Could the Veering Phenomenon be a Mechanical Design Instrument?

Abstract

During the design process, especially in systems where dynamic characteristics are crucial, modal analysis is an instrument to understand the response of systems subject to external loads. The presence of a resonance into the component operative range usually sounds like an alarm bell, and modal analysis highlights this. But modal analysis gives just an indication, only the calculation of a forced response provides the actual behaviour of the analyzed system. This is principally due to the fact that resonances are excited only if the mode displacements are directed along the exciting force direction. So, in particular conditions, modal analysis highlights possible resonances, but in actual situations they do not occur. Setting a particular geometry, veering phenomenon between mode shapes can arise, related to a design parameter. Mode shapes can deeply interact and change the response of the system. As a matter of fact, two mode shapes affected by veering can be in the operating range, but just one of them can be excited by the external force. So, changing geometry and selecting the non-excitable mode, the component can be however used in the resonance conditions. On the basis of this considerations, in this paper, the possibility to use veering as a design instrument is investigated and this procedure is applied to high speed gears. As a principal result, the possibility to set a geometrical parameter in order to switch between two different mode shapes is underlined and potentials of the technique are explored.