Acceleration of Iterative Vibration Analysis for Form Changes in Large Degrees-of-Freedom Engine Model

Operational analysis of automotive engines using flexible multi-body dynamics is increasingly important from the viewpoint of multi-objective optimization as it can predict not only vibration, but also stress and friction at the same time. Still, the finite element (FE) models used in this analysis have large degrees-of-freedom, so iterative calculation takes a lot of time when there is form change. This research therefore describes a technique that applies a modal differential substructure method (a technique that reduces the degrees of freedom in a FE model) that can simulate form changes in FE models by changing modal mass and modal stiffness in reduced models. By using this method, non-parametric form change in FE model can be parametrically simulated, so it is possible to speed up repeated vibration calculations. In the proposed method, FE model is finely divided for each form change design area, and a reduced model of that divided structure is created. This makes it possible to simulate the form change by changing modal mass and modal stiffness in the reduced model without converting to the physical structure when there is form change. The method was applied to a 1.5-liter inline four-cylinder engine model, and as a result, demonstrated that a large number of parameter studies can be made while maintaining enough precision for practical purposes.