Numerical Analysis of Steep Wave-Induced Seabed Response and Liquefaction Around Gravity-Based Offshore Foundations

2018 ◽  
Author(s):  
Yuzhu Li ◽  
Muk Chen Ong ◽  
Ove Tobias Gudmestad ◽  
Bjørn Helge Hjertager
Keyword(s):  
Interaction Model ◽  
Wave Structure ◽  
Cylindrical Shape ◽  
Soil Consolidation ◽  
Order Stream ◽  
Soil Response ◽  
Pressure Distributions ◽  
Poroelastic Soil ◽  
Wave Induced ◽  
Fifth Order

Gravity-based offshore foundations generally consist of a bottom slab and one or more cylindrical shafts on top of it. The geometry of the structure can strongly affect the flow pattern, dynamic wave pressure and further soil response and the liquefaction risk in the vicinity of the foundation. In this work, gravity-based foundations with bottom slabs of cylindrical shape and hexagonal prismatic shape are investigated. An integrated wave-structure-seabed interaction model applied in this work is developed in Open-FOAM, incorporating a nonlinear wave solver, a linear elastic structure solver and an anisotropic Biot’s poroelastic soil solver consisting of consolidation and liquefaction modules. Soil consolidation behavior in the presence of the foundations is investigated. It is found that the corners of the hexagonal foundation cause stress concentration in the soil. Therefore the initial effective stress around the hexagon corners is relatively high. Then, fully nonlinear waves modelled by fifth-order stream functions are simulated. Wave-induced pressure distributions and momentary liquefaction depths around the foundations are predicted.

Wave-Induced Oscillatory Soil Response Around Circular Rubble-Mound Breakwater Head

2017 ◽  
Author(s):  
Dagui Tong ◽  
Chencong Liao ◽  
Jianhua Wang ◽  
Dongsheng Jeng
Keyword(s):  
Pore Pressure ◽  
Numerical Scheme ◽  
Wave Motion ◽  
Three Dimensional ◽  
Wave Structure ◽  
Soil Response ◽  
Seabed Interaction ◽  
Rubble Mound ◽  
Wave Induced

The wave-structure-seabed interaction (WSSI) around circular rubble-mound breakwater head is investigated using a three-dimensional (3D) numerical scheme. The result reveals that the presence of breakwater has strong effect on wave motion and seabed response. The turbulence induced by the breakwater head gives rise to extensive pore pressure around the breakwater head, which could further lead to liquefaction or scour and might eventually result in breakwater failure.

scholarly journals The effects of slab geometries and wave directions on the steep wave-induced soil response and liquefaction around gravity-based offshore foundations

2019 ◽  
Vol 15 (8) ◽  
pp. 866-877
Author(s):  
Yuzhu Li ◽  
Muk Chen Ong ◽  
Ove Tobias Gudmestad ◽  
Bjørn Helge Hjertager
Keyword(s):  
Soil Response ◽  
Wave Induced ◽  
Steep Wave

scholarly journals Wave-Induced Seabed Response around a Dumbbell Cofferdam in Non-Homogeneous Anisotropic Seabed

2019 ◽  
Vol 7 (6) ◽  
pp. 189 ◽  
Author(s):  
Linya Chen ◽  
Dong-Sheng Jeng ◽  
Chencong Liao ◽  
Dagui Tong
Keyword(s):  
Shear Modulus ◽  
Vertical Distribution ◽  
Pore Pressure ◽  
Wave Structure ◽  
Offshore Structures ◽  
Hydrodynamic Process ◽  
Response Analysis ◽  
Depth Function ◽  
Wave Induced ◽  
The Vertical Distribution

Cofferdams are frequently used to assist in the construction of offshore structures that are built on a natural non-homogeneous anisotropic seabed. In this study, a three-dimensional (3D) integrated numerical model consisting of a wave submodel and seabed submodel was adopted to investigate the wave–structure–seabed interaction. Reynolds-Averaged Navier–Stokes (RANS) equations were employed to simulate the wave-induced fluid motion and Biot’s poroelastic theory was adopted to control the wave-induced seabed response. The present model was validated with available laboratory experimental data and previous analytical results. The hydrodynamic process and seabed response around the dumbbell cofferdam are discussed in detail, with particular attention paid to the influence of the depth functions of the permeability K i and shear modulus G j . Numerical results indicate that to avoid the misestimation of the liquefaction depth, a steady-state analysis should be carried out prior to the transient seabed response analysis to first determine the equilibrium state caused by seabed consolidation. The depth function G j markedly affects the vertical distribution of the pore pressure and the seabed liquefaction around the dumbbell cofferdam. The depth function K i has a mild effect on the vertical distribution of the pore pressure within a coarse sand seabed, with the influence concentrated in the range defined by 0.1 times the seabed thickness above and below the embedded depth. The depth function K i has little effect on seabed liquefaction. In addition, the traditional assumption that treats the seabed parameters as constants may result in the overestimation of the seabed liquefaction depth and the liquefaction area around the cofferdam will be miscalculated if consolidation is not considered. Moreover, parametric studies reveal that the shear modulus at the seabed surface G z 0 has a significant influence on the vertical distribution of the pore pressure. However, the effect of the permeability at the seabed surface K z 0 on the vertical distribution of the pore pressure is mainly concentrated on the seabed above the embedded depth in front and to the side of the cofferdam. Furthermore, the amplitude of pore pressure decreases as Poisson’s ratio μ s increases.

