Snap Tension in Mooring Lines of Deepwater Platform

Based on the theory of impact dynamics, the motion equations for a mooring line-floating body system before and after impact loading are established with consideration of the viscoelastic property of mooring lines. The factors that influence the taut-slack conditions of a mooring system are analyzed through classifying the taut-slack regions, which are defined by non-dimensional ratios of displacement, frequency, and damping of the system. The mooring system of Jip spar platform is analyzed, and the snap tension characteristics of mooring lines are given. The factors that influence the maximum tension in mooring lines, including the mass of the floating body, length of mooring lines, frequency and amplitude of external excitation, and pretension in mooting lines, are also analyzed through computing the dynamic response of system and parametric study. It is shown that the maximum tension increases with the increasing mass of the floating body, external excitation and pretension. Also, it is found that the influence of the non-dimensional ratio of damping increases with the increase of the pretension in mooring lines.

Probability Distribution of the Hull Motion and Mooring Line Tension of Two Floating Systems

The statistical and distribution characteristics of the responses of a floater and its mooring lines are essential in designing floating/mooring systems.In general,the dynamic responses of offshore structures obey a Gaussian distribution,assuming that the structural system,and sea loads are linear or weakly nonlinear.However,mooring systems and wave loads are considerably nonlinear,and the dynamic responses of hull/mooring systems are non-Gaussian.In this study,the dynamic responses of two types of floaters,semi-submersible and spar platforms,and their mooring lines are computed using coupled dynamic analysis in the time domain.Herein,the statistical characteristics and distributions of the hull motion and mooring line tension are discussed and compared.The statistical distributions of the dynamic responses have strong non-Gaussianity and are unreasonably fitted by a Gaussian distribution for the two floating and mooring systems.Then,the effects of water depth,wave parameters,and low-frequency and wave-frequency components on the non-Gaussianity of the hull motion,and mooring line tension are investigated and discussed.A comparison of the statistical distributions of the responses with various probability density functions,including the Gamma,Gaussian,General Extreme Value,Weibull,and Gaussian Mixture Model(GMM)distributions,shows that the GMM distribution is better than the others for characterizing the statistical distributions of the hull motion,and mooring line tension responses.Furthermore,the GMM distribution has the best accuracy of response prediction.

Dynamic Analysis of Semi-Submersible Production Platform Under the Failure of Mooring Lines

This paper quantitatively studies the transient dynamic response of a semi-submersible production platform with the loss of one or several positioning mooring lines.A semi-submersible platform,production risers,and positioning mooring lines are all included in the numerical simulation.Increased motion of the semi-submersible platform,tension variation of the remaining mooring lines/risers and the risk of mooring line or riser clashing are all investigated through fully coupled time-domain analysis.Combined environmental loads are selected from irregular waves and the steady current varying from very rough to extreme sea conditions.Three dimension radiation/diffraction theories and Morison’s equation are applied to calculate first-order wave force and second-order mean drift force of floating semi-submersible platform.Nonlinear time-domain finite element methods are employed to analyze the behavior of mooring lines and risers.Results show that the failure of mooring lines seriously reduce the platform’s stability performance.The tension of the rest lines is also increased accordingly.Remaining lines which are closer to the failed lines will have larger tension increase to compensate.Line-Line distance provides practical information for the risk of clashing investigation.

Use of Different Mooring Models on Global Response Analysis of an Innovative Deep Draft Platform

The global responses of an innovative deep draft platform are investigated using catenary, semi-taut, and taut mooring models, respectively. The three mooring systems have the same arrangements and similar static restoring force characteristics. The dynamic coupling effects between the platform and the mooring systems are calculated in the time domain. Free-decay and 3-h simulations are conducted under 1-year and 100-year return period environmental conditions in the South China Sea. The mooring damping contributions, the response characteristics, and the mooring line tensions are investigated.

Performance of Two Types of Mooring Systems in the Heave Motion of a Two-body Floating Wave Energy Converter

This work investigated the influence of two types of mooring systems on the hydrodynamic performance of a two-body floating wave energy converter(WEC). It also investigated the effects of the physical parameters of the mooring system on the amount of extractable power from incident waves in the frequency domain. The modeled converter comprised a floating body(a buoy), a submerged body with two mooring systems, and a coupling system for two bodies. The coupling system was a simplified power take-off system that was modeled by a linear spring-damper model. The tension leg mooring system could drastically affect the heave motion of the submerged body of the model and increase relative displacement between the two bodies. The effects of the stiffness parameter of the mooring system on power absorption exceeded those of the pretension tendon force.

