Abstrakt

The work focuses on aspects of multibody dynamics. Investigated object is a mass driven by rotations of an inertial shaker. Resulting vibrational set consists of two counter-rotating identically-unbalanced rotors. Since the mass centres of the rotors do not coincide with the axes of their rotations, significant centrifugal forces arise during rotations. As both rotors are identically unbalanced, the inter-axial force components balance each other, and only the summed transverse components generate the requested resultant of the sinusoidal-variable exciting force. Abovementioned description refers to a simplified theory of the force generation, since it omits several significant aspects which are difficult to their on-hand estimations, e.g., inertial terms created by the inertia products and gyroscopic effects. These effects, reasonable omitted in case of the stationary fixed shakers, are investigated in the paper, as the vibration-based angular motion of the excited base is significant and interacts with the relative spin motion of the rotors. What is more, variability of the angular speed of the spin should be considered, if power of the implemented drives is limited. Also, the angular and the linear kinematics resulting of the two motions are recombined, e.g. centrifugal terms resulting of rotation are modified by accelerations of transport motion of the base. Taking all of the facts under consideration, effective forces of the real exciter can differ from these which was initially requested, and thus, numerical verification of dynamics of the exciter is recommended, especially, if amplitudes of the resulting vibrations are significant. According to the indicated aspects, multibody model of the exciter is proposed and described in the paper. Simulated behaviours of the model are compared with behaviours a reference model interpreted as a rigid body driven by an ideal external exciter able to perfectly create a force which is described by a purely harmonic mathematical formula. Difference of the obtained results and applicability of the investigated exciter is discussed.

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