Model test study on hydrodynamic characteristics of submarine pipelines with spiral strakes

To reveal the influence of free surface variation on the hydrodynamic loads of submarine pipelines with spiral strakes installed and verify the vortex-induced vibration (VIV) suppression effect of spiral strakes under partial detachment, hydrodynamic model tests were conducted on submarine pipelines equipped with spiral strakes. The tests investigated the changes in drag coefficient in the near-free-surface region (with a ratio of immersion depth to pipeline diameter is 1-4) and the near-false bottom region (with a ratio of bottom clearance to pipeline diameter is 1-4) under different Reynolds numbers. Additionally, the VIV suppression effect of spiral strakes was analyzed when 30% of their length was damaged. The test results show that when the submarine pipeline is immersed from a depth of four times the diameter to approaching the free surface, its drag coefficient gradually increases; when the submarine pipeline approaches the false bottom from an initial distance of four times the diameter, its drag coefficient decreases. With the increase in the Reynolds number, the suppression efficiency of VIV by the 30% damaged spiral strake exhibits a trend similar to that of the full-coverage scheme, both showing a decrease. Nevertheless, it still maintains a considerable suppression effect.