Evaluation of horizontal submarine slide impact force on pipeline via a modified hybrid geotechnical – fluid dynamics framework

Abstract

There are situations in offshore energy development where potential impact forces between submarine slides and pipelines need to be estimated. The horizontal slide-pipeline impact force, parallel to the main travel direction of the sliding mass and normal to the pipeline axis, is generally dominant compared to other force components, and hence of particular concern. In practice, pipelines may be suspended at varying distances above the seabed (gap) and existing methods do not consider how this will affect the horizontal slide-pipeline forces. This paper investigates the effects of pipeline-seabed gap and pipeline diameter on the horizontal slide-pipeline impact force via 181 computational fluid dynamics (CFD) simulations at Reynolds numbers of 0.36 - 287. Results show that variation in the pipeline-seabed gap and pipeline diameter alters the slide mass flow behavior as it flows past the pipeline and hence the impact force when the pipeline-seabed gap is below a critical value. A modified hybrid geotechnical-fluid dynamics framework for estimating the horizontal impact force is proposed by considering the effects of the pipeline-seabed gap and pipeline diameter, which is validated with existing experimental datasets.

Feasibility of submerged floating tunnel with polygonal cross-sections — investigation from a viewpoint of submarine slide hazards

“…In addition, the load level of peak horizontal impact forces is higher than that of peak vertical impact forces, which is mainly related to the tunnelseabed gap size (two times of tunnel diameter) in this study. Meanwhile, the influence of the thickness conditions of submarine slides on peak impact forces can also be found, and similar results of previous studies (forces during the submarine slide-pipeline interaction, with a thicker thickness compared with pipelines and gap ratio of 2.0, from Fan et al, 2021a;Fan et al, 2021b) are also presented and compared. It can be seen that the impact forces vary greatly with different slide mass thicknesses; In addition, some results of this study (H t /D=10.0 and 11.0, with a larger thickness) are close to those of previous studies.…”

“…The standard k-ϵ model was adopted for turbulence enclosure. The reliability of the above numerical modelling process on submarine slide-structure interaction has been well verified by the data from flume experiments and geo-centrifuge experiments in previous studies (e.g., Zakeri et al, 2009;Zakeri and Hawlader, 2013;Fan et al, 2018;Fan et al, 2021a).…”

“…The position of the polygonal tunnels was set against a distance of 5.5D from the left boundary of the computational domain to the tunnel center (here, the tunnel structure was set as fixed to reflect its normal working state). The gap between the tunnel bottom and seabed surface (H ps ) was adopted 2D to reduce the influence of velocity boundary layers on the seabed surface (Fan et al, 2021a). Then, the computational domain was meshed via the ICEM-CFD module in the ANSYS Workbench, based on the rules of using tetrahedral elements.…”

“…It should be noted that the expression in the flooded impact state is a hybrid geotechnical-fluid dynamics framework for evaluating the impact forces during the submarine slide-cylindrical structure interaction with a large enough slide mass thickness. The determination method of those coefficient values can refer to previous studies (Fan et al, 2021a;Fan et al, 2021b).…”

“…Through the above results analysis, existing evaluation approaches show limitations in predicting the impact forces of submerged floating tunnels with polygonal cross-section under the impact of submarine slides. On the one hand, the approach for evaluating the impact forces during the submarine slides-cylindrical structures (e.g., pipelines, from Fan et al, 2021a;Fan et al, 2021b) interaction cannot cover the results at a partial impact state. On the other hand, the impact forces during submarine slides-tunnels interaction of the polygonal tunnel have differences from circular tunnels.…”