  Multibody dynamics simulations are currently widely accepted as valuable
means for dynamic performance analysis of mechanical systems. The evolution of
theoretical and computational aspects of the multibody dynamics discipline make
it conducive these days for other types of applications, in addition to pure
simulations. One very important such application is design optimization. A very
important first step towards design optimization is sensitivity analysis of
multibody system dynamics. Dynamic sensitivities are often calculated by means
of finite differences. Depending of the number of parameters involved, this
procedure can be computationally expensive. Moreover, in many cases, the
results suffer from low accuracy when real perturbations are used. The main
contribution to the state-of-the-art brought by this study is the development
of the adjoint sensitivity approach of multibody systems in the context of the
penalty formulation. The theory developed is demonstrated on one academic case
study, a five-bar mechanism, and on one real-life system, a 14-DOF vehicle
model. The five-bar mechanism is used to illustrate the sensitivity approach
derived in this paper. The full vehicle model is used to demonstrate the
capability of the new approach developed to perform sensitivity analysis and
gradient-based optimization for large and complex multibody systems with
respect to multiple design parameters.
