It impacts upon the screws located at the top of the secondary beams positioned on one or both sides of the oscillating mass. The rig comprises of a steel mass supported by a pair of parallel leaf springs to maintain the pure vertical motion of the mass. The design of an experimental rig vertically excited by a shaker was presented by Sin and Wiercigroch in, and a comprehensive experimental study of this system is conducted by the same authors in. Bounded, non-periodic or chaotic vibration were observed experimentally and studied theoretically using impact oscillator model. The clamped end of the beam was attached to a large electromagnetic shaker and driven periodically. The considered system consisted of a cantilever beam clamped at one end and free at the other end, where the motion of the free end was constrained by an aluminium stop. In previous experimental investigations, a common approach was to provide the system excitation through the base, as was done, for example, by Moon and Shaw in.
Impacting systems have been extensively studied theoretically both considering rigid and soft constraints. Another illustration of a practical relevance of impacts is the behaviour of mooring lines which are repeatedly slacken and then tighten again under wave forcing, and a small floating structure moored to a large one can unexpectedly modify the motion of the whole system. For example, in rotor dynamics, effects of bearing clearances are very important, and they were investigated using Jeffcott rotor model where the interactions between a mass imbalanced rotor and a snubber ring without preloading of the snubber ring and with a preloading were considered, and different impacting scenarios depending on the regimes of operation of the rotor were described. In some cases, impacts are imperative part of the system operation, but they also may result from ageing of parts, thermal deformation or design tolerances. Impacts appear in a wide range of real systems, and understanding of these nonlinear phenomena is essential for further improvement in machine design and drilling processes amongst others.
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