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。     

Finite Element Analysis of Deformed Legs of Offshore Platform Structures

The element stiffness matrix of the equivalent beam or pipe element of the deformed leg of the platform is derived by the finite element method. The stresses and displacements of some damaged components are calculated, and the numeri-cal solutions agree well with those obtained by the fine mesh finite element method. Finally, as an application of this method, the stresses of some platform structures are calculated and analyzed.     

Developing a robust SHM method for offshore jacket platform using model updating and fuzzy logic system

Structural monitoring is essential for ensuring the structural safety performance during the service life. The process is of paramount importance in case of the offshore jacket-type platforms due to the underwater structural parts subjected to the marine environmental conditions. This work is an experimental investigation on a laboratory model of a jacket platform with the objective of establishing a baseline finite element (FE) model for long-term structural health monitoring for this type of structures. A robust damage diagnosis system is also developed which is less sensitive to both the measurements and the modeling uncertainties. Experimental vibration tests are conducted on a physical platform model to obtain dynamic characteristics and then, the initial FE-model of the intact structure is developed to determine them numerically. Some differences between numerically and experimentally identified characteristics emerge due to various uncertainties in the FE-model and measured vibration data. To minimize these differences, initial FE-model is updated according to the experimental results. The updated FE-model is employed to predict the changes in the dynamic characteristics under variety of damage scenarios which are imposed by reducing the stiffness at the components of the model. Fuzzy logic system (FLS) and probabilistic analysis is developed for linguistic classification of damage and global damage diagnosis. Incorporation of the FLS fault isolation technique into FE-model updating method are proposed and evaluated for two different FLS methods to develop a vigorous damage diagnosis method. The efficiency of the technique is validated by different damage scenarios foreseen on the physical model. This technique is shown to be effective for diagnosing the presence of degradation and quantify it.     

A Simple Empirical Formula for Predicting the Ultimate Strength of Ship Plates with Elastically Restrained Edges in Axial Compression

An investigation is conducted on the static ultimate limit state assessment of ship hull plates with elastically restrained edges subjected to axial compression. Both material and geometric non-linearities were considered in finite element(FE) analysis. The initial geometric imperfection of the plate was considered, while the residual stress introduced by welding was not considered. The ultimate strength of simply supported ship hull plates compared well with the existing empirical formula to validate the correctness of the applied boundary conditions, initial imperfection and mesh size. The extensive FE calculations on the ultimate strength of ship hull plates with elastically restrained edges are presented. Then a new simple empirical formula for plate ultimate strength is developed, which includes the effect of the rotational restraint stiffness, rotational restraint stiffness, and aspect ratios. By applying the new formula and FE method to ship hull plates in real ships, a good coincidence of the results between these two methods is obtained, which indicates that the new formula can accurately predict the ultimate strength of ship hull plates with elastically restrained edges.     

聚酯系缆损伤对绷紧式系泊系统动力响应影响的数值分析

由于聚酯缆绳具备优异的力学性能,促使以其为主体系缆的绷紧式系泊系统得以广泛应用和发展。但聚酯系缆具有复杂的黏弹性和黏塑性,且由于在安装和使用过程中可能产生不同程度的损伤,使得聚酯系缆的动刚度特性发生演变,从而对系泊系统的动力响应产生直接影响。以一系泊于1 020 m水深的Spar平台为例,运用ABAQUS软件建立了由聚酯缆绳组成的系泊系统有限元模型,并利用ABAQUS子程序将损伤缆绳动刚度经验公式进行导入计算,以更好地反映系缆真实的动刚度变化。基于该有限元模型,计算了在相同水流、波浪工况下,不同损伤度、不同损伤系缆的系缆张力历程和平台的横荡、纵荡位移响应,分析了不同损伤度、不同损伤系缆对系缆张力及平台位移的影响。这些成果对把握绷紧式系泊系统在聚酯系缆有损伤情况下的非线性动力响应及其安全应用具有重要的参考价值。     

Vibration Characteristics of An Offshore Platform and Its Vibration Control

A template offshore platform, located in the Bohai Bay of China, has exhibited excessive, unexpected vibration un-der mildly hostile sea conditions, which has affected the normal operation of the platform. Since the structure was de-signed to sustain more severe wave climate, the cause of the excessive vibration has been suspected to originate from other sources. The main objectives of this study are to investigate the causes of the excessive vibration, and to explore possible remedies to solve the problem, In this paper, the vibration behavior of the offshore platform is analyzed by means of finite element (FE) modeling, field measurements and laboratory test. Results of analysis suggest that relative movement and impact between the piles and the jacket legs exist, i. e. the piles and the jacket are not perfectly connected. The discon-nection of the piles and jacket weakens the overall stiffness of the platform, and therefore produces unexpected excessive vibration. In this study, measures for reducing     

