Aeronautics and astronautics

Permanent URI for this collectionhttps://digital.lib.washington.edu/handle/1773/4889

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Design, Integration, and Experimental Validation of a Lifting-Body Quadrotor
(2026-04-20) Zhou, Jason S.K.; Açıkmeşe, Behçet
This thesis describes the design, integration, and experimental validation of a lifting-body tailsitting quadrotor intended to retain vertical takeoff and landing capability while generating meaningful aerodynamic lift in forward flight. The work is divided into four areas. The first covers a PX4 Autopilot firmware port onto a custom flight controller with software-defined hardware, validated through manual and autonomous flight on a conventional quadrotor platform. The second presents the aerodynamic design of the tailsitter airframe through parametric modeling, vortex-lattice simulation, and wind tunnel testing. The third addresses mechanical design, covering structural reinforcement, manufacturability, and electronics packaging for an airframe manufactured entirely by FDM. The fourth presents hover flight results and a longitudinal transition simulation. The results establish a baseline for future work on multirotor vehicles that combine hover capability with efficient high-speed flight.
Computational Investigation into the Multi-Axial Response of Quasi-Isotropic and Discontinuous Fiber Composites
(2026-04-20) Thakare, Alisha Sangram; Salviato, Marco
Discontinuous Fiber Composites (DFCs) have surfaced as a feasible substitute fortraditional continuous fiber laminates owing to their superior manufacturability, geo- metric adaptability, low production costs and suitability for high-volume production. Their platelet-based stochastic meso-structure facilitates the formation of intricate shapes while preserving advantageous mechanical properties. The unpredictability in platelet orientation and distribution results in variations in strength, stiffness and fracture characteristics. Despite extensive research aimed at characterizing the ten- sile and shear fracture responses of DFC coupons, most investigations are limited to uniaxial loading conditions. In actual structural components, composite materials are rarely exposed to pure tension or pure shear forces. Brackets, joints, stiffened panels, and molded automotive and aerospace components undergo combined tension-shear loading, with the inter- play of normal and shear loads determining the onset and progression of damage. In multi-axial stress states, fiber-matrix interactions and gradual stiffness degradation are pivotal in the progression of failure. Current strength assessment methods that concentrate exclusively on tensile or shear properties are inadequate for capturing the coupled stress interactions and the nonlinear structural response. his study conducts a computational analysis of the multi-axial behavior of Quasi- Isotropic (QI) continuous fiber and Discontinuous Fiber Composite notched coupons under combined loading circumstances. Experimental data acquired by an Arcan fixture are utilized to determine stress envelopes, load–displacement responses and energy dissipation patterns under different ratios of normal and shear stress. A fi- nite element framework is established in Abaqus/Explicit utilizing the integrated Hashin failure criteria to represent fiber and matrix failure processes. The formula- tion includes damage initiation based on discrete failure modes and gradual stiffness degradation to model failure development in notched specimens under various loading angles. The suggested framework enhances traditional uniaxial composite characterisa- tion by advancing to a comprehensive multi-axial damage evaluation. The model- ing approach facilitates the capture of advanced composite failure mechanisms, such as matrix splitting and distributed fracture processes in QI laminates, along with platelet-driven damage in DFC systems.
Advanced Techniques for Hall Thruster Research and Development
(2026-02-05) Thoreau, Peter; Little, Justin M
Hall thrusters are the most common form of electric propulsion on spacecraft currently in Earth orbit, they offer excellent efficiency, high thrust to power, and have relatively simple power processing units. They have seen significant development since their first commercial flight in 1972, however, methods for characterizing their operation for both development and flight have remained relatively consistent. Therefore, advanced techniques have been developed to more effectively, efficiently, and expeditiously characterize thruster operation. These methods have been advanced through four primary approaches. The first approach was the development of a magnetically shielded Hall thruster with a movable inner pole to investigate the influence of magnetic field shape on thruster operation. The use of magnetically shielded geometries has been demonstrated to drastically reduce the rate of erosion on Hall thruster channel walls. However, the switch to a magnetically shielded configuration can increase plume divergence contributing to a decrease in efficiency and thrust. Varying the magnetic field shape near the exit of the thruster has been demonstrated to decrease plume divergence, however, the impact on thruster behavior is unknown. Three test campaigns on iterations of the ACME thruster, operating on both xenon and krypton, investigate the plume divergence, performance and efficiency changes, and map the plume of the thruster across a range of pole positions. The divergence, voltage, and current utilization efficiencies have strong dependencies on the relative pole position across all operating points. The dependence of anode efficiency on pole position can be mapped to the other efficiencies within the uncertainty of the experiment. The change in inner pole position of -1 mm on xenon and - 4 mm on krypton has been shown to significantly increase the anode efficiency of the thruster, primarily through divergence and voltage utilization efficiency gains. The second approach assesses the standard methods for characterizing thruster efficiency using plume diagnostics. The standard practice of measuring a centerline Ion Energy Distribution Function (IEDF) is insufficient for electric propulsion systems with unknown or highly divergent plume structures. This method is compared to spatially resolved IEDF measurements using a swept retarding potential analyzer to generate an angularly resolved IEDF. Using an adjustable Hall thruster, plumes ranging from highly divergent to over-focused