A SYNTHETIC RESEARCH FOR AIRCRAFT ACTIVE FLUTTER SUPPRESSION

In this paper a new idea, based on discussing the essence of flutter, to investigate flutter problems is proposed that we only study a few modes of an aeroelastic system instead of studying the whole. In the light of this, an approach to analysing flutter characteristics which combines the merit of graphic and analytic methods, is presented. Also an optimal cost function with clear physical meaning which can overcome some inherent drawbacks of linear quadratic technique, is developed. The paper has shown a numerical example of an elastic wing, in which some comparisons between the approach and 'V-G' method for calculating the critical point (Vf,wf ) are carried out as well.

Active flutter suppression of nonlinear fin-actuator system via inverse system and immersion and invariance method

Structural nonlinearities such as freeplay will affect the stability and even flight safety of the fin-actuator system.There is a lack of a practical method for designing Active Flutter Suppression (AFS) control laws for nonlinear fin-actuator systems.A design method for the AFS controller of the nonlinear all-movable fin-electromechanical actuator system is established by combining the inverse system and the Immersion and Invariance (I&I) theory.First,the composite control law combining the inverse system principle and internal model control is used to offset the nonlinearity and dynamics of the actuator,so that its driving torque can follow the ideal signal.Then,the ideal torque of the actuator is designed employing the I&I theory.The unfavorable oscillation of the fin is suppressed by making the output torque of the actuator track the ideal signal.The simulation results reveal that the proposed AFS method can increase the flutter speed of the nonlinear finactuator system with freeplay,and a set of controller parameters is also applicable for wider freeplay within a certain range.The power required for the actuator does not exceed the power that can be provided by the commonly used aviation actuator.This method can also resist a certain level of noise and external disturbance.

Investigation on transonic flutter active auppression with CFD-Based ROMs

The calculation of accurate unsteady aerodynamic forces is critical in the analysis of aeroelastic problems,however the efficiency is low because of high computational costs of the computational fluid dynamics(CFD)portion.Additionally,direct integrated CFD and computational structural dynamics(CSD)technique is unsuitable for the analysis of ASE and the flutter active suppression in state-space form.A reduced-order model(ROM)based on Volterra series was developed using CFD calculation and used to predict the flutter coupled with the structure.The closed-loop control systems designed by the sliding mode control(SMC)and linear quadratic Gaussian(LQG)control were constructed with ROM/CSD to suppress the AGARD 445.6wing flutter.The detailed implementation of the two control approaches is presented,and the flutter suppression effectiveness is discussed and compared.The results indicate that SMC method can make the controlled object response decay to the stable equilibrium more rapidly and has better control effects than the LQG control.

Computational methods and engineering applications of static/dynamic aeroelasticity based on CFD/CSD coupling solution

The CFD/CSD coupling method is turning into the main research direction for the static/dynamic aeroelastic analyses. If one wants to use the method for the complex engineering aeroelastic problems, he needs to investigate the relative aeroelasfic algorithms, such as the numerical computational method of unsteady aerodynamic forces, equivalent low-dimensional structural fi- nite element model and the solution method of structural dynamic equations, data transfer technique between fluid and structure, the moving grid method, etc. Besides, he also needs to improve the computational efficiency by such as massive parallel CFD algorithm, reduced-order model （ROM） of unsteady aerodynamic forces, etc. In this paper, based on the authors＇ recent investigations, the research progresses in computational aeroelastic methods and their applications to engineering problem are summarized.