Hydrodynamic Regimes for an Oscillating Body*

This work experimentally investigates the hydrodynamics of a vertically oscillating body, tested across a range of frequencies and amplitudes and at multiple geometric scales. These bodies are common features of offshore structures, including floating platforms for renewable energy generation, and their hydrodynamics are traditionally described by the Keulegan-Carpenter (KC) number.  In regular waves, KC reduces to a ratio of oscillation amplitude to body diameter. Prior work has shown that added mass and drag coefficients are primarily a function of KC. This work has further explored the effect of non-dimensional frequency, the Roshko number, on the added mass coefficients. These coefficients fall onto one of two planes in a 3D KC-Roshko space, suggesting two, distinct regimes governing the hydrodynamics of an oscillating body. The two regimes are likely dictated by vortex formation and shedding, and a better understanding will improve knowledge of how the hydrodynamics behave across geometric scales. Knowledge of the full scale operating regime will more successfully dictate model tests, allowing for accurate scaling of these results.