Theoretical Model and Dynamic Analysis of Soft Yoke Mooring System

As a popular solution for mooring an FPSO （Floating Production, Storage and Offloading） permanently in shallow water, the soft yoke mooring system has been widely used in ocean oil production activities in the Bohai Bay of China. In order to simulate the interaction mechanism and conduct dynamic analysis of the soft yoke mooring system, a theoretical model with basic dynamic equations is established. A numerical iteration algorithm based on error estimation is developed to solve the equations and calculate the dynanfic response of the mooring system due to FPSO motions. Validation is conducted by wave basin experimentation. It is shown that the numerical simulation takes only a few iteration times and the final errors are small. Furthermore, the calculated results of both the static and dynamic responses agree well with those ones obtained by the model test. It indicates that the efficiency, the precision, the reliability and the validity of the developed numerical algorithm and program are rather good. It is proposed to develop a real-time monitoring system to further monitor the dynamic performance of the FPSO with a soft yoke mooring system under various real sea environments.     

Lateral Vibration Behavior Analysis and TLD Vibration Absorption Design of the Soft Yoke Single-Point Mooring System

Mooring system is the key equipment of FPSO safe operation. The soft yoke mooring system is regarded as one of the best shallow water mooring strategies and widely applied to the oil exploitation in the Bohai Bay in China and the Gulf of Mexico. Based on the analysis of numerous monitoring data obtained by the prototype monitoring system of one FPSO in the Bohai Bay, the on-site lateral vibration behaviors found on the site of the soft yoke subject to wave load were analyzed. ADAMS simulation and model experiment were utilized to analyze the soft yoke lateral vibration and it was determined that lateral vibration was resonance behaviors caused by wave excitation. On the basis of the soft yoke longitudinal restoring force being guaranteed, a TLD-based vibration damper system was constructed and the vibration reduction experiments with multi-tank space and multi-load conditions were developed. The experimental results demonstrated that the proposed TLD vibration reduction system can effectively reduce lateral vibration of soft yoke structures.     

基于多体分析的浅水FPSO和水下软钢臂系泊系统运动特性研究

基于多体动力分析方法进行FPSO和水下软钢臂系泊系统的运动特性研究。相较于非线性弹簧模拟软钢臂系泊系统或者其他近似模拟方法,多体分析方法可以充分考虑系泊系统具体结构形式及其动力项对FPSO运动性能的影响,更好的预报系统运动响应和系泊力。本文将FPSO和水下钢臂结构模拟成2个具有6自由度的独立结构,两者用系泊链组进行连接。基于三维势流理论应用汇源分布法,首先在频域内进行FPSO的水动力参数分析,进而在时域内对系统进行耦合动力分析。本文重点讨论系泊系统黏性力和二阶波浪力对系统响应的影响,计算结果发现系泊系统黏性力对系泊力有一定影响,而在浅水条件下二阶波浪力的计算对准确预报系统运动及系泊力非常重要。     

软刚臂系泊系统水平恢复力特性数值预报

建立软刚臂系泊系统的理论模型以及6自由度静恢复力特性计算分析的数学模型,模拟实际几何关系与力学作用机制。提出基于误差判断的变步长迭代搜索的数值逼近求解方法,以QHD32-6 FPSO软刚臂系泊系统的纵向和横向水平恢复力特性为例进行数值预报,并与国外设计公司计算结果以及模型试验结果进行比较分析。对比显示,该模型的数值计算结果符合良好,而且迭代计算次数少、收敛快、误差小,可用于海上软刚臂系泊系统静恢复力特性的预报。     

Multibody dynamical modeling of the FPSO soft yoke mooring system and prototype validation

The Soft Yoke Mooring System (SYMS) is a single point mooring system for shallow water. It is composed of a mooring framework, mooring legs, yoke, and single point, and is located at the Floating Production Storage and Offloading (FPSO) through 13 hinge joints, such as universal joints and thrust bearings. Mooring restoring force, motions and postures of mooring components, and mechanical behaviors of hinge joints are major criteria for the structural design of the SYMS. Aiming at the difficulties of the multibody dynamics in traditional design of the SYMS, a multi-body dynamic mathematical modeling with seven independent degrees of freedom (DOFs) which is applicable to prototype field engineering was developed in this study. The proposed mathematical modeling of the SYMS multibody dynamic system has several advantages: 1. Internal tribological behaviors in hinge joints are considered within the presented multibody dynamics model to illustrate the good dynamic effects of the SYMS. 2. The multibody dynamic model can be applied in field service. Correctness and feasibility of the proposed multibody dynamic simulation method for describing motions and postures of hinges and single-body were validated by the prototype monitoring data. 3. The horizontal restoring force of the SYMS was calculated according to field measurement data. The motion state of each single body and internal stress distributions at each hinge joint in the SYMS are given. 4. The multibody dynamics calculation program can be directly used for the real-time monitoring of mechanical behaviors of the SYMS under the service state. The simulated results can provide real-time guarantee for safety alarming of the system. The vulnerability of the mooring system in service was evaluated based on long-term monitoring data analysis.     

