performance flight, the wing geometry is best tailored according to the specific flight mission needs. In this study, the steady level flight and the coordinated turn flight are considered, and the optimum wing deformations with the minimum drag at these flight conditions are searched by using a modal-based optimization procedure, subject to the trim and other constraints. The numerical study verifies the feasibility of the modal-based optimization approach, and it shows the resulting optimum wing configuration and its sensitivity under different flight profiles.Item Optimum wing shaping and gust load alleviation of highly flexible aircraft with finite actuations(University of Alabama Libraries, 2018) Hammerton, Jared; Su, Weihua; University of Alabama TuscaloosaThe idea of improved flight performance is a constant goal within the aircraft design industry. In order to have aircraft which can fly further and for longer durations improved aerodynamic efficiency is required. Traditionally this is achieved through the use of discrete control elements such as flaps and slats. These mechanisms have a useful purpose in instances such as take off and landing, but are not often useful in other flight conditions because they tend to generate large amounts of drag. Recent research has shown that the potential for a continuously deformable wing is desired to effectively improve flight performance at any given flight condition. One example of this technology is NASA's Variable Camber Continuous Trailing Edge Flap (VCCTEF) which creates a trailing edge for an aircraft wing which can change the camber of individual sections without creating any discontinuities which generate drag. This application deals with small scale deformations (camber change) which can be improved to dealing with large scale deformations (bending, torsion, etc.) through the use of flexible structures and actuator systems. The first step in utilizing these large scale deformations to improve flight performance is to determine what wing geometries produce the most efficient performance. One method of determining this is to utilize an aeroelastic optimization process to define the wing geometry. Exploration of this optimization requires a definition of improved flight performance. The work expressed within this project used a reduction in drag as a measure of improved flight performance. This was chosen because if one considers an electric aircraft its range and endurance can be improved by reducing the drag experienced by the aircraft. The optimization was further improved when additional objectives were considered. The control cost required for these geometries gave insight into how much energy is required to gain the energy savings by increasing efficiency. Additionally some wing geometries were shown to produce better results at reducing the effects of wind gusts. After these optimizations were defined, an additional optimization was constructed to determine the best placement and number of actuators used to generate these wing geometries. Moving forward, the optimization will be applied over a range of velocities which will be used to develop a linear parameter varying controller. This controller will be designed to seamlessly transition between the optimum wing geometries at varying flight conditions.Item Path Planning Multi-Vehicle Missions with Random Finite Set Based Tracking(University of Alabama Libraries, 2023) Thomas, Ryan; Larson, JordanMulti-vehicle missions pose many problems including, Multi-Object Tracking (MOT) with non-Gaussian noise, optimal vehicle to target assignment, and optimal path planning. The contributions of this work are two fold, (1) non-Gaussian extensions to MOT filters, and (2) creating algorithms for multi-vehicle mission planning; both for a centralized architecture. To achieve (1), non-Gaussian extensions to existing Random Finite Set (RFS) based MOT filters are derived focusing on heavy-tailed distributions. The RFS-based MOT filters were selected due to their ability to rigorously model vehicle birth, death, and spawn, and measurement clutter. Student's t, and a Gaussian Scale Mixture (GSM) versions of the Generalized Labeled Multi-Bernoulli (GLMB) filter were developed. The Sequential Monte Carlo (SMC) GLMB was improved by utilizing Unscented Particle filters with a Markov Chain Monte Carlo movement step. Performance was compared via simulations and non-Gaussian filters performed better in the presence of non-Gaussian noise. Finally, the Student's t and GSM-GLMB were run on hardware, with the Student's t version running in real time. The key takeaway was real time performance, despite an un-optimized implementation. For (2), a hierarchical Guidance Navigation and Control (GNC) architecture was proposed, allowing a large team to navigate through static debris with vehicle death. Additionally, single vehicle Extended LQR (ELQR) was recast for the multi-vehicle case in two variants; analogous to Iterative LQR (ILQR). The first variant is like ILQR with an additional automatic transformation of