【作者】 苑健康；

【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， 硕士

【摘要】 泻涡脱落诱发的涡激振动是海洋立管疲劳破坏的主要诱因,利用相关的扰流装置抑制涡激振动对立管的损伤,越来越受到海洋工程界的关注。目前在螺旋侧板的物理实验和数值模拟等方面仍面临很多难题。本文以CFD(计算流体力学)数值模拟在涡激振动计算仿真中的应用,通过物理模型实验和数值模拟相结合对光滑立管和覆盖螺旋侧板的立管的泻涡脱落和与之对应的涡激振动形态等进行了综合研究。本文采用物理实验验证和数值模拟结合的方法深入研究光滑立管的涡激振动机理,以及螺旋侧板对立管涡激振动的抑振原理。其中物理模型实验和数值模拟工作相互补充,前者为后者提供模型建立的方向性指导并作为判断计算结果可靠性的依据；经过优化设计的后验型数值模拟则为物理模型实验提供对应的螺旋侧板尾流区泻涡发放形态及结构位移和变形的瞬时综合信息,从漩涡发放形态随时间和沿立管轴向变化阐释螺旋侧板对立管涡激振动的影响。同时,本文对数值模拟的结果和物理模型实验观测的结果之间存在的差异给予合理的说明,并提出改进方案。在物理实验中,取光滑立管与螺旋侧板高为0.10D(D为立管的直径)立管进行对比,研究立管在不同流速下的应变和立管尾部涡街的变化,分析螺旋侧板螺距对立管涡激振动的影响。在数值模拟过程中,将实验中比较有代表性的两组雷诺数：Re=200和Re=1500,两种流速下对光滑立管和覆盖螺旋侧板的立管分2D和3D两种情况进行模拟分析。在2D数值模拟中,光滑立管取一圆形截面进行分析,对于覆盖螺旋侧板的立管取其中四个比较有代表性的截面,研究拖曳力,升力以及拖曳力系数和升力系数在不同雷诺数,不同截面下变化,进而研究螺旋侧板对立管涡激振动的影响。在3D数值模拟过程中,将取光滑立管和P5_H0.10, P5_H0.14, P5_H0.25和P16_H0.25四种覆盖螺旋侧板的立管在雷诺数Re=200和Re=1500下,通过研究拖曳力系数和升力系数随Re的变化与2D数值模拟的结果进行对比,分析螺旋侧板高和螺距对立管涡激振动的影响,并通过对三维立管的疲劳寿命的计算得出最优的螺旋侧板尺寸。这些先验的模拟工作对指导今后的物理模型实验以至相关的实际海洋工程实践都具有重要的参考价值。本文创新性的工作体现在：通过实验、模拟结果对螺旋侧板的研究提供可靠的数据,将物理模型实验与数值模拟相关的很多重要结论结合起来研究涡激振动对立管的影响。同时,通过物理模型实验与数值模拟的结合,对很多刚性管涡激振动抑振相关的振动模态、振幅间相互作用、泻涡发放变化规律及尾流区复杂的泻涡发放形态等方面都给予了合理的解释。更多还原

【Abstract】 Vortex-Induced Vibration (VIV) acts as the dominant fatigue damage to risers systems widely used in offshore engineering. Although there are many research works have been done concerning model tests and numerical simulation, many problems are still unsolved. For the sake of actualizing the numerical application of CFD method to VIV study, a parametric study of the efficiency of Helical strakes to suppress VIV has been carried out, including the interpretation between vortex shedding pattern and riser oscillation. This paper is a systematic report about suppressing VIV. It’s the combination of model tests and numerical simulation, which using the FEM software system ANSYS-CFX.In actual practice, the model tests and numerical simulation task works as supplementary to each other. On one hand, the former provided the orientation and instrument for the setup of the latter, and acted as reliable criteria for numerical simulation result; on the other hand, the well-designed post-test numerical simulation offered the corresponding vortex shedding visualization behind the wake of riser and the corresponding instantaneous displacement information. Taking advantage of the combination between Helical strakes oscillation from model tests and vortex shedding patterns from numerical simulation, some coupled phenomena about fluid-structure interaction have been well comprehended.In the model tests, a series of riser models with F5 H0.10 Helical strakes and bare riser configurations have been tested. As the current speeds vary, the results of the bare riser and Helical strakes show that the drag coefficient and lift coefficient change with Re and have been compared to the related tests.A series of pre-test numerical simulation tasks aiming at solving more complicated problems have been accomplished, including 2D and 3D of bare riser and Helical strakes on the Re=200 and Re=1500. In the 2D condition, a set of different heights of strakes have been simulation and four different sections of the strakes have been taken into account. The results which show the drag coefficient and lift coefficient change with Re have been compared to Morison formula and the related tests. In the 3D condition, both the pitch and the height of the strakes have been systematically changed. Bare riser and four different strakes have been simulated; they are P5_H0.10, P5_H0.14, P5_H0.25 and P16_H0.25. A comparison with results of the two conditions with strake and bare riser is given. The effects on suppressing VIV fatigue of long risers vary considerably according to the geometrical shapes of Helical strakes. The pre-test simulation work accomplished in this paper will be an available orientation and reference to the further model tests and even to the practical engineering application.The innovations in this thesis can be concluded as follows:the model tests and numerical simulation have provided a powerful tool to study the Helical strakes; many important conclusions are obtained from model tests and numerical simulation; taking advantage of the combination of these two methods, some problems related to the vibration mode, the amplitude and the vortex shedding mode have been well explained.更多还原