波浪作用下海底管道振动与局部冲刷耦合作用数值研究
发布时间:2018-04-28 22:33
本文选题:波浪 + 海底管道 ; 参考:《大连理工大学》2016年博士论文
【摘要】:铺设在海底的管道,在波浪和水流等复杂海洋水动力条件作用下,极易发生局部泥沙冲刷,致使海底管道发生悬空。在交变流体作用力下,悬空的海底管道会发生涡激振动,诱发疲劳破坏。管道振动响应也会进一步与泥沙冲刷发生相互作用。泥沙局部冲刷引起的管道悬空以及管道振动都会危及管道的安全。一旦管道发生破坏,不但会造成巨大的经济损失,还会引起严重的环境污染。目前对于海底管道局部冲刷的数值研究多限于简单的单向水流作用下,固定管道的局部冲刷问题。而对于波浪运动、管道振动和泥沙运动耦合的数值分析尚未见开展。针对波浪作用下,振动管道的局部泥沙冲刷问题建立数值模型,探索海底管道涡激振动与局部泥沙冲刷之间的耦合动力作用机理,具有清晰的工程背景和重要的科学价值。本文将建立综合考虑波浪运动、管道振动和泥沙输运的耦合动力数值分析模型,并基于所建立的数值模型对波浪作用下振动管道的局部泥沙冲刷耦合问题进行数值研究。第二章首先建立了基于Navier-Stokes方程的高阶迎风有限元数值模型,对低雷诺数下固定多圆柱绕流的基本理论问题开展了数值研究。在串联双圆柱绕流方面:首次发现在圆柱间距比为G/D=0.9的情况下,前、后圆柱的升力系数和涡脱落频率也都存在突变的现象,这主要是由流动不稳定所导致的流态改变而引起的。进一步的研究表明,在整个G/D的区间内,双圆柱周围流场存在4种截然不同的流态,这是对以往研究工作的重要补充;在附属多圆柱群绕流问题研究方面:通过数值模拟表明,在主圆柱周围均匀布置多个附属小圆柱后,能够在较大的间距比(G/D)范围内,有效的减小主圆柱所受的升力和拖曳力。进一步的研究表明,主从圆柱的直径比对主圆柱的受力影响较小。第三章在任意拉格朗日-欧拉方法的基础上,建立了粘性流体与结构相互作用的通用计算流体动力学分析模型,并在前一章的基础上,对圆柱群结构的涡激振动问题进行了数值模拟研究。研究工作表明,在主圆柱周围均匀布置多个附属小圆柱能够有效减小圆柱群涡激振动的响应幅值及“锁定”带宽,并且圆柱群的”锁定”区间随着间距比G/D的增大向低约化速度方向移动。第四章建立了波浪作用下,固定海底管道局部冲刷数值分析模型。该模型通过动网格技术统一处理波浪自由表面和底床冲刷动边界问题,不再将波浪作用简化为振荡流。在水深较浅、波高较大的情况下,波浪自由表面的非线性效应显著,不能忽略。所以建立考虑自由表面效应的管道冲刷模型具有更好的通用性。数值结果表明,入射波波高和周期均对管道的局部泥沙冲刷深度有较大的影响作用。进一步对铺设在斜坡上的管道局部冲刷问题开展的数值研究表明,由于斜坡的存在而导致的波浪自由表面变形,使得斜坡上的海底管道周围的局部冲刷与平底情况下存在显著不同,管道迎浪侧和背浪侧分别以淤积和冲刷作用为主。这是振荡流模型不能考虑的。第五章建立了可综合考虑波浪运动、管道振动、泥沙输运过程以及底床变形的耦合动力数值分析模型。基于建立的数值模型重点研究了管道在波浪作用下的振动与局部冲刷的耦合作用。数值模拟结果表明:当约化速度Ur=2.73时,振动管道周围的最大冲刷深度是相同条件下固定管道冲刷深度的2倍。当约化速度介于2.05Ur3.28的范围内时,冲刷深度、管道受力以及振动响应相互作用显著,体现了三者间的相互依赖关系。
[Abstract]:Under the action of complex marine hydrodynamic conditions such as wave and water flow, the pipeline is easily scoured under the action of wave and water flow, causing the submarine pipeline to be suspended. Under the alternating fluid force, the vortex shedding vibration will occur in the suspended submarine pipeline and induce fatigue damage. The vibration response of the pipeline will be further interacted with the sediment scour. The pipe suspension and pipe vibration caused by the local scour of sediment will endanger the safety of the pipeline. Once the pipeline is damaged, it will not only cause huge economic losses, but also cause serious environmental pollution. At present, the numerical study on the local scour of the submarine pipeline is mostly limited to the part of the fixed pipe under the action of simple and unidirectional flow. For the wave motion, the numerical analysis of the coupling between the pipeline vibration and the sediment movement has not yet been carried out. A numerical model is set up for the local sediment scour problem under the action of the wave, and the mechanism of the coupling dynamic action between the vortex induced vibration and the local scour is explored. In this paper, a numerical model of coupled dynamic analysis of wave motion, pipeline vibration and sediment transport will be established in this paper. The numerical model is used to study the local sediment scour coupling problem of a vibrating pipe under the action of waves. In the second chapter, the high order upwind based on the Navier-Stokes equation is established. The finite element numerical model