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 transferring oil, gas and other liquids from the seabed.Free spans may occur due to the natural uneven seabed or by under-scouring. Vortex InducedVibration (VIV) can happen in such free spans at high Reynolds number. Resonance will occur if the frequency of vortex shedding is close to the pipeline’s natural frequencyleading to its fatigue that canbreak the pipeline causing economical and environmental losses. In literature, there are differentmethods for suppressing the vortex shedding and pipeline vibration and consequent scouring under thepipe such as the usage of splitter plates. In this paper, the effect of splitter plate’s angle on the scouringbeneath the pipeline is studied experimentally. For this purpose, a new experimental setup is designedand constructed in order to allow for the cylinder to vibrate in both in-line and cross flow directionsover an erodible bed. The reduced velocity for the experiments is in the range of 2.45-5.06 withdifferent gap ratios.Experimental results indicate that the relative scour depth is reduced withincreasing the ratio of gap to pipe diameter. The relative vibration frequency approaches to a constantvalue for large gap ratio (1 < e < 2) and the pipe does not have more effect on the bed. Therefore,the usage of splitter plate with the angle of 0-30 degrees with the horizon reduces the scouring depthbelow the mean location of the pipe compared with a pipe without splitter plate. Vice versa, the resultswere reversed for the pipes which used splitter plates with the angle of 60-90 degrees.