Behavior of unbonded flexible risers subject to axial tension

Owing to nonlinear contact problems with slip and friction, a lot of limiting assumptions are made when developing analytical models to simulate the behavior of an unbonded flexible riser. Meanwhile, in order to avoid convergence problems and excessive calculating time associated with running the detailed finite element （FE） model of an unbonded flexible riser, interlocked carcass and zeta layers with complicated cross section shapes are replaced by simple geometrical shapes （e.g. hollow cylindrical shell） with equivalent orthotropic materials. But the simplified model does not imply the stresses equivalence of these two layers. To solve these problems, based on ABAQUS/Explicit, a numerical method that is suitable for the detailed FE model is proposed. In consideration of interaction among all component layers, the axial stiffness of an eight-layer unbonded flexible riser subjected to axial tension is predicted. Compared with analytical and experimental results, it is shown that the proposed numerical method not only has high accuracy but also can substantially reduce the calculating time. In addition, the impact of the lay angle of helical tendons on axial stiffness is discussed.     

Finite element analysis of ship structures using a new stiffened plate element

A new stiffened plate element is developed for the three-dimensional finite element analysis of ship structures. The plate element can accommodate any number of arbitrarily oriented stiffeners and obviates the use of mesh lines along the stiffeners. The new element provides a very economic global analysis of the complete ship structure with fewer elements and without any loss of accuracy. The global analysis of a rectangular box shaped vessel is carried out with the present element and compared with the general-purpose finite element software NISA. An Offshore Tug/Supply Vessel is analysed for crest at perpendiculars.     

Stress Variation Model of Bond Stress-Slip Relationship Between Steel Bar and Concrete

Based on the experimental data, a stress variation model of the bond stress-slip relationship between steel bar and concrete is established. The characteristic of the model is that the boundary conditions are satisfied very well; the effects of the material properties, the concrete cover, the crack spacing and the distance from the cracked cross section are considered. Good agreement between measured and calculated bond stress-slip relationship is found. This model is useful for the study of the stiffness, deformation and crack width of reinforced concrete members, and for the nonlinear analysis of reinforced concrete structures by the finite element method.     

多稳态夹芯金属压杆的滞后阻尼增强机制与被动减振性能

破碎波浪砰击于导管架等海洋工程结构,产生瞬态强载荷及长时振动。高刚度金属结构可抵抗瞬时强载,但金属固有阻尼极低而难以有效抑制振动,从而加剧结构损伤乃至失效。为使单一结构同时具有高刚度和高阻尼,设计一种多稳态夹芯金属压杆,有限元模拟表明该类压杆稳态随循环载荷依序转换,对应刚度变化使力—位移间产生滞后关系,使高刚度金属压杆具有高效耗散能力;采用夹芯结构弹性理论和发展变边界结构稳定理论,给出了该类压杆的稳态转换阈值和刚度变化过程,与有限元模拟一致;以有限元模拟方法获得了承载和阻尼特性的几何参数相关性;以该类压杆替换导管架斜撑,用有限元方法模拟瞬态强载下结构振动,计算结果表明多稳态夹芯金属压杆保证导管架高刚度同时显著增强了阻尼。     

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     

靠球减震系统在导管架平台中的应用

导管架生产储油平台在油轮靠泊和外输期间,如遇风浪天气,平台的晃动非常明显,为此引入橡胶靠球减震系统。运用ANSYS有限元分析软件,建立导管架生产储油平台的真实有限元模型,计算平台在靠船碰撞力和波浪力共同作用下平台关键点位置应力变化及振动响应过程,为靠球减震系统在实际工程中应用提供理论依据。     

On the external pressure capacity of deepwater sandwich pipes with inter-layer adhesion conditions

Sandwich pipes (SP), a composite structure consisting of two concentric steel tubes and a polymeric or cement-based core has been proposed to be well-insulated and withstand high installation and operational loads in deepwater oil and gas field. In the paper, the post-buckling responses and pressure capacity of sandwich pipes filled with the solid polypropylene annular were investigated. The degree of the inter-layer adhesion condition between the core layer and the surrounding pipes was modeled by the contact surfaces adopting different maximum shear strength values to allow the relative displacement between the layers. The effects such as inter-layer adhesion interactions, thickness-to-radius ratios, the core thickness, the material parameters, the relative initial ovality directions and the inelastic anisotropy on the collapse pressure of SPs were discussed. More than 2000 finite element (FE) models of the sandwich pipes with practical configurations were constructed and analyzed using the programming language Python within the FE software package ABAQUS. Based on the FE results, a simplified equation was developed and recommended for the collapse pressure calculation of sandwich pipes with the polypropylene annular.     

