Experimental study on vortex-induced vibration of rough and smooth risers under variable incident angles arrangement

The interference effect between adjacent risers in a riser group has been an important research topic for a long time. To investigate the VIV responses of rough and smooth risers in a double riser system, and elucidate the impact of interference effect on rough and smooth risers. VIV experiments were conducted in a flume for rough and smooth risers under variable incident angles. The results indicate that the wake interference has the most significant impact on "lock-in" displacement when the roughness of the rough riser is lowest within the sub-critical Reynolds number range. The wake interference effect is more likely to exacerbate the vibration displacement of rough risers in the IL direction as the reduced velocity increases. Furthermore, the smooth riser at an incident angle of 0° is significantly excited by the wake from the rough riser, resulting in an expanded "lock-in" region, a shift in the dominant mode, and the excitation of higher-order frequency responses. The displacement response of the smooth riser at an incident angle of 90° is akin to that of an isolated smooth riser.