Meshfree Model for Wave-Seabed Interactions Around Offshore Pipelines

Xiao Wang,Dong-Sheng Jeng,Chia-Cheng Tsai

doi:10.3390/jmse7040087

Abstract

The evaluation of the wave-induced seabed instability around a submarine pipeline is particularly important for coastal engineers involved in the design of pipelines protection. Unlike previous studies, a meshfree model is developed to investigate the wave-induced soil response in the vicinity of a submarine pipeline. In the present model, Reynolds-Averaged Navier-Stokes (RANS) equations are employed to simulate the wave loading, while Biot’s consolidation equations are adopted to investigate the wave-induced soil response. Momentary liquefaction around an offshore pipeline in a trench is examined. Validation of the present seabed model was conducted by comparing with the analytical solution, experimental data, and numerical models available in the literature, which demonstrates the capacity of the present model. Based on the newly proposed model, a parametric study is carried out to investigate the influence of soil properties and wave characteristics for the soil response around the pipeline. The numerical results conclude that the liquefaction depth at the bottom of the pipeline increases with increasing water period (T) and wave height (H), but decreases as backfilled depth ( H b ), degree of saturation ( S r ) and soil permeability (K) increase.

Highlights

Offshore pipelines have been a commonly used facility for transportation of offshore oil and gas
The aim of this study is to investigate the wave-pipeline-seabed interactions around a trenched pipeline by employing the proposed time-dependent meshless seabed model
Zen and Yamazaki [53] introduced and verified the concept of “oscillatory” excess pore pressure by conducting a series of experiments, and their criterion to determine the soil oscillatory liquefaction is used in this study, which can be expressed as σ0(z, 0) ≤ ue(z, t) = −[p(0, t) − p(z, t)]

Summary

Introduction

Offshore pipelines have been a commonly used facility for transportation of offshore oil and gas. In addition to construction causes, another key failure mode is the wave-induced seabed instability in the vicinity of pipelines [1,2]. Ocean waves will exert fluctuations of dynamic pressures over the sea floor, which will further induce excess pore pressures and effective stresses within the seabed. The shear resistance in the vicinity of pipelines may be loss due to the liquefaction of surrounding soil, when the excess pore pressure increases. The mechanisms of the wave-induced soil liquefaction can be classified into two categories, residual and oscillatory, in accordance with the way how the excess pore pressure is generated [4]. The residual liquefaction mechanism is resulted from the build-up of pore pressure induced by volumetric contraction under cyclic loading [5].

Objectives

Results

Conclusion