【作者】 吴浩；

【导师】 孙大鹏； 吕林；

【作者基本信息】 大连理工大学 ， 港口、海岸及近海工程， 2013， 博士

【摘要】 涡激振动是导致深海立管发生结构失稳以及疲劳破坏的重要原因之一,实际工程中为减小或者消除涡激振动的影响,增加深海立管的安全使用寿命,往往需要使用涡激振动抑制措施。我国涡激振动抑制措施的研究工作与国外相比还存在很大差距,尤其是针对大长细比柔性立管方面的研究仍非常有限。深海油气开发工程的快速发展,迫切需要开展细长柔性立管涡激振动抑制措施的创新性研究工作。本文依托国家863计划项目,提出了一种新型的多根控制杆涡激振动抑制措施,通过水池大尺度实验和数值模拟相结合的方法,以细长柔性立管作为主要研究对象,对多根控制杆抑制措施的抑制效果、抑制性能的影响因素和抑制机理进行了比较系统的研究,并就多根圆柱体涡激振动问题进行了一些基础理论研究探索。文中首先简要介绍了涡激振动的基本理论,主要包括圆柱体涡激振动基本概念,研究中涉及的主要无量纲参数,以及涡激振动的研究方法。第三章开展了水池大尺度实验,利用拖曳方法产生均匀流,综合考虑来流方向、间距和覆盖率对抑制性能和张力的影响,比较系统地研究了多根控制杆抑制措施对大长细比柔性立管涡激振动的抑制效果。实验结果表明多根控制杆对立管涡激振动响应有非常显著的抑制作用,能够同时消减立管CF和IL两个方向最高达90%的位移响应,使疲劳破坏减小2个数量级以上,并且由多根控制杆造成的张力增加不明显。抑制性能对来流方向具有较强的适应性,间距越小、覆盖率越高则抑制效果越好,文中给出了建议优化的间距和覆盖率。第四章利用二维数值模拟方法研究了多根圆柱体横向受迫振动问题。首先通过计算单根圆柱体固定绕流和横向受迫振动对数值模型进行了验证,然后利用该模型对多根圆柱体固定绕流和横向受迫振动进行了数值模拟。发现当结构振动频率接近于固定不动时的涡脱落频率时,流体-结构能量传递关系、结构位移和升力的相位关系以及涡脱落模式会都会发生显著的改变,从而造成了升力振幅和振荡模态的突变。通过分析单圆柱和不同来流角下多圆柱的涡脱落模式和流体压力分布,揭示了多根控制杆抑制措施对立管涡激振动的抑制机理。第五章基于切片法建立了准三维流固耦合数值模型,通过引入并行计算技术,显著提高了数值计算效率,实现了对大长细比柔性立管涡激振动问题的求解。选取长细比为1750的柔性立管实验模型和长细比为3691的工程实际深海立管作为研究对象,利用该模型分别对单根立管附加多根控制杆和串列双立管的横向涡激振动进行了数值模拟。数值计算结果表明附加多根控制杆以后立管的横向位移振幅显著减小,位移和流体力的振荡特性以及涡脱落模式都发生了显著变化。串列双立管上游立管的涡激振动响应特性与单根立管很相似,振动处于周期稳定的锁定状态。由于尾流干涉作用,下游立管的涡激振动响应特性与上游立管大不相同,其横向位移最大值明显比上游立管大,而位移标准差最大值却比上游立管小,整个立管上的涡激振动具有很强的随机性,处于非锁定的不稳定状态,涡脱落形态极不规则。更多还原

【Abstract】 Vortex induced vibration (VIV) is one of the important reasons of the structural instability and fatigue damage of deepwater riser. Practically, it is necessary to use VIV suppression measures to reduce or eliminate the influence of VIV and increase the service life of deepwater riser. There is still a big gap in the research work of VIV suppression measures between China and developed countries, especially in the research of large slenderness ratio flexible riser, which is still very limited. The rapid development of the deep-sea oil and gas development projects urgently needs to carry out innovative research of VIV suppression measures of long flexible riser.In this paper, relying on the national863plan project, a new type of VIV suppression measures of multiple control rods is proposed. With long flexible riser as the main research object, the suppression effect, the influencing factors of suppression performance and the suppression mechanism are systematically studied by combining the methods of large scale tank experiment and numerical simulation. In addition, this paper also carried out some basic theoretical exploration on aspect of the multiple cylinders VIV.This paper first briefly introduces the basic theory of VIV, which mainly includes the basic concepts of cylinder VIV, main dimensionless parameters involved in the research and research methods of VIV.In the third chapter, a large scale tank experiment is conducted which using towing method to generate uniform flow. The suppression effect of multiple control rods on VIV of long flexible riser is systematically studied, by using UPVC and steel riser model with slenderness ratio of1750respectively, and with comprehensive consideration of the influence of flow direction, spacing and coverage rate on suppression performance and tension. The experimental results show that the multiple control rods have a significant suppression effect on VIV of long flexible riser, which can simultaneously reduce the displacement response of riser up to90%in both CF and IL direction, and decrease the fatigue damage more than2orders of magnitude, and meanwhile the increase of tension is not obvious. It has robust suppression performance irrespective of flow direction, and the smaller the spacing, the higher the coverage rate produce better suppression effect. The optimized spacing and coverage rate are suggested in this paper.In the fourth chapter, the2D numerical simulation method is used to study the lateral forced vibration of multiple cylinders. Firstly, the numerical model is verified by calculation of the flow around single fixed cylinder and the lateral forced vibration of single cylinder. Then the flow around multiple fixed cylinders and the lateral forced vibration of multiple cylinders are simulated. The numerical results show that fluid-structure energy transfer relationship, phase relationship between structural displacement and lift force, and vortex shedding pattern will significantly change when structural vibration frequency is close to the vortex shedding frequency of stationary body, which cause abrupt change of the amplitude and oscillating mode of lift force. The suppression mechanism of multiple control rods on riser VIV is revealed by analyzing vortex shedding pattern and fluid pressure distribution of single cylinder and multiple cylinders in different attack angle.In the fifth chapter, the quasi3D fluid-structure coupling numerical model is established based on strip theory. By introducing parallel computing technology, the efficiency of the numerical calculation is significantly improved, which enable us to solve the problem of long flexible riser VIV. By selecting the experimental flexible riser model with slenderness ratio of1750and the practical deepwater riser model with slenderness ratio of3691as research objects, this numerical model is used to simulate the lateral VIV of single riser with multiple control rods and tandem double risers. The numerical results show that the lateral displacement amplitude of the riser with multiple control rods is significantly reduced, compared to the bare riser, and the oscillating characteristic of displacement and fluid force and the vortex shedding mode are significantly changed. The VIV response characteristics of the upstream one of tandem double risers is similar to single riser, whose vibration is under periodic and stable lock-in state. Because of the wake interference effect, the VIV response characteristic of the downstream riser is quite different from the upstream one. The maximal lateral displacement of the downstream riser is significantly larger than the upstream one, while the maximal standard deviation of displacement of the downstream riser is smaller than the upstream one. The VIV response of the whole downstream riser shows strong randomness, under nonlocking unstable state, and its vortex shedding pattern is highly irregular.更多还原