Craig A Woolsey

Virginia Tech | VT · Department of Aerospace and Ocean Engineering

A symmetry-preserving, reduced-order state observer is presented for the unmeasured part of a system's state, where the nonlinear system dynamics exhibit symmetry under the action of a Lie group. The proposed observer takes advantage of this symmetry through the use of a moving frame that constructs invariant mappings of the measurements. Sufficien...

This paper examines the value of incorporating unsteady aerodynamics in a model-based wind estimator for a small, fixed-wing aircraft and presents results of an experimental implementation. An extended Kalman filter is designed for two motion models identified from flight data: one that includes unsteady effects and another that does not. An air da...

This paper presents the design of an invariant extended Kalman filter (IEKF) for model-based wind estimation using a fixed-wing uncrewed aerial vehicle (UAV) in constant-altitude, horizontal plane motion. It is shown that the planar dynamics of the UAV and the output are invariant and equivariant, respectively, with respect to the Lie group SE(2) o...

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...

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 surfac...

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...

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,...

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/machin...

Near-surface simulation methods for shallowly submerged underwater vehicles are necessary for the population of a variety of free-surface-affected, coefficient-based maneuvering and seakeeping models. Simulations vary in complexity and computational costs, often sacrificing accuracy for simplicity and speed. One particular simplifying assumption, t...

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...

An observer is designed to estimate the disturbance force and moment acting on an underwater vehicle. The observer design leverages the structure of the nonlinear dynamic model. Provided the dynamics are sufficiently slow, the designer may choose observer parameters to ensure that the estimate error is locally, ultimately bounded and converges to a...

This paper extends algorithms that remove the fixed point bias of decentralized gradient descent to solve the more general problem of distributed optimization over subspace constraints. Leveraging the integral quadratic constraint framework, we analyze the performance of these generalized algorithms in terms of worst-case robustness and convergence...

Recent efforts at Virginia Tech have produced a 6-degree of freedom (6DOF) lumped parameter maneuvering model (LPM) that is able to accurately predict the deeply submerged maneuvering motions for a variety of underwater vehicles, including the VT 690 AUV. This model consists of 50 non-negligible hydrodynamic derivatives that are estimated through a...

This paper describes methods to identify an integrated propulsion–airframe aerodynamic model and a decoupled propulsion model for fixed-wing aircraft with propellers using flight data. Propulsion aerodynamics and airframe aerodynamics for propeller aircraft are usually modeled separately, which fails to describe unavoidable interaction effects and...

A fixed time-step variational integrator cannot preserve momentum, energy, and symplectic form simultaneously for nonintegrable systems. This barrier can be overcome by treating time as a discrete dynamic variable and deriving adaptive time-step variational integrators that conserve the energy in addition to being symplectic and momentum-preserving...

The paper addresses the time-varying directional stabilization problem for a small, fixed-wing unmanned aircraft by using nonlinear feedback control of the thrust and the three control moments about the roll, pitch, and yaw axes. The control law makes use of the passivity property gained by modeling the aircraft as a port-Hamiltonian system. The st...

The capability of an oscillating trailing edge flap to enhance the lift generated by a rigid NACA-0012 airfoil at 2.1 × 104 Reynolds number is investigated. Experiments are performed at two angles of attack, namely α0=0∘ that represents a fully attached flow and α0=10∘ that represents a near-stall flow condition. The presented data and analysis cov...

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...

In this paper, we present two Hermite polynomial based approaches to derive one-step numerical integrators for mechanical systems. These methods are based on discretizing the configuration using Hermite polynomials which leads to numerical trajectories continuous in both configuration and velocity. First, we incorporate Hermite polynomials for time...

View Video Presentation: https://doi.org/10.2514/6.2022-1160.vid 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 and a novel vector decompo...

View Video Presentation: https://doi.org/10.2514/6.2022-0554.vid Wind reconstruction from unmanned aircraft systems (UASs) uses estimation algorithms that combine sensor measurements with aircraft dynamic models. Many studies focus on the impact that various sensors have on the accuracy of estimated wind states. This paper describes how fixed-wing...

View Video Presentation: https://doi.org/10.2514/6.2022-1159.vid This paper presents the development and simulation of a robust, periodic linear control law to direct a fixed-wing unmanned aircraft in a stall spin along a desired path. As a flight termination sequence, a spin dissipates energy in a stable, controlled manner. Because control deflect...

View Video Presentation: https://doi.org/10.2514/6.2022-1014.vid Passive visual tracking performance has drastically improved in recent years, thanks to advances in hardware and algorithms, but scenarios in which small mobile threats are indistinguishable from complex backgrounds remain challenging. There is an opportunity to explore whether the ma...

