Structural Analysis of a Bearingless Rotor Using an Improved Flexible Multibody Model

Abstract

This paper presents an improved structural analysis for a bearingless helicopter rotor. The bearingless rotor usually features a significantly large elastic twist in the flexbeam and additional unique structural characteristics. Thus, it will require sophisticated structural analysis and relevant numerical validation procedures due to its multiple load paths, as induced by the single or multiple flexbeams and the torque tube. In this paper, an extended finite element formulation was derived to consider the multiple components as individual beam elements. A geometrically exact beam formulation was adopted to describe the nonlinear behavior of these major components in the rotor precisely. To implement the interconnecting kinematic relationship with the major components, Lagrange multipliers were used. The present static analysis was validated through comparisons with the existing multi-body dynamics analysis DYMORE. Additional results were obtained for rotating conditions in both a vacuum and a set atmosphere in a wind tunnel. Finally, an experimental full-scale bearingless rotor system was coupled with finite-state dynamic inflow aerodynamics to simulate forward flight. The present predictions of the rotor responses and aerodynamics were well correlated with those by CAMRAD II.