Analysis of vibration characteristics of lifting rigid pipe in deep-sea mining under ship movement

In deep sea mining systems, the bottom-suspended lifting rigid pipe, spanning several kilometers, exhibits significant deformations and nonlinear vibration characteristics under the influence of vessel motion and oceanic environment. This study focuses on the lifting rigid pipe applicable to deep sea mining systems operating at a water depth of 6000 m. An actual-scale model comprising the mining vessel, the lifting rigid pipe, lifting pumps, and the buffer station is established using the marine structural dynamics analysis software OrcaFlex. The effects of vortex-induced vibration and parameter excitation on the motion response and force characteristics of the rigid pipe are considered. The Iwan-Blevins wake oscillator model is employed for numerical simulations to analyze the impact of buffer station mass, flow velocity, and vessel heave motion on the vibration characteristics of the lifting rigid pipe. The results indicate that the lateral vibration band distribution in the middle section of the pipe is wider and exhibits more regular vibrations. With the increase in buffer station mass, the number of vibration modes excited in the pipe decreases, accompanied by a decrease in vibration amplitude. The lifting rigid pipe exhibits two different dynamic characteristics under different heave periods and amplitudes. For small-period and large-amplitude motions, significant parameter excitation phenomena occur, resulting in increased bending stress and VIV amplitudes in the pipeline.