Free vibration analysis of a rotating double-tapered Timoshenko beam undergoing flapwise transverse vibration is presented. Using an assumed mode method, the governing equations of motion are derived from the kinetic and potential energy expressions which are derived from a set of hybrid deformation variables. These equations of motion are then transformed into dimensionless forms using a set of dimensionless parameters, such as the hub radius ratio, the dimensionless angular speed ratio, the slenderness ratio, and the height and width taper ratios, etc. The natural frequencies and mode shapes are then determined from these dimensionless equations of motion. The effects of the dimensionless parameters on the natural frequencies and modal characteristics of a rotating double-tapered Timoshenko beam are numerically studied through numerical examples. The tuned angular speed of the rotating double-tapered Timoshenko beam is then investigated.
IntroductionThe modal characteristics, i.e., the natural frequencies and the corresponding mode shapes, of rotating beams, especially tapered ones, are critical to the design and analysis of rotating structures, such as the rotating machinery, helicopter blades, wind turbine blades, etc., since most rotating beams in engineering applications are tapered. The modal characteristics of rotating beams often vary significantly from those of non-rotating beams due to the influence of centrifugal inertia force. Due to this significant variation of modal characteristics resulted from rotation, the modal characteristic of rotating beams has been widely investigated.Study of the modal characteristics of rotating beams originated from the pioneering work of Southwell and Gough [1]. Based on the Rayleigh energy theorem, an equation, known as the Southwell equation, that relates the natural frequency to the rotating frequency of a uniform beam was developed. This study was further extended by Liebers [2], Theodorsen [3] and Schilhansl [4], to obtain more accurate natural frequencies of rotating beams. However, due to the large amount of calculation and lack of computational devices, the mode shapes were not available in these investigations. Later, using digital computers, investigations in mode shapes and more accurate natural frequencies were published for uniform rotating and non-rotating beams [5][6][7][8][9][10][11][12][13].The modal characteristics of rotating and non-rotating tapered beams have also been widely investigated. Hodges and Dowell [14] derived the non-linear equations of motion of twisted non-uniform rotor blades based on the Hamilton's Principle and the Newtonian method. Klein [15] analyzed the vibration of a non-rotating tapered beam with a method which combined the advantages of a finite element approach and of a RayleighRitz analysis. Downs [16] applied a dynamic discretization technique to calculate the natural frequencies of a