Rick Lind

University of Florida, Mechanical and Aerospace Engineering, Faculty Member

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Papers by Rick Lind

Developing uncertainty models for robust flutter analysis using ground vibration test data

19th AIAA Applied Aerodynamics Conference, Jun 11, 2001

Since its founding, NASA has been dedicated to the advancement of aeronautics and space science. ... more

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Efficient Numerical Analysis of Stability of High-Order Systems With a Time Delay

arXiv (Cornell University), Oct 27, 2017

Time delays are a common perturbation in systems with many states, such as networked, distributed... more Time delays are a common perturbation in systems with many states, such as networked, distributed, or decentralized systems. Current methods analyzing the stability of large systems with time delay typically produce very conservative results. While more exact methods exist, these become inefficient for large systems. This paper provides a methodology for analyzing the stability of time-delayed systems that is derived from exact methods but is efficient for high-order systems. The computa

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Uncertainty Estimation from Volterra Kernels for Robust Flutter Analysis

Journal of Guidance Control and Dynamics, Mar 1, 2003

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Overview of recent flight flutter testing research at NASA Dryden

thrust vectoring control system input uncertainty weighting time domain data time-frequency domai... more thrust vectoring control system input uncertainty weighting time domain data time-frequency domain data input and output data for spectral estimates parametric variation of dynamic pressure input multiplicative uncertainty real parametric modal uncertainty structured singular value wavelet time shift parameter radian frequency complex conjugate transpose

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Estimation of modal parameters using a wavelet-based approach

ny lateral acceleration nz normal acceleration Nomenclature _ radian frequency ARW-1 first aeroel... more ny lateral acceleration nz normal acceleration Nomenclature _ radian frequency ARW-1 first aeroelastic research wing Engineering Department for his assistance under Similary, the Laplace tfa analysis given in figure 8 the NASA-ASEE Summer Faculty Fellowship and indicates the impending instability. The estimated damping in figure 8e shows the same decrease in NASA/University Joint Venture (JOVE) programs. damping from (_ 0.02 to near zero after 40 seconds of data.

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Lyapunov-Based Exponential Tracking Control of a Hypersonic Aircraft with Aerothermoelastic Effects

Journal of Guidance Control and Dynamics, Jul 1, 2010

Hypersonic flight conditions produce temperature variations that can alter both the structural dy... more Hypersonic flight conditions produce temperature variations that can alter both the structural dynamics and flight dynamics. These aerothermoelastic effects are modeled by a nonlinear, temperature-dependent, parameter-varying state-space representation. The model includes an uncertain parameter-varying state matrix, an uncertain parameter-varying nonsquare (column-deficient) input matrix, and a nonlinear additive bounded disturbance. A Lyapunov-based continuous robust controller is developed that yields exponential tracking of a reference model, despite the presence of bounded nonvanishing disturbances. Simulation results for a hypersonic aircraft are provided to demonstrate the robustness and efficacy of the proposed controller.

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Worst-case flutter margins from F/A-18 aircraft aeroelastic data

An approach for computing worst-case flutter margins has been formulated in a robust stabilityfra... more An approach for computing worst-case flutter margins has been formulated in a robust stabilityframework. Uncertainty operators are included with a linearmodel to describe modeling errors and flightvariations. The structured singularvalue,/_,computes a stability margin which directly accounts for these uncertainties. This approach introduces a new method of computing fluttermargins and an associated new parameter for describing these margins. The p margins are robust margins which indicate worst-case stabilityestimates with respect to the defined uncertainty. Worst-case flutter margins are computed forthe F/A-18 SRA using uncertainty sets generated by flight data analysis. The robust margins demonstrate flightconditions for flutter may liecloserto the flight envelope than previously estimated by p-k analysis.

