Submarine debris flow impact on pipelines — Part II: Numerical analysis

doi:10.1016/j.coastaleng.2008.06.005

Coastal Engineering

Volume 56, Issue 1, January 2009, Pages 1-10

https://doi.org/10.1016/j.coastaleng.2008.06.005 Get rights and content

Abstract

Computational Fluid Dynamics (CFD) numerical analysis was employed to analyze the situations tested experimentally, as described in Part I. The methodology and results of the CFD analyses are discussed and compared with the observations made from the experiments. The numerical model performed satisfactorily with regard to obtaining the impact forces exerted on the model pipe as well as simulating the hydroplaning phenomenon and estimating slurry flow heights. The experimental results were combined with the results of the CFD analyses to develop a practical method to compute the drag force caused by a submarine debris flow impact on a pipeline. The CFD analyses provided some insight to the separated region characterization, but the attempt to analyze the vortex shedding phenomenon as observed in the experiments was unsuccessful. Additional studies are required for better understanding of both the separated region characteristics and vortex shedding.

Introduction

Computational Fluid Dynamics (CFD) numerical methods have been successfully used to analyze multiphase and multicomponent flows and to investigate fluid–structure interaction in various settings. The situations tested experimentally in this investigation as described in the accompanying paper (Zakeri et al., 2008), have been analyzed using the CFD software, ANSYS CFX 11.0. In the first paper, a method was proposed for estimating the drag force on a suspended or laid-on-seafloor pipeline when impacted by a submarine debris flow normal to its axis. The experimental data, which formed the basis of the proposed method, were complemented by the results of the CFD analysis. Herein, comparisons are made between the CFD theoretical predictions and the experimental results and the comparisons are discussed. The theory and methodology used to numerically analyze the flume experiments are discussed. Comments are also made on the limitations of the CFD numerical model.

Section snippets

CFD simulation approach and theory

ANSYS CFX 11.0 is a general purpose CFD program that includes a solver based on the finite volume (FV) method for unstructured grids, as well as pre- and post-processing tools for simulation definition and data extraction, respectively. The FV method uses the integral form of the conservation equations. With tetrahedra or hexahedra Control Volumes (CVs), unstructured girds are best adapted to the FV approach for complex 3D geometries (Ferziger and Perić, 2002). In general, there are two types

General

The experimental program consisted of measuring the drag and vertical forces exerted on a circular cylinder upon impact with a subaqueous clay-rich slurry gravity flow perpendicular to its axis. Two installation scenarios were modeled: 1) suspended pipeline, and 2) laid-on-seafloor pipeline. The experiments were carried out in a 0.2 m wide and 9.5 m long flume that was fully submerged in a tank filled with water. An instrumented pipe was placed 6.15 m downstream of the gate from where the

Slurry head flow characteristics

From the experimental data and observations such as hydroplaning, drag force response curve and wake characteristics it was inferred that the first 0.3 to 0.4 m of the slurry head features the ‘plug flow’ characteristics. That is, the velocity field within this section of the slurry flow is practically uniform and steady. Further, it was presupposed that the model pipe located above the flume base by a distance equal to its diameter can represent a suspended pipe prototype as long as the

Conclusions

The CFD multiphase numerical model performed very satisfactorily in simulating the flume experiments with respect to the analysis of the drag and vertical forces as well as the slurry flow characteristics such as hydroplaning, velocity fields and heights. The calculated results agreed well with those measured in the experimental program and made it possible to complement the experimental data for both the suspended pipe and laid-on-seafloor pipe models. Such numerical analysis tools may

Acknowledgements

The work presented here (ICG contribution No. 197) was supported by the Research Council of Norway through the Centre of Excellence, “International Centre for Geohazards (ICG)” and the Leif–Eiriksson stipend awarded to the first author. Their support is gratefully acknowledged. We also extend our thanks to the support staff at the CFX UK Technical Services Office of ANSYS Inc. as well as to Peter Gauer and Maarten Vanneste of the Norwegian Geotechnical Institute (NGI) for their help and input

References (9)

BarthT.J. et al.
The design and application of upwind schemes on unstructured meshes
American Institute of Aeronautics and Astronautics (AIAA)
(1989)
BrennenC.E.
Fundamentals of multiphase flow
(2005)
CFX
CFX Solver Models, CFX-Program (Version 11.0) Physical Modelling Documentation
(2007)
CFX
CFX Solver Theory, CFX-Program (Version 11.0) Theory Documentation
(2007)

There are more references available in the full text version of this article.

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Submarine debris flow impact on pipelines — Part II: Numerical analysis

Abstract

Introduction

Section snippets

CFD simulation approach and theory

General

Slurry head flow characteristics

Conclusions

Acknowledgements

The design and application of upwind schemes on unstructured meshes

American Institute of Aeronautics and Astronautics (AIAA)

Fundamentals of multiphase flow

CFX Solver Models, CFX-Program (Version 11.0) Physical Modelling Documentation

CFX Solver Theory, CFX-Program (Version 11.0) Theory Documentation