Experimental Investigation on Vortex-Induced Vibration of Deep-Sea Risers of Different Excitation Water Depths

The vortex-induced vibration test of the deep-sea riser was carried out with different excitation water depths in the wave-current combined water flume. By dimensionally changing the multi-stage water depth and hydrodynamic parameters such as outflow velocity at various water depths, the dynamic response parameters such as dominant frequency, dimensionless displacement and vibration trajectory evolution process of the riser under different excitation water depths were explored to reveal the sensitive characteristics of the dynamic response of vortex-induced vibration of the risers under different excitation water depths. The results show that different excitation water depths will change the additional mass of the riser and the fluid damping and other parameters, which will affect the spatial correlation and stability of the vortex shedding behind the riser. In the lock-in region, the distribution range of the characteristic frequency becomes narrow and centered on the lock-in frequency. The increase of the excitation water depth gradually advances the starting point of the lock-in region of the riser, and at the same time promotes the excitation of the higher-order vibration frequency of the riser structure. Within the dimensionless excitation water depth, the dominant frequency and dimensionless displacement are highly insensitive to the excitation water depth at high flow velocity. The change of the excitation water depth will interfere with the correlation of the non-linear coupling of the riser. The “8-shaped” gradually becomes irregular, and the vibration trajectories of the riser show “O-shape”, “X-shape” and “Crescent-shape”.