组合动力锚水动力特性数值模拟研究

Numerical investigations on the hydrodynamic characteristics of the hybrid dynamically installed anchor

作为海上浮式结构物的一种新型锚固基础,动力锚具有自安装、不受水深影响、适用范围广的特点。在动力锚的基础上研发的组合动力锚结合了动力锚自安装和板锚法向受荷的特点,具有安装快速、适用多种类型海床、承载效率高等性质。组合动力锚在水中自由下落时的水动力学特性(下落速度、方向稳定性等)会受到锚链、尾翼宽度和助推器质量等因素影响。若下落速度过小或方向稳定性过差,则会影响锚的安装成功率。采用计算流体动力学方法模拟流体对锚的冲击和锚在水中自由下落过程,以优化组合动力锚的尾翼尺寸;其次研究锚链作用力和助推器质量对组合动力锚下落速度和偏角的影响规律。计算结果表明:组合动力锚的拖曳阻力系数为0.45左右,尾翼宽度最优尺寸为翼板宽度的1.25倍。连接在锚眼处的锚链会减小组合动力锚的下落速度并加剧锚的偏转,需综合锚的下落速度和偏角来确定锚在水中下落高度。

The dynamically installed anchor(DIA),as a new anchoring foundation for the offshore floating structure,is self-installed so that the anchor installation is not affected by water depth and can be applied widely in offshore engineering.The hybrid dynamically installed anchor,a newly proposed DIA,owns the advantages of the self-installation of the DIA and the normal loading mobilization of the plate anchor.The hydrodynamic characteristics of the hybrid anchor(including fall velocity,directional stability,etc)during the free-fall process in water are affected by the interaction force of the attached chain,the width of the rear fins and the mass of the booster.The anchor installation will fail if the falling velocity is too small or if the directional stability is too poor.Numerical analyses based on the computational fluid dynamics(CFD)approach were performed to simulate the impact of fluid on a fixed anchor in position and the free fall process of the anchor in water.Through numerical simulations,the fin width was optimized,and the effects of the chain drag and booster weight on the fall velocity and tilt of the anchor were investigated.The numerical results indicate that the drag coefficient of the hybrid anchor is about 0.45,and the optimal width of the fin is 1.25 times the anchor width.The chain attached at the padeye of the anchor will reduce the fall velocity and exacerbate the tilt of the hybrid anchor.Therefore,an appropriate vertical fall displacement should be made based on both the fall velocity and the directional stability of the anchor.