Modal and Kineto-elastodynamic Analyses of Flexible-body Mechanisms by Using MD Patran, MD Nastran and MD Adams

When developing new mechanisms or machines, foreseen to run at a high speed, designers should take into consideration the elastodynamic behaviour of their links, by properly modelling and simulating the system. The motion of the links may be influenced so deeply by their flexibility that the mechanism could fail to properly perform its task; moreover, high accelerations and dynamic stress may occur, causing early fatigue failure, and high levels of vibration and noise. Modal and kineto-elastodynamic (KED) analyses of the mechanism models are fundamental tools to predict the system behaviour considering also the effects of the compliance of links and joints. In particular, modal analyses provide the natural frequencies and the vibrational mode shapes of the system, that generally vary with the mechanism configuration; KED analyses provide the driving forces/torques, the reaction forces, the actual motion of a given link… In order to study the Flexible-body Dynamics, a finite element (FEM) approach is often followed. This work offers a procedure to effectively develop the FEM model of flexible links using MD Patran/Nastran in a form suitable to be assembled in MD Adams, where modal and KED analyses of the mechanism are performed. A planar four-bar linkage is taken as reference to illustrate the main steps to be followed, from the link modelling to the mechanism simulation and results extraction. In particular the alternative options offered by the softwares are analysed and discussed, to provide the MSC-Software users with all the information necessary to develop an effective tool for their simulations.