Understanding wave effects on the hydrodynamic characteristics of knotless nylon netting and flow field analysis around netting

Abstract

Knotless nylon (PA) netting has been extensively employed in aquaculture cages, fishing gears and trash-blocking nettings, with its hydrodynamic characteristics playing a vital role in both operational efficiency and structural performance. This study investigated the hydrodynamic characteristics of knotless nylon (PA) netting under different wave cases through a series of flume experiments. Particle Image Velocimetry (PIV) technology was employed to analyze the flow field around the netting, further elucidating the mechanisms behind its hydrodynamic performance. The results show that: (1) wave period, wave height, and solidity ratio are positively correlated with the horizontal wave force on the nettings. Inertial forces cannot be neglected and increases with the increase in period and amplitude; (2) the drag coefficients for the four nettings range from 1.169 to 2.625, while the inertial coefficients range from 1.642 to 23.845. The drag coefficient decreases with increasing Re and KC, whereas the inertial coefficient shows no consistent variation trend; (3) PIV-measured velocities have an average absolute error of 4.855 % compared to theoretical values. The velocity exhibits a cosine-like trend, consistent with the variation pattern of horizontal wave forces; (4) higher wave heights and periods increase water particle velocities and the amplitude of velocity variations across phases. This study serves as a foundational reference for optimal design of efficient aquaculture cages and trash-blocking nettings, fostering enhanced the performance of marine structures.