Numerical study of scour around a pipeline bundle

A well-established two-dimensional numerical model was employed to study the scour-hole development around a pipeline bundle, which was composed of a main pipeline and a piggyback pipeline. Both the current and wave flow situations were simulated with parameters chosen to represent prototype pipeline scour in adverse weather conditions. Under the same hydraulic and soil conditions, the scour around the main pipeline alone and around an equivalent pipeline was also simulated, and these served as reference cases for studying the scour around pipeline bundles. The focus of this paper is the equilibrium scour depth and the development rate. It was found that the pipeline bundle produced a deeper scour depth with a larger time-scale in comparison with the scour occurring for the single-pipeline case; thus the equivalent-pipeline representation may lead to an unsafe design. The differences between the pipeline bundle and single pipeline scour were larger under the current alone flow condition than those under the wave condition. These differences in the scour development can be explained by examining the flow fields around the pipeline.