深水作业船锚索锚泊性能研究

为了探索深水作业船的锚索锚泊性能,运用悬乖线理论分析了钢索和复合锚索的无因次长度、重量与位能,推导出了钢索和复合锚索位能对外力导数的公式,从锚索静载荷角度研究了钢索和复合锚索吸收动载荷的能力.模拟计算结果表明,与钢索相比,复合锚索对增加卧底锚索重量、保持锚的稳定性和抓力是有利的,对减小锚泊船漂移范围也有益处,但吸收动载荷能力下降.复合锚索中设置的锚链的长度取1节(27.5 m)为宜,锚泊时甲板以下锚索长度以2.5～3.0倍水深较为合适.此结论对深水作业船的锚泊操纵有一定的参考意义.     

Numerical modelling of hydrodynamic responses of Ocean Farm 1 in waves and current and validation against model test measurements

With the continuous growing of the aquaculture industry and increasingly limited fish farming sites at close to shore areas both in Norway and worldwide, there is a need to develop fish farms suitable for aquaculture production in typical offshore environments. For this purpose, SALMAR has developed and deployed the Ocean Farm 1 facility for offshore fish farming.The main purpose of this paper is to develop a reliable numerical model and investigate the motion responses of the Ocean Farm 1 structure in waves and current. The established numerical model consists of the Ocean Farm 1's frame structure (with rigidly-connected circular column components), the net and the mooring system. The hydrodynamic external loads and coefficients of the frame structure are obtained by using potential flow theory. The quadratic drag load on the individual circular columns of the frame structure is formulated by a given drag coefficient. The loads on the net are formulated by using the screen model, where the Reynold number dependent lift and drag forces are formulated as a function of the solidity ratio Sn of the net, relative inflow angle and velocity. The hydrodynamic loads on the mooring lines are formulated using the Morison's equation and the structural responses of the mooring lines are obtained using a nonlinear FE model.With the developed numerical model, time domain simulations are performed. The simulation results are firstly validated against measured data from the decay tests, current tests, and regular wave tests. After the validation, numerical simulations are performed in different irregular wave and current combined weather conditions and the obtained motion response of Ocean Farm 1 are discussed and compared with available measurement data.     

基于优化算法的锚泊系统设计数值方法

港口系泊系统的设计关系到船舶停靠的安全问题,是船舶与海洋工程研究的热点之一,以往的研究中,对于动荷载的考虑较少。在动荷载的基础上研究港口系泊系统的设计,首先,分析了港口系泊系统主要组成的钢管、钢桶、重物球、电焊锚链和抗拖移锚的受力情况;然后,基于物体受力平衡方程以及悬链线模型建立了系统受力模型,采用遗传算法进行数值模拟求解;最后,通过MATLAB编程得出了在不同情况下钢桶、钢管的倾斜角度、锚链形状、浮标的吃水深度和游动区域,并讨论了各影响因素对系泊系统组成部分的影响程度。     

Inhomogeneous wave load effects on a long,straight and side-anchored floating pontoon bridge

In this paper, we present a numerical study on the hydroelastic response of a 4.6 km long fjord crossing floating bridge subjected to wave loads. The bridge is straight in design and supported by 35 pontoons along its full length. To limit the response to horizontal loads, four clusters of deep water mooring lines are engaged to increase the transverse stiffness of the bridge. Owing to the very large span across the fjord, inhomogeneity in the wave field exists. This study examines the various effects of inhomogeneous wave loads on the dynamic responses of the floating bridge. These include the spatial variations of the wave direction, significant wave height and peak period as well as the coherence and correlation of waves along the entire length of the floating bridge. For the purpose of comparison, the dynamic bridge responses under homogeneous wave load cases are also studied. In addition, the effects of wave load components and short-crestedness are presented and discussed.     

