Coupled dynamics of tethered buoy systems

The three-dimensional coupled behavior during the interaction of buoys with their mooring systems is numerically analyzed. A time-domain model was developed to predict the response of a tethered buoy subject to hydrodynamic loadings. External loadings include hydrodynamic forces, tethers tensions, wind loadings and weight. System nonlinearities include large rotational and translational motions, and non-conservative fluid loadings. The mooring problem is formulated as a combined nonlinear initial-value and two-point-boundary-value problem which is directly integrated both in time and space. Buoy equations of motion are derived using small Eulerian angles. Coupling between rotational and translational degrees of freedom is included and coupling between the buoy and cable is effected by adopting the buoy equations of motion as boundary conditions at one end for the mooring problem. Numerical examples are provided to validate the formulation and solution technique; predicted responses of three types of buoy (sphere, spar, and disc) are compared with experimental results.     

有效吸收和传递波浪能的锚泊系统的设计制作

将传统定位浮标加以改进,可以形成一种能有效吸收和传递波浪能的锚泊系统。此系统的最上端是漂浮着的海面浮标,海面浮标下端连着锚泊钢缆,锚泊钢缆下端到海底之间又依次连有张紧锤、储链和重物锚块。锚泊系统中的海面浮标随波浪同步上下起伏,从而带动与其连在一起的由张紧锤绷直的锚泊钢缆上下振动,于是海面浮标吸收波浪能并由引导缆向下传递。20 m长的储链可以保证整个装置在涨潮、退潮的极限水深情况下,仍旧可以有效地传递海表面波浪能;合适的重物锚块可以起到为整个系统定位的功能。最后给出了一个实际应用波浪能的例子。设计制作的锚泊系统可以有效吸收和传递波浪能,为波浪能的利用提供了一种行之有效的方法。     

深海资料浮标体及系泊系统的阻力试验研究

本文结合国家“七五”重点科技攻关项目“深海资料浮标”研制而进行浮标体和系泊系统的各种阻力试验研究，试验成果已直接应用于深海资料浮标系泊系统设计。实践表明本文介绍的各种阻力试验结果是可靠的。     

新型激光雷达浮标运动响应特性数值研究

以新型激光雷达浮标系统为研究对象,基于ANSYS/AQWA开展了激光雷达浮标系统运动响应特性数值研究,研究了浮标吃水深度、形状参数对于激光雷达浮标运动响应的影响规律,分析了附加质量、辐射阻尼、运动响应RAO及一阶、二阶波浪力等水动力参数。采用时域分析方法对不同风浪流荷载入射角度下的激光雷达浮标锚泊系统张力特性进行了计算分析。研究结果表明:随着浮标吃水深度的增加,浮标纵荡方向响应无明显变化,垂荡响应显著增大;随着浮标底部圆台直径的增大,浮标纵荡方向响应变化较小,而圆柱形浮标垂荡运动响应显著大于圆台形浮标;当浮标系泊锚链发生松弛—张紧状态变化时易出现极端张力,且极端张力出现的幅值和频率随有效波高的增大和谱峰周期的减小而增大。     

基于STAR-CCM+的浮标锚泊系统数值研究

浮标锚链因磨损而断裂会导致浮标丢失,所以针对浮标锚泊系统的研究对锚链设计具有重要意义。为解决锚链系泊力计算方法精度不足和锚链力学简化模型与锚链实际形态不一致的问题,通过VOF （Volume of Fluid） 界面捕捉法建立了三维风、浪耦合流场,基于流体力学计算软件STAR-CCM+对一种滚塑浮标及锚链进行数值仿真计算。在建立双链节锚链物理模型基础上,通过求解浮标在风、浪中的受力及浮标与锚链连接处的受力损失求取锚链系泊力。结果显示,风浪越大,锚链的系泊力损失越大,2、3、4 级海况下浮标阻力损失分别为17.1%、36.6%、55.8%。锚链的双链节受力并非均等,主受力链节在2、3 级海况时承担90%以上的锚链系泊力,次受力链节的系泊力随着总系泊力的增加而增加,可见双链节锚链规格应与单链节相同。     

深海资料浮标体及系泊系统的阻力试验研究

本文结合国家“七五”重点科技攻关项目深海资料浮标研制，而进行浮标体和系泊系统的各种阻力试验研究，其试验成果已直接应用于深海资料浮标的系泊系统设计。实践表明，本文中各种阻力试验数据的应用是可靠的。     

刚臂式单点系泊系统在波浪作用下的链力分析

第一个刚臂式单点系泊储油装置(SBS)于1974年在突尼斯建成,以后在各地又建成了很多个这类装置,据报导其使用效果是令人满意的[1,2].为了发展我国海洋石油勘探、开发的科学技术,在海洋石油研究所的协助下,我们对这种系泊系统进行了波浪模型试验研究,本文在试验成果的基础上,主要研究单点浮筒多链系统的静力特性和波浪要素、水深等对链力的影响,还研究了减小中链力的措施.     

