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

Abstract

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 Induced Vibration (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 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 beneath 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 with different gap ratios. Experimental results indicate that the relative scour depth is reduced with increasing the ratio of gap to pipe diameter. The relative vibration frequency approaches to a constant value 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 depth below the mean location of the pipe compared with a pipe without splitter plate. Vice versa, the results were reversed for the pipes which used splitter plates with the angle of 60-90 degrees.