Determination of hydrodynamic coefficients of the floating cage collar with forced oscillation experiments

The hydrodynamic coefficients of the full scaled segment of an offshore fish cage collar are obtained experimentally and verified by numerical modeling. The oscillation experiments are conducted under the attack angle of 90° in a custom-developed flume so that the range of Keulegan-Carpenter (KC) number is from 5 to 25. For numerical modeling, this paper utilizes an overset mesh technique to solve the Reynolds-averaged Navier-Stokes equation (RANS) in the moving mesh region. The free surface and the turbulence are described by Volume of Fluid (VOF) method and Shear-Stress Transport (SST) k−ω turbulence model respectively. The results show that for the single-pipe model of the floating collar in oscillating flow, the drag coefficient decreases with the KC number increasing, reaching approximately 0.5. With the increasing of the KC number, the inertia coefficient reaches approximately 1.5 for the considered range of KC and Reynolds (Re) numbers. For the double-pipe specimen of the floating collars, the hydrodynamic coefficient for the upstream pipe is almost identical to that of the single-pipe model. For the downstream pipe, the hydrodynamic coefficient increases as the distance between the pipes increases. The paper provides the empirical formulae for hydrodynamic coefficients as functions of KC number.