Statics of a three component mooring line

Catenary equations are solved for a three component mooring made up of two lines, connected at a point buoy or sinker where water depth and fairlead tension are given. This configuration is typical of deep water moorings and solutions are required for preliminary design of mooring systems and measurement of stability in service of moored floating platforms. The problem is transformed to a single polynomial equation of degree eight and is solved by Laguerre's iteration. Where there is no buoy or sinker the equation reduces to a quartic and can be solved in closed form. Elongation of the lines is shown to be equivalent to small uncertainties in the weights per unit length. The method is computationally efficient.     

三锚式浮标综合观测平台的研究和应用

在我国近海海域渔业活动频繁的情况下,为实现具有实时、连续、长期和稳定特征的近海海洋水体剖面观测,满足海洋科学研究对剖面水体数据的需求,通过借鉴目前我国近海广泛使用的10 m大型综合观测浮标的优点,在结构和稳性方面进一步优化,设计完成直径15 m的三锚式浮标综合观测平台,该平台通过在浮标中间预留中央透水井,使用绞车上下驱动多参数观测设备实现水体剖面的实时、连续、长期和稳定观测,并通过三锚式锚泊方式有效避免了剖面观测设备与固定锚系的缠绕问题,同时还具有智能判断、远程监控等功能,是一种新型的近海水体剖面观测平台。经过在我国东海海域一年的试验性观测表明,三锚式浮标综合观测平台整体运行效果良好,取得大量的水体剖面观测数据,在我国近海具有广泛的适用性。     

三锚系大型浮标运动响应特性数值研究

以三锚系浮标系统为研究对象,基于AQWA与OrcaFlex软件开展了三锚系大型浮标系统运动响应特性数值模拟研究。对直径10 m的浮标结构在波浪荷载下的水动力特性进行研究,校核了浮标的初稳性和大倾角稳性特征,计算分析了浮标的附加质量、辐射阻尼、运动响应幅值算子RAO等水动力参数,阐明了不同风、浪、流工况下三锚系浮标与辅助浮筒的运动响应特性,揭示了浮标三锚链导缆孔处锚泊张力随入射角度、波高和周期等的变化规律。研究结果表明：该浮标稳性和随波性能较好。与无浮筒三锚系浮标相比,带辅助浮筒的三锚系浮标系统的运动响应和锚泊张力减小,随着波高和周期增大,三锚系浮标系泊锚链的极端张力值逐渐增大,尤其是在极端海况下,迎浪向锚链极端张力急剧增大。     

深海锚泊浮标的二阶动力分析

计算了规则波上深海锚泊浮标的运动响应和锚泊线的动力响应。在对浮标的二阶漂移力计算时考虑了锚系的影响,并将浮标平均漂移的计算结果与不考虑锚系影响的结果进行了比较。本文计算所用浮标为单点系泊浮标,锚链由不同重量的分段组成。     

一种浅海锚泊测流浮标系统的实验

早在五十年代,海洋科技工作者已开始利用浮标布设海洋调查仪器,进行海上观测的试验工作。目前被采用的浮标系统,大体有三种类型:(1)锚泊浮标系统,利用各类自含式海洋调査仪器进行测量,定期收回资料;(2)遥测浮标系统,利用无线电遥控和收发各种海洋观测数据;(3)漂移浮标系统,利用浮标本身的漂移,进行海流和其他要素的观测。本文主要介绍浅海锚泊浮标系统的设计和使用情况。 对锚泊浮标系统的研究和实验,许多国家已做了大量有成效的工作。目前关于浮标的设计和锚泊方法尚无統一意见,但是可以看出,大多趋向于采用水下浮标张缆锚泊。这种方法使得浮标系统比起遥测浮标系统来,较为轻小、经济、方便,适合于进行多站同步观测。国外在海洋调查中经常利用这种系统作较长期的海流观测。 我所在六十年代初就已开始了锚泊浮标系统的研究、实验,1964年进行了新的研究设计工作,并在“全国海洋仪器会战”期间,完成了整套系统的计算设计与海上实验,经过鉴定,建议作小批量生产。 近年来,国家海洋局第一海洋研究所、中国科学院南海海洋研究所利用该浮标系统作过多次海上试用,取得了海流长期观测资料,初步考验了该系统的性能。我们最近又对某些部件作了一定的改进,并进行了海上实验。但是,实验也表明:此方法不宜在渔场区和台风盛行季节使用,因易被渔网拖损和丢失。现综合报告如下。     

New buoy observation system for tsunami and crustal deformation

We have developed a new system for real-time observation of tsunamis and crustal deformation using a seafloor pressure sensor, an array of seafloor transponders and a Precise Point Positioning (PPP ) system on a buoy. The seafloor pressure sensor and the PPP system detect tsunamis, and the pressure sensor and the transponder array measure crustal deformation. The system is designed to be capable of detecting tsunami and vertical crustal deformation of ±8 m with a resolution of less than 5 mm. A noteworthy innovation in our system is its resistance to disturbance by strong ocean currents. Seismogenic zones near Japan lie in areas of strong currents like the Kuroshio, which reaches speeds of approximately 5.5 kt (2.8 m/s) around the Nankai Trough. Our techniques include slack mooring and new acoustic transmission methods using double pulses for sending tsunami data. The slack ratio can be specified for the environment of the deployment location. We can adjust slack ratios, rope lengths, anchor weights and buoy sizes to control the ability of the buoy system to maintain freeboard. The measured pressure data is converted to time difference of a double pulse and this simple method is effective to save battery to transmit data. The time difference of the double pulse has error due to move of the buoy and fluctuation of the seawater environment. We set a wire-end station 1,000 m beneath the buoy to minimize the error. The crustal deformation data is measured by acoustic ranging between the buoy and six transponders on the seafloor. All pressure and crustal deformation data are sent to land station in real-time using iridium communication.     

