Fatigue Damage Study of Helical Wires in Catenary Unbonded Flexible Riser Near Touchdown Point

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Kunpeng Wang ◽  
Chunyan Ji ◽  
Hongxiang Xue ◽  
Wenyong Tang
Keyword(s):  
Analytical Model ◽  
Fatigue Damage ◽  
Global Analysis ◽  
Axial Stress ◽  
Flexible Riser ◽  
Steel Catenary Riser ◽  
Finite Element Software ◽  
Seabed Stiffness ◽  
Touchdown Point ◽  
Unbonded Flexible Riser

This study presents an analytical model of flexible riser and implements it into finite-element software abaqus to investigate the fatigue damage of helical wires near touchdown point (TDP). In the analytical model, the interlayer contact pressure is simulated by setting up springs between adjacent interlayers. The spring stiffness is iteratively updated based on the interlayer penetration and separation conditions in the axisymmetric analysis. During the bending behavior, the axial stress of helical wire along the circumferential direction is traced to determine whether the axial force overcomes the interlayer friction force and thus lead to sliding. Based on the experimental data in the literature, the model is verified. The present study implements this model into abaqus to carry out the global analysis of the catenary flexible riser. In the global analysis, the riser–seabed interaction is simulated by using a hysteretic seabed model in the literature. The effect of the seabed stiffness and interlayer friction on the fatigue damage of helical wire near touchdown point is parametrically studied, and the results indicate that these two aspects significantly affect the helical wire fatigue damage, and the sliding of helical wires should be taken into account in the global analysis for accurate prediction of fatigue damage. Meanwhile, different from the steel catenary riser, high seabed stiffness may not correspond to high fatigue damage of helical wires.

Time domain prediction approach for cross-flow VIV induced fatigue damage of steel catenary riser near touchdown point

2013 ◽  
Vol 43 ◽  
pp. 166-174 ◽  
Author(s):  
Kunpeng Wang ◽  
Hongxiang Xue ◽  
Wenyong Tang
Keyword(s):  
Fatigue Damage ◽  
Time Domain ◽  
Cross Flow ◽  
Steel Catenary Riser ◽  
Domain Prediction ◽  
Touchdown Point ◽  
Prediction Approach

Sensitivity Study of Critical Parameters Influencing the Uncertainty of Fatigue Damage in Steel Catenary Risers

2010 ◽  
Author(s):  
Feng Zi Li ◽  
Ying Min Low
Keyword(s):  
Fatigue Damage ◽  
Cost Effective ◽  
Sensitivity Study ◽  
Structural Safety ◽  
Critical Parameters ◽  
Design Parameters ◽  
Steel Catenary Riser ◽  
Bending Stresses ◽  
Steel Catenary Risers ◽  
Touchdown Point

The most challenging aspect of a deepwater development is the riser system, and a cost-effective choice is the Steel Catenary Riser (SCR). Fatigue is often a governing design consideration, and it is usually most critical at the touchdown point (TDP) where static and dynamic bending stresses are highest. Unfortunately, it is also at this region that uncertainty is the maximum. The increased uncertainty casts doubt on the applicability of generic safety factors recommended by design codes, and the most consistent way of ensuring the structural safety of the SCR is to employ a reliability-based approach, which has so far not received attention in SCR design. As the number of basic random variables affects the complexity of a reliability analysis, these variables should be selected with caution. To this end, the aim of this paper is to draw up a comprehensive list of design parameters that may contribute meaningfully to the uncertainty of the fatigue damage. From this list, several parameters are selected for sensitivity studies using the commercial package Orcaflex. It is found that variations in seabed parameters such as soil stiffness, soil suction and seabed trench can have a pronounced influence on the uncertainty of the fatigue damage at the touchdown point.

