| Light cover is mainly be used about fishing the fishery resources in South China sea,as part of falling-net,the main target including phototaxis fish and cephalopods,the representative population is Oualaniensis,tuna,round scad and mackerel.But there is little Chinese research report about falling-net,and the research report appeared in nearly a year.Because it is illegal to do light trap in foreign,so there is no related research report is found.This study based on the data of the sinking speed and ocean environmental data collected on the light falling-net used by 320 k W fishing fleet.To study the features of the falling-net in South China Sea,TDR is used to study the sinking performance under different conditions.CTD and current meter are used to record the ocean environmental data,then study the sinking characteristics of light falling-net.While computer software is used to built the mathematical model of resistance of light falling-net.(1)Analyzes and summarizes the parameters of the 320 k W fishing vessel and the information of the light falling-net.The vessel is transformed from lighting purse vessel,the length is 32.8m,the breath is 6.2m,the height from water to vessel is0.57 m,arm length is 26 m,the host power is 320 k W,the auxiliary power is 250 k W.The main scale of light falling-net is 280×80m which mains the length of the net port is280 m,the straightened length is 80 m.(2)CTD and current meter are used to record the ocean environmental data.The results show that the range of the wind speed of fishing ground is 0—8m/s,the average speed is 2.5m/s.The wind speed is mainly 1.0—3.0m/s which accounting for 57% of the total.Current case shows that the range of the current speed in the x direction is-0.102— 0.321m/s,the average speed is 0.094m/s.The range of the current speed in the y direction is-0.1987—0.064m/s,the average speed is-0.005m/s.(3)TDR1 and TDR2 are used to analysis the sinking speed and the sinking depth oflight falling-net.The results show that the max sinking depth of TDR1 is 86 m,the max sinking depth of TDR2 is 85 m.The range of the sinking depth of TDR1 is76 m —86m,The range of the sinking depth of TDR2 is73m—85m.The sinking trends of the light falling-net is that TDR1 and TDR2 were horizontal at begin,then TDR2 was higher than TDR1 at mid-term which shows the trends that the right side was higher than the left side.The range of the sinking speed of TDR1 is 0.15—0.55m/s,the average speed is0.35m/s.The range of the sinking speed of TDR2 is 0.17—0.64m/s,the average speed is0.34m/s.The difference range of sinking speed of TDR1 and TDR2 is 0.01—0.13m/s,the average difference is 0.06m/s.The sinking speed of TDR2 is faster than TDR1 at first40 s when the falling-net is dropping,the sinking speed of TDR1 is faster than TDR2 between 40s — 120 s,the sinking speed of TDR1 did not change significantly after120 s,while the sinking speed of TDR2 began faster between 120s—200s.(4)Polynomial regression is used to analysis the the relationship between sinking depth(sinking speed) and time.the relation between the sinking depth and the time could be described using the formula:H=3.84+0.57t-0.001t2(R2=0.9963);and the relationship between the sinking speed and time could be described using the formulas:V=7.9×10-1- 6.26×10-3t+1.544×10-5t2(R2=0.9599).(5)Relative weighting showed that the relative importance of predictor variables,the result is the current speed of 60 m in x direction by 33.32%,the current speed of 60 m in y direction by 2.85%,the current speed of 60 m in z direction by44.65%,the wind speed by 0.76%, the max falling depth by 10.8%,catch by 7.54%.The regular succession of relative weighting of predictor is showed as follows:the current speed of 60 m in z direction,the current speed of 60 m in x direction,the current speed of60 m in y direction,the max falling depth,catch and wind speed.(6)Subset regression is used to select the predictor variables to built the best model.Predictor variables include the current speed of 60 m in z direction,the current speed of 60 m in x direction,the max falling depth and catch.the results of the GLM model showed that the current speed of 60 m in z direction had effect on sinking speed(P<0.01),the current speed of 60 m in x direction had some effect on sinking speed(P=0.01),sinking depth and catch had no significant effect on the sinking speed(P>0.1)(7)The mathematical model is built to calculate the resistance of lightfalling-net,the mathematical model is validated by the data collected from sea.Results show that errors were less than 20% in 10 times allocations in addition to the two major mistakes.Linear trend of resistance of light falling-net was similar to the net weight in sea,which is same as the actual situation.(8)Through the study of the sinking depth,sinking speed and mathematical model,light falling-net can be improved by following improvements. Aspects of material,PA material can be used to make the bag of light falling-net.Aspects of mesh size,mesh size can be increase to 30—40mm.Aspects of sinker,ball sinker can be used to instead of the original cylindrical sinker. |
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