Analysis of an actively twisted rotor by multibody global modeling

The paper presents a procedure and the integrated tools for the aeroelastic analysis of an active twist helicopter rotor (ATR). The active twisting of rotor blades is carried out by induced-strain actuators distributed into the structure of the blade. Active fiber composites (AFC), made of piezoelectric fibers actuated by interdigitated electrodes (IDE), are used to obtain anisotropic induced-strain actuation capable of twisting the blade. The elastic, inertial and piezoelectric properties of the blade section are determined by a dedicated semi analytical formulation that accounts for the nonhomogeneity and the anisotropy of the elastic and piezoelectric materials. A threedimensional finite element analysis of the piezoelectric fiber with interdigitated electrodes is used to estimate the equivalent homogeneous material properties required for the blade section characterization. A four-blade, articulated rotor is analyzed in hover and forward flight conditions. The system is modeled by an original multibody formulation, implemented in a code named Multi-Body Dynamics (MBDyn). The equilibrium equations and the momenta are written for each body, together with the constraint equations, as a redundant coordinate set formulation. The blades are modeled as beam elements, by an original finite volume formulation for the analysis of nonlinear, initially curved and twisted beams subject to large displacements and rotations. The formulation is extended to include the effects of embedded piezoelectric devices as actuators. Electric and control-related degrees of freedom and elements have been added to MBDyn. Preliminary results related to the actuation authority of the active blade are presented.