Integrated Aeroservoelastic Analysis of Induced Strain Rotor Blades

This paper presents an application of an original formulation for the characterization of generally anisotropic, non-homogeneous beam sections including induced-strain devices (in this case piezo-electric patches) to the aeroservoelastic analysis and optimization of actively twisted helicopter rotor blades. The induced-strain inclusions can have arbitrary shape and orthotropy. The beam section characterization is based on a semi-analytical approach to the analysis of the beam, where the section is modeled as a 2-D FE model. The linear and angular strains of the beam, the free warping of the section and the electric potential are solved in terms of unit internal forces, moments and electric charge density on the electrodes under appropriate boundary conditions to provide the elastic and electro-static solution of the compliance problem. This solution yields the 6 × 6 generalized elastic and inertia properties, the 6 × N generalized piezo-electric properties and the N × N dielectric properties of a piezo-electric beam section characterized by N independent piezo-electric patches. These properties, and detailed information about the strain and stress state inside the beam section for each span-wise location are used to synthesize noteworthy geometric, mechanical, aeroelastic and piezo-electric properties to be used in the definition of the objective function and the constraints of an aeroservoelastic optimization problem. The piezo-electric blade section characterization is detailed; the optimization procedure is illustrated, and relevant results are presented and discussed in view of indications arising from simplified models based on the monocoque theory.