View Video Presentation: https://doi.org/10.2514/6.2022-2406.vid A nonlinear energy-based control law was flight tested on a small, fixed-wing unmanned aircraft. This paper summarizes the selected aircraft, instrumentation system, data processing techniques, system identification methods, and the control laws that were implemented. The flight test...

View Video Presentation: https://doi.org/10.2514/6.2022-2171.vid This paper describes methods to identify an integrated propulsion-airframe aerodynamic model and a decoupled propulsion model for fixed-wing aircraft with propellers using flight data. Propulsion aerodynamics and airframe aerodynamics for propeller aircraft are usually modeled separat...

A fixed time-step variational integrator cannot preserve momentum, energy, and symplectic form simultaneously for nonintegrable systems. This barrier can be overcome by treating time as a discrete dynamic variable and deriving adaptive time-step variational integrators that conserve the energy in addition to being symplectic and momentum-preserving...

View Video Presentation: https://doi.org/10.2514/6.2021-2393.vid An unmanned aircraft system (UAS) can use a heterogeneous stereo vision system to detect and localize other aircraft which may pose a threat. The error in the triangulated location may be large, however, because of the short baseline between the two cameras mounted on the host aircraf...

View Video Presentation: https://doi.org/10.2514/6.2021-2316.vid The current proposed unmanned aircraft system (UAS) detect and avoid standards require the same well clear and near mid-air collision (NMAC) volumes, even when when the UAS is in close proximity to the ground or structures. This requirement has the potential to hinder low altitude sma...

View Video Presentation: https://doi.org/10.2514/6.2021-2792.vid System identification of a nonlinear aerodynamic model was conducted on a fixed-wing, small unmanned aircraft using flight test data. A flight test experiment was designed and conducted including remotely piloted and automated conventional and advanced flight test maneuvers. Flight te...

View Video Presentation: https://doi.org/10.2514/6.2021-2802.vid The phenomenon of a light-weight sphere floating within a vertical jet illustrates a variety of fundamental concepts in fluid dynamics and rigid body mechanics. The phenomenon is described here in the context of several learning objectives that are revisited throughout the paper. The...

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-diffe...

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...

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;...

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-Hamilt...

Disturbance estimation can be used to to characterize the dynamics of an environment or to improve control system performance by compensating for undesired, unmeasured inputs. This paper considers the application of disturbance estimation for a small unmanned aircraft system that is used as a wind sensor. The aircraft's small mass and high wing loa...

The three-dimensional rectilinear path following problem is addressed for a quadrotor vehicle whose propellers provide vertical thrust, and control moments in roll, pitch, and yaw. The vehicle's equations of motion are recast as a port-Hamiltonian system. The control design proceeds in stages, beginning with a particle dynamic model and backsteppin...

This paper investigates the use of a heterogeneous stereo vision system in mitigating the effects of time delays present in the display that is presented to a human operator. Time delays in the display system of a telerobotic operation refer to the time difference between the operator's input action and the corresponding visible outcome. In man-mac...

Disturbance estimation can be used to to characterize the dynamics of an environment or to improve control system performance by compensating for undesired, unmeasured inputs. This paper considers the application of disturbance estimation for a small unmanned aircraft system that is used as a wind sensor. The aircraft's small mass and high wing loa...

As unmanned aircraft systems (UASs) become more common in civilian and military applications , certifying agencies must ensure the safety of third parties on the ground. In order to leverage existing knowledge, approaches based on re-purposing manned aircraft airworthiness standards have been proposed. Standards for manned aircraft often ensure saf...

This paper presents an experiment conducted to study the pisciform locomotion of an improved modular biolocomotion emulator in which the hydrodynamic and kinematic data are collected as the device mimics the body shape of real fishes in swimming action while being towed along a water tank at a steady speed. The results not only provide insights on...

This paper describes vibrational control and stability of a planar, horizontal 2-link mechanism using translational control of the base pivot. The system is a 3-DOF two-link mechanism that is subject to torsional damping, torsional stiffness, and is moving on a horizontal plane. The goal is to drive the averaged dynamics of the system to a desired...

A design method is proposed for a nonlinear disturbance observer based on the notion of passivity. As an initial application, we consider here systems whose structure comprises a set of integrator cascades, though the proposed approach can be extended to a larger class of systems. We describe an explicit procedure to choose the output of the system...

This paper presents computational schemes for optimizing a real-valued function defined on the special orthogonal group. Gradient-based optimization algorithms on a Lie group are interpreted as a continuous-time dynamic system on the group, which is discretized by a Lie group variational integrator that concurrently preserves the symplecticity and...