Fatigue Analysis of the Taut-Wire Mooring System Applied for Deep Waters

Precisely predicting the fatigue life of taut-wire mooring systems has become an interesting and important problem for scientists and engineers since there are still difficulties in the inspection and maintenance of mooring lines in a rough sea environment especially in deep waters. In this paper, a comprehensive fatigue analysis is performed for a polyester taut-wire mooring system of an FPSO based on the time domain dynamic theory, rainflow cycle counting method and linear damage accumulation rule of Palmgren-Miner. Three influential factors in the fatigue analysis including the pre-tension, dynamic stiffness and T-N curve are investigated in detail. Two polyester T-N curves, one is from the DNV- 0S-E301 and the other is from the API-RP-2SM, are adopted in the calculation. The fatigue analysis of the mooting system after one-line failure is also carried out. The calculation results indicate that the fatigue life is significantly affected by the T-N curve. The fatigue life decreases with increasing pre-tension, and is largely reduced if taking into account the dynamic stiffness caused by cyclic loading. The analysis also proves that one-line failure has remarkable effects on the fatigue lives of other mooting lines. The present parametric and comparative study is believed to be meaningful to further understanding of the taut-wire mooting system for deepwater applications.

海上风机与养殖网箱融合系统中网箱系泊绳张力与导管架基础结构的安全性

海洋牧场与海上风电融合发展是现代渔业和清洁能源产业融合发展的典型代表,有利于构建“海上粮仓+清洁能源”的新产业模式。本研究基于福建漳浦六鳌海上风电场风机导管架构建养殖网箱与海上风机融合系统,运用Aqua-FE™有限元工具探究极端波流条件下不同网箱布设深度、波流入射角、生物附着程度对网箱系泊绳张力的影响;采用海洋工程专用设计软件SACS,计算分析风机导管架结构在波流及网箱系泊绳张力作用下的应力分布,评估养殖网箱系泊绳张力对风机导管架基础结构安全性的影响。结果显示,网箱布设深度的增加能够减少网箱系泊绳最大张力,显著改善网箱风机整体结构受力状态;波流入射角的改变对于网箱风机整体结构安全性影响不大;网衣生物附着程度的增加会显著增加网箱系泊绳最大张力,从而造成风机导管架基础杆件大量失效。研究表明,养殖网箱可布设于适当水深以减少受力,同时应及时清理附着生物,适当增加网箱系泊点附近的导管架杆件和导管架底部桩土点杆件的壁厚,以确保养殖网箱与海上风机融合系统结构安全。该结果可为深入研究网箱与风机融合系统的受力,评估该系统的安全性,优化设计养殖网箱与风机融合系统提供数据支撑。

超长尺度浮式防波堤多模块耦合动力响应分析

为研究多模块浮式防波堤模块之间的耦合动力响应规律,基于目标海域环境条件,提出一种能够提供特大掩护水域的超长尺度浮式防波堤总布置设计方案,并对超长尺度浮式防波堤的构型、连接结构及系泊系统进行设计。在此基础上,基于三维势流理论对超长尺度浮式防波堤的水动力性能进行频域和时域分析,考虑环境载荷作用下浮式防波堤多模块耦合运动,并对其中间及两侧模块的运动响应及系泊缆张力进行对比分析。研究结果表明:横浪和斜浪工况下,超长尺度浮式防波堤中间模块在垂荡、横摇和纵摇方向上的运动均最剧烈。由于防波堤首部模块在横浪和斜浪工况下横荡运动最剧烈,因此浮式防波堤首部模块迎浪运动侧系泊缆在2种工况下所受张力最大,这在超长尺度浮式防波堤系泊系统设计过程中需重点关注。数值模拟结果可为此后超长尺度浮式防波堤设计及工程化应用提供技术支撑。

基于LSTM模型的浮式风机系泊监测数据解算方法

针对浮式风机系泊倾角监测数据如何准确解算为系泊张力响应的问题,提出一种基于长短时记忆(LSTM)网络与全连接网络(FCN)相结合的系泊张力解算模型。首先,针对在役的“扶摇号”浮式风机,建立风-浪-流耦合时域仿真模型,用以获取不同工况下系泊张力与倾角数据,从而形成神经网络的训练与验证数据集。在Keras框架下,开发FCN与LSTM的组合网络模型,选取Adam优化器进行训练,获得验证集损失函数最小的网络参数。最后,分别采用传统悬链线方程与神经网络模型对系泊张力响应进行预测,并与实际结果进行比对分析。结果表明:神经网络能够考虑到不同系泊倾角对应的导缆孔平均高度变化以及系泊运动的动态过程,在系泊张力时程曲线、均值、标准差及最大值等预测上比传统悬链线方程具有更高的精度,两者对于系泊张力最大值的预报误差分别为6.4%和17.1%。

