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Articles 1 - 13 of 13
Full-Text Articles in Navigation, Guidance, Control and Dynamics
Experimental Investigation Of Stochastic Parafoil Guidance Using A Graphics Processing Unit, Nathan Slegers, Andrew Brown, Jonathan Rogers
Experimental Investigation Of Stochastic Parafoil Guidance Using A Graphics Processing Unit, Nathan Slegers, Andrew Brown, Jonathan Rogers
Faculty Publications - Biomedical, Mechanical, and Civil Engineering
Control of autonomous systems subject to stochastic uncertainty is a challenging task. In guided airdrop applications, random wind disturbances play a crucial role in determining landing accuracy and terrain avoidance. This paper describes a stochastic parafoil guidance system which couples uncertainty propagation with optimal control to protect against wind and parameter uncertainty in the presence of impact area obstacles. The algorithm uses real-time Monte Carlo simulation performed on a graphics processing unit (GPU) to evaluate robustness of candidate trajectories in terms of delivery accuracy, obstacle avoidance, and other considerations. Building upon prior theoretical developments, this paper explores performance of the …
High-Efficiency Thrust Vector Control Allocation, Jeb S. Orr, Nathan Slegers
High-Efficiency Thrust Vector Control Allocation, Jeb S. Orr, Nathan Slegers
Faculty Publications - Biomedical, Mechanical, and Civil Engineering
A generalized approach to the allocation of redundant thrust vector slew commands for multi-actuated launch vehicles is presented, where deflection constraints are expressed as omniaxial or elliptical deflection limits in gimbal axes. More importantly than in the aircraft control allocation problem, linear allocators (pseudoinverses) are preferred for large booster applications to facilitate accurate prediction of the control-structure interaction resulting from thrust vectoring effects. However, strictly linear transformations for the allocation of redundant controls cannot, in general, access all of the attainable moments for which there is a set of control effector positions thatsatisfles the constraints. In this paper, the control …
Robust Parafoil Terminal Guidance Using Massively Parallel Processing, Jonathan Rogers, Nathan Slegers
Robust Parafoil Terminal Guidance Using Massively Parallel Processing, Jonathan Rogers, Nathan Slegers
Faculty Publications - Biomedical, Mechanical, and Civil Engineering
Terminal guidance of autonomous parafoils is a difficult problem in which wind uncertainty and system underactuation are major challenges. Existing strategies almost exclusively use impact error as the criterion for optimality. Practical airdrop systems, however, must also include other criteria that maybe even more important than impact error for some missions, such as ground speed at impact or constraints imposed by drop zones with restrictions on flight patterns. Furthermore, existing guidance schemes determine terminal trajectories using deterministic wind information and may result in a solution that works in ideal wind but may be sensitive to variations. The work described here …
Specialized System Identification For Parafoil And Payload Systems, Michael Ward, Mark Costello, Nathan Slegers
Specialized System Identification For Parafoil And Payload Systems, Michael Ward, Mark Costello, Nathan Slegers
Faculty Publications - Biomedical, Mechanical, and Civil Engineering
There are a number of peculiar aspects to parafoil and payload systems that make it difficult to apply conventional system identification procedures used for aerospace systems. Parafoil and payload systems are unique because typically there is very little sensor information available, the sensors that are available are separated from the canopy by a complex network of flexible rigging, the systems are very sensitive to wind and turbulence, the systems exhibit a number of nonlinear behaviors, and the systems exhibit a high degree of variability from flight to flight. The current work describes a robust system identification procedure developed to address …
Evaluation Of Multibody Parafoil Dynamics Using Distributed Miniature Wireless Sensors, Chrystine M. Gorman, Nathan Slegers
Evaluation Of Multibody Parafoil Dynamics Using Distributed Miniature Wireless Sensors, Chrystine M. Gorman, Nathan Slegers
Faculty Publications - Biomedical, Mechanical, and Civil Engineering
Guided parafoils arc composed of two primary bodies, a payload and parafoil. The payload encompasses the majority ofthe ovcrdll system mass; however, the parafoil generates the majority of aerodynamic loads and is the sole source of control. Despite the canopy being the source of control, the sensor systems used for guidance are located away from the parafoil. Many multi body models exist in literature and use different degrees of freedom to represent parafoil-payload relative motion. However, in many cases, simulations are used to investigate how the relative motion between bodies affects the overall dynamics without experimental validation determining the accuracy …
Terminal Guidance Of Autonomous Parafoils In High Wind-To-Airspeed Ratios, Nathan Slegers, O A. Yakimenko
Terminal Guidance Of Autonomous Parafoils In High Wind-To-Airspeed Ratios, Nathan Slegers, O A. Yakimenko
Faculty Publications - Biomedical, Mechanical, and Civil Engineering
