冰区自升式平台桩腿动强度的安全评估

应用ANSYS软件建立了自升式平台和冰相互作用的数学仿真模型,对自升式平台进行了动力分析和桩腿的极限强度和疲劳强度校核。应用本模型对渤海某自升式平台桩腿进行的强度校核和不同海冰参数下平台桩腿的冰激疲劳损伤实例分析表明,本文的研究结果为自升式平台冰激疲劳设计提供了一个有效的方法,并为自升式平台在冰区的使用提供了依据。     

碰撞条件下高弹模CFRP加固自升式平台桩腿性能分析

由于腐蚀、海生物附着等因素导致老龄化海洋平台在与船舶碰撞的事故作用下,桩腿变形加大,降低了承载性能。为减少碰撞对桩腿的损伤,提高其耐撞性能,提出了利用吸收能力较强的高弹模CFRP材料加固平台桩腿的方法。以某自升式海洋平台桩腿为例,利用有限元法建立简化的碰撞模型,通过在局部损伤部位粘贴高弹模CFRP材料来提高桩腿的耐撞性能,验证高弹模CFRP加固方法,提高其耐撞性能的有效性。研究表明,相同的碰撞条件下,加固前碰撞力使桩腿产生了接近屈服强度的应力;粘贴2层CFRP布后,桩腿吸能下降56.3%,极值应力下降了14.7%;粘贴CFRP板后,桩腿吸能下降70.68%,桩腿的极值应力下降57.36%。     

自升式平台拖航工况桩腿设计标准研究

本文对自升式钻井平台拖航工况桩腿的外力、内力和应力设计标准进行了综合分析。分别按照美国船检局、英国劳氏船级社、挪威船级社和我国船检局的近海移动式钻井平台入级和建造规范对我国建造的自升式平台桩腿结构进行分析计算。将所得的结果列表并绘出曲线,进行了综合分析。其结论为应用近海移动式钻井平台入级与建造规范和对这种自升式平台设计提供适当的依据.     

自升式平台穿刺过程结构响应研究

为减少自升式平台穿刺造成的损失,需要对自升式平台穿刺过程中的结构响应进行研究。根据某典型平台图纸,使用有限元法建立细化模型。在穿刺过程中采用CONNECTOR单元及非线性弹簧模拟自升式平台围阱区的齿轮齿条接触及桩土作用。考虑到模型中包含的高度非连续过程,穿刺过程采用显式动力学方法求解。通过分析模型穿刺后的结构形态,危险点分布,穿刺速度对结构的影响及预压载值的变化,探讨自升式平台穿刺过程中的结构响应特征。结果表明:平台导向板附近桩腿结构最容易在穿刺中损坏;穿刺速度对与桩靴相连的桩腿结构影响很大;为减少穿刺对结构的影响,可以考虑主动刺穿或减少气隙进行单桩预压载等措施。     

海上自升式钻井平台结构非线性分析

本文分析海上自升式钻井平台结构特征及其桩腿结构非线性大位移特点,采用非线性有限元分析方法,提出考虑剪切影响的三维梁单元几何非线性分析新的方法,并编制相应分析程序,对自升式钻井平台桩腿结构非线性问题进行了合理地分析,取得合理的分析结果.文中还通过自升式钻井平台实例分析说明了此法的应用.     

KK型管节点应力集中系数几何敏感性分析

KK型管节点是自升式平台桁架式桩腿中的一种管节点,其应力集中系数是影响桩腿疲劳寿命的重要参数。应力集中系数与管节点的几何形式密切相关,为分析KK型管节点应力集中系数对几何参数的敏感性,利用ANSYS软件对某KK型管节点进行几何参数化建模,利用有限元数值模拟方法对各工况下的热点应力进行分析,并分别计算各相应工况下的名义应力,然后将热点应力与名义应力相比得到不同几何参数下的热点应力集中系数。对计算结果进行整理分析,得到了KK型管节点应力集中系数对无量纲几何参数的敏感性规律。结果表明,应力集中系数与撑杆受力状态、管节点结构形式有关,在满足结构布置、建造工艺和其他安全性指标的前提下,分析结果能够为KK型管节点的结构设计和疲劳分析提供技术支撑。     

自升式海上钻井平台结构的模态分析及地震反应的谱分析

本文对某自升式钻井平台结构进行了模态和地震反应分析。用等效桩腿的处理方法把平台结构简化为空间梁系有限元力学模型,采用我国《海上固定平台入级与建造规范》中规定的标准地震谱曲线.首先计算了平台结构前五阶固有频率和模态,然后用基于模态叠加法的谱分析法求出平台结构和桩腿各部位的最大位移和应力反应。最后给出了该平台结构在30m和50m水深海域、桩腿为插桩式和沉垫式两种固定型式下的计算结果和比较。     