were fully characterized and compared to the anode efficiency calculated using thrust stand measurements. Both centerline and spatially resolved measurements of the IEDF were sufficient to accurately measure the voltage utilization efficiency on well focused plumes. As the plume diverged, more complex plume structures were observed, and only the spatially resolved measurement maintained agreement with the thrust stand based efficiency. . The third approach to expedite Hall thruster development created a method to rapidly and autonomously optimize thruster performance. This method combines rapid thrust measurement, thruster-in-the-loop control, and derivative-free optimization schemes to automate thruster optimization and rapidly find operational areas of interest, thus reducing the reliance on current-voltage-magnetic field (IVB) maps. Rapid thrust measurements are achieved by comparing test points to a known operating point, allowing fast and accurate thrust measurement while minimizing the effects of long-term thermal drift. Fast mapping of a Hall thruster's operation was demonstrated at 72 test points per hour, with an average thrust measurement error of < 1% compared to conventional thrust measurements. Two-dimensional (thruster discharge voltage and magnetic field strength) Nelder-Mead and Powell optimization schemes are shown to converge rapidly to maxima in total efficiency or specific impulse in fewer than 15 test points. The Powell optimization scheme remained effective in five dimensions, further increasing the peak thruster efficiency while adjusting three additional thruster dimensions (keeper current, cathode flow fraction, and magnetic field skew). The fourth approach developed a method for autonomous optimization and modeling of an electric thruster that applies Bayesian optimization on a Gaussian Process Regression model generated in real time from experimental telemetry. The method can be combined with a prescribed objective function and optimization scheme to optimize the thruster for different mission objectives. A notional extrasolar probe mission powered by a Hall effect thruster is considered as an example where the goal of the optimization is to find the propellant gas mixture (argon:krypton:xenon) that minimizes overall mission cost. The results show that a thruster running on a mixture ratio of 11:87:2 benefits from a 7% reduction in total cost compared to the same thruster running on pure xenon. Analysis of the model reveals how the optimal propellant mixture depends strongly on propellant storage technologies, fluctuations in propellant price, and launch costs. Results from this analysis match trends seen in the commercial market with the move to cheaper propellants.
Real-Time Trajectory Optimization for High-Performance Guidance & Control
(2026-02-05) Kamath, Abhinav Girish; Açıkmeşe, Behçet
Autonomous systems of today rely on trajectory planning to achieve complex tasks. With the increasing capabilities of such systems, there is a need for a framework that not only allows for accurate modeling of these tasks, but also enables real-time generation of feasible trajectories to achieve them. This dissertation presents trajectory generation methods, using gradient-based optimization and set-based dynamic programming, for a large class of optimal, robust, and resilient control problems. These methods are intended for adoption onboard agile autonomous systems—such as reusable rockets—that mandate high-performance guidance & control.
Experimental Investigation of Plasma-Electrode Interactions on the ZaP-HD Flow Z-Pinch Device
(2026-02-05) Bin Khairi, Amierul Aqil; Shumlak, Uri
The electrodes of sheared-flow-stabilized (SFS) Z-pinch devices directly face the core plasma and supply the pinch current. The high temperature, high density plasma environment produces intense particle and heat fluxes, leading to concerns of electrode erosion that limit durability and contaminate the plasma. An improved understanding of these plasma-electrode interactions is required, especially at the high temperatures and current densities required for fusion applications. An experimental investigation is conducted on the ZaP-HD SFS Z-pinch device, which produces plasma temperatures up to 1 keV, densities of 10^23 m^-3, and drives pinch currents up to 150 kA. In-situ measurements of the gross carbon erosion flux from the graphite electrode are obtained with S/XB spectroscopy. The measured fluxes exceed the theoretical values from physical sputtering, but are comparable with the expected sublimation flux. An analysis of the ionization mean free paths of neutrals produced by both erosion processes indicates that ionization of sublimated carbon occurs within the electrode sheath, while sputtered neutrals are ionized outside of the sheath. This suggests significant redeposition of sublimated carbon, leading to a process of carbon recycling. The sputtered carbon is therefore primarily responsible for the net erosion. Initial measurements of the electrode surface temperature with a two-color pyrometer are also presented. Ex-situ analysis of electrode material is enabled by the design of a removable coupon. Three different plasma exposure cases were tested that involved varying the pinch current and the particle fluence to the electrode. Net mass loss measurements imply net erosion fluxes far smaller than indicated by spectroscopic measurements of total erosion, which supports the theory of high redeposition rates. Erosion rates range from 0.01 to 0.1 mg/C, which are comparable to existing arc discharge devices. Measurements of the microscopic surface morphology and roughness indicate substantial material rearrangement and general smoothing except at high plasma exposure conditions. The granular matrix of graphite is mostly replaced by larger consolidated structures that reduce the number of visible voids. Crack formation is apparent, possibly due to thermal cycling, which suggests the importance of surface heating and possible phase change of graphite. Definitive features of sputtering such as pitting and cratering are absent, and further study is needed to attribute the observed morphology to other physical processes. Overall, these results indicate some alignment with erosion and recycling processes in high-current arc discharges, which have successfully operated with solid electrodes in extreme environments. Further investigation into these similarities may yield useful understanding that can be applied to the management of erosion on SFS Z-pinch electrodes.