A New User Defined Element for Nonlinear Riser-Soil Interaction Analysis of Steel Catenary Riser Systems

2016 ◽  
Author(s):  
Jiayue Liu ◽  
Mehrdad Kimiaei ◽  
Mark Randolph
Keyword(s):  
Interaction Analysis ◽  
Global Analysis ◽  
Cost Effective ◽  
Steel Catenary Riser ◽  
Analysis And Design ◽  
Static And Dynamic Analysis ◽  
Finite Element Software ◽  
Nonlinear Springs ◽  
Fatigue Design ◽  
Software Packages

Steel Catenary Risers (SCRs) provide a technically feasible and commercially efficient solution for the offshore field developments in deep waters. Fatigue design of SCRs in the touchdown zone (TDZ) is among the most complicated engineering challenges in riser design. The cyclic interaction of the riser with seabed leads to a number of complex nonlinear behaviors including soil suction, separation of the riser from the soil, trench formation and degradation of soil resistance during cyclic loading. Accurate simulation of the riser-soil interaction has significant effects on the fatigue performance in the TDZ. Few hysteretic nonlinear riser-soil interaction models have recently been introduced and some of them have been implemented in commercial software packages for analysis and design of riser systems. Due to complexity of the models and also limited access to special software packages with in-built nonlinear soil models, traditional simple linear soil models are still being used widely for riser analysis, in particular for fatigue design. In this paper, one of the existing nonlinear hysteretic seabed model, already been used in a commercial analysis program OrcaFlex [1], has been implemented into general finite element software Abaqus [2], through the coding of a user defined element (UEL) subroutine. The paper documents the implementation of UEL into Abaqus and the establishment of global riser model for both static and dynamic analysis on which the pipe is modelled efficiently as series of unidirectional beam elements from floater to seabed, resting on a bed of nonlinear springs. Longitudinal friction between pipe and seabed has also been considered. A series of simulations are performed to illustrate the capabilities of the model. All these results have good agreement with those from OrcaFlex. Results indicate that the proposed UEL is capable of modelling nonlinear riser-soil interaction phenomena and has been verified to be a cost-effective alternative to OrcaFlex in terms of global analysis of SCRs. In addition, as an open source code, UEL provides the required tool for future development on nonlinear soil models. A new type of nonlinear soil with bilinear soil shear strength is modeled and its effect on structural performances of SCRs is investigated.

scholarly journals VIV-induced fatigue damage study of helical wires in catenary unbonded flexible riser in time domain

2016 ◽  
Vol 17 (1) ◽  
pp. 1-11 ◽  
Author(s):  
Kunpeng Wang ◽  
Chunyan Ji ◽  
Hongxiang Xue ◽  
Wenyong Tang
Keyword(s):  
Fatigue Damage ◽  
Time Domain ◽  
Flexible Riser ◽  
Unbonded Flexible Riser ◽  
Damage Study

Study of Seabed Trench Induced by Steel Catenary Riser and Seabed Interaction

2016 ◽  
Author(s):  
Kunpeng Wang ◽  
Ying Min Low
Keyword(s):  
Frequency Response ◽  
Static Analysis ◽  
Fatigue Damage ◽  
Surrogate Model ◽  
Unit Length ◽  
Low Frequency ◽  
Steel Catenary Riser ◽  
Cubic Polynomial ◽  
Seabed Interaction ◽  
Touchdown Point

Seabed trench profile has significant effect on the fatigue damage of steel catenary riser near touchdown point. This study briefly demonstrates an approach in literature to determine the seabed trench induced by wave frequency response based on the cubic polynomial model. In this approach, a criterion for the matching between catenary riser and seabed trench is proposed, which is an optimization problem, and needs iterative static analysis of catenary riser. Based on the criterion, the sensitivity of the trench length and position to three parameters is parametrically studied: riser mass per unit length, ratio of horizontal span to vertical span of catenary part, trench depth. The obtained data are employed to fit the equations of trench length and position, which is taken as surrogate model since the iterative static analysis is very complicated. For completeness, the validation against data obtained from hysteretic seabed model is also illustrated. Based on the surrogate model, this study investigates the effect of trench depth on the fatigue damage near touchdown and the effect of the low frequency response on the seabed trench, and some useful conclusions are obtained.

Frequency Domain Fatigue Analysis for a Unbonded Flexible Riser: Damage Induced by Dynamic Tension

2019 ◽  
Author(s):  
Jiabei Yuan ◽  
Yucheng Hou ◽  
Zhimin Tan
Keyword(s):  
System Design ◽  
Frequency Domain ◽  
Fatigue Damage ◽  
Deep Water ◽  
Computational Time ◽  
Flexible Riser ◽  
Dynamic Tension ◽  
Irregular Wave ◽  
Unbonded Flexible Riser ◽  
Frequency Domain Approach

