Freestanding drilling riser (FSDR), a new type of riser in deepwater drilling, though not in commercial use, can significantly reduce the engineering sensitivity to severe weather compared to the conventional risers. The optimal installation depth of the near surface disconnection package (NSDP) and the optimal number of buoyancy cans are two important parameters in the FSDR system. In this paper, the key mechanical problems of the FSDR system have been proposed and the mechanics of the FSDR system in normal drilling mode and freestanding mode have been studied. The above two optimal parameters have been calculated on the basis of a specific marine environment and system configuration. The operating envelope of the FSDR system has been figured out through parameter sensitivity analysis. Analysis results show that the NSDP should be installed 200 m below the sea surface to avoid strong wave-current profile and enhance the performance of the FSDR in freestanding mode. From the mechanical point of view, the weakest section of the FSDR is located at the junction between the buoyancy cans and the riser joints, where stress joint should be equipped to improve the stress condition of the system. Further, the maximum von Mises stress of the FSDR in normal drilling mode is the dominant factor restricting the increase of the number of buoyancy cans. The normal operating envelope of the FSDR is mainly limited by the deflection angle of the upper flexible joint (UFJ) and the von Mises stress. On the basis of the mechanics and operating criteria of the FSDR, the optimal number of buoyancy cans is six and the vessel offset should be less than 2% of the water depth to ensure the safety of the FSDR in normal drilling mode. Finally, suggestions on the future study on the FSDR system have been proposed.

自立式钻井隔水管（FSDR）是深水钻井中的一种新型隔水管，尽管不用于商业用途，但与常规隔水管相比，可以显着降低工程设计对恶劣天气的敏感性。FSDR系统中的两个重要参数是近表面分离包装（NSDP）的最佳安装深度和浮力罐的最佳数量。本文提出了FSDR系统的关键力学问题，并研究了FSDR系统在常规钻进模式和独立式钻进模式下的力学特性。以上两个最佳参数是根据特定的海洋环境和系统配置计算得出的。FSDR系统的运行范围已通过参数敏感性分析确定。分析结果表明，应将NSDP安装在海面以下200 m处，以避免强烈的波浪流剖面并增强FSDR在独立模式下的性能。从机械角度来看，FSDR的最薄弱部分位于浮力罐与立管接头之间的连接处，应在其中安装应力接头以改善系统的应力状况。此外，在常规钻孔模式下，FSDR的最大冯·米塞斯应力是限制浮力罐数量增加的主要因素。FSDR的正常工作范围主要受上挠性接头（UFJ）的偏转角和von Mises应力的限制。根据FSDR的机制和操作标准，浮力罐的最佳数量为六个，并且容器偏移量应小于水深的2％，以确保FSDR在常规钻井模式下的安全性。最后，对未来的FSDR系统研究提出了建议。