螺旋列板——深水立管涡激振动抑制装置

立管是海洋油气开采中必不可少的组成部分,它承担着流体输送和钻探的重要功能。深水立管在来流作用下容易产生涡激振动,涡激振动是造成立管疲劳破坏的主要原因之一,它会加速立管的疲劳破坏,因此需要采取适当的措施抑制深水立管涡激振动。海洋工程中涡激振动的削弱方法多是在立管外侧添加抑制装置,螺旋列板作为一种广泛应用的深水立管涡激振动抑制装置,在墨西哥湾、北海、西非等深水项目中有多年的应用。文中介绍了螺旋列板的设计、加工制作及安装方法,着重阐述了列板形状尺寸、海洋生物、包覆比例等对其抑制效率的影响,最后对螺旋列板的未来发展方向进行了展望。     

基于能量竞争载荷模型的海洋立管双向涡激振动时域预报方法研究

海洋立管是深海油气开发中用于连接海底井口和水面浮体的唯一通道。立管在洋流作用下极易发生涡激振动（vortex-induced vibration,简称VIV）,发展快速经验性涡激振动时域预报方法对立管的安全设计具有重要意义。通过柔性立管模型试验,结合载荷重构方法和最小二乘法,识别建立了能量竞争载荷模型下的经验水动力载荷系数模型。应用识别建立的经验水动力载荷系数模型,发展形成了海洋立管顺流向及横流向双向涡激振动时域预报方法。将预报结果与试验结果对比,结果表明：基于能量竞争载荷模型的海洋立管双向涡激振动预报方法能够有效预报海洋立管涡激振动主导模态、主导频率、流向平均位移响应和涡激振动位移响应等力学行为特性。研究成果对发展更为有效的涡激振动预报手段具有有益参考。     

基于MATLAB的海洋立管涡激振动数值模拟系统研究

基于MATLAB开发海洋立管涡激振动数值模拟系统NSVIV 1.0,系统采用尾流振子模型模拟外流对立管结构的作用,考虑内流对立管结构的影响,对立管的涡激振动动力响应和疲劳寿命进行预测分析。系统界面简洁清晰,使用方便,适用于顶张力立管,为进一步集成功能齐全的海洋立管设计分析软件打下基础。     

海洋立管抑振装置优化布置的实验研究

设计1种梯形截面的三螺旋导板抑振装置,在实验室大型水槽进行海洋立管涡激振动实验.通过改变这种抑振装置的覆盖方式和覆盖范围,研究梯形截面螺旋导板的不同覆盖方式和覆盖范围对抑制海洋立管涡激振动的作用.实验时用动态电阻应变仪采集立管模型横向和顺流向的动态响应数据,并利用雨流计数法对模型进行疲劳分析.实验结果表明:在外流流速相同的条件下,三螺旋导板各种覆盖方案对涡激振动都有抑制作用;随着螺旋导板覆盖率的增加,立管的振动减弱,疲劳寿命增加;覆盖螺旋导板的立管顺流向振动频率明显降低,横向振动频率当覆盖率较高时有所降低,覆盖率较低时基本没有变化.     

凸起型螺旋导板扰流抑制试验研究

为深入研究安装螺旋导板的深水立管涡激振动规律,设计一种月牙凸起型螺旋导板抑振装置,月牙凸起采用橡胶材料,在凸起两端肋高最低处连接成螺旋状。通过变化螺旋导板的螺旋数、螺距及螺高等形状参数,在风-浪-流联合水槽中进行安装该抑振装置的立管涡激振动试验,研究该抑振装置对涡激振动的抑制效率及其对立管动力响应的影响规律。研究结果表明,凸起型螺旋导板可取得优异的抑制效率,有效地降低由漩涡脱落引起的横向振动幅值;随着螺旋数的增加,螺旋导板抑制效率有所提高,但增幅降低,增加螺距对抑制效率影响不大,而随着螺高的增加,抑制效率有较大增幅;同时该抑振装置能有效地扰乱立管振动的主导频率,各抑振立管模型在示波区间内基本没有出现明显的主导频率。     

