系列自升式钻井平台桩靴设计与强度评估

自升式平台桩靴的设计形式和结构强度关系到整个平台性能和安全。针对所设计的400ft水深自升式平台两种桩靴结构形式,应用MSC/NASTRAN软件建立有限元模型,依据ABS规范要求并根据实际环境设计结构强度评估工况,对两种桩靴结构进行强度校核,同时计算桩靴各部分质量,分析计算结果最终得出一种较优的桩靴结构形式。     

自升式钻井平台桩靴结构强度分析

桩靴是钻井平台的重要支撑构件,其结构强度对整个钻井平台的安全起着至关重要的作用。以某自升式钻井平台桩靴为研究对象,根据ABS(美国船级社)规范要求,建立桩靴结构强度的力学模型,并合理简化,分析了预压载和自存两种工况下的设计载荷。利用有限元软件MSC.Patran/Nastran对两种工况下桩靴的强度进行分析,研究得到桩靴强度工程化分析流程以及结构强度特性,分析结果为自升式钻井平台的桩靴设计提供参考。     

自升式平台桩靴强度分析

合理的桩靴设计是立插桩式海洋自升式平台在海上安全工作的关键因素之一。以某自升式海洋平台桩靴为研究对象,利用规范和SACS软件对桩靴结构设计进行强度校核和屈曲强度分析,并对桩靴的承载力和计算方法进行研究。     

多种自升式海洋平台桩靴上拔过程仿真分析

本文以自升式海洋平台桩靴为主要研究对象,运用Ansys Workbench中的Design Modeler建立桩靴与土的模型,通过LS-DYNA来模拟桩靴上拔过程,并计算了3种桩靴形式的拔桩力和研究了3种桩靴的上拔过程土体的变形,并将桩靴上拔阻力的理论计算值与数值模拟计算的结果进行比较分析。本文对未来海洋平台的发展有一定的工程意义。     

关于自升式海洋平台插桩特性的分析研究

采用通用程序语言VBA,结合工程技术人员对相关规范和理论的理解和实际工程经验,开发出适用于自升式平台桩靴插桩计算分析的程序,实现计算的相对标准化,针对300ft、400ft自升式海洋平台桁架式桩腿结构形式在中国南通海域插桩特性分析研究,阐述了同类海洋平台的插桩深度预测分析过程及方法,该方法和思路的应用对海洋平台的结构安全评估有重要意义。     

自升式钻井平台桩靴裂纹分析、处理及修复研究

桩靴是自升式平台的重要组成部分,主要作用是支撑整个平台,将平台所受的载荷传递到海床.一旦桩靴失效,将导致桩腿下沉,平台无法保持水平.文章利用有限元方法研究了自升式平台桩靴在出现裂纹后的应力水平,并研究相关的应对措施与修复方法.     

桩靴充水对自升式平台拖航稳性的影响

综合考虑自升式钻井平台的完整稳性及破损稳性的衡准要求,以某自升式钻井平台为例,分别校核该平台在桩靴充水及不充水状态下拖航作业时的完整稳性及破损稳性,并对计算结果进行比较和分析,得出桩靴充水对自升式平台静水力、静稳性曲线以及许用重心高度曲线等方面的诸多影响,提出提高自升式平台拖航稳性的措施。     

自升式钻井平台进坞方法分析

<正>自升式钻井平台"南海石油931"需要进坞对桩腿和桩靴进行检查、修理。本技术通过在坞内设置砂箱,使自升式钻井平台进坞时,桩腿可插设在砂箱上,避免了桩腿、桩靴和坞底的损坏,并且可使平台沿着桩腿上下移动,方便对桩腿和桩靴的检查和维修。     

自升式平台水密桩靴内部介质与桩靴结构承压性能计算分析

根据不同填充介质(不同的海水与空气比例)压缩特性下自升式平台水密型桩靴变形与内压的变化情况,利用有限元计算得到桩靴变形(体积压缩量)与内外压力差值之间的关系和回归公式,给出反应内部介质、桩靴内压和桩靴容积变化量关系的解析方程组.利用某400 in自升式平台桩靴的实例定量绘制了在100 m水深下空气含量与桩靴内压支撑之间...     

桩靴支护结构对桩端极限承载力的影响

以渤海湾"胜利五号"自升式作业平台桩基贯入工程实例为基础,优化自升式平台桩靴支护结构位置,采用有限元数值模拟位置优化后的桩端极限承载力,并与实际桩端承载进行比较。优化结果表明:沿桩靴径向和垂向优化发现桩端极限承载力由内向外是先增大、后减小,支护结构在r'/r=0.6,h/H=0.4处优化达到预期效果;合理优化桩靴支护结构的位置可以改变桩靴上端面土体流动方向,减小土体对桩靴上端面冲量及桩靴上、下端面土体流速差,稳定贯桩过程,能够增加桩端极限承载力。     

Advances in the prediction of spudcan punch-through in double-layered soils

Punch-through failure of jack-up spudcan foundations occurs in active oil and gas drilling exploration regions, where relatively stiff soil overlies soft marine layer. Therefore, installation of spudcan foundations in such seabed formations threatens the stability of the jack-up rig. A site-specific assessment of the potential and severity of failure must be completed before the commencement of the installation. However, the accuracy of the prediction is limited by the validity of the design method currently in use. This paper presents advances in the prediction of punch-through failure of jack-up platforms in sand/stiff clay over soft clay soils. New analytical models for spudcan installation in double-layered soils are reviewed and compared to the existing methods in the ISO 19905-1 standard and SNAME standard. The capabilities and limitations of each method are summarised and recommendations are drawn for the theoretical predictions of spudcan punch-through in double-layered soils.     

