Hydrodynamic Performance Analysis And Profile Optimization Of Trawl Door

The trawl door is an indispensable equipment for single vessel fishing operation of ocean trawlers.With the rapid development of Chinese pelagic fishery,the quantity and quality of fishing vessels and equipment is necessary to be improved,but there are few researches on the trawl door in China.In this paper,CFD numerical simulation and response surface methodology are combined to establish a simplified numerical model of trawl door.The efficient method for hydrodynamic performance analysis and profile optimization of trawl door is constructed.In this paper,the mathematical model required for the optimization of the profile of the trawl door is constructed,including the mathematical model of the numerical simulation of the trawl door and the mathematical model of the response surface experimental design.Based on these theories,the considerate analysis process of the trawl door is constructed.Then,the single hydrofoil which is the element of the trawl is constructed.After the effectiveness verification,the influence of different shapes of hydrofoil on the hydrodynamic performance of single hydrofoil is studied.It is found that the hydrodynamic performance of asymmetric hydrofoil is better than that of symmetrical hydrofoil,and the performance of V-shaped hydrofoil is the best.Finally,the asymmetric hydrofoil is selected as the element of the trawl door.Based on the numerical model of single hydrofoil,the simplified numerical model of single-flap trawl door is constructed.The hydrodynamic performance of trawl door is studied by response surface methodology.After verifying the effectiveness of the numerical model,firstly,the corresponding sample test points are selected within the set spatial parameter range,and the response surface is obtained through data processing and fitting to study the hydrodynamic performance and law within the parameter range.It is found that the angle of attack α value is the decisive factor affecting the overall hydrodynamic performance of the trawl door,and the staggered angle θ value with the transverse distance Xs/c value affect the performance of the diversion hole of the trawl door,which are limited by the angle of attack α Value.Then,based on the response surface obtained by fitting in the optimal interval,the profile of the single-flap trawl door is optimized to obtain the optimal prediction point in the interval.Finally,after numerical verification,the maximum lift drag ratio of the singleflap trawl door is 17.104.Based on the numerical model of single-flap trawl door,firstly,the simplified numerical model of double-flap trawl door is constructed.Based on the conclusion of hydrodynamic performance of single-flap trawl door,the range of spatial parameters is reduced.The corresponding sample test points are selected within the ideal parameter range to study the hydrodynamic performance and law within the parameter range.It is found that the angle of attack α value still has the decisive influence on the hydrodynamic performance of the double-flap trawl door,and the staggered angle δ value must be less than the stagger angle θ Value,while ensuring the stagger angle θ taking the high value.The difference between the two angles should not be too large,and it is best to control the value difference between the stagger angle δ and stagger angle θ within 12.5 °.Then,based on the comparison of the hydrodynamic performance of single-flap and double-flap,the influence of the number of flaps on the overall hydrodynamic performance of the trawl door is studied.It is found that the number of flaps has a certain impact on the overall hydrodynamic performance of the trawl door,but it is still limited by the angle of attack α value.Finally,based on the response surface obtained by fitting in the optimal interval,the profile of the double-flap trawl door is optimized.After numerical verification,the maximum lift drag ratio of the double-flap trawl door is 17.481.