水深对超大型FPSO波浪载荷响应影响试验研究

随着超大型浮式生产储卸油装置FPSO（floating production storing and offloading）在渤海浅水海域的广泛应用,水深对FP—SO波浪载荷响应的影响问题突现出来。对缩尺比为1：100的三模块分节模型进行了水深对超大型FPSO波浪载荷响应影响的试验研究,试验结果表明水深对FPSO波浪诱导载荷的影响很大。     

FPSO运动实测数据统计研究——“南海奋进号”FPSO实船测量研究Ⅰ

由于海洋平台现场实测受到种种客观和主观因素的制约,国内外相关研究很少.“南海奋进号”FPSO开展了长达25个月的实测试验,测量了FPSO六个自由度的运动.对该FPSO在2008年和2009年的运动数据进行统计分析,总结了“南海奋进号”FPSO在这两年不同季节中的运动规律,弥补了中国在海洋工程浮式结构物的运动及载荷实地测量技术方面的空白.     

FPSO限位技术

浮式生产储油船(FPSO)具有强大的油气处理、存储等功能,是海洋石油特别是深海油气开发的重要设备。在FPSO旋转半径内作业时,为保证其安全,并尽量减少FPSO停产时间,需要对FPSO进行限位操作。根据实践经验,总结了FPSO限位的相关技术,为以后的限位作业提供了有益参考。     

基于风洞试验的FPSO风载荷特性研究

当FPSO服役于目标油田时,将受到风浪流的作用力。其中,风力给FPSO一个恒定的静力,使其偏离原来的位置。风力计算在FPSO系泊系统的分析过程中是非常重要的。设计人员常常参考OCIMF进行风力计算,或者参考API规范得出。OCIMF为针对油轮的计算规范,但使用OCIMF计算FPSO风力及流力的方法,与FPSO的适应性仍需要进一步论证。API规范针对海上浮式系统,其计算风流力的方法使用也非常广泛,其原理为将FPSO上部各个模块风力叠加得出。以FPSO风载荷为研究对象,开展了风洞模型试验,获得了典型FPSO风载荷特性曲线,并将试验结果分别与OCIMF结果和API规范计算结果进行对比分析,最终给出FPSO风力计算方法的建议。本数据可用于FPSO的风力计算,也可为FPSO运动、系泊的设计研究提供参考。     

FPSO甲板上浪研究现状

浮式生产储油轮（FPSO）是当今海洋石油开发的主流设施。FPSO通常采用单点系泊系统,船首暴露在波浪作用下,定位于特定海域进行长达数年的长期作业,上浪的风险很大。甲板上浪及其产生的载荷已是当前国际FPSO工程和研究领域的热点之一。介绍了国内外在试验研究和理论研究两方面对FPSO甲板上浪研究的进展情况,并建议我国开展这方面的研究。     

南海复杂海况下FPSO压力容器关键结构安全性分析及试验研究

压力容器是FPSO油气处理模块的关键装置,其内部原油在船体横摇运动作用下,对内壁产生冲击载荷,致使封头出现应力集中现象甚至开裂,严重威胁海洋石油开采和FPSO工作人员安全.本文以南海118号FPSO压力容器为例,结合南海实际海况,建立了船舶运动响应方程;开展了基于FLU-ENT 数值模拟计算的压力 容器关键结构安全性评...     

FPSO串靠外输时的碰撞性能分析

FPSO与穿梭油轮进行串靠外输过程中,穿梭油轮首部可能与FPSO尾部发生碰撞事故,称为"尾碰"。目前的相关研究主要集中在碰撞过程中的风险分析,缺少对FPSO"尾碰"事故碰撞性能的合理分析与评估。本文针对某15万吨级FPSO,基于动态非线性有限元分析软件ABAQUS,采用同步损伤分析技术,研究了串靠外输过程中FPSO与穿梭油轮之间由于过分纵荡运动而引起的碰撞事故。通过数值仿真计算,分析了包括"尾碰"后结构的损伤变形、应力应变关系、碰撞力和吸能情况的船舶碰撞内部动力学,进而对FPSO尾部结构的碰撞性能进行评估。结果表明,FPSO尾部结构中板材结构吸收的能量约占尾部结构总吸能的75.5%,其吸能能力显著优于T型骨材结构,研究结果对FPSO尾部结构的耐撞性设计具有一定的参考意义。     

