The influence of wing deformation on animal propulsion and movement has sparked a significant interest in biomimetics across academic and industrial fields. This research addresses these dynamics by developing an advanced numerical tool for analyzing biological motion in fluid environments, crucial for understanding fluid-structure interaction (FSI) phenomena and designing hydro-elastic energy harvesters. We developed a flexible framework integrating advanced numerical tools for FSI analysis. Using a mesh motion tool based on a modified overset technique, the method combines the OpenFOAM fluid solver and the CalculiX structural solver, creating a comprehensive framework for capturing intricate fluid-solid interactions. In [1], we developed and validated an enhanced mesh motion library, oversetZoneFvMesh, based on OpenFOAM’s default overset technique, with its methodology and performance benchmarked on cases involving both mesh motion and deformation. Building on this foundation, we developed a coupled solver that integrates OpenFOAM and CalculiX via the open-source library preCICE, enabling robust fluid-structure interaction simulations, as detailed in our work in [2]. The solver was validated through propulsion generation scenarios, including a rigid heaving foil case study, with results compared to established literature [3], and by solving the Turek-Hron benchmark problem, demonstrating excellent agreement with published results [4]. The extended FSI-6DOF solver was further validated through analytical solutions and a fully passive flapping foil problem [5]. Finally, the solver was applied to both active-passive and passive-passive flexible foils, incorporating active heaving and passive deformation, as well as passive flapping motion. The results demonstrated the significant role of flexibility in improving energy harvesting efficiency, whether through active or passive foil motion.