Postbuckling Analysis for Offshore Pipelines with Residual Stresses

Based on the finite displacement theory of elastic shells, the postbuckling behaviour of submarine pipelines with residual stresses is investigated by using a new finite element formula. The corresponding complementary energy functional is first constructed, and then a geometrical stiffness matrix suitable for the postbuckling of a cylindrical shell is derived. In this matrix the effects of initial stresses and harmonic coupling terms have been considered. The formulation presented in this paper can be used to solve a significant class of problems in the analysis of elastic shells.     

考虑桩土作用独桩海洋平台横向振动特性研究

采用动Winkler弹性地基梁模型模拟桩土问动力相互作用，并考虑了流体与桩问相互作用，通过组合成层土中、水中桩单元的刚度阵，推得了独桩海洋平台连续系统横向振动的动刚度阵及在波浪力作用下平台甲板处的频率响应函数，进而求得了在确定性波浪力及随机波浪力作用下桩身任意点的位移响应。最后，通过算例研究和分析了在随机波浪力作用下成层土参数、甲板上重量及冲刷淘深等因素对平台振动响应的影响。     

Full-range nonlinear analysis of fatigue behaviors of reinforced concrete structures by finite element method

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Static Analysis of Collision Strength of Offshore Platform

In this paper a numerical analysis method combining FEM incemental technique with limit analysis concept is proposed for the study of the static strength of offshore platform in collision. Large deformation and plasticity are accounted for and the limit yield surface expressed by generalized stress for a tubular section is derived. The modified stiffness matrix of space beam element is formulated by Plastic Node Method. The buckling behavior of beam columns can also be taken into account. It can trace the generation of plastic hinges during loading and finally the ultimate strength of offshore platform against collision is obtained.     

有限元方法在台湾以东海域黑潮流速计算中的应用

1956-1960年间由Turner[13],Clough[16]等引入有限元概念、方法以来,首先在结构分析领域内取得极大进展.与此同时,它也应用于固体力学的许多领域[2,4,7].在七十年代,有限元方法较广泛地应用于流体力学的许多领域[3,11,12].最近几年来,有限元方法也应用于物理海洋学中的一些问题中,例如湖泊与海洋环流问题[14,15,19],潮汐与风暴潮问题[17]等.本文从流体力学原理出发,应用有限元理论建立了黑潮的三维流场有限元方程组.采用了海流理论中常见的物理模式[1,5,18],考虑了压力梯度、柯氏力、重力、水平与垂直方向上的湍流摩擦效应,而不考虑惯性力的影响.本文对所应用的有限元几何形状——三角棱柱进行了插值误差分析,证明了三角形棱面不能出现较大的钝角,也证明了完备性的问题.并将动力计算和有限元二种方法计算的流速进行了比较.     

固定式海洋平台极限强度试验研究

根据墨西哥湾某海域一典型固定式海洋平台为原型,按照几何相似准则和刚度相似准则设计并制作海洋平台试验模型,开展极限强度模型试验研究,观察并记录其破坏过程。并采用非线性有限元方法(ANSYS)对试验模型进行极限强度数值计算,将计算结果与试验结果对比,结果表明计算结果与试验结果吻合较好,验证非线性有限元方法的有效性。     

正压冲固平台结构分析中基础边界条件的影响

正压冲固平台是一种采用短桩加固基础的新型海洋采油平台,对于这种新型的平台结构,在结构分析和构件强度校核中必须考虑其有限元模型的基础边界条件处理问题。本文提出了正压冲固平台有限元计算模型中基础边界条件的一种简化方法,将两个水平方向的扭转自由度简化为扭转弹簧边界元,其余自由度简化为固定约束。通过计算分析得到了不同的边界约束刚度系数的取值对平台总体位移和强度校核应力的影响及变化趋势。结论是,平台结构对约束刚度系数K的反应在10^4～10^4之间时比较明显,对K的敏感度最为强烈：在此范围之外,平台反应分别接近于简支约束情况和刚性约束情况。尤其对于接近约束边界的单元,其应力变化最敏感。