Method for an In-situ Diagnostic for Inner Pole Erosion of a Magnetically Shielded Hall Thruster
(2026-02-05) Phung, Connie; Little, Justin
Erosion in Hall-effect thrusters poses a critical challenge to propulsion efficiency and mission longevity. While erosion is not a new phenomenon for electrical propulsion devices, recent research has identified inner pole erosion as the current primary driver for mission length limitations. This study investigates sensor integration and resistance-based measurement techniques to quantify erosion at the inner pole. An unwired sensor was exposed to 600W (300V, 2A) plasma conditions for two hours, resulting in 3 μm of erosion, calculated from manual resistance measurements. A fully integrated in-situ sensor was exposed to 225W (90V, 2.5A) conditions for one hour and experienced 3-5 μm of erosion, which was calculated from remote measurement data. Sputter yield modeling and experimental erosion rates aligned well with existing literature, while erosion rate modeling underpredicted actual erosion rates, consistent with prior findings. These results support the viability of accelerated, in-situ diagnostics for erosion monitoring at the inner pole. Future work is recommended to improve integration techniques and modeling fidelity.
Reconfigurability, Tunability, and Controllability of Origami-based Mechanical Metamaterials
(2026-02-05) Yamaguchi, Koshiro; Yang, Jinkyu
Mechanical metamaterials, materials with architecture-driven properties, hold promise for applications ranging from aerospace components to soft robotic devices. Yet these engineered structures often face challenges in practical applications due to costly fabrication and fixed, non-adjustable properties once made. Origami-inspired design offers a path to overcome these limitations: by folding flexible architectures, metamaterials can gain reconfigurability and tunable behavior. In this dissertation, we introduce technical approaches for assessing reconfigurability, tunability, and controllability of origami-based mechanical metamaterials, focusing on Tachi–Miura Polyhedron (TMP) and Miura-ori patterns as model systems. Our goal is to advance these metamaterials toward the vision of highly reconfigurable origami-based mechanical metamaterials; materials that can be reshaped or repurposed on demand. To navigate the enormous design space of origami metamaterials, we develop a graph-based algorithm that systematically generates all geometrically valid TMP configurations. This approach avoids the combinatorial explosion that hampers brute-force searches, running roughly 20–100 times faster and enabling the analysis of much larger systems. By mapping the full range of configurations, our method also reveals highly heterogeneous, non-intuitive designs that would be impractical to discover otherwise. Next, we demonstrate a post-fabrication programming technique to fine-tune the metamaterial’s mechanical properties. By heating the TMP-based structures in a controlled manner, we reconfigure their internal folding geometry (zero-energy state) and achieve dramatic changes in stiffness and density. This thermomechanical tuning method increased the effective Young’s modulus by approximately 60-fold and reduced the material’s density by tenfold in experiments. Interestingly, we observed an unusual inverse correlation between stiffness and density, a beneficial trait for lightweight materials, and showed that Poisson’s ratio can be adjusted from negative (auxetic) to positive values. We also tackle the challenge of investigating the controllability of these compliant structures for deployment. Using a state-space model of a Miura-ori origami array, we analyze the system’s controllability to determine where actuators should be placed for the most effective shape change. The optimal actuation scheme predicted by our model was validated experimentally, yielding a fourfold increase in deployment efficiency compared to the least effective actuator configuration. This result demonstrates that even highly flexible metamaterials can be efficiently deployed through intelligent control strategies. Together, these advances establish a foundation for origami metamaterials that can be efficiently designed, adjusted on demand, and actively controlled as needed. By bridging geometric design, material tuning, and dynamic actuation, this work paves the way toward intelligent, adaptive origami-based structures with potential applications from aerospace and robotics to biomedical engineering.
