A Proposal of Dynamic Behaviour Design Based on Mode Shape Tracing: Numerical Application to a Motorbike Frame

Abstract

A modal based method to design and to improve the dynamic behaviour of flexible multibody systems is proposed in this paper. The dynamic behaviour of a flexible multibody system depends on the dynamics of its components and on the effects of the connections. When dynamics problems are experienced in particular working conditions, changes to the design are required. Usually connections are standard and there is not space for changes, therefore the components should be improved. Changes at components level improve the global system behaviour, but it is not so easy to identify the most effective component for each specific case. The purpose of the proposed method is to identify the most influent components in specific working frequency ranges of a multibody system. The method is based on a hierarchical procedure from assembly to components which leads to the identification of the components to be modified in order to improve assembly performance. The method is applied to a whole motorbike frame, a multibody system with comparable components stiffnesses. Numerical modal analysis is performed on the full assembly with connections, front and rear sub-assemblies and on single components: chassis, swingarm, engine and wheel. The method is applied to the selection of the most influent components mode shapes in the motorbike behaviour during manoeuvres at high velocity. The selected components are the most suitable for structural, geometric and material modifications to effectively improve the global motorbike behaviour, performances and driveability.