Abstract: The study on the dynamic response of the PIP system under the effect of vortex-induced vibration is carried out for the vortex-induced vibration of the pipe-in-pipe system. The effects of different dimensionless wave numbers, inner and outer pipe diameter ratios, joint layer stiffness, and tension on the displacement response of the marine riser under the action of eddy excitation vibration are also analyzed. In the study, based on the Euler-Bernoulli double-beam theory and using the wake oscillator model, a dynamics model is established, and the expressions of the vibration response of the inner and outer pipes were obtained using the harmonic balance method. The results show that there is instability in the vibration of the PIP under the action of different dimensionless wave numbers and that the vibration of the pipe appears to vibrate at a single frequency in the seventh-order mode. In the high-frequency ratio region, with the increase of the dimensionless connection layer stiffness, the displacements of both internal and external pipes show a trend of first decreasing and then increasing, and gradually stabilizing. The effect of tension on the displacement of the external pipe is relatively complex, and the displacement of the internal pipe shows a decreasing trend with the increase of tension.

Key words: pipe-in-pipe system, Euler-Bernoulli double-beams, wake oscillator model, harmonic balance method, response studies