Active Vibration Control of Scaled Wing Box Model Using Piezoelectric Stack Actuators

Abstract

The paper presents a numerical and experimental study aimed at investigating the potential of pre-stressed piezoelectric stack actuators for vibration control of a typical aircraft wing box structure with a tip store. The focus of the study is to assess, through simulation, the control authority of the stack actuators for effectively controlling specific modes of interest and experimentally verify the same. Towards this, a geometrically similar, 1:1.6 scaled model of a typical wing box structure has been designed from data available for a actual aircraft wing box with attached tip store. The model is designed and fabricated such that the first three natural frequencies of the actual wing box and the corresponding mode shapes were replicated closely in the model. Finite element analyses of the actuated structure are performed using ANSYS®. The piezoelectric stack is modeled as a beam element and a thermal analogy concept has been used to simulate the electro-mechanical coupling in the stack actuator. A finite element model is created for the fabricated scaled model along with its mounting rig to include the effects of the rig flexibility. Experimental modal testing results show a good match with numerical computations. Sensitivity studies carried out to study the effectiveness of a single stack actuator at different locations on the front and rear spar of the wing box suggest the different locations where the stack has highest actuation authority over the individual bending and torsion modes. This was verified by the open loop experiments. Comparison between open loop dynamic response simulations and corresponding experimental results establish the validity of the simplified modeling of the stack actuator fairly well within experimental uncertainties. The closed loop model is formulated in state space using experimentally validated modal model for the system characteristics as well as the modal generalized piezoelectric actuation forces. Accelerometers are used for response sensing. The closed loop implementation is aimed at achieving maximum damping of the controlled modes, through a negative velocity feedback control law. The acceleration output is integrated once to obtain the combined velocity signal from all the modes that are sensed. However, the rate gain is designed assuming only first three vibration modes to be significant. Simulations are carried out in SIMULINK® to characterize the effect of control gains on the overall response of the close loop control to a disturbance input, with the constraint on the stack actuator voltage to be within 0-150V. The results show significant improvement in the damping of the first three modes. Closed loop experiments are being implemented.