CT-Spar平台及其系泊与立管系统优化

以CT-Spar平台及其系泊与立管系统为对象,识别出平台垂荡板数目、张紧式系泊缆预张力、钢悬链线立管上浮子位置及浮力大小为CT-Spar平台-系泊-立管系统设计时的关键参数。基于SESAM运用频域分析、时域耦合分析等手段,以系统运动响应及受力为指标,对这些关键参数进行分析与优化,结果表明,垂荡板数目由4调整为3、张紧式系泊缆预张力为1800 kN、3600 kN的浮子安装在距钢悬链线立管距顶端悬垂长度段的60%处的参数设计是适应1500 m深海风-浪-流复杂动力环境的优选方案。对该方案在极端动力条件及平台系统部分破损状态下进行时域耦合分析,发现该方案也能满足石油平台安全相关规范要求,并显著改善系泊缆、立管受力状态。

深远海大兆瓦级半潜式风机基础运动特性数值模拟及试验研究

针对水深百米以上的深远海浮式风电开发需求,本文面向可搭载大兆瓦级(15 MW)风机的新型半潜式风机基础的运动特性展开研究。利用AQWA软件建立了该基础与系泊系统的数值模型,基于南海实际海况确定了风机塔筒的载荷,并开展了缩尺比为1∶64的水池模型试验,验证了数值模型计算的准确性;基于验证的数值模型分析了新型风机基础在南海恶劣海况下的运动特性及系泊张力,发现该新型风机基础的运动极值和系泊张力均满足规范要求。相同海况下,新型风机基础与经典半潜式风机基础OC4-DeepCwind(三浮筒平台)的运动性能及系泊缆张力对比结果表明:发电工况下,新型风机基础的垂荡和倾角的极值较三浮筒平台的分别下降62.8%和81.3%;停机工况下,垂荡和倾角的极值则分别下降46.1%和41.4%,充分说明该新型风机基础具有优越的运动性能;而在停机工况下1、2号缆系泊张力最大值分别下降17.4%和9.6%,大大降低了系泊系统的设计难度。研究结果为中国深远海浮式风电开发船型的选择提供了借鉴。

海啸波作用下浮式水平板防波堤消浪性能试验研究

通过物理模型试验,对孤立波作用下浮式单排水平板、浮式双排水平板、浮式三排水平板和浮式开孔水平板防波堤的消浪性能开展研究,对比分析在不同相对波高和系泊线倾角下4种浮式水平板防波堤的透射系数、反射系数、波能耗散系数和系泊张力。结果表明,浮式单排水平板防波堤的透射系数最小,浮式三排水平板防波堤的透射系数最大;相较于浮式单排水平板防波堤,浮式双排水平板、浮式三排板和浮式开孔水平板防波堤的系泊张力均明显减小;适度调整系泊线的倾角能够改善浮式水平板防波堤的消浪效果和改变系泊线张力特性。

较长周期波浪作用下系泊船舶离泊波浪标准的试验研究

系泊船舶的离泊波浪标准是保证船舶系泊安全的重要参数,尤其是在较长周期波浪作用下,系泊船舶安全是需要关注的重要问题之一。本文对不同吨位油船、LNG船和散货船进行了较长周期波浪作用下的系泊试验研究,分析了船舶缆绳拉力随波浪周期的变化规律,提出了用以估算缆绳最大拉力的经验计算公式,并结合相关规范要求,给出了较长周期波浪作用时离泊波高随周期变化的折减系数。研究成果可以为实际工程设计提供参考。

系泊连接装置发展现状及其在漂浮式风电中的应用

连接装置是海洋浮体系泊系统的重要组成部分,用于不同系泊组件之间以及系泊系统与浮体的连接。近几年,漂浮式风电发展迅猛,全球报道了多个示范项目,成规模的风场建设已见规划。要实现商业化,就必须进一步控制项目成本,而系泊系统作为漂浮式风电的重要组成部分,驱需通过技术创新实现降本增效。在海工行业,各种系泊连接装置已经过多年应用和验证,在系泊连接、安装、维护、更换等方面相对成熟。针对漂浮式风电应用场景,开展系泊系统优化设计,优化配置各种系泊连接装置,并在此基础上开发新的连接组件,进而提升漂浮式风电的系泊设计、制造和安装能力,从而实现风电成本有效控制。

