Impact of high-speed turbidity currents on offshore spanning pipelines

Abstract

Pipelines in the deep sea are at risk of damage due to submarine landslides, which can result in the loss of costly infrastructure and pollution stemming from hydrocarbon leaks. Submarine landslides can exhibit a wide range of flow characteristics, which in turn can affect how they interact with pipelines. Researchers have previously focused on pipelines impacted by submarine debris and/or mud flows described by non-Newtonian fluid rheological models and the laminar model. However, the impact of larger-scale and higher-speed submarine turbidity currents described by turbulence models on pipelines has been overlooked. In this study, we address this gap by utilizing a more accurate turbulence simulation method, namely, the large eddy simulation (LES) method, to analyze the effect of submarine turbidity currents on fixed spanning pipelines, and we validate the effectiveness of the proposed method via typical circular cylinder flow experiments and numerical simulations. We find that the lift force on the pipeline impacted by submarine turbidity currents under high-Reynolds number (Re) conditions is particularly significant relative to debris and/or mud flows under low-Re conditions. In parallel, the vortex shedding frequency increases with increasing Re, and the Strouhal number basically remains unchanged and ranges from 0.2–0.25 at 1,112 ≤ Re ≤ 333,559. Furthermore, the vortex structure and its arrangement behind the spanning pipeline become irregular with increasing Re, forming a turbulent vortex street, which reveals the mechanism of pipeline vibration. Finally, a methodology for predicting characteristic drag force and lift force coefficients is established for submarine pipeline design.