Configuration and Performance Analysis of Deep Ocean Mining Flexible Riser

Y. Gai, Shuang‐Xi Guo, Yilun Li, Min Li, Weimin Chen
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Abstract

Deep-sea minerals such as polymetallic nodule, hydrothermal sulphides and ferro-manganese crusts have for long attracted attention as an alternative source of metals to terrestrial deposits. To bring these minerals up to the land, flexible risers are needed. As the mining industry developing towards deep sea area, the conveying system is usually designed as a combination of steel riser and flexible riser. According to different transport requirements, various flexible riser configurations, such as steel catenary riser, lazy-wave riser and saddle-shaped riser, have been proposed. During mining operation, the riser bears gravity, buoyancy, wave and current force, therefore the assessment of structural safety and reliability is quite challenging. In addition, the riser response caused by the mining vehicle motion during working process in a large area should also be considered. To guarantee a safe operation and service life of the riser, it is necessary to carefully design its configuration and to analyze its performance. In this study, taking the saddle-shaped riser as our model, the influences of main design parameters on the riser configuration, tension and stress are examined. These parameters include the installation position of buoyancy modules, the buoyancy ratio and motion of mining vehicle. Firstly, the analysis model of the riser response is established based on FEM in which the nonlinear large displacement and deformation of the structure are considered. Secondly, through our FEM simulation, the distribution and variation of tension and stress along the axial length of risers with different configurations are presented. Finally, the impacts of the mining vehicle motion on riser response are discussed. Our numerical results show that a small change of the buoyancy position and buoyancy ratio may lead to a significant change of the riser configuration, but a little change of riser tension/stress. And the saddle-shaped riser has a good tolerance performance to the bottom-end excitation.
深海采矿柔性立管结构与性能分析
多金属结核、热液硫化物和锰铁结壳等深海矿物长期以来作为陆地矿床的另一种金属来源而引起人们的注意。为了将这些矿物带到陆地上,需要柔性立管。随着矿山工业向深海方向发展,输送系统通常采用钢立管和柔性立管的组合设计。根据不同的输送要求,提出了多种柔性立管结构,如钢悬链线立管、懒波立管和马鞍形立管。在采矿作业中,隔水管承受重力、浮力、波浪和水流的作用,因此结构的安全性和可靠性评估具有很大的挑战性。此外,还应考虑采矿车辆在大范围内作业过程中运动引起的隔水管响应。为了保证立管的安全运行和使用寿命,有必要仔细设计立管的结构并对其性能进行分析。本文以马鞍形立管为模型,考察了主要设计参数对立管结构、张力和应力的影响。这些参数包括浮力模块的安装位置、浮力比和采矿车的运动。首先,基于有限元法建立了考虑结构非线性大位移和大变形的隔水管响应分析模型;其次,通过有限元模拟,给出了不同结构立管的拉应力沿轴向的分布和变化规律。最后,讨论了矿车运动对隔水管响应的影响。数值计算结果表明,浮力位置和浮力比的微小变化会导致隔水管结构发生显著变化,但隔水管张力/应力变化不大。鞍形立管对底端激励具有良好的容忍性能。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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