喷冲系统降低拔桩阻力有效性的试验研究

自升式作业平台是勘探开采海洋油气资源的重要装备。在其使用期内,需要多次移动位置。移动之前,自升式平台通过桩腿拔出桩靴。拔桩过程可能因地质条件复杂而费时费力。喷冲系统对降低拔桩阻力的功效明显。通过单喷嘴试验,本文研究不同地质条件下的喷冲参数变化规律,并探讨参数之间的相互影响。通过桩靴模型喷冲试验,验证喷冲系统降低拔桩阻力的有效性。试验结果将为进一步设计能够有效降低自升式平台拔桩阻力的喷冲系统提供技术支持。     

自升式平台水平偏移的数值模拟方法研究

自升式平台的水平偏移会增加作业难度,严重时降低平台的坐底稳定性。基于平台主体发生水平偏移U的原因,将水平偏移分成三部分:桩腿弯曲引起的水平偏移Ub,桩靴转动引起的水平偏移Ur以及桩靴平移引起的水平偏移Ud。利用有限元软件ABAQUS建立圆柱腿自升式平台-地基耦合模型,考虑桩土之间法向挤压、切向摩擦的接触关系,利用Coulomb定律计算摩擦力。利用子程序DLOAD实现波浪力的加载,波浪采用Airy波模型。针对桩周无回填土体、桩周土体未完全固结以及固结完成三个阶段,探究桩靴直径、回填土强度、以及埋置深度对U,Ud和Ub的影响。并与中国船级社《海上移动平台入级与建造规范》(2005)中推荐的方法进行对比。最后给出了相关的结论。     

自升式平台分段延时插桩法在浅层气海域的应用

海底浅层气一般指海床浅地层内聚集的气体,是一种典型的海洋灾害地质类型,施工作业时一旦发生灾害,将对生命财产造成不可估量的损失。本文通过介绍海底浅层气的性质和危害,同时对辽东湾浅层气海域的进行工程物探资料分析,结合浅层气海域地层物性的特点,针对带桩靴的自升式平台在浅层气海域桩的插桩过程中存在的风险,提出了自升式平台分段延时插桩方法。并通过实践,指导中油海6平台在该海域的成功插桩,验证了该方法在浅层气海域插桩的可行性,同时实现了桩靴式自升式平台在该区块作业的零突破,具有一定的指导意义。     

Evaluation method for Green jack-up drilling platform design scheme based on improved grey correlation analysis

This paper presents an evaluation method for green jack-up drilling platform(GJDP) design scheme based on the improved grey correlation analysis(IGCA). Under the situation of the low-carbon economy it is important and complicated for jack-up drilling platform design to select the optimum design scheme from the feasible schemes. In this paper, the evaluation index system for GJDP has been proposed which includes 3 factors: advanced technology, economic feasibility and environmental coordination, as well as 13 sub-indices. At the same time, a multi-objective combinatorial optimization model is established by using IGCA, in which the analysis hierarchy process (AHP) is used to obtain the weight values of the indices. The IGCA method is fully considered the connection of the indices reflecting the objective true nature of the things, and the subjective interest of the platform owner and the needs of the designer. This research can not only conduct to green design of jack-up drilling platform, but also can contribute to the development, popularization and application of low-carbon technology on offshore platform. Finally, the case study results demonstrate the feasibility and efficiency of the proposed evaluation method.     

自升式平台冰激动力响应分析

应用ANSYS软件建立了平台和冰相互作用的有限元模型,构建了自升式平台的冰激振动模型,并计算基于2种冰力模型的自升式平台的动力响应。此动力分析方法具有建模方便和计算精度高的特点。以某自升式平台为例,计算了冰和平台结构相互作用的耦合效应,为自升式平台冰激振动安全评估提供了参考依据。     

Simulation analysis and experimental study of defect detection underwater by ACFM probe

This article studies the application of the alternating current field measurement (ACFM) method in defect detection for underwater structures. Numerical model of the ACFM system is built for structure surface defect detection in seawater environment. Finite element simulation is performed to investigate rules and characteristics of the electromagnetic signal distribution in the defected area. In respect of the simulation results, underwater artificial crack detection experiments are designed and conducted for the ACFM system. The experiment results show that the ACFM system can detect cracks in underwater structures and the detection accuracy is higher than 85%. This can meet the engineering requirement of underwater structure defect detection. The results in this article can be applied to establish technical foundation for the optimization and development of ACFM based underwater structure defects detection system.     

