Flexible Riser Bending Hysteresis Influence on Bend Stiffener Response

2014 ◽  
Author(s):  
Marcelo Caire
Keyword(s):  
Dynamic Analysis ◽  
Segment Length ◽  
Analysis Tool ◽  
Flexible Riser ◽  
Element Analysis ◽  
Irregular Wave ◽  
Global Dynamic ◽  
Flexible Risers ◽  
Curvature Distribution ◽  
Internal Pressures

The bending stiffness response is an important parameter in the lifetime assessment of unbounded flexible risers. Its behavior is governed by interlayer friction mechanisms leading to a non-linear moment x curvature relationship that is highly dependent on the internal pressure. In order to investigate its influence on the critical bend stiffener hang-off region response, a detailed finite element analysis is carried out using a specialized tool for a short segment length of a selected 2.5″ ID riser cross section. Different internal pressures are numerically analyzed and the resulting local hysteretic bending response is then adjusted and directly incorporated into a global dynamic analysis tool that uses an equivalent elasto-plastic formulation with a hardening parameter that controls the behavior of the slippage mechanism. A fully coupled irregular wave dynamic analysis is then carried out and the flexible riser curvature distribution response in the bend stiffener region compared for different bending hysteresis models adopted.

Flexible Riser Top Connection Analysis With I-Tube Interface and Bending Hysteresis Effect

2019 ◽  
Author(s):  
Yangye He ◽  
Hailong Lu ◽  
Murilo Augusto Vaz ◽  
Marcelo Caire
Keyword(s):  
Kinematic Hardening ◽  
Bending Moment ◽  
Element Model ◽  
Beam Model ◽  
Flexible Riser ◽  
Nonlinear Bending ◽  
Cross Sectional ◽  
Irregular Wave ◽  
Global Dynamic ◽  
Curvature Distribution

Abstract The flexible riser top connection to the floating production platform is a critical region for fatigue lifetime (re)assessment. The interface with the I-tube and its curved sleeve combined with the gap between the riser and bend stiffener may lead to different curvature distribution when compared to the traditional modeling approach that considers the bend stiffener attached to the pipe. For a more accurate top connection assessment, the flexible riser bending hysteresis can also be directly incorporated in the global dynamic analysis helping to reduce curvature amplitude and lifetime prediction conservatism. This work investigates a 7” flexible riser-bend stiffener top connection with I-tube interface by performing irregular wave global dynamic analyses with the OrcaFlex package and considering a nonlinear bending moment vs curvature riser behavior obtained from a detailed cross sectional model developed in Abaqus. OrcaFlex curvature distribution results are also compared with a quasi-static finite element model that uses an elasto-plastic formulation with kinematic hardening to represent riser hysteresis through an equivalent beam model. A good curvature distribution correlation is observed for both top connection models (OrcaFlex x Abaqus) in the bend stiffener area with reduced amplitudes when riser bending hysteresis is considered.

scholarly journals Use of Dynamic Analysis to Investigate the Behaviour of Short Neutral Sections in the Overhead Line Electrification

2021 ◽  
Vol 6 (5) ◽  
pp. 62
Author(s):  
John Morris ◽  
Mark Robinson ◽  
Roberto Palacin
Keyword(s):  
Dynamic Analysis ◽  
Dynamic Simulation ◽  
Model Simulation ◽  
Analysis Tool ◽  
Overhead Line ◽  
Element Analysis ◽  
Novel Approach ◽  
Section Model ◽  
The Uk ◽  
Neutral Section

The ‘short’ neutral section is a feature of alternating current (AC) railway overhead line electrification that is often unreliable and a source of train delays. However hardly any dynamic analysis of its behaviour has been undertaken. This paper briefly describes the work undertaken investigating the possibility of modelling the behaviour using a novel approach. The potential for thus improving the performance of short neutral sections is evaluated, with particular reference to the UK situation. The analysis fundamentally used dynamic simulation of the pantograph and overhead contact line (OCL) interface, implemented using a proprietary finite element analysis tool. The neutral section model was constructed using physical characteristics and laboratory tests data, and was included in a validated pantograph/OCL simulation model. Simulation output of the neutral section behaviour has been validated satisfactorily against real line test data. Using this method the sensitivity of the neutral section performance in relation to particular parameters of its construction was examined. A limited number of parameter adjustments were studied, seeking potential improvements. One such improvement identified involved the additional inclusion of a lever arm at the trailing end of the neutral section. A novel application of pantograph/OCL dynamic simulation to modelling neutral section behaviour has been shown to be useful in assessing the modification of neutral section parameters.

