海底对系缆运动及张力影响研究

对系缆运动及张力进行分析,并考虑海底对系缆的影响。采用细长弹性杆单元模拟系缆微段,建立系缆运动控制方程,采用有限元法对其进行离散,将海底弹性和阻尼作用力添加到离散控制方程中。利用牛顿法和Newmark-β法对离散后的系缆非线性运动方程组进行数值求解。模拟长600 m的系缆顶端受到垂向正弦激励时的运动,分别求得考虑和不考虑海底作用时系缆运动响应和动态张力。通过对比系缆的运动、速度和动态张力结果,发现海底的弹性阻尼作用对系缆的运动及张力特性有极大影响。上述研究工作为计算海底对系缆的作用力提供了新方法。     

深海系泊系统动张力有限元计算

考虑深海聚酯尼龙系泊缆的拉伸和弯曲变形,取正交坐标和切向量描述任意结点的6个广义位移,缆变形的几何非线性,基于细长杆理论推导缆索单元的刚度矩阵和质量矩阵,得到12×12的非线性单元特性矩阵,利用有限元软件计算系泊系统的动张力.针对水深1 800 m由12根缆定位的Spar平台,考虑水流对系泊系统的作用,计算了不同外激励下的系缆动张力,讨论了激励频率对系缆张力的影响.结果表明,建立的缆索单元特性矩阵可以较好模拟深海聚酯缆的力学性能,并且得到的深海系泊缆动张力变化规律和力学特性是合理的.     

深海半潜式平台与系泊系统动力耦合的边界约束效应研究

深海浮式平台与其系泊系统的耦合作用显著,在数值分析中,需要合理确定二者耦合边界的模拟方法。本文以深水半潜式钻井平台及其系泊系统为研究对象,将浮体与系泊之间复杂的连接边界简化为固接、铰接和弹簧连接三种边界约束模型,提出了弹簧连接中相关参数的确定方法,并将不同边界约束下系缆张力的计算结果与模型试验数据进行对比验证。通过算例分析,探讨不同边界约束对平台运动、系缆张力及其疲劳损伤的影响,给出设计分析的选择建议。     

深海SPAR平台系泊系统耦合动力分析

随着海洋石油向深水领域的拓展,SPAR平台以其诸多优点逐渐成为海上油气生产的主流设施。主要研究SPAR与系泊系统间的耦合响应问题,在讨论了浮体在波浪中运动求解方法之后,阐述了如何利用非线性有限元技术对系泊缆索和立管进行动力分析和张力计算,以及浮体与系泊系统耦合计算的相关理论,对浮体和系泊系统耦合计算模型进行了描述。通过对某SPAR进行系泊系统耦合计算和对计算结果的讨论,证明了深海SPAR系泊系统耦合计算的正确性。     

新型深水系泊系统非线性循环动力分析

深水绷紧式系泊系统以合成纤维材料系缆作为主体系缆,由于系缆复杂的力学特性以及绷紧式系泊方式的特点,在设计、分析和工程应用中会带来新的有待深入认识的问题。以一系泊浮体的动力响应分析为例,考察了循环载荷作用下纤维系缆的动刚度特性,比较了悬链式系泊与绷紧式系泊动力响应的特点。分析表明,绷紧式系泊具有优良的系泊性能,但同时会发生复杂的张力响应。这些认识对于绷紧式系泊系统的研发和工程应用具有重要的参考价值。     

深海系泊系统动力特性研究进展

系泊系统设计是深海平台开发的关键问题之一。由于深海环境载荷和系泊材料物理特性及系缆构型影响,系泊系统分析涉及流固耦合非线性、非线性流体动力及整个系泊系统的运动稳定性。总结深海系泊系统关键理论和技术研究的前沿问题,包括系泊系统系缆建模、系泊系统耦合动力分析的理论和方法等,重点分析系泊系统非线性动力学问题的研究进展,并且提出了深海系泊系统需要深入研究的若干动力学问题。     

规则波中铰接塔-油轮系统的动力响应分析

论文研究铰接系泊塔-油轮系统波流联合作用下的动力响应。考虑铰接塔-油轮单点系泊系统系缆刚度的非线性,将尼龙系缆处理为分段非线性刚度模型,采用M orison公式计算铰接塔的波浪载荷,采用线性波浪绕射理论计算波浪对油轮的作用,建立了两自由度耦合的分段非线性运动微分方程。计算了高177 m的铰接系泊塔和93 500 t油轮构成的FPSO系统的耦合动力响应,并讨论了系统运动对于系缆张力的影响。     