Uncertainty analysis of extreme mooring loads associated with environmental contours and peak tension distributions

This paper aims to assess the uncertainty on the extreme mooring loads of floating system considering short-term variability. Two environmental contour approaches based on the inverse First and Second Order Reliability Methods are employed to identify critical sea states that may give rise to extreme loads. The uncertainty related to the construction of environmental contours is addressed including significant differences due to marginal distribution fitting, parameter estimation methods and joint models. Three measured datasets are analysed using a known conditional joint distribution and proposed mixed copula model. 3-h time domain numerical simulation for each sea state is conducted and the characteristic extreme responses of mooring lines subjected to design loads are assessed. The uncertainties due to various statistical models including the average conditional exceedance rate method as well as global maxima, peak-over-threshold method combined with Gumbel distribution, Generalized Extreme Value distribution, Generalized Pareto distribution and 3-parameter Weibull distribution are investigated and quantified. It is observed that marginal distributions, joint models and parameters estimation methods have apparent effect on design loads estimation, and the extreme tensions of the semi-submersible platform shows significant difference using various probabilistic models. The results indicate that those epistemic uncertainties should be account for in the reliability analysis or safety factor calibration for mooring systems.     

深海系泊缆的动刚度特性

针对纤维缆在交变载荷作用下存在的动刚度问题,基于集中质量法的思想建立了系缆的动张力计算模型,编制了能够有效分析系泊系统动力响应的源程序.将张力程序计算结果与商业软件计算结果进行对比,验证了算法程序的准确性,并在此基础上分析了纤维缆复杂的应力应变行为,采用统计的原理计算平均张力和张力幅值,将动刚度引入模型中探究其对系泊张力的影响.此外,分析系统在不同运动形式及环境载荷下的张力结果,研究考虑动刚度后系统参数对系泊张力的影响规律.     

沉埋式海底隧道管段海上系泊水动力性能分析

沉埋式海底隧道管段海上系泊阶段的结构运动响应及缆索受力,影响其水上施工的安全性和经济性。以一管段系泊工程为例,利用基于三维势流理论的水动力软件AQWA建立管段海上系泊数值仿真计算模型,首先对系泊系统进行频域分析,然后在时域内考虑JONSWAP波浪谱和水流联合作用,研究环境载荷方向、环境载荷组合方式等因素对系统运动响应及缆索受力的影响。结果表明:管段在高频区域内稳定性较好,响应幅值很小;水流对管段的运动响应影响很大;当环境力以60°入射管段时,管段的系泊缆张力最大。     

基于拖曳锚轨迹方程的拖曳锚系泊优化分析

拖曳锚系泊作为目前海洋工程使用最为广泛的系泊方式，因其较低的制造和安装成本使其成为小型浮式平台系泊方式的首选。目前拖曳式系泊设计大多根据以往工程经验进行选择设计，由于经验设计中并没过多的泥面表面及以下锚链安装信息，因此在设计之初很难对系泊材料用量准确计算。不同重量的拖曳锚在同样的嵌深和同样的锚倾角条件下，所能提供的系泊力大不相同。同时，不同重量的拖曳锚的在相同土壤条件下拖曳嵌入轨迹不同，因而最大埋深不同。上述两方面原因导致不同重量的拖曳锚提供的系泊力不一样。因此，需要达到同样的系泊效果，泥线以下反悬链线和卧底链的长度在不同重量锚的系泊系统中是不同的。参照系泊成本各个分项在其生命周期各阶段的占比，材料制造成本与安装成本占据系泊成本的大部分，且安装成本往往正比于材料成本。因此降低系泊锚链的材料成本对整个系泊系统的成本降低起到了巨大的优化作用。通过结合拖曳锚的极限平衡法拖曳轨迹理论方程，以不同重量的拖曳锚在粘性土壤中的不同拖曳距离下提供额定系泊力时所需要的材料重量为系泊成本评价依据，从而得到浮式结构物系泊系统的一种设计优化方法。     

深水半潜平台的环境载荷分析

通过对南海水域环境下的深水式半潜生产平台的自存和作业两种工况的风载荷、波浪载荷和海流载荷计算,得到该平台的环境载荷特点,从计算结果看,风载荷、流载荷和波浪载荷对平台的影响相近,因此,在确定系泊系统的设计时,这三个因素的影响都不可忽视。     

FLNG系统旁靠外输作业时的水动力性能数值研究

对大型浮式液化天然气(FLNG)系统与LNG运输船以旁靠方式进行LNG外输作业时船体的水动力性能开展数值研究。全面考虑了双船体之间的水动力相互干扰,以及船体与系泊系统和连接系统之间的耦合作用。在验证了数值计算模型正确性的基础上,对旁靠外输作业时各典型工况进行数值计算,从而得到在风、浪、流共同作用下FLNG与LNG运输船间的相对运动情况、系泊系统和两船之间连接系统的受力情况,为后续设计提供参考。     