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Flow Control in a Driven Cavity Incorporating Excitation Phase Differential

AIAA Guidance, Navigation, and Control Conference and Exhibit, Jun 22, 2003

... CCC. ∗Graduate Student, Department of Mechanical and Aerospace Engineer-ing; [email protected]. S... more

An H-Infinity Approach to Control Synthesis with Load Minimization for the F/A-18 Active Aeroelastic Wing

The F/A-18 Active Aeroelastic Wing research aircraft will demonstrate technologies related to aer... more The F/A-18 Active Aeroelastic Wing research aircraft will demonstrate technologies related to aeroservoelastic effects such as wing twist and load minimization. This program presents several challenges for control design that are often not considered for traditional aircraft. This paper presents a control design based on 7-/00 syn-1Structural Dynamics, MS 4840/D,

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A Worst-Case Approach for On-Line Flutter Prediction

Worst-case flutter margins may be computed for a linear model with respect to a set of uncertaint... more Worst-case flutter margins may be computed for a linear model with respect to a set of uncertainty operators using the structured singular value. This paper considers an on-line implementation to compute these robust margins in a flight test program. Uncertainty descriptions are updated at test points to account for unmodeled time-vurying dynamics d the airplane by ensuring the robust model is not invalidated by measured flight data. Robust margins computed with respect to this uncertainty remain conservative to the changing dynamics throughout the flight. A simulation clearly demonstrates this method can improve the efficiency of flight testing by accurately predicting the flutter margin to improve safety while reducing the necessary flight time.

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Robust Flutter Margin Analysis that Incorporates Flight Data

The authors would like to thank the NASA Dryden employees and associates who voluntarily served o... more The authors would like to thank the NASA Dryden employees and associates who voluntarily served on a technical review committee to evaluate and improve this paper. This committee was chaired by Larry Freudinger and staffed by Mark Stephenson and John Carter of the NASA Dryden Controls and Dynamics Branch and visiting professor Rick Howard from the U.S. Navy Postgraduate School. This committee provided an exhaustive review and indicated several improvements that greatly increased the value of this paper. All remaining errors and poor explanations are a direct indication of the authors' inability to sufficiently address the many comments and suggestions. The authors would also like to thank the NASA Dryden Structural Dynamics group. Leonard Voelker was instrumental in developing the µ method by continuously providing comments and suggestions relating to the physics of flutter and how to interpret µ in terms of this phenomenon. Larry Freudinger helped develop the concepts of uncertainty in aeroelastic models and the introduction of additional uncertainty from signal processing. Dave Voracek was the Chief Engineer for the F/A-18 Systems Research Aircraft (SRA) project during the µ-method development and helped provide the large database of flight data and key information regarding the F/A-18 SRA flight systems and characteristics. Roger Truax and Tim Doyle generated the finite-element model of the F/A-18 SRA and computed theoretical aerodynamic-force matrices for this model. Mike

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Modeling and Control of Aerothermoelastic Effects

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Parameter Varying Estimation Toolbox for Flutter Prediction

AIAA Atmospheric Flight Mechanics Conference, 2010

μ Control for Satellites Formation Flying

Journal of Aerospace Engineering, 2007

In this paper, a controller is designed for a satellite formation flying system around the Earth ... more In this paper, a controller is designed for a satellite formation flying system around the Earth based on an uncertainty model derived from a nonlinear relative position equation. In this model, nonzero eccentricity and varying semimajor axis are included as parametric uncertainties. J 2 perturbation, atmospheric drag, and actuation and sensor noise are bounded by functional uncertainties. The controller design based on the nominal mission ͑an 800 km altitude circular reference orbit͒ is capable of achieving desired performance, is robust to uncertainties, and satisfies fuel consumption requirements even in a challenge nonnominal mission ͑a 0.1 eccentricity and 7,978 km semimajor axis elliptic reference orbit͒ with the same control gain. In this nonnominal mission, the designed controller is able to keep formation with almost the same level of the ⌬V budget ͑43.86 m/s/year͒ as used in the nominal mission ͑39.65 m/s/year͒. For comparison, linear quadratic regulator ͑LQR͒ and sliding mode controllers ͑SMC͒ are developed and extensively tuned to get the same ⌬V consumption as that of the designed controller for the nominal mission. However, as shown in the simulation, the designed linear robust controller ͑LQR͒ and nonlinear robust controller ͑SMC͒ have a serious ⌬V consumption penalty ͑1.72 km/ s / year for SMC͒ or are unstable ͑for LQR͒ in the nonnominal mission.