船型海洋资料浮标的设计

介绍了我国船型海洋资料浮标浮标体和锚泊系统的设计方案 ,该浮标可适用于远海、深海海域布放 ,定点实时获取布放海域的水文、气象等有关要素的现场参数     

A single mooring system with sag-extensibility and flexural rigidity applied to offshore platform

Floating platform system has been extensively used in ocean exploitation, particularly for a tension-leg platform (TLP) system in deep water. Most of the TLPs are multi-mooring systems, where multi-joints are connected to the tension-legs so that the platform is not allowed to twist freely and may subject to enormous force induced by large incident waves in the weak-direction of the structure. This study aims to exploit a single moored offshore platform system that may attract less force and can be operated with less effort. In our analysis, in addition to mechanical properties of the tether, two important properties are also taken into consideration for the single mooring tether with expanded cross sectional dimension and utilization of stronger material, namely, the sag-extensibility and the flexural rigidity. Finally, the dynamic structural behavior produced by the mechanical effects on the new system is investigated and compared with that of traditional design while the wave-structure interactions of large body are also accounted for. Our study finds that the neglect of sag-extensibility or the flexural rigidity of large, strong mooring cable may result in a conservative but not necessarily safe design.     

Fatigue damage induced by nonGaussian bimodal wave loading in mooring lines

Catenary mooring lines are typically subjected to bimodal loads, comprising of a wave frequency (WF) component due to the first-order wave forces and a low frequency (LF) component induced by the second-order wave forces. For moored vessels, the LF forces due to current and wind also play a role. Only dynamic wave loads are considered herein, while current and wind loads are modeled as constant forces. Because of the nonlinearities of the mooring line characteristics, the dynamic line tension and the second-order responses, both the WF and LF line tensions are in principle nonGaussian. These facts make it difficult to estimate the combined fatigue damage of mooring lines in the frequency domain. A fatigue combination rule based on the Jiao and Moan’s theory has been extended to cover the nonGaussian case. The purpose of this paper is to improve and validate the frequency-domain method by time-domain analysis based on a simplified, but accurate mechanical model of the dynamic line tension. Improvements on the LF and combined fatigue damage estimation have been made by considering the nonsymmetrical property of the LF line tension distribution. Both the WF and LF mooring line tensions due to wave loading have been simulated in the time domain for different sea states and the combined fatigue damage has been estimated by using the rainflow cycle counting algorithm. The accuracy of the frequency-domain method for estimating the bimodal nonGaussian fatigue damage of mooring lines has been verified by the time-domain simulations and is considered to be acceptable.     

On the capsize performance of a discus buoy in deep sea breakers

The mode of capsize of a discus buoy in breaking waves is discussed. The results of model tests are given; these show that a judicious choice of mooring design can substantially reduce the chance of capsize. A comparison is made with the performance of the buoy on station.     

Nonlinear response of a moored buoy

The nonlinear dynamic analysis of a multipoint slack moored buoy is performed under the action of first and second order wave forces. The nonlinearity of the system is caused by the geometric nonlinearity of the mooring lines. The resulting nonlinear equation of motion is solved by an incremental time marching scheme. The nonlinear responses of the system are analysed to investigate different kinds of dynamic instability phenomena that may arise due to the nonlinearity of the system. As an illustrative example, a hollow cylindrical buoy anchored to the sea bed by means of six slack mooring lines is considered. The responses of the system are obtained and analysed for three regular waves namely, 5 m/5 s, 12 m/10 s and 18 m/15 s. The results of the study show that different kinds of instability phenomena like nT subharmonic oscillations, symmetry breaking bifurcation and aperiodic responses may occur in slack mooring systems. Further, a second order wave force may considerably influence the dynamic stability of such systems.     

Fundamental analysis of deep sea mooring line in static equilibrium

The integrated equations of deep sea mooring lines in static equilibrium under consideration of gravity force and line elongation are obtained. The most useful forms of the equations for designing deep sea mooring system are those in which horizontal displacement and horizontal and vertical components of tension are obtained as functions of line length, water depth, critical tension and unit weight of line.When the dynamic simulation of a buoy system is carried out, line tensions acting on the buoy should be represented as a linear function of displacement. Therefore the linearisation method is introduced by use of linearisation coefficient matrix. Translation formulae for the matrix from two to three dimensions is also presented.The influence of line elongation on the horizontal component of tension in a taut mooring condition is important, therefore the elongation of stretched deep sea mooring line must be considered carefully. Also, the scaling law under consideration of line elongation in static equilibrium, which is necessary in estimation from a small sized experiment, is discussed.