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Daniel Guggenheim School of Aerospace Engineering
Daniel Guggenheim School of Aerospace Engineering
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ItemEvaluation of Convolutional Neural Networks for Modeling Blast Propagation in Multi-room Bunkers(Georgia Institute of Technology, 2023-12-15) Luo, FelixThe rapid evaluation of blasts in enclosed geometrically complex spaces has long eluded the design of safer blast-resistant structures. Traditional methods of determining blast responses in enclosed geometrically complex spaces oftentimes rely on the use of traditional computational fluid dynamics (CFD) solvers to compute the entire flow field of the structure. This method has an enormous computational burden, especially considering that blasts are highly transient in nature and require the transient pressure fluctuations to be determined to formulate an accurate blast response prediction. However, more efficient methods of blast evaluation are desired such that parametric sweeps or optimization processes can be performed at low cost to provide a tool for iterative design. To rectify this gap in capabilities, a convolutional neural network based (CNN) model was developed to provide rapid blast predictions for 2D structures to establish this capability to aid in the design of more blast resistant structures. This approach leverages the inherent spatial awareness of CNNs to provide predictions for peak pressures since blasts in enclosed spaces are highly dependent on the spatial relationships between blast locations and wall location. This approach provides a nearly 5,000 times speed up against CFD simulations used within this study with good convergence of errors, correlation coefficients, predicted and truth values and distributions in all situational evaluations. These computational advantages, in part, comes from using the CNN based model to directly predict peak pressures whereas traditional CFD solvers require iterations to propagate fluid flows over time. However, some limitations do exist with respect to higher errors, such as model training costs, and the capability to predict 3D structures. Nonetheless, the results provide a characterization of the capabilities CNN based models in predicting peak pressures from blasts in enclosed spaces. From these evaluations and studies, a model which can provide significant computational savings while maintaining a similar accuracy can be obtained, which enables the rapid iterative design of more blast resistant structures.
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ItemA Sliding-Window Matrix Pencil Method for Aeroelastic Design Optimization with Limit-Cycle Oscillation Constraints(Georgia Institute of Technology, 2023-12-15) Golla, TarunThis paper presents a new approach for constraining limit-cycle oscillations in aeroelastic design optimization. The approach builds on a gradient-oriented limit-cycle oscillation constraint that bounds the recovery rate to equilibrium, bypassing the need for bifurcation diagrams. Previous work demonstrated the constraint using recovery rates approximated via a conservative approach. This work introduces a new approach to accurately evaluate recovery rates from transient simulations. The approach uses the matrix pencil method within a time window that slides along the time history for the quantity of interest, allowing this damping identification method to resolve amplitude-variant nonlinear effects. The new sliding-window matrix pencil method is verified with reference recovery rates from envelope finite differencing of the dynamic responses induced with a large initial perturbation of a typical aeroelastic section. Sensitivity analyses identify optimal parameters to obtain accurate recovery rates while minimizing computational costs. The new developments are then demonstrated by optimizing the typical section subject to the proposed limit-cycle oscillation constraint along with flutter and side constraints. The results are compared with previous work that solved the same optimization problem by evaluating the limit-cycle oscillation constraint using approximate recovery rates. The limit-cycle oscillation constraint based on the new sliding-window matrix pencil method allows the optimizer to achieve a less conservative design solution while satisfying the constraints. This methodology was additionally extended through the optimization of a more complex 3-variable optimization. The implementation was further ported into a modular framework within which results were verified, allowing for future extensions to this methodology. This work is anticipated to pave the way for larger-scale aeroelastic design optimizations subject to limit-cycle oscillation constraints.