A Nonlinear Dynamic Substructuring Approach to Global Dynamics of Flexible Riser Systems

2014 ◽  
Author(s):  
Arya Majed ◽  
Phil Cooper
Keyword(s):  
Dynamic Analysis ◽  
Nonlinear Dynamic ◽  
Nonlinear Dynamic Analysis ◽  
Nonlinear Effects ◽  
Global Dynamics ◽  
Computationally Efficient ◽  
Flexible Riser ◽  
Dynamic Simulations ◽  
Stick Slip ◽  
Global Dynamic

Standard riser global dynamic analysis software packages utilize line element models that cannot capture the complex behavior of flexible risers. This paper presents a computationally efficient nonlinear dynamic analysis methodology capable of incorporating detailed finite element models and scalable to global dynamic simulations of entire flexible riser systems. Subject methodology captures the global geometric nonlinear effects and its coupling to stick-slip friction — a clear requirement for accurate armour stress predictions. In addition, the method enables the formulation of stress transformation matrices which allow the direct recovery of armour stresses from the global simulations. A demonstration problem involving the nonlinear dynamic simulation of a 500m flexible riser system is presented.

Three-Stage Multiscale Nonlinear Dynamic Analysis Platform for Building-Level Loss Estimation

2015 ◽  
Vol 31 (2) ◽  
pp. 1021-1042 ◽  
Author(s):  
In Ho Cho ◽  
Keith Porter
Keyword(s):  
Dynamic Analysis ◽  
Information Transfer ◽  
Large Scale ◽  
Nonlinear Dynamic Analysis ◽  
Loss Estimation ◽  
Element Analysis ◽  
Global Dynamic ◽  
Micro Level ◽  
Analysis Platform ◽  
Vulnerability Functions

Large-scale loss estimation needs vulnerability functions that relate ground motion to repair cost for each of many building classes. A challenge to generating analytical vulnerability functions for a building class is that one needs to reflect seismic performance at several scales, from the size of cracks to the whole building. Here, we propose a three-stage multiscale platform tackling a general reinforced concrete (RC) building containing complex walls: (1) at the micro level, a microphysical mechanism-based parallel finite element analysis (FEA) engine captures microscopic nonlinearities; (2) the macro level handles computationally expensive dynamic analyses of buildings; (3) the meso level manages interscale information transfer and describes floor-specific variability. Multiple parallel FEA engines run in concert with a stand-alone dynamic analysis platform. Importantly, the micro level resolves damage phenomena explicitly—no fragility inference is required—propagating component damage to global dynamic analysis. Now, one can link microscopic damage to building seismic loss.

Methodology for Calculating Irregular Wave Stress Time Histories of Tensile Wires in Flexible Risers

2007 ◽  
Author(s):  
Krassimir Doynov ◽  
Christoffer Nilsen-Aas ◽  
Rune Haakonsen ◽  
Wan Kan ◽  
Robert Bjærum
Keyword(s):  
Time Domain ◽  
Transfer Functions ◽  
Stress Transfer ◽  
Regular Wave ◽  
Flexible Riser ◽  
Irregular Wave ◽  
Wave Approach ◽  
Stress Components ◽  
Time Histories ◽  
Flexible Risers

Flexible risers are being deployed in more and more demanding applications in terms of water depth, remote locations, temperature, pressure and corrosive fluids. Focus has been put on long term riser integrity in general, and on fatigue performance in particular, as knowledge of pipe behavior and properties has been advanced over the last decade. In this context, accurate and consistent estimation of riser global and local response to external loading is essential. A methodology has been developed to efficiently calculate irregular wave stress time histories of tensile armour wires for flexible risers. The stress time histories are calculated directly from the global loads which are usually generated by using commercially available well proven global analysis tools. The methodology elevates the dynamic analysis of flexible risers from the conventional regular-wave approach to irregular-wave time-domain approach. This in turn allows a better assessment of the fatigue performance and provides a better fit-for-service assessment or an opportunity to reduce design conservatism. This methodology also allows for consistent stochastic fatigue evaluations to be performed in time domain simulations using the well established stochastic analysis approach. All flexible riser non-linear hysteretic effects are included and phase shift between tension and curvature is also fully accounted for. The key ingredient lies in the generation of transfer functions of all stress components using a validated local analysis (LA) tool based on finite element method. This is done because direct use of the LA tool for long time domain simulations is very computationally intensive and impractical. The stress transfer functions allow direct mapping of the tension and curvature readings to individual stress components, which are combined in a phase consistent manner to obtain the total stress-time histories. This methodology should also work well for other systems having complicated cross sections such as dynamic umbilicals and integrated production bundle, etc. Accuracy of the proposed methodology should be equivalent to that of using the LA tool directly provided that the stress transfer functions are constructed appropriately. In comparison with the traditional regular-wave methodology, this irregular wave approach has been shown to provide a significant fatigue-life improvement for the flexible riser tensile-wire in a deep water West Africa application.

