A Comparison of Coupled and Uncoupled Dynamic Analysis for the Flexible Riser in Shallow Water

2013 ◽  
Author(s):  
Chul-hee Jo ◽  
Do-youb Kim ◽  
Yu-ho Rho
Keyword(s):  
Shallow Water ◽  
Time Domain ◽  
Production Systems ◽  
Single Point ◽  
Gas Permeation ◽  
Dynamic Responses ◽  
Coupled Analysis ◽  
Flexible Riser ◽  
Extensive Experience ◽  
Flexible Risers

Flexible risers have been used extensively in recent years for floating and early production systems. Such risers offer the advantage of having inherent heave compliance in their catenary thereby greatly reducing the complexity of the riser-to-rig and riser-to subsea interfaces. Another advantage with flexible risers is their greater reliability. Concerns about fatigue life, gas permeation and pigging of lines have been overcome by extensive experience with these risers in production applications. In this paper, flexible riser analysis results were compared through coupled and uncoupled dynamic analyses methods. A time domain coupled analysis capability has been developed to model the dynamic responses of an integrated floating system incorporating the interactions between vessel, moorings and risers in a marine environment. For this study, SPM (Single Point Mooring) system for an FSU in shallow water was considered. This optimization model was integrated with a time-domain global motion analysis to assess both stability and design constraints of the flexible riser system.

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.

Technical Solutions Applied for the Treatment of Damaged Dynamic Risers

2002 ◽  
Author(s):  
Thomas S. Taylor ◽  
Michael V. Joosten ◽  
Frank Smith
Keyword(s):  
Corrosion Fatigue ◽  
Treatment Process ◽  
Fatigue Testing ◽  
Production Systems ◽  
Flexible Riser ◽  
Hydraulic Test ◽  
Test Analysis ◽  
Safety Critical ◽  
Flexible Risers ◽  
Technical Solutions

The objective of this paper is to provide operators of floating production systems that utilise dynamic flexible risers an opportunity to review the technology and procedures adopted by PGS Production. These procedures were utilised in order to verify/re-use the damaged/seawater annulus flooded Banff risers. Most of these risers were also classified as being safety critical. The scope of the work carried out covers the development of a seawater displacement treatment system using an inhibitor fluid. The feasibility and efficacy of the flushing treatment were rigorously developed based on hydraulic test analysis using sections taken from an actual flexible riser. An extensive corrosion fatigue-testing programme using seawater/CO2/inhibitor was carried out to establish optimal safe service lives for the “damaged and treated” case for these risers. This paper presents the successful results from this work covering the development of the remedial treatment process and the resulting corrosion fatigue work that has been conducted.

Time Domain Simulation of the 3D Bending Hysteresis Behavior of an Unbonded Flexible Riser

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Zhimin Tan ◽  
Peter Quiggin ◽  
Terry Sheldrake
Keyword(s):  
Dynamic Simulation ◽  
Time Domain ◽  
Bending Moment ◽  
Dynamic Responses ◽  
Life Assessment ◽  
Flexible Riser ◽  
Detailed Model ◽  
Hysteresis Behavior ◽  
Wave Approach ◽  
The Difference

This paper presents a “state-of-the-art” development in time domain dynamic simulation of 3D bending hysteresis behavior of a flexible riser under offshore environment loading. The main technical challenge is to understand and model the riser tensile armor behavior under continuous changes in both the magnitude and direction of bending, and its subsequent impact on the riser’s bending hysteresis characteristics. On account of this technical obstacle, the current industry practice is to model the riser as a linear structure, with certain conservatism enforced, and then to extract the global dynamic loads to a detailed local model for stress and life assessment. Two 3D flexible riser bending hysteresis models developed by Wellstream and Orcina are introduced in this paper, with their calibrations against the bending hysteresis loops measured in full scale tests. Both models are implemented using the analysis program ORCAFLEX. The Wellstream model is a detailed model that calculates both the total bending moment and the stresses in the tensile armor, whereas the Orcina model is a simpler model that only calculates the total bending moment. The study presented illustrates the difference in riser dynamic responses with and without consideration of the bending hysteresis behavior and assesses the difference in dynamic responses between the Wellstream and Orcina 3D bending hysteresis models. This development permits the modeling of more realistic riser structural properties in the dynamic simulation and reports detailed time history stress or strain results for strength components of the riser, and so expands the current practice of riser fatigue analysis, which uses the regular wave approach only, to using an irregular wave approach employing the rainflow counting method.

