【作者】 魏娜；

【导师】 唐国强；

【作者基本信息】 大连理工大学 ， 港口、海岸及近海工程， 2024， 硕士

【摘要】 深水立管的涡激振动问题（Vortex-Induced Vibration,VIV）是海洋工程的重要研究内容。当海流经过水下立管结构时,在其背流侧会形成交替的涡旋脱落,进而引起周期性横向升力,诱发涡激振动响应。而当多个结构物近距离放置,又会产生复杂的流动干涉现象。涡激振动是深水立管疲劳损伤的重要诱因,一旦立管发生断裂破坏,其直接经济损失和环境灾害都将是十分严重的。本文在任意拉格朗日-欧拉（Arbitrary Lagrangian-Eulerian,ALE）观点下,建立了双圆柱流固耦合的时域数值模型,用基于特征线分裂（Characteristic Based Split,CBS）的有限元方法求解流动控制方程,采用弹簧法进行计算域内ALE区的网格更新。运用该模型进行了串列双圆柱横流向强迫振动的二维数值研究,在Re=160条件下,研究上、下游圆柱运动相位差、间距比和直径比对强迫振动双圆柱水动力特性的影响。首先,在振动幅值A/D=0.2～0.7,振动频率比f_e/f_st=0.5～1.8的范围内研究了相位差对固定间距比下横流向强迫振动双圆柱的影响。随上、下游圆柱运动相位差的增加,结构的运动响应模态组成由复杂变得简单,主要表现为高阶同步模态的减少,模态区域界限变得分明;且随相位差增大,上游圆柱3/1模态显著增多。在不同相位差下,均可以观察到1/1模态、高阶同步模态与准周期模态伴随出现的现象,这种组合现象多发生在不同模态区域的边界,是模态转换的重要标志。对结构受力,上游圆柱的升力几乎不受相位差的改变的影响。下游圆柱的升力变化规律在φ=0°、30°、90°一致,在,φ=150°发生明显改变;随相位差增大,上、下游圆柱升力的差值逐渐减小。通过分析圆柱横流向强迫振动的位移和圆柱横流向受力的相位差,在f_d/f_e=3时相位动力学特征表现为相位滑移,无论是同步模态还是准周期模态;而在相位差φ=0°、30°观察到的2/1模态,则观察到相位捕获;在f_d/f_e>1且不等于n（n=2,3……）时表现为相位滑移。然后,在振动幅值A/D=0.2～0.7,振动频率比f_e/f_st=0.5～1.8的范围内研究了间距比对横流向同相强迫振动双圆柱的影响。随间距比增大,结构的运动响应模态组成由简单变得复杂,主要表现为高阶同步模态的增多,模态区域的增多。在间距比L/D为2.5、5.0时,观察到高阶同步区域;且在L/D=5.0的低频率比条件下,上、下游圆柱均观察到f_d/f_e>1的同步区域,且部分工况控制频率为f_st。对结构受力分析,在频率比较大时,间距比L/D=1.5、5.0的值均大于L/D=2.5。通过分析圆柱横流向强迫振动的位移和圆柱横流向受力的相位差,在L/D=5.0时,f_d/f_e>1的模态的相位动力学特征表现均为相位滑;且对f_d/f_e=2、5/3时相位动力学特征,不同于在L/D=2.5的相位捕获、相位滑移。最后,在振动幅值A/D=0.2～0.7,振动频率比f_e/f_st=0.5～1.8的范围内研究了直径比对横流向同相强迫振动双圆柱的影响。随直径比减小,结构的运动响应模态组成由复杂变得简单,主要表现为高阶同步模态的减少,模态区域的减少;且1/1模态区域随直径比减小而减少。对结构受力分析,频率比较大时,上游圆柱受力随直径比减小增加,曲线上抬;下游圆柱受力随直径比减小而减小,使得上、下游圆柱之间的差值变大。且随直径比减小,上游圆柱受力超过下游圆柱的范围增大。通过分析圆柱横流向强迫振动的位移和圆柱横流向受力的相位差,直径比d/D为0.75、0.5时,f_d/f_e>1的模态的相位动力学特征表现均为相位滑移,不同于d/D为1.0时,f_d/f_e=2、5/3表现的相位捕获、相位滑移。更多还原