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ItemA Sliding-Window Matrix Pencil Method for Aeroelastic Design Optimization with Limit-Cycle Oscillation Constraints(Georgia Institute of Technology, 2023-12-13) Golla, TarunThis thesis presents a new approach to constraining limit-cycle oscillations (LCOs) in aeroelastic design optimization. LCOs are self-excited oscillations that can develop in nonlinear aeroelastic systems experiencing flutter, and they must be avoided during operation to keep safety and performance. One approach to addressing this problem is to design the system using an optimization process that includes an LCO constraint. Previous efforts have proposed various LCO constraints for aeroelastic design optimization but have not addressed realistic design applications. This gap persists because existing LCO constraints are not oriented toward scalable gradient-based optimization algorithms. The proposed approach builds on a recent LCO constraint that bounds the recovery rate to equilibrium and is suited to gradient-based optimization. The new contribution from this thesis consists of introducing a new matrix pencil method for accurately evaluating the recovery rate within the LCO constraint using output data from transient responses. The amplitude-varying behavior of the recovery rate in the presence of dynamic nonlinearities is captured using a sliding time window along the transient response for a chosen quantity of interest. This new approach differs from the conventional matrix pencil method, which considers an entire transient response at once under linearized assumptions. Sensitivity studies are conducted to identify the optimal singular-value decomposition tolerance, sliding window size, stride size, output data sampling step, and aggregation parameters for obtaining accurate results. The new sliding-window matrix pencil method is then used to optimize a typical aeroelastic section model with a subcritical LCO behavior, enforcing no flutter or LCOs at chosen operation conditions. Optimization results are compared with previous work that used the same LCO constraint formulation combined with an approximate, conservative method to evaluate the recovery rate. The LCO constraint evaluated using the new sliding-window matrix pencil method allows the optimizer to completely suppress subcritical LCOs within the specified operating conditions while minimizing design changes, achieving a less conservative optimized solution. This work is a step toward constraining LCOs in large-scale aeroelastic design optimization to enable higher-performance designs while avoiding undesirable dynamics, such as subcritical LCOs. Future work includes formulating adjoint derivatives of the LCO constraint and demonstrating the methodology for aeroelastic models of increasing physical and computational complexity.
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ItemDevelopment of empirical models for the analysis of multirotor aerodynamic interactions(Georgia Institute of Technology, 2023-12-10) Marangoni, GioeleIn the 21st century, the concept of Advanced Air Mobility (AAM) has emerged as a highly promising transportation solution for urban and regional areas, attracting considerable interest from both private companies and government agencies. In this dynamic and innovative environment, a multitude of new aerial vehicle designs is emerging. During the initial conceptual phase of designing a new vehicle, empirical methods based on institutional knowledge are typically employed, while Computational Fluid Dynamics (CFD) methods are reserved for later stages of the design process. This is because CFD tools require more detailed design information that is not available during the conceptual phase such as accurate Computer-Aided Design (CAD) models and properties of materials, which are typically obtained as the design progresses and becomes more refined. However, the novelty of these multirotor configurations poses unprecedented challenges due to the limited research, experimentation, and available data on the aerodynamic interactions among the rotors and the impact of various design choices on performance. In this context, traditional empirical methods do not prove effective as they fail to account for design choices unique to these new multirotor configurations and the aerodynamic interactions between the rotors. This can lead to costly redesigns and schedule delays. This effort proposed to conduct a parametric study of various eVTOL configurations, observe general trends and derive empirical-based models that can guide engineers in making informed configuration choices during the conceptual phase of a new vehicle design. To traverse a vast configuration design space quickly, the mid-fidelity analysis tool Comprehensive Hierarchical Aeromechanics Rotorcraft Model (CHARM) has been adopted. CHARM, which is based on lifting line and distorting wake methods, has demonstrated its capability in accurately predicting vehicle performance while maintaining cost-effectiveness in terms of setup and execution time. This approach is correlated with theory and experiment to build confidence in the analysis and conclusions.
