海洋输液立管涡激振动响应及其疲劳寿命研究

以FrancisBiolley改进的vanderPol尾流振子模型为基础,考虑管内流动流体和管外海洋环境荷载共同作用,建立了海洋立管涡激振动微分方程,用Hermit插值函数对立管微分方程进行离散,并用Miner理论对立管的疲劳寿命进行分析,通过编程和实例计算,分析了管内流速对涡激响应幅值和疲劳寿命的影响。结果表明,当管内流体流速变化使立管的固有频率接近漩涡脱落频率时,立管涡激振动响应将会增大,疲劳寿命将会显著减少。     

线性剪切流中深海立管顺流涡激振动响应及疲劳损伤研究

采用圆柱体顺流受迫振荡试验数据,并引入顺流流体力放大因子,建立考虑横流对顺流响应影响的深海立管顺流涡激振动预报模型。该模型假定对应顺流涡激振动两个不稳定区的涡脱落模式相互独立,因此允许对应于不同不稳定区的两个模态能量输入区相互叠加。运用建立的涡激振动预报模型对HanØtangen试验模型进行分析,并与试验结果的位移均方根和主要控制模态进行了比较,结果均吻合较好。采用S-N方法,对顺流涡激振动诱发的深海立管疲劳损伤进行分析,研究了能量比截断值、顶端张紧力和流速分布对疲劳损伤的影响,得到一些有意义的结论。     

细长立管两向自由度涡激振动数值研究

采用ANSYS-CFX软件对细长立管的两向自由度涡激振动进行了数值模拟,分析了小变形（A/D=0.07）和大变形（A/D=1）两种条件下的立管涡激振动特性。在小变形条件下,锁定区的顺流向振动和横向振动的幅值比小于非锁定区;在非锁定区,顺流向振动频率是横向振动频率的两倍,而在锁定区两者振动频率相同,等于升力频率。在大变形条件下,锁定区的顺流向振动和横向振动的幅值比明显大于非锁定区;不论在锁定区还是非锁定区,都满足顺流向振动频率是横向振动频率的两倍关系,顺流向振动频率等于拖曳力频率,横向振动频率等于升力频率。     

深海顶张力立管参激-涡激耦合振动响应分析

该文研究顶张力立管参激-涡激耦合振动计算方法和动力特性。考虑立管顶端动边界条件,建立顶张力立管模型,研究其在剪切流中的涡激振动响应和参激-涡激耦合振动响应。提出立管的动力响应分析方法,分析参数激励对立管横向涡激振动的影响。结果表明,立管的横向振动响应频率存在0.5倍参激亚谐成分,参数激励对于立管横向振动具有重要影响。     

海洋平台涡激振动响应研究

本文根据海洋钻井平台的工作环境,研究了其对涡激振动的响应。计算结果表明其重要性,对海洋钻井平台设计具有一定的指导意义。     

深水立管两向自由度涡激振动的数值分析

对更加符合实际情况的两向自由度涡激振动进行数值分析。研究四种不同质量比(m*=14.45,8.30,3.50和m*=1.87)情况时,流向振动与横向振动幅值和频率之间的关系。结果表明,在大质量比（m*=14.45,8.30）时,流向振动频率基本可以看做横向振动频率的2倍,并且流向振动幅值相对于横向振动幅值来说可以忽略不计,符合现有实验研究结果;当质量比较小（m*=3.50,1.87）时,顺流向振动幅值并不能被忽略,尤其在顺流向处于锁频时。两向振动的主频率基本维持2倍关系,但是除主频率外还具有相同或相似的振动频率。     

细长柔性立管涡激振动的数值模拟研究

应用基于浸入边界法（IBM）的三维水动力并行计算程序CgLES_IBM,并结合隐式结构动力计算程序X-code,研究了低雷诺数条件下细长柔性立管的涡激振动问题。研究发现：立管的振动体现出明显的驻波振动特征。立管在顺流向主要激发奇数阶模态,而横流向处于激发状态模态的奇偶性取决于涡激振动卓越频率和立管固有频率之间的关系。涡激振动的频谱呈现为单谱模式,所有的振动能量都集中在一个窄频段上,波节处能量较弱,波腹处能量较强。波节处,时均能量传递系数为负值,涡激振动处于抑制状态,相邻波节之间,时均能量传递系数为正值,并沿展向呈现出“马鞍形”分布,涡激振动处于激发状态。柔性立管涡激振动的泻涡模式呈现出三维特性,近尾流区为2S模式,但由于倾斜泻涡造成尾涡沿展向移动,尾涡模式随后变为2P₀模式,随着较弱漩涡的耗散,在远尾流区,尾涡模式又回到2S模式。     