浅海新型FPSO-IQFP多点系泊系统设计研究

海上油气生产要求FPSO具有低幅运动的特性,因此系泊系统性能的优劣直接影响生产作业的效率和安全。针对新概念FPSO-IQFP(圆角倒棱台形FPSO)的浮体特点和边际油田经济性开发的需要,设计一套经济有效的多点系泊系统。首先,将钢制悬链线系泊系统和聚酯纤维张紧式系泊系统作为备选方案,根据定常力计算结果并参照工程经验,给出两种系泊系统的初始设计方案,并进行二者的静特性分析,探讨系泊参数对系泊系统受力和位移的影响规律;在此基础上,结合时域计算结果,确定系泊系统的优化设计方案;最后,给出系泊系统的回复力和浮体位移之间的关系曲线,并在静力范围内比较两种系泊系统的优劣性。静力分析结果初步验证,较之悬链线系泊系统,张紧式系泊系统用于浅水作业的IQFP上更具优越性。     

Three-dimensional Motion of Multichain-Buoy Mooring System in shallow Water and Survival Conditions

An engineering numerical model for three-dimensional motion of multichain-buoy mooringsystem in shallow water and survival condition is given in this paper.Shooting-aim method is employedfor solving the dynamic equations of chain system in order to match the computation of buoy motion.Theresponses of buoy and chain have been computed for different wind-wave-current directions and differentrigidity of chain.The results show that the present numerical model is reasonable.     

Investigation on Touching Sea Bottom by a FPSO in Bohai Oilfield with Shallow Water

As one of the key safety problems, the motion performance and touching sea bottom of a FPSO are paid much attention by the ocean oil companies when the FPSO is exposed to survival storms in the shallow-water working areas. In this paper, timedomain numerical simulations are carried out on a 160 kDWT FPSO with a Yoke mooring system moored in the BZ25-1 oilfield with a water depth of 16.7m. The results are compared with those of the corresponding model tests. Good agreement shows that the time-domain simulations can be used to predict the performance of the FPSO in shallow-water reasonably. It is found that the touch of seabed by a fully loaded FPSO occurred few times under survival storm conditions. Therefore, the FPSO should be less loaded than that in the fully loaded condition under the survival storms.     

水深对软刚臂单点系泊FPSO动力响应的影响

系泊系统的定位能力是浅水油田作业的软刚臂式单点系泊FPSO安全作业的重要保障,为研究不同水深/吃水比下单点系泊系统的受力性能,针对一艘16万吨级软刚臂单点系泊FPSO,在线性三维势流理论的基础上,基于多体动力学方法,建立FPSO-系泊腿-软刚臂的耦合模型,采用Newman近似法和Pinkster近似法分析了FPSO所受二阶波浪力,在时域内计算了不同水深/吃水比对系泊系统动力响应性能的影响。结果表明,随着水深/吃水比的增加,Newman近似法计算得到二阶波浪力先增大后减小,引起单点系泊系统载荷先增大后减小;而Pinkster近似法计算得到的二阶波浪力逐渐减下,引起单点载荷逐渐减下。在浅水条件下,Pinkster近似法具有较好的适用性,Newman近似法严重低估了FPSO所受的二阶波浪力;在深水条件下,Newman近似法能满足工程计算的要求;适用两种方法的临界水深/吃水比为1.64。     

浅水浮式生产储油系统(FPSO)二阶定常力数值仿真研究

应用三维线性势流理论和Ir J A Pinkster的近场分析方法,对超大型浮式生产储油系统(32万吨FPSO)的二阶波浪定常力进行了数值仿真分析,研究浅水情况下,不同水深对FPSO受到二阶波浪定常力的影响,对浅水油田中FPSO的设计应用有一定的实用意义。     

圆筒型FPSO优化设计与水动力性能分析

针对圆筒型海上储油装置FPSO垂荡运动性能较差、无法安装干式井口的问题,设计了带延伸筒体与矩形阻尼结构的圆筒型FPSO,根据延伸筒体与矩形阻尼结构是否通海分为两种型式。建立水动力计算模型,比较分析不同延伸筒体和阻尼结构型式对FPSO水动力性能的影响。针对南海作业海域,设计了悬链式系泊系统,基于JONSWAP波浪谱对FPSO的运动进行时域预报,并对系泊系统进行校核。分析结果表明:通海型FPSO垂荡固有周期显著提升,可以错开南海百年一遇谱峰周期,通海型FPSO满足钻井、安装干式井口的运动响应要求,系泊系统系缆张力满足规范要求。     

渤海油田浅水软刚臂系泊FPSO触底分析

在线性三维势流理论的基础上,采用时域计算方法对BZ25—1油田16万吨级FPSO不同吃水条件下的碰底情况作了分析研究。数值计算结果与模型试验进行了比较,两者吻合较好,说明应用时域计算方法可以从理论上预报FPSO在浅水中的触底情况。这对我国渤海等浅水海域油田应用FPSO系统进行开发具有一定的意义。     