Analysis of the Mechanically Choked Ram Accelerator
(2026-02-05) Clevenger, Jackson Louis; Knowlen, Carl
The ram accelerator is a hypervelocity launch concept which uses a ramjet-like propulsive cycle to accelerate a projectile to hypersonic velocities. Research surrounding this technology has thus far been primarily focused on the thermally choked mode of operation, which relies on acceleration to sonic conditions of subsonic flow after the diffuser via constant area heat addition in order to bind the end of the combustion zone. However, early work suggested the possibility of using a nozzle to mechanically choke the flow, allowing the flow to be accelerated to greater than Mach one at the exit. Numerical work done with this mode demonstrated a substantial increases in thrust, sometimes double the non-dimensional thrust produced by the thermally choked mode at the same non-dimensional heat release value. Additionally, due to the mode’s ability to have the flow exit supersonically, the mode’s flight Mach number was shown to be able to exceed the Chapman-Jouguet detonation velocity, expanding the operable Mach number range. In order to validate these claims, a set of projectiles was manufactured and fired in the University of Washington’s ram accelerator laboratory. Over the course of these experiments the projectile showed a consistent and meaningful increase in both thrust and acceleration as compared to their thermally choked counterparts by an average of 50.1% and 20.5% respectively. This was in spite of increased mass accrued from the tail sections. The mode showed difficulty in starting in the first baffled tube when entering below 900 ms and showed consistent structuralfailure between 1150 - 1200 ms . Due to system limitations, these results were only shown through the baffled tube section of the system, and railed tube operation, which would be needed to fully validate theoretical claims, was unable to be successfully achieved. Regardless, the test series showed promising results and further testing will be required to validate the mode’s effectiveness as compared to theory.
Control Methodologies for Systems with Set-Valued Uncertainties
(2026-02-05) Deole, Aditya; Mesbahi, Mehran
This dissertation develops control methodologies for systems with set-valued uncertainties in modeling and estimation, with applications spanning spacecraft navigation and neuromodulation. The work is organized into two major parts. The first part addresses estimation-related uncertainties in vision-guided navigation and their integration into planning and control. The second part focuses on modeling uncertainty in neuronal systems, presenting a controller design and model inference framework for neuromodulation.In the context of spacecraft navigation, we design a pose-estimation pipeline supported by a photorealistic simulation environment for satellite rendezvous operations. A Machine Learning (ML)-based platform is developed to detect the pose of a target spacecraft, and the simulation environment is used to generate test and validation data with a minimal simulation-to-reality (sim2real) gap. The platform also serves as a tool for modeling ML-based uncertainties, thereby enabling robust controller design. Building on this foundation, two approaches are proposed for incorporating ML-based estimation into navigation systems. The first introduces a controller design methodology that constructs invariant funnels for slope-bounded uncertainty models around nominal trajectories. The second employs a passivity-based framework to characterize uncertainties that define a family of feasible controllers. Furthermore, we demonstrate that multi-agent consensus, viewed as an interconnection of passive agents, can enhance estimation performance in distributed settings. We further investigate estimation-aware trajectory design for improving the performance of state-dependent sensors such as perception maps. A class of state-dependent, set-valued output uncertainty models is formalized as state-to-output uncertainty set maps. An observability-based metric is introduced to quantify the estimator’s sensitivity to output perturbations, and this metric is optimized to generate trajectories that improve estimation performance. Extensions of this framework to multi-agent trajectory planning are also presented. The final part of the dissertation develops a feedback control framework for neuromodulation. By analyzing neuronal system trajectories during experimental sessions, we show that average neuronal dynamics in closed-loop scenarios can be approximated as a linear parameter-dependent system, with parameter-dependent internal processes. For a fixed parameter, the trial-averaged dynamics exhibit closed-loop linear behavior. A proportional–integral (PI) feedback controller is demonstrated to effectively track reference signals over a finite horizon, outperforming feedforward control in both tracking accuracy and disturbance rejection, while also reducing trial-to-trial variability. Moreover, in a ``reward-induced'' brain state with more consistent parameters, a sample-based approach is shown to enable controller optimization. Together, these contributions advance the integration of machine learning, robust control, and trajectory optimization in the presence of set-valued uncertainty, providing new methodologies for controlling uncertain dynamical systems in both engineering and biological domains.
