This study applies the mass-spring system to model the dynamic behavior of a submerged net panel similar to the shooting process in actual purse seine fishing operation. Modeling indicates that there is insufficient s...This study applies the mass-spring system to model the dynamic behavior of a submerged net panel similar to the shooting process in actual purse seine fishing operation. Modeling indicates that there is insufficient stretching with the net panel under the floatline in the prophase of the shooting process. Sinkers at different locations along the leadline descend successively after submergence, and the sinking speed decreases gradually with elapsed time until attainment of a stable state. Designs with different current speeds and sinker weights are executed to determine the dimensional shape and sinking characteristics of the net. The net rigged with greater sinker weight gains significantly greater sinking depth without water flow. Compared with the vertical spread of the net wall in static water, the middle part of the netting presents a larger displacement along the direction of current under flow condition. It follows that considerable deformation of the netting occurs with higher current speed as the sinkers affected by hydrodynamic force drift in the direction of current. The numerical model is verified by a comparison between simulated results and sea measurements. The calculated values generally coincide with the observed ones, with the former being slightly higher than the latter. This study provides an implicit algorithm which saves computational loads for enormous systems such as purse seines, and ensures the accuracy and stability of numerical solutions in a repetitious iteration process.展开更多
A constant-depth ichthyoplankton sampler is vital equipment for monitoring fish recruitment and assessing fishery stocks.Its depressor,a critical component,maintains towing stability during sampling by balancing the s...A constant-depth ichthyoplankton sampler is vital equipment for monitoring fish recruitment and assessing fishery stocks.Its depressor,a critical component,maintains towing stability during sampling by balancing the sinking force of the depressor and the drag force of the sampler.Conventional depressors often fail to maintain this equilibrium due to their limited sinking force.This study proposes a biplane depressor,inspired by the aerodynamics of biplane hyper-lift trawl doors.In the hydrodynamic experiment,the maximum sinking force coefficient for the proposed biplane depressor with a stagger angle of 30◦reached 2.02,which was significantly higher than that for conventional depressors(less than 1.60).Moreover,substituting metal with canvas for 40%of the wing area reduced the weight without compromising sinking performance(maximum sinking force coefficient:1.86).A towing experiment demonstrated a consistent sinking force and towing stability for the depressor with and without canvas.Operating angles of attack of 27°and 23°are recommended for the depressor made of all metal and a combination of metal and canvas,respectively.The results indicate the potential of the proposed biplane depressor to replace conventional depressors to enhance the constant-depth performance of the sampler and ensure reliable sample collection for ichthyoplankton surveys.展开更多
基金financially supported by the National High Technology Research and Development Program of China (No. 2012AA092302)the Specialized Research Fund for the Doctoral Program of Higher Education (No. 20103104120006)the Project of First-class Disciplines Shanghai Universities: Eco-Friendly Fishing Gear and Fishing Methods in the Field of Fisheries Science (B-5005-12-0001-4C)
文摘This study applies the mass-spring system to model the dynamic behavior of a submerged net panel similar to the shooting process in actual purse seine fishing operation. Modeling indicates that there is insufficient stretching with the net panel under the floatline in the prophase of the shooting process. Sinkers at different locations along the leadline descend successively after submergence, and the sinking speed decreases gradually with elapsed time until attainment of a stable state. Designs with different current speeds and sinker weights are executed to determine the dimensional shape and sinking characteristics of the net. The net rigged with greater sinker weight gains significantly greater sinking depth without water flow. Compared with the vertical spread of the net wall in static water, the middle part of the netting presents a larger displacement along the direction of current under flow condition. It follows that considerable deformation of the netting occurs with higher current speed as the sinkers affected by hydrodynamic force drift in the direction of current. The numerical model is verified by a comparison between simulated results and sea measurements. The calculated values generally coincide with the observed ones, with the former being slightly higher than the latter. This study provides an implicit algorithm which saves computational loads for enormous systems such as purse seines, and ensures the accuracy and stability of numerical solutions in a repetitious iteration process.
基金financially supported by the National Natural Science Foundation of China under Grant No.32202997the project ZR2022QD010 supported by Shandong Provincial Natural Science Foundation.
文摘A constant-depth ichthyoplankton sampler is vital equipment for monitoring fish recruitment and assessing fishery stocks.Its depressor,a critical component,maintains towing stability during sampling by balancing the sinking force of the depressor and the drag force of the sampler.Conventional depressors often fail to maintain this equilibrium due to their limited sinking force.This study proposes a biplane depressor,inspired by the aerodynamics of biplane hyper-lift trawl doors.In the hydrodynamic experiment,the maximum sinking force coefficient for the proposed biplane depressor with a stagger angle of 30◦reached 2.02,which was significantly higher than that for conventional depressors(less than 1.60).Moreover,substituting metal with canvas for 40%of the wing area reduced the weight without compromising sinking performance(maximum sinking force coefficient:1.86).A towing experiment demonstrated a consistent sinking force and towing stability for the depressor with and without canvas.Operating angles of attack of 27°and 23°are recommended for the depressor made of all metal and a combination of metal and canvas,respectively.The results indicate the potential of the proposed biplane depressor to replace conventional depressors to enhance the constant-depth performance of the sampler and ensure reliable sample collection for ichthyoplankton surveys.
