【作者】 杨超；

【导师】 易孟林；

【作者基本信息】 华中科技大学 ， 机械制造及自动化， 2007， 博士

【摘要】 注水是油田增加原油产量的重要措施。注水系统是典型的充液管系统,其中的流动为高压非恒定流动,系统中存在液体的压力脉动和管壁的结构振动,彼此耦合,不仅会造成振动和噪声污染,而且严重的耦合振动可导致灾难性后果。因此,有必要研究注水系统的耦合振动特性及其影响因素,预测其振动响应,以便采取必要措施来抑制或减小系统的振动,减小或避免事故的发生,保障注水管网的安全运行。本文首先以Timoshenko梁理论为基础,导出了非恒定流充液管道的耦合非线性振动方程组,在周期性载荷作用下横向平面内的非线性耦合运动方程及其无量纲形式,进而导出了流固耦合拟线性振动方程。为了准确预测充液管系统在考虑流固互动效应时的振动响应,对时域响应计算方法进行了研究。提出了简单充液管系统时间步长和管道分段数的确定方法及网格加密方法,可以更好地捕捉到水击压力的变化;提出了“阻尼重分管道钢化优化法”,建立了确定复杂管系统时间步长及管道分段数的优化模型,从而解决了复杂充液管系统特征线法(MOC)计算时各管道时间步长必须相同的问题,并对一复杂充液管系统的计算结果和文献实验结果进行比较,验证了方法的正确性。使用特征线法-有限差分法(MOC-FDM),对一复杂充液管系统的非线性耦合振动响应进行了预测,计算结果与实验结果的比较,验证了方法的有效性。对连接耦合、泊松耦合、摩擦耦合、管道壁厚、结构阻尼及管材等因素对充液管系统振动响应的影响进行了研究。弱约束的连接耦合将液体的部分压能转换成管壁的振动能量,但泊松耦合效应又将管壁的部分振动能量转换成液体压能,泊松耦合与连接耦合起着能量转换器的作用;管系统结构阻尼对管道振动响应的衰减作用远大于液体粘性阻尼的作用,但大的结构阻尼引起液体压力升高;管道外径相同时,随管道壁厚的增大,管道振动能量减少,液体压能增加;使用铜管和钢管的充液系统,振动时的能量主要集中在液体里,而使用PVC管和PE管的充液系统,振动时的能量主要集中管道上;提高约束的相对弹簧刚度k可有效降低管道速度响应,与此同时,可显著增大铜管和钢管系统统的液体压能,但对PVC管和PE管系统统液体压能的影响很小。研究了充液管系统模态分析的方法,计算结果表明,FSI效应对充液管系统振动模态的影响非常显著,考虑FSI效应的固有频率阶数(在一定的频率范围内)明显多于忽略FSI效应的固有频率阶数,且固有频率值发生显著变化。运用MOC-FFT方法,在忽略管道及液体阻尼影响的情况下,求解了一简单充液管系统的固有频率,计算结果与模态分析结果以及文献的计算结果基本一致。最后以一联合站内注水子系统为研究对象,分别对调整约束位置和采用阻尼材料的振动抑制效果进行了仿真分析,结果表明:改变约束位置以减小弯头的伸出距离,可显著降低管道的振动速度和位移,但液体的压能增大;在管道表面覆盖合适的阻尼材料能够有效地降低充液管系统液体和管道的振动响应,减振效果明显。非恒定流充液管系统广泛存在于输油管道工程、动力水能工程、生物工程、航天工程、钻井工程、液压系统、建筑工程、核工业等领域,研究其耦合振动特性及其影响因素,预测其振动响应,以便采取必要措施来抑制或减小系统的振动,减小或避免事故的发生,对保障其正常运行具有非常重要的现实意义。更多还原

