Optimal Comfort Response of Road Vehicles Using Flexible Multibody Dynamics

Abstract

The design process of road vehicles, very often based in intuition and experience, can be greatly enhanced through the use of optimization techniques concurrently with multibody codes. The approach proposed here for flexible multibody models allows for the representation of complex shaped bodies using general finite element discretizations, which deform during the dynamic loading of the system, while the gross rigid body motion of these bodies is still captured using body fixed coordinate frames. Components of the system for which the deformations are relatively non-important are represented with rigid bodies. This methodology is applied to a road vehicle, where the flexibility plays an important role in its ride and handling dynamic behavior. The use of sparse matrix systems solvers and modal superposition, to reduce the number of flexible coordinates, in the computer simulation assures a fast and reliable analysis tool for the optimization process. The vehicle optimum design is achieved through the use of an optimization algorithm with finite differences sensitivities, where the characteristics of the vehicle components are the design variables to which appropriate constraints are imposed. The ride optimization is achieved finding the optimum of a ride index that results from a metric that accounts for the acceleration in several key points in the vehicle, weighted in face of their importance to the occupant comfort. Simulations with different road profiles are performed for different speeds accounting for various ride situations.