基于贝叶斯算法的自升式平台桩靴基础砂-黏地层峰值阻力预测

自升式平台在含有砂-黏地层井位就位过程中,受下卧软土层影响,易发生桩靴大位移贯入下卧地层造成穿刺破坏,准确预测桩靴基础砂-黏地层峰值阻力及相应深度,对保障平台安全至关重要。基于已有离心机模型试验数据,通过引入服从Beta-PERT分布的不确定性因子,构建了自升式平台桩靴基础砂-黏地层潜在峰值阻力及对应深度的先验概率和似然概率计算模型;结合桩靴贯入过程中的监测数据,利用贝叶斯算法计算并持续更新后验概率,以提高桩靴基础砂-黏地层峰值阻力的预测精度。在此基础上,通过反分析25组离心机模型试验,对基于贝叶斯算法的桩靴基础砂-黏地层峰值阻力预测方法的有效性进行了验证。结果表明,相较于现行ISO规范和SNAME规范推荐的荷载扩展法和冲剪法以及新近发展的3种峰值阻力计算方法,基于贝叶斯算法的概率预测方法可有效提高桩靴基础砂-黏地层峰值阻力的预测精度。研究成果为自升式平台桩靴基础在含有砂-黏地层井位就位安全评估提供了方法支持。

桁架-齿轮齿条式平台桩腿导向装置设计优选

位于升降基础内的导向装置是桩腿升降过程中所依赖的重要组件,平台的频繁升降也极易使导向装置造成损伤和脱落。通过选取三型具有典型代表意义的自升式平台,对其导向装置布置、限位方式、耐磨板与齿尖间隙以及固定方式等方面进行理论论证和案例分析,对所选取的三型平台导向装置设计特点和优劣进行对比并得出结论。

Study on General Performance of Jack-up Under Elevated Condition

Method of checking for jack-up elevated performance including leg structure strength, fixation system or jacking system beating capacity, pre-load requirements, spud can beating capacity and overturning stability is suggested in this paper. As an example, a jack-up with truss legs is analyzed by finite element analysis method. This paper may be helpful to the rig owners, operators and designers.

Soil-Structure Interaction Analysis of Jack-up Platforms Subjected to Monochrome and Irregular Waves

As jack-up platforms have recently been used in deeper and harsher waters, there has been an increasing demand to understand their behaviour more accurately to develop more sophisticated analysis techniques. One of the areas of significant development has been the modelling of spudean performance, where the load-displacement behaviour of the foundation is required to be included in any numerical model of the structure. In this study, beam on nonlinear winkler foundation （BNWF） modeling--which is based on using nonlinear springs and dampers instead of a continuum soil media--is employed for this purpose. A regular monochrome design wave and an irregular wave representing a design sea state are applied to the platform as lateral loading. By using the BNWF model and assuming a granular soil under spudcans, properties such as soil nonlinear behaviour near the structure, contact phenomena at the interface of soil and spudcan （such as uplifting and rocking）, and geometrical nonlinear behaviour of the structure are studied. Results of this study show that inelastic behaviour of the soil causes an increase in the lateral displacement at the hull elevation and permanent unequal settlement in soil below the spudcans, which are increased by decreasing the friction angle of the sandy soil. In fact, spudeans and the underlying soil cause a relative fixity at the platform support, which changes the dynamic response of the structure compared with the case where the structure is assumed to have a fixed support or pinned support. For simulating this behaviour without explicit modelling of soil-structure interaction （SSI）, moment- rotation curves at the end of platform legs, which are dependent on foundation dimensions and soil characteristics, are obtained. These curves can be used in a simplified model of the platform for considering the relative fixity at the soil- foundation interface.

Design of A Bionic Spudcan and Analysis of Penetration and Extraction Performances for Jack-up Platform

The mechanisms of soil structure interaction have drawn much attention in the past years in the installation and operation of jack-up platform. A bionic spudcan produced by biomimetic of egg and snail shell is proposed, and the performance of the penetration and extraction are analyzed by numerical method. The geometric contour of egg and snail shell is measured, and its mathematical model is established respectively. According to the structure of existing spudcan of jack-up platform, three kinds of typical biomimetic spudcan are designed. Furthermore, numerical analysis models of biomimetic spudcan are established respectively to study the soil structure interaction mechanism in the process of penetration and extraction, and contrastive analysis of resistance characteristics are carried out. To conclude, the results show that the biomimetic spudcan facilitates the platform installation, and it is also beneficial to the improvement of the bearing capacity of spudcan.