target states into a distribution. Compared to ILQR, ELQR had better run time performance. The second used the Optimal Sub-Pattern Assignment (OSPA) for its cost and was compared to LQR-Rapidly-exploring Randomized Tree* (LQR-RRT*). The OSPA ELQR had better runtime and trajectories than either RRT* or density ELQR. Finally, an exploratory scenario, a Rendezvous and Proximity Operation (RPO), was formulated to combine tracking and planning; a spacecraft must track a dynamic debris field, calculate safe paths to a Resident Space Object (RSO), and track RSO features to estimate attitude and rate. RFS-based MOT filters performed tracking and attitude estimation conducted via a coupled sequential Extended KF and GLMB. ELQR was used for planning and predicted forward debris states assuming Clohessy-Wiltshire-Hill dynamics.Item Propeller whirl flutter analysis of the nasa all-electric X-57 through multibody dynamics simulations(University of Alabama Libraries, 2018) Hoover, Christian; Shen, Jinwei; University of Alabama TuscaloosaWith ridesharing companies researching into intracity air vehicles, aircraft efficiency has a significant impact on cost and resources. To increase efficiency, thinner and higher aspect ratio wings are used to reduce drag along with propellers due to their high propulsion efficiency. This research presents a whirl flutter analysis of the NASA all-electric X-57 and how it influences the design of the vehicle. Multibody dynamics analysis (MBD) is used for this study, Dymore, with correlating data from CAMRAD II given by NASA. Along with numerous studies of the X-57 using these MBDs, two cases are presented for validating the use of multibody dynamics: a Goland wing undergoing torsion bending flutter and an isolated propeller in whirl flutter. The whirl flutter stability of the X-57 is conducted in stages, starting with an isolated propeller and closing with a full free-flying aircraft. The wing is input into Dymore as an equivalent beam derived from the full NASTRAN FEM of the X-57. This dissertation is divided into four parts for the whirl flutter analysis: isolated propeller, semi-span, full-span, and a free-flying model. The isolated propeller has a large margin of safety with the pylon pitch and yaw stiffness values having to be reduced by two orders of magnitude for whirl flutter to occur. The semi-span undergoes three design revisions to ensure whirl flutter is not encountered for any of the symmetric wing modes. The full-span does not experience whirl flutter for the wing symmetric or anti-symmetric modes, and a parametric study is performed on various design variables. The free-flying model is stable for all the wing modes and shows the longitudinal flight dynamics modes interact with the flexible wing modes. When the stiffness in one of the pylon mounts is reduced to simulate damage, the system becomes unstable when the short period mode crosses the wing symmetric out-of-plane bending mode. This shows the need to include the flight dynamic modes when considering the whirl flutter stability of future aircraft.Item Propeller Whirl Flutter Study of a Distributed Electric Aircraft Using Multibody Dynamics Analysis(University of Alabama Libraries, 2022) Nelson, Kyle J; Shen, Jinwei; University of Alabama TuscaloosaThe NASA X-57 experimental aircraft, is an adaptation of the twin turbo-propItalian Tecnam P2006T. Designed to be lighter, quieter, and more efficient optionalthan the traditional internal combustion option, the X-57 utilizes an electric propulsionsystem. Coupled with an electric propulsion system, a new lighter, thinner wing hasbeen developed by NASA to increase the cruise efficiency of the aircraft. An electric propulsion system removes the need for fossil fuels, creates a zero emission aircraft, andhelps achieve to a net 500% increase in cruise efficiency. Fourteen total propellers willbe fitted to the X-57. Two main propellers located at the wingtip will be used throughout all phases of flight. The other 12 propellers are lift-augmentation devices only used in the take-off and landing phases of flight. The propeller downwash increases the flow speed of the wing and avoid stall at low speed. A unique feature of the high-lift propellers is that they can fold against their nacelles to reduce drag during cruise; then deploy with centrifugal force when needed. These changes to the wing and propulsion system for the X-57 has increased concern for its aeroelastic stability, in particular, propeller whirl flutter. Propeller whirl flutter is an aeroelastic instability where the coupled motion of the airframe and propeller becomes unstable. This study uses multibody dynamics analysisto predict the propeller whirl flutter stability of the X-57 Maxwell. Multibody dynamics software has become increasingly popular in the rotorcraft communities because of their generality and capability to model complex, coupled systems. Dymore is a finite element (FE) based multibody dynamics code for the comprehensive modeling of nonlinear flexible multibody systems. The elements