Scholarly Works, Aerospace and Ocean Engineering
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- ALMO: Active Learning-Based Multi-Objective Optimization for Accelerating Constrained Evolutionary AlgorithmsSingh, Karanpreet; Kapania, Rakesh K. (MDPI, 2024-10-31)In multi-objective optimization, standard evolutionary algorithms, such as NSGA-II, are computationally expensive, particularly when handling complex constraints. Constraint evaluations, often the bottleneck, require substantial resources. Pre-trained surrogate models have been used to improve computational efficiency, but they often rely heavily on the model’s accuracy and require large datasets. In this study, we use active learning to accelerate multi-objective optimization. Active learning is a machine learning approach that selects the most informative data points to reduce the computational cost of labeling data. It is employed in this study to reduce the number of constraint evaluations during optimization by dynamically querying new data points only when the model is uncertain. Incorporating machine learning into this framework allows the optimization process to focus on critical areas of the search space adaptively, leveraging predictive models to guide the algorithm. This reduces computational overhead and marks a significant advancement in using machine learning to enhance the efficiency and scalability of multi-objective optimization tasks. This method is applied to six challenging benchmark problems and demonstrates more than a 50% reduction in constraint evaluations, with varying savings across different problems. This adaptive approach significantly enhances the computational efficiency of multi-objective optimization without requiring pre-trained models.
- Spin Aerodynamic Modeling for a Fixed-Wing Aircraft Using Flight DataGresham, James L.; Simmons, Benjamin M.; Hopwood, Jeremy W.; Woolsey, Craig A. (American Institute of Aeronautics and Astronautics, 2024-01)Novel techniques are used to identify a nonlinear, quasi-steady, coupled, spin aerodynamic model for a fixed-wing aircraft from flight-test data. Orthogonal phase-optimized multisine inputs are used as excitation signals while collecting spinning flight data. A novel vector decomposition of explanatory variables leads to an elegant model structure for spin flight data analysis. Results show good agreement between model predictions and validation flight data. This effort is motivated by interest in developing a flight termination system for a fixed-wing unmanned aircraft that controls a descending spiral trajectory flight path toward a designated impact area. While investigating the feasibility of a robust control method to guide the spinning trajectory, it was helpful to compare a level flight dynamic model with one of the aircraft dynamics and control authority in the neighborhood of a stable, oscillatory spin. In this paper, a nominal flight aerodynamic model is developed and compared to the stall spin model and the spin model outperforms the nominal model for spinning flight.
- Remote Uncorrelated Pilot Input Excitation Assessment for Unmanned Aircraft Aerodynamic ModelingGresham, James L.; Simmons, Benjamin M.; Fahmi, Jean-Michel W.; Hopwood, Jeremy W.; Woolsey, Craig A. (American Institute of Aeronautics and Astronautics, 2023-05)
- A Study of the Wind Sensing Performance of Small Pusher and Puller HexacoptersGonzález-Rocha, Javier; Sharma, Prashin; Atkins, Ella; Woolsey, Craig A. (American Institute of Aeronautics and Astronautics, 2023-09)
- Port-Hamiltonian Flight Control of a Fixed-Wing AircraftFahmi, Jean-Michel W.; Woolsey, Craig A. (IEEE, 2022-01)This brief addresses the problem of stabilizing steady, wing level flight of a fixed-wing aircraft to a specified inertial velocity (speed, course, and climb angle). The aircraft is modeled as a port-Hamiltonian system and the passivity of this system is leveraged in devising the nonlinear control law. The aerodynamic force model in the port-Hamiltonian formulation is quite general; the static, state feedback control scheme requires only basic assumptions concerning lift, side force, and drag. Following an energy-shaping approach, the static state feedback control law is designed to leverage the open-loop system’s port-Hamiltonian structure in order to construct a control Lyapunov function. Asymptotic stability of the desired flight condition is guaranteed within a large region of attraction. Simulations comparing the proposed flight controller with dynamic inversion suggest it is more robust to uncertainty in aerodynamics.