3D Particle Tracking Velocimetry of the Convective Structure in Transient Evaporating Liquid Films
(2026-02-05) Jansen, Andrew Gunther; Hermanson, James C; Dabiri, Dana
Evaporation plays a critical role in many terrestrial and micro-gravity engineering problems including component cooling, fuel vaporization, and coating processes. 3D-particle tracking velocimetry(PTV) was implemented to allow for non-intrusive velocity measurement of the transient convective structure in liquid, upward facing, evaporating films. Dichloromethane films, 2-5mm thick, in their own vapor were subjected to an impulsive superheat via pressure modulation and the development of the resulting convective structure was observed. 2mm films were used for comparison to previous visualization and heat transfer results. Two primary convective structures were observed via 3D-PTV: vermiculated rolls and polygonal cells. The roll structure consisted of adjacent rolls typically 3mm wide and 2mm tall with an overturning velocity of 1.3mm/s. The polygonal cells had a central up-welling with down-welling along the perimeter. The cells were approximately 2mm tall and 12mm across with a typical overturning velocity of 1.1mm/s. These flow structures were consistent with previous schlieren visualization results. Distinct peaks in the median speed in the films were observed 3.5 and 11 seconds after the application of the superheat. These peaks generally aligned with previously reported peaks in heat transfer of similar superheated films. The median speed peak at 3.5 seconds lagged behind the first peak in heat transfer by about 1.5 seconds suggesting a brief conduction only phase before the convective structure in the film is developed. The second peaks in median speed and heat transfer were closely aligned in time suggesting an increase in film activity drives thermal transport across the film at that time. Both peaks in median film speed occurred during previously reported visual transitions in the convective structure. Trends in the measured film velocities and the observed convective structure suggest the entire film is engaged in convective motion within 3.5 seconds of the application the superheat, much sooner than previously hypothesized.
Robust Sequential Convex Programming for Quadrotor Trajectory Planning with Obstacle Avoidance Under Wind Disturbances
(2025-10-02) Demiralay, Kutay; Acikmese, Behcet
In this work, we address the problem of trajectory planning for a 3D quadrotor navigatingaround three spherical obstacles under bounded wind disturbances. The goal is to reach a desired final state from a given initial state within a fixed time, while minimizing fuel consumption and avoiding obstacles. We first compute a nominal trajectory in a no-wind setting using Sequential Convex Programming (SCP) applied to a 6-state, 3-DoF quadrotor model. This trajectory satisfies all state, control, and obstacle constraints while minimizing fuel use. However, in the presence of constant wind, the nominal path becomes unreliable due to unmodeled drift, leading to potential obstacle violations—unacceptable in safety-critical applications. To improve robustness without relying on any low-level controller, we implement three strategies: (i) LQR-based tracking of the wind-free nominal trajectory, (ii) a receding-horizon SCP approach that re-solves the optimization at each node using updated state feedback, convex half-space approximations, and Wind-Adaptive Residual Correction (WARC), and (iii) a tracking-style method using smaller SCP subproblems to increase responsiveness. Finally, we apply funnel synthesis along the nominal trajectory to certify allowable deviations at each node. This framework enables safe, fuel-efficient flight despite bounded disturbances.
Multiscale Optimization of Weav3D Lattice-Reinforced Composites for Lightweight Structural Design
(2025-10-02) Mehta, Jainam Chetan; Salviato, Marco
This thesis evaluates the effectiveness of conventional optimization methods applied to lattice-reinforced composite structures, specifically panels manufactured using Weav3D technology. Weav3D integrates thermoplastic composite tapes into tailored lattice geometries, enabling strategic reinforcement placement. Material properties of the carbon fiber tapes were first experimentally characterized through mechanical testing on a universal testing machine (UTM), with strain fields measured using Digital Image Correlation (DIC). These validated properties served as inputs to a computational optimization framework using Altair HyperStudy for parameter exploration, Jpanel for generating homogenized orthotropic material models, and OptiStruct for finite element analysis. A Design of Experiments (DOE) based on Latin Hypercube Sampling (LHS) guided surrogate modeling and global optimization. Results showed a consistent preference for warp-direction reinforcement under bending loads, with fill-direction material significantly reduced. The final optimized lattice-based configuration achieved a 21% reduction in mass compared to a continuous baseline panel, confirming that classical surrogate-based optimization techniques can effectively streamline composite design without compromising performance.
