Aquaculture net drag force and added mass scaling

Five plane net samples of different geometry are selected and the hydrodynamic loads on them in quasi-static (steady current) and oscillating flow (harmonic waves) are measured in a towing tank and a wave basin. The data from the experiments is compared with existing empirical formulae and a numerical model. It is revealed that drag coefficients for nets and cylinders as a function of the Reynolds number have identical trends with steady offsets from each other. It is concluded that the drag coefficient for nets is equivalent to the drag coefficient for cylinders (and spheres for knotted nets) modified by a function of net porosity. A two-factorial experimental design was applied to screen individual and interaction effects of net solidity and steady current velocity. This analysis shows that solidity and velocity have a synergetic effect on drag. The drag component and added mass are extracted from the total wave force by applying a vector approach. It is shown that drag and added mass coefficients could not be expressed by conventional non-dimensional parameters. Based on data analysis, unsteady drag coefficient is suggested as a function of wave particle velocity and net porosity. It is recommended to estimate added mass through an effective thickness, the width of water affected by the net, which is a function of wave frequency and net solidity.