- Experimental Validation of Port-Hamiltonian-Based Control for Fixed-Wing Unmanned AircraftFahmi, Jean-Michel W.; Gresham, James L.; Woolsey, Craig A. (American Institute of Aeronautics and Astronautics, 2023-06)
- A Structure-Inspired Disturbance Observer for Finite-Dimensional Mechanical SystemsChen, Ying-Chun; Woolsey, Craig A. (IEEE, 2024-03)This article describes a disturbance observer (DO) design for systems whose dynamics are piecewise differentiable and satisfy certain structural conditions. Provided a Lipschitz continuity condition holds with a sufficiently small Lipschitz constant—a condition that is implied by “sufficiently slow” dynamics—the observer ensures local ultimate boundedness of the disturbance estimate error, which converges exponentially to a positively invariant set whose size can be made arbitrarily small. This observer is appropriate for finite-dimensional mechanical systems. We demonstrate the design in two examples—a tutorial example of a nonlinear mass-damper-spring system and a practical example of an experimental underwater vehicle.
- A Maneuvering Model for an Underwater Vehicle Near a Free Surface—Part II: Incorporation of the Free-Surface MemoryBattista, Thomas; Valentinis, Francis; Woolsey, Craig A. (IEEE, 2023-07)Using energy-based modeling techniques, we propose a nonlinear, time-dependent, parametric motion model for an underwater vehicle maneuvering near an otherwise undisturbed free surface. By augmenting the system Lagrangian used to derive Kirchhoff's equations for a rigid body moving through an unbounded fluid, we directly incorporate the free surface into the derivation of the equations of motion. This is done using a free-surface Lagrangian , which accounts for the instantaneous energy stored within the free surface due to an impulsive vehicle motion as well as fluid memory effects. The system Lagrangian then enables us to derive the six-degree-of-freedom nonlinear equations of motion using the Euler–Lagrange equations. The model structure is similar to standard maneuvering models for surface ships, although additional complexities are present since the hydrodynamic parameters are shown to depend on the vessel position and orientation relative to the free surface. For the proposed model, the vessel motion is unrestricted. This is in contrast to traditional seakeeping models, which use convolution integrals to incorporate memory effects for a vessel, which experiences only small perturbations from steady, forward motion. The proposed motion model is amenable to real-time simulation, design performance analysis, and nonlinear control design. Other important hydrodynamic effects due to viscous flow, for example, may then be incorporated into a robust, nonlinear, closed-loop control system as lumped parameter effects or model uncertainties.
- A Maneuvering Model for an Underwater Vehicle Near a Free Surface—Part III: Simulation and Control Under WavesValentinis, Francis; Battista, Thomas; Woolsey, Craig A. (IEEE, 2023-07)This article incorporates free-surface and ambient wave effects into a nonlinear parametric model. Subsequently, its use is demonstrated via simulation of a scale model submarine maneuvering under the control of a nonlinear depth-keeping control system in a seaway. An energy-based model is presented, which represents the underactuated submarine in a free-surface-affected state. This model is then used to synthesize a control law using port-Hamiltonian theory and interconnection and damping assignment passivity-based control. The Lyapunov analysis is used to study the stability of the closed-loop system, and a simulation-based demonstration illustrates the performance of the control law. The results demonstrate that a closed-loop nonlinear controller is able to improve the quality of near-surface depth keeping by automatically compensating for parasitic effects in the hydrodynamics that can compromise depth-keeping performance during maneuvers.
- On closed-loop vibrational control of underactuated mechanical systemsTahmasian, Sevak; Woolsey, Craig A. (Springer Nature, 2022-01)This paper discusses vibrational stabilization of a class of single-input, two degree-of-freedom mechanical systems. Considering two different control formulations—position-input and force-input—and both open- and closed-loop control, we find that the sets of attainable equilibrium positions for the unactuated coordinate are identical in every case. The subset of positions that are stabilizable, however, depends on the formulation. In general, the set of equilibria that can be stabilized using open-loop force-input is larger than the set that can be stabilized using open-loop position-input. And the use of feedback expands this stabilizable set even further. As examples, this paper presents the dynamic analysis, open- and closed-loop vibrational control, and the mechanics behind the stability of two underactuated systems, the Kapitza pendulum and a one-link horizontal pendulum.
