Numerical study on hydrodynamic load and vibration of pipeline exerted by submarine debris flow

Abstract

Submarine debris flow, as one of the natural phenomena of marine disasters, often occurs in different sea areas, which has a strong impact on marine structure due to its large specific gravity and high velocity. Submarine pipeline is an important submarine structure which is extremely vulnerable to the marine environment, especially under the submarine debris flow. Many studies have been conducted on the interaction between the debris flow and the pipeline. Based on previous studies, the effects of the debris flows under the water-air interface on the pipeline with degree of freedom are investigated in this study where the debris flow volume, density, slide slope angle, the spring stiffness coefficient, pipeline location and tandem pipeline are considered. According to the computational fluid dynamics theory, a numerical tank is established using the Immersed Boundary (IB) method, in which the three-phase media (air, water and debris flow) are embedded. The results demonstrate that when the debris flow occurs, the water-air free surface is affected by the debris flow propagation, generating a surface wave. When the debris flow passes through the pipeline, with the increase of debris flow density and volume, the force on the pipeline increases, but the vibration frequency of pipeline decreases. Meanwhile, the vibrating pipeline will cause strong turbulence to the debris flow. In addition, the force and the vibration frequency of the pipeline are closely related to the flow pattern of debris flow reaching the pipeline. When the debris flow passes through the tandem pipeline, the closer the distance between the two pipelines is, the more significant the mutual influence between two pipelines is, because the negative pressure area formed behind the upstream pipeline can affect the downstream pipeline to a certain extent.