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Optimally Scaled Ji^ Full Information Control Synthesis with Real Uncertainty

An algorithm to synthesize optimal controllers for the scaled Tioo full information problem with ... more An algorithm to synthesize optimal controllers for the scaled Tioo full information problem with real and complex uncertainty is presented. The control problem is reduced to a linear matrix inequality, which can be solved via a finite dimensional convex optimization. This technique is compared with the optimal scaled 1-C^ full information with only complex uncertainty and D-K iteration control design

Wavelet filtering to reduce conservatism in aeroservoelastic robust stability margins

39th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference and Exhibit, Apr 20, 1998

Wavelet analysis for filtering and system identification was P(s) used to improve the estimation ... more

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A hardware in the loop simulation platform for vision-based control of unmanned air vehicles

Mechatronics, Oct 1, 2009

Design and testing of control algorithms for unmanned air vehicles (UAV's) is difficult due to th... more Design and testing of control algorithms for unmanned air vehicles (UAV's) is difficult due to the delicate and expensive nature of UAV systems, the risk of damage to property during testing, and government regulations. This necessitates extensive simulation of controllers to ensure stability and performance. However, simulations cannot capture all aspects of a flight control, such as sensor noise and actuator lag. For these reasons, hardware in the loop simulation (HILS) platforms are used. In this paper, a novel HILS platform is presented for vision-based control of UAV's. This HILS platform consists of virtual reality software to produce realistic scenes projected onto a screen and viewed by a camera. Flight hardware includes an UAV with onboard autopilot interfaced to the virtual reality software. This UAV can be mounted in a wind tunnel, allowing attitude regulation through servoing the airfoils.

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A Hardware-in-the-Loop Experiment and Simulation Facility for Vision-Based Control of Micro-Air-Vehicles

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Maneuvering and Tracking for a Micro Air Vehicle Using Vision-Based Feedback

SAE Technical Paper Series, Nov 2, 2004

Missions envisioned for micro air vehicles may require a high degree of autonomy to operate in un... more Missions envisioned for micro air vehicles may require a high degree of autonomy to operate in unknown environments. As such, vision is a critical technology for mission capability. This paper discusses an autopilot that uses vision coupled with GPS and altitude sensors. One use of vision processing analyzes a horizon to estimate roll and pitch information. Another use tracks a feature point to estimate position relative to a target. This paper presents examples of waypoint navigation and hom- ing using vision-based feedback. The examples indicate the vi- sion provides sufcient information to achieve the missions.

Linear Parameter-Varying Flow Control for a Driven Cavity Using Reduced-Order Models

AIAA Guidance, Navigation, and Control Conference and Exhibit, Jun 22, 2003

Flow control can potentially impact many engineering applications; however, the design of such co... more Flow control can potentially impact many engineering applications; however, the design of such controllers is extremely challenging. Some of the reasons for the challenging nature of this control design problem is the complexity of the uid dynamics, inherent nonlinearity and the associated numerical cost of computation. The degree of dicult y is increased when the boundary conditions or functional parameters change through control intervention during the normal evolution of the system. This paper presents a method to model uid dynamics and design associated o w controllers using the linear parameter-varying framework. The formulation of a model which is amenable to control design makes use of proper orthogonal decomposition to derive reduced-order representations of the open-loop uid dynamics. The resulting representations are shown to depend anely on a parameter, which is dened as the product of the Strouhal number and the Reynolds number, in a linear parameter-varying fashion. Controllers are then designed for this special model that are scheduled to work across a range of the parameter. A disturbance rejection problem is solved to demonstrate how this method generates controllers that achieve desired levels of performance even acting on the full-order nonlinear system.