Enhanced Multi-Layer Fatigue-Analysis Approach for Unbonded Flexible Risers

This paper proposes an enhanced approach for evaluating the fatigue life of each metallic layer of unbonded flexible risers. Owing to the complex structure of unbonded flexible risers and the nonlinearity of the system, particularly in the critical touchdown zone, the traditional method is insufficient for accurately evaluating the fatigue life of these risers. The main challenge lies in the transposition from global to local analyses, which is a key stage for the fatigue analysis of flexible pipes owing to their complex structure. The new enhanced approach derives a multi-layer stress-decomposition method to meet this challenge. In this study, a numerical model validated experimentally is used to demonstrate the accuracy of the stress-decomposition method. And a numerical case is studied to validate the proposed approach. The results demonstrate that the multi-layer stress-decomposition method is accurate, and the fatigue lives of the metallic layers predicted by the enhanced multi-layer analysis approach are rational. The proposed fatigue-analysis approach provides a practical and reasonable method for predicting fatigue life in the design of unbonded flexible risers.     

Enhanced multi-layer fatigue-analysis approach for unbonded flexible risers

This paper proposes an enhanced approach for evaluating the fatigue life of each metallic layer of unbonded flexible risers. Owing to the complex structure of unbonded flexible risers and the nonlinearity of the system, particularly in the critical touchdown zone, the traditional method is insufficient for accurately evaluating the fatigue life of these risers. The main challenge lies in the transposition from global to local analyses, which is a key stage for the fatigue analysis of flexible pipes owing to their complex structure. The new enhanced approach derives a multi-layer stress-decomposition method to meet this challenge. In this study, a numerical model validated experimentally is used to demonstrate the accuracy of the stress-decomposition method. And a numerical case is studied to validate the proposed approach. The results demonstrate that the multi-layer stress-decomposition method is accurate, and the fatigue lives of the metallic layers predicted by the enhanced multi-layer analysis approach are rational. The proposed fatigue-analysis approach provides a practical and reasonable method for predicting fatigue life in the design of unbonded flexible risers.     

组合载荷作用下深海非粘结柔性管力学性能对比分析

建立深海非粘结柔性管新型力学数值分析模型,分析其在复合载荷工况下的力学性能。深海非粘结柔性立管是深水资源开发的关键设备,安装成本低,适用于恶劣深海环境。然而,由于非粘结柔性管本身的结构型式复杂以及层与层之间的摩擦、接触等诸多强非线性特性,使其局部力学性能分析面临众多挑战。研究针对非粘结柔性立管特殊的结构型式,建立一个高效的数值分析模型,对其刚度进行数值求解并与实验结果进行对比,探讨了内压和拉伸、扭转、弯曲的组合载荷工况和拉扭组合载荷工况对非粘结柔性立管刚度的影响。研究表明,本文所建立的简化模型计算结果与实验结果吻合较好。此外,柔性立管所受到的内压可以在一定程度上增加非粘结柔性立管的刚度;拉扭组合载荷工况使非粘结柔性立管的拉伸刚度降低明显,而使其扭转刚度少量增加,总体上较单一载荷工况更加危险。     

盛夏高温干旱对柑桔产量影响及指标

80年代以来,盛夏高温干旱发生机率升高,因此而造成的柑桔减产问题愈来愈被人们重视.汪铎、黎勃等在柑桔产量模式研究中,逐步分析了高温干旱对柑桔产量形成的影响.金衢地区,由于地面地形的盆地性作用,盛夏期间温度高、蒸发强,周围群山连绵,明显阻碍了台风影响,缺水量(自然供水——作物需水量)最多,是我省的多旱区.然而,柑桔性喜温暖而畏低温和干旱,夏季期间,20～25℃气温较适宜,呆实增长最快,气温超过35℃果实趋于停止生长.雨水充沛,土壤水分相对充足,促进果实快速膨大,反之抑制果实膨大,并持续影响整个果实膨大的发展进程,最终减产.如1978年受盛夏高温干旱影响,衢州市石梁乡西头塘村,柑单果重竟不到20克,常山柑桔园的衢粘60多个才一公斤,单果重平均只有常年的40%,并且品质低劣.针对高温干旱常影响金衢地区柑桔产量稳定和发展柑桔生产的实际问题,结合我县历年气象资料和柑桔产量资料进行统计分析,总结出盛夏高温干旱对柑桔产量形成的影响及危害指标,为防御灾害提供参考.