Fatigue damage assessment of steel catenary risers in the touchdown zone accounting for soil remoulding and reconsolidation effects

IF 4.3 2区 工程技术 Q1 ENGINEERING, OCEAN
Hossein Janbazi, Hodjat Shiri
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引用次数: 0

Abstract

The design of steel catenary risers (SCRs) is mainly affected by fatigue performance in the touchdown zone (TDZ), where the riser cyclically interacts with the seabed. This cyclic motion leads to seabed soil softening and remoulding. However, over an extended period of riser operations, the seabed soil undergoes a drainage because of small motion amplitudes of the floating vessel during calm weather or a limited contact with the seabed due to vessel relocation. This may cause recovery of the soil strength associated with excess pore pressure dissipation resulting in an extra fatigue damage accumulation in the TDZ. In the current study, a global SCR analysis has been conducted using a series of coded springs along the TDZ to model advanced SCR-seabed interactions. The instantaneous undrained shear strength of the soil is determined by using a recently developed effective stress framework. The effects of soil remolding and consolidation were integrated during both the dynamic motion of the SCR and intervening pause periods within the critical-state soil mechanics. The model updates the SCR-soil interaction spring at every time increment of dynamic analysis, calculating the cross-section stress range while taking into account the overall configuration of the riser on the seabed. The study showed that the consolidation may result in an increased fatigue damage of about 23 %, which is currently neglected by the existing non-linear SCR-soil interaction models.
考虑土壤重塑和再固结效应的着陆区钢悬链立管疲劳损伤评估
钢悬链线立管(scr)的设计主要受触地区(TDZ)疲劳性能的影响,该区域是立管与海床循环相互作用的区域。这种循环运动导致海底土壤软化和重塑。然而,在长时间的立管作业中,由于在平静天气下浮动船只的运动幅度很小,或者由于船只搬迁而与海底的接触有限,海底土壤会发生排水。这可能导致土的强度恢复与超孔隙压耗散有关,从而导致TDZ内额外的疲劳损伤积累。在目前的研究中,使用沿TDZ的一系列编码弹簧进行了全球SCR分析,以模拟高级SCR-海床相互作用。土的瞬时不排水抗剪强度是通过使用最近开发的有效应力框架来确定的。在临界状态土力学中,土壤重塑和固结的影响在SCR的动态运动和中间暂停期间都得到了综合考虑。该模型在动力分析每次增量时更新scr -土相互作用弹簧,在考虑海床立管整体构型的情况下计算截面应力范围。研究表明,固结可能导致疲劳损伤增加约23%,这是目前现有的非线性scr -土相互作用模型所忽略的。
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来源期刊
Applied Ocean Research
Applied Ocean Research 地学-工程:大洋
CiteScore
8.70
自引率
7.00%
发文量
316
审稿时长
59 days
期刊介绍: The aim of Applied Ocean Research is to encourage the submission of papers that advance the state of knowledge in a range of topics relevant to ocean engineering.
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