To optimize the design of their windturbines, manufacturers make use of simulation tools to predict the loads that the different components need to transmit along the drivetrain from the blades to the generator. Using detailed 3D Multibody simulation allows for in-depth studies, capturing the dynamic behavior of the overall system. Multi-body simulation is used to assess the structural reliability of components such as the gearbox and to make sure they resist the extreme and unpredictable loads from the wind for a reasonable lifetime. LMS Virtual.Lab provides state-of-the art methods to model gearboxes and the meshing of gears with varying stiffness. It also provides capabilities to model the rotorblade as well as the generator. The complete system is built from the subsystems assembled in a versatile and modular way. Using LMS Virtual.Lab Motion, a dynamic simulation is finally performed to visualize the behavior of the system trough graphs and animations. The integrated simulation capabilities within LMS Virtual.Lab environment also offer an efficient solution to analyze and optimize the durability performance, noise emissions and overall yield of wind turbines. Accurate loads are easily generated with LMS Virtual.Lab Motion thanks to state-of-the-art contact formulations suited for system level analysis. Those loads lead the engineers to evaluate the stresses occurring in each component and the vibrations generated in the structure. The environment enables to quickly analyze the effect of design changes on a specific performance attribute, which allows engineering teams to perform fast optimization loops from the early development stages onwards.