Assessing appropriate stiffness levels for spudcan foundations on dense sand

Before a jack-up can operate at a given location, a site-specific assessment of its ability to withstand a design storm during operation must be performed. During this assessment, the complex state of stress and strain under a spudcan is usually simplified to a value of foundation stiffness that is integrated as a boundary condition into the structural analysis. Soil stiffness is a critical parameter affecting the foundation and structural load distribution and displacements, and the jack-up natural period and dynamic response. The level of spudcan stiffness is an area of intense interest and debate. This paper assesses appropriate stiffness levels for numerical simulation. Utilising results from a detailed “pushover” experiment of a three-legged model jack-up on dense sand, the paper compares the experimental pushover loads and displacements on the hull and spudcans to numerical simulations using different assumptions of spudcan stiffness. These include pinned and encastré footings, linear springs and a force-resultant model based on displacement-hardening plasticity theory. Constant stiffness levels are shown to be inadequate in simulating the experimental pushover test. The non-linear degradation of stiffness associated with the latter force-resultant model is critical.     

Controlled installation of spudcan foundations on loose sand overlying weak clay

Offshore jack-up rigs are often used for site exploration and oil well drilling. The footings of jack-up rigs are known as spudcan foundations. The risk of rapid uncontrolled penetration of spudcan in seabed (“punch-through”) exposes jack-ups to significant risk during installation in strong over weak layered seabeds. An example for this is a thin loose sand layer overlying a weaker stratum of clay. To prevent spudcans from “punch-through”, an in-situ measurement concept is suggested in this paper to control the installation process of spudcan foundations. First, three-dimensional finite element studies using a Coupled Eulerian–Lagrangian method are carried out to simulate the penetration process. The numerical results have been validated with existing analytical solutions and centrifuge model test data. Furthermore, parametric studies are carried out to quantify the influences of the sand thickness and shear strength of the clay on the bearing capacity of spudcans. Based on the numerical studies an idea for the development of an in-situ measurement concept is suggested to control the spudcan penetration process in-situ.     

The undrained bearing capacity of a spudcan foundation under combined loading in soft clay

Mobile jack-up drilling rigs are typically supported by individual, large diameter spudcan foundations. Before deployment, the suitability of a jack-up to a location must be shown in a site-specific assessment under loads associated with a 50-year return period storm, which ultimately need to be resisted by the foundations. The capacity of the spudcans under combined vertical, horizontal and moment loading is therefore integral to the overall site-specific assessment of the jack-up.In soft clays, spudcans can penetrate deeply into the seabed, sometimes up to several footing diameters, with soil flowing around the downward penetrating footing, sealing the cavity. Although this is generally believed to provide some additional bearing capacity to the footing, no detailed study or formal guidance is available to date. This study, therefore, investigates the influence of soil back-flow on the failure mechanisms and quantifies the effect on the capacity of a spudcan under general loading through finite element analyses. A closed-form analytical expression is developed that describes the capacity envelope under combined loading, applicable to embedment depths ranging from shallow to deep.     

自升式平台层状地基条件下插桩过程数值模拟研究

对于采用独立式桩靴结构的自升式平台,桩靴的入泥深度是保障平台安全作业的关键问题之一。采用ABAQUS软件的Explicit求解器,以位移增量步方式计算地基极限承载力;在施加初始地应力场的前提下,引入无限元边界处理方法,考虑了土壤无限大边界条件的影响,并使用ALE自适应网格技术有效地解决了土壤模型的大变形问题;最后,将有限元计算与经验公式计算进行比对分析。结果表明,在一定预压载荷条件下,有限元计算结果能较全面精确地反映插桩结果,弥补经验公式考虑参数单一、无法解决层状土承载力之间不连续问题以及无法动态模拟插桩过程的不足。     

自升式平台桩靴/地基承载力的数值分析

桩靴/地基承载力的准确预报是确保自升式平台进行海上插桩作业安全性的重要前提,常规的规范算法在处理复杂地基条件时存在困难。基于非线性数值分析方法,在对加载点位置、网格尺寸、地基边界等关键技术进行研究的基础上,以某400ft水深自升式平台为例,分别对海底均质土和成层土的承载力进行了研究。同时,对各土层参数的影响进行了详细分析,为探索插桩过程中地基破坏原理和承载力计算提供了一些参考。     

自升式钻井平台的抗冰性能评价

自升式钻井平台属于典型的柔性结构。由于冰与柔性抗冰结构相互作用的复杂性,长期以来尚未形成基于动冰力响应分析的结构设计。结构抗冰设计中大都是从极端荷载出发,只考虑最大静冰力或最大倾覆力矩是否能推倒平台。基于对渤海辽东湾柔性抗冰平台的多年监测,发现强烈的冰激振动引起平台管节点疲劳失效、上部设施的非正常运行、作业人员不舒适等问题的风险性要远大于极端静冰荷载下结构的整体安全问题。文中基于多年现场冰与结构作用观测及冰荷载的研究成果,提出了柔性抗冰结构设计中应考虑的主要失效模式及评价方法。最后,以渤海某典型自升式钻井平台为例,对其抗冰性能进行评价。该文的研究可为寒区自升式平台的抗冰概念设计提供合理依据。