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Alvarez D.J.,Systems Technology Inc. | Lu B.,California State University, Long Beach
Journal of Guidance, Control, and Dynamics | Year: 2011

Piloted simulation is often regarded as an intermediate step between traditional desktop analysis and flight test. It is a valuable tool in the assessment of how changes in flight control system parameters affect closed-loop vehicle performance. This paper focuses on the piloted simulation evaluation of classical proportional-integral-derivative, robust H∞, and linear parameter-varying control design methods. Three different controllers are designed for the longitudinal flight dynamics of the F-16 variable stability in-flight simulator test aircraft within a defined flight envelope. After assessing the performance of each controller using the desktop analysis and simulation, a piloted simulation study is provided to gather qualitative pilot ratings and comments to validate or refute the results and conclusions which were based on the preliminary desktop analysis. The pilot-in-the-loop flight simulator, simulation test plan, and controller evaluation procedure are described. The data obtained from a two-pilot simulation test are then used to conduct a full-handling-qualities study comparing the performance and robustness of each controller. The paper concludes with the selection of the controller that is best suited for application to a modern, fighter-type aircraft. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc.

Thompson P.M.,Systems Technology Inc.
AIAA Modeling and Simulation Technologies Conference 2011 | Year: 2011

A multi-body problem has six degrees of freedom for each body. Constraints are used to restrict motion, for example by defining joints that tie the bodies together. These constraints reduce the total degrees of freedom. Two methods are described to create a transformation matrix used to create a reduced order, unconstrained multi-body problem. One method starts from the constraint function, computes the Jacobian of the constraint function, and then the desired transformation matrix is the null space of the Jacobian. The second method is more direct and creates the same transformation matrix starting from the velocity relationships that define the joints. Equivalence of the two methods is proved. Closed form expressions are given of the transformation matrix, which can be used either for numerical simulation or as a starting for further symbolic expansion. Methods for linearization of the multi-body problem are discussed. This paper is tutorial and starts by defining a general and precise notation. The Newton-Euler dynamics problem is reviewed, a catalog is presented of constraint functions used for joints, and then a catalog of generalized forces appropriate for aerospace problems. Examples are presented using combinations of rigid bodies including an overview of satellite, rotorcraft, and wind turbine problems. The examples in this paper are considered complete when the transformation matrix used to create the reduced order problem is defined. © 2011 by Systems Technology, Inc. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.

Thompson P.M.,Systems Technology Inc. | Padin S.,California Institute of Technology
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

CCAT will be a 25-meter telescope for submillimeter wavelength astronomy located at an altitude of 5600 meters on Cerro Chajnantor in northern Chile. This paper presents an overview of the preliminary mount control design. A finite element model of the structure has been developed and is used to determine the dynamics relevant for mount control. Controller strategies are presented that are designed to meet challenging wind rejection and fast scan requirements. Conventional inner loops are used for encoder-based control. Offset requirements are satisfied using innovative command shaping with feedforward and a two-command path structure. The fast scan requirement is satisfied using a new approach based on a de-convolution filter. The de-convolution filter uses an estimate of the closed loop response obtained from test signals. Wind jitter requirements remain a challenge and additional sensors such as accelerometers and wind pressure sensors may be needed. © 2014 SPIE.

Macmartin D.G.,California Institute of Technology | Thompson P.M.,Systems Technology Inc. | Colavita M.M.,Jet Propulsion Laboratory | Sirota M.J.,TMT Observatory Corporation
IEEE Transactions on Control Systems Technology | Year: 2014

Current and planned large optical telescopes use a segmented primary mirror, with the out-of-plane degrees of freedom of each segment actively controlled. The primary mirror of the Thirty Meter Telescope (TMT) considered here is composed of 492 segments, with 1476 actuators and 2772 sensors. In addition to many more actuators and sensors than at existing telescopes, higher bandwidths are desired to partially compensate for wind-turbulence loads on the segments. Control-structure interaction (CSI) limits the achievable bandwidth of the control system. Robustness can be further limited by uncertainty in the interaction matrix that relates sensor response to segment motion. The control system robustness is analyzed here for the TMT design, but the concepts are applicable to any segmented-mirror design. The key insight is to analyze the structural interaction in a Zernike basis; rapid convergence with additional basis functions is obtained because the dynamic coupling is much stronger at low spatial-frequency than at high. This analysis approach is both computational efficient, and provides guidance for structural optimization to minimize CSI. © 2013 IEEE.

Danowsky B.P.,Systems Technology Inc. | Chrstos J.R.,Systems Technology Inc. | Klyde D.H.,Systems Technology Inc. | Farhat C.,CMSoft, Inc. | Brenner M.,NASA
Journal of Aircraft | Year: 2010

Flutter is a destructive and potentially explosive phenomenon that is the result of the simultaneous interaction of aerodynamic, elastic, and inertial forces. The nature of flutter mandates that flutter flight testing be cautious and conservative. Because of this, further investigation of uncertainty analysis with respect to the flutter problem is desired and warranted. Prediction of flutter in the transonic regime requires computationally expensive high-fidelity simulation models. Because of the computational demands, traditional uncertainty analysis is not often applied to transonic flutter prediction, resulting in reduced confidence in the results. The work described herein is aimed at exploring various methods to reduce the existing computational time limitations of traditional uncertainty analysis. Specifically, the coupling of design of experiment and response surface methods and the application of μ analysis are applied to a validated aeroelastic model of the AGARD 445.6 wing. From a high-fidelity nonlinear aeroelastic model, a linear reduced-order model is produced that captures the essential dynamic characteristics. Using reduced-order models, the design of experiment, response surface methods, and μ-analysis approaches are compared with traditional Monte Carlo-based stochastic simulation. All of these approaches to uncertainty analysis have advantages and drawbacks. Results from these methods and their robustness are compared and evaluated. Copyright © 2010 by Systems Technology, Inc.

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