is used to study the basic theoretical problem of the flow around a fixed multi cylinder under the low Reynolds number. In the series of double cylindrical flow, it is found for the first time that when the cylinder spacing ratio is G / D=0.9, the lift coefficient and the vortex shedding frequency of the rear cylinder are also mutated, which is mainly due to the flow instability. The further study shows that there are 4 completely different flow patterns in the flow field around a double cylinder in the whole G / D interval, which is an important supplement to the previous research work. After a small cylinder, it can effectively reduce the lift and drag force of the main cylinder at a larger distance than (G / D). Further research shows that the diameter of the main cylinder has less influence on the force of the main cylinder. In the third chapter, the interaction between the viscous fluid and the structure is established on the basis of any Lagrange Euler method. On the basis of the previous chapter, the numerical simulation of vortex induced vibration of cylindrical group structure is studied. It is shown that the response amplitude and "locking" bandwidth of the cylindrical vortex excited vibration can be effectively reduced and the "lock" of the cylinder group is locked. In the fourth chapter, the numerical analysis model of local scour for fixed submarine pipelines under the action of wave is established in the fourth chapter. The model is used to deal with the dynamic boundary problem of wave free surface and bottom bed by dynamic grid technology, and the wave action is no longer simplified as oscillating flow. In the case of shallow and high wave height, the nonlinear effect of the free surface of the wave is remarkable and can not be ignored. Therefore, the establishment of a pipe scour model considering the free surface effect is of better generality. The numerical study on the local scour on the slope shows that the free surface deformation of the waves caused by the existence of the slope makes the local scour around the submarine pipeline on the slope significantly different from that in the flat bottom, which is mainly deposited and scour on the wave side and the back wave side. This is the inability of the oscillating flow model. In the fifth chapter, a numerical model for coupled dynamic analysis of wave motion, pipe vibration, sediment transport and bottom bed deformation is established. Based on the numerical model, the coupling effect of vibration and local scour under the action of waves is studied. The numerical simulation results show that when the reduction rate is Ur=2.73, The maximum scour depth around a vibrating pipe is 2 times as high as the depth of a fixed pipe under the same condition. When the reduction speed is within the range of 2.05Ur3.28, the depth of the scour, the force of the pipe and the vibration response interact significantly, which reflects the interdependence of the three.
【学位授予单位】:大连理工大学
【学位级别】:博士
【学位授予年份】:2016
【分类号】:P756.2
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