Model Testing of Ultra-Deepwater Floater Systems: Truncation and Software Verification Methodology

2006 ◽  
Author(s):  
Rolf Baarholm ◽  
Ivar Fylling ◽  
Carl Trygve Stansberg ◽  
Ola Oritsland
Keyword(s):  
Time Domain ◽  
Software Verification ◽  
Production Systems ◽  
Coupled Analysis ◽  
Mooring Line ◽  
Test Results ◽  
Set Up ◽  
Verification Methodology ◽  
Good Agreement

Model tests for global design verification of floating production systems in depths beyond 1000m–1500m cannot be made directly at reasonable scales. Truncation of mooring line and riser models, software calibration, as well as extrapolation and transformation to full depth and full scale, are required. Here, the first two of the above three items are addressed. The paper emphasizes the important matters to be taken into account. The choice of proper procedures for the set-up and the interpretation, and consistent and well documented methods, are essential. A case study with a deep-water semisubmersible is presented. In general, good agreement between model test results and analytical results from time-domain coupled analysis of the floater system responses is found.

Flexible Riser Configuration Design for Extremely Shallow Water With Surrogate-Model-Based Optimization

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Jinlong Chen ◽  
Jun Yan ◽  
Zhixun Yang ◽  
Qianjin Yue ◽  
Minggang Tang
Keyword(s):  
Shallow Water ◽  
Time Domain ◽  
Surrogate Model ◽  
Optimization Design ◽  
Time Domain Analysis ◽  
Kriging Model ◽  
Domain Analysis ◽  
Configuration Design ◽  
Optimized Design ◽  
Flexible Riser

The aim of this paper is to study the optimization design of a steep wave configuration based on a surrogate model for an extremely shallow water application of a flexible riser. As the traditional technique of riser configuration design is rather time-consuming and exhaustive due to the nonlinear time domain analysis and large quantities of load cases, it will be challenging when engineers address an extreme design, such as the configuration design in the case of extremely shallow water. To avoid expensive simulations, surrogate models are constructed in this paper with the Kriging model and radial basis function (RBF) networks by using the samples obtained by optimal Latin hypercubic sampling (LHS) and time domain analysis in a specified design space. The RBF model is found to be easier to construct and to show better accuracy compared with the Kriging model according to the numerical simulations in this work. On the basis of the RBF model, a hybrid optimization is performed to find the minimum curvature design with corresponding engineering constraints. In addition, an optimized design is found to meet all of the design criteria with high accuracy and efficiency, even though all of the samples associated with construction of the surrogate model fail to meet the curvature criterion. Thus, the technique developed in this paper provides a novel method for riser configuration design under extreme conditions.

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.

Evaluation of Contact Forces in the Vertical Connection of a Flexible Riser in the Subsea Equipment

2019 ◽  
Author(s):  
Yuri Coelho Del’ Sarto ◽  
Ricardo Franciss ◽  
Celso Kazuyuki Morooka
Keyword(s):  
Production Systems ◽  
Bending Moment ◽  
Contact Forces ◽  
Flexible Riser ◽  
Shear Forces ◽  
Flexible Pipe ◽  
Operational Procedure ◽  
Numerical Simulation Result ◽  
Operational Design ◽  
Flexible Risers