Experimental Investigation of Influence of Crack Parallel Tension on Fracture Energy in Carbon Fiber Composites
(2025-10-02) Vemparala, Ashok HVS; Salviato, Marco
This work investigates the influence of crack-parallel tensile stress on the global Mode I interlaminar fracture behavior of carbon fiber polymeric matrix composites. Traditional Linear Elastic Fracture Mechanics (LEFM) assumes that stresses parallel to a crack have negligible impact on fracture toughness, an assumption challenged by recent studies such as the Gap Test. In quasibrittle materials like fiber-reinforced composites, the presence of crack-parallel stress can significantly modify crack propagation, fracture energy, and the associated fracture process zone (FPZ). The study's goal is to quantify these effects systematically through controlled experiments and to provide insights into fracture mechanics beyond conventional assumptions. By understanding how parallel stresses alter crack growth and energy dissipation, this work helps improve predictive models for composite structures, providing a valuable reference for academic research and practical applications. The findings aim to refine the characterization of composite fracture behavior, highlighting the need for methods that account for FPZ effects under complex stress states. A novel experimental method, the Half-Open I test, was developed to investigate the effect of crack-parallel tension on Mode I fracture. Specimens consist of cross-ply IM7/977-3 carbon fiber laminates with a controlled initial crack introduced using a Teflon film. The key innovation involves inserting a GFRP tab into the crack seam, generating a bending moment at the crack front that induces tension along the crack propagation direction while simultaneously applying a crack-opening moment. By varying tab thickness, the magnitude of the induced bending moment and parallel tension is systematically controlled. Crack propagation is tracked using high-resolution imaging, with crack lengths measured at regular intervals. The negative geometry of the design promotes stable crack growth, providing an advantage over traditional DCB tests. However, the only limitation is the inapplicability of Bazant's size effect law, preventing direct estimation of fracture energy and FPZ size. The experiments reveal that increasing the thickness of the inserted tab, and consequently the crack-parallel tension, enhances the fracture resistance of the composite. Measured crack propagation lengths are converted into energy release rates using Abaqus finite element simulations, and R-curves are reconstructed for each tab thickness and laminate. Despite data noise, trends indicate an rightward shift in fracture energy with increasing parallel stress, suggesting that low-to-moderate crack-parallel tension strengthens the laminate through mechanisms such as fiber bridging and extended FPZ development. Thicker tabs produce more stable crack propagation, while thinner tabs exhibit initial instability. These findings demonstrate that Mode I fracture energy in composites is not a fixed material property but is influenced by the local stress state, challenging traditional LEFM assumptions. Overall, the study provides a robust methodology for assessing crack-parallel effects and highlights the importance of incorporating FPZ considerations in modeling and designing composite structures.
Patient Specific Computational Fluid Dynamic in the Left Atrium. Atrial Fibrillation vs Sinus Rhythm
(2025-10-02) Sharda, Savier Yogita; Dabiri, Dana
Atrial fibrillation (AF) is the most common sustained arrhythmia and a leading cause of stroke, yet the direct hemodynamic consequences of AF remain difficult to isolate in clinical practice. Imaging captures anatomy, and ECGs record rhythm, but neither alone can resolve the full, three-dimensional, time-resolved blood flow patterns that link AF to clot formation.This study develops a patient-specific computational framework to address this limitation. Critically, we analyze the same patients under both sinus rhythm (SR) and AF, enabling direct comparison of how rhythm alone alters atrial flow. Using imaging and ECG data, we reconstruct left atrial (LA) geometries, incorporate motion across the cardiac cycle, and simulate blood flow to evaluate changes in transport dynamics and stasis between the two conditions. The comparisons reveal clear hemodynamic signatures of AF: reduced atrial emptying, irregular contraction, and disrupted flow organization, all of which contribute to conditions favorable for thrombus formation. At the same time, differences in atrial appendage morphology and rhythm-specific electrical patterns highlight the patient-to-patient variability that shapes risk. By directly contrasting SR and AF within the same individuals, this framework bridges a critical gap between clinical observation and mechanistic understanding. It shows how computational modeling can uncover hidden flow dynamics inaccessible to imaging alone and offers a foundation for personalized assessment of AF-related stroke risk.
Characterization of Gas Dynamic Effects in Baffled Tube Ram Accelerators
(2025-10-02) Correy, John P; Knowlen, Carl
The ram accelerator is a hypervelocity launch technology which uses a ramjet-like propulsion cycle to accelerate payloads to velocities in the kilometers-per-second range. The smooth bore ram accelerator (SBRA) has shown impressive performance at high velocities, drawing attention for its potential as an orbital launch device, as well as defense, emergency response, and mining possibilities. Recent developments have extended the capability of the system in the low-velocity regime. The most novel development is the inclusion of baffles within the launch tube, creating the baffled tube ram accelerator (BTRA). These baffles serve to isolate combustion regions within the launch environment, and have been proven to allow stable operation with propellants of higher energy densities. This work investigates secondary effects which arise from the more complicatedgasdynamic environment of the BTRA. Testing of the BTRA system has confirmed that predictions from quasi-one-dimensional SBRA theory are not always accurate in this more complicated geometry. In conjunction with computational efforts from other works, this study characterizes the impact of varying baffle dimensions in inert gas and combustive environments. Inert gas phenomena were investigated pertaining to spacing between baffles, baffle wall thickness, and projectile-to-bore variation, and using a a novel shadowgraph imaging technique. Performance phenomena were characterized by variation of baffle inserts within the BTRA test system, with projectile velocity and thrust or drag measured for both inert and non-combustive configurations. The discovery of starting capabilities below established minimum limits permitted easier injection of projectiles into BTRA systems, with profound implications on large-scale implementation of the technology. Additionally, gasdynamic environments were imaged for projectiles of differing bore occlusion, suggesting the development of a distinct operating mode at high occlusion percentages which explains previous difficulties and inconsistencies in experiments with near-full-bore projectiles. Finally, it was found that both the spacing between baffles and the baffle chamber radius had direct effects on projectile thrust environment, permitting increased performance at the expense of energy density tolerance, and suggesting that optimization of the BTRA design may be a multi-dimensional effort with promising potential.