柔性立管涡激振动抑制装置试验研究

为深入研究带螺旋列板的柔性立管涡激振动响应特性,进行立管螺旋列板抑制装置的拖曳水池试验。由拖车拖动立管产生来流测得应变数据,基于模态叠加法获得立管位移响应等参数。分析螺旋列板抑制装置的螺距变化,系统研究不同螺旋列板状态下立管应变、位移响应等参数。结果表明,流向响应与横向响应同样重要不可忽略;裸管响应特性与带螺旋列板的立管响应特性区别较大,响应特性与螺旋列板几何形状紧密相关。     

深海立管涡激振动及其抑制方法研究

涡激振动是造成深海立管疲劳乃至失效的重要因素之一,会严重影响立管的使用寿命.现采用数值模拟的方法对深海顶张式立管的涡激振动及其抑制方法进行了研究.即利用有限元软件ABAQUS模拟了立管在不同流速下裸管和安装螺旋侧板的不同实例,得到其横向位移响应.结果表明,裸管条件下,当约化速度4.5相似文献   

采用改进尾流振子模型的柔性海洋立管的涡激振动响应分析

建立了柔性杆件在非均匀流作用下的涡激振动响应预测模型,考虑了涡激振动锁频阶段流体附加质量的变化,以及振动响应和来流简缩速度的非线性关系。该模型通过经验公式结合迭代求解的方式,计算方便、速度快,避免了数值计算(CFD)的繁琐,较为适合于海洋工程实际应用。与试验和数值结果的比较表明采用该文提出的计算模型,可以更合理、准确地给出结构涡激振动响应。最后,结合实际平台参数,进行了柔性立管在非均匀流场的作用下的涡激振动响应分析,并研究了立管的预张力、流场分布等参数的影响。分析结果表明:随着立管张力和流场分布的改变,各阶模态锁频区域发生了变化,从而改变了结构的总体响应     

考虑附属管的实尺寸钻井隔水管系统涡激振动二维数值模拟研究

实际钻井隔水管通常含6根附属管线,近期研究表明,实际隔水管外挂的附属管线对主管有一定的流动控制效果,它是否有涡激振动(vortex-induced vibration,VIV)抑制作用亟待研究,针对这一问题开展数值模拟研究.基于RANS(Reynolds-averaged Navier-Stokes)方程,结合k-ω湍...     

深海钢悬链立管时域疲劳寿命预估研究

研究了钢悬链立管(SCR)时域非线性动力分析用于疲劳寿命预估。随着海洋工业不断往深海进发,过去十年内钢悬链立管成为众多油田开发的优选方案。然而,对于钢悬链立管设计而言疲劳是个关键难题。钢悬链立管的非线性动力特性显著,与频域方法相比,时域分析能够模拟非线性水动力载荷以及结构的非线性特性。本文数值模拟了海洋环境载荷作用下SCR的非线性结构动力响应,利用S-N曲线对立管进行整体疲劳寿命预估。对影响SCR疲劳寿命的各参数进行敏感度分析,输入的敏感度分析参数包括拖曳力系数、浮力因子、海床土体硬度等,研究表明疲劳寿命的预估结果与这些参数相关,所给出的结论便于设计人员更好理解钢悬链立管动力特性,选择合适的参数用于立管疲劳设计。     

Ultrasonic birefringence as a measure of mechanically induced fatigue damage in laminated composites

A non-destructive testing method based on polarization effects of ultrasonic transverse waves is suggested to monitor fatigue damage in polymer matrix composites. Using a transverse wave probe in reflection mode, phase and amplitude of its output signal are measured as a function of the polarization angle. From the material properties of a single ply and the proposed calculation approach, the birefringence response of carbon fibre reinforced polymers composed of many plies with different fibre orientations is predicted. The effect of ply sequence is investigated using two types of quasi-isotropic specimens with different layups. Cyclic tensile loading of composites results in fatigue damage that is characterised by matrix cracking along the fibre direction through the thickness of each ply. These myriads of transverse cracks affect the ultrasonic attenuation and degrade the homogenised stiffness of single plies. In the experiments, stepwise increase of fatigue damage is alternated with ultrasonic measurements, which show the effect of ply-dependent crack densities on the birefringence behaviour. Simulated and measured transverse wave response are matched by variation of the input parameters shear moduli and attenuations, which are therefore the final results. The obtained data from the investigated composite specimens is proposed to characterise the distinct fatigue state for each ply orientation.     