单点系泊方式下的浮标系统运动响应分析

浮式激光雷达测风塔在恶劣的海洋环境下,其运动稳定性受到风、浪、流等多种环境载荷的耦合作用,呈现出典型的非线性特征,对其观测精度造成重要影响。建立浮动式基础设计分析平台,对浮标及其系泊系统进行水动力性能模拟分析,求解不同载荷作用下浮标平台与单点式系泊系统之间的运动响应。计算结果表明,浮标体在单点式系泊方案下具有良好的安全性和稳定性,系泊张力最大值为466.4k N,满足设计BVNR493规范要求,浮标平台的运动半径极值和最大垂荡距离分别为50.0m和6.3 m,可保证安全运行。

基于AquaSim软件的浮式钢制网箱新型锚泊系统研究

锚泊系统对于钢制浮式网箱的安全性及成本影响较大,开展锚泊系统研究对于浮式钢制网箱的设计具有重要意义。基于商业软件AquaSim建立浮式钢制网箱数值模型,介绍AquaSim软件计算机理与规范中锚链校核规则;介绍一种新型的锚缆方案,并与传统纯锚链形式的系泊方案进行对比,探究其优劣性;利用控制变量法,研究导缆孔位置对于网箱浮态的影响,研究锚缆数量及锚缆布置角度对于锚链张力的影响,探讨其安全性。由数值模型计算结果可知,在一定的海况条件下,新型锚缆方案比传统的纯锚链方案成本更低,稳定性更好;导缆孔的位置处于网箱底部时,网箱在波流作用下最不易发生触底现象,浮态较为稳定;锚缆数量的减少会急剧增大网箱锚缆在破断工况下的轴向力,导致安全系数急剧下降;锚缆沿着浪流作用力大的方向布置,能够有效增大锚泊系统的安全性。

20000t自航转载驳船的系泊设计要点

为提升自航转载驳船停泊和装卸作业的稳定性和安全性,以某20000 t自航转载驳船为例,对其系泊系统设计进行探讨,重点分析船舶靠泊和离泊过程中的系泊安全、作业时间、吃水变化和浪涌对船舶装卸作业的影响等问题。结合港口设施的布置和船舶驳运的特点,设计符合船舶和港口需求的缆绳自动张紧控制系统、自动系泊缆桩、舷侧安全防护装置和控制系统、系泊绞车远程集中控制系统,提升船舶停靠的稳定性和作业效率。该研究可供类似转载驳船的系泊系统设计参考。

集中质量法计算深海系泊冲击张力

采用三维集中质量法建立深海系缆模型,计算系缆的构型及张力.根据各点的初始条件和系缆两端点处的位移边界条件,求解系缆的三维运动方程;分析系缆在不同激励频率和激励幅值下的运动响应,并预测系缆松弛-张紧运动的发生条件和系缆冲击载荷的大小.研究表明,系缆张力随系缆的上端点的运动而变化.当系缆上端点的激励频率和幅值达到一定值时,系缆会出现交替松弛-张紧的现象,产生冲击载荷.

波流作用下圆柱形近海抗风浪网箱缆绳的张力特性

HDPE框架圆柱形网箱是目前我国应用最广泛的抗风浪网箱养殖设施。作者以40m×6m该种网箱为原型，选择λ=1／16和λ’=1／3．625～1／4．333的尺度比制造模型，于2003年7月在大连理工大学开展了模型试验，研究其在纯流（0～1．25m·s^-1）、纯波（0m、3m和6m）及其联合作用下的运动状态和缆绳张力特性。结果表明，缆绳张力对台风浪的响应过程复杂，纯波浪时呈“波群”状态，波流联合时呈“漂移”状态，而对季风浪响应则无此现象，其对网箱在台风浪下的破坏作用需继续研究；台风浪下，张力回归方程为T=95423V^2-42546V＋63329（R^2=0．8736）（无底框架）和T=54161V^2＋8613．7V＋67319（F^2=0．8862）（带底框架）；流速从1m·s^-1增到1．25m·s^-1时，张力增幅分别达92．5％（无底框架）和61．7％（带底框架），表明该网箱应布置在流速小于1m·s^-1的海区；在波流联合作用下，左右缆绳张力存在一定差异，试验中相差约25％，实际工况下波流分布更复杂，张力差异更大，建议取迎波流面两缆力和的统计最大值作为单锚及锚缆绳的允许受力值。

舰载直升机系留座的布置优化

本文根据舰载直升机系留索的受力特点,推导出系留索的张力计算表达式,利用遗传算法对系留点的位置进行优化,得到了各海况下系留点的优化布局形式和系留索的张力值,最后对得到的结果进行综合分析比较,确定了最佳的系留座布局形式。