剪切流中螺旋侧板抑制柔性立管涡激振动的数值模拟

摘要

Risers in waves and currents suffer from a constant periodic vortex shedding on either side.Vortex-in-duced vibration (VIV)is a major factor that causes the structural fatigue damage.With the rapid development of the deep sea engineering,the complexity of the deep sea environment and the large deformation of the flexible riser make the study of vortex induced vibration and its suppression method more important.In this paper,based on Ansys Workbench platform,we conduct a series of calculations on smooth rigid risers and risers with helical strakes for different geometry parameters under uniform flow.By the compare and analysis of hydrodynamic coef-ficient of vortex induced vibration,it is found that the helical strake of P17.5D/H0.25D is the best for the sup-pression of VIV.Then through two-way fluid solid coupling,we make three-dimensional numerical simulation on smooth flexible risers and risers with helical strakes of P17.5D/H0.25D under shear flow,the ratio of length to diameter of the risers being 482.Their hydrodynamic characteristics and structural dynamics characteristics are also studied.Our results show that smooth flexible riser exhibits various vibration modes under shear flow,the wake vortex shedding presents a variety of vortex structures,and the dynamic characteristics of vortex shows obvi- ous three-dimensional feature change in different sections.Helical strakes increase the longitudinal resistance, but in-line(IL)vibration amplitude decreases;the riser′s maximum amplitude in cross flow (CF)direction falls from 0.85D to 0.14D.Transverse vibration suppression efficiency is up to 83.5%.%处于波浪和洋流中的立管两侧不断产生周期性的涡旋脱落，其诱发的涡激振动已经成为引起结构疲劳损伤的主要因素．随着深海工程的迅速发展，深海环境的复杂性及柔性立管的大变形使涡激振动及其抑制方法的研究尤为重要．文中基于Ansys Workbench平台，首先对均匀来流下的刚性光滑立管及附加不同几何参数螺旋侧板立管进行了系列运算，通过水动力系数对比分析发现P17.5D／H 0.25D的螺旋侧板涡激振动抑制效果最好；然后采用双向流固耦合技术对剪切来流下长径比为482的光滑柔性立管及附加螺旋侧板参数为P17.5D／H 0.25D的柔性立管进行了三维直接数值模拟，通过水动力特性及结构动力学特性两个方面进行研究．结果表明：光滑柔性立管在剪切来流下出现了多阶振动模态，其尾流场漩涡脱落呈现多种涡结构模式，尾涡动力特性在不同截面的变化体现出明显的三维特征．附加螺旋侧板后加大了顺流向的阻力，但立管振动幅值有所减小；立管横流向的振幅最大值由0.85D降至0.14D，横向振动抑制效率高达83.5％．