| The stick-held net originated from the Chiba and Kanagawa areas in Japan,It is one of the main ways of saury fishing,and the fishing operations divided into three processes: delivering net,luring net,hauling net.The principle of the stick-held net is,setting the netting gear in the operating area,and useing the fish lamp to trap the saury to the side of ship,and then the fishing vessel will be twisted through the deck and the side of the drum.Surrounded the fish and forced the saury to fish section,to prevent the saury fleet escape,to achieve fishing purposes.The saury is a large-scale migratory fish,swimming fast,quick action,fishing environment,complex sea currents in the process of the network,often because of the depth of settlement in the middle of the net is not enough to reduce the space Volume,as well as the outline of the upgrade speed is too small,so that the network can not be promoted soon in place led to the fish from the gap to escape,so the stability of the network performance and enhance the performance of the performance of the mainline part of the performance,It is also important to have rope tension performance.The hydrodynamic characteristics of the mesh are the key factors in determining the mechanical properties of the net.It is also necessary to study the influencing factors of the shape change under the flow of the net.Therefore,according to the data of model test,field measurement and numerical simulation,the following aspects were studied on the stick-held net :(1)Factors influencing the rope tension of saury stick-held lift nets;(2)Sinking and rising performance of Saury Stick-held based on field measurements;(3)Evaluation of saury stick-held net performance between from model test and sea trials;(4)Study on the influencing factors of the dynamic shape of the net under the water flow by numerical simulation.The results showed that:(1)The model stick-held net was made following the Tautis modeling law with ?=15:1 and ?'=3:1.The same hanging ratio between the model net and prototype is kept.The main dimensions of the model stick-held net were: float line length 2.6 m,lead line length 2.6m,side line length 2.8m,basic weight of the lead line 0.353kg/m,buoyancy of the float line 28.46 N,We evaluated the influence of haul speed and leadline weight on net tension in Cololabis saira stick-held lift nets.Tests were carried out in a water tank using a scale model net in November–December,2014.The tension on the siderope and leadline of the model net increased with haul time.The tension approached a maximum near the end of the haul.The tension on the model net siderope and leadline increased as the hauling speed increased and the rate of increase in net speed accelerated as the hauling speed increased.The hauling speed at 0.36–0.60 m/s had a significant effect on rope tension(P<0.05),while at hauling speed of 0.12–0.36 m/s,the change in rope tension was stable.The tension in the model net sideline and the leadline increased when the lead-line weight increased,though there was no effect on rope tension;The maximum sideline tension and the maximum leadline tension increased as the hauling speed increased.The hauling time is decreasing with the increase of the hauling speed of the sideline and the leadline.The influence of the lead-line weight on the maximum sideline tension and the maximum leadline tension is different,which has a significant effect on the maximum leadline tension.The increase in lead-line weight has no significant effect on the hauling time.(2)Based on the data collected by saury stick-held operating in the Northwest Pacific from July to October in 2015 and from June to October,We analyzed the sinking depth and the rising depth of netting,sinking speed,rising speed of different parts of saury stick-held at various sinking and rising stages of the net.Results showed that: the sinking depth of netting increases along with the time in gradually increasing trend,the sinking speed of leadline and sideline increased rapidly at first,then declined gradually along with the time,the sinking speed of netting fluctuated considerably with no regular changes;The rising speeds of leadline and sideline declined gradually with increasing time,the highest rising speed of leadline is faster than the sideline,the rising speed of netting fluctuated considerably.The analysis of stepwise GAM showed that three factors had significant impacts on the sinking depth(P< 0.05),in which the significance faded V30,L1 and V60;two factors had a significant impact on the rasing speed(P< 0.05)and the significance can be ordered by V0,V30.(3)The result of Bootstrap showed that: the average sinking depth of standardized full-scale stick-held net is 20.37~29.54 m,95% confidence interval is 21.76~28.13 m.The average sinking depth of model net is 26.42~37.58 m,95% confidence interval is 27.70 ~ 36.20 m.The average sinking depth of full-scale stick-held net is 73.1%~78.27% of the average sinking depth of model net.The average rasing speed of standardized full-scale stick-held net is 0.107~0.193m/s,95% confidence interval is 0.111~0.191m/s,The average rasing speed of model net is 0.204~0.316m/s,95% confidence interval is 0.207~0.312m/s.The average rasing speed of full-scale stick-held net is 59.14%~61.07% of the average rasing speed of model net.(4)Based on the lumped mass method,The Runge-Kutta-Verner fifth-order and sixth-order method is used to solve these simultaneous equations.The numerical simulation of the single-layer mesh is carried out by MATLAB.The results show that: The longer the flow time,the greater the degree of deformation of the netting.The maximum displacement of the netting increases with the flow time,the relationship can be expressed by the formula y = 3.529 t + 0.0005(R2=0.9976)The degree of deformation and the maximum displacement of the netting are gradually decreasing with the increase of the twine diameters.The relationship between the twine diameters and the maximum displacement of the netting is y=0.0002d-1.202(R2=0.9949).The relationship between the multiple of hydrodynamic coefficients and the maximum displacement is y= 0.1715x-0.554(R2=0.9864).The numerical simulation shows that the numerical model established in this study has good stability and convergence of solution,which can lay a good theoretical foundation for the simulation of the next step under the combination of wave and flow. |
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