In many cases, when we want to study the dynamic behavior of complex mechanical systems that are subjected to large displacements and rotations, the resulting equation of motion is nonlinear. Therefore, the mathematical model is too complex to provide an analytical solution. Nowadays the dynamic of complex systems it is usually studied with multi-body codes through numerical integration of the equations. High-performance mechanical system requires a compromise between efficiency and effectiveness. The mathematical model as well as the parameters of the model are contaminated with uncertainties, therefore to improve the predictability of the model uncertainties must be take into account. The aim of the project is to show through an industrial application, how to take into account all the possible source of uncertainties that may arise in a multi-body (MB) system and a flexible MB system, in order to increase the robustness of the numerical model.