【作者】 李江涛；

【导师】 吴志强；

【作者基本信息】 天津大学 ， 一般力学与力学基础， 2018， 硕士

【摘要】 随着经济的发展,社会的进步,世界各国对石油、天然气等资源的需求越来越大。于此同时,陆上石油产量进入低速、平稳、缓慢增长期,因此加强海洋尤其是深海油气资源开发已成为各国发展的必然趋势。因此,海洋采油平台及装备从浅水向深水发展是必然趋势。立管作为钻井、输液、勘探的必需设备,在服役过程中,不仅时刻受到周围风、流、浪的环境载荷,立管内部还会受到其内部流过高温高压石油或天然气的作用力。这些载荷长期性、周期性的作用以及它们之间的存在的耦合效应,会导致立管发生往复运动,将极大的降低结果的疲劳寿命,减短结构的服役时间,甚至可能会使结构发生大幅度振动,直接发生强度失效。所以对立管动力特性的研究具有重要的工程与理论意义。立管的涡激振动一直以来都是立管结构发生疲劳失效重要因素,也是海洋工程结构长期面临的难点问题。本文以Spar平台顶张力立管为研究对象,基于尾流振子模型,研究了立管耦合系统的多稳态行为,并考虑了随机因素对系统的影响,主要包括以下内容:(1)为研究深海立管的涡激振动现象,在其流固耦合非线性动力学模型中考虑了流体阻尼的平方非线性特性以及结构惯性耦合。基于一阶Galerkin模态离散方程,通过特征值计算分析了流速对系统稳定性的影响,通过Poincaré映射分岔方法分析了流速对响应非线性特征(频率、幅值)的影响。结果表明:涡激振动锁频区范围,可用无阻尼情况下的耦合颤振区来估计;锁频区左右两侧均存在双稳态现象,左侧为概周期运动与锁频运动共存,右侧为锁频运动与小幅周期运动共存。小流速下,响应中同时存在结构模态和涡激模态,锁频时响应表现为结构模态,而大流速时响应只含有涡激模态。(2)随着立管长度的增加,参与涡激振动的立管模态阶数会增加,从而导致高阶涡激共振现象的出现。了解和认识其机理,对于立管的设计和安全运行有重要的参考价值。本文采用包含尾流振子的立管流固耦合弯曲振动模型,根据所考虑最高流速下立管振动幅值包络收敛性结果,确定包含直到7阶模态的Galerkin离散系统为仿真计算模型。以1000米工程管道为例,利用Poincare映射分岔的方法计算得到响应幅值随流速的变化图,从时间历程、相图、频率图分析了典型行为的非线性特点。研究发现,由于非线性因素的影响,涡激共振响应的频率与系统线性固有频率有明显的差别。除一阶涡激共振区外,还存在二阶、三阶涡激共振区。一阶、二阶、三阶共振区间存在重叠部分,形成双稳态区。双稳态区立管振动幅值差别较大,工程应用中应关注周围环境中突发性干扰、持续性随机干扰引起的突发性大幅振动,防止灾难事故的发生。(3)在海洋工程中,随机激励是影响系统稳定性和诱发疲劳破坏的重要因素,本文初步分析了随机因素对立管振动行为的影响,通过确定性系统的振动响应分岔图,根据其响应的特点,将流速范围划分为6个不同的区域,并分析了各个区域内噪声强度对系统响应的影响。结果表明:随机激励对确定性系统中双稳态区及双稳态区附近流速范围内立管响应影响较大。更多还原

【Abstract】 With the development of the economy and the progress of the society,the demand for oil,gas and other resources is becoming more and more important in all countries.At the same time,the oil production on land had entered a steady and slow growth period.Therefore,the development of oil and gas of the ocean,especially the deep sea has become the inevitable trend of all countries.The development of production platform and equipment from shallow water to deep water is an inevitable trend.As a necessary equipment for drilling,infusion and exploration,risers are not only always subjected to ambient loads of wind,waves and waves but also inside the risers during service.The long-term,periodic loads and the coupling effect between them will lead to the occurrence of reciprocating motion of the riser.These will greatly reduce the fatigue life of the structure,shorter service time.It may even make the structure vibrate greatly,and the strength failure will occur directly.It may even make the structure vibrate greatly,and the strength failure will occur directly.Therefore,investigation of the dynamic characteristics of the riser has important engineering and theoretical value.The vortex-induced vibration of the riser has always been an important factor in the fatigue failure of structure.In this paper,the top-tensioned riser is taken as the research object.Based on the wake oscillator model,the multi steady state behavior of riser coupling system is studied,and the influence of stochastic factors on the system is also considered.The main contents are as follows:(1)In order to study the vortex-induced vibration of deep-sea riser,the square nonlinearity of fluid damping and the inertial coupling of the structure are considered in the fluid-solid nonlinear coupling dynamic model.Based on the first order Galerkin modal discrete equation,the influence of flow velocity on the stability of the system is analyzed by eigenvalue calculation.The influence of flow velocity on the response nonlinear feature(frequency and amplitude)is analyzed by Poincaré mapping method.The results show: coupled flutter region can be used to estimate the range of vortex induced vibration frequency-locked region;On both sides of the frequency-locked region,there are respectively two types of bistable phenomena: the coexistence of quasi-periodic motion and locking movement on the left side,the coexistence of small amplitude periodic motion and locking movement on the right side.There are structural modal and vortex modes simultaneously under small flow velocity,and the response is expressed as structural modal.At large flow velocity,the response only contains vortex excited modal.(2)With the increase of the length,in considering the vortex induced vibration of riser mode number will increase,which could lead to higher order vortex resonance phenomenon.According to the consideration of the maximum velocity of the riser under the vibration amplitude envelope convergence results,determine the Galerkin discrete system contains until 7th order model for simulation model.Taking the 1000 meter engineering pipeline as an example,the variation diagram of the response amplitude of the riser system with the flow velocity is obtained,the nonlinear characteristics of typical behavior are analyzed from time history,phase diagram and frequency diagram.It is found that due to the influence of nonlinear factors,the frequency of vortex induced resonant response is significantly different from the linear natural frequency of the system.Except for the first order vortex induced resonance region,there are second order and third order vortex induced resonance regions.The first order,the second order and the third order resonance interval overlap,forming the bistable region,the vibration amplitude of the riser in the bistable region is quite different.In engineering application,attention should be paid to in the surrounding environment and sudden large amplitude vibration caused by sudden interference and continuous random interference in the surrounding environment,so as to prevent the occurrence of disaster accidents.(3)In marine engineering,random excitation is an important factor affecting the stability of the system and induced fatigue damage.In this paper,the influence of the random factors on the vibration behavior of the riser is analyzed.Based on the response bifurcation diagram of deterministic system,according to the characteristics of its response,the velocity range is divided into 6 different regions,and the influence of noise intensity in each area on the system response is analyzed.The results show that the effect of random excitation on the response of bistable region and nearby velocity in deterministic system is obvious.更多还原