Pore pressure on a submarine pipeline in a cross-anisotropic nonhomogeneous seabed under water-wave loading

1999 ◽  
Vol 36 (3) ◽  
pp. 563-572 ◽  
Author(s):  
D S Jeng ◽  
Y S Lin
Keyword(s):  
Pore Pressure ◽  
Element Model ◽  
Relative Difference ◽  
Soil Characteristics ◽  
Pipe Surface ◽  
Pressure Pipeline ◽  
Submarine Buried Pipeline ◽  
Anisotropic Soil ◽  
Soil Behaviour ◽  
Wave Induced

Conventional investigations for the wave–seabed–pipe interaction problem have dealt with a uniform and isotropic seabed, despite the influences of anisotropic soil behaviour and variable soil characteristics. This paper proposes a finite-element model to investigate the effects of cross-anisotropic soil behaviour and variable soil characteristics (permeability and shear modulus) on the wave-induced oscillatory pore pressures on a submarine buried pipeline. The present model is verified with previous experimental data for the case of a uniform and isotropic seabed. The numerical results indicate that the effects of cross-anisotropic soil behaviour and variable soil characteristics on the pore pressure around the pipe surface cannot always be ignored. The maximum relative difference of pore pressure may reach 10% of the amplitude of the wave pressure at the seabed surface.Key words:pore pressure, pipeline, cross-anisotropic, nonhomogeneous

scholarly journals 3-D Poro-Elastoplastic Model for Short-Crested Wave-Induced Pore Pressures in a Porous Seabed

2015 ◽  
Vol 9 (1) ◽  
pp. 408-416 ◽  
Author(s):  
Z. S. Wong ◽  
C. C. Liao ◽  
D. S. Jeng
Keyword(s):  
Pore Pressure ◽  
Present Model ◽  
Three Dimensional ◽  
Volumetric Strain ◽  
Soil Characteristics ◽  
Elastoplastic Model ◽  
Experiment Data ◽  
Pore Pressures ◽  
Wave Induced ◽  
Plastic Volumetric Strain

In this paper, a three-dimensional poro-elastoplastic model for the short-crested wave-induced pore pressures in a porous seabed is presented. Unlike the previous models, both elasticity and plasticity of seafloor are considered in the present model. This study considers the effects of wave and soil characteristics on the pore pressures and was validated with the previous wave experiment data. As the numerical analysis shows, higher value of plastic parameter leads to a faster residual pore pressure accumulation, which is closely related to the occurrence of seabed liquefaction. In particular, at the dissipation stage, residual pore pressure sharply decreases when enlarging plastic parameter , which dominates the velocity of accumulation of plastic volumetric strain.

scholarly journals Effective stresses in a porous seabed of finite thickness: inertia effects

2000 ◽  
Vol 37 (6) ◽  
pp. 1383-1392 ◽  
Author(s):  
D S Jeng ◽  
M S Rahman
Keyword(s):  
Pore Pressure ◽  
Finite Thickness ◽  
Relative Difference ◽  
Inertia Force ◽  
Soil Conditions ◽  
Inertia Effects ◽  
Effective Stresses ◽  
Present Solution ◽  
Wave Induced ◽  
Inertia Forces

The evaluation of wave-induced pore pressure and effective stresses is an important factor in the design of offshore installations. However, to simplify a complicated problem, most previous investigations have ignored the effects of inertia forces. This paper presents a new semi-analytical solution to the equations governing the wave-induced seabed response, including inertia terms for the whole problem. The numerical results show that the inertia forces cannot always be ignored. The relative difference between the present solution (with inertia items) and the previous solution (without inertia items) may reach 17% of po under certain combinations of wave and soil conditions. Key words: inertia force, pore pressure, effective stresses.