Robust Predictive Control for Uncertain Nonlinear Systems via Funnel Synthesis
(2025-10-02) Kim, Taewan; Açıkmeşe, Behçet
This thesis studies robust predictive control for uncertain nonlinear systems, with an emphasis on constrained control synthesis through convex optimization-based approaches. Ensuring constraint satisfaction and robustness under disturbances and model uncertainty is a central challenge in the design of control systems for safety-critical applications. The control framework consists of two modules: a trajectory generation module that computes a nominal state and an open-loop input, and a state feedback module that compensates for deviations from the nominal. The combined input is applied to the system to ensure robustness and constraint satisfaction. This thesis develops novel methods and theoretical results that enable the design of such systems under broader classes of nonlinearities and uncertainties, while improving computational efficiency and enhancing the accuracy of constraint satisfaction. A central element is funnel synthesis, in which time-varying invariant funnels and associated feedback controllers are synthesized around nominal trajectories. New formulations are introduced using time-varying incremental quadratic constraints, enabling the handling of nonlinearities beyond Lipschitz continuity. The funnel invariance condition is derived via a differential linear matrix inequality using Lyapunov theory. To solve the continuous-time funnel synthesis problem, an optimal control framework supporting higher-order funnel representations is proposed. Three convex approaches are developed to address continuous-time constraint satisfaction (CTCS) for funnel synthesis. The first introduces intermediate constraint-checking points without increasing the number of decision variables. The second reformulates continuous-time linear matrix inequalities as nodal constraints via an exterior penalty on constraint violations, evaluated at discrete time points and solved using a subgradient-based successive convexification algorithm. The third approach, based on a matrix copositivity condition, achieves CTCS without additional intermediate checking points or constraint reformulation, offering a structured but conservative alternative. Finally, joint synthesis algorithms are proposed to compute both the nominal trajectory and the associated funnel within a unified framework, reducing the conservatism that arises when they are optimized separately. The proposed methods are demonstrated on systems including a unicycle, a 6-degree-of-freedom (6-DoF) free-flyer, a 6-DoF quadrotor, and a powered descent guidance scenario for a 6-DoF rocket.
Splitter Plate Design for Side Wall Testing in the Kirsten Wind Tunnel
(2025-10-02) Osorio Tovar, Juanita; Williams, Owen J. H.
Half-model and side-wall balance capabilities are being developed for an ongoing High-Lift Common Research Model (CRM-HL) testing campaign at the University of Washington. As part of this effort, a well characterized splitter plate is required to provide a symmetry plane. This thesis outlines the design and testing of this splitter plate, as well as requirements to obtain a well-characterized, zero-pressure gradient, uniform, canonical turbulent boundary layer that is free of artifacts. The splitter spans the entire test section wall, avoiding the geometric chamfers, and consists of three main body plates, a rounded leading edge, trailing edge flap, and instrumentation for pressure and velocity diagnostics. The design meets requirements for flatness, stiffness, modularity, and repeatability. It also complies with the tunnel's safety standards, while adapting to the challenges of building a large-scale structure with tight tolerances using available fabrication tools. The plate will be validated via boundary layer measurements using a pitot-traverse system and static pressure taps to confirm flow uniformity over the plate and verify that the splitter enables a zero-pressure-gradient environment. The system is expected to significantly reduce experimental uncertainty and minimize biases due to interactions with the model's symmetry plane.