Autonomous precision placement of parafoils is challenging because of their limited control authority and sensitivity to winds. In particular, when wind speed is near the airspeed, guidance is further complicated by the parafoils inability to penetrate the wind. This article specifically addresses the terminal phase and develops an approach for generating optimal trajectories in real-time based on the inverse dynamics in the virtual domain. The method results in efficient solution of a two-point boundary-value problem using only a single optimization parameter allowing the trajectory to be generated at a high rate, mitigating effects of the unknown winds. It is shown …
Tethered Aerostat Modeling Using An Efficient Recursive Rigid-Body Dynamics Approach, Brad Hembree, Nathan Slegers
Tethered Aerostat Modeling Using An Efficient Recursive Rigid-Body Dynamics Approach, Brad Hembree, Nathan Slegers
Faculty Publications - Biomedical, Mechanical, and Civil Engineering
A tethered aerostat model is developed using a computationally efficient recursive tether model. The recursive rigid-body tether model results in unconstrained ordinary differential equations and maintains much of the simplicity of simple lumped-mass tether models, while avoiding numerical difficulties associated with using many stiff elastic elements with low mass. Further efficiency is achieved by treating each tether link as a body of revolution and assuming that tether spin is negligible to the dynamics. The tether is attached to a six-degree-of-freedom aerostat model using a single viscoelastic element. The final recursive tethered aerostat model is well suited for a variety of …
Efficient Tether Dynamic Model Formulation Using Recursive Rigid-Body Dynamics, Brad Hembree, Nathan Slegers
Efficient Tether Dynamic Model Formulation Using Recursive Rigid-Body Dynamics, Brad Hembree, Nathan Slegers
Faculty Publications - Biomedical, Mechanical, and Civil Engineering
A computationally efficient discrete model for low-strain tethers used in many engineering applications is developed without the use of elastic elements. The tether is modelled using N links, with each link treated as a body of revolution where it is assumed the tether spin is negligible to the dynamics, resulting in each link having only two degrees of freedom. A recursive algorithm is developed for the dynamic equations, with the solution procedure being an order N method requiring only a 2 x 2 matrix inversion, resulting in approximately half the computations of the general recursive algorithm. A comparison between the …
Effects Of Canopy-Payload Relative Motion On Control Of Autonomous Parafoils, Nathan Slegers
Effects Of Canopy-Payload Relative Motion On Control Of Autonomous Parafoils, Nathan Slegers
Faculty Publications - Biomedical, Mechanical, and Civil Engineering
An 8 degree-of-freedom model is developed that accurately models relative pitching and yawing motion of a payload with respect to a parafoil. Constraint forces and moments are found analytically rather than using artificial constraint stabilization. A turn rate controller common in precision placement algorithms is used to demonstrate that relative yawing motion of the payload can result in persistent oscillations of the system. A model neglecting relative payload yawing failed to predict the same oscillations. It is shown that persistent oscillations can be eliminated by reduction of feedback gains; however, resulting tracking performance is poor. A reduced order linear model …
Variable Structure Observer For Control Bias On Unmanned Air Vehicles, Nathan Slegers, Mark Costello
Variable Structure Observer For Control Bias On Unmanned Air Vehicles, Nathan Slegers, Mark Costello
Faculty Publications - Biomedical, Mechanical, and Civil Engineering
No abstract provided.
Nonlinear Model Predictive Control Technique For Unmanned Air Vehicles, Nathan Slegers, Jason Kyle, Mark Costello
Nonlinear Model Predictive Control Technique For Unmanned Air Vehicles, Nathan Slegers, Jason Kyle, Mark Costello
Faculty Publications - Biomedical, Mechanical, and Civil Engineering
A nonlinear model predictive control strategy is developed and subsequently specialized to autonomous aircraft that can be adequately modeled with a rigid 6-degrees-of-freedom representation. Whereas the general air vehicle dynamic equations are nonlinear and nonaffine in control, a closed-form solution for the optimal control input is enabled by expanding both the output and control in a truncated Taylor series. The closed-form solution for control is relatively simple to calculate and well suited to the real time embedded computing environment. An interesting feature of this control law is that the number of Taylor series expansion terms can be used to indirectly …
Model Predictive Control Of A Parafoil And Payload System, Nathan Slegers, Mark Costello
Model Predictive Control Of A Parafoil And Payload System, Nathan Slegers, Mark Costello
Faculty Publications - Biomedical, Mechanical, and Civil Engineering
No abstract provided.
Aspects Of Control For A Parafoil And Payload System, Nathan Slegers, Mark Costello
Aspects Of Control For A Parafoil And Payload System, Nathan Slegers, Mark Costello
Faculty Publications - Biomedical, Mechanical, and Civil Engineering
A parafoil controlled by parafoil brake deflection offers a lightweight and space-efficient control mechanism for autonomous placement of air-dropped payloads to specified ground coordinates. The work reported here investigates control issues for a parafoil and payload system with left and right parafoil brakes used as the control mechanism. It is shown that parafoil and payload systems can exhibit two basic modes of lateral control, namely,roll and skid steering. These two modes of lateral steering generate lateral response in opposite directions. For example, a roll steer configuration turns left when the right parafoil brake is activated, whereas a skid steer configuration …