Time Scale of Scour Below Submarine Pipeline Under Combined Waves and Currents With Oblique Incident Angle Available to Purchase

Available formulae for the time scale of scour below a submarine pipeline are so far mainly restricted to waves-only and currents-only conditions with normal incidence and no burial of the pipeline. This paper presents experimental results on temporal and spatial developments of local scour below a partially buried pipeline under combined waves and currents with oblique incident angle. There are also some tests with waves-only and current-only conditions for validation purpose. All tests were conducted under live-bed conditions. The maximum Shields parameter is used to formulate the nondimensional time scale of local scour under combined waves and current conditions. The effects of flow incident angle and embedment depth on the time scale of scour were investigated. The results show that the time scale increases with the increase of incident angle and also increases with the increase of the embedment depth for combined waves and current conditions. The effective shields parameter is applied to account for the effect of the oblique incident angle based on the fact that both the normal component and the axial components of the flow contribute to the scour process when the currents or waves approach the pipeline with an oblique angle. It is found that the previously proposed empirical formula for time scale of scour for waves-only and current-only conditions, is also applicable to the combined waves and current conditions, if the maximum Shields parameter is used as the governed parameter in quantifying the time scale.