Mode transitions in vortex-induced vibrations of a flexible pipe near plane boundary

A pipe model with a mass ratio (mass/displaced mass) of 4.30 was tested to investigate the vortex-induced vibrations of submarine pipeline spans near the seabed. The pipe model was designed as a bending stiffness-dominated beam. The gap ratios (gap to diameter ratio) at the pipe ends were 4.0, 6.0, and 8.0. The flow velocity was systematically varied in the 0–16.71 nondimensional velocity range based on the first natural frequency. The mode transition between the first and the second mode as the flow velocity increases was investigated. At various transition flow velocities, the research indicates that the peak frequencies with respect to displacement are not identical along the pipe, nor the frequencies associated with the peak of the amplitude spectra for the first four modes as well. The mode transition is associated with a continuous change in the amplitude, but there’s a jump in frequency, and a gradual process along the pipe length.