- A Tutorial Review of Indirect Wind Estimation Methods Using Small Uncrewed Air VehiclesAhmed, Zakia; Halefom, Mekonen H.; Woolsey, Craig A. (American Institute of Aeronautics and Astronautics, 2024-08)
- Flight-Test System Identification Techniques and Applications for Small, Low-Cost, Fixed-Wing AircraftSimmons, Benjamin M.; Gresham, James L.; Woolsey, Craig A. (American Institute of Aeronautics and Astronautics, 2023-09)This paper provides an overview of flight-test system identification methods applied in the Virginia Tech Nonlinear Systems Laboratory that focus on modeling small, inexpensive, fixed-wing aircraft controlled by a ground-based pilot. The general aircraft system identification approach is outlined with details provided on the flight-test facilities, experiment design methods, instrumentation systems, flight-test operations, data processing techniques, and model identification methods enabling small aircraft flight dynamics model development. Specific small aircraft system identification challenges are overcome, including low-cost control surface servo-actuators and instrumentation systems, as well as a greater sensitivity to atmospheric disturbances and limited piloting cues. Four recent system identification research advancements using the general system identification process are featured, including application of uncorrelated pilot inputs for remotely piloted aircraft, aero-propulsive model development for propeller aircraft, spin aerodynamic model development, and nonlinear dynamic modeling without mass properties information. Although this paper provides a summary of several research efforts, the core system identification approach is presented with sufficient detail to allow the methods to be readily adapted to other research efforts leveraging small, low-cost aircraft.
- Nonlinear Dynamic Modeling for Aircraft with Unknown Mass Properties Using Flight DataSimmons, Benjamin M.; Gresham, James L.; Woolsey, Craig A. (American Institute of Aeronautics and Astronautics, 2023-05)
- Time Delay Mitigation in Aerial Telerobotic Operations Using Heterogeneous Stereo-Vision SystemsSakib, Nazmus; Gahan, Kenneth C.; Woolsey, Craig A. (American Institute of Aeronautics and Astronautics, 2023-09)This paper investigates the use of a heterogeneous stereo-vision system to mitigate the effects of time delays in a drone-based visual interface presented to a human operator. Time delays in the display for a telerobotic interface refer to the time difference between the operator’s input action and the corresponding visible outcome. In human/machine interfaces, time delays can arise due to computation, telecommunication, and mechanical limitations. These delays can degrade the performance of the human/machine system. A heterogeneous stereo-vision predictive algorithm is presented that can reduce the negative effects of time delays in the operator’s display. The heterogeneous stereo-vision system consists of an omnidirectional camera and a pan/tilt/zoom camera. Two predictive display setups were developed that modify the delayed video imagery that would otherwise be presented to the operator in a way that provides an almost immediate visual response to the operator’s control actions. The usability of the system is determined through human performance testing with and without the predictive algorithms. The results indicate that the predictive algorithm allows more efficient, accurate, and user-friendly operation.
- A free surface corrected lumped parameter model for near-surface horizontal maneuvers of underwater vehicles in wavesLambert, William; Miller, Lakshmi; Brizzolara, Stefano; Woolsey, Craig A. (Elsevier, 2023-06)We provide theory and results obtained from the application of a 6-degree of freedom lumped parameter maneuvering model (LPMM) able to predict the maneuvering motions of underwater vehicles navigating at shallow depth below free surface waves. The parameters of the maneuvering model are identified using a combination of steady and unsteady captive maneuvers, simulated with high fidelity computational fluid dynamic (CFD) methods. This work focuses on correcting the LPMM, which is accurate for deep water motions, to account for free surface effects. A frequency domain strip theory method is used to account for changes in the added mass due to free surface proximity, to calculate memory forces, and to estimate wave excitation forces while a 3D time domain boundary element method is used to predict steady-state wave making forces. The result is a combined maneuvering and seakeeping model for underwater vehicles operating at shallow depths below the free surface. Near-surface horizontal zig-zag motion predictions in both calm water and under waves reveal the importance of including the free surface as vehicle trajectories at shallow depths differ substantially from those at deeper submergences for identical maneuvering inputs.