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。     

基于模糊Petri网络的FPSO单点多管缆干涉风险评估

FPSO单点系泊系统水下管缆众多,受环境等因素影响,管缆容易发生拉伸、扭转、弯曲和碰撞,引发干涉现象,危及工程安全.针对FPSO单点多管缆干涉风险,提出了基于模糊Petri网络的风险评估方法.首先,辨识风险因素来构建风险评估指标体系,并转化为模糊Petri网模型;其次,采用层次分析法确定风险因素的常权重,并引入模糊置信结构来提高专家主观评价的准确性;然后,将变权理论与模糊推理算法相结合来迭代求解库所可信度和状态矩阵;最后,以南海某内转塔式FPSO为例进行了风险评估.结果表明:该FPSO的风险评估等级为中等,环境与设备因素是影响管缆干涉的主要因素.通过风险排序结果对综合评估值较高的风险指标提出了风险控制措施,可有效降低管缆干涉风险发生的概率与危害.     

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。     

浅水FPSO限位作业系泊分析

以浅水单点系泊装置水下软钢臂维修解脱为背景,研究在拖轮限位状态下FPSO运动与限位缆绳张力。计算在不同水深及浪向条件下,FPSO的二阶传递函数(QTF);分别应用Newman近似方法、全QTF法以及使用部分QTF值的方法,计算FPSO时域低频波浪载荷,并对其限位响应进行对比;计算不同长度时的限位缆绳张力响应,分析限位缆绳长度及FPSO波频运动对缆绳张力的影响。分析表明:Newman近似的适用性,应根据FPSO的QTF与海浪谱能量集中范围综合判断;为减少QTF计算量,可根据FPSO低频运动固有频率,确定频率间隔△ω的计算上限,采用部分QTF值计算低频波浪载荷,其响应预报结果与全QTF法接近;若FPSO的RAO能够避开海浪谱能量集中的频率范围,则在限位分析中可忽略FPSO波频运动的影响。     

FPSO软刚臂单点系泊系统定量风险分析

针对FPSO软刚臂单点系泊系统出现过的系泊腿失效及背向工况风险事件,以渤海某16万吨级FPSO为例,采用数值模拟的方法,计算FPSO及单点系统在百年一遇海况下的载荷效应,通过统计学方法拟合效应的概率分布,完成定量风险分析。对于系泊腿旋转失效后的风险,使用故障假设(what-if)方法,依据失效后果判断其风险权重。计算结果表明,系泊腿结构在正常情况下受拉失效的概率很小;系泊腿纵摆失效后导致的结果比横摆失效更为严重,风险权重更大。背向工况下,船艏与YOKE的间距要明显小于顺向工况,在设计时增大二者间距可有效减小碰撞风险。     

新型圆筒型FPSO垂荡抑制结构优化设计

针对传统圆筒型FPSO垂荡运动剧烈的特点,提出一种带有垂荡抑制结构的圆筒型FPSO。采用1∶77.8的缩尺比制作模型,进行垂荡纵摇衰减试验,得到带有不同垂荡抑制结构模型的固有周期和无因次阻尼系数,进而选取最优的垂荡抑制结构型式。之后计算并对比传统圆筒型FPSO和新型圆筒型FPSO垂荡纵摇运动的固有周期和幅频响应函数。在此基础上,结合我国南海海洋环境条件,设计新型圆筒型FPSO的系泊系统,计算分析自存工况下的耦合动力响应,并与传统圆筒型FPSO进行对比。结果表明,文中提出的垂荡抑制结构可以有效增大系统垂荡纵摇运动的固有周期,改善运动性能,提高系泊的安全性。     

单点系泊FPSO气隙预报的时域和频域分析

以单点系泊的FPSO为研究对象,Matlab软件为计算工具,在百年一遇的极限海况下,采用频域和时域方法对FPSO的气隙进行了数值模拟。针对频域计算结果,预报FPSO在不同浪向下的上浪危险点,并基于时域和频域计算结果,比较FPSO的气隙预报的差异。分析表明:频域方法能够用来快速预测气隙危险点的位置,但是会相对低估各个上浪分析点处的气隙高度值,而且无法考虑风标效应,频域方法无法模拟FPSO在实际环境中真实的气隙变化过程,这会高估在横浪下的FPSO的危险性。     

浅海环境观测专用浮标和潜标锚泊系统的研究

文中着重介绍为改进浅海环境观测专用浮标和潜标锚泊系统所做的三件工作。一是提高水面标志浮标的抗台风、抗倾覆和抗沉能力以及连接件的流线型化;二是通过理论计算和水池试验,选用抗风能力强的配套的浮标／潜标系统系列;三是应用设计新型的打捞钩,及时而方便地将丢失在海底的仪器等打捞回来。