library in Dymore includes rigid and deformable bodies as well as joint elements. The aerodynamics are modeled using a built-in lifting line model but can also be coupled with an external code. The differential-algebraic equations of motion are established using a Lagrange multiplier method that is solved in a time marching scheme. The X-57 model being used in Dymore has: 1. a beam model of the propeller blades, and 2. a modal super element representation of the aircraft. The beam models in Dymore are derived from NASTRANFEM model for the wing and propeller blades. Tuned springs are used at the wingtip to capture the pylon modes of the tip propeller. A torsional spring is used to constrain the folding motion of the high-lift propellers. The modal super element model that is used is a reduced order model of the full NASTRAN model of the X-57 Maxwell. This model retains 6 rigid-body modes, the first 100 elastic modes as well as the degrees of freedom associated with the interface nodes chosen to be included in the model. CAMRAD II is another multibody dynamics code that was developed by Wayne Johnson and it will be a source of comparison for Dymore. Both codes have been established as being able to accurately predict the whirl flutter boundary of tilt-rotoraircraft [1, 2]. The scope of this study is to subject the X-57 propellers and a modal representation of the full-span wing with fuselage to a variety of conditions to determine the whirl flutter boundary of the aircraft. Isolated propellers are developed and compared against wind tunnel data to validate the aerodynamic models used. A study to subject an isolated propeller with increasing viscous damping about the folding hinge is performed to validate the stability of the folding blade motion and compared against experimental data. A baseline modal super-element model is used to compared against previous Dymore and CAMRAD results for a full-span model. This study only considers the influence of the tip-propeller to whirl flutter stability. The high-lift propellers are modeled as rigid bodies in the previous Dymore and CAMRAD models. A sensitivity study is carried out to compare the location of the high-lift propellers onthe stability of the X-57. This study showed that the out-board propellers have the highest damping contribution to model. A study is performed to determine the whirl flutter stability of the full system with contribution from all 14 propellers.Item Rapid On-Demand Launch Mission Planning for Timely Delivery of Spacecraft Constellations(University of Alabama Libraries, 2021) Simpson, Christopher Ross; Branam, Richard D.; O'Neill, Charles R.; University of Alabama TuscaloosaOn-demand launch from an airborne launch vehicle can provide a nanosatellite overhead in under an hour anywhere in the world. On-demand launch can support capabilities already on-orbit and provide tailored or new capabilities rapidly. A military rapid on-demand launch fulfills operational requirements for on-demand space support and reconstitution. Current capabilities in tracking and denial of space-assets limits the effectiveness of constellations already on-orbit to be operationally responsive in military space. Time-sensitive returns using scheduling algorithms for the timely deployment of a nanosatellite constellation can be achieved. Four case studies show the capability to provide persistent coverage of a moving target to provide terminal guidance to a net-enabled weapon, provide reconstitution of a PNT constellation, view persistence, and on-demand coverage of natural phenomena for disaster response. The three novel contributions of this work are creation of a mission planning system to deliver a constellation on-demand to observe a target from anywhere in the world using tactical airborne aircraft, combining existing vehicle models for aircraft, launch vehicle, satellite, and optimization tools to modify on-demand launch scheduling of a constellation for optimal coverage, and applying previously existing coverage quality measurements to measure replenishment and reconstitution value added by on-demand launch. A mission planning system for delivery of multiple satellites from multiple similar air-launched platforms for constellation installation over any selected point constrained for reaction time with optimized coverage quality is delivered.Item Scalable Deep Learning-Based Quantitative Ultrasound Tomography for Medical Imaging(University of Alabama Libraries, 2025) Anwar, Shoaib; Su, WeihuaQuantitative ultrasound tomography (QUT), powered by full waveform inversion (FWI), enables precise tissue differentiation and diagnosis through fast, affordable scanning without the need for sedatives or X-rays. However, the extended processing times and reconstruction errors of this physics-based method limit their application in time-sensitive areas. This dissertation aims to overcome these challenges by developing a robust cyberinfrastructure that integrates advanced artificial intelligence techniques into the FWI workflow for breast tissue characterization