聚酯系缆损伤对绷紧式系泊系统动力响应影响的数值分析

由于聚酯缆绳具备优异的力学性能,促使以其为主体系缆的绷紧式系泊系统得以广泛应用和发展。但聚酯系缆具有复杂的黏弹性和黏塑性,且由于在安装和使用过程中可能产生不同程度的损伤,使得聚酯系缆的动刚度特性发生演变,从而对系泊系统的动力响应产生直接影响。以一系泊于1 020 m水深的Spar平台为例,运用ABAQUS软件建立了由聚酯缆绳组成的系泊系统有限元模型,并利用ABAQUS子程序将损伤缆绳动刚度经验公式进行导入计算,以更好地反映系缆真实的动刚度变化。基于该有限元模型,计算了在相同水流、波浪工况下,不同损伤度、不同损伤系缆的系缆张力历程和平台的横荡、纵荡位移响应,分析了不同损伤度、不同损伤系缆对系缆张力及平台位移的影响。这些成果对把握绷紧式系泊系统在聚酯系缆有损伤情况下的非线性动力响应及其安全应用具有重要的参考价值。     

顺应式海洋平台慢漂运动物理模型试验研究

为研究顺应式海洋平台慢漂运动的影响因素,以截断圆柱和漂浮方箱为例进行了不规则波作用下的慢漂运动模型试验。测量了不同系泊刚度条件下的漂浮方箱以及相同系泊刚度条件下的截断圆柱和漂浮方箱在静水中自由衰减运动和在不规则波中的运动响应,并将运动响应分解成一阶波频运动响应和二阶低频运动响应,分析了系泊刚度和浮体形状对浮体运动的影响。通过物理模型试验发现了系泊刚度及浮体形状对顺应式系泊浮体一阶运动标准差和二阶低频运动平均漂移值和标准差的关系。结果表明由于顺应式浮体的固有周期远离波浪谱峰周期时,系泊刚度以及浮体形状对慢漂运动的一阶运动响应影响不大;二阶低频运动相对偏离平衡位置的平均值和标准差均随系泊刚度增大而减小,浮体形状同样对慢漂运动的二阶低频纵荡运动响应影响较大。试验结果为实际海洋工程的外形选择和系泊刚度选择提供数据支持。     

考虑浮体升沉及张紧环运动深海立管固有振动特性研究

研究深海顶张力立管(TTR)的固有振动特性。通过考虑两种不同的分析模型,研究沿水深变化的轴力以及张紧环运动对于立管固有振动频率和振型的影响。考虑立管顶端动边界条件及立管轴力随水深变化,提出了计算深水顶张力立管固有振动频率的方法,给出考虑浮体升沉及张紧环运动时顶张力立管的固有振动特性。结果表明,考虑变轴力和张紧环的影响是计算立管固有频率需要考虑的;立管浮体的运动,导致立管频率显著变化,从而改变立管的共振特性。     

Quasi-static three-dimensional analysis of suction anchor mooring system

The suction anchor has been widely used in taut or semi-taut mooring systems as an effective and economical solution to anchoring problems. To ensure high reliability, the profile of the mooring cable connecting the fairlead and the pad-eye must be accurately designed. However, previous studies have rarely considered the effect of cable slippage in soil on the mooring behavior, or embedded cables have been studied with an assumed tension at the seabed. This paper, by treating the cable suspended in water and the cable embedded in soil as a single cable, presents a two-dimensional (2D) static model and a three-dimensional (3D) quasi-static model for the cable during pretensioning and in service, respectively. The two models take into account the comprehensive effects of ocean currents, soil resistance and cable elasticity, all of which are critical for the design of a mooring system. Three examples are analyzed using the models and some useful conclusions are drawn.     

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.     

光电复合缆绞车牵引系统力学分析

针对深海光电复合缆绞车牵引系统的复合缆和卷筒的设计缺乏理论依据的关键问题,根据光电复合缆的特性和大容量收放的特点,运用微积分和MATLAB仿真的方法对复合缆在双卷筒上的受力进行详细分析,得到牵引卷筒上复合缆力学模型,进而讨论了牵引卷筒上复合缆的张力衰减情况。最后,基于ANSYS软件对复合缆进行有限元分析验证缆绳应力变化。仿真结果证明,所建立的牵引卷筒上缆绳的力学模型符合条件,为大载荷绞车的牵引系统设计提供了理论依据,有一定的工程意义。     

