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
The Knowledge of turbulent flow developing inside and around the bottom trawl net is of great importance not only for improving the hydrodynamic performance of the gear but also for the selectivity via the fish respon...The Knowledge of turbulent flow developing inside and around the bottom trawl net is of great importance not only for improving the hydrodynamic performance of the gear but also for the selectivity via the fish response,such as the herding response or escape behavior.The 3-D Electromagnetic Current Velocity Meter(ECVM)measurements were performed to investigate the effect of turbulent flow on the bottom trawl net performance and to analyze the turbulence intensity and velocity ratio inside and around different parts of the trawl net.Proper orthogonal decomposition(POD)method was applied in order to extract the phase averaged mean velocity field of turbulent flow from each available ECVM instantaneous velocity.The results demonstrated the existence of turbulence flow,consisting of turbulent boundary layer flow and the turbulence due to the trawl wake developing all inside and around the bottom trawl net.Increasing input streamwise velocity results in faster trawl movement and a significant turbulent flow.The maximum turbulence intensity inside and around trawl wing,square part,first belly,second belly,third belly,cod-end is 0.95%,1.34%,3.40%,4.10%,4.25%and 3.80%,respectively.It was found that the mean velocity field in a turbulent flow inside and around trawl net cod-end recovered on the average was~77.58%of the input streamwise velocity.It is~12.92%,~13.07%,~11.40%,~13.00%and~0.45%less than that inside and around trawl wing,square part,first belly,second belly,and third belly of the bottom trawl net,respectively.The turbulent flow behavior depends strongly on the structure oscillation,input streamwise velocity and,porosity of the net structure.It is necessary to take into account the velocity reduction inside and around a different part of the trawl net to improve the entire drag force determination,cod-end design,and further selectivity control of the fishing gear.展开更多
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.
基金Projects supported by the National Natural Science Foundation of China(Grand No.31902426).vThis work was supported by the Shanghai Sailing Program(Grant No.19YF1419800)the Special project for the exploitation and utilization of Antarctic biological resources of Ministry of Agriculture and Rural Affairs(Grant No.D-8002-18-0097).
文摘The Knowledge of turbulent flow developing inside and around the bottom trawl net is of great importance not only for improving the hydrodynamic performance of the gear but also for the selectivity via the fish response,such as the herding response or escape behavior.The 3-D Electromagnetic Current Velocity Meter(ECVM)measurements were performed to investigate the effect of turbulent flow on the bottom trawl net performance and to analyze the turbulence intensity and velocity ratio inside and around different parts of the trawl net.Proper orthogonal decomposition(POD)method was applied in order to extract the phase averaged mean velocity field of turbulent flow from each available ECVM instantaneous velocity.The results demonstrated the existence of turbulence flow,consisting of turbulent boundary layer flow and the turbulence due to the trawl wake developing all inside and around the bottom trawl net.Increasing input streamwise velocity results in faster trawl movement and a significant turbulent flow.The maximum turbulence intensity inside and around trawl wing,square part,first belly,second belly,third belly,cod-end is 0.95%,1.34%,3.40%,4.10%,4.25%and 3.80%,respectively.It was found that the mean velocity field in a turbulent flow inside and around trawl net cod-end recovered on the average was~77.58%of the input streamwise velocity.It is~12.92%,~13.07%,~11.40%,~13.00%and~0.45%less than that inside and around trawl wing,square part,first belly,second belly,and third belly of the bottom trawl net,respectively.The turbulent flow behavior depends strongly on the structure oscillation,input streamwise velocity and,porosity of the net structure.It is necessary to take into account the velocity reduction inside and around a different part of the trawl net to improve the entire drag force determination,cod-end design,and further selectivity control of the fishing gear.
