【作者】 龙飞飞；

【导师】 戴光；

【作者基本信息】 大庆石油学院 ， 化工过程机械， 2008， 博士

【摘要】 管道运输是五大运输方式之一,在世界范围内都得到了广泛的应用与发展,而且油气管道一直是世界经济的大动脉。随着社会经济的不断发展,输油管道这种输送方式,成了各个国家生命线工程中的重要组成部分。然而,管线在带给人们方便和快捷的同时,由于管线老化等多种原因,导致因裂纹等缺陷引发的恶性安全事故时有发生,造成巨大损失,同时给经济的发展,社会和财产安全,生态环境带来巨大影响。我国穿越河流的输油管道在长距离输油管道工程中占相当比例。早期铺设的原油管线大部分已运行三十年左右,而且还在担负重要任务。再者当时的穿越多数采取大开挖的方法,有些未达到设计深度,再加上多年的冲刷和枯水季老百姓取土,很多管线已外露。这类管道在水流作用下,可能因冲刷而形成悬跨。管道悬跨段由于没有土壤约束,在水流尾流旋涡的作用下易产生振动。若管道存在缺陷,其承压能力会下降,再加上旋涡引起的疲劳载荷,在服役中会导致其突然失效,影响正常生产、带来环境污染,给国民经济造成巨大损失。本文针对上述问题,对水流作用下悬空管道绕流场进行数值分析。并在此基础上,研究含裂纹缺陷悬空管道在多种载荷联合作用下缺陷处的应力和管道疲劳循环次数。主要内容如下:1、高雷诺数下管道绕流特性及绕流机理研究水下管道形成悬跨后,在一定流速时,管道后面旋涡泄放频率可能接近管道的自振频率,从而出现垂直于水流的类似共振现象,并导致沿水流方向的振动和拖曳力的增大。管道两个方向的振动可产生很大的交变应力,使管道发生疲劳破坏。2、高雷诺数下静止管道绕流数值分析根据流体力学和计算流体力学理论,研究高雷诺数情况下静止管道绕流场,在计算模拟中监视管壁的升力系数和阻力系数,并得出管道绕流的涡量等值线分布、压力分布、切应力分布及静止管道的旋涡自然脱落频率。3、高雷诺数下悬空管道横向振动数值分析研究了悬空管道的横向振动;横向涡激振动对疲劳失效的影响远大于顺流涡激振动的影响,因此,为避免发生横向涡激振动,计算不同频率比条件下的升力系数、阻力系数、升力系数功率谱及涡量等值线分布图,确定管道发生“锁频现象”的频率比,得出水下输油管道悬空段的临界长度曲线。4、水流作用下含周向裂纹悬空管道数值分析建立悬空管道的计算模型,结合管道的支撑条件,研究含周向裂纹管道在多种载荷联合作用下的峰值应力和循环次数。并具体分析了裂纹处弯矩、裂纹长度、裂纹深度、管道内压、水流载荷和裂纹在管道横截面上的钟点这些因素对管道峰值应力和循环次数的影响。5、水流作用下含轴向裂纹悬空管道数值分析建立计算模型,结合管道的支撑条件,研究含轴向裂纹管道在多种载荷联合作用下的峰值应力和循环次数。并具体分析了裂纹处弯矩、裂纹长度、裂纹深度、管道内压和水流载荷和这些因素对管道峰值应力和循环次数的影响。6、水流作用下含双裂纹悬空管道数值分析建立含两个裂纹缺陷的管道的模型,研究两个缺陷在相互影响区域内,相对位置对管道峰值应力和循环次数的影响。比较得出管道含双缺陷时比单个缺陷时危险,而单个缺陷时含周向缺陷管道要比含轴向缺陷管道安全度低。更多还原

【Abstract】 As one of the five most important transport manners, pipelines have been used all over the world. Also, oil and gas pipelines have been being the aorta of the world economy. With the development of economy, pipelines become a important part of lifeline works in every country. But, at the same time that they bring us convenience and fast transport, they also induce many safety accidents which cause huge losses for aging of pipe, cracks, etc. These accidents seriously affect the development of economy, safety of society and property, also, the ecological environment.In china, the oil pipelines across the river account for a considerable proportion among long distance pipelines. Most of the oil pipelines laid early have run about 30 years, and still shoulder the important tasks. Further, the parts across the river are laid with the method of excavation, part of them do not reach the design depth, coupled with the erosion of water and fetching soil of people, some pipelines has been bared. Under the eroding of water, such pipelines are easy to be suspended. For there being no constraint of soil, the suspended part is very easy to oscillate under the effect of water wake vortex. If there are defects in the suspended part of the pipeline, its pressure capacity will decrease. Coupled with the action of vortex, it is easy to failure suddently, which will affect normal production, pollute envorinment and cause huge losses.Aiming at above problems, numerical simulation of water flowing around a suspended pipe is done. On the basis of that, the maximum stress and fatigue cycles of suspended pipe with cracks are studied. Main content of the paper is as follows1、Flow characteristic and theory under high Reynolds numberIn a certain velocity, relief frequency eddy behind the suspended pipe can be close to the natural frequency channels. Thus similar resonance effect vertical to the flow appears. It leads the vibration along the flow direction and drag increase. Two directions of vibration can produce great alternating stress, which will cause the pipeline to fail.2、Numerical analysis of water flowing around pipe under high Reynolds numberAccording to hydromechanics and computation hydromechanics theory, numerical analysis of flow around a pipe under high reynold number is studied. Lift and drag coefficients are monitored. The distribution of eddy contours, pressure distribution, shear stress distribution and vortex shedding natural frequency of immobile pipe are gained. 3、Numerical analysis of viscous flow around a suspended pipe which is resonant transversely in a uniform stream under high Reynolds numberTransverse vibration of suspended pipe is studied. The influence on fatigue life of transverse vortex-induced vibration is far greater than that of flow direction. Therefore, in order to avoid the transverse vortex-induced vibration, lift coefficient, drag coefficient, the distribution of vortex contours and power spectrum of lift coefficient under different frequency ratios are calculated. The frequency ratio is specified when“frequency-locking phenomenon”occurs, further underwater suspended pipe’s critical lengthes are calculated under different flow rates.4、Numerical simulation of underwater pipe with a circumferential crack flawComputation model of a suspended pipe with a circumferential crack flaw is established. Combined with support conditions, peak stresses and fatigue cycles of pipe with a circumferential crack flaw under several loads are calculated. Also, the influence of moment, length of the crack, depth of the crack, defect position, internal pressure of the pipe and water load is analyzed on peak stress and fatigue life.5、Numerical simulation of underwater pipe with a longitudinal crack flawComputation model of a suspended pipe with a longitudinal crack flaw is established, combined with support conditions, peak stresses and fatigue cycles of pipe with a circumferential crack flaw under several loads are calculated. Also, the influence of moment, length of the crack, depth of the crack, internal pressure of the pipe and water load is analyzed on peak stress and fatigue life.6、Numerical simulation of underwater pipe with two crack flawsComputation model of a suspended pipe with two crack flaws is established. The influence of relative position of the defects is studied when they are in the region that affecting each other. After comparative analysis, the result shows that the pipeline with two flaws is more dangerous than that with one flaw. If there is only one defect in the pipeline, the circumfetential flaw is more harmful.更多还原