海上桶基平台基础边界条件的简化方法与结构优化

海上桶型基础平台采用桶型基础这一新型的基础型式,桶基平台在结构强度校核计算和结构优化中必须考虑其有限元分析模型的基础边界条件简化问题。本文提出了桶基平台有限元分析模型中的基础边界条件简化方法,将桶型基础边界简化为位移弹簧边界元,给出了弹簧刚度的计算方法。通过模型试验与本文提出方法的计算结果的比较,证明本文提出的方法是正确的。同时,将本文提出的方法应用于桶基火炬平台的结构优化,表明该方法是实际可行的并且对于桶基平台的结构强度校核计算与结构优化有重要意义。对于桶基火炬平台的结构优化采用了适合离散变量优化求解的遗传算法,优化的结果有效地降低了结构重量,降低了工程造价。     

考虑翘曲应力的半潜平台扭转极限强度计算方法研究

半潜平台由于结构和受力复杂,目前主要采用非线性有限元整体模型计算其扭转极限承载力,存在建模和计算时间较长、精度较差和不易收敛等问题。一方面进行半潜平台的整体有限元模型的简化研究,提高其计算效率和收敛性;另一方面基于薄壁杆件理论,将该半潜平台截面简化为单壁室截面计算其翘曲应力,提出了基于一跨模型且考虑翘曲应力影响的半潜平台约束扭转极限强度计算的简化增量迭代方法,并编制了相应的计算程序。计算结果表明,所提简化增量迭代方法计算精度较高,能很好地反应翘曲应力对半潜平台约束扭转极限强度的影响,大幅减少了计算约束扭转极限强度的时间,可用于半潜平台的设计。     

薄壁梁约束扭转极限承载能力简化计算方法研究

为了快速并有效地计算海洋平台等薄壁箱型梁结构的约束扭转极限承载能力,进行了薄壁梁约束扭转极限承载能力简化计算方法研究.基于塑性极限状态分析理论,提出了薄壁梁约束扭转极限状态应力分布假设,将薄壁梁视作为一系列由主要支撑构件和扶强材支撑的板格,推导了薄壁梁约束扭转极限承载能力上限的计算公式.应用非线性有限元方法验证了所提假设和计算公式的精度,将所提方法应用于箱型梁模型和半潜平台的约束扭转极限承载能力的计算分析,并与非线性有限元结果进行了比对,结果表明,本方法具有较高的精度,可用于海洋平台等薄壁梁的扭转极限承载力上限的估算.     

喷冲气举机构试验研究

介绍了气举机构的工作原理,并对正压冲固平台特定沉贯施工条件下的多种气举泵设计方案进行了来列试验研究．试验研究获取了气举装置的骑气量与排水量的关系和气举高度特性以及各种泵体结构参数,为正压冲固平台基础的沉贯设备设计提供了科学依据．     

“勘探三号”半潜式平台节点应力分析

本文对“勘探三号”半潜式平台的典型节点进行了有限元应力分析。文中对该典型节点进行了粗、细两种网格的计算,得到了相应的热点位置和应力集中系数。当有了平台总强度计算的节点应力后,根据文中定义的设计应力集中系数就可以方便地得到节点热点处的应力值,这对平台节点设计和校核是有实用意义的。     

海洋平台简化模型与系统参数的试验修正

利用动柔度法来进行桩基导管架平台损伤部位诊断,需要有一个能真实地反映原始平台动力特性的模型作为比较的基准。一般可用设计过程中的有限元模型作基准,但由于材料、工艺等因素,其有限元刚度阵特别是接头刚度很难准确地确定,故需通过模态实验来修正计算模型。通常,实测模志均少于测量自由度数,更远小于有限元自由度数。为了使测点与有限元分析自由度相对应,本文提出一种计算方法,将结构分为主、次自由度,主自由度对应测试点,用凝聚得到简化模型,并对简化模型的特征解进行灵敏度分析,利用实验测得的模态来修正有限元值,从而得到一个能够正确地反映结构特性的较为精确的有限元计算模型,然后,利用广义动柔度法检测损伤位置,提出一种确定损伤位置的计算方法。在文中给出了二层框架的计算和实验结果以及修正参数和二层框架损伤位置的确定。结果表明,利用实验模态修正计算数学模型,该方法是一种可行的途径。     

