Experimental Investigation of the Effect of Splitter Plate Angle on the Under-Scouring of Submarine Pipeline Due to Steady Current and Clear Water Condition

Submarine pipelines are appropriate method for transmission of oil and gas from sea bed. Free spans may occur due to the natural uneven seabed or by under-scouring. Vortex Induced Vibration (VIV) can happen in such free spans at high Reynolds number. Resonance occurs if the frequency of vortex shedding is close to the pipeline’s natural frequency leading to its fatigue that can break the pipeline causing economical and environmental losses. In literature, there are different methods for suppressing the vortex shedding and pipeline vibration and consequent scouring under the pipe such as the usage of splitter plates. In this paper, the effect of splitter plate’s angle on the scouring under the pipeline is studied experimentally. For this purpose, a new experimental setup is designed and constructed in order to allow for the cylinder to vibrate in both in-line and cross flow directions over an erodible bed. The reduced velocity for the experiments is in the range of 2.45-5.06 and gap ratio is zero. Experimental results indicate that the relative scour depth is reduced with increasing the ratio of gap to pipe diameter. By comparing between relative frequency and reduce velocity, we can conclude that the relative frequency gives a constant value for a large air gap ratio ( ) and also, the pipe has not more effect on the bed. Finally, the scouring depth below the mean location of vibration related to the pipes with a splitter plate and angles 0-30 degrees are less than those without a splitter plate. While, inversely, the scouring depth related to the pipes with a splitter plate and an angle between 60-90 is more than those without a splitter plate.