Suppression Of Limit Cycle Oscillations Research Articles

Fuzzy control of nonlinear aeroelastic system based on neural network identification

This article presents a fuzzy control method for the limit cycle oscillation (LCO) suppression of nonlinear aeroelastic systems based on the neural network identification algorithm. A prototypical 2D wing section with a single control surface at the trailing edge of the main wing, which contains a symmetrical free play nonlinearity in the pitch degree of freedom, is modeled to illustrate the proposed method. A neural network is used to identify the fuzzy control rules from the existing LCO suppression input and output data. A new fuzzy control rate of the nonlinear aeroelastic system is obtained by adjusting the parameters of the fuzzy control surface. Numerical simulations are conducted to verify the effectiveness of the proposed method.

Galloping suppression of a suspended cable with wind loading by a nonlinear energy sink

In this paper, an adaptive and passive galloping suppression of a suspended linear cable is investigated. The limit cycle oscillation (LCO) of cable due to nonlinear wind loading is effectively eliminated by a lightweight, easy-to-make attachment: nonlinear energy sink (NES). Analytical mechanism of LCO is explored by using harmonic balance method, implying that NES is valid for LCO suppression under any wind speed. Finally, the influences of mass ratio, damping, stiffness and location of NES on vibration suppression are highlighted in detail.

A Sliding Mode LCO Regulation Strategy for Dual-Parallel Underactuated UAV Systems Using Synthetic Jet Actuators

A sliding mode control- (SMC-) based limit cycle oscillation (LCO) regulation method is presented, which achieves asymptotic LCO suppression for UAVs using synthetic jet actuators (SJAs). With a focus on applications involving small UAVs with limited onboard computational resources, the controller is designed with a simplistic structure, requiring no adaptive laws, function approximators, or complex calculations in the control loop. The control law is rigorously proven to achieve asymptotic regulation of both pitching and plunging displacements for a class of systems in a dual-parallel underactuated form, where a single scalar control signal simultaneously affects two states. Since dual-parallel underactuated systems cannot be expressed in a strict feedback or cascade form, standard backstepping-based control techniques cannot be applied. This difficulty is mitigated through careful algebraic manipulation in the regulation error system development, along with innovative design of the sliding surface. A detailed model of the UAV LCO dynamics is utilized, and a rigorous analysis is provided to prove asymptotic regulation of the pitching and plunging displacements. Numerical simulation results are provided to demonstrate the performance of the control law.

Limit cycle oscillation suppression of 2-DOF airfoil using nonlinear energy sink

This paper presents a novel mechanical attachment,i.e.,nonlinear energy sink(NES),for suppressing the limit cycle oscillation(LCO)of an airfoil.The dynamic responses of a two-degree-of-freedom(2-DOF)airfoil coupled with an NES are studied with the harmonic balance method.Diferent structure parameters of the NES,i.e.,mass ratio between the NES and airfoil,NES ofset,NES damping,and nonlinear stifness in the NES,are chosen for studying the efect of the LCO suppression on an aeroelastic system with a supercritical Hopf bifurcation or subcritical Hopf bifurcation,respectively.The results show that the structural parameters of the NES have diferent influence on the supercritical Hopf bifurcation system and the subcritical Hopf bifurcation system.

Limit cycle oscillation suppression of 2-DOF airfoil using nonlinear energy sink

This paper presents a novel mechanical attachment, i.e., nonlinear energy sink (NES), for suppressing the limit cycle oscillation (LCO) of an airfoil. The dynamic responses of a two-degree-of-freedom (2-DOF) airfoil coupled with an NES are studied with the harmonic balance method. Different structure parameters of the NES, i.e., mass ratio between the NES and airfoil, NES offset, NES damping, and nonlinear stiffness in the NES, are chosen for studying the effect of the LCO suppression on an aeroelastic system with a supercritical Hopf bifurcation or subcritical Hopf bifurcation, respectively. The results show that the structural parameters of the NES have different influence on the supercritical Hopf bifurcation system and the subcritical Hopf bifurcation system.

Bifurcation Control of Aeroelastic Limit Cycle Oscillations

An active flutter suppression using linear saturated control is investigated for a 2dof wing section with nonlinear torsional stiffness and limited deflection amplitude of its single control effector. The suppression of limit cycle oscillations in the nonlinear closed-loop system is achieved through maximization of the stability region of the linearized system. A bifurcation sequence leading to limit cycle disappearance is revealed. With increase of the maximum control input amplitude, the closed-loop limit cycle is transformed into a stable torus, which disappears at higher control amplitude through a nonlocal bifurcation similar to a boundary crisis in chaotic systems. Finally, a saddle-node bifurcation of the limit cycle gives necessary conditions for global stability in the closed-loop system.

Suppression of limit cycle oscillations in the van der Pol oscillator by means of passive non-linear energy sinks

We study suppression of the limit cycle oscillations (LCOs) of a van der Pol (VDP) oscillator, utilizing two configurations of non-linear energy sink (NES)—grounded and ungrounded. Through computational parameter studies we verify LCO elimination for certain ranges of NES parameters. Then, we establish the slow-flow equations to perform numerical and analytical studies of the transient and steady-state dynamics of the configuration studied. The transient dynamics turns out to involve resonance captures, through which irreversible, passive energy transfer (called non-linear energy pumping) is achieved from the VDP oscillator to the NES. We also perform computational bifurcation analysis by means of numerical continuation to gain some understanding of the dynamics of generation and elimination of non-linear energy pumping. The steady-state dynamics shows that the system may possess either subcritical or supercritical LCOs, leading to different degrees of robustness of suppression. The results reported in this work support the applicability of the NES concept to suppression of instabilities in self-excited systems. Copyright © 2005 John Wiley & Sons, Ltd.

Structured Model Reference Adaptive Control for a Wing Section with Structural Nonlinearity

The recently derived structured model reference adaptive control (SMRAC) method is considered for the active suppression of limit cycle oscillations for a typical wing section with a structural nonlinearity. The SMRAC method uses the specific structure of the equations of motion governing general mechanical systems. This adaptive control method is implemented and tested in wind tunnel experiments to validate the performance. For comparison, results obtained with adaptive feedback linearization are also presented. It is shown that the derived SMRAC is advantageous in that it suppresses limit cycle oscillations at higher velocities, and also it can rigorously treat actuator saturation a priori.

On the suppression of limit-cycle oscillations

A procedure is presented for the suppression of limit-cycle oscillations in unity-feedback control systems which have an on-off type nonlinearity in cascade with a linear transfer function. The procedure is based on the introduction of a minor loop into the system. This produces a high-frequency periodic signal at the input of the nonlinearity, and thereby limit-cycle oscillations are suppressed.