Vibration Reduction In Helicopter Rotor With Dynamic Stress Constraints Using Response Surface Methods

Abstract

An optimization procedure to reduce oscillatory hub loads for a four bladed soft-in plane hingeless helicopter rotor is developed. The objective to be minimized consists of scalar norms of 4/rev vibratory hub loads transmitted by a 4-bladed helicopter rotor to the fuselage. The mass and stiffness properties of the rotor blades are considered as the design variables. Constraints are imposed on the dynamic stresses caused. by the blade root loads, and move limits on the design variables. An aeroelastic analysis based on finite elements in space and time is. used to construct the response surface approximation .for the objective function and constraints. The response surface approximations decouple the analysis problem from the optimization problem. The numerical sampling is done using the central composite design of the theory of design of experiments. The approximate optimization problem expressed in terms d response surfaces is solved using genetic algorithms. Optimization results in forward flight with unsteady aerodynamic modeling show a reduction in the objective function of about l5 percent. The dominant loads in vehicle vibration are the vertical hub shear and the rolling and pitching moments which are reduced by 22-26 percent. This paper proposes a multidisciplinary design which is suited to industrial application due to the decoupling of the analysis and optimization problems.