基于模型试验的罩网沉降性能研究OA

Previous studies on the performance of falling nets have mainly relied on at-sea measurement.To further investigate the factors influencing the sinking performance of falling nets and to clarify their shape variations during the sinking process,model-scale falling-net experiments were conducted.Based on the Tauti criterion,a falling-net model was fabricated,and flume-tank experiments were conducted to analyze the effects of shooting duration(T),hauling speed(Vh),current speed(Vc),and weight(W)on sinking performance,with parameter levels set as follows:T(1 s,2 s),Vh(0.245 m/s,0.348 m/s,0.467 m/s),Vc(0 m/s,0.2 m/s,0.4 m/s),and W(0.705 kg,0.775 kg,0.845 kg).The results showed that:(1)during the sinking process,the falling-net exhibited a bell-shaped configuration.After hauling commenced,the net-mouth rope initially retracted,hindering the sinking of the upstream netting and causing the falling-net to assume on a long-skirt shape.When the net mouth was fully closed,the internal space of the falling-net exhibited a waist drum shape,with a larger upper section and a smaller lower section.(2)The falling-net moved in the direction of water flow,and the upstream netting became more vertical than the downstream netting under hydrodynamic forcing.(3)As T increased,the maximum sinking depth(D)exhibited an increasing trend,with mean values of 1.321 m and 1.590 m,respectively.As Vh increased,D exhibited a decreasing trend,with mean values of 1.611 m,1.430 m,and 1.325 m,respectively.As Vc increased,D showed a decreasing trend,with mean values of 1.622 m,1.482 m,and 1.263 m,respectively.As W increased,D exhibited an increasing trend,with mean values of 1.711 m,1.740 m,and 1.770 m,respectively.(4)The sinking speed varied irregularly within approximately 1 s after the falling net entered the water.Subsequently,the sinking speed decreased with increasing sinking time,although minor fluctuations were observed.(5)The average sinking speed decreased with increasing T(mean values of 0.345 m/s and 0.340 m/s),increased with increasing W(mean values of 0.345 m/s,0.356 m/s and 0.366 m/s),and exhibited no consistent pattern in response to variations in hauling speed or current speed.The study suggests that(1)during falling-net operations,excessively high hauling speed should be avoided,as they not only hinder sinking but also increase the higher risk of hooking due to elevated friction between the net mouth rope and the ring,thereby impeding the net mouth.(2)The sinking process of falling nets appears to be strongly influenced by ambient currents.Higher current speeds resulted in greater horizontal displacement of the falling-net,and the net mouth rope would become tight earlier,hindering the sinking of the falling net causing the net-mouth rope to become taut earlier and thereby restricting further sinking.(3)The weight of the falling net used in this test was already within a reasonable operational range.Further increasing the weight did not substantially improve sinking performance and could adversely affect operational safety.This study provides a practical reference for improving fishing-net fishing efficiency and optimizing fishing-gear design.