Preface

Abstract

Multibody dynamics is a rapidly evolving field.Going back to 1983 when an important NATO-NSF-ARO Advanced Study Institute on Computer-aided Analysis and Optimization of Mechanical System Dynamics was held at the University of Iowa, one may notice that less than 10 years ago the state of the art was almost completely restricted to rigid body systems, and that the discipline of multibody dynamics had almost no interaction yet with finite element methodology.This special issue aims at presenting the state of the art in the field as it appears at the end of 1990.It demonstrates that both recursive and absolute methods still have their proponents, and that both have evolved slowly, in response to growing engineering needs, toward the more general field of multibody dynamics.The resulting equations are not only highly non-linear in nature, as is already known from the study of rigid systems, but the move from rigid to elastic systems requires one to take into account the high frequency content of the vibration response in the system dynamics.In order to simplify the problem, several papers hereafter propose implementations of the classical mode superposition method in which it is assumed that elastic deformation remains linear when expressed in body co-ordinates.Some of them, however, indicate what are the limitations of the linearized approach to simulate correctly large flexible systems whenever geometrically non-linear effects become important.Much emphasis is placed in this issue on formulation and solution methods.Some of the authors advise the use of symbolic computation to generate faster and more reliable programmes, and the time integration methods applicable to differential-algebraic systems are revisited to take into account the specific nature of flexible systems.Parallel computing is also presented as an alternative to speed up the numerical solution of very large systems.Determination of periodic solutions is recognized as an important topic in the field of mechanism analysis, while the very specific properties of systems with time-varying mass may also be of great importance in some aerospace engineering applications.Interaction with control engineering is also recognized as a topic of primary importance in the fields of robotics, aerospace engineering, and vehicle design.It is the editors' belief that this special issue, by giving the current trends in multibody dynamics and focussing on the challenging problem of flexible systems, will be a document of great value to all the researchers in the field.M. GERADIN 0. FRIBERG