深水浮式平台垂荡运动与水下柔性立管涡激振动的动力耦合

基于有限元数值模拟,进行了"平台垂荡-顶张力立管涡激振动"整体系统的动响应数值模拟。动响应模型考虑了立管尾迹流场的水动力与结构动力的耦合和垂荡引起的立管结构刚度的时变特性;分析了平台垂荡运动的频率、模态阶数等因素对水下顶张力立管涡激振动的影响。数值结果表明:与不考虑平台运动相比,立管的动响应位移会增大;立管响应幅值随着模态阶数的降低而增大;在响应过程中,尤其对于低阶模态,会出现响应的模态转换现象。鉴于在平台垂荡和涡激振动的共同作用下,立管的动响应会大于涡激振动、参数激励分别单独作用的响应,建议在立管实际工程设计中应该考虑平台运动和涡激振动耦合激励作用下的结构动响应。     

海洋立管涡激振动模型的实验验证

考虑内流作用利用功能原理建立顶张力立管涡激振动响应数值模型,采用尾流振子模型模拟涡激振动升力,利用Hermit插值函数将其离散得到立管振动响应的矩阵方程形式,运用Newmark-β法在时域内迭代求解其动力响应。在山东省海洋工程重点实验室进行了阶段流作用下的大长细比海洋立管涡激振动试验,对比数值模拟和试验结果表明该模型对于考虑内流作用的大长细比海洋立管涡激振动响应预报是有效的,为深水立管涡激振动研究提供一定的借鉴。     

海洋立管涡激振动的研究现状、热点与展望

随着深海油气资源的开采,越来越多的研究者开始关注海洋立管的涡激振动问题.在海洋环境下,洋流是海洋立管的涡激振动的主要原因.当洋流流经立管时会在立管的两侧产生交替的泄涡,导致立管受到横流向和顺流向的脉动流体力.这被认为是海洋立管涡激振动的主要诱因.海洋立管的涡激振动是一个异常复杂的工程问题,它涉及许多科学上悬而未决的难题,如紊流、流动分离、分离点的漂移等等.此外,事先无法确定的立管的位置和立管与洋流之间的相互作用又大大增加了解决这一问题的难度.尽管近几十年里科学界在此方面做了大量的研究工作,一个能够准确、高效、经济地预报海洋立管涡激振动的方法仍然没有得到.即便如此,最近的研究工作依然在许多方面作出了突出的成就.首先介绍了涡激振动的背景知识和基础理论.随后,回顾了近年来海洋立管涡激振动方面的研究成果.接着,重点介绍了当前海洋立管涡激振动领域内的两个热点研究问题,即:在多大程度上立管的顺流向振动能够影响立管的横流向振动,以及尾流的三维效应是如何影响立管的涡激振动响应的.最近的研究发现,当结构与流体的质量比小于6时,顺流向振动能显著增大横流向振动的振幅.最近的研究还发现,立管尾流的三维特性和立管受到流体力的轴向相关度有密切关系.随着流动的发展(海流折合速度从0增加到12),立管尾流的三维特性发生变化,在初期,立管尾流的三维特性不明显,流体力的轴向相关度基本等于1,也就是说,流体力和立管的位移响应是同步的,因此能量不断地由海流向立管转移,导致立管的振幅不断增大.当海流折合速度大于6时,流体力的轴向相关度由1锐减到负值,此时,立管尾流的三维效应显著.最后针对今后海洋立管的涡激振动的研究提出一些建议.     

深海悬链线立管涡激疲劳损伤研究

讨论海洋平台钢质悬链线式立管SCR(Steel Catenary Riser)的涡激疲劳损伤问题。对于悬链线立管外的流体,给出涡脱落频率和升力对立管作用的计算方法。悬链线立管采用索结构模型,进行动力学分析并利用模态叠加法对其进行动力响应分析。根据Palmgren-Miner线性累积损伤准则并结合S-N曲线,分析在不同流速下立管的涡激疲劳损伤。以工程中实际使用的1 500 m Spar海洋平台悬链线立管为例,对立管的涡激疲劳损伤进行了预报。并通过立管的参数研究,分别就立管外不同来流速度、立管壁厚、内部流体密度和柔性接头刚度对其疲劳损伤的影响进行了分析,得到了一些有意义的研究结果。     

海流作用下子母管结构横向涡激振动

基于量纲分析,设计模型试验研究稳态海流作用下子母管结构的横向涡激振动。通过对结构横向振动位移、水动力载荷和流场速度的同步测量分析,研究子母管结构横向涡激振动幅值和频率随约减速度的变化规律以及母管的水动力特性。实验结果表明,子母管间距比和质量比对管道横向振动和水动力有较大影响。在管间距比为0.1～0.5范围内,子母管结构涡激振动存在明显的不对称性。随着子母管间距比的减小,结构横向最大振幅增大,涡激振动的约减速度范围变宽;随着质量比的增大,涡激振动的约减速度范围变窄。母管的平均阻力系数随子母管间距比的增大单调递减,而平均升力系数则呈现非单调变化的特征。     

