﻿ 串列双立管螺旋列板抑制涡激振动的数值模拟
 舰船科学技术  2019, Vol. 41 Issue (4): 100-105 PDF

Three dimensional numerical simulation of VIV of tandem double risers by helical strakes
LI Yan-xiao, ZHANG Shu-jun
College of Mechanics and Materials, Hohai University, Nanjing 210098, China
Abstract: Deepwater riser in waves and currents suffer from a periodic vortex shedding, which can cause vortex-induced vibration(VIV) and the structural fatigue damage. When the riser is close to each other, the flow field interference effect occurs. In this paper, we investigate the interaction between risers and the effect on suppressing VIV of helical strakes. Three-dimensional numerical analysis is carried out for the smooth tandem double risers and the fixed tandem double riser with helical strakes at Re=3900 by large eddy simulation (LES).In view of the different riser spacing (3D, 5D, 8D, D as riser diameter) and additional helical strakes case, the hydrodynamic coefficients of riser are analyzed, further exploring the effect of helical strakes on Vortex-induced Vibration of Double risers. The results show that the lift coefficient of downstream riser is maximum in case that the spacing of riser is 3D, the drag coefficient and lift coefficient are the same as that of the singe riser in case of 8D. The lift coefficient and the amplitude response of the double riser is significantly reduced after adding the helical strakes. Due to the shunting effect of the helical strakes, the vortex removal method of the riser was completely destroyed, and a very small parallel nearly trailing vortex appeared behind the riser.
Key words: helical strakes     tandem double risers     vortex-induced vibration     numerical simulation
0 引　言

1 数学模型 1.1 大涡模拟的控制方程

 $\begin{split} & \!\!\!\!\!\!\frac{\partial }{{\partial t}}(\rho {u_i}) + \frac{\partial }{{\partial {x_j}}}(\rho {u_i}{u_j}) = \rho {F_i} - \frac{{\partial p}}{{\partial {x_i}}} + \frac{\partial }{{\partial {x_j}}}(2\mu {s_{ij}})\text{，} \\ & \!\!\!\!\!\!{s_{ij}} = \frac{1}{2}\left[ {\frac{{\partial {u_i}}}{{\partial {x_j}}} + \frac{{\partial {u_j}}}{{\partial {x_i}}}} \right] \text{。} \end{split}$ (1)

 $\frac{{\partial {u_i}}}{{\partial t}} + \frac{{\partial \overline {{u_i}{u_j}} }}{{\partial {x_j}}} = - \frac{1}{\rho }\frac{{\partial \bar p}}{{\partial {x_i}}} + \nu \frac{{\partial {}^2\overline {{u_i}} }}{{\partial {x_j}\partial {x_j}}}\text{，}$ (2)
 $\frac{{\partial {u_i}}}{{\partial {x_i}}} = 0 \text{，}$ (3)

$\overline {{u_i}{u_j}} = \overline {{u_i}} \overline {{u_j}} + (\overline {{u_i}{u_j}} - \overline {{u_i}} \overline {{u_j}} )$ ，并称

 $\overline {{\tau _{ij}}} = - (\overline {{u_i}{u_j}} - \overline {{u_i}} \overline {{u_j}} ) \text{，}$ (4)

 $\frac{{\partial \overline {{u_i}} }}{{\partial t}} + \frac{{\partial \overline {{u_i}} \overline {{u_j}} }}{{\partial {x_j}}} = - \frac{1}{\rho }\frac{{\partial \overline p }}{{\partial {x_i}}} + \nu \frac{{{\partial ^2}\overline {{u_i}} }}{{\partial {x_j}\partial {x_j}}} + \frac{{\partial {{\overline \tau }_{ij}}}}{{\partial {x_j}}}\text{，}$ (5)

 ${u'_j} = {u_j} - \overline {{u_j}} \text{，}$ (6)

 $\overline {{\tau _{ij}}} = (\overline {{u_i}} \overline {{u_j}} - \overline {\overline {{u_i}} \overline {{u_j}} } ) - (\overline {\overline {{u_i}} {{u'}_j}} + \overline {{{u'}_i}\overline {{u_j}} } ) - \overline {{{u'}_i}{{u'}_j}} \text{。}$ (7)
1.2 结构动力学方程

 $\begin{split} & mx + cx + kx = {F_x}(t) \text{，} \\ & my + cy + ky = {F_y}(t)\text{。} \end{split}$ (8)

1.3 水动力系数

 $\begin{split} & {C_d}(t) = \frac{{{F_x}(t)}}{{\displaystyle\frac{1}{2}\rho U_c^2}} = \displaystyle\frac{{\int {p(t)\cos \alpha {\rm d}A} }}{{\frac{1}{2}\rho U_c^2}} \text{，} \\ & {C_l}(t) = \frac{{{F_y}(t)}}{{\displaystyle\frac{1}{2}\rho U_c^2}} = \displaystyle\frac{{\int {p(t)\sin \alpha {\rm d}A} }}{{\frac{1}{2}\rho U_c^2}} \text{。} \end{split}$ (9)

2 数值模拟结果分析 2.1 几何模型及工况设置

 图 1 流域模型 Fig. 1 Model of fluid field

 图 2 附加螺旋列板 Fig. 2 Model of riser with helical strakes
2.2 网格划分及计算设置

 图 3 网格划分 Fig. 3 Mesh generation

 图 4 光滑单管阻力系数与升力系数曲线 Fig. 4 Drag and lift coefficients of smooth riser
2.3 光滑立管结果分析

 图 5 光滑双立管的受力系数 Fig. 5 Drag and lift coefficients of double smoothed risers

 图 6 附加列板后双立管的受力系数 Fig. 6 Drag and lift coefficients of risers with helical strakes
2.4 光滑串列双立管模拟分析

2.5 附加螺旋列板双立管结果分析

 图 7 附加螺旋列板前后升力标准差和阻力均值的对比 Fig. 7 Standard deviation of lift coefficients and mean drag coefficient of smoothed riser and risers with helical strakes

 图 8 光滑双立管与附加螺旋列板双立管涡量切片图 Fig. 8 Vorticity slice graph of smoothed riser and risers with helical strakes
3 结　语

1）对于双立管情况，上游立管受力与单立管情况相似，而下游立管受到来自上游立管脱落的剪切层以及自身脱落的漩涡的力的叠加影响，受力情况复杂，与单立管情况相比，其阻力系数明显减小，而升力系数幅值增大。

2）研究发现，立管间距为3 D时上下游立管间的相互影响较大，导致下游立管升力系数幅值显著增加；立管间距为5 D时，下游立管升力系数的增加趋于平缓；立管间距为8 D时，上下游立管间相互影响最小，升阻力系数接近单立管情况。

3）螺旋列板可以有效地抑制双立管的涡激振动。附加螺旋列板后，双立管升力系数幅值显著降低，从而减少了立管的振幅响应，但是阻力系数比光滑管时更大。双立管加板前后，上下游立管之间相互作用的总体趋势相似。并且由于列板的分流作用，彻底破坏了立管的脱涡方式，在立管后形成间距很小，近乎平行的尾涡。

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