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ItemEffects of Aero-Propulsive Interactions for Various Wing Integration Techniques on Electric Ducted Fan Performance(Georgia Institute of Technology, 2023-12-10) Safieh Matheu, Derek AnthonyThis study explores the aero-propulsive coupling effects of wing blended electric ducted fans (EDF) lifting systems over the EDF unit. Wing blended EDFs and isolated EDF are on the rise as a solution to increase efficiency on regional mobility platforms. Electrification of platforms has permitted the introduction of novel integration concepts that use phenomena like BLI to enhance their performance. The lack of complex mechanical links permits designers to place propulsive devices practically anywhere on the aircraft, opening opportunities for research and development. As noted in the literature review section, little attention has been given to understanding the effects of novel integrations on the EDF. This experimental study aims to examine two edge cases: the leading edge integration and the trailing edge integration. The leading edge integration studied in this work is characterized by having the leading edge of the inlet of the EDF and the leading edge of the wing flushed. The trailing edge features the EDF mounted with the exhaust of the duct flushed with the wing’s trailing edge; the angle between the freestream and the EDF is parallel. The duct is translated vertically so that the inlet of the trailing edge EDF is tangent with the wing’s surface. Note that this is not an optimization study; simplified integrations that represent the generalized qualities of each integration were adopted. What is novel about the research is that the EDF forces are decoupled from the system loads, providing unprecedented insight into each integration’s effects on the EDF itself. The study was formed by three major test rigs described in the methodology section. The first rig was designed to test EDFs in isolation at various angles of attack. In this test, various sizes of EDFs were tested with a common duct geometry; the sizes ranged from 51 cm2 fan-swept area to 215 cm2 fan-swept area. The EDFs were tested between the cruise condition, edgewise flight, and descent stages; performance data and 6 forces and moments are explored in the results section. The second rig focused on studying the integration of the EDF in both cases, but by introducing a symmetric airfoil design, the upper surface and lower surface integration was studied. This rig permitted to study such configuration in the low-turbulence tunnel at lower airspeeds and mostly the cruise condition. For these tests, a Clark-Y duct shape coupled with Schuebeler Technologies DS51-HST formed the EDF system. These tests provided insight into all 4 possible integration edge cases and presented interesting findings on pitching moment, thrust output, and performance effects that the integration had on the EDF. The last test rig focused on studying the EDF integration in a more realistic platform (slimmer airfoil) and studying the transition cases, cruise flight, wing stall scenario, and high angles of attack. This test rig was placed in the Low Turbulence Wind Tunnel and the Harper Wind Tunnel. The tests in the low turbulence tunnel focused on edgewise flight, early transition, and the descent cases, studying airspeeds between 2 m/s and 10 m/s. The tests on the Harper Wind Tunnel study the integration in cruise and wing stall conditions at airspeeds between 10 m/s and 20 m/s. In that test, the performance, thrust output, and normal force generated by the duct are investigated.
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ItemAn Inertial and Aerodynamic Approach to Active Flutter Suppression Control Law Design and Wind Tunnel Evaluation(Georgia Institute of Technology, 2023-12-07) Szymanski, JacobThis thesis examines multiple continuous time adaptive control methodologies for use in Active Flutter Suppression (AFS). Typical AFS control methodologies rely on feedback in the form of inertial and elastic data such as acceleration and strain. This approach has been shown to be effective, however potential improvements may be made with the inclusion of additional information in the form of surface pressure data. Aeroelasticity involves the interaction of aerodynamic, inertial, and elastic forces, thus the inclusion of surface pressure data completes this triangle of forces. There are two main parts of this thesis. The simulation portion examines the effectiveness of three adaptive control methodologies at mitigating flutter of a nonlinear aeroelastic simulation model. Due to the difficulty of simulating surface pressure fluctuations, the simulation models relied on the inertial data in the form of the pitch and plunge motions of the model for feedback. Analysis in both the time and frequency domains provided a complete spectral analysis of the closed loop behavior of the model which provided insights into the underlying mechanisms acting within the adaptive controllers. Key pieces of information were the energy transfer between modes of motion, frequency trends over time, and relative phase between deflections and control inputs. The most effective controller from the simulations was selected for implementation on an experimental aeroelastic test rig in the experimental portion of this thesis. The test rig was used to examine the effects of including the surface pressure data within a feedback control loop. Experimental testing was conducted on a cantilever wing model which was instrumented with an angular rate sensor, an accelerometer, and upper and lower surface pressure transducers. Trailing edge flaps on the wing were used as the control effectors. The open loop behavior was characterized, then control with angular rate feedback into an adaptive controller was evaluated. Multiple configurations of inertial and surface pressure feedback control were evaluated, with the final configuration achieving a 25% increase in flow velocity over the open loop case. Each control configuration was evaluated using spectral analysis to determine the modifications necessary to improve the control. Overall, it was shown that the inclusion of surface pressure data provided information which was not present in the inertial data which enabled more stable control of the test rig. Controller tuning via examining the spectral information within the signals was found to be a valid approach which did not rely on precise modelling of the entire test rig.