【Abstract】 Vortex-Induced Vibration（VIV）problem of deepwater risers is an important research in ocean engineering.When the sea current passes through a submerged riser structure,alternating vortex shedding will be formed on its backflow side,which in turn causes periodic transverse lift and induces vortex-induced vibration response.And when multiple structures are placed in close proximity,a complex flow interference phenomenon is generated.Vortex-induced vibration is one of the important causes of fatigue damage of deep-water risers,and once the risers are fractured and damaged,the direct economic loss and environmental disaster will be very serious.In this paper,the time-domain numerical model of tandem twin circular cylinder fluid-structure coupling is established in the frame of Arbitrary Lagrangian-Eulerian（ALE）,and the equations are solved by the finite element method based on Characteristic Based Split（CBS）,and the spring method is adopted to carry out the mesh updating in the computational domain.The spring method is used to update the mesh in the ALE region of the computational domain.A two-dimensional numerical study of the tandem twin circular cylinder oscillating in the transverse flow direction is carried out by using this model,the effects on hydrodynamic characteristics of the phase difference,the spacing ratio and the diameter ratio on the oscillating tandem twin circular cylinder are investigated under the condition of Re=160.Firstly,the effect of phase difference is investigated in the range of oscillating amplitude A/D=0.2～0.7 and oscillating frequency ratio f_e/f_st=0.5～1.8.With the increase of the phase difference,the mode compositions of the structure become simpler from complex,which is mainly manifested in the reduction of the high-order synchronization mode,and the boundaries of the modal regions become distinct;and with the increase of the phase difference,there is an increasing of the 3/1 mode in the upstream cylinder.The phenomenon of 1/1 mode,high-order synchronization mode and quasi-period mode can be observed under different phase differences,and this combination phenomenon mostly occurs at the boundary of different modal regions,which is an important sign of modal transition.For the structural force,the lift force of the upstream cylinder is almost unaffected by the change of phase difference.The rule of the lift force of the downstream cylinder is consistent atφ=0°,30°,90°,and changes atφ=150°;the difference between the lift force of the upstream and downstream cylinder decreases gradually with the increase of the phase difference.By analyzing the phase difference between the displacement and lift force,the phase dynamics feature at f_d/f_e=3 exhibits phase slipping,both in synchronization and quasi-period mode;whereas phase trapping is observed in the 2/1 mode observed at the phase differenceφ=0°,30°;and in the case where f_d/f_e>1 and is not equal to n（n=2,3......）exhibits phase drifting.Then,the effect of the spacing ratio is investigated in the range of oscillating amplitudes A/D=0.2～0.7 and oscillating frequency ratios f_e/f_st=0.5～1.8.As the spacing ratio increases,the mode composition of the structure becomes complex from simple,which is mainly manifested by the increase of high-order synchronization mode and the increase of mode regions;high-order synchronization region can be observed at L/D of 2.5 and 5.0;and at low frequency ratio of L/D=5.0,synchronization region with f_d/f_e>1 is observed for both upstream and downstream cylinder,and the domain frequency of some conditions is f_st.For the structure force,the lift forces of L/D=1.5 and 5.0 are greater than that of L/D=2.5 at higher frequency ratios.The phase dynamic characteristic of the modes with f_d/f_e>1 at L/D=5.0 is all characterized by phase slipping;and the phase dynamic characteristics of the modes with f_d/f_e=2,5/3,are different from L/D=2.5.Finally,the effect of the diameter ratio is investigated in the range A/D=0.2～0.7 and f_e/f_st=0.5～1.8.The mode composition of the structure becomes simpler from complexity with decreasing diameter ratio,which is mainly manifested by the reduction of the high-order synchronization mode and the decrease of the mode regions;and the 1/1 mode region decreases with decreasing diameter ratio.When the frequency ratio is large,the lift force of upstream cylinder increases with the decrease of the diameter ratio;the lift force of downstream cylinder decreases with the decrease of the diameter ratio,which makes the lift differences between the upstream and downstream become larger.And with the decrease of diameter ratio,the range of upstream cylinder force over downstream cylinder increases.By analyzing the phase difference,the phase dynamic characteristic of the mode with f_d/f_e>1 at the diameter ratios of d/D=0.75and 0.5 are all characterized by phase slipping,which is different from the phase trapping and phase drifting exhibited by f_d/f_e=2 and 5/3 at d/D=1.0.更多还原