and lesion detection. The scarcity of clinical data is a foundational challenge in deep learning (DL) approaches. As an alternative, synthetic numerical datasets offer considerable promise. However, generating such data at a sufficient scale and fidelity is time-consuming. To address this limitation, this research develops an efficient, scalable, and high-performance computing (HPC)-based framework for the accelerated generation of FWI-based datasets of realistic numerical breast phantoms (NBPs). This framework drastically reduces dataset production timelines from several months to just a day. Building upon the datasets generated by HPC, the dissertation introduces a novel deep learning approach called adjoint theory with generative adversarial network (ATGAN). This method is designed to accelerate the FWI process. ATGAN integrates the traditional adjoint-tomography theory with a GAN architecture into FWI-based QUT by embedding strong physics-based priors into the conditional GAN. This approach significantly reduces computational demands. Comparative analyses demonstrate that ATGAN substantially outperforms classical U-Net models, demonstrating improved generalization, greater training stability, and enhanced preservation of critical structural details, particularly when reconstructing high-resolution wave speed maps from initial low-fidelity estimates. In addition to the data-driven ATGAN approach, a second method known as physics-guided neural network FWI (PNFWI) has been developed. PNFWI employs a fully unsupervised, physics-guided neural network strategy that operates directly with raw ultrasound measurement data eliminating the need for initial wave speed assumptions or ground-truth wave speed maps. Central to the PNFWI approach is the cycle-consistency loss, which enables the network to train while solving the physics of wave propagation. This significantly mitigates the risk of cycle skipping and ensures stable convergence even under conditions of added data noise. Therefore, this approach holds substantial promise for clinical applications by potentially reducing false-positive rates.Item Static and dynamic characteristics of membrane wings at low Reynolds number(University of Alabama Libraries, 2014) Zhang, Zheng; Hubner, James Paul; University of Alabama TuscaloosaTo lessen the deterioration of fixed-wing aerodynamic performance associated with Reynolds numbers (Re) below 100,000, flexible membrane wing designs have been studied and proposed as an alternative for micro air vehicle (MAV) use. The beneficial effects of a flexible membrane can include higher lift, steeper lift-curve slope, delayed stall, gentle stall characteristics, and greater efficiency. These benefits have been attributed to both the time-averaged and dynamic deformation of the membrane. The background literature search shows that few investigations regarding membrane wings have focused on low aspect ratio (AR) wings (AR < 2) with a free (or unattached) trailing edge (TE), where the spanwise flow over the wing surface is dominant. Additionally, no study has looked at introducing membrane vibration at the leading edge (LE), which could potentially improve the aerodynamic performance by reducing the LE separation for the thin airfoil. Therefore, this work discusses the static and dynamic characteristics of a simplified membrane wing and airfoil configuration in the low Re flow (Re = 40,000 - 70,000). The global aerodynamic forces on the free TE membrane wing with varying wing AR, cell AR, and pre-strain level were measured. The result shows that the aerodynamic advantages of the flexible membrane are retained for the low AR wings. The optimal membrane cell AR is found to be approximately one. The comparison of the aerodynamic forces between the low AR membrane wings and the corresponding 3D- printed wings with the time-averaged deformation indicates the importance of membrane dynamic motion for the derived aerodynamic benefits. The effect of LE vibration was studied by performing wake velocity profile scans and aerodynamic load measurements on a spanwise tensioned, tip-bounded membrane cell. The LE vibration increased the lift coefficient in pre-stall region, but also resulted in a deeper wake, greater momentum loss, and less peak aerodynamic efficiency and power efficiency. Because the aerodynamic benefits by the membrane are attributed to the static and dynamic characteristics, the nondimensional deformation scaling and frequency scaling are proposed. For the stiff membrane, as the aerodynamic-induced strain is small, the membrane deflection can be reasonably predicted using a wave equation with a constant tension. For the flexible membrane, the trend of aerodynamic-induced strain with respect to dynamic pressure and angle-of-attack is qualitatively predicted using a catenary curve model. Compared with the traditional Strouhal scaling, the proposed nondimensional frequency scaling with the linear combination of applied strain and aerodynamic-induced strain better characterizes the fluid-structure interaction.