On the choice of boundary conditions for mode shapes in flexible multibody systems

The modal representation of the deformation field is a widespread and efficient approach in the analysis of flexible multibody systems. However, it requires a pre-processing in advance to the actual multibody survey that includes the imposition of boundary conditions for the evaluation of the mode functions as an essential user input. Quite often the appropriateness of these boundary conditions is a point of discussion. Therefore the present paper reviews the theoretical background and the implications of this task. Then, a consistent and comprehensive proposal is made how these boundary conditions may be chosen. The suggestion is justified by theoretical considerations and compared to alternative approaches from the literature in a simulation study with three representative examples. It may be concluded that several approaches lead to reasonable results for a sufficient number of mode functions. However, the proposed approach turned out to be the most efficient one and provides a consistent framework.