Drag Force on Cylinders Oscillating at Small Amplitude: A New Model

A new semi-empirical model is derived for calculations of hydrodynamic damping (or drag) forces on smooth or rough cylinders oscillating at small amplitude and high frequency. This model covers the attached flow regime where the conventional Morison’s equation fails to simulate the drag forces acting on circular cylinders. It involves the calculation of the energy dissipated in the boundary layer on the cylinder surface. The empirical input data for the model are amplitude and phase of the wall shear stresses on the cylinder. The model is verified against fluid force measurements from a test tank and published data. These experiments were carried out at small-amplitude / high-frequency with smooth and rough circular cylinders. Data from the literature is also included for verification. Results from the present work can be used to estimate hydrodynamic damping forces for the analysis of jack-up response around resonant frequency. Other applications are dynamic behavior of jackets during installation, SALMs, TLPs and risers.