新型海洋平台裙装套筒结构的强度分析

从有限元的基本理论出发，对新型海洋平台裙装套筒结构进行有限元强度分析及计算。通过实例计算可知其强度、安全性、稳性等都满足规范要求，并能详细体现出结构应力和载荷特征，对模型模拟情况良好。     

具有裂纹损伤桩腿的海洋石油平台有限元分析

采用有限元分析方法和断裂力学方法,将含裂纹构件的裂纹以线弹簧处理,建立了带有裂纹损伤桩腿的等效梁和管单元的单元刚度矩阵的计算方法。对检验方法的正确性,使用该方法对几种损伤构件进行了强度计算,并与有限元细化网格计算结果和实验结果进行比较,最后将等效单元计算程序接入大型有限元程序ＳｕｐｅｒＳＡＰ,对受损后的平台整体结构进行了应力计算和强度分析。     

半潜平台疲劳热点应力长期分布参数研究

明确热点应力长期Weibull分布的参数是船舶与海洋工程结构应用疲劳简化分析方法的关键之一。以某深水半潜式平台为研究对象,通过整体结构有限元计算得到热点应力传递函数,结合波浪散布图计算热点应力长期分布概率函数,采用最小二乘法对热点应力长期Weibull分布进行参数估计。研究结果可为疲劳简化分析方法在半潜平台上的应用提供参考。     

船舶与海上移动平台焊接系数安全性验证研究

建立一套验证船体结构与海上移动平台规范焊缝安全性的理论方法,提出了船体与海上移动平台结构焊缝应力计算的3种模型和焊缝应力计算方法,确定了焊缝强度的应力标准。通过5个板条梁和4个短柱的焊缝强度试验,验证了焊缝的强度标准、焊缝应力公式的正确性和适用性。进行了11艘船体结构焊缝应力的提取和焊接系数利用因子的计算,获得了船体结构各类角焊缝利用因子的统计结果,证明现有规范的焊接系数符合GBS的要求。     

Elastic lateral-torsional buckling analysis of permanent means of access structure

International Maritime Organization (IMO) adopted a new regulation to request permanent means of access (PMA) for a regular inspection of ship structure. Horizontal platforms for an inspector to walk on should be provided at specified locations. The platform is attached perpendicular to longitudinal bulkheads or side shell like a common longitudinal stiffener. Since the platform is much wider than ordinary stiffeners, a mid-flat-bar is welded in the middle of the platform. The wide platform (i.e. the tall web plate) makes PMA structure prone to lateral torsional buckling prior to overall flexural Euler buckling subjected to axial compression. This study employs the Rayleigh-Ritz method to treat the elastic lateral-torsional buckling of the PMA structure. The deformation of the cross-section can be expressed using six independant parameters. Compared to the previous research for an ordinary stiffened plate (Hughes and Ma, 1996a), two additional parameters are employed to model the deformation of the mid flat bar. This study also proposes a new strain distribution of lateral bending introducing two respective neutral axes for the flange and the mid-flat-bar. Two mathematical models are developed for two cases; one without associated plating, and the other with both the plating and its rotational restraint. In the former, the coupling between the lateral torsional buckling (“tripping”) and the Euler buckling is investigated. In the latter, a plate rotational spring constant is suggested based on extended deformed shape of the plating. For each model, the validity of the proposed method is verified by a comparison with a number of linear buckling analyses carried out using the NASTRAN finite-element program.     

