Non-linear analysis of jack-up structures subjected to random waves
Non-linear analysis of jack-up structures subjected to random waves
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发表时间：
1999
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通讯作者：
Mark Jason Cassidy
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作者：
Mark Jason Cassidy
在更深的水域和更恶劣的环境中使用自升式钻井平台的需求正在稳步增长。在这些环境中使用它们的信心需要自升式分析技术来准确反映发生的物理过程。自升式平台是自升式平台长期可靠性研究中的一个重要问题，本文研究了适合自升式平台动态评估的模型。其动机是在考虑结构、基础和波浪荷载的非线性时达到一种平衡的方法。建立了密实砂土上柱脚竖向、弯矩和水平联合加载的加工硬化塑性模型。给出了复合荷载空间屈服面的经验表达式和屈服过程中基础位移预测的流动规律。导出了砂土中锥形基础的理论下限承载力系数，并将其用于应变硬化规律中，以定义屈服面尺寸随竖向侵彻塑性分量的变化。完整的增量数值模型已在平面框架分析程序JAKUP中实现。用新波理论考虑了波浪荷载的谱内容，并通过将确定性新波约束为完全随机的表面高程来表明随机波浪历史的重要性。利用这种技术，演示了确定海况短期极端响应统计的方法。在北海中部的自升式平台上进行的数值实验表明，根据不同的基础假设，长期极端响应存在差异。还强调了海况严重程度在短期极端反应统计变化中的作用。最后，利用概率方法进一步了解自升式平台的响应行为。使用响应面方法对影响变量（采用概率公式而不是确定性值）进行了敏感性研究。
There is a steadily increasing demand for the use of jack-up units in deeper water and harsher environments. Confidence in their use in these environments requires jack-up analysis techniques to reflect accurately the physical processes occurring. This thesis is concerned with the models appropriate for the dynamic assessment of jack-ups, an important issue in long-term reliability considerations. The motivation is to achieve a balanced approach in considering the non-linearities in the structure, foundations and wave loading. A work hardening plasticity model is outlined for the combined vertical, moment and horizontal loading of spudcan footings on dense sand. Empirical expressions for the yield surface in combined load space and a flow rule for prediction of footing displacements during yield are given. Theoretical lower bound bearing capacity factors for conical footings in sand have been derived and are used in a strain-hardening law to define the variation in size of the yield surface with the plastic component of vertical penetration. The complete incremental numerical model has been implemented into a plane frame analysis program named JAKUP. The spectral content of wave loading is considered using NewWave theory, and the importance of random wave histories shown by constraining the deterministic NewWave into a completely random surface elevation. Using this technique, a method for determining short-term extreme response statistics for a sea-state is demonstrated. A numerical experiment on an example jack-up and central North Sea location is shown to emphasise the difference in long-term extreme response according to various footing assumptions. The role of sea-state severity in the variation of short-term extreme response statistics is also highlighted. Finally, probabilistic methods are used to develop further understanding of the response behaviour of jack-ups. A sensitivity study of influential variables (with probabilistic formulations as opposed to deterministic values) has been conducted using the response surface methodology.