【作者】 唐世振；

【导师】 黄维平；

【作者基本信息】 中国海洋大学 ， 港口、海岸及近海工程， 2010， 博士

【摘要】 涡激振动是造成深水立管疲劳损伤的一个重要因素,关于涡激振动的研究逐步完善。但是,前期涡激振动的研究主要针对立管横向振动,结构在顺流向的振动往往被限制,很少有研究对立管的两向自由度振动进行研究,这主要是因为前期的研究认为顺流向振动的幅值相对较小,可以不考虑。但是近期发现顺流向振动影响到漩涡的脱落模式以及横向振动的响应幅值。但是迄今为止,国内外研究者并没有对两向涡激振动进行系统研究。本文的研究目的就是通过数值方法研究顶张力立管两向涡激振动动力特性及疲劳损伤,并开发用于顶张力立管动力分析及疲劳分析的软件。研究内容主要包括：提出了考虑横向流固耦合的横向升力及顺流向脉动拖曳力的修正模型,考虑了附加质量和附加阻尼的影响；并对其模型进行了验证；研究质量比肌术和频率比(f*=顺流向振动频率/横向振动频率)对立管动力特性及疲劳损伤的影响；通过MATLAB编程开发立管动力分析及疲劳分析系统,提出非等效管模型。研究认为：当质量比m*>6.0时,顺流向振动相对于横向振动来说可以忽略不计,并且顺流向振动频率与横向振动频率之间维持2倍的关系,结果同现有的实验结果符合；当质量比m*<6.0时,顺流向振动幅值明显增大,尤其是顺流向振动处于锁频状态时。并且,两者频率成分中不仅具有2倍的关系,同时还存在着部分相同频率。频率比不同时,在较宽的低约化速度带顺流向对横向振动起到一定的抑制作用；在6.3<Ur<8.0时,顺流向振动的考虑使得横向振动幅值具有一个小的增幅。但是,不同频率比时,横向振动的考虑都使得顺流向振动幅值具有较大的增幅。低质量比时,当横向振动响应幅值处于“初始支”时,顺流向振动产生的疲劳等同于横向振动的疲劳,不可忽略；在“超上支”时,顺流向振动疲劳在较宽的约化速度范围对立管的疲劳损伤并不起主要的作用。但是,两向自由度时横向振动产生的疲劳相对于单自由度时的横向疲劳在6.5≤Ur≤8.5时增加一倍,可见考虑顺流向振动时,立管的疲劳损伤增幅较大。在“下支”时,顺流向振动对横向振动疲劳的影响不明显。当频率比为1.0时,顺流向振动在5.0≤Ur≤8.0时影响横向振动疲劳。在频率比为2.0时,顺流向振动对横向振动疲劳影响不是很明显,略有增大；在两种频率情况下,横向振动的考虑都将增大顺流向振动疲劳。开发的立管动力分析及疲劳分析系统可以有效地预测立管的动力特性和疲劳损伤。由非等效管模型计算得到的外套管和内套管的强度更加符合工程实际。顶张力立管的两向涡激振动是国内外都比较新的研究课题,本文的研究得到了一些结论,可以用于工程实际。但是还有许多特性与现象需要更多的研究。更多还原

【Abstract】 Vortex induced vibration is the key factor that causes the fatigue damage of deepwater risers.The theory is being enriched gradually. But, the early studies are mainly about the cross-flow vibration, the in-line vibration was restrained. Few studies have focused on the two-degrees-of-freedom vibration of the risers. Which because the early phenomena presented the amplitude of the in-line vibration was small, it can be neglected.But recent studies found that the consideration of in-line vibration will affect the mode of the vortex and also the amplitude of the cross-flow vibration. But so far, there isn’t a systematic study for the two-degrees-of-freedom vibration both at home and abroad.The aim of this paper is to study the dynamic characteristics and the fatigue damage of the deepwater top-tensioned risers with two-degrees-of-freedom, and also develop the relative system.The contents are as following.Putting forward the modified lift force model considering the added mass and the added damping. Test and verify the lift force model.To study the influence of the mass ratio m* and the frequency ratio (f*=frequency in in-line direction/ frequency in cross-flow direction) on the dynamic characteristics and the fatigue damage of the deepwater top-tensioned risers.To develop the dynamic analysis and fatigue analysis system based on the MATLAB language. The above-mentioned contents are the main contents included in the study.The followings are the main conclusions.When m*>6.0, the in-line vibration can be neglected compared to the cross-flow vibration, and also the in-line frequency will be twice of the cross-flow frequency. When m*<6.0, the amplitude of the in-line vibration shows a remarkable increase especially for the’lock-in’ state in in-line direction. Meanwhile, the f* is equal to 1.0 besides 2.0.With different f*, the in-line vibration restricts the cross-flow vibration with a wide bound for the low reduced velocity. When the 6.3<Ur (reduced velocity)<8.0,the amplitude in cross-flow direction presents small increase. But the amplitude in in-line direction will increase sharply considering the cross-flow vibration with each frequency ratio. With a low mass ratio,consideration of the IL vibration shows an important factor to the fatigue damage under initial branch. The in-line vibration isn’t the main contributor to the fatigue damage of the riser under the’super-upper’branch with a wide reduced velocity bound. But the fatigue damage in cross-flow direction with two-degrees-of-freedom will be twice of it with one-degree-of-freedom at 6.5≦Ur≦ 8.5.The in-line vibration doesn’t affect the cross-flow fatigue obviously under the ’Iower’branch. When the f*=1.0, the in-line vibration influences the cross-flow fatigue at 5.0≦Ur≦8.0.When the f*=2.0, the in-line vibration also doesn’t effect the cross-flow fatigue obviously. The cross-flow fatigue only increases a little.With the two frequency ratios, the consideration of the cross-flow vibration makes a great increase of the in-line fatigue. The system can be used to effectively forecast the dynamic characteristics and the fatigue damage of the deepwater top-tensioned risers. The strength of the outer pipe and the inner tube calculated by the non-equivalent model are more in accordance with the actual engineering situation.The study of the two-degrees-of-freedom vortex-induced vibration of risers is a new problem.The conclusions obtained in this paper are suitable for the engineering. But there are always more characteristics that need further researches.更多还原