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Handling Flexible Bodies in Multibody Dynamics


Multibody Dynamics (MBD) simulation is a niche field of Computer-Aided Engineering (CAE). Despite the relatively low diffusion, its importance is increasing over time as the mechanical systems are progressivley evolving into mechatronic systems. Indeed, the simulation of mechanical systems in time domain helps the engineers in understanding the relationships between actuators, control systems, and final performances. Not only. The knowledge of the behavior in transient conditions is the key to know the internal loads and reach a proper sizing of the parts.

Many analysts perform multi-body-dynamics simulation under the assumption that all bodies are ideally rigid. This is fair in a large number of situations, when the bodies do not undergo significant deformations and the main goal of the simulation is understanding the kinematics. If the combination of inertial loads and bodies compliance induces appreciable deformations in the system, then the rigid multi-body approach return unreliable outputs. In such a circumstance the use of flexible multi-body simulation is mandatory and the consequent modelling choices strongly affect both CPU time and accuracy of results.

For many years, flexible bodies in multi-body simulation have been implemented through modal reduction methods (also known as Component Mode Synthesis, Craig-Bumpton method, Reduced Flexiblity, Linear Flexibility). Behind these methods there is the assumption that real deformations can be described as linear combination of elementary deformations, given by vibration modes and static constraint modes. When applicable, the reduced methods provide excellent results, with limited CPU efforts. However, for a mechanical system either undergoing large deformations or including other non-linearities (moving contacts, non-linear materials) modal reduction methods provide unreliable outputs. In these complex situations, the flexible bodies must be treated as Finite Element entities. A used solution consists of connecting the multi-body solver with a finite element solver, but the resulting efficiency is rather poor and limitations still apply. The best approach therefore is to describe the finite element problem within the multi-body dynamics equations, by making use of relative coordinates and other numerical tricks. Only a few commercial tools adopt the second method and allow for the correct simulation of non-linear flexibility.

This webinar provides a general overview of the topics listed above, drafting the best practices to include flexible bodies in multi-body simulation. Additionally, a real industrial application is presented, to best highlight the effects of wrong modelling choices.

About the presenter

Fabiano Maggio graduated in Mechanical Engineering with honor at University of Padova in 2001 and he got a PhD in Motorcycle Engineering in 2004. In 2005 he joined EnginSoft S.p.A., which is a multinational company operating in the field of Simulation Based Engineering Science (SBES). At EnginSoft Fabiano has been managing a team of engineers fully focused on System Dynamics analysis. Across his career Fabiano has been working on hundreds of projects in any industrial sector, which let him gain a solid expertise in Multi-Body-Dynamics Simulation, Data Analysis, and Finite Element Analysis. In 2015 Fabiano has started collaborating with the Korean company FunctionBay, Inc., which develops and distributes worldwide the RecurDyn software, which is known for its excellent performances in Multi-Body-Simulation of flexible systems. Since 2019 Fabiano is leading the company FunctionBay Italy S.r.l., whose mission is to disseminate the culture of Multi-Body-Simulation and promote the use of RecurDyn within industries located in Europe.


Document Details

AuthorMaggio. F
Date 20th June 2023


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