Cnoidal Wave-Induced Residual Liquefaction in Loosely Deposited Seabed under Coastal Shallow Water

2021 ◽  
Vol 11 (24) ◽  
pp. 11631
Author(s):  
Xiuwei Chai ◽  
Jingyuan Liu ◽  
Yu Zhou
Keyword(s):  
Shallow Water ◽  
Pore Pressure ◽  
Water Environment ◽  
Lateral Spreading ◽  
Stokes Wave ◽  
Cnoidal Wave ◽  
Liquefaction Resistance ◽  
Liquefaction Process ◽  
Wave Induced ◽  
Seabed Soil

This study is aimed at numerically investigating the cnoidal wave-induced dynamics characteristics and the liquefaction process in a loosely deposited seabed floor in a shallow water environment. To achieve this goal, the integrated model FSSI-CAS 2D is taken as the computational platform, and the advanced soil model Pastor–Zienkiewicz Mark III is utilized to describe the complicated mechanical behavior of loose seabed soil. The computational results show that a significant lateral spreading and vertical subsidence could be observed in the loosely deposited seabed floor due to the gradual loss of soil skeleton stiffness caused by the accumulation of pore pressure. The accumulation of pore pressure in the loose seabed is not infinite but limited by the liquefaction resistance line. The seabed soil at some locations could be reached to the full liquefaction state, becoming a type of heavy fluid with great viscosity. Residual liquefaction is a progressive process that is initiated at the upper part of the seabed floor and then enlarges downward. For waves with great height in shallow water, the depth of the liquefaction zone will be greatly overestimated if the Stokes wave theory is used. This study can enhance the understanding of the characteristics of the liquefaction process in a loosely deposited seabed under coastal shallow water and provide a reference for engineering activities.

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.

scholarly journals Finite Element Modeling of Orthogonal Machining of Brittle Materials Using an Embedded Cohesive Element Mesh

2019 ◽  
Vol 3 (2) ◽  
pp. 36
Author(s):  
Behrouz Takabi ◽  
Bruce L. Tai
Keyword(s):  
Finite Element ◽  
Cutting Force ◽  
Cohesive Zone ◽  
Manufacturing Industry ◽  
Brittle Materials ◽  
Element Model ◽  
Relative Difference ◽  
Unstable Crack ◽  
Element Mesh ◽  
Regular Elements

Machining of brittle materials is common in the manufacturing industry, but few modeling techniques are available to predict materials’ behavior in response to the cutting tool. The paper presents a fracture-based finite element model, named embedded cohesive zone–finite element method (ECZ–FEM). In ECZ–FEM, a network of cohesive zone (CZ) elements are embedded in the material body with regular elements to capture multiple randomized cracks during a cutting process. The CZ element is defined by the fracture energy and a scaling factor to control material ductility and chip behavior. The model is validated by an experimental study in terms of chip formation and cutting force with two different brittle materials and depths of cut. The results show that ECZ–FEM can capture various chip forms, such as dusty debris, irregular chips, and unstable crack propagation seen in the experimental cases. For the cutting force, the model can predict the relative difference among the experimental cases, but the force value is higher by 30–50%. The ECZ–FEM has demonstrated the feasibility of brittle cutting simulation with some limitations applied.

scholarly journals Numerical Simulations of Wave-induced Soil Erosion in Silty Sand Seabeds

2019 ◽  
Vol 7 (2) ◽  
pp. 52 ◽  
Author(s):  
Zhen Guo ◽  
Wenjie Zhou ◽  
Congbo Zhu ◽  
Feng Yuan ◽  
Shengjie Rui
Keyword(s):  
Soil Erosion ◽  
Pore Pressure ◽  
Wave Height ◽  
Fine Particles ◽  
Critical Concentration ◽  
Mass Conservation ◽  
Wave Period ◽  
Silty Sand ◽  
Fluidized Particles ◽  
Wave Induced

Silty sand is a kind of typical marine sediment that is widely distributed in the offshore areas of East China. It has been found that under continuous actions of wave pressure, a mass of fine particles will gradually rise up to the surface of silty sand seabeds, i.e., the phenomenon called wave-induced soil erosion. This is thought to be due to the seepage flow caused by the pore-pressure accumulation within the seabed. In this paper, a kind of three-phase soil model (soil skeleton, pore fluid, and fluidized soil particles) is established to simulate the process of wave-induced soil erosion. In the simulations, the analytical solution for wave-induced pore-pressure accumulation was used, and Darcy flow law, mass conservation, and generation equations were coupled. Then, the time characteristics of wave-induced soil erosion in the seabed were studied, especially for the effects of wave height, wave period, and critical concentration of fluidized particles. It can be concluded that the most significant soil erosion under wave actions appears at the shallow seabed. With the increases of wave height and critical concentration of fluidized particles, the soil erosion rate and erosion degree increase obviously, and there exists a particular wave period that will lead to the most severe and the fastest rate of soil erosion in the seabed.

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