- Development of a Peripheral–Central Vision System for Small Unmanned Aircraft TrackingKang, Changkoo; Chaudhry, Haseeb; Woolsey, Craig A.; Kochersberger, Kevin (American Institute of Aeronautics and Astronautics, 2021-09)Two image-based sensing methods are merged to mimic human vision in support of airborne detect-and-avoid and counter–unmanned aircraft systems applications. In the proposed sensing system architecture, a peripheral vision camera (with a fisheye lens) provides a large field of view, whereas a central vision camera (with a perspective lens) provides high-resolution imagery of a specific target. Beyond the complementary ability of the two cameras and supporting algorithms to enable passive detection and classification, the pair forms a heterogeneous stereo vision system that can support range resolution. The paper describes development and testing of a novel peripheral–central vision system to detect, localize, and classify an airborne threat. The system was used to generate a dataset for various types of mock threats in order to experimentally validate parametric analysis of the threat localization error. A system performance analysis based on Monte Carlo simulations is also described, providing further insight concerning the effect of system parameters on threat localization accuracy.
- Scheduled Imaging of Multiple Threat Aircraft Using a Modified Traveling Salesman ProblemKang, Changkoo; Woolsey, Craig A. (American Institute of Aeronautics and Astronautics, 2021-07)
- Parameter computation for a Lagrangian mechanical system model of a submerged vessel moving near a free surfaceJung, Seyong; Brizzolara, Stefano; Woolsey, Craig A. (Elsevier, 2021-06)This paper describes the computation of parameters for a Lagrangian mechanical system model of a submerged vessel moving near an otherwise calm free surface using a medium-fidelity potential flow code. The software uses the boundary element method to solve for the flow potential on the body and the free surface. The model, a system of integro-differential equations involving functions of the velocity potential, is the “maneuvering” component of a Lagrangian nonlinear maneuvering and seakeeping model that was introduced in earlier work. Here, this nonlinear maneuvering model is reformulated and the potential flow software is modified to support parameter computations. Parameters are computed for a prolate spheroid moving parallel to a calm free surface at a constant forward speed. This motion induces a steady flow with respect to the body, which results in a steady surge force, heave force and pitch moment. These longitudinal forces and moment are computed using the reformulated Lagrangian nonlinear maneuvering model and the results are compared with basic panel code solutions for various depths and Froude numbers and for various computational parameter values.
- An Approach for Computing Parameters for a Lagrangian Nonlinear Maneuvering and Seakeeping Model of Submerged Vessel MotionJung, Seyong; Brizzolara, Stefano; Woolsey, Craig A. (IEEE, 2021-03)In this study, hydrodynamic forces on a submerged vessel maneuvering near a free surface are determined using a reformulated Lagrangian nonlinear maneuvering and seakeeping model derived using Lagrangian mechanics under ideal flow assumptions. A Lagrangian mechanics maneuvering model is first reformulated to simplify the computation of parameters; then, incident wave effects are incorporated into the reformulation; finally, the parameters are computed using a medium-fidelity time-domain potential-flow panel code. Predictions from the reformulated Lagrangian nonlinear maneuvering and seakeeping model, whose parameters are computed using the methods described here, are compared with direct numerical computations in two steps for a prolate spheroid maneuvering in the longitudinal plane near the free surface. First, the hydrodynamic force and moment predicted by the model are compared with solutions from the panel code for sinusoidal motion in surge, heave, and pitch in calm water. Second, the hydrodynamic force and moment are investigated for cases where the spheroid maneuvers to approach the surface in calm water and in plane progressive waves. To conclude, a physically intuitive formulation of the Lagrangian nonlinear maneuvering and seakeeping model is presented for control applications and simulations.
- Robust Stall Spin Flight Path Control with Flight Test ValidationHopwood, Jeremy W.; Gresham, James L.; Woolsey, Craig A. (American Institute of Aeronautics and Astronautics, 2023-03)