An approach to elastic-dynamic-aeroelastic multiobjective optimization of rotor blades

An efficient multiobjective function optimization method is developed and applied in design of a minimum weight, minimum vibration and maximum material strength rotor blade with requirements on the aeroelastic stability. The design study is a high aspect ratio articulated flexible blade with a thin-walled multicell cross section at high tip Mach numbers. The rotor blade analysis sets consist of three subsets in order to increase efficiency in numerical methods used in each discipline. The first subset is an elastic analysis using an idealized model by chordwise segments and spanwise elements which allows systematic evaluation of not only the blade cross sectional properties but also the axial stresses and shear flows in all chordwise segments of all spanwise elements. This approach provides efficient material reassignment for minimum weight design. The second subset is a dynamic analysis for optimal natural frequency placement and vibratory vertical hub shear reduction by using a high order finite element from the Gradient Adaptive Transfinite Element (GATE) family in order to reduce computational requirements and to improve results without increasing the number of elements. The third subset is an aeroelastic analysis for accurate instability boundary predictions using Rayleigh-Ritz method with new shape functions, which adapt to the changes of aspect ratio and material properties. For multiobjective function optimization, the utility function formulation, global criterion formulation and multilevel decomposition approach are applied. In the multilevel decomposition approach, the optimization procedure is decomposed into two levels for more efficient handling of the design variables and objective functions, and their correlation. In level 1, the goal is the design for minimum weight and maximum material margin of safety simultaneously using the global criterion formulation. In level 2, the goal is the design for minimum vibratory vertical hub shear load using the modal shaping technique. The numerical results show the effects of the important design parameters on the performance of rotor blades, the efficiency of the analytic method developed in this research, the comparison of the multiobjective function optimization techniques, the effects of tuning masses and their locations on the hub shear reduction, and the comparison of designs using isotropic and composite materials.