Abstract
This article derives the time scale of pipeline scour caused by 2D (long-crested) and 3D (short-crested) nonlinear irregular waves and current for wave-dominant flow. The motivation is to provide a simple engineering tool suitable to use when assessing the time scale of equilibrium pipeline scour for these flow conditions. The method assumes the random wave process to be stationary and narrow banded adopting a distribution of the wave crest height representing 2D and 3D nonlinear irregular waves and a time scale formula for regular waves plus current. The presented results cover a range of random waves plus current flow conditions for which the method is valid. Results for typical field conditions are also presented. A possible application of the outcome of this study is that, e.g., consulting engineers can use it as part of assessing the on-bottom stability of seabed pipelines.
Highlights
This article addresses the time scale of pipeline scour due to 2D andTo the best of our knowledge, no study exists in the open literature on the investigation of the time scale for scour beneath pipelines caused by 2D and 3D nonlinear irregular waves plus current
Myrhaug et al [1] provided the time scale for the equilibrium scour depth beneath pipelines exposed to 2D and 3D nonlinear irregular waves
A practical stochastic method is derived for the time scale of equilibrium pipeline scour due to 2D and 3D nonlinear irregular waves and current for wave-dominant flow valid for Ucwrms = Uc /(Uc + Urms ) in the range 0 to 0.5, wave steepness
Summary
This article addresses the time scale of pipeline scour due to 2D (long-crested) and. Myrhaug et al [1] provided the time scale for the equilibrium scour depth beneath pipelines exposed to 2D and 3D nonlinear irregular waves. Most of the works on pipeline scour have considered current alone, regular waves alone, and combined regular waves and current, except Sumer and Fredsøe [7], who provided results from an experimental investigation on scour beneath pipelines exposed to random waves plus current. Results are obtained adopting the Larsen et al [4] parameterized time scale formula for pipeline scour valid for regular waves plus current jointly with a stochastic method.
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