Solving Downslope Pipeline Walking on Non-Linear Soil With Brittle Peak Strength and Strain Softening

2017 ◽  
Author(s):  
Adriano Castelo ◽  
David White ◽  
Yinghui Tian
Keyword(s):  
Finite Element ◽  
Strain Softening ◽  
Peak Strength ◽  
Design Stage ◽  
Rigid Plastic ◽  
Soil Model ◽  
Interaction Behavior ◽  
Study Results ◽  
Non Linear

In 2000 the first case of pipeline walking (PW) was properly documented when this phenomenon seriously impacted a North Sea high pressure and high temperature (HP/HT) pipeline (Tornes et al. 2000). By then, the main drivers of this problem were accordingly identified for the case studied. On the other hand, to study other aspects related not only to PW, the industry joined forces in the SAFEBUCK Joint Industry Project (JIP) with academic partners. As a result, other drivers, which lead a pipeline to walk, have been identified (Bruton et al. 2010). Nowadays, during the design stage of pipelines, estimates are calculated for pipeline walking. These estimates often use a Rigid-Plastic (RP) soil idealization and the Coulomb friction principle (Carr et al. 2006). Unfortunately, this model does not reflect the real pipe-soil interaction behavior, and in practice time consuming finite element computations are often performed using an Elastic-Perfectly-Plastic (EPP) soil model. In reality, some observed axial pipe-soil responses are extremely non-linear and present a brittle peak strength before a strain softening response (White et al. 2011). This inaccuracy of the soil representation normally overestimates the Walking Rate (WR) (a rigid plastic soil model leads to greater walking). A magnified WR invariably leads to false interpretations besides being unrealistic. Finally, a distorted WR might also demand mitigating measures that could be avoided if the soil had been adequately treated. Unnecessary mitigation has a very strong and negative effect on the project as whole. It will require more financial and time investments for the entire development of the project — from design to construction activities. Therefore, having more realistic and pertinent estimates becomes valuable not only because of budgetary issues but also because of time frame limits. The present paper will show the results of a set of Finite Element Analyses (FEA) performed for a case-study pipeline. The analyses — carried out on ABAQUS software — used a specific subroutine code prepared to appropriately mimic Non-Linear Brittle Peak with Strain Softening (NLBPSS) axial pipe-soil interaction behavior. The specific subroutine code was represented in the Finite Element Models (FEMs) by a series of User Elements (UELs) attached to the pipe elements. The NLBPSS case is a late and exclusive contribution from the present work to the family of available pipeline walking solutions for different forms of axial pipe-soil interaction model. The parametric case-study results are benchmarked against theoretical calculations of pipeline walking showing that the case study results deliver a reasonable accuracy level and are reliable. The results are then distilled into a simplified method in which the WR for NLBPSS soil can be estimated by adjusting a solution derived for RP and EPP soil. The key outcome is a genuine method to correct the WR resultant from a RP soil approach to allow for peak and softening behaviour. It provides a design tool that extends beyond the previously-available solutions and allows more rapid and efficient predictions of pipeline walking to be made. This contribution clarifies, for the downslope walking case, what is the most appropriate basis to incorporate or idealize the soil characteristics within the axial Pipe-Soil Interaction (PSI) response when performing PW assessments.

Seismic Fault Displacement of Buried Pipelines Using Continuum Finite Element Methods

2009 ◽  
Author(s):  
Lanre Odina ◽  
Roger Tan
Keyword(s):  
Finite Element ◽  
Large Deformation ◽  
Ground Deformation ◽  
Slope Instability ◽  
Asia Pacific ◽  
The Arctic ◽  
Design Stage ◽  
Buried Pipeline ◽  
Non Linear ◽  
Fault Displacement

