On the application of current blockage model to steady drag force on fish net

Abstract

This paper introduces a hydrodynamic model to characterise steady drag force on fish net. The proposed method is based on the current blockage model commonly used in offshore engineering, which is capable of accounting for fluid flow reduction due to the presence of fish net acting as an obstacle array. Based on available measurements reported in the literature, the proposed method is applied and compared against the measurements. This paper demonstrates that the proposed method is able to produce respectable agreements both in terms of drag force as well as velocity reduction factor for a wide range of Reynolds numbers (Re), solidity ratios (Sn) and inflow angles (defined as the angle between the flow direction and the normal vector of the net panel). In particular, for forces acting on a rectangular fish panel with 0∘ inflow angle, the proposed method shows that the fitted drag coefficients (Cd) are independent of Re ranging from 35 to 5000, and that Cd can be grouped into three flow regimes depending on Sn ranging from 0.12 to 0.32. The proposed method provides a different perspective in the modelling and may contribute to a more accurate prediction of hydrodynamic loads on fish net in steady flow.