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ItemInternal Flow Dynamics in Liquid Swirl Injectors with Coaxial Gas Flow(Georgia Institute of Technology, 2023-12-06) Trucchi, MatteoInjectors are essential components in aerospace propulsion systems, serving a crucial role in achieving high-quality propellant atomization and mixing, as well as engine stability. They are integral components within a complex dynamic system and are responsible for coupling the feed system to the combustion chamber. Thus, a profound understanding of injector dynamics is imperative to attain a robust engine design. Since the early studies, the typical configurations of interest have involved closed-head injectors, where the liquid propellant swirls around a stationary gas core. Gas-liquid interactions were introduced with recessed coaxial swirl injectors and air-blast injectors with major emphasis on the atomization process. The classical theory on injector dynamics lacks the consideration for the effect of the shear stress at the liquid-wall and gas-liquid interfaces in the governing equations. Therefore, the damping effect on propagating waves is modelled exclusively through an artificial viscosity factor. This work conducts a theoretical and numerical investigation for an alternative configuration of open-end swirl injectors. The distinctive feature of this configuration is an open head and a high speed gas that flows coaxially with the swirling liquid towards the injector exit. Unlike a recessed coaxial injector, the gas immediately interacts with the tangentially injected liquid into the chamber where the gas is flowing. The comprehensive review of classical steady-state and transient theories on swirl injectors led to the identification and resolution of inconsistencies. The analytical inclusion of shear stress at the liquid-wall and gas-liquid interfaces produced a modified wave equation, and the new solution was employed to extend the classical theory to Open-Head-Open-End injectors. A parametric study for frequencies up to 2000 Hz involving gas flow velocity, injector pressure drop, and geometric parameters highlighted the significance of friction coefficients tuning for an accurate calculation of the injector transfer function. Computational Fluid Dynamics provided a qualitative description of the flow physics involved in the injector configuration of interest.
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ItemSpace Object Tracking from CubeSats utilizing Low-Cost Software Defined Radios(Georgia Institute of Technology, 2023-12) Mealey, Alex
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ItemVISORS Mission Orbit & Dynamics Simulation Using a Realtime Dynamics Processor(Georgia Institute of Technology, 2023-12-01) Kimmel, ElizabethVIrtual Super-resolution Optics using Reconfigurable Swarms (VISORS) is a precision formation-flying mission which uses two 6U CubeSats with a Science Mode separation distance of 40 meters to emulate a 40-meter focal length diffractive optic telescope. Due to the novelty of the technology used to achieve the stringent relative positioning requirements, the dynamics of these orbits must be simulated to verify the concept of operations (ConOps), the commercial spacecraft bus flight software (FSW), the guidance, navigation, and control (GNC) formation-keeping algorithm, and the attitude determination and control system (ADCS) performance, among others. Verifying these aspects helps ensure that issues such as reaction wheel saturation, pointing errors, or collision risks, among others, do not arise during the mission. This paper describes the work done in simulating the spacecraft dynamics during the mission’s Science Operations using COSMOS to interface with the Realtime Dynamics Processor (RDP) and spacecraft bus Engineering Design Unit (EDU) provided by Blue Canyon Technologies (BCT).
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ItemDevelopment of an Open Source Data Visualization and Automated Testing Platform for CubeSat Subsystems(Georgia Institute of Technology, 2023-08) Bustos, Alexander