Abstract Flexible risers are commonly used in ultra deepwater offshore fields to convey fluids from the subsea equipment to the floating production unit. During the development of the production systems, the flexible pipe installation is a critical operation. In this scenario, an operational procedure for the installation frequently used in offshore Brazil is known as Direct Vertical Connection. In this concept, the Vertical Connection Module (VCM) is connected to the flexible pipe through a flanged joint, and lowered in to the subsea equipment with assistance of an installing cable. During the installation procedure, excessive loads may occur in the VCM due to reaction loads induced by the flexible pipe. The present paper aims to describe the Direct Vertical Connection installation and to propose a methodology to study the forces induced by the flexible pipe into the VCM during such operation. For this purpose, a numerical model is developed for the Direct Vertical Connection and it is represented to simulate the installation procedure through a commercial software OrcaFlex. The dynamic behavior of the system is investigated by varying the payout velocity of the installing cable, and the results are shown in terms of bending moment, wall tension and shear forces acting in the flange of the VCM. Numerical simulation result in the present work allows to evaluate the range of loading which acts during the Direct Vertical Connection to help operational design of the installation process, and avoid failure of components during the procedure.

Time Domain Simulation of the 3D Bending Hysteresis Behaviour of an Unbonded Flexible Riser

2007 ◽  
Author(s):  
Zhimin Tan ◽  
Peter Quiggin ◽  
Terry Sheldrake
Keyword(s):  
Dynamic Simulation ◽  
Time Domain ◽  
Bending Moment ◽  
Dynamic Responses ◽  
Life Assessment ◽  
Flexible Riser ◽  
Detailed Model ◽  
Wave Approach ◽  
The Difference ◽  
Hysteresis Behaviour

This paper presents a ‘state of art’ in the development of the time domain dynamic simulation of 3D bending hysteresis behaviour of a flexible riser under offshore environment loading. The main technical challenge is to understand and model the riser tensile armour behaviour under continuous changes in both the magnitude and direction of bending, and its subsequent impact on the riser’s bending hysteresis characteristics. Because of this technical obstacle, the current industry practice is to model the riser as a linear structure, with certain conservatism enforced, and then to extract the global dynamic loads to a detailed local model for stress and life assessment. This paper introduces two 3D flexible riser bending hysteresis models, developed by Wellstream and Orcina respectively, and their calibrations against the bending hysteresis loops measured in full scale tests. Both models are implemented using the analysis program OrcaFlex; the Wellstream model is a detailed model that calculates both the total bending moment and the stresses in the tensile armour; the Orcina model is a simpler model that only calculates the total bending moment. A study is presented to illustrate the difference in the riser dynamic responses with and without consideration of the bending hysteresis behaviour, and to assess the difference in the dynamic responses between the Wellstream and Orcina 3D bending hysteresis models. This development permits more realistic riser structural properties to be modeled in the dynamic simulation, and reports detailed time history stress or strain results of the strength components of the riser. This expands the current practice of riser fatigue analysis of only using the regular wave approach, to using an irregular wave approach employing the rainflow counting method.

Time Domain Simulations on a Single Point Moored Submerged Sphere of Variable Radius

2005 ◽  
Author(s):  
Joa˜o M. B. P. Cruz ◽  
Anto´nio J. N. A. Sarmento
Keyword(s):  
Wave Propagation ◽  
Time Domain ◽  
Physical Phenomenon ◽  
Single Point ◽  
Vertical Direction ◽  
Equation Of Motion ◽  
Hydrodynamic Coefficients ◽  
Energy Converter ◽  
Submerged Sphere ◽  
The Time Domain

This paper presents a different approach to the work developed by Cruz and Sarmento (2005), where the same problem was studied in the frequency domain. It concerns the same sphere, connected to the seabed by a tension line (single point moored), that oscillates with respect to the vertical direction in the plane of wave propagation. The pulsating nature of the sphere is the basic physical phenomenon that allows the use of this model as a simulation of a floating wave energy converter. The hydrodynamic coefficients and diffraction forces presented in Linton (1991) and Lopes and Sarmento (2002) for a submerged sphere are used. The equation of motion in the angular direction is solved in the time domain without any assumption about its output, allowing comparisons with the previously obtained results.

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