ABSTRACT: The shape optimization of composite flexbeam sections of a bearingless helicopter rotor is studied usinga finite element (FE) sectional analysis integrated with an efficient evolutionary optimization algorithm called particleswarm assisted genetic algorithm (PSGA). The sectional optimization framework is developed by automating theprocesses for geometry and mesh generation, and the sectional analysis to compute the elastic and inertial properties.Several section shapes are explored, modeled using quadratic B-splines with control points as design variables, througha multiobjective design optimization aiming minimum torsional stiffness, lag bending stiffness, and sectional masswhile maximizing the critical strength ratio. The constraints are imposed on the mass, stiffnesses, and critical strengthratio corresponding to multiple design load cases. The optimal results reveal a simpler and better feasible section withdouble-H shape compared to the triple-H shape of the baseline where reductions of 9.46%, 67.44% and 30% each arereported in torsional stiffness, lag bending stiffness, and sectional mass, respectively, with critical strength ratio greaterthan 1.5.

Keywords: Flexbeam, Cross-section, Bearingless rotor, Shape optimization, Evolutionary algorithm