The Calculating Model of Structural Analysis for Jack-Up Rig Legs

The selection or establishment of structural calculating model is a matter of primary importance in structural analysis. By analysing the irrationality of the calculating models used by some research organizations at home and abroad in structural analyses for truss jack-up rig legs, this paper introduces a new calculation model which is more reasonable. This model can simulate better the load situation of a rig reflecting more precisely the effects of the leg loads caused by the spring support of gearboxes of the jacking system and the secondary bending moment raised by hull displacement under extreme conditions. The rig conversion was completed in 1989. In July 1991 the rig safely stood the frontal hitting of Typhoon with the wind speed of 52 m / s, which shows that the checking on the structure is correct.

Prediction Methods of Spudcan Penetration for Jack-up Units

Jack-up units are extensively playing a successful role in drilling engineering around the world, and their safety and efficiency take more and more attraction in both research and engineering practice. An accurate prediction of the spudcan penetration depth is quite instrumental in deciding on whether a jack-up unit is feasible to operate at the site. The prediction of a too large penetration depth may lead to the hesitation or even rejection of a site due to potential difficulties in the subsequent extraction process; the same is true of a too small depth prediction due to the problem of possible instability during operation. However, a deviation between predictive results and final field data usually exists, especially when a strong-over-soft soil is included in the strata. The ultimate decision sometimes to a great extent depends on the practical experience, not the predictive results given by the guideline. It is somewhat risky, but no choice. Therefore, a feasible predictive method for the spudcan penetration depth, especially in strata with strong-over-soft soil profile, is urgently needed by the jack-up industry. In view of this, a comprehensive investigation on methods of predicting spudcan penetration is executed. For types of different soil profiles, predictive methods for spudcan penetration depth are proposed, and the corresponding experiment is also conducted to validate these methods. In addition, to further verify the feasibility of the proposed methods, a practical engineering case encountered in the South China Sea is also presented, and the corresponding numerical and experimental results are also presented and discussed.

Jack-up日费对钻修井机具比选的敏感性分析

低油价下大量自升式钻井平台(Jack-up)资源处于闲置状态,在油服公司为降低损失,允许Jack-up日费有较大谈判空间的情况下,对于推荐采用固定式钻修井机具开发的油气田,有必要反算出与推荐方案投资相平衡的Jack-up日费,从而与油服公司谈判,以不高于平衡日费的条件租赁Jack-up,达到降低开发成本的目的。通过研究Jack-up日费对油气田开发各组成费用的影响,得出了油气田开发投资随日费变化的计算方法,对海上油气田开发的钻修井机具选择具有重要的指导意义。

Discussion on Key Points of Wind Load of Jack-up Unit

The anti-overturning ability and structure safety of jack-up unit in in-place condition are often affected by environment loads, especially wind load. According to the MODU rule, the projected area method is used for calculating the wind load. However, the calculated results are conservative and not good for structure optimization design. In this paper, a 400 ft jack-up is studied as an example. Based on the wind tunnel test and numerical simulation method, some key points of wind load calculation, such as shielding effect, lift effect and shape coefficient of component, are discussed. The study shows that the points mentioned above, which are ignored in the MODU rule calculation, result in the conservative result.

新型平台桩靴在“砂-黏”地层中穿刺的数值模拟研究

开发了一种新型平台桩靴,可通过活动板转动实现自升式平台不同阶段桩靴受力面积的灵活变化。基于大变形有限元方法,模拟新型桩靴基础在“砂-黏”地层中的贯入过程,分析了活动板转角、砂层厚度比、摩擦角和黏土层不排水抗剪强度对新型桩靴贯入阻力的影响,并与普通桩靴的贯入响应比较。数值分析中,上覆砂土和下层黏土分别采用摩尔库伦模型和修正Tresca模型进行模拟。结果表明:新型桩靴穿刺时,土层参数对峰值阻力的影响规律与普通桩靴相同,但其峰值阻力随活动板转角的变化而变化,无法直接使用具有等效面积普通桩靴的穿刺预测方法。考虑各项关键影响因素,结合穿刺破坏时的地基破坏模式,基于数值模拟结果提出了适用于新型桩靴的贯入阻力预测公式。

Uplift Resistance Calculation and Sensitive Analysis of Jack-up Wind Installation Vessels

