# Regular Wave Effects on the Hydrodynamic Performance of Fine-Mesh Nettings in Sampling Nets
## 4 Discussion  
The hydrodynamic performance of fine-mesh netting under various linear wave conditions was investigated through a combination of wave tank experiments and numerical simulations. In the wave environment, the horizontal force acting on the netting was significantly greater than the vertical force, consistent with previous studies suggesting that vertical forces may be neglected [24; 28; 29]. Therefore, only the horizontal forces exerted on the fine-mesh netting were considered in this study. The overall trend of the experimental data for horizontal force was found to be in good agreement with the simulation results (See Figure 6). Small discrepancies in the peak values and phase of the wave force can be attributed to the fact that the netting was fixed with bridle lines during the wave tank experiments. This setup allowed for slight oscillations of the netting under wave actions, which were not accounted for in the numerical simulations. In this study, the drag coefficient of both fine-mesh nettings generally decreased with an increasing Reynolds number and _KC_ number, which is consistent with findings from previous studies [26; 28; 29; 32]. However, the variation of the inertia coefficient contrasts with previous studies. In our results, the inertia coefficient decreased as both the Reynolds number and _KC_ number increased (see Figure 8). [PERSON] et al. reported a slight decrease in the inertia coefficient with an increasing Reynolds number and _KC_ number, but the trend was less pronounced [26]. Similarly, [PERSON] et al. found no clear relationship between the inertia coefficient and either the Reynolds number or _KC_ number when studying biofouled netting [28]. Conversely, [PERSON] et al. observed an increase in the inertia coefficient with rising _KC_ numbers [29]. These discrepancies may be attributed to differences in the netting materials and solidity ratios. In contrast to previous studies that used standard mesh-sized netting, the netting in this study had varying solidity ratios, which could affect the inertia coefficient. Additionally, the inertia coefficient was found to be much smaller than the drag coefficient, consistent with the findings of [PERSON] et al. [25]. This disparity is likely due to the relatively small twine diameter compared to the wave height, rendering drag the dominant force in wave-netting interactions and diminishing the contribution of inertial effects. Notably, the drag coefficient for Net 1 was higher than that for Net 2 (see Figure 7), consistent  
Figure 14: Water particle velocity field distribution of the Net 2. Wave condition: \(T=0.13\,\mathrm{s},H=0.19\) m; (**a**–**d**): \(T/4\), \(T/2\), \(3T/4\), and \(T\), respectively. (I)–(III): Global view of the numerical tank, local view around the netting in numerical simulation, and PIV measured around the netting, respectively. with previous observations that associate higher drag coefficients with increased solidity ratios [29]. In this study, the hydrodynamic coefficients were validated under regular wave conditions. However, in the more complex conditions of open-sea environments, the nonlinear wave-structure interactions, flow unsteadiness, and dynamic deformation of the netting may lead to deviations from the simplified flow assumptions underlying the porous media approach [31; 37; 39]. These factors can alter the effective resistance experienced by the netting. Therefore, further research incorporating irregular wave conditions and fully coupled fluid-structure interaction models is recommended to enhance the applicability of the present hydrodynamic coefficients to realistic ocean environments. Wave attenuation through fine-mesh netting was investigated using a numerical model that combines the porous media model with a numerical wave tank. The results demonstrate a significant damping effect of fine-mesh netting on wave propagation (see Figures 9 and 10).