FPSO结构低周疲劳寿命计算方法研究

FPSO在海洋环境中频繁地进行装载与卸载操作,使FPSO船体结构产生较大的应力幅值,尤其是承受货油压力的内底纵骨。由于局部的应力集中,应力幅值超过材料的屈服强度,其装卸载次数小于104时,结构将产生低周疲劳。研究一种新的计算方法,根据Neuber假设进行塑性修正,通过应变范围得到伪热点应力范围,并确定热点应力与伪热点应力之间的关系。推导出一种新的S-N曲线作为低周疲劳的设计曲线,以伪热点应力作为计算量来预测低周疲劳寿命,降低了船体结构低周疲劳寿命计算的难度。     

随机变幅载荷下焊接接头的海水腐蚀疲劳研究

海上平台经受的波浪力作用是随机变幅循环载荷,本工作采用板状焊接接头模拟管节点热点焊趾处的受力状态,并模拟实际海洋环境与加载条件,海水温度为20℃循环流动,阴极保护电位为-850mV.(SCF),加载频率为0.2Hz,应力比为-1,进行随机变幅载荷下的海水腐蚀疲劳试验,试验结果与常幅载荷下的腐蚀疲劳寿命作了比较。本文利用线性累积损伤Miner法则,以随机变幅加载下的腐蚀疲劳寿命进行了估算,结果表明,估算的寿命与试验数据很接近,效果令人满意。     

Truss Spar平台桁架管节点疲劳分析

Truss Spar平台在风、浪、流的作用下,结构受力十分复杂,准确分析其疲劳强度相当困难。通过建立Truss Spar平台三维有限元模型,利用HydroD软件进行载荷预报、波浪搜索,得到产生最大应力幅响应的最不利浪向和相位角。运用Sestra软件进行整体有限元分析,得到的结果作为桁架管节点细化模型的边界条件,再用Nastran软件进行局部分析求得节点的热点应力,修正壁厚影响。最后根据DNV规范的S-N曲线计算了管节点的疲劳寿命。     

The Influence of Residual Stress on Plastic Buckling of Cylindrical Shells

-This paper adopts approximate formulas for residual stresses caused by cold bending for plates with stress-strain curve form a = K n. A typical distribution of the longitudinal residual stress due to welding is also assumed. The effects of residual stress due to cold bending and welding on plastic buckling of axially compressed cylindrical shells are studied by the finite element method.     

Prediction method of seismic residual deformation of caisson quay wall in liquefied foundation

The multi-spring shear mechanism plastic model in this paper is defined in strain space to simulate pore pressure generation and development in sands under cyclic loading and undrained conditions,and the rotation of principal stresses can also be simulated by the model with cyclic behavior of anisotropic consolidated sands.Seismic residual deformations of typical caisson quay walls under different engineering situations are analyzed in detail by the plastic model,and then an index of liquefaction extent is applied to describe the regularity of seismic residual deformation of caisson quay wall top under different engineering situations.Some correlated prediction formulas are derived from the results of regression analysis between seismic residual deformation of quay wall top and extent of liquefaction in the relative safety backfill sand site.Finally,the rationality and the reliability of the prediction methods are validated by test results of a 120 g-centrifuge shaking table,and the comparisons show that some reliable seismic residual deformation of caisson quay can be predicted by appropriate prediction formulas and appropriate index of liquefaction extent.     

动力型鱼雷锚基本结构与特性

鱼雷锚(torpedo anchor)自1996年被巴西石油公司(Petrobras)开发以来,一直得到国内外的广泛研究,并成功应用于巴西坎普斯湾的浮式生产储油卸油装置(FPSO)等系泊系统中。本文在分析现有鱼雷锚技术发展现状的基础上,介绍了一种拥有自主知识产权的动力型鱼雷锚技术,并描述了其内部结构和工作原理。通过实验室模型实验展示了其优越性能,最后指出了其工程应用前景。     

Simulation of green water flow on deck using non-linear dam breaking theory

Experiments carried out with models of floating production, storage and offloading platforms (FPSOs) showed that the flow of water over the deck edge, onto the deck resembled a suddenly released wall of water rather than a breaking wave. Therefore green water flow onto the deck was simulated using dam breaking theory, but the theory’s shallow-water assumptions may be limiting. In this paper a non-linear dam breaking problem is formulated. Equations of motion in the Lagrangian form are used and the solution is sought as an infinite series in time. Comparisons with the shallow water approximation are carried out.     

