Abstract. The geometrically nonlinear vibrations of 3D beams that rotate about a fixed axis are investigated by the p-version finite element method. The beams are considered to be tapered, i.e. with variable thickness along its length, and with arbitrary cross sections. The beam model is based on
INTRODUCTIONRotating beams are used to model and investigate the dynamics of helicopter blades, jet engine turbine blades, robot arms, wind turbine blades, etc. Many studies have been performed for modeling rotating beams about a fixed axis. The linear natural frequencies of beams that rotate with constant speed were investigated by many researchers, for example in [1][2][3][4][5]. Works that consider geometrically nonlinear models of rotating beams may be found, for example [6][7][8]. In what concerns modern wind turbine blades, most of them are constructed with load carrying box girder inside the blade and shells on the surface of the blade [9]. The purpose of the box girder is to make the blade stronger and stiffer while the shells around the box girder form the aerodynamic shape. Thus, the dynamic behavior of the wind turbine blade might be determined mainly from the load carrying box, even though the shells contribute small bending strength.In the current work, a model of beams rotating about a fixed axis with constant speed of rotation is presented. A setting angle and a rigid hub are included in the model. The equation of motion is derived in the rotating coordinate system, and the rotation is taken into account by the inertia forces [10]. The beam may vibrate in space, i.e. it may perform longitudinal, torsional and bending deformations, the model is based on Timoshenko's theory for bending and assumes that under torsion, the cross section deforms only in longitudinal direction due to warping [11]. Geometrical type of nonlinearity is considered and the equation of motion is derived by the principle of virtual work.Thin-walled box beams with linearly varying thickness and width are investigated. First, the derived model is validated by generating a fine mesh of three-dimensional finite elements. Then, the influence of the setting angle and the speed of rotation on the natural frequencies is examined. Forced vibrations of rotating beams due to harmonic forces are presented.