Signaling properties of asymmetric spider webs
(2025-10-02) Masmeijer, Thijs; Habtour, Ed
Spiders rely on vibrations transmitted through their webs to mlocate and classify prey, and spider will adjust their behavior according to the gained information. Yet, the cues spiders use to interpret these signals, especially from the initial impact, remain poorly understood. These webs are lightweight, mechanically nonlinear structures that serve as extended sensory systems. Understanding how the design of such systems affects signaling can offer insight into sensing in engineering sensing systems, in the field of for example structural health monitoring, feedback control systems, and optimal sensor placement. This dissertation investigates how specific vibrational cues—those that spiders can realistically measure—contribute to prey localization and classification. A central question is whether structural irregularities, such as eccentricity and narrowness, enhance these cues. The study also examines whether such cues remain reliable despite changes in web design and external parameters like prey mass and impact location, which is critical for robust sensing in systems operating with limited information, like spider webs. Previous research on spider web dynamics has primarily focused on idealized circular webs and local geometric features, overlooking how global web shape and prey mass influence vibrational behavior. While several promising mechanisms for prey detection and localization have been proposed, it remains unknown whether these cues remain reliable across the diverse range of web shapes seen in nature and under varying prey sizes. Critically, spiders must act based on limited local information, measured only at their leg positions, so any effective cue must be robust to changes in design and external conditions without relying on global knowledge of the web dynamics or prey. The study combines a numerical and experimental investigations to explore how spider webs design affects vibrational cues. Spiderweb-like structures were fabricated with biologically accurate tension gradients and tested under dynamic loading to analyze their vibrational behavior, enables with high speed cameras. These experiments were complemented by numerical simulations using the Finite Element method. This dissertation presents three main discoveries. First, a robust pitching mode was identified that allows spiders to localize prey using directional vibrations, independent of web irregularities. Second, a specific cue was found to reflect prey mass through system dynamics. However, ambiguity arises due to overlap between the effects of prey mass and distance to impact, and introducing geometric irregularities actually increases this ambiguity. Still, these cues support robust classification of prey type based on mass. Third, building on these biological insights, the thesis introduces a design method for 3D-printed networks with programmable tension gradients and develops Directional Digital Image Correlation (D-DIC), a displacement measurement technique for optical methods that enables full-field experimental modal analysis from a single impact. This includes tracking edges, not just at intersections, as was possible with DIC. Engineering sensing systems are typically designed for structures with known geometry and dynamics. Sensors can be placed with flexibility, and external perturbations are often treated as non-intrusive to the system's behavior. In contrast, spiders must sense and interpret vibrations in webs with unknown and variable properties. They are limited to sensing vibrations near the web's center, and must rely on cues that remain informative despite variation in design, prey mass, and impact location. Moreover, in spider webs, an impact event significantly alters the system's dynamics, making sensing inherently more challenging. This work shows that spiders overcome these limitations by relying on robust structural cues. These findings offer a foundation for designing sensing systems that perform reliably in uncertain and constrained environments, where full modeling is not feasible and disturbances cannot be ignored.
Universal Atrial Coordinate (UAC) for Wall Motion Deep Learning
(2025-10-02) Gupta, Akshay; Dabiri, Dana
Atrial fibrillation (AF), the most common persistent arrhythmia, increases stroke risk through altered left atrial (LA) wall motion and blood stagnation in the left atrial appendage (LAA). Standard scores like CHA₂DS₂-VASc overlook patient-specific motion patterns, while AF's episodic nature and anatomical variability hinder consistent analysis. This thesis presents a standardized framework for LA wall motion analysis using 4D cardiac CT in both sinus rhythm (SR) and AF. LA geometries were segmented, temporally aligned via Coherent Point Drift (CPD) registration, and mapped to a 2D Universal Atrial Coordinate (UAC) system. Wall motion, quantified from Signed Distance Fields (SDF) and decomposed via fast Fourier transform (FFT), showed coordinated low-frequency contraction in SR and reduced amplitude with higher-frequency content in AF. The framework enables anatomy-independent motion comparison and has the potential to predict AF signatures using SR data alone.
Evaluating Energy and Visibility Trade-offs in LEO Satellite Edge Computing for Airplane Detection
(2025-10-02) Kim, Eomji; Mesbahi, Mehran
This thesis investigates the efficiency of various Low Earth Orbit (LEO) configurations for autonomous airplane detection using onboard edge computing in space. The study evaluates the trade-off between maximizing target visibility—defined as daytime passes suitable for optical detection over Incheon International Airport—and minimizing energy consumption for satellite operations. A baseline Sun-Synchronous Orbit (SSO) is compared against multiple Non-Sun-Synchronous Orbits (NSSOs) with varying inclinations (45°–110°), RAANs, and arguments of perigee. For each configuration, orbital visibility is simulated over 1-day and 7-day windows using Python-based tools with J2 perturbation modeling validated against GMAT. Daytime visibility is filtered using local KST-based illumination constraints. To quantify operational efficiency, a composite scoring system is introduced that aggregates normalized visibility metrics, followed by an energy modeling framework that estimates consumption per image strip and per orbit. The model incorporates realistic assumptions: an optical payload based on KOMPSAT-3 specifications, onboard inference with YOLOv5n on NVIDIA Jetson Xavier NX, and S-band downlink of detection results. A simplified solar generation model evaluates the power budget. The findings reveal that mid-inclination NSSOs (especially at 70°) strike the most effective balance between data yield and energy sustainability. The methodology provides a scalable framework for orbit design tailored to edge-AI missions requiring both high revisit rates and energy efficiency.

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