Vortex-induced vibration mechanism of drilling riser under shear flow

Vortex-induced vibration of the drilling riser under shear flow was studied by experimental method, and the characteristic parameters of vortex-induced vibration under the shear flow were obtained. The vortex-induced vibration response in both in-line and cross-flow directions were captured by measuring technique based on the fiber Bragg grating sensor. The influence of the pre-tension during the experiment was eliminated and the experimental data was analyzed by modal analysis method. Results show that, under the shear flow, the shedding frequencies at different locations are different, however the dominant frequencies of the drilling riser at different locations are the same; when the vortex shedding frequency is close to the maximum order of the natural frequency, the lock-in phenomenon occurs, and the dominant frequency equals to this natural frequency; the vortex-induced vibration caused by shear flow is in the form of multi-modal for the influence of modal competition; a single vibration period of the riser's displacement trajectory appears as an inclined “8” shape, and the multiple vibration period of the riser's overlapped displacement trajectory appears as a crescent shape in the experimental condition.