Nonlinear behavior investigation of typical section with structural nonlinearities

Abstract

In order to forecast LCO (Limit cycle oscillation) brought on by nonlinear features associated with the control surface degree of freedom, this work examines the nonlinear aeroelastic behavior of the control surface of a typical section. Since traditional techniques of aeroelastic stability solution, which rely on linear models, cannot foresee these effects, the aeroelastic stability investigation around the effects of structural nonlinearities has gained significant relevance in the field of aeroelasticity study. In this context, control surfaces with freeplay are widely used as a case study of the approaches provided in the literature around aeroelastic stability from the standpoint of representing real cases of unwanted nonlinear behavior that can lead the system to critical unstable conditions prior to unstable conditions predicted by linear models and solutions. For the purpose of predict and characterize LCO cases, this work uses frequency and time domain analyses, taking into account the simultaneous actions of dry friction, nonlinear damping, and freeplay on the system control surface. As a function of LCO characteristics obtained by the HM (Harmonic Balance method), the nonlinear functions are treated as linear equivalent properties for the frequency domain analysis. These properties are then associated with the linear aeroelastic model and traditional flutter solutions using the ELT (Equivalent Linearization Technique) process to develop the LCO map. The LCO map for the time domain analysis is derived from the use of the Fast Fourier Transform in time simulation samples involving a nonlinear aeroelastic model that is solved using a fourth-order Range-Kutta solver in the Simulink software. The linear aeroelastic model and nonlinear aeroelastic model used for both processes are represented by state space equations with aerodynamic approximations done through the RFA (Rational Functions Approximation) method. In comparison to the dynamic system response observed in the time simulations, the results show that the RFA applied to frequency domain analysis produces an effective prediction of LCO characteristics in terms of frequency and amplitude. Additionally, depending on the imposed disturbance, the time domain results also demonstrate that the system can reach alternative LCO processes under the same conditions. Above all, the method worked satisfactorily to examine the LCO situations for an aeroelastic model.