STUDY ON VORTEX-INDUCED VIBRATION SUPPRESSION OF MARINE RISER BASED ON ENERGY TRANSFER

Vortex-induced vibration is an important factor which may cause serious fatigue damage of marine risers. The suppression of vortex-induced vibrations can ensure structural safety and prolong service life of marine risers. Most of the suppression methods of vortex-induced vibrations are based on disturbing the flow fields. In some complex environmental conditions, only disturbing the flow fields behind marine risers may have limited effect on the suppression of vortex-induced vibration. Therefore, the vortex-induced vibration suppression of marine risers was studied from the perspective of structure. Based on the theory of energy transfer, the law of energy transfer during vortex-induced vibrations of marine riser was described. The vibration energy propagates from the energy input region to the energy dissipation region in the form of traveling wave and is mainly consumed in the energy dissipation region. By locally increasing the damping in the energy dissipation region, the consumption of vibration energy in the propagation process can be increased to achieve the suppression of vortex-induced vibrations. In order to solve the vortex-induced vibration response of the marine riser, a theoretical model was established based on the wake oscillator model, and the reliability of the theoretical model was verified by the experimental results. The energy input region and energy dissipation region of the vortex-induced vibrations were determined by the energy coefficients calculated from the theoretical method. The suppression effect of the vortex-induced vibrations was studied by comparing the response of the marine riser before and after increasing the damping. If the damping in the energy input region is increased, the suppression effect of vortex-induced vibrations is not obvious. The vibration displacements in the upper and bottom locations of the marine riser significantly decrease when the energy attenuation coefficient reaches the critical value by increasing the damping in the energy dissipation region. When the energy attenuation coefficient exceeds the critical value, the suppression effect of vortex-induced vibrations is not improved by increasing damping in the energy dissipation region.