1. Selected Challenges in Realistic Multibody Modeling of Machines and Vehicles

Multibody modelling involves taking fundamental decisions during the multibody model construction that not only condition its validity for the particular application foreseen but also have fundamental implications on the suitability of the numerical methods used on its analysis. The decision on allowing a particular flexible body to exhibit linear or nonlinear deformations or even to consider it part of the multibody system or as a structural component with which the system interacts is a crucial part of the modeling process. The description of the kinematic relations between moving components can be represented by perfect kinematic constraints or by contact pairs, as when local effects in the joints, generally associated with deviations from nominal conditions or to functional features, must be considered. The interaction of the multibody model with the ‘environment’ may require a substantial modelling effort that involves decisions on geometric description of features, on contact mechanics or even on numerical methodologies to handle co-simulation of systems with equilibrium equations that are solved with different numerical methods. Several areas are transversal to all the challenges identified and discussed here. The suitability of the numerical time integrators not only to handle the multibody model assumptions but also their interaction with other systems are of fundamental importance in the correct solution of the system dynamics. Descriptive and differential geometry also plays a very important role not only in the description of the relative kinematics of the systems but also in the modelling of the interactions.