Vibration reduction in an articulated rotor blade using structural optimization

Some recent efforts at application of structural optimization techniques for minimizing vibration in an articulated rotor blade are described. Two different optimization problems are discussed. In the first, the 4/rev vertical root shear and the blade weight are simultaneously minimized with constraints on natural frequencies, autorotational inertia and centrifugal stress. In the second, a more comprehensive vibration reduction problem is addressed. The 4/rev vertical and the 3/rev inplane shears, at the blade root, are minimized with constraints on the 3/rev radial shear, the 3/rev flapping and torsional moments, the 4/rev lagging moment, natural frequencies, autorotational inertia, centrifugal stress, blade weight and rotor thrust. Rotor aerodynamic and dynamic analyses are coupled with an optimizer to obtain the blade designs for a forward flight condition. The program CAMRAD is used for the blade aerodynamic and dynamic analyses and the program CONMIN is used for optimization. The global criteria approach is used to formulate the multiple objective optimization problem and the optimum designs are compared with a reference blade. A wind tunnel model of an advanced articulated rotor blade is used as the baseline or reference design.