基于多重波形串行布置的深水缓波型柔性立管动力响应与疲劳损伤研究

With the offshore oil and gas exploitation constantly advancing into deepwater and ultra-deep waters, lazy wave flexible risers are employed instead of traditional steel catenary risers to conduct the undersea oil and gas transportation, which can relieve the top tension failure and touchdown zone fatigue failure due to harsh operating environment and excessive water depth condition. In this project, the combined research methods of theoretical model analyses, model test and numerical simulation are applied to carry out the following studies on the dynamic response and fatigue damage of deepwater lazy wave flexible risers based on multiple waveform serial arrangement: develop a multiple lazy wave flexible riser’s dynamic response model on the basis of large deflection and slender beam theory to realize the accurate judgment of coupling contact and reasonable simulation of nonlinear dynamic response, which is compared and verified by model test and numerical simulation, and reveal the influence rule of the factors such as lazy wave number and shape on the riser dynamic response, then explore the coupling mechanism between the trench/suction effect and bending hysteretic effect of the flexible pipe during the riser-soil interaction in the touchdown zone; put forward an effective fatigue damage assessment method for the multiple lazy wave flexible riser under wave frequency and slow drift coupled motions, and explain the influencing mechanism of floating structure slow-drift motion on the riser total fatigue damage under the deepwater environment condition; finally establish a comprehensive evaluation system for the ultimate strength and fatigue damage of deepwater multiple lazy wave flexible risers. The research findings will lay a solid theoretical foundation for the deepwater lazy wave riser configuration design.

随着海洋油气开发不断向深海和超深海域推进，采用缓波型柔性立管进行海底油气输送，能够缓解由于恶劣作业环境和过大水深工况导致的顶端张力破坏和触地区疲劳失效。本项目拟采用理论分析、模型试验和数值模拟相结合的方法，针对多重波形串行布置下深水缓波型柔性立管的动力响应和疲劳损伤开展如下研究：基于大挠度细长梁理论建立多重缓波型柔性立管动力响应模型，实现耦合接触的准确判断和非线性动力学响应的合理模拟，并与模型试验和数值模拟进行对比验证，揭示缓波波形数量和形态等因素对立管动力响应的影响规律，探究触地区管土相互作用过程中成沟和吸力效应与柔性管弯曲滞回效应之间的耦合机制；提出浮式结构波频和慢漂耦合运动作用下多重缓波型柔性立管疲劳损伤的高效评估方法，阐明深水环境下浮式结构慢漂运动对立管总疲劳损伤的影响机制；建立完善的深水多重缓波型柔性立管极限强度和疲劳损伤评估体系，为深水缓波型柔性立管线型设计奠定坚实的理论基础。

海洋油气资源作为目前世界上重要的能源形式，在当今社会经济发展中发挥着越来越重要的作用。而海洋立管作为海洋油气开发系统的重要组成部分，是油气运输最为经济有效的方式。本文采用理论分析、数值模拟以及室内模型试验相结合的方法开展研究，建立深水钢悬链线立管和多重缓波型柔性立管动力响应的高效理论模型，探究深水钢悬链线立管和多重缓波型柔性立管的动力响应影响机制，揭示缓波波形数量和形态对立管触地区运动的解耦机理以及防弯器约束和柔性管弯曲滞回对柔性立管的耦合作用；提出波频和慢漂组合运动作用下深水立管疲劳损伤的合理高效评估方法，阐明深水复杂环境下浮式结构慢漂运动对波频运动致使立管疲劳损伤的影响机制。本项目的主要研究工作包括以下内容：（1）提出基于多重波形串联布置的深水缓波型立管构型概念，探究基于缓波布置构型的深水立管在浮式结构运动以及海流荷载作用下的运动响应特征和性能优势，为深水立管构型设计提供参考依据。（2）提出综合考虑浮式结构波频和慢漂组合运动作用下深水立管疲劳损伤计算的位置组合叠加法，通过与全耦合法、权重组合叠加法等方法对比研究，论证位置组合叠加法在计算精度和效率等方面的优越性。（3）防弯器可以改善立管顶端区域的疲劳寿命，立管顶角对立管顶端区域弯曲曲率分布影响较大，降低立管平均弯曲曲率可能会导致更大的疲劳损伤。（4）与单一方向的顶部激励相比，立管触地区在垂向和侧向耦合运动下的应变和位移响应更为强烈。随着顶部浮体运动幅值的增大和运动周期的减小，立管触地区的动力响应显著增强，管道埋深将会增大。上述研究有助于完善深水多重缓波型柔性立管极限强度和疲劳损伤评估体系，为深水缓波型柔性立管线型设计奠定坚实的理论基础。