波浪作用下圆形网箱浮架系统的运动特性分析

Movement characteristics of floating circular collar of net cages subjected to waves

作为深水养殖网箱的重要组成部分，浮架系统在网箱抗风浪性能中扮演着极为重要的角色，研究浮架系统在波浪作用下的运动特性是深入了解网箱抗风浪性能的关键。基于集中质量法将圆形浮架离散成众多微元，并运用线性波浪理论和刚体运动学原理，建立了波浪作用下网箱浮架系统的运动响应数学模型。针对圆形浮架的实际尺寸参数，在不同波高（H=4．2—7．0m）和周期（T=7．2，8．6s）条件下，采用计算机数值模拟方法，对浮架前后点运动轨迹、浮架质心水平和垂直位移、浮架倾角进行了数值计算。通过对计算结果的比较及分析表明：（1）浮架垂直位移幅度大于水平位移幅度，波浪周期对浮架垂直位移的影响要小于对水平位移的影响；（2）浮架水平位移、垂直位移以及倾角都和波高具有显著的正比关系。在波高H=4．2～7．0m范围内，周期T=7．2 s时，水平位移、垂直位移和倾角的增量分别为1．84m、1．0m和7．18。；周期T=8．6 s时，三者的增量分别为1．66m、1．05m和5．43°；（3）周期增大，浮架垂直位移增加，水平位移和倾角减小。

Floating collar, an important component of deep-water net cage, plays a great important role in the performance of withstanding strong winds and waves for net cage, and studying the movement characteristics of floating collar exposed to waves is a key to deeply understand the properties of withstanding strong winds and waves about net cage. In this paper, based on the lumped mass method, floating circular collar is discreted with lots of micro-elements, and by using the linear wave theory and the rigid body kinematics principle, a numerical model for movement response of floating collar exposed to waves is set up. Reference to practical floating collar parameters： 40 m in circumference, 12.7 kN in total weight, 15 m in water depth, r = 125 mm, t = 15 mm,ρ = 953 kg/m^3. Under the conditions of different wave heights （ H = 4.2 - 7.0 m） and wave periods （ T = 7.2 s, 8.6 s）, the motion trajectories of the fore and rear points of the floating collar, the horizontal and vertical displacement of the central point of floating collar, pitch angles of floating collar are calculated in the way of computer numerical simulation method. By comparing and analyZing, the calculated results show that： （ 1 ） The vertical motion amplitude of the collar is greater than the horizontal one, and the influence of wave period on the vertical displacement of the collar is less than that of the horizontal one; （2） The horizontal displacement, the vertical displacement and the pitch angle of the collar all have direct proportional relation with wave height. Under the condition of wave height of 4.2 - 7.0 m, the increase of the horizontal displacement, the vertical displacement and the pitch angle of the collar are 1.84 m, 1.0 m and 7.18° when T=7.2 s, while they are 1.66 m, 1.05 m and 5.43° when T = 8.6 s; （3）When wave period increases, the vertical displacement of the collar increases accordingly, while the horizontal displacement and the pitch angle of the collar decrease.