【Abstract】 Waterflooding is an important measures to improve output of crude oil in oil field. Waterflooding system is a typical fluid-filled pipe syetem, flow in the system is unsteady and high-pressure flow, pressure pulsation of fluid and vibration of pipe wall exist in the system and they interacts each other, which brings about pollution of vibration and noise, and even disaster if the coupled vibration is severe. It is necessary to study the coupled vibration characteristics of unsteady-fluid-filled pipe system and influence factors of the vibration, to predict response of the system, to take some necessary measures to restrain or minish vibration of the system, to lessen the chance of accident or avoid accident, to safeguard the safty of the waterflooding system.Based on the Timoshenko beam theory, coupled nonlinear differential equation, lateral differential equations under periodic loads and corresponding dimensionless expressions of unsteady-fluid-filled straight pipe were developed, and quasilinear equations of the fluid-filled straight pipe with consideration of fluid-structure interaction (FSI) was obtained.Numerical methods to exactly get the vibration response solutions of fluid-filled pipe system with consideration of FSI in time-domain were studied. Method to define the time step, divided number of simple fluid-filled pipe system and method to subdivide the mesh spacing were advanced to better capture the change of waterhammer pressure;“Optimization method of damping-redistribution and pipe-steel”was put forword to establish the optimization model of time step and divided numbers of pipes for complex fluid-filled pipe system, which ensured time steps of all pipes being the same during numerical computing by the method of characteristics (MOC). A complex fluid-filled pipe system was adopted to study with the present method, the results agree with the experimental results from literature very well.MOC-FDM was applied to get fully-coupled nonlinear vibration responses of a complex fluid-filled pipe system, comparison between the numerical results and those of test from literature validates the validity of the method.Influences of junction coupling, Poisson coupling, frictional coupling, thickness of pipe wall, structural damping of pipe and material of pipe on the responses of fluid-filled pipe system were studied, the results show that weak-restriction junction converts some pressure energy of fluid into vibration of pipe wall, meanwhile Poisson coupling converts some kinetic energy of pipe into pressure energy of fluid, Poisson coupling and junction coupling act as energy transformer. Structural damping of pipe has greater peak attenuation of pipe vibration than viscous damping of fluid, but greater damping ration can causes rise of fluid pressure.When pipes’outer diameters are the same, the pipes with thicker wall have less kinetic energy, but increase pressure energy of fluid. The vibration energy of fluid-filled steel pipe and copper pipe system mainly concentrates in fluid, but the vibration energy of fluid-filled PVC pipe and PE pipe system mainly concentrate in pipes. Dynamic response of pipe wall can be reduced effectively with larger relative stiffness of restriction, at the same time, pressure energy of fluid in steel pipe or copper pipe system is strengthened remarkably, however, pressure energy of fluid in PVC pipe or PE pipe system is hardly influenced.Method of modal analysis of fluid-filled pipe system was studied, numerical results show that FSI has graet influence on modal characteristics, natural frequency modes with consideration of FSI is obviously more than that without consideration of FSI in a definite frequency range, and the natural frequency values changed evidently. MOC-FFT was advanced and adopted to get natural frequencies of a fluid-filled pipe system with neglect of structural damping of pipes and frictional damping of fluid, the results agree with the results of transfer matrix method (TMM) and those from literature.Finally, a waterflooding system was adopted to study. Vibration restrain results of adjusting restriction positions and using damping material were obtained by simulation, which show that vibration of pipe can be reduced remarkably by minishing out-length of pipe, but the pressure of fluid rises. Responses of pipe and fluid can be reduced by covering the pipe with appropriate damping material.Unsteady-fluid-filled pipe systems have been widely applied in many engineering realms such as oil transporting, waterpower, biology, spaceflight, drilling, hydraulic system, construction, nuclear industry and so on. researching the coupled vibration characteristics and influence factors of the vibration of the systems are helpful to predict their vibration responses, to take some necessary measures to restrain or minish their vibrations, to lessen the chance of accident or avoid accident, which is very important and necessary for safty of the pipe systems.更多还原