圆柱形网箱锚绳受力特性的数值模拟

Numerical simulation on the tension and displacement of the mooring rope of cylindrical cage

根据动力学原理,研究在水流作用下圆柱形网箱锚绳的受力特性,导出锚绳形状和张力的一阶微分方程组,并利用四阶Runge-Kutta计算法,结合Matlab工具,对圆柱形网箱的系泊锚绳,在水流速度、水流冲角、水深和锚绳长度等参数下的空间位置及张力变化进行数值求解和仿真模拟。模拟结果显示,在给定的初始条件下,锚绳长度对锚绳的空间位置影响最显著,水流冲角对锚绳张力的影响最大,水深对形状和张力的影响最不明显;锚绳张力随长度的增加而减小,随水流冲角、流速的增加而增加。

With operations in the aquaculture industry moving to deeper waters, the cages are more likely to be exposed to very harsh environment and extremely large currents. As the main tools for maintaining the stability of the cages, the mooring ropes are undoubtedly very important in the whole system. Therefore, it is essential and necessary to study the mechanical characters of the mooring ropes for the sake of keeping the cages working safely and efficiently. However, systemic relative studies have rarely been seen in the publications. This study was conducted mainly on the mechanical characters of the mooring rope on the basis of the hydrodynamic theory. A first-order ordinary differential equation of the tension and displacement of the submerged part of the mooring rope has been derived with the hydrodynamic analysis. A fourthorder Runge-Kutta scheme, which has been programmed by using the MatLab toolbox, is extended to solve shis equation. According to the measured data from the actual cylindrical cages which have been on operation, a series of cases were selected for systemic investigation on the effect on the tension and displacement of the mooring rope produced by different factors such as weights of the anchor, currents, water depths, and lengths of the mooring ropes. Through analyzing the numerical da-ta, the following results have been obtained： （1） the length ot the mooring rope is the important factor which affects the shape of the submerged mooring rope, while the angle of the incident currents mainly affects the tension of the mooring rope; （2） the water depth has least effect on both the shape and the tension of the mooring rope; （3） the tension of the mooring rope decreases with the increase of the length of the mooring rope, but it increases with the rise in the angle of the incident current and the velocity of the current. Finally, it is concluded that the length of the mooring rope and the angle of the incident current must be taken into account when a cage is designed. Besides, the investigation on the tension of the mooring rope also provides an advanced understanding for the design of the anchor, i.e. the shape, the material and the weight. The numerical efficiency and visualization of the computational results are also presented in this paper.