Risers are structures commonly found in the offshore engineering scenario. These structures are responsible, among other functions, for conveying fluid. Risers are subjected to several dynamic phenomena, particularly those related to parametric instability and to internal flow. In this study, parametric instability occurs when the stiffness parameter of the equation of motion explicitly depends on time. In the risers' scenario, such a variation is associated with the normal forces modulation caused by the motions of the floating units on the vertical plane. The focus of this research is to analyze a simplified model of riser composed of two rigid pipes, connected by rotational springs and ejecting fluid from its free end. Parametric instability arises from vertical and harmonic motions applied to the support. Herein, the study of the linearized problem is carried out by means of the Floquet Theory. This approach allowed identifying, in the plane of parameters that govern the problem, stability and instability regions of the trivial solution. In addition to this linear analysis, maps showing the post-critical response as a function of some control parameters are obtained using the non-linear mathematical model. Among other findings, the present dissertation shows that the presence of internal flow significantly affects the stability of the trivial solution. Furthermore, the concomitant parametric excitation and internal flow effects led to maps of post-critical response with a marked erosion.