Static optimisation of prismatic structures as applied to helicopter rotor blades

• Main Author: Lemanski, Stuart Lucien
• Other Authors: Weaver, Paul
• Published: University of Bristol 2004
• Subjects: 629.133352
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399925

The elastic coupling properties of anisotropic composite materials offer the potential for aeroelastic tailoring and other structural couplings that are not fully exploited in current helicopter rotor blade designs. The full 3-dimensional analysis of slender prismatic structures (such as helicopter rotor blades) is routinely reduced to analysis of a 1- dimensional beam with associated cross-sectional stiffness and mass properties. It is therefore desirable to design the cross-section of such prismatic structures to given values of these cross-sectional properties. Although use of anisotropic composite materials offers additional degrees of freedom with which to obtain the desired values of cross-sectional properties, this introduces non-intuitive structural couplings and interactions between design variables, which increases the complexity of the design process. Rigorous optimisation techniques are therefore required to reliably and efficiently obtain an optimum design. This thesis addresses the main issues relating to the static optimisation of prismatic structures and their application to composite helicopter rotor blade design. Existing literature in composite materials, optimisation, and helicopter blade design is surveyed. A 4-ply laminated cylindrical shell is examined from analytical and computational perspectives as a simplified case study, which is used to develop understanding of how the choice of design variables affects the nature of the design space, and hence the solution methods which can be used. Flap-torsion coupling is an important variable in aeroelastic tailoring, and is therefore examined in some detail. A new analytical model is derived which is validated using finite element analysis, and compares favourably against existing models in the literature. Flap-torsion behaviour of laminated composite beams is studied experimentally, and compared with finite element results. Finally, the validity of the method has been demonstrated through the application of this work to the design of a generic helicopter rotor blade section, which meets given target values of cross-sectional stiffness.