流速分布及锚链自身刚度对弹性单锚链系统变形和受力的影响

在锚链系统中,锚链本身的刚度和水流对其作用是影响锚链变形和受力的主要因素。应用分段外推的数值方法,分别对不同刚度和同一弹性锚链在均匀流作用以及同一弹性锚链在不同流速分布(流速在水深方向呈抛物线分布、对数分布)的水流作用下的变形和受力进行了分析和计算,得出了锚链自身的不同刚度及不同流速对锚链的变形及受力的影响情况。结果表明,刚度对锚链受力及变形影响明显,不同流速分布对锚链的偏移量几乎无影响,但对锚链的受力影响较大,选取抛物线型流速分布对锚链安全有利。     

A tension measurement method of a towing cable or a buoy cable

An indirect tension measurement method of a towing cable in midwater or a buoy cable is proposed using underwater acoustic positioning systems, etc., to give the in-water cable tension. The most simple and traditional cable tension measurement method is to apply a mechanical tension meter at the one end of the cable, but the method has limits in the aspects of continuous monitoring and manual operation. However, the technique in this study is to apply the Pode's analysis of the equilibrium configuration and tension of a flexible twine, in which the cable tension is given as a function of the geometric positions of both ends of the cable. A set of nonlinear integral equations is formulated and solved numerically by the Newton-Raphson method. Then the inclination angles and the tensions at the lower and the upper ends of the cable could be obtained. The derived method enables us to track a towed object, to measure the tension of a towing cable or a buoy cable and is also applicable to the remotely operated vehicle (ROV) tethered to a mother ship.     

Static Design of Cable Mooring Arrays for Offshore Guyed Towers

The key consideration in controlling the dynamic response of an offshore guyed tower subjected to environmental loading is the selection of the stiffness characteristics of the cable mooring array. In the present study, each cable in the array consists of three segments: a leading segment attached to the tower, a short heavy middle segment, and a seabed trailing segment attached at the extremity to an anchor pile. A nonlinear static model is presented in algorithmic form that defines the stiffness characteristics of the cable array. The model involves the inelastic static catenary equations coupled with conditions of geometric compatibility, formulated in terms of seven nondimensional system parameters. The effects of varying each of the system parameters on the stiffness characteristics of example cable arrays are presented and the implications for cable design are discussed.     

波浪作用下刚性框架浮体及其锚绳运动数值模拟精度分析

由小尺度刚性杆件构成的复杂结构近年来多用于海洋平台建设和海洋监测浮标制作以及海洋增养殖人工浮鱼礁的设计。采用有限单元法和集中质量点法建立波浪作用下刚性框架浮体及其锚绳运动数值模型,探讨空间单元划分、时间离散步长、数据保存格式对刚性框架浮体和柔性锚绳运动模拟精度的影响,分别给出此三者之间的匹配关系。研究结果表明:框架浮体的单元划分可依据是否出水给定,单元的划分比建议取0.05;锚绳的单元划分与其上端连接的浮体浮力有关,当锚绳的拉力主要由上端浮体浮力产生时锚绳单元的划分影响较小,当锚绳的拉力主要由波浪力产生时锚绳单元的划分比建议取0.02;空间单元划分与时间离散步长存在匹配关系,通过减小时间步长来追求数值模拟精度时必须同时考虑保存运动物理量截断误差的影响。     

Nonlinear dynamics of an elastic cable during laying operations in rough sea

A numerical approach for predicting motion and tension of extensible marine cables during laying operations in a rough sea is presented here. The solution methodology consists of dividing the cable into straight elements, which must satisfy an equilibrium equation and compatibility relations. The system of nonlinear differential equations is solved by the Runge–Kutta method, taking the effect of regular and/or irregular waves into account explicitly.

Illustrative applications of the method are given for a typical cable laying ship. The results are presented as rms values of the cable dynamic tension and corresponding dynamic factor for two different types of cable and several values of cable stiffness. The effect of axial deformation on the maximum tension at the shipboard pulley location is highlighted.     

海底光缆工程发展20年

对全球第一条海底光缆问世后20年来海底光缆工程发展的历程作了简要回顾。随着光纤传输技术的不断进步,海底光缆的通信技术得到了飞速发展,近20年来,其商用系统已经历了四代。海底光缆工程发展的重要标志,还体现在海底光缆施工技术的日趋完善,水下定位、海底数字式高分辨率的地球物理探测、海底原位测试等高新技术在海缆路由调查与埋设评价调查中的广泛应用。此外,对海底光缆市场与行业结构所经历的深刻变化作了分析,并预测了国际海底光缆网络的发展和市场前景。