NUMERICAL MODELLING OF WAVE-INDUCED SOIL RESPONSE AROUND BREAKWATER HEADS

2011 ◽  
pp. 789-796
Author(s):  
D.-S. JENG ◽  
Y. ZHANG ◽  
J.-S. ZHANG ◽  
C. ZHANG ◽  
P. L.-F. LIU
Keyword(s):  
Numerical Modelling ◽  
Soil Response ◽  
Wave Induced

Effects of river bed restructuring on fish and benthos of a fifth order stream, melk, Austria

1993 ◽  
Vol 8 (1-2) ◽  
pp. 195-204 ◽  
Author(s):  
Mathias Jungwirth ◽  
Otto Moog ◽  
Susanne Muhar
Keyword(s):  
Order Stream ◽  
River Bed ◽  
Fifth Order

Numerical Modelling of Wave-Induced Pore Pressure Around a Buried Pipeline: WSPI-3D Model

2010 ◽  
Author(s):  
Behnam Shabani ◽  
Dong-Sheng Jeng ◽  
Jianhong Ye ◽  
Yakun Guo
Keyword(s):  
Pore Pressure ◽  
3D Model ◽  
Present Model ◽  
Three Dimensional ◽  
Comsol Multiphysics ◽  
Fe Model ◽  
Soil Consolidation ◽  
Buried Pipeline ◽  
Wave Induced ◽  
Soil Responses

In this paper, a three-dimensional numerical model is developed to analyze the ocean wave-induced seabed response. The pipeline is assumed to be rigid and anchored within a trench. Quasi-static soil consolidation equations are solved with the aid of the proposed Finite Element (FE) model within COMSOL Multiphysics. The influence of wave obliquity on seabed responses, the pore pressure and soil stresses, are studied. A comprehensive tests of FE meshes is performed to determine appropriate meshes for numerical calculations. The present model is verified with the previous analytical solutions without a pipeline and two-dimensional experimental data with a pipeline. Numerical results suggest that the effect of wave obliquity on soil responses can be explained through the following two mechanisms: (i) geometry-based three-dimensional influences, and (ii) the formation of inversion nodes. However, the influences of wave obliquity on the wave-induced pore pressure are insignificant.

scholarly journals DYNAMIC RESIDUAL SEABED RESPONSE AROUND A MOVABLE PILE FOUNDATION

2018 ◽  
pp. 20
Author(s):  
Titi Sui ◽  
Chi Zhang ◽  
Jinhai Zheng ◽  
Dong-Sheng Jeng
Keyword(s):  
Pile Foundation ◽  
Wave Model ◽  
Residual Soil ◽  
Governing Equations ◽  
Soil Response ◽  
Oscillatory Mechanism ◽  
Soil Skeleton ◽  
Inertial Terms ◽  
Residual Response ◽  
Wave Induced

Wave-induced seabed soil response and its resultant liquefaction is common observed in a silt seabed with relative poor drainage condition, which poses a great threaten to the foundation safety of marine structures. Regarding the governing equations, three different approaches namely the Fully-dynamic (FD), Partialdynamic (PD) and Quasi-static (QS) model, have been used in the previous studies. Among these, both PD and FD approaches consider the effect of the inertial terms of soil skeleton/fluid. It has been reported in the literature that effects of the inertial terms on the seabed response could not be neglected, especially for the seabed around a movable structure (Ulker et al., 2010). However, these studies only focused on the oscillatory mechanism which are probably seen in a sandy seabed with high permeability. Recently, Zhao et al. (2017) investigated the residual soil response around a pile foundation by integrating a RANS wave model and a QS seabed model. In their study, the inertial terms of soil skeleton and pore water were neglected. To the authors’ best knowledge, up to now, effects of the inertial terms on the residual response of a silt seabed have not been investigated.

Simple Numerical Models for Pipeline Walking Accounting for Mitigation and Complex Soil Response

2011 ◽  
Author(s):  
Daniel Carneiro ◽  
David Murphy
Keyword(s):  
Numerical Models ◽  
Three Dimensional ◽  
Interaction Model ◽  
Soil Response ◽  
Dimensional Finite Element ◽  
Loading And Unloading ◽  
Three Dimensional Finite Element ◽  
Internal Pressures ◽  
Subsea Pipelines ◽  
Pipeline Design

Non-buried subsea pipelines subjected to high internal pressures and high operational temperatures (HP/HT) may experience significant axial expansion. Asymmetries in the loading and unloading in startups and shutdowns (e.g. due to seabed slope, temperature transients or riser tension) may cause the axial displacements to accumulate over operational cycles, in a ratcheting process often called “pipeline walking”. Despite the complexity of the pipe-soil interaction governing this behavior, several analytical and simple numerical models have been used for estimating the total accumulated pipeline axial displacement. These simple models are powerful tools in preliminary phases of a pipeline design, although their use is limited due to the simplifications. This paper presents results of a simple numerical model able to account for additional features in the preliminary walking assessment, such as loads on mitigation systems. The models were originally prepared to assess walking mitigation for some rigid flowlines in a recently installed subsea system, and remarkable agreement with complex three-dimensional finite element models was observed. The effect of different types of mitigation systems on the global behavior of the pipelines is presented and discussed. The influence of the pipe-soil interaction model employed is also investigated.

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