Abstract Evaluation of fatigue damage of offshore flexible risers is critical in flexible riser system design. For deepwater application, irregular wave time domain approach is often adopted as the state of practice to avoid excessive conservatism due to its better representation of the stochastic offshore environment. The approach can indeed fully capture the non-linear behaviors of the system at a significant cost of computational time. For example, computational time typically takes over 3∼4 weeks for a deep water free hanging riser system with thousands of fatigue load-cases and the full 3-hour simulations. On the other hand, the same scope of simulation can be completed in frequency domain within day(s), which will enable the designer to accelerate the optimization of riser system design. This paper presents an analysis method in frequency domain for assessing the fatigue damage of tensile armour wires inside the top end fitting (EF), which is induced by dynamic tension variation and often governs the riser service life in deep water applications. A validation measurement is also implemented to ensure the accuracy and practicability of this frequency domain approach in riser system design.

Finite Element Analysis of Seafloor-SCR Interaction in Touchdown Zone

2019 ◽  
Author(s):  
Zhang Wei ◽  
Peng Peng
Keyword(s):  
Finite Element ◽  
Cyclic Loading ◽  
Interaction Model ◽  
Bending Moment ◽  
Element Analysis ◽  
Nonlinear Load ◽  
Linear Interaction ◽  
Steel Catenary Riser ◽  
Finite Element Software ◽  
Touchdown Point

Abstract The touch down zone (TDZ) of steel catenary riser (SCR) is subject to fatigue damage. As a significant fatigue indicator, the variation of the stress range largely depends on the instantaneous changing bending moment. In this paper, a non-linear interaction model between seafloor and SCR is developed to consider the formation of trench at TDZ and its effect on the variation of bending moment. The seafloor soil is modeled by the nonlinear springs, whose stiffness is calculated according to nonlinear load-deflection relationship, such that the effect of cyclic loading can be simulated. The modeling of trench evolution and bending moment variation near the touchdown point (TDP) under cyclic loading are further conducted using the finite element software ABAQUS. The results show that the trench shaping is related to the uplift displacement of SCR and its number of cycles. The dependence of the bending moment on the displacement cycles near TDP is also investigated.

Experimental Investigation on the Suppression Device of VIV of a Flexible Riser

2014 ◽  
Author(s):  
Yun Gao ◽  
Shixiao Fu ◽  
Leijian Song ◽  
Tao Peng ◽  
Runpei Lei
Keyword(s):  
Fatigue Damage ◽  
Experimental Results ◽  
Experimental Investigations ◽  
Flexible Riser ◽  
Excited Mode ◽  
Response Characteristics ◽  
Helical Strakes ◽  
Uniform Current ◽  
Viv Suppression ◽  
Synchronization Regime

Experimental investigations were conducted on a flexible riser with and without helical strakes. A uniform current was obtained by towing a riser model in a tank, and the vortex-induced vibration (VIV) suppression of strakes with different heights and pitches was studied. The results of the bare riser show that the characteristics of the synchronization of the VIV for a flexible riser have many orders, and the excited mode jumps from one to another abruptly. During the high order synchronization regime, the VIV response decreases with the increased order of the synchronization. The experimental results also indicate that the response characteristics of a bare riser can be quite distinct from those of a riser with helical strakes, and the suppression performance depends on the geometry of the helical strakes. The fatigue damage in the CF direction is of the same order as that in the IL direction for the bare riser. However, for the riser fitted with helical strakes, the fatigue damage in the CF direction is much smaller than that in the IL direction. The experimental results also confirmed that strake height has a greater influence on the VIV response than the strake pitch, and the drag exerted on the riser increases with strake pitch and height.

Theoretical and numerical methods to predict the behaviour of unbonded flexible riser with composite armour layers subjected to axial tension

2020 ◽  
Vol 199 ◽  
pp. 107038 ◽  
Author(s):  
Qingsheng Liu ◽  
Hongxiang Xue ◽  
Wenyong Tang ◽  
Yuchao Yuan
Keyword(s):  
Numerical Methods ◽  
Flexible Riser ◽  
Axial Tension ◽  
Unbonded Flexible Riser

Flexible riser-bend stiffener top connection analytical model with I-tube

2020 ◽  
Vol 71 ◽  
pp. 102707 ◽  
Author(s):  
Yangye He ◽  
Murilo Augusto Vaz ◽  
Marcelo Caire
Keyword(s):  
Analytical Model ◽  
Flexible Riser
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