In deep waters, pipelines are usually installed exposed on the seabed, as burial is generally not required to ensure on-bottom stability. These exposed pipelines are nevertheless susceptible to seismic geohazards like slope instability at scarp crossings, soil liquefaction and fault movements which may result in failure events, although larger diameter pipelines are generally known to have good tolerances to ground deformation phenomena, provided the seismic magnitudes are not too onerous. Regardless of the pipeline size, these seismic geohazard issues are usually addressed during the design stage by routing the pipeline to avoid such hazardous conditions, where possible. However, extreme environmental conditions like hurricanes or tropical cyclones, which are typically experienced in the Gulf of Mexico and Asia-Pacific regions, are also factors which can cause exposed pipelines to be susceptible to large pipeline displacements and damage. Secondary stabilisation in the form of rock dump is sometimes employed to reduce the hydrodynamic loads from high turbidity currents acting on the pipeline. However, rock dumping (or burying the displaced pipeline) on a fault line could again pose a threat to its integrity following a seismic faulting event. The traditional method of assessment of a buried pipeline subjected to seismic faulting is initially carried out using analytical methods. Due to the limitations of these techniques for large deformation soil movement associated with fault displacement, non-linear finite element (FE) methods are widely used to assess the pipeline integrity. The FE analysis typically idealises the pipeline using discrete structural beam-type elements and the pipeline-soil interaction as discrete non-linear springs, based on the concept of subgrade reactions proposed by Winkler. Recent research from offshore pipeline design activities in the arctic environment for ice gouge events have however suggested that the use of the discrete Winkler element model leads to over-conservative results in comparison to the coupled continuum model. The principal reason for the conservatism is related to the poor modeling of realistic surrounding soil behaviour for large deformation events. This paper discusses the application of continuum FE methods to model the fully coupled seabed-buried pipeline interaction events subject to ground movements at active seismic faults. Using the continuum approach, a more realistic mechanical response of the pipeline is established and can be further utilised to confirm that calculated strains are within allowable limits.

Development of Simple Design-Oriented Procedure for Predicting the Collision Damage of FPSO Caisson Protection Structures

2010 ◽  
Author(s):  
Sang-Rai Cho ◽  
Jang-Hyun Jeong ◽  
Paul A. Frieze
Keyword(s):  
Structural Design ◽  
Parametric Study ◽  
Design Stage ◽  
Test Results ◽  
Simple Analytical Expression ◽  
Study Results ◽  
Commercial Package ◽  
Non Linear ◽  
Modification Factor ◽  
Protection Structures

Protection structures for FPSO caissons are required to be strong enough not to contact caisson pipes even when the protection structure is damaged by impact by attendant vessels. In the present structural design process, non-linear commercial packages are employed for the collision analyses. However, non-linear collision analyses using commercial packages are still time-consuming and expensive to operate especially at the initial design stage. In this study, validation of the adopted commercial package was firstly performed using collision test results on unstiffened tubulars. Then, a rigorous parametric study was conducted on simple protection structures by changing the collision velocity and the scantling of the protection structure. A simple analytical expression was derived assuming that the kinetic energy of the striking vessel is dissipated by plastic elongation of tubulars and rotation of plastic hinges. Using the parametric study results, an equation for the modification factor was obtained by which the effects of local denting and dynamic behavior can be considered. The developed procedure was also substantiated using numerically predicted extent of damages of an actual protection structure.

scholarly journals Comparative Study of Peridynamics and Finite Element Method for Practical Modeling of Defects Cracks in Topology Optimization

Symmetry ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1407
Author(s):  
Peyman Lahe Motlagh ◽  
Adnan Kefal
Keyword(s):  
Finite Element ◽  
Topology Optimization ◽  
Comparative Study ◽  
Strain Energy ◽  
Optimality Criteria ◽  
Design Stage ◽  
Design Domain ◽  
Optimum Topology ◽  
Strain Stress

