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.

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.

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.

Efficient Computation of Irregular Wave Wire Stresses in Flexible Risers

2018 ◽  
Author(s):  
Gabriel Rombado ◽  
Nathan Cooke ◽  
Dharma Pasala ◽  
Xianglei Ni ◽  
Andrew Low ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Dynamic Simulation ◽  
Irregular Waves ◽  
Local Model ◽  
Regular Wave ◽  
Flexible Riser ◽  
Irregular Wave ◽  
Wave Approach ◽  
Dynamic Substructuring ◽  
Time Histories

Accurate computation of tensile armor wire stresses remains a major challenge in flexible riser fatigue life predictions and integrity management. Accuracy of the results relies heavily on capturing the kinematics of the flexible’s helically contra-wound tensile armor layers and their interaction with the other metallic and thermo-plastic layers in a dynamic simulation. The standard industry practice to assess the fatigue life of flexibles is to use high fidelity 3D Finite Element Models (FEMs) to capture the complex kinematics and produce accurate stresses. However, direct simulation of flexible riser detailed FEMs is limited to regular wave analyses and computation of wire stress time-histories subjected to irregular waves have been computationally infeasible. This is due to the complexity of the nonlinear FEM and the long simulation time of the irregular wave environment coupled with large number of fatigue sea states. As a result, simplified approaches which do not directly simulate the local model and instead assume that wire stresses can be interpolated based on static stress versus curvature material curves within a pre-defined tension /pressure envelope have been utilized. This paper utilizes Nonlinear Dynamic Substructuring (NDS), a simulation-based approach that that extends the framework of dynamic substructuring to nonlinear problems. NDS enables the efficient nonlinear dynamic simulation of multiple pitch lengths of detailed flexible riser FEM subjected to irregular wave inputs and the computation of wire stress time-histories at any location on the local model. In this paper, a 14-inch diameter flexible riser under consideration by ExxonMobil is subjected to vessel motion and wave load in irregular wave environments and is modeled using a detailed 3D FEM and simulated via NDS. The flexible riser design features four tensile armor layers to mitigate localized lateral buckling of the wires near the touch down point. Tension and curvature time-histories of the riser near the hang-off, calculated from a conventional beam model global analysis, is used to drive a 5.1m long local model. Irregular wave wire stress time-histories extracted at the corners of the tensile armor wires are used to compute the fatigue life of the flexible. To demonstrate the inaccuracies associated with the regular wave approach, fatigue life is computed via the regular wave approach and compared against the irregular wave approach. It is shown that the NDS capability to efficiently compute irregular waves mitigates over- and under-predictions due to environment idealizations leading to a more accurate and reliable flexible riser life prediction and structural integrity assessment.

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.

An Investigation of Fatigue Damage due to VIV in Flexible Riser With Different Methodologies

2011 ◽  
Author(s):  
Yanqiu Zhang ◽  
Zhimin Tan
Keyword(s):  
Dynamic Simulation ◽  
Fatigue Damage ◽  
Time Domain ◽  
Detailed Comparison ◽  
The Other ◽  
Flexible Riser ◽  
Commercial Software ◽  
Tracking Method ◽  
Global Dynamic ◽  
Wake Oscillator

An investigation was carried out for the fatigue damages due to VIV in a flexible riser evaluated with three different VIV simulation methodologies. One methodology is provided in commercial software Shear7 which is established based on mode superposition. The other two are provided in commercial software OrcaFlex which are established based on global dynamic simulation in time domain. One of the two time-domain methods is referred to as Iwan and Blevings model formed with a wake oscillator, and the other is referred to as Tracking (1) model made with vortex tracking method. Fatigue damages in tensile armoring wires of the riser were evaluated with RMS curvature ranges resulting from the three methodologies separately. A detailed comparison between the damages and between RMS curvature ranges is made and then some discussions and recommendations are presented.

