Rover egress for Martian exploration: multibody analysis with flexible wheels

Mars has always captured humankind imagination. The desire for discovery has led scientists and engineers to develop new technologies to reach the Red Planet in order to understand its geology and its habitability potential. The means by which this desire for exploration becomes reality is to send vehicles to Mars that can explore the planetary surface, take samples of the environment and analyze them. ExoMars 2020 is the mission managed by the European Space Agency (ESA) intended to send a Rover on the martian surface to search for signs of life. The mission will deliver the European ExoMars Rover and the Russian Surface Platform to the surface of Mars with the aim of carrying out scientific research looking for organic molecules and surface characterization. Rover's design is achieved thanks to multibody software, fundamental tools to support engineering activities. Multibody simulation is a numerical simulation method for studying the motion of mechanical systems caused by external forces acting on it. One challenging activity of the Mechanical Design group of Domain Exploration and Science Italy of Thales Alenia Space Italia S.p.A. in Turin, where this thesis has been developed, focuses on the construction of a dynamic model of the six wheeled planetary Rover belonging to ExoMars Mission in order to study the Rover egress from the Surface Platform, evaluating different configurations and scenarios. Moreover, the Mechanical Design group requires to build a flexible model of the Rover's wheels that will give to the whole multibody model, made by rigid bodies, the right physical properties in terms of flexibility. The main objective of this thesis is to develop the multibody model of the ExoMars Rover's wheel using nonlinear finite element (NLFE) bodies, a particular kind of elements present in the multibody code that allows to create flexible bodies. The model is built in MotionView environment, the pre-processor for multibody simulation and simulated through MotionSolve, its solver. These tools guarantee optimal performances when dealing with multibody simulation. As preliminary analysis, it is necessary to find the stiffness curves of this component because the experimental data are not yet available. This is done through static nonlinear analyses, run into FE environment with HyperMesh (pre-processor) and OptiStruct (solver), in order to obtain a relationship between forces and displacements when the point of force application varies. The flexible wheel is then created with a hierarchical structure in the multibody environment and its stiffness is tuned, varying the thickness of the elements of which it is composed, with the average force-displacement curve extrapolated from the various trends obtained from nonlinear static analyses. A simplified version of the Rover is created in order to easily perform some configurations and the results obtained are compared with those obtained with rigid ones. Finally, the advantages and disadvantages deriving from the use of this methodology for the creation of flexible bodies in a multibody environment are presented in order to evaluate their use in more complex systems, such as the real model of the Rover. All the software used in this thesis activity are part of the HyperWorks package of the Altair software house.