Seismic response of submerged floating tunnel tether

A mathematical equation for vibration of submerged floating tunnel tether under the effects of earthquake and parametric excitation is presented.Multi-step Galerkin method is used to simplify this equation and the fourth-order Runge-Kuta integration method is used for numerical analysis.Finally,vibration response of submerged floating tunnel tether subjected to earthquake and parametric excitation is analyzed in a few numerical examples.The results show that the vibration response of tether varies with the seismic wave type;the steady maximum mid-span displacement of tether subjected to seismic wave keeps constant when parametric resonance takes place;the transient maximum mid-span displacement of tether is related to the peak value of input seismic wave acceleration.     

Parametric vibration of submerged floating tunnel tether under random excitation

For the study of the parametric vibration response of submerged floating tunnel tether under random excitation,a nonlinear random parametric vibration equation of coupled tether and tube of submerged floating tunnel is set up.Subsequently,vibration response of tether in the tether-tube system is analyzed by Monte Carlo method.It may be concluded that when the tube is subjected to zero-mean Gaussian white noise random excitation,the displacement and velocity root mean square responses of tether reach the peak if the circular frequency of tube doubles that of tether;the displacement and velocity root mean square responses of tether increase as the random excitation root mean square increases;owing to the damping force of water,the displacement and velocity root mean square responses of tether decrease rapidly compared with tether in air;increasing the damping of the tether or tube reduces the displacement and velocity root mean square responses of tether;the large-amplitude vibration of tether may be avoided by locating dampers on the tether or tube.     

水下悬浮隧道锚索稳定性分析

为研究水下悬浮隧道锚索的稳定性,建立锚索在涡街激励作用下振动的数学方程,采用伽辽金法对其进行化简,锚索振动的稳定性通过Lyapunov指数法进行判断,分析了锚索动静张力比的大小、悬浮隧道系统的阻尼比和锚索参数激励频率对锚索振动稳定性的影响。计算结果表明,锚索振动失稳的范围取决于锚索的动静张力比、锚索的阻尼比和频率比(锚索参数激励频率与锚索1阶模态固有频率的比值);当频率比为1和2左右时,随着锚索动静张力比的增大和阻尼比的减小,锚索逐渐从稳定状态转变为不稳定状态,且锚索的不稳定区域逐渐增大。     

Non-Linear Response of Tethers Subjected to Parametric Excitation in Submerged Floating Tunnels

For the study of the non-linear response of inclined tethers subjected to parametric excitation in submerged floating tunnels,a theoretical model for coupled tube-tether vibration is developed.Upon the assumption that the static equilibrium position of the tether is a quadratic parabola,the governing differential equations of the tether motion are derived by use of the Hamilton principle.An approximate numerical solution is obtained by use of Galerkin method and Runge-kutta method.The results show that,when the static equilibrimn position of the tether is assumed to be a quadratic parabola,the tether sag effect on its vibration may be reflected;the tether sag results in the asymmetry of tether vibration amplitude;for the reduction of the tether amplitude,the buoyant unit weight of the tether should approach to zero as far as possible during the design.     

Parametric Vibration Analysis of Submerged Floating Tunnel Tension Legs

According to the characteristics of submerged floating tunnel anchored by tension legs,simplifying the tube as point mass and assuming that the tension leg is a nonlinear beam model hinged at both ends,the nonlinear vibration equation of the tension leg is derived.The equation is solved by the Galerkin method and Runge Kutta method.Subsequently,numerical analysis of typical submerged floating tunnel tension leg is carried out.It is shown that,the parametric vibration response of the submerged floating tunnel tension leg is related to the amplitude and frequency of the end excitation.Without considering axial resonance and transverse resonance,it is reasonable that higher order modes are abandoned and only the first three modes are considered.The axial resonance amplitude of the second or third order mode is equivalent to the first order mode axial resonance amplitude,which should not be ignored.     