海上平台桶基沉贯渗流场的有限元法数值模拟

桶形基础平台是一种新型的海洋平台,这种型式的平台与传统的导管架式平台的主要区别在于采用桶形基础代替打下桩基础,桶形基础的负压沉贯过程是一个复杂的水动力过程,其关键在于主动脉施加的桶内外压力差产生渗流场,渗流场的形成与发展对于负压沉贯有决定性的影响。本文用有限元分析方法对桶形基础负压沉贯流流场进行动态模拟,建立了桶形基础负压沉贯过程中渗流场的有限元分析模型,模型试验的结果与按有限元分析计算模型得一的     

Calculation of Hydro-Dynamic Stability of the Soil Inside Bucket in the Process of Bucket Foundation Penetration

—The offshore platform with bucket foundations is a new type of offshore platform that distin-guishes from traditional template platforms by replacing driven piles with bucket foundations.The suctionpenentration of bucket foundation is a complicated hydro-dynamic process.The key of this process is theseepage field caused by the difference of pressure applied on purpose inside and outside the bucket.The ap-pearance and developement of seepage field has a decisive influence on the suction penetration process.Inthis study,the finite element analysis method is applied to the dynamic simulation of the seepage field ofsuction penetration of bucket foundation.A criterion is suggested to distinguish the hydro-dynamic stabili-ty of the soil inside the bucket according to the critical hydraulic gradient method.The reliability of themodel and its applicability to engineering practice have been proved through comparison between the re-sults of model test and finite element calculation.     

Energy Anaiysis for TMD-Structure Systems Subjected to Impact Loading

This paper investigates the characteristics of reduction of the lateral vibration by use of a Tuned Mass Damper (TMD) for offshore jacket platforms under impact loading. Unlike traditional analysis, the present analysis focuses on the energy concept of TMD/structure systems. In this study, a time domain is taken. The platform is modeled as a simplified single-degree-of-freedom (SDOF) system by extraction of the first vibration mode of the structure and the excited force is assumed to be impact loading. The energy dissipation and energy transmission of the structure-TMD system are studied. Finally, an optimized TMD design for the modeled platform is demonstrated based on a new type of cost function - maxi-mum dissipated energy by TMD. Results indicate that TMD control is effective in reducing the Standard deviation of the deck motion but less effective in reducing the maximum response under impact loading.     

单立柱桶基平台整体结构静,动力分析

桶基平台是以桶形基础代替传统的桩基础,是海洋工程结构的一种新型基础形式,该平台是板壳和梁组成的空间结构,受力复杂,本文采用弹性抗力法解决桶形基础与土壤相互作用,用水平弹簧模拟桶基与土壤相互作用,采用板壳和梁的计算模型对平台结构进行分析,为平台的结构设计提供了依据。     

软土地基中插入式大直径薄壁圆筒结构的一种简化数值计算方法

简述了对插入式大直径薄壁圆筒进行数值分析采用的力学机制，用弹簧元模拟薄壁圆筒与地基土体接触面间的连接所形成一种简化的数值计算模型，运用大型通用有限元软件ANSYS进行二次开发后对其进行数值计算与分析，比较了对筒内外淤泥粘土采用不同加固处理方法以及考虑相邻圆筒间采用不同边界约束条件时，对圆筒的应力和稳定性的影响。通过实例计算，验证了该数值模型的有效性与可行性，并得出一些有益结论。     

Case study on pile running during the driving process of large-diameter pipe piles

The super-long and large-diameter steel pipe piles are often adopted for the construction of offshore oil platforms in deep sea. One constructability issue related to driving heavy pipe piles is the pile running. The term pile running refers to the quick penetration of a pile into the seabed as a result of its high self-weight and low resistance from the seabed. The unexpected pile running can cause the steel wire of the hammer to break or even the loss of the hammer. A case study of pile running at an oil platform is introduced in this paper. A simplified theoretical method is proposed to explain the mechanisms of the pile running in this case. A factor of friction degradation is proposed to calculate the dynamic skin friction from the static ultimate skin friction of surrounding soil. The comparisons between the predictions to the case history show that the proposed simplified method can be used to predict the pile running condition.