Analysis of fatigue damage in composite laminates

The degradation of laminated composite materials under service loading occurs by means of a complex combination of damage modes and damage mechanisms. These damage events combine to produce a damage state which controls the state of stress and the state of strength of the degraded laminate. Although data have been generated dealing with various details of this process, an understanding or philosophy of the precise nature of damage development has not, heretofore, been developed. This paper makes such an attempt for the general case of damage development in laminated plates under cyclic (fatigue) loading. The philosophy is based on the discovery of a ‘characteristic damage state’ in such plates which forms independently of load history, and is determined only by the properties of the laminae, their orientations, and their stacking sequence. The detailed nature of this characteristic damage state, the nature of its formation, and its influence on strength, life and stiffness is discussed. The general need for further work in this, and related fields is also assessed.     

A method for accurate estimation of the fatigue damage induced by bimodal processes

This paper presents a method for calculating the fatigue damage from a stochastic bimodal process, in which the high frequency (HF) and low frequency (LF) components are narrowband Gaussian processes. Rainflow cycle counting identifies the following: small but numerous cycles, and large but fewer ones. In existing methods, the small-cycle amplitudes are assumed to be identical to that of the HF cycles, whereas the large-cycle amplitudes are approximated as the sum of the HF and LF amplitudes. The novelty of the present approach lies in the recognition and incorporation of two effects, which concern the reduction of the small-cycle amplitudes caused by the LF process, and the offset between the HF and LF peaks. Parametric studies are conducted, investigating a wide range of parameters. Using time domain simulation as a benchmark, the present method is found to provide a vast improvement over existing methods, with a root-mean-square error of 1%.     

Control of a 2-DOF manipulator with a flexible forearm

In this paper we present experimental results on the position and vibration control of the end-effector of a 2-DOF parallelogram manipulator with a flexible forearm. A dynamic model of the manipulator is first obtained. Control strategies are implemented to control the manipulator. The first control strategy uses the computed torque method based on a reduced-order dynamic model of the manipulator which is obtained by assuming that all the links are rigid. This method is referred to as the reduced-order computed torque (ROCT) method. Experimental results demonstrate that such a strategy is not good for vibration control of the end-effector of the manipulator. The second control strategy is a state feedback control law designed based on a local linearization of the nonlinear dynamic model. Experimental results show that this control strategy achieves good vibration control of the end-effector of the manipulator. However, since the strategy is based on local linearization, it is valid only in a neighbourhood of the operating point. A hybrid controller that uses the ROCT method for the initial large movement of the manipulator is then implemented. Based on a switching rule, the controller is switched to the state feedback controller based on the linearized model when the manipulator is sufficiently close to the equilibrium state. Experimental results are reported and the successful performance of the controller in dampening out end-point vibrations is demonstrated.     

斜拉索风致动力疲劳损伤的研究

研究了斜拉索风致振动的疲劳损伤问题。首先,根据 Miner 线性累积损伤原理,给出了结构疲劳损伤的计算公式。其次,根据高周疲劳的特性,我们假设斜拉索的疲劳损伤符合 Basquin 疲劳估算模型。第三,在综合目前疲劳损伤既有研究的基础上,进一步提出评价不同风速和不同风攻角对斜拉索疲劳损伤影响的框架。最后,以松花江斜拉桥中的斜拉索为对象,基于动力时程法计算分析了在不同风速和不同风攻角情况下斜拉索上各节点的应力时程,再使用雨流计数法统计斜拉索的应力-应变循环历史,估算出在不同风速和不同风攻角下斜拉索的疲劳损伤。于是,定量地评价了在不同风速和不同风攻角对斜拉索疲劳损伤的影响。