深水悬链复合锚泊线疲劳损伤计算

以某座Spar平台的锚泊系统为研究对象,首先利用三维绕射理论计算Spar平台主体波浪力,得到平台的总体运动响应时程。再建立复合锚泊线的二维非线性有限元动力分析模型,基于DelVecchio(1992)提出的经验公式,采用迭代的方法计算复合锚泊线的刚度。锚泊线和海床之间的接触作用基于刚性海床假定,基于Morrison公式计算锚泊线的惯性力和拖曳力荷载,根据计算得到的平台主体运动响应时程作为锚泊线顶端输入条件,在时域范围内进行复合锚泊线的动力分析。计算得到中国南海某海域各短期海况条件下复合锚泊线应力的时间历程曲线,采用雨流法对其计数得到对应于各短期海况条件下的疲劳载荷谱。最后根据Miner线性累积损伤模型,对复合锚泊线在长期海况条件下的疲劳损伤进行比较计算。     

作业水深对浮式半潜平台波浪砰击的影响

结合模型试验,基于数值重构和外推的计算模型,采用时域全耦合分析方法,对浮式半潜平台全尺寸锚泊系统以及风、浪、流载荷的联合作用进行模拟,针对动力辅助锚泊定位平台与锚泊定位平台在不同作业水深下的波浪砰击进行对比研究。研究结果表明：浮式半潜平台关注点处波浪砰击次数受作业水深的影响敏感。平台在同等环境工况下,关注点处负气隙以及波浪砰击次数随着作业水深的增加而加剧。动力辅助锚泊定位平台较之于锚泊定位平台的随动性更好,可有效减小平台与水质点的相对运动,作业水深变化引起的动力辅助锚泊定位平台同一关注点的砰击次数、气隙变化以及改善幅值明显优于锚泊定位平台。在平台设计过程中,作业水深对平台气隙和波浪砰击的影响应引起重视。     

深海工程船锚泊仿真系统研究

为了实现工程船定位和控位快速模拟仿真,本文以45000DWT海洋工程船为例,采用均匀设计试验方法,确定深海船舶工作不同的工况组合,基于Ansys-Aqwa软件对工程船深海锚泊动态响应进行仿真分析,对仿真结果进行回归处理,得到船舶位移和锚索张力与锚索长度、风浪流环境载荷变化的数学响应模型,再对位移数学响应模型进行求反函数处理,获取船舶控位调整锚索长度的方法,为深海锚泊软件仿真系统提供模型支撑。     

Dynamic analysis of a dual-spar floating offshore wind farm with shared moorings in extreme environmental conditions

The concept of a shared mooring system was proposed to reduce mooring and anchoring costs. Shared moorings also add complexity to the floating offshore wind farm system and pose design challenges. To understand the system dynamics, this paper presents a dynamic analysis for a dual-spar floating offshore wind farm with a shared mooring system in extreme environmental conditions. First, a numerical model of the floating offshore wind farm was established in a commercial simulation tool. Then, time-domain simulations were performed for the parked wind farm under extreme wind and wave conditions. A sensitivity study was carried out to investigate the influence of loading directions and shared line mooring properties. To highlight the influence of the shared line, the results were compared to those of a single spar floating wind turbine, and larger platform motions and higher tension loads in single lines are observed for the wind farm with shared moorings. The loading direction affects the platform motions and mooring response of the floating offshore wind farm. Comparing the investigated loading directions to the 0-deg loading direction, the variation of mean mooring tension at the fairlead is up to 84% for single lines and 16% for the shared line. The influence of the shared line properties in the platform motions and the structural responses is limited. These findings improve understanding of the dynamic characteristics of floating offshore wind farms with a shared mooring system.     

开敞式码头系泊缆绳的优化研究

运用OPTIMOOR系泊软件,以减小环境荷载作用下船舶运动量及均衡缆绳张力分布为优化目标,结合江苏某港10万吨级石化码头,通过对比不同的缆绳材质、调整缆绳长度、调节缆绳预张力来优化开敞式码头系泊缆绳的布置。计算结果表明:增加缆绳长度可降低缆绳张力,设置尾缆能显著降低系泊钢缆的动力负荷,减少船舶的运动量;施加合理大小的预张力能有效降低船舶的位移量,均衡缆绳张力;建议大船主缆选用钢缆。     

