Structural Optimization Of Composite Rotor Blade And Software Implementation

The vibration problem is always one of the most significant problems that affect the development and application of helicopters.Therefore the structural dynamic optimization design becomes a popular topic in the field of helicopter design.This thesis studies the techniques of dynamic analysis and optimization of helicopter composite rotor blades,and develops a CAD software with multifunction,including structural modeling,section property analysis,dynamic analysis and optimization,which provides designers with an effective and convenient tool.Topology optimization of beam cross section considering the torsional stiffness is studied.As an numerical example,a section optimization design of a flexible beam with minimal torsional stiffuess in hingeless rotor hub of helicopter is carried out successfully.A finite element method for beam cross-section properties considering the warping effects of cross section developed by Giavotto is introduced.The dynamic analysis method for rotating beams considering the effects of warping of cross section,coupling deformation and gyroscopic acceleration is detailed in this paper.The results of numerical examples show the accuracy of the calculations for cross-section properties and dynamic analysis.The parametric description of rotor blade structure is studied and the optimization models of rotor blades are proposed.The flow of optimization is presented.The weight of blades, spanwise position of center of gravity of blade,autorotation inertia,the maximum chordwise position of center of gravity of cross-sections,minimum torsion stiffness of cross-sections,the largest thickness of skin and the natural frequency are considered,the first three factors could be considered as objective or constraints.The shape of the cross-section,the layer thickness of outer panel skin and the locations of the lump masses/strips are treated as design variables.The effectiveness of optimization is verified by numerical examples.Using visual programming techniques,a rotor blade structural optimization design software ROBSOD(V1.0) is developed.Multi functions are carried out in this software,such as interactive parametric modeling,section properties analysis,coupled dynamic analysis and optimization,graphical display and post-processing of calculation results.More and more composite beams with outstanding properties are used in engineering practice instead of complex mechanical structures,and the stiffness of these composite beams always need to meet some specific requirements.It is necessary to determine the shape and size of the cross sections reasonably by optimization.The formulation and corresponding solving method for the topology optimization of beam cross section are proposed in this thesis.In the optimization problem,the properties of the stiffness of the beam are taken as objective and constraints,and the material density of each element is considered as design variable.The analysis of the cross section stiffness is based on an anisotropic beam theory which is proposed by Giavotto et al.considering warping of sections and coupling deformations.The standard SIMP scheme is used.The effectiveness of the formulation and optimization scheme is verified by numerical examples.Optimal topology of the cross-section of a flexible beam used in hingeless rotor hub of helicopter providing torsion stiffness for the blade is obtained by optimization.The final section design for engineering application is achieved by sizing optimization according to the optimal topology.