Active twist control methodology for vibration reduction of a helicopter with dissimilarrotor system

Abstract

In this work, an active vibration reduction of hingeless composite rotor blades withdissimilarity is investigated using the active twist concept and the optimal control theory.The induced shear strain on the actuation mechanism by the piezoelectric constantd15 from the PZN–8% PT-based single-crystal material is used to achieve more active twistingto suppress the extra vibrations. The optimal control algorithm is based on theminimization of an objective function comprised of quadratic functions of vibratory hubloads and voltage control harmonics. The blade-to-blade dissimilarity is modeled using thestiffness degradation of composite blades. The optimal controller is applied tovarious possible dissimilarities arising from different damage patterns of compositeblades. The governing equations of motion are derived using Hamilton’s principle.The effects of composite materials and smart actuators are incorporated into thecomprehensive aeroelastic analysis system. Numerical results showing the impact ofaddressing the blade dissimilarities on hub vibrations and voltage inputs requiredto suppress the vibrations are demonstrated. It is observed that all vibratoryshear forces are reduced considerably and the major harmonics of moments arereduced significantly. However, the controller needs further improvement to suppress1/rev moment loads. A mechanism to achieve vibration reduction for the dissimilar rotor systemhas also been identified.