Abstract
Railway ballast tamping is a process through which geometrical defects of railways are corrected by moving the sleepers to their correct positions and inserting vibrating tamping tines into the ballast bed. The tines compacts the ballast underneath the sleeper, thus ensuring proper load transfer between the sleeper and the subballast. This thesis presents a DEM-MBD co-simulation framework to model the tamping procedure, and explores the differences between a conventional tamping machine, where the vibrations are generated through an eccentric shaft, and a novel fully hydraulic tamping machine, where the vibrations are generated through hydraulics. The ballast bed is modeled through the Discrete Element Method (DEM) solver Demify®, developed in-house at FCC, and the tamping machine is modelled through a Multibody Dynamic (MBD) package called Simscape Multibody found in Simulink. Furthermore, a parameter study of different tamping design parameters is performed. The fully hydraulic tamping model is validated against real-world data, showing that the model lies within the expected distribution of real-world tamping operations. The results of the simulations shows that the fully hydraulic tamping model is able to compact the ballast bed to a higher degree while maintaining lower forces acting upon the ballast particles as compared to the conventional tamping model. The parameter study reveals that the vibrational amplitude significantly affects the results of the tamping process, both for the conventional and for the fully hydraulic tamping model. Different vibrational frequencies affect the fully hydraulic tamping model significantly, while it only has some minor effects for the conventional tamping model.