Forced motion experiments using cylinders with helical strakes

The hydrodynamic coefficients for straked cylinders were obtained from a set of forced motion experiments with a constant towing speed. Based on results from previous studies, two helical strake configurations were tested. The amplitude and frequency ratios of the in-line (IL) and cross-flow (CF) oscillations were fixed. This gave three free parameters of forced motion: CF oscillation amplitude, CF oscillation frequency, and phase angle between IL and CF oscillations. The hydrodynamic coefficients obtained for the straked cylinders were compared with results from forced oscillation tests using a bare cylinder. Clear differences between the designs were demonstrated. The hydrodynamic coefficients obtained from this study can be used in empirical models to predict vortex-induced vibration for structures with strakes.