The uplift resistance calculation is an important basis for the construction decisions of the jack-up wind installation vessel and the design of the jacking system,and determines the operation risk and reliability in the installation process of the wind turbine. The influence factors of the pile shoe's penetration depth and uplift resistance are analyzed,and the calculation model and flow of the uplift resistance are given. Based on a construction example,the influence rules are analyzed for the change of the pile shoe's structural parameters on the penetration depth and uplift resistance.The analysis results show that the penetration depth is more sensitive to the width of the pile shoe,and the height has greater influence on the uplift resistance than the length and width of the spud. With the increase of the height,the uplift resistance may increase rapidly.Although the decreases of the length,width and height of the pile shoe may reduce the uplift resistance,the penetration depth may increase in the meantime. This will increase the pulling pile time and reduce the construction efficiency. So the parameters of the pile shoe should be optimized according to the adaptable geology condition so as to obtain the optimal uplift resistance and working efficiency.

砂土中桩靴插桩对临近筒型基础的影响研究

通过物理模型试验和有限元法研究砂土中风电安装船桩靴插桩对临近筒型基础的影响。首先通过物理模型试验,验证有限元模型的合理性,初步确定桩靴在砂土中贯入的影响范围大致在2.5倍桩靴直径。基于有限元CEL方法进一步研究桩靴和筒型基础的净距与桩靴直径之比(S/D)对筒型基础在位稳定性的影响。结果表明:筒型基础的倾斜率、最大竖向位移以及筒壁应力随着S/D的增大而逐渐减小,插桩过程中,靠近桩靴一侧的筒裙和分舱板应力远大于远离桩靴一侧的筒型基础应力,且筒顶的土压力远小于筒底土压力。

一种海洋自升式修井平台船型分析

针对渤海海域油气开发中自升式修井平台的船型设计,进行系统分析。从桩腿数量维度出发,考虑波流载荷、风载荷和平台重力的共同作用,通过有限元数值模拟软件,建立自升式修井平台的仿真模型,计算不同方向角下平台的波流载荷、桩腿位移和抗倾力矩等评价指标,综合对比分析三桩腿和四桩腿两种不同船型的设计特点,以揭示各自在平台方案、预压载能力和稳定性等方面的特点。研究结果发现,四桩腿平台在舱内设备布置、预压载能力和抗倾稳性方面具有明显优势,特别是在单桩失效情况下,四桩腿平台的稳定性和安全性更高。研究结论对自升式修井平台的设计优化具有重要的指导意义,为进一步提升平台的安全性和高效性提供理论依据。

自升式平台桩靴周围土体冲刷机制及数值模拟

为了评估自升式平台插桩后桩靴周围土体受波流-海流作用局部冲刷的安全性,基于计算流体动力学通过数值模拟建立波流作用下的桩靴周围土体局部冲刷的三维有限元数值模型,通过求解Navier-Stokes方程,准确模拟桩靴周围流场变化情况;基于现场作业场址参数和实际海况条件下建立适用于自升式平台桩靴周围土体局部冲刷的工程分析方法,将数值结果与试验结果进行对比;讨论自升式平台在不同入泥深度和作业周期下桩靴周围土体局部冲刷问题。结果表明:波流共同作用下自升式平台桩靴入泥深度对桩靴周围土体局部冲刷深度具有较大影响,当桩靴入泥深度越小时,桩靴周围越容易发生局部冲刷;基于桩靴不同入泥深度工况针对性地制定冲刷防护措施,降低桩靴周围土体局部冲刷深度,有效降低工程作业风险。

多跨预应力混凝土连续梁整体平移改造施工关键技术

宿迁古黄河老桥为(22.5+3×30+22.5)m四幅分离式连续梁桥,两侧为非机动车道桥,中间为机动车道桥。由于该桥位于生态保护区且梁体质量良好,为满足迎宾大道二期快速化改造需要,采取在不中断交通的前提下,通过交通导改先后将西侧和东侧机动车道桥分别往两侧整体平移3.25 m,再于中间修建新桥的改造方案。结合桥位处水文地质情况,采用在非机动车道桥外侧设置“钢板桩+过水钢管”围堰进行无水条件下的基础墩身拼宽施工。改造施工时,根据单侧机动车道桥支座处顶升荷载及梁底空间选配布置顶升千斤顶和步履器;通过有限元计算确定梁体顶升与平移施工过程中各支点竖向和横向位移偏差控制指标,采用PLC液压同步控制系统操控步履器与千斤顶交替顶升与平移,既能保证梁体整体顶升与平移的精度又能有效控制梁体应力突变;待梁体平移到设计位置后,拆除步履器和顶升千斤顶,复原垫石、支座及挡块。