Collision Analysis Between Spudcan and Seabed During the Process of Jack-up Platform Lowering Jack-up Legs

China Ocean Engineering - In the leg-lowering process, the offshore jack-up platform is in a floating state, and the spudcan may collide with the seabed due to the platform motion in waves, thereby...     

The influence of pull-out load on the efficiency of jetting during spudcan extraction

Mobile jack-up drilling rigs are deployed at many locations during their service life. This necessitates retrieval of the platform’s legs and spudcan footings before the rig move. In soft soils, where the spudcans embed deeply, the extraction process can be difficult, time consuming and therefore costly. Water jetting systems, devised to ease spudcan extraction, are a common feature on modern jack-up units. However, their effectiveness in reducing the pull-out load required is questioned by the offshore industry. To investigate their efficiency, centrifuge experiments of a reduced scale spudcan model with jets have been performed at the University of Western Australia. The footing was extracted from penetrations of up to 1.5 diameters in normally consolidated clay. Similar to spudcan extraction in the field, these were carried out under load control, applying a constant extraction force. Both influences of pull-out load magnitude and jetting flow rate were investigated. The study demonstrates that jetting is efficient in facilitating spudcan extraction, as it reduces the required uplift load. Practical guidance is provided in applying the results to field conditions.     

海洋黏土超固结性和结构性对沉垫基础离底吸附力的影响

我国近海区域海床表面广泛存在一层深厚软黏土,具有一定的超固结性与结构性。自升式海洋平台沉垫基础的离底吸附力对海上平台的起浮回收影响显著。通过数值方法模拟了沉垫基础的作业工况,将可以描述土体超固结性和结构性的弹塑性本构模型通过UMAT子程序嵌入有限元软件ABAQUS中,采用可以描述材料强度破坏和刚度衰减的黏结接触模型模拟基础底与海床的相互作用,并通过现场模型试验对数值模型进行了验证。在此基础深入探讨了黏土海床超固结性和结构性对基础离底吸附力的影响规律。研究结果表明：沉垫基础上拔时,底部会产生负孔隙水压力,随上拔时间先减后增,且沉垫基础边缘位置率先发生离底;黏土超固结性越强,离底吸附力越大;黏土结构性越强,离底吸附力越小。     

Practical stochastic fatigue analysis of offshore platforms

A method for stochastic fatigue analysis of offshore platforms is presented. The method accounts for the nonlinearity in the drag loading term, and for the systematic deviation from a Gaussian process for a platform response. The method is based on an assumed form of the stress response process at a hot spot. A number of full scale measurements for elements in fixed platforms and for marine risers show very good agreement with this assumed form. A conventional spectral fatigue approach with stochastic linearization of the drag term in the basis for the new method, which uses results from linearizations in two or more sea states. The method is easily implemented in standard computer programs presently used within the offshore oil industry for fatigue analysis.     

海洋平台结构超声相控阵检测成像技术的发展及应用

介绍了超声相控阵检测成像技术的基本原理及其在海洋平台结构检测中的最新进展。超声相控阵技术采用区域划分法将焊缝分成垂直方向的若干区,由扫查器携带超声相控阵探头运动,对其分区进行电子扫查,检测结果以图像形式显示。探讨了超声相控阵技术用于海洋平台结构管节点焊缝检测时存在的一些问题,提出解决方法,指出其在海洋平台结构、压力容器、航空航天等工业无损检测领域将具有应用前景。     

海洋平台现场动态应力测试

迄今为至胜利浅海油田已相继建成大小平台几十座,平台结构型式是导管架式,志管架平台的结构计算理论已基本成熟,现场应力测试是对平台结构设计的验证、补充和发展,但是有关平台的现场应力测试在海洋工程界则是一个空白。本文主要介绍埕北２５Ａ井组平台现场应力测试的方法、结果以及与理论计算的对比。     

Estimation of Probability of Damage Detection in Offshore Structural Inspection

- To characterize the uncertainty and fuzziness in offshore structural inspection, probability of detection (POD) must be determined. This paper presents the expressions for the POD of four different damage forms mainly existing in offshore structures. The fuzzy-set theory is applied to estimate human errors through the definition of inspection quality. Expressions of inspection quality are achieved. To verify the validity and correctness of the expressions, the data from an offshore platform field inspection of evaluation results of human errors affecting inspection quality are used to estimate the parameters of the POD. The results show that the present models can provide basis for further study of ofTshore structural inspection reliability.