Adaptive-passive control of flow-induced vibrations of a sphere

While active methods have proven effective for controlling flow-induced vibrations (FIV) of a sphere, they require power input, and often present major implementation challenges. In contrast, passive flow control methods are easily implemented, do not require power input, and are more suitable for practical applications. However, despite their immense potential, the utilization of passive methods for controlling the FIV of spheres has remained largely unexplored. In this study, a series of systematic experiments were performed to study the effect of a simple passive device of a trip wire on the FIV of a sphere for a wide range of Reynolds numbers of ~ 5000-30000. It was found that a strategically placed trip wire can effectively control (suppress or enhance) the sphere vibrations. However, the optimal size of the trip wire varies with the reduced velocity. To achieve optimal control over a wide range of reduced velocities (Mode I to Mode III of sphere vibrations), we propose an adaptive-passive mechanism involving a trip wire attached to a spring that adjusts its size based on flow velocity without using power. This approach could potentially be applied to optimize energy output in renewable energy harvesting systems based on FIV or reduce maintenance costs for offshore structures.