Recently, topology optimization of structures with cracks becomes an important topic for avoiding manufacturing defects at the design stage. This paper presents a comprehensive comparative study of peridynamics-based topology optimization method (PD-TO) and classical finite element topology optimization approach (FEM-TO) for designing lightweight structures with/without cracks. Peridynamics (PD) is a robust and accurate non-local theory that can overcome various difficulties of classical continuum mechanics for dealing with crack modeling and its propagation analysis. To implement the PD-TO in this study, bond-based approach is coupled with optimality criteria method. This methodology is applicable to topology optimization of structures with any symmetric/asymmetric distribution of cracks under general boundary conditions. For comparison, optimality criteria approach is also employed in the FEM-TO process, and then topology optimization of four different structures with/without cracks are investigated. After that, strain energy and displacement results are compared between PD-TO and FEM-TO methods. For design domain without cracks, it is observed that PD and FEM algorithms provide very close optimum topologies with a negligibly small percent difference in the results. After this validation step, each case study is solved by integrating the cracks in the design domain as well. According to the simulation results, PD-TO always provides a lower strain energy than FEM-TO for optimum topology of cracked structures. In addition, the PD-TO methodology ensures a better design of stiffer supports in the areas of cracks as compared to FEM-TO. Furthermore, in the final case study, an intended crack with a symmetrically designed size and location is embedded in the design domain to minimize the strain energy of optimum topology through PD-TO analysis. It is demonstrated that hot-spot strain/stress regions of the pristine structure are the most effective areas to locate the designed cracks for effective redistribution of strain/stress during topology optimization.

scholarly journals A case study and implication: particle finite element modelling of the 2010 Saint-Jude sensitive clay landslide

Landslides ◽  
2019 ◽  
Vol 17 (5) ◽  
pp. 1117-1127 ◽  
Author(s):  
Xue Zhang ◽  
Liang Wang ◽  
Kristian Krabbenhoft ◽  
Stefano Tinti
Keyword(s):  
Finite Element ◽  
Slope Failure ◽  
Strain Softening ◽  
Failure Process ◽  
Numerical Approach ◽  
Strength Reduction ◽  
Particle Finite Element Method ◽  
Computational Framework ◽  
Sensitive Clay

AbstractModelling of landslides in sensitive clays has long been recognised as a challenge. The strength reduction of sensitive clays when undergoing plastic deformation makes the failure proceed in a progressive manner such that a small slope failure may lead to a series of retrogressive failures and thus to an unexpected catastrophic landslide. The clay in the entire process may mimic both solid-like (when it is intact) and fluid-like (when fully remoulded, especially for quick clays) behaviours. Thereby, a successful numerical prediction of landslides in sensitive clays requires not only a robust numerical approach capable of handling extreme material deformation but also a sophisticated constitutive model to describe the complex clay behaviour. In this paper, the particle finite element method (PFEM) associated with an elastoviscoplastic model with strain softening is adopted for the reconstruction of the 2010 Saint-Jude landslide, Quebec, Canada, and detailed comparisons between the simulation results and available data are carried out. It is shown that the present computational framework is capable of quantitatively reproducing the multiple rotational retrogressive failure process, the final run-out distance and the retrogression distance of the Saint-Jude landslide. Furthermore, the failure mechanism and the kinematics of the Saint-Jude landslide and the influence of the clay viscosity are investigated numerically, and in addition, their implications to real landslides in sensitive clays are discussed.

scholarly journals A Model for the Design of a Pomelo Peel Bioinspired Foam

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Jonel Ortiz ◽  
Guanglu Zhang ◽  
Daniel A. McAdams
Keyword(s):  
Finite Element ◽  
Pore Size ◽  
Cell Structure ◽  
Voronoi Tessellation ◽  
Three Dimension ◽  
Element Analysis ◽  
Static Compression ◽  
Pomelo Peel ◽  
Study Results

The structure of pomelo peel arouses research interest in recent years because of the outstanding damping and energy dissipating performance of the pomelo peel. Researchers found that pomelo peel has varying pore size through the peel thickness; the pore size gradient is one of the key reasons leading to superior energy dissipation performance of pomelo peel. In this paper, we introduce a method to model pomelo peel bioinspired foams with nonuniform pore distribution. We generate the skeletal open cell structure of the bioinspired foams using Voronoi tessellation. The skeleton of the bioinspired foams is built as three-dimension (3D) beam elements in a full-scale finite element model. The quasi-static and dynamic mechanical behaviors of the pomelo peel bioinspired foams could be derived through a finite element analysis (FEA). We illustrate our method using a case study of pomelo peel bioinspired aluminum foams under quasi-static compression and free fall impact circumstances. The case study results validate our method and demonstrate the superior impact resistance and damping behavior of bioinspired foam with gradient porosity for designers.

