Hydrodynamic Coefficients of Netting in Relation to Different Materials and Twine Thickness

Abstract

In this study the hydrodynamic coefficients were measured by various nettings to analyse the change of drag coefficient and the lift coefficient. The data on hydrodynamic forces was obtained from the flume tank tests. The drag and lift coefficients were measured using 9 kinds of nettings which had the same total projected area but different twine thickness sizes (0.9, 2.5, 3.5 mm) and different materials (Copper, Polyamide and Polyethylene). The different netting systems were subject to various attack angles (0-90o) in the interval of 10o, and flow speeds of (0.3-0.6 m/s) in the interval of 0.1m/s. The results of hydrodynamic coefficient of netting tests were as follows: The drag coefficient increased as the angle of attack increased but as the twine thickness increased the drag coefficient decreased. The lift coefficient increased as the attack of angle increased until 40-50° but began to decrease after 50°. The netting with Copper material showed lower drag coefficient than Polyamide (PA) and Polyethylene (PE). The PA and PE showed similar behaviour. The netting with 3.5 mm twine thickness showed lower drag coefficient than the 2.5 and 0.9 mm diameter of twine. The drag coefficient was higher in the 0.9 mm twine thickness than 2.5 and 3.5 mm twine thickness. There was no significant difference in the lift coefficient among the different twine thicknesses, but among different materials, copper netting showed slightly lower lift coefficient than other materials. In consideration of Reynolds number, as the Reynolds number increased, the drag coefficient of netting by attack of angle tended to decrease.