With the rapid proliferation of small unmanned aircraft systems (sUAS), there is an increasing need for these aircraft to detect and predict each other's motion in order to avoid collisions. This concern arises in addition to the well-established need to detect and avoid manned aircraft. The two threats pose distinct challenges. For example, while...

Accurate numerical simulation of dynamical systems is essential in applications ranging from particle physics to geophysical fluid flow to space hazard analysis. However, most traditional numerical methods do not account for the underlying geometric structure of the physical system, leading to simulation results that may suggest nonphysical behavio...

Modern techniques to estimate wind from a flight vehicle often combine onboard sensor measurements with mathematical models of the aircraft’s dynamics. Whereas prior studies have investigated the impact of sensor errors on estimate accuracy, this work presents a method to study the impact of a simplified flight dynamic model. The method begins by e...

We present a model-based approach to estimate the vertical profile of horizontal wind velocity components using motion perturbations of a multirotor unmanned aircraft system (UAS) in both hovering and steady ascending flight. The state estimation framework employed for wind estimation was adapted to a set of closed-loop rigid body models identified...

We present a model-based approach to wind velocity profiling using motion perturbations of a multirotor unmanned aircraft system (UAS) in both hovering and steady ascending flight. A state estimation framework was adapted to a set of closed-loop rigid body models identified for an off-the-shelf quadrotor. The quadrotor models used for wind estimati...

The transport of material through the atmosphere is an issue with wide ranging implications for fields as diverse as agriculture, aviation, and human health. Due to the unsteady nature of the atmosphere, predicting how material will be transported via the Earth’s wind field is challenging. Lagrangian diagnostics, such as Lagrangian coherent structu...

This paper presents a comparison of three model-based algorithms to estimate the wind vector from quadrotor motion, based on increasingly refined models. The three vehicle motion models are the kinematic particle model, dynamic particle model, and rigid-body model. These motion models were characterized using results from wind-tunnel experiments an...

This paper describes system identification of a nonlinear flight dynamic model for a small, low-cost, fixed-wing unmanned aircraft with a limited instrumentation system. Unique challenges include greater sensitivity to atmospheric disturbances and degraded data quality. Methods are presented to improve the fidelity of the identified model, includin...

This paper presents a nonlinear parametric model and proof-of-concept motion control system for a scale model submarine undertaking an emergency ascent. An energy-based model is presented that represents the underactuated submarine in a non-neutrally buoyant state. This model is then used to synthesize a control law using Port-Hamiltonian theory an...

We present experimental measurements of forward forces and external torques generated during forced oscillations of a tail on a fish-like body. The experiments were performed in a towing basin. Three panels having different flexural rigidity were tested over a range of oscillatory frequencies and leading edge amplitudes at 0 m/s and 0.35 m/s. The r...

This paper presents experimental measurements of the internal and external forces and moments generated during forced oscillation of a modular biolocomotion emulator executing four distinct gaits at three reduced frequencies and three Reynolds numbers (including zero). The purpose of the experimental program is to develop a database of hydrodynamic...

A motion model for a prolate spheroid moving beneath a calm free surface is used to develop a gain-scheduled controller for longitudinal, near-surface maneuvering. The motion model that is used for control design is the impulsive (memory-free) component of a Lagrangian mechanical system model that was recently developed for submerged vessels maneuv...

Small unmanned aircraft systems can increase efficiency and reduce risk to humans during the inspection of truss-supported structures such as steel bridges. This paper describes a method to mathematically represent a truss and subsequently to plan an efficient collision-free inspection path. The algorithm checks user-defined perspectives for feasib...

In this paper, we propose a Lagrangian mechanics framework for modeling the motion of a submerged vehicle operating near a free surface in calm water. By augmenting the system Lagrangian used to derive Kirchhoff’s equations for a rigid body moving in an unbounded fluid, we directly incorporate the free surface into the derivation of the equations o...

The goal of this paper is to develop energy-preserving variational integrators for time-dependent mechanical systems with forcing. We first present the Lagrange-d'Alembert principle in the extended Lagrangian mechanics framework and derive the extended forced Euler-Lagrange equations in continuous-time. We then obtain the extended forced discrete E...

This paper discusses planar self-propelled motion of a primary body in water generated by using a hinged flap at its trailing edge. The coupled dynamic model incorporates unsteady loads based on Theodorsen's unsteady lifting theory for sinusoidal flapping at a given reduced frequency and tailored for their application within the framework of the bo...

A combination of vibrational inputs and state feedback is applied to control the flight of a biomimetic air vehicle. First, a control strategy is developed for longitudinal flight, using a quasi-steady aerodynamic model and neglecting wing inertial effects. Vertical and forward motion is controlled by modulating the wings’ stroke and feather angles...