The purpose of this master's thesis project is to develop a Fluid-Structure Interaction model to examine how the flexibility of anti-sloshing devices influences the dynamics of propellant in Vega-E cryogenic tanks. The parameter used for the comparison between the rigid and the flexible cases is the damping coefficient of the forces acting on the tank walls. The analyses are conducted on a shelf-shaped anti-sloshing device inside a parallelepiped shaped tank. The sloshing condition is simulated by imposing a lateral forcing on the tank for a specified time interval. Initially, to establish a baseline understanding of fluid dynamics within the tank, two CFD analyses are compared: one without any baffle and another with an anti-sloshing device assumed to be infinitely rigid.