网衣对自升式桁架网箱结构响应的影响

自升式桁架网箱凭借便于将养殖箱体下潜入水的结构特性,为更好地适应深远海养殖极端环境提供了一种选择。网衣作为桁架网箱关键部件,通过纲绳系缚于桁架管上,在外部环境载荷作用下可能会对网箱主体结构强度产生影响。针对一种自升式桁架网箱,基于SESAM/GeniE建立其有限元分析模型,分析了在有无网衣及不同网衣参数条件下的网箱主体结构响应。结果表明:网衣对网箱主体结构响应评估存在较大影响,尤其在流速较高时,网衣阻力大幅增加,直接影响网箱桩腿受力和桁架利用系数(Utilization factor,UF)值,证明在校核网箱主体结构强度时不可忽略网衣的作用;不同网目群化比下,网衣对自升式深海网箱整体结构响应评估结果影响不大,在网箱主体结构响应仿真计算中可以考虑使用较大的网衣群化比来提升计算效率;网衣系缚纲绳数量变化对网箱主体结构的响应评估基本无影响,但增加系缚纲绳可以有效减少纲绳受力。

黏土中大直径钢圆筒在桩靴贯入时的稳定性研究

某在建水下生产系统附近有自升式平台的频繁桩靴插拔作业,采用了大直径薄壁钢圆筒作为水下生产系统的保护结构,因此钢圆筒在自升式平台桩靴插拔过程中的受力与变形备受关注。开展了离心模型试验,揭示了桩靴贯入过程导致的钢圆筒受力与变形规律;进而应用经离心试验验证的耦合欧拉与拉格朗日数值模拟方法,开展了筒-靴不同相对位置工况下,桩靴贯入对钢圆筒稳定性的影响分析。结果表明:桩靴贯入导致的筒壁附加应力及位移随筒-靴间距的增加而衰减,其衰减程度随筒靴间距的增加而减小,且由于筒靴间距的不同,钢圆筒对应存在两种受力模式。筒靴间距为2倍桩靴直径时,筒身附加应力可达110 MPa,表明桩靴对钢圆筒的影响距离可达2倍桩靴直径以上。

浅海高压立管涡激振动及疲劳特性分析工艺

随着东海油气资源的不断开发,开发成本较低的自升式平台将得到广泛应用。立管所在海洋环境复杂多变,其结构长度与直径比值较大,在海流作用下会发生涡激振动。采用尾流振子模型对高压立管涡激振动响应进行预报,并基于DNV规范,根据S-N曲线法对结构疲劳进行计算。模型通过有限差分法进行离散求解。研究重点关注顶张力对立管的涡激振动及疲劳特性影响。结果表明,顶张力会影响立管的涡激振动响应,并进一步改变结构的疲劳寿命,影响结构安全性。

基于模型拖曳试验与CFD阻力计算的自升式平台主机功率估算

为了确定具有自航能力的自升式平台主机功率,分别采用缩尺比模型拖曳试验与CFD数值计算两种方法计算设计航速下平台模型的静水阻力,分析阻力中各主要成分的比重,结合实尺度平台CFD计算结果对实际平台的阻力和主机功率进行估算,试验与数值分析结果均表明,平台首部存在水流堆积现象,平台的粘压阻力较大,占总阻力中的比重也大;采用二因次法从缩尺比模型阻力推算到实尺度平台阻力会有较大误差,采用实尺度CFD计算方法给出较为合理的平台主机功率估算结果。

海上自安装平台高应力区域有限元分析及应力监测点选择

自安装平台是海洋油气勘探开发的重要设施,但其关键结构长期面临风、浪、流等交变载影响,易产生交变应力,进而造成疲劳损伤,因此监测自安装平台关键结构应力十分必要。利用有限元软件,分析自安装海洋平台的桩腿和主体部分结构的应力分布,以便确定平台桩腿、上下环梁、围阱区、隔水管架及海水泵架结构的高应力区域,然后选取适用的应力传感器及安装位置。结果表明,选择自安装平台桩腿结构的桩销连接处、上下环梁区域的提升装置与甲板的连接处、围阱区下甲板区域、隔水套管与甲板连接点及海水泵架与甲板连接处作为高应力区域监测点,有利于准确诊断平台状况和及时预警,消除安全隐患。