低阻力自适应旋转尾流隔板的涡激振动抑制方法和机理研究

This project focuses on the flow control of Vortex-Induced Vibration (VIV) of deepwater risers. Based on model test, numerical simulation and nonlinear analysis, a novel VIV suppression strategy by using rotatable splitter plate attached will be closely examined. The investigations of this project will bring deep insight into the fundamental mechanism involved in the proposed VIV suppression method, and lead to comprehensive understandings of its dependence on the flow conditions and structural parameters. Special attention will be paid on the conditions for the application of the present VIV suppression strategy. The physical mechanism behind the occurrence of bifurcate solutions and the nonlinear hysteresis phenomenon associated with the rotary response of the splitter plate will be examined. It was know that the bifurcate/bi-stable rotary oscillation with its equilibrium position deflecting the free-stream direction may lead to undesirable galloping response. In order to avoid this disadvantage, a possible method by introducing additional torsional stiffness into the rotating system will be studied. This concept is inspired by our recent understanding based on fully coupled numerical simulations of fluid-structure interaction. It was confirmed that the bifurcation disappears at relatively low reduced velocity (with structural stiffness) for specific plate length and Reynolds number. The investigations of this project will also include the sectional rotatable splitter plates for practical deepwater risers with large aspect ratio. The three-dimensional effects aroused from the two lateral ends of the rotating splitter plate are concerned. A simplified empirical approach will be proposed for the fast prediction of hydrodynamic coefficients by using two-dimensional CFD simulation rather than the much time-consuming three-dimensional computations. With the available hydrodynamic coefficients, a quasi-three-dimensional numerical model will be further developed for the prediction of the dynamic response of deepwater rises with sectional rotatable splitter plates attached.

本项目将针对深水立管的涡激振动问题开展流动控制研究。在综合利用物理实验、数值模拟和非线性动力分析方法的基础上，对“旋转尾流隔板涡激振动抑制方法”开展深入研究。理解和认识该流动控制措施的基本力学原理，揭示其对流动条件和结构参数的依赖作用，全面把握其有效适用条件。重点研究该涡激振动抑制方法所具有的非线性动力分叉特性（旋转尾流隔板的稳定平衡振动位置偏离流向），以及非线性迟滞响应行为的发生机理和作用机制。在此基础上，针对非线性流固耦合系统的动力分叉现象可能诱发驰振运动的潜在危害，探索通过引入结构回转刚度来消除动力分叉，进而避免大幅驰振响应的可能途径。针对轴向分段旋转尾流隔板，探索通过二维流动数值模拟来近似三维水动力学系数的参数化近似计算方法，进一步建立准三维分层流固耦合数值分析模型，为分段旋转尾流隔板抑制措施的优化设计和工程应用提供有效的技术支持。

流致振动严重威胁深海细长柔性立管结构的服役安全，涡激振动是其中的典型问题。如何通过发展有效的流动控制措施来减小涡激振动危害，一直是工程界和学术界关心的重要问题。本项目主要针对旋转尾流隔板这一被动型流动措施开展研究，可在有效降低涡激振动响应的同时，减小作用在立管上的拖曳力。项目研究工作重点是通过发展有效的流固耦合数值分析方法，来揭示流固耦合作用机制，特别是其中的动力分叉行为，及其可能对涡激振动抑制效果带来的负面效应。项目主要开展了一下8各方面的研究工作：① 圆柱-尾流隔板系统流致旋转振动特性的数值研究；② 流固耦合振动系统动力分叉行为的发生机理研究；③ 立管-尾流隔板系统流致振动的低阶降维模型研究；④ 立管-尾流隔板系统横流-旋转两自由度流固耦合振动特性的数值研究；⑤ 管束阵列的流固耦合动力响应及水动力干涉特性研究；⑥ 受迫振动流固耦合系统的相位动力学分析方法；⑦ 基于特征分解与截断边界的有限元CFD模型建立；⑧ 非线性水动力砰击荷载对结构作用的数值和实验研究。在本项目资助下，项目组成员共发表研究论文16篇，其中SCI期刊论文7篇。项目注重高质量研究成果的产出，有3篇研究论文发表在国际流体力学顶尖期刊J. Fluid Mech.和Phys. Fluids。其它代表性研究成果发表在国际海洋工程权威期刊Ocean Eng.、Appl. Ocean Res.和Int. J. Offshore & Polar Eng.。以本项目部分研究成果作为重要支撑材料，获省部级科技奖励2项，分别为：2020年度中国海洋工程科学技术一等奖——“深海细长柔性结构的流固耦合作用机理和振动控制”（项目负责人排名第一）；2019年度教育部自然科学二等奖——“非线性波浪对复杂海洋结构作用的高阶边界元数值分析”（项目负责人排名第三）。

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