Abstract :
[en] This paper presents a framework, called EasyDyn, developed for the simulation of dynamics problems and in particular, multibody systems. The system is not classically defined from a data file but from a C++ file where the user must program the kinematics and the expression of applied forces acting on each body. By kinematics, we mean the expression of position, velocity and acceleration of each body in terms of generalized coordinates. From the kinematics and the efforts, EasyDyn automatically builds and integrates the equations of motion, according to methods described in the paper. To help the user in his task, the library provides on one hand object-oriented classes for vector algebra (vectors, rotation and inertia tensors, homogeneous transformation matrices) so that vector expressions can be written as is in the C++ code without having to manage the coordinates. On the other hand, a MuPAD script is distributed with the library to automatically generate a core C++ program from a minimal information. In particular, the script uses the symbolic features of MuPAD to derive the expressions of velocities and accelerations from only the position information. The user just needs to add the contribution of the efforts in the C++ initial code, which is made easier by the vector library and the availability of some basic routines. The library and all the tools it relies on are available for free on the internet and can be used either under Windows or Unix. It was not designed as a replacement of commercial softwares. The latter are developed for the purpose of efficiency and productivity for high-end applications. On the contrary, EasyDyn has been written so as to get the maximum compacity, readability, and scalability of the code, often to the detriment of efficiency. It is particularly well-suited for teaching and, as it is open source, offers a foundation for collaborative or research work.
