深海立管参激-涡激联合振动试验
Experiment on Vortex Induced Vibration of Deep Sea Risers Considering Parametric Excitations

深海立管在海流作用下发生涡激振动，在平台垂荡作用下发生参数激励振动，参数激励-涡激联合振动使立管动力特性更为复杂．在船舶拖曳水池通过拖车带动立管运动模拟均匀流下立管涡激振动，并设计频率和行程均可调的连杆装置带动连接立管顶端的弹簧，以模拟立管顶端受平台垂荡运动的影响，从而进行立管参数激励-涡激联合振动试验，研究流速、顶张力及参数激励对深海立管涡激振动的影响．结果表明，流速越大，立管振动应力越大，振动主频率越高；顶张力越大，振动应力越小，顶张力变化对立管涡激振动主频率影响不大；参数激励加剧了立管的涡激振动，立管振动应力随平台垂荡幅值增大而增大，随垂荡频率升高而增大，立管振动频率出现了参数激励频率的成分．
The dynamic behavior of deep sea risers is more complicated under vortex induced vibration(VIV)due to the current considering parametric excitations aroused by the heave of the platform. In this experiment，the riser model was dragged by a towing tank in the pool to imitate the riser’s movement of VIV under uniform current and the top of the model was connected to a tensioner，which was made by a linkage with controlled frequency and stroke，to imitate the influence of the heave of the platform to the top of the riser. In this way，the experiment of the riser under VIV considering parametric excitations was made and the effects of the current speed，top tension as well as the parametric excitations to the risers were studied. The results show that the vibration stress of riser increases as thecurrent speed increases and decreases as the top tension increases. The dominant frequency of riser is controlled by the current speed and is hardly influenced by the top tension. The VIV response of riser is larger due to the parametric excitation. The vibration stress of the riser increases as the heave amplitude or frequency of the platform increase. The parametric excitation frequency occurs and becomes a part of vibrational frequency of the riser