Topic
Describing function
About: Describing function is a research topic. Over the lifetime, 1742 publications have been published within this topic receiving 26702 citations.
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01 Jul 2017
TL;DR: In this article, the authors deal with the stability analysis of an aeroelastic system affected by freeplay and uncertainties, and propose an approach to validate the main results by means of Integral Quadratic Constraints.
Abstract: This work deals with the stability analysis of an aeroelastic system affected by freeplay and uncertainties. Nonlinearities can trigger Limit Cycle Oscillations (LCOs), self-sustained periodic responses likely to provoke critical damages. Moreover, uncertainties in the models might lead to inaccurate predictions in terms of onset and features of these instabilities. The paper shows a possible strategy to tackle this problem, pivoting on the Describing Functions method to model freeplay and μ analysis to study stability in the face of parametric uncertainties. The simplifying hypotheses underlying the framework are commented, and an approach to validate the main results, by means of Integral Quadratic Constraints, is finally proposed.
1 citations
TL;DR: Analysis by describing functions shows that a dual-mode system may be unstable even though its linear and relay modes of operation are stable as systems by themselves, and the mode-switching circuitry is perfect.
Abstract: Dual-mode servomechanisms have several advantages such as light weight and simplicity, but a serious study of the stability problems encountered in such devices has not appeared in the literature. An analytical method is presented here for determining the stability of dual-mode servomechanisms by an extension of the describing function method of analysis. The method is illustrated with examples, and laboratory data are presented. Analysis by describing functions shows that a dual-mode system may be unstable even though its linear and relay modes of operation are stable as systems by themselves, and the mode-switching circuitry is perfect. It is also shown that for certain mode boundary shapes the describing function is a function of frequency as well as amplitude.
1 citations
01 Nov 2009
TL;DR: In this article, the authors present two methods which allow nonlinear actuators to present a linear response and therefore allow their incorporation in linear multivariable control design methods, based on a closed-loop describing function approximation, and using an equivalent nonlinearity concept to linearise the relay which represents the fixed-speed limitation.
Abstract: Fixed speed actuators have a characteristic nonlinear transient response While this may not present a problem for single-input, single-output (SISO) control systems containing such actuators, the mixture of different fixed speed actuators is usually problematic in multivariable control applications This paper presents two methods which allow such nonlinear actuators to present a linear response and therefore allow their incorporation in linear multivariable control design methods The first method is based on a closed-loop describing function approximation, while the second uses an equivalent nonlinearity concept to linearise the relay which represents the fixed-speed limitation A simulation study, demonstrating the performance of both schemes in a multivariable control setting, is presented
1 citations
TL;DR: In this correspondence Popov's method is used to find the minimum amplitude of the dither to be applied to quench the limit cycles occurring in relay type nonlinear control systems.
Abstract: In a previous paper [1], a new method called the dual input discrete describing function (DIDDF) was presented, which enables one to determine the minimum amplitude of sinusoidal dither to be applied, to stabilize a relay type sampled-data control system. In this correspondence Popov's method is used to find the minimum amplitude of the dither to be applied to quench the limit cycles occurring in relay type nonlinear control systems. Furthermore, the dependence of the minimum value of the dither on sampling time is explicitly seen in Popov's method.
1 citations
19 Dec 1991
TL;DR: In this paper, an artificial neural net controller was developed for a typical fighter aircraft's longitudinal Stability and Control Augmentation System (SCAS), using elevator and thrust-vector-angle controls, and operating at high angle of attack.
Abstract: : An artificial neural net controller was developed for a typical fighter aircraft's longitudinal Stability and Control Augmentation System (SCAS) , using elevator and thrust-vector-angle controls, and operating at high angle of attack. The 'baseline' neurocontroller (NC) was in the feedforward loop (Kawato Type-C), with inputs from the pilot's pitch rate commands and rates and SCAS feedback error. An Adaptive Clustering Network algorithm was used to train the radial-basis-function neurons. Significant improvements in performance resulted from the NC action and these effects were analyzed by frequency domain describing functions. Thrust vector failures were handled satisfactorily, but reconfiguration of the SCAS was not possible within the simplified aircraft and NC effects. Phase II recommendations are included, such as: ways to choose signals for the neural net to more efficiently identify and separate failures of correlated control effectors; the further use of frequency domain describing functions to identity neurocontroller dynamic processes; and the development of a Neuro-controller Analysis Toolbox with diagnostic forcing functions, methods, analyses, and benchmark criteria for evaluation to a common NC standard.
1 citations