The paper focuses on the study of a semiactivated system, based on a combination of a two movements of forced pitching and free heaving motion. Therefore, quantifying with accuracy the hydrodynamic forces applied on the hydrofoil seems to be crucial. This is investigated throughout a numerical modeling of a 2D f lexible hydrofoil dynamics, immersed in a fluid flow with a Reynolds number of 2000. In this study, the hydrofoil is animated by a combined forced pitching and heaving movements. Various materials of the structure are studied, from the rigid material to a more flexible one. The Fluid-Structure Interaction (FSI) effects are considered using a partitioned implicit coupling scheme. The Arbitrary Lagrangian-Eulerian (ALE) formulation of the NavierStokes equations is applied. Both the viscous incompressible Navier-Stokes equations and the elasticity equation are solved using finite volume method. The study is based on the analysis of the hydrodynamic loads acting on the structure. Therefore, the induced dynamics and the power coefficient of the structure are investigated. It is shown that the flexibility of the hydrofoil has an effect on its hydrodynamic behaviour and that in some configurations, the structure deformations can improve the device energy efficiency.