“…This effect is addressed in [77] with a standard Euler-Bernoulli model and in [12] with a Timoshenko model. The effect of various parameters on the natural frequencies of rotating beams has also been widely studied: the effect of variable and non-symmetrical cross sections, pre-twist [60,63], precone, pre-lag, setting angle [11,44], root offset [14,43], taper and rotary inertia, attached masses [5,38,57], shrouds, springs [22] and various boundary conditions [10]. The finite-element method has also been used widely used: see, i.e., [8] and the textbook [32].…”