Tension during parametric excitation in submerged vertical taut tethers

The construction of a suspension bridge with floating pylons or a submerged floating tunnel requires the installation of a mooring system. The option of taut vertical tethers, similar to those used in tension-leg platforms, has been suggested in preliminary designs. The environmental loading on the tether, mainly due to wind waves and swell, results in a parametrically excited system. Certain loading conditions develop instabilities that translate into large horizontal motion. However, the effects of parametric resonance on the tension values have rarely been investigated. This paper aims to clarify the relation between lateral displacement and tether tension and to quantify the extreme tension values in the event of parametric resonance. The presented analysis is based on a full numerical model of the tether that includes geometric and hydrodynamic nonlinear effects. This model is used to investigate a representative example that illustrates parametric resonance and multiple parametric studies to assess the effects of the excitation frequency, amplitude, initial pretension, tether length and inclination angle on the tether’s response. The results reported here provide the basis for a recommendation on designing a tether under parametric resonance regarding the ultimate extreme values and fatigue life.     

Dynamic Risk Analysis of Permanent Deformation of Sea Embankment

For evaluation of the permanent deformation of a sea embankment under stochastic earthquake excitation, a robust dynamic risk analytical method is presented based on conventional permanent deformation analysis and stochastic seismic response analysis. This method can predict not only the mean value of maximum permanent deformation but also the reliability corresponding to different deformation control standards. The earthquake motion is modelled as a stationary Gaussian filtered white noise random process. The predicted average maximum horizontal permanent displacement is in agreement with the conventional result. Further studied are the reliability of permanent deformation due to stochastic wave details at one seismic motion level and the risk of permanent deformation due to stochastic seismic strength, i. e., the maximum acceleration in a long period. Therefore, it is possible to make the optimal design in terms of safety and economy according to the importance of a sea embankment. It is suggested tha     

Seismic stability analysis of subsea tunnels under the effects of seepage and temperature

This study used the strength reduction method to analyze the seismic stability of a subsea tunnel under the effects of seepage and temperature. Excess pore water pressure within the rock mass was first eliminated by calculating the consolidation; then, an earthquake wave was applied to begin the dynamic and time-history analysis and to obtain the maximum horizontal displacement of the model boundary. Finally, a temperature field model was established for the thermal analysis of the structure. The temperature of each node of the structure was regarded as a form of outside load applied to the reduction model; both sides of the vertical horizontal displacement of the boundary nodes and gravity were used as inputs for the static analysis when the vertex horizontal displacement reached its maximum value. By continuously decreasing the shear strength parameters, the safety factor of the tunnel structure was determined. The results show that the plastic zone first appeared in a smaller range on both sides of the tunnel arch feet near the lining and vault of both sides. The safety factor decreased with increasing water depth and overburden layer thickness.     

在平台振荡条件下TLP张力腿的涡激非线性响应

给出了预测张力腿涡激横向振动的时域分析,考虑了波浪、海流、张力腿平台的横漂与垂荡诸因素.张力腿平台的垂荡引起张力周期性变化,对张力腿的涡激横向振动起参数激励的作用,使其动力响应更为复杂.讨论了参数激励下涡激响应的共振条件;以尾流振子模型为基础,发展了分析张力腿在动张力作用下的涡激振动的工程方法,并分析了一座TLP实例,给出了在横漂周期内张力腿上质点的相对位移、弯矩、剪力幅值的时间历程.结果表明,平台垂荡使张力腿的涡激响应幅值升高、高频成分增加,因此它对张力腿的疲劳设计是重要的.     

多频参激—涡激联合作用下顶张力立管分岔分析

复杂海洋环境中,顶张力立管顶部平台受到不同分量叠加的波浪作用,导致其轴向张力与多个频率相关,系统产生多频参激与涡激的联合振动,其动力学行为变得更为复杂,尤其是分岔和混沌等非线性振动特性有待进一步分析。首先,基于欧拉—伯努利梁理论,引入范德波尔尾流振子,建立和推导受多频参激—涡激联合作用下立管的动力学模型及其运动微分方程;接着,利用伽辽金法得到离散后的常微分方程组,采用多尺度法得到系统共振响应的调谐方程;最后,通过数值算例探究系统在多源和多频载荷联合作用下的共振响应。结果表明：对于多频参数激励,其中一个参数激励幅值在立管振动中起主导作用,而另一个会引起分岔的位置、数量和性质发生改变;随质量—阻尼参数增大,系统共振响应幅值整体先增大后减小,各分岔点出现的位置整体先向泄涡频率较大处移动,随后向泄涡频率较小处移动;质量—阻尼参数的变化还可能诱使系统发生倍周期分岔和混沌现象,危害结构安全。此外,采用直接数值积分求解微分方程组,验证近似分析结果,两者吻合较好。