A Multi-Level Approach for the Numerical Modelling of Complex Monumental Buildings

2015 ◽  
pp. 546-575
Author(s):  
Siro Casolo ◽  
Andrea Fiore ◽  
Francesco Porco ◽  
Domenico Raffaele ◽  
Carlo Alberto Sanjust ◽  
...  
Keyword(s):  
Finite Element ◽  
Degrees Of Freedom ◽  
Numerical Models ◽  
3D Finite Element ◽  
Computational Approaches ◽  
Linear Behavior ◽  
Significant Damage ◽  
Non Linear ◽  
Multi Level

Monumental buildings are characterized by elements (such as columns, vaults, arches …) that can suffer significant damage even under moderate earthquakes. Unfortunately, the available modeling approaches require a huge amount of computing resources. The chapter presents a multi-level strategy that is able to overcome these difficulties by a rational adoption of different computational approaches. As a case study, the non-linear seismic assessment of the medieval “Maniace Castle”, in Syracuse (Sicily, Italy) is developed, by using different numerical models. First, the linear behavior of the building is studied by means of two 3D Finite Element models. Then, results are used to calibrate a 2D plane Rigid Body and Spring Model (RBSM), specifically formulated for approximating the macroscopic behavior of masonry texture with a small number of degrees of freedom. In order to account for the variability of the material characteristics, parametric non-linear analyses have been performed and compared.

Combined Approximation Reanalysis Coupled With Finite Element Stress Analysis for Multiple Geometric Changes in Early Design Stage

2005 ◽  
Author(s):  
Sachin S. Terdalkar ◽  
Joseph J. Rencis
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Design Stage ◽  
Finite Element Technique ◽  
Early Design ◽  
Early Design Stage ◽  
Machine Element ◽  
Element Technique ◽  
Geometric Changes

In this work a new graphically driven interactive stress reanalysis finite element technique has been developed so that an engineer can easily carry out manual geometric changes in a machine element during the early design stage. The interface allow an engineer to model a machine element in the commercial finite element code ANSYS® and then modify part geometry graphically to see instantaneous graphical changes in the stress and displacement contour plots. A reanalysis technique is used to enhance the computational performance for solving the modified problem; with the aim of obtaining results of acceptable accuracy in as short a period of time in order to emphasize the interactive nature of the design process. Two case studies are considered to demonstrate the effectiveness of the prototype graphically driven reanalysis finite element technique. The finite element type considered is a plane stress four-node quadrilateral based on a homogenous, isotropic, linear elastic material. Each case study considered multiple redesigns. A combined approximation reanalysis method is used to solve each redesigned problem. The first case study considers a plate with a hole with the goal to determine the hole shape that will minimize the stress concentration. The second case study considers a support bracket. The goal is to design the cantilever portion of the bracket to have uniform strength and to minimize the stress concentration at the fillet.

scholarly journals A Multi-Level Approach for the Numerical Modelling of Complex Monumental Buildings

2016 ◽  
pp. 1352-1378
Author(s):  
Siro Casolo ◽  
Andrea Fiore ◽  
Francesco Porco ◽  
Domenico Raffaele ◽  
Carlo Alberto Sanjust ◽  
...  
Keyword(s):  
Finite Element ◽  
Degrees Of Freedom ◽  
Numerical Models ◽  
3D Finite Element ◽  
Computational Approaches ◽  
Linear Behavior ◽  
Significant Damage ◽  
Non Linear ◽  
Multi Level

Monumental buildings are characterized by elements (such as columns, vaults, arches …) that can suffer significant damage even under moderate earthquakes. Unfortunately, the available modeling approaches require a huge amount of computing resources. The chapter presents a multi-level strategy that is able to overcome these difficulties by a rational adoption of different computational approaches. As a case study, the non-linear seismic assessment of the medieval “Maniace Castle”, in Syracuse (Sicily, Italy) is developed, by using different numerical models. First, the linear behavior of the building is studied by means of two 3D Finite Element models. Then, results are used to calibrate a 2D plane Rigid Body and Spring Model (RBSM), specifically formulated for approximating the macroscopic behavior of masonry texture with a small number of degrees of freedom. In order to account for the variability of the material characteristics, parametric non-linear analyses have been performed and compared.

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