Vibration and sound radiation analysis of the final drive assembly considering the gear-shaft coupling dynamics

2016 ◽  
Vol 230 (7-8) ◽  
pp. 1258-1275 ◽  
Author(s):  
Yawen Wang ◽  
Junyi Yang ◽  
Dong Guo ◽  
Teik C Lim
Keyword(s):  
Dynamic Models ◽  
Acoustic Analysis ◽  
Bending Moment ◽  
Moment Of Inertia ◽  
System Dynamic ◽  
Dynamic Responses ◽  
Propeller Shaft ◽  
Hypoid Gear ◽  
Gyroscopic Effect ◽  
Gear Mesh

A generalized dynamic model of driveline system is formulated that includes the coupling effect and gyroscopic moments of the propeller shaft and hypoid gear rotor assembly. Firstly, the dynamic models with only gear-shaft coupling, with only gyroscopic effect, and with both gear-shaft coupling and gyroscopic effect are analyzed and compared. The results show that the combined effects of the gear-shaft interaction and gyroscopic behavior have considerable influence on the system dynamic responses surrounding gear bending resonances, especially for the bearing responses. However, the gear out-of-phase torsional modes still dominate the gear mesh frequency response. Secondly, the influence of pinion bending moment of inertia, propeller shaft stiffness and bearing stiffness on the system dynamic responses are examined. The system responses are then applied to perform further vibration and acoustic analysis for an axle housing structure. Computational results reveal that NVH (noise, vibration, and harshness) refinement can be achieved by tuning the pinion bearing rotational stiffness and pinion bending moment of inertia for the example considered. This study provides an understanding of the interaction between hypoid gear pair and propeller shaft, and can be employed to enhance driveline system design.

Dynamic Simulation Control Algorithm Based on the Time Domain

2014 ◽  
Vol 568-570 ◽  
pp. 1020-1025
Author(s):  
Zhuo Wei Jiang ◽  
Chun Ming Gao
Keyword(s):  
Dynamic Simulation ◽  
Time Domain ◽  
Control Algorithm ◽  
Low Cost ◽  
Analog Filter ◽  
Cost Performance ◽  
Dynamic Simulator ◽  
Simulation Control ◽  
The Time Domain ◽  
Computation Speed

In view of badly transplanting of analog filter and low cost performance of digital filter for the washing out signal methods used by dynamic simulator, this paper proposed a computer intelligent time domain method. We decompose signal with the computer intelligence in the time domain, and convert the signal into the corresponding movement form respectively, then get the final result by overlaying them. The experimental results show that this method not only can achieve the effect of the traditional methods, better portability and faster computation speed, but also can be achieved directly on general computers.

Transverse Young's Moduli and Cell Shapes in Coniferous Early Wood

Holzforschung ◽  
2002 ◽  
Vol 56 (1) ◽  
pp. 1-6 ◽  
Author(s):  
Ugai Watanabe ◽  
Minoru Fujita ◽  
Misato Norimoto
Keyword(s):  
Young’S Modulus ◽  
Young's Modulus ◽  
Bending Moment ◽  
Cell Models ◽  
Young’S Moduli ◽  
Cell Shapes ◽  
The Difference ◽  
Square Cells ◽  
Experimental Values ◽  
The Relationship

Summary The relationship between transverse Young's moduli and cell shapes in coniferous early wood was investigated using cell models constructed by two dimensional power spectrum analysis. The calculated values of tangential Young's modulus qualitatively explained the relationship between experimental values and density as well as the difference in experimental values among species. The calculated values of radial Young's modulus for the species having hexagonal cells agreed well with the experimental values, whereas, for the species having square cells, the calculated values were much larger than the experimental values. This result was ascribed to the fact that the bending moment on the radial cell wall of square cell models was calculated to be small. It is suggested that the asymmetrical shape of real wood cells or the behavior of nodes during ell deformation is an important factor in the mechanism of linear elastic deformation of wood cells.

A time domain prediction method for the vortex-induced vibrations of a flexible riser

2018 ◽  
Vol 59 ◽  
pp. 458-481 ◽  
Author(s):  
Mengmeng Zhang ◽  
Shixiao Fu ◽  
Leijian Song ◽  
Xiaoying Tang ◽  
Yue He
Keyword(s):  
Time Domain ◽  
Prediction Method ◽  
Flexible Riser ◽  
Vortex Induced Vibrations ◽  
Domain Prediction
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