Validation and application of nonlinear hydrodynamics from CFD in an engineering model of a semi-submersible floating wind turbine

Nonlinear hydrodynamics play a significant role in accurate prediction of the dynamic responses of floating wind turbines (FWTs), especially near the resonance frequencies. This study investigates the use of computational fluid dynamics (CFD) simulations to improve an engineering model (based on potential flow theory with Morison-type drag) by modifying the second-order difference-frequency quadratic transfer functions (QTFs) and frequency-dependent added mass and damping for a semi-submersible FWT. The results from the original and modified engineering models are compared to experimental data from decay tests and irregular wave tests. In general, the CFD results based on forced oscillation tests suggest increasing the frequency-depending added mass and damping at low frequencies compared to first order potential flow theory. The modified engineering model predicts natural periods close to the experimental results in decay tests (within 5%), and the underprediction of the damping is reduced compared to the original engineering model. The motions, mooring line tensions and tower-base loads in the low-frequency response to an irregular wave are underestimated using the original engineering model. The additional linear damping increases this underestimation, while the modified QTFs based on CFD simulations of a fixed floater in bichromatic waves result in larger difference-frequency wave loads. The combined modifications give improved agreement with experimental data in terms of damage equivalent loads for the mooring lines and tower base.     

悬链浮筒式多点系泊设计

悬链浮筒式多点系泊(MBM)是油船常见的一种离岸系泊方式。针对浮筒式多点系泊设计的适用规范、平面布置、波浪荷载、系缆分析等基本设计问题进行论述,采用国内外规范对比研究、OPTIMOOR软件模拟、工程项目案例研究等方法,给出MBM系泊设计的平面基本布局、船舶荷载计算方法、系缆分析方法。结果表明,利用OPTIMOOR作为动态模拟分析软件,采用频域分析的方法可以有效地对浮筒式多点系泊设计进行设计与优化。     

基于锚泊系统的半潜式海洋平台定位方法研究

以工作水深1200m、8缆系泊的半潜式海洋平台为对象,研究其系统定位方法,通过改变锚泊系统系泊缆长度来实现平台的定位。建立反映半潜式海洋平台锚泊系统动力响应的多目标优化模型,通过求解得到船体目标位移与最优系泊缆长度,借助多学科软件iSIGHT,通过开发程序接口,调用水动力分析软件ANSYS/AQWA求解器求解,实现了半潜式平台锚泊系统的结构动力响应优化设计。对半潜式平台进行风、浪、流联合作用下的水动力耦合分析,实时控制系泊缆长度来实现平台的定位并保证平台的稳定性。     

Non-linear dynamic analysis of the response of moored floating structures

The complexity of the dynamic response of offshore marine structures requires advanced simulations tools for the accurate assessment of the seakeeping behaviour of these devices. The aim of this work is to present a new time-domain model for solving the dynamics of moored floating marine devices, specifically offshore wind turbines, subjected to non-linear environmental loads. The paper first introduces the formulation of the second-order wave radiation-diffraction solver, designed for calculating the wave-floater interaction. Then, the solver of the mooring dynamics, based on a non-linear Finite Element Method (FEM) approach, is presented. Next, the procedure developed for coupling the floater dynamics model with the mooring model is described. Some validation examples of the developed models, and comparisons among different mooring approaches, are presented. Finally, a study of the OC3 floating wind turbine concept is performed to analyze the influence of the mooring model in the dynamics of the platform and the tension in the mooring lines. The work comes to the conclusion that the coupling of a dynamic mooring model along with a second-order wave radiation-diffraction solver can offer realistic predictions of the floating wind turbine performance.     

FPSO单点系泊系统动力截断优化设计

浮体系泊系统在海洋工程水池进行模型试验时，由于水池尺度有限，首先对系泊线进行等效截断设计，是被动式混合模型试验的重要一步。截断设计时，基于细长杆理论，模拟系泊线的非线性动力特性，将计算所得时域内的系泊力转换到频域响应，选择有代表性的频率及响应建立目标函数，结合NSGA II优化算法，确定最优截断系泊参数，计算快速准确。针对一作业水深420m的FPSO单点系泊系统，进行水平截断设计。截断前后系泊系统和单根系泊线的静力特性吻合很好。截断系泊系统在不同环境载荷作用下的总体响应和系泊动力，都与截断前一致。证明了截断设计的合理性和准确性，为后续的模型试验工作打下了基础。