Model-based design is a widely used methodology for the development of embedded critical software, such as a discrete controller for a continuous plant. In this setting, numerical simulation of both the plant and the controller plays a crucial role, since it is used to validate the design choices in the early stages of development. However, classical numerical simulation has inherent limitations: it is of limited precision and cannot deal with the intrinsic non-determinism present in complex systems. In this article, we present a tool named HySon that overcomes these drawbacks. It takes as input a Simulink model of a control-command system with non-deterministic uncertainties and automatically computes flow-pipes that contain all possible trajectories of the system. We show on some examples how HySon can be used to improve the quality of model-based design.