In this paper, the vortex-induced vibration experiment of the risers with different wall thicknesses in wave-flow combined water flume was carried out. The dynamic strain sensing technology was adopted. The sensitivity and micro evolution pattern of riser VIV response relative to wall thickness were examined by varying the wall thickness of various riser models, comparing the dimensionless root mean square of strain, vibration frequencies and trajectories by varying different wall thicknesses of the risers. The results indicate that the wall thickness does not have a large influence on the Strouhal numbers of the vibration of the risers, which are always around 0.18; the larger the wall thickness is, the earlier the lock-in region is jumped out, as wall thickness increases, the outflow velocity corresponding to the occurrence of an “8” or oblique “8” shape vibration trajectory continues to delay, and the velocity range for such trajectories gradually narrows.

Diameter design of the riser is a very important link in offshore riser engineering, which will affect a series of parameter changes of the riser. In this paper, the riser is a variable-diameter riser with different cross-sections spliced by riser sections with diameters of 18, 25, and 30. In the wave-flow combined flume, dynamic response parameters such as strain-time history curve and root-mean-square of dimensionless strain were obtained by changing the outflow velocity and diameter of the riser, the effect of variable diameter on vortex-induced vibration of the riser was studied in detail. The results show that the vibration amplitude of the variable diameter riser varies with the axial position of the riser, but the frequency is dominated by the excitation of the thickest section riser; the variable diameter riser is always dominated by the first-order frequency in the outflow velocity range, and the relationship between the in-line and the cross-flow dominant frequency is always 2 times. With the increase of the flow velocity, the root mean square value of strain increases steadily.