Measurement of platform conductor preload in streamlining the life extensions of ageing offshore wells

The life extension of ageing oil wells is becoming an ever more crucial part of an operator's activities in recent years, mainly due to slumping oil price which discourages new exploration and the potential extended operation of some older fields with sufficient producing capacity still remaining. The conductor forms one of the primary structural components of wells and its deterioration over time warrants immediate integrity assessment and rehabilitation plans. The construction residual loading or preloads on the conductor are calculated as per standard guidelines and by analytical means during its design and installation phase, but may not be realistic when assessing aged conductors, due to the high levels of over-conservatism built in to address the various uncertainties during the well drilling phase, hence a more practical means of evaluating this residual load is required in carrying out the integrity assessments. This article presents the novel use of ultrasonic based non-destructive technique (NDT) to measure the conductor preload by observing the travel time of the longitudinal critical refracted (LCR) waves and employing the acoustoelastic method to determine the structural stresses. The measurement of the time of flight (TOF) of this wave component is evaluated from the signals measurement under a range of preload stresses induced into the specimen, and the acoustoelastic calibration curve is obtained as a result, for various section geometries and dimensions. Numerical analyses are also carried out to correlate and validate the magnitude order of the acoustoelastic constant of typical conductor steel grade (grade-B). These are in good agreement with each other and can be a very reliable tool for the on-site preload measurements during oil well integrity assessment. This measurement of conductor preload results in minimising any associated uncertainties, assumptions and the corresponding over-conservatisms carried over from the design stage, hence streamlining the repair and rehabilitation strategies to the most critical well-conductor groups in the field, thus significantly reducing the costs and resources for operators in extending life of aged wells.     

The new simple design equations for the ultimate compressive strength of imperfect stiffened plates

The new simple design equations for predicting the ultimate compressive strength of stiffened plates with initial imperfections in the form of welding-induced residual stresses and geometric deflections were developed in this study. A non-linear finite element method was used to investigate on 60 ANSYS elastic–plastic buckling analyses of a wide range of typical ship panel geometries. Reduction factors of the ultimate strength are produced from the results of 60 ANSYS inelastic finite element analyses. The proposed design equations have been developed based on these reduction factors. For the real ship structural stiffened plates, the most general loading case is a combination of longitudinal stress, transverse stress, shear stress and lateral pressure. The new simplified analytical method was generalized to deal with such combined load cases. The accuracy of the proposed equations was validated by the experimental results. Comparisons show that the adopted method has sufficient accuracy for practical applications in ship design.     

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.     

Ultimate strength of ship hulls under torsion

For a ship hull with large deck openings such as container vessels and some large bulk carriers, the analysis of warping stresses and hatch opening deformations is an essential part of ship structural analyses. It is thus of importance to better understand the ultimate torsional strength characteristics of ships with large hatch openings. The primary aim of the present study is to investigate the ultimate strength characteristics of ship hulls with large hatch openings under torsion. Axial (warping) as well as shear stresses are normally developed for thin-walled beams with open cross sections subjected to torsion. A procedure for calculating these stresses is briefly described. As an illustrative example, the distribution and magnitude of warping and shear stresses for a typical container vessel hull cross section under unit torsion is calculated by the procedure. By theoretical and numerical analyses, it is shown that the influence of torsion induced warping stresses on the ultimate hull girder bending strength is small for ductile hull materials while torsion induced shear stresses will of course reduce the ship hull ultimate bending moment.     

Evaluation of storm wave-induced silty seabed instability and geo-hazards: A case study in the Yellow River delta

Models based on the theoretical framework of soil mechanics are presented to evaluate storm wave-induced silty seabed instability and geo-hazards through a case study in the Yellow River delta. First, the transient and residual mechanisms of wave-induced pore pressure are analyzed. Three typical models (i.e., elastic model, pore pressure development mode and elasto-plastic model) are proposed to calculate wave-induced stresses in the seabed. Next, mechanisms and calculation methods of wave-induced seabed instability modes such as scour, liquefaction, seepage instability and shear slide are proposed. Typical results of storm wave-induced excess pore pressure and seabed instability are given and relevant discussions are made. At last, the formation mechanism of geo-hazards in the Yellow River delta is analyzed based on the proposed mechanism and calculated results. Results and analysis indicate that both transient and residual mechanisms are important to storm wave-induced response of silty seabed and hence the elasto-plastic model is more appropriate. Complete liquefaction does not happen, while other types of instability occur mostly within 2–6 m under the seabed surface. Wave-induced scour, seepage instability and shear slide are all possible instability modes under the 1-year storm waves, and scour is predominant for the 50-year storm waves. The formation mechanism of geo-hazards such as shallow slide and storm wave reactivation, pockmarks, silt flow and gully, disturbed stratum and hard crust in the Yellow River are well explained based on the proposed mechanisms and calculated results of storm wave-induced silty seabed instability.