This paper presents a survey of ground experiments primarily conducted in the United States and U.S. facilities dedicated to the study of active control of flexible structures. The facilities are briefly described in ...
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This paper presents a survey of ground experiments primarily conducted in the United States and U.S. facilities dedicated to the study of active control of flexible structures. The facilities are briefly described in terms of capability, configuration, size, and instruments. Topics on the experiments include vibration suppression, slewing control, and systemidentification. The experiments are listed in tables containing the experiment's name, the responsible organization, a brief description of the test article configuration, and the actuator/sensor devices used in the experiment. Selected experiments will be further discussed to help illustrate the control problems. Some of the test facilities dedicated to ground testing of large space structures are discussed in more detail, to give the reader a better appreciation of ground-testing work. Several research issues are mentioned, including real-time computer systems, test article suspension, and new actuator/sensor technology development.
The Subsonic Ultra Green Aircraft Research Truss-Braced Wing aeroservoelastic wind-tunnel test was conducted in the NASA Langley Transonic Dynamics Tunnel. The primary goals of the test were to identify the open-loop ...
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The Subsonic Ultra Green Aircraft Research Truss-Braced Wing aeroservoelastic wind-tunnel test was conducted in the NASA Langley Transonic Dynamics Tunnel. The primary goals of the test were to identify the open-loop flutter boundary and then demonstrate flutter suppression. A secondary goal was to demonstrate gust load alleviation. Open-loop flutter and limit cycle oscillation onset boundaries were identified for a range of Mach numbers and various angles of attack. Two sets of control laws were designed for the model, and both sets of control laws were successful in suppressing flutter. Control laws optimized for gust load alleviation were not designed;however, the flutter suppression control laws were assessed using the Transonic Dynamics Tunnnel airstream oscillation system. This paper describes the experimental apparatus, procedures, and results of the truss-braced wing wind-tunnel model test. Acquired systemidentification data used to generate aeroservoelastic models are also discussed.
This paper discusses the control methodology, flight dynamics identification, and disturbance rejection analysis in hover of a revolutionary horizontal-axis rotary-wing concept: the twin cyclocopter. The vehicle has a...
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This paper discusses the control methodology, flight dynamics identification, and disturbance rejection analysis in hover of a revolutionary horizontal-axis rotary-wing concept: the twin cyclocopter. The vehicle has a gross weight of 500g (1.25 by 1.67 by 1ft in dimensions) and comprises two highly optimized cyclorotors along with a tail rotor for pitch control. Stable hover flight required fast control of the rpm and thrust vectoring of the rotors through onboard feedback regulation. A six-degree-of-freedom flight dynamics model of the vehicle was extracted through input excitation and time-domain identification. The longitudinal and heave degrees of freedom were decoupled and independent from the rest of the dynamics. Longitudinal translation damping was higher than in the heave mode, indicating differences in restoring forces at different blade azimuth positions due to the different pitch angles. Strong gyroscopic coupling was observed between lateral and yaw degrees of freedom because the rotors spin in the same direction, resulting in unbalanced angular momentum, which is an important characteristic of the twin cyclocopter. Coupling between lateral velocity perturbation and yaw response was also observed. Analysis based on a control-theoretic framework indicated sufficient maneuverability potential of the vehicle in open-loop condition. The longitudinal and lateral gust tolerances were calculated to be about 7.9 and 17 m/s, respectively.
Spacecraft periodic-disturbance rejection using a realistic spacecraft hardware simulator and its associated models is investigated. The effectiveness of the dipole-type disturbance rejection filter on the current rea...
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Spacecraft periodic-disturbance rejection using a realistic spacecraft hardware simulator and its associated models is investigated. The effectiveness of the dipole-type disturbance rejection filter on the current realistic nonlinear rigid-body spacecraft model is validated. However, it is shown that the rejection filter is not robust to disturbance frequency uncertainty. Therefore, systemidentification techniques are needed if the disturbance frequency is unknown or changing. Based on experience with the current test bed, two simple closed-loopsystemidentification methods are introduced to experimentally identify the disturbance frequency using data from the control input torque signal. It is shown that an incorrect filter frequency results in beating of the control input torque. Examination of the beat envelope leads to tuning of the rejection filter.
Unlike fixed-gain robust control, which trades off performance with modeling uncertainty, direct adaptive control uses partial modeling information for online tuning. The present paper combines retrospective cost adap...
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Unlike fixed-gain robust control, which trades off performance with modeling uncertainty, direct adaptive control uses partial modeling information for online tuning. The present paper combines retrospective cost adaptive control (RCAC), a direct adaptive control technique for sampled-data systems, with online systemidentification based on recursive least squares (RLS) with variable-rate forgetting (VRF). The combination of RCAC and RLS-VRF constitutes data-driven RCAC (DDRCAC), where the online systemidentification is used to construct the target model, which defines the retrospective performance variable. This paper investigates the ability of RLS-VRF to provide the modeling information needed for the target model, especially non-minimum-phase (NMP) zeros. DDRCAC is applied to single-input, single-output and multiple-input, multiple-output numerical examples with unknown NMP zeros, as well as several flight control problems, namely, unknown transition from minimum phase to NMP lateral dynamics, flexible modes, flutter, and nonlinear planar missile dynamics.
Black box modelling and identification was applied to the motor-sensory feedback of a posture control system without external disturbances, The standing upright subject was modelled using an inverted-pendulum model. A...
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Black box modelling and identification was applied to the motor-sensory feedback of a posture control system without external disturbances, The standing upright subject was modelled using an inverted-pendulum model. Analysis was extended to 28 healthy subjects engaged in cognitive verbal and visuo-spatial tasks, Further, 3 pathological subjects were examined, who were suffering from multiple sclerosis. The transfer function of the whole closedloopsystem was then considered, and the relative poles were computed, The distribution of the above poles on the z-plane showed an overall stabilizing effect of the cognitive tasks, both for healthy and pathological subjects, if compared to stance with open and closed eyes. Between the two tasks, the visuo-spatial one was found to be more stabilizing than the verbal one. On the other hand, differences on the model order of the controller were found among the tested pathological and healthy people. In fact the order remained unchanged both interindividually for healthy subjects performing the same task, both among different tasks performed by the same subject. Instead, pathological subjects were found to be characterized by a different model order, with respect to the healthy population, for the controller block of the posture control system.
This paper presents a free model reduction closedloop subspace identification method for multivariable systems operating in a well posed closedloop environment. This allows to determine the impulse response of the s...
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This paper presents a free model reduction closedloop subspace identification method for multivariable systems operating in a well posed closedloop environment. This allows to determine the impulse response of the system from the identification of the control system sensitivity functions. The rational behind the proposed method is twofold. Firstly, the general purpose design features of the subspace systemidentification approach and its inherent numerical robustness. Secondly, the model reduction performed in the available subspace identification is removed by a proper order selection procedure. A bias analysis is carried out to emphasize the robustness features.
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