A Study for Riser Response From Global Dynamic Analysis With Irregular Wave (Continued)

2015 ◽  
Author(s):  
Yanqiu Zhang ◽  
Yucheng Hou ◽  
Jiabei Yuan ◽  
Zhimin Tan
Keyword(s):  
Dynamic Analysis ◽  
Regular Wave ◽  
Wave Analysis ◽  
Sea State ◽  
Statistic Method ◽  
Irregular Wave ◽  
Global Dynamic ◽  
The Mean ◽  
Universal Applicability ◽  
Water Depths

The results of a study on the statistic properties of the stochastic processes of both irregular wave and riser response were presented in the paper OMAE2014-23196. Following on from that work, the present paper is devoted to the statistic properties of the mean-crossing maxima of the stochastic process of riser response and the statistic properties of the largest maxima, resulting from a number of 3-hour simulations with different wave seeds. The objective of the study is to find a more efficient method for evaluating the most probable maximum (MPM) value of riser response, i.e. using as few as possible simulations to find a reliable expectation to the MPM. Global dynamic analysis with irregular wave is widely used in riser system design, though it is very time-consuming compared with regular wave. This is because irregular wave can more realistically model the sea state in the field of the riser system compared with regular wave. However time consuming irregular wave analysis may be there remains a perplexing issue, which is the randomness in the analysis results induced by wave seed; i.e. the extreme value of riser response resulting from a 3-hour simulation varies with the wave seed which is arbitrarily selected for the simulation. If a number of 3-hour simulations are performed, then a statistic method is used to evaluate the MPM value, two questions must be answered. First, how many simulations should be run, and second, what statistic method should be used? Based on the study to the statistic properties of the maxima of riser response and the largest maxima, answers to the above questions are proposed. For universal applicability the study was conducted reflecting four risers which had different configurations and water depths.

Multiscale Finite Element Analysis of Unbonded Flexible Risers

2014 ◽  
Author(s):  
Ben Edmans ◽  
Dinh Chi Pham ◽  
Zhiqian Zhang ◽  
Tianfu Guo ◽  
Sridhar Narayanaswamy ◽  
...  
Keyword(s):  
Finite Element ◽  
Constitutive Model ◽  
Dynamic Analysis ◽  
Large Scale ◽  
Failure Modes ◽  
Life Extension ◽  
Equivalent Material ◽  
Analysis Model ◽  
Element Analysis ◽  
Flexible Risers

Unbonded flexible risers are a key technology in existing and proposed offshore developments. With increasing water depth, the demands on risers increase and the design against hydrostatic and tension loads becomes more of a challenge. In addition, many existing subsea production systems are approaching the end of their design life and operators need to know if they can remain in-service. To enable the benefits from deepwater production and life extension projects to be realized while minimizing risks to life, property and the environment, accurate modelling and analysis tools are required to improve the prediction of failure modes and to develop a better understanding of the conditions leading to progressive failure. In this work, a multi-scale approach is adopted whereby a global dynamic analysis model is employed to determine the overall displacements of the riser and this is linked with a local model that can provide accurate forces and stresses for the prediction of collapse, fatigue damage and buckling of tensile armour wires. Firstly, we describe a nonlinear constitutive model for use in large-scale dynamic analysis of flexible risers based on an analytical homogenization of composite cylinders using the analogy between slip between pipe layers and plastic flow in continua. The model is able to reproduce the bending hysteresis behaviour observed in flexible pipes and its dependence on internal and external pressure. Secondly, we show a procedure for obtaining equivalent material parameters for this model from finite element local analyses of a flexible pipe. Finally, we show the implementation of this constitutive model in a riser system using two-dimensional co-rotational hybrid beam finite elements.

Flexible Riser Fatigue Re-Evaluation to Extend the Service Life

2008 ◽  
Author(s):  
Carlos A. D. Lemos ◽  
Fernando J. M. Sousa ◽  
Jose´ R. M. Sousa
Keyword(s):  
Fatigue Life ◽  
Service Life ◽  
Phase Difference ◽  
Coupled Analysis ◽  
Wave Analysis ◽  
Flexible Riser ◽  
Irregular Wave ◽  
Deep Waters ◽  
Special Procedure ◽  
Flexible Risers

Some PETROBRAS fields are near mature now, around 15 years of production, and their production still important to the company portfolio, the possibility of extending the service life of these flexible risers becomes extremely attractive. This work addresses the re-evaluation of the fatigue life of old flexible risers aiming to extend their fatigue life at the same environment conditions or at new and less challenging ones. To fulfill this condition a special procedure is being applied to stretch the service life of the installed flexible risers, considering irregular wave analysis conditions, distributions of damage around the circumference and along the bend stiffener area and phase difference between tension and bending and in some cases a coupled analysis of the ship, mooring and risers systems. This kind of new fatigue procedure could also become of paramount importance to Petrobras to allow the design of conventional flexible risers for ultra deep waters.

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