Design Optimization of a Semi-Active Flapping Foil in an Energy Extraction Mode

The application of bio-inspired flapping foils as energy harvesters has been studied in detail during the past decade. However analytical, numerical and experimental studies have primarily focused on investigation of basic underlying physical principles as well as performance enhancement of flow-induced flapping foil energy harvesters especially those related to fully active systems. In this paper, performance analysis of a semi-active flapping foil system has been carried out, where pitch mode is activated while useful energy is extracted through an idealized damper via flow-induced oscillating foil energy harvesters. Governing equation of motion is modeled through a spring-damper system while modeling of hydrodynamic forces and moments is achieved through a Theodorsen's 2D thin plate model. Parametric analysis has exhibited a strong dependence on various factors including kinematic (pitch and heave amplitudes), geometric (pivot location) and structural (damping and stiffness) parameters. All these parameters are optimized to achieve an enhanced performance, where efficiencies of approximately 23% have been achieved at specific parametric range. Analysis shows that due to strong fluid-structure interaction, flapping foils are capable of being deployed as potential energy harvesters whose capacity can be enhanced through regulation of various flow and structural parameters.