接地惯容式减振器对悬臂输流管稳定性和动态响应的影响研究

输流管道广泛应用于机械、航空、核电和石油等重要工程领域.为防止管道结构因流致振动破坏造成的损失, 很有必要对其稳定性、动力学响应及其调控进行深入研究.本文提出一种由惯容器、弹簧和阻尼器并联组成的减振器模型, 研究了这种接地惯容减振器对悬臂输流管稳定性和非线性振动的影响. 首先, 基于哈密顿原理给出了带有接地惯容减振器非保守系统的非线性动力学模型; 然后, 利用高阶伽辽金方法对非线性方程进行离散化; 最后, 分别从线性和非线性角度分析了不同减振器参数下输流管道的被动控制效果, 着重讨论了惯容系数和减振器安装位置对悬臂管稳定性和动态响应的影响机制.线性理论模型的研究结果显示, 接地惯容减振器可显著影响悬臂管的失稳临界流速, 故通过调节减振器参数能有效提高输流管道的稳定性;惯容系数和弹簧刚度对系统稳定性的控制效果还与减振器的安装位置密切相关.非线性理论模型的分析结果显示, 惯容系数和减振器位置对输流管的非线性动态响应也有显著影响, 且这种影响还依赖于管道的流速取值; 在某些参数条件下, 减振器还可使输流管道由周期运动演化为复杂的混沌行为. 本文研究结果表明, 通过设计合理的惯容式减振器参数, 可提升悬臂输流管道的稳定性并有效抑制其颤振幅值.      

波动钻压下阶梯钻柱系统稳定性研究

处于狭长井筒中的钻柱,其动力响应受到钻具组合、内外钻井液流动以及钻井参数等因素的影响,钻柱动力失稳导致的剧烈振动是井壁坍塌和钻具失效的重要原因。考虑到钻杆和钻铤在刚度和线密度上存在很大的差别,论文将钻柱简化为单阶梯输液管柱,钻井液沿着钻柱内部向下泵入并从环空返回地面。耦合考虑钻柱自重、随时间简谐变化的波动钻压、稳定器以及钻井液的水动力和阻尼力,建立了直井中钻柱横向振动的解析模型。利用有限单元法离散为四阶常微分方程后,采用Bolotin法得到临界频率方程确定系统的不稳定区范围,研究了钻压、钻杆长度、稳定器安装位置、钻井液的流速和密度等参数对系统稳定性影响的机理。研究表明：钻压的平均值和波动幅值都是钻柱失稳的驱动因素,而系统的稳定性对处于受拉状态的钻杆的长度变化不敏感。在论文所研究的参数范围内,降低钻井液流速和密度、下移稳定器的安装位置均有助于增强系统的稳定性。     

Extremely large-amplitude oscillation of soft pipes conveying fluid under gravity

In this work, the nonlinear behaviors of soft cantilevered pipes containing internal fluid flow are studied based on a geometrically exact model, with particular focus on the mechanism of large-amplitude oscillations of the pipe under gravity. Four key parameters, including the flow velocity, the mass ratio, the gravity parameter, and the inclination angle between the pipe length and the gravity direction, are considered to affect the static and dynamic behaviors of the soft pipe. The stability ...     

The stability of a circumferential crack in a pipe II. A simple procedure for determining the effective pipe length

A simple procedure is currently used to determine the effective pipe length associated with the instability of circumferential crack growth in a piping system. This procedure involves a separation of the complete piping system into two elastic parts at the cracked cross-section, the application of equal and opposite moments M to the cut faces, and the equation of the effective pipe length with $\text{El∥φ∥}\text{M}$ where φ is the rotational discontinuity generated at this section, E is Young's modulus and I is the second moment of area of the pipe at the cracked section. It is presumed that the pipe-ends remain fixed, i.e. they are built-in, throughout this operation. This paper shows that this procedure refers to the stability of a crack in a piping system which is subject to either a fixed displacement or a fixed rotation at a built-in end. The viability of the simple procedure is therefore underscored by the present paper's analysis.     

Experimental investigation of dynamic stability of a cantilever pipe aspirating fluid

The dynamic stability of a submerged cantilever pipe conveying fluid from the free end to the fixed one is considered as one of the unresolved issues in the area of fluid–structure interaction. There is a contradiction between theoretical predictions and experiments. Reported experiments did not show any instability, while theory predicts instability beyond a critical fluid velocity. Recently, several papers appeared, improving the theoretical modelling of pipe dynamics. All theories predict instability, either oscillatory or static, referred to here as flutter and divergence, respectively. A new test set-up was designed to investigate the hypothesis that previous experimental set-ups could not allow observations of pipe instability or the pipe aspirating water is unconditionally stable. In this new test set-up, the fluid velocity could exceed the theoretically predicted critical velocities. A cantilever pipe of about 5 m length was partly submerged in water. The free open end of the pipe was in the water, whereas the fixed end was above the waterline. The experiments clearly showed that the cantilever pipe aspirating water is unstable beyond a critical velocity of water convection through the pipe. Below this velocity the pipe is stable, whereas above it the pipe shows a complex motion that consists of two alternating phases. The first phase is a nearly periodic orbital motion with maximum amplitude of a few pipe diameters, whereas the second one is a noise-like vibration with very small amplitudes. Increasing the internal fluid velocity results in a larger amplitude of the orbital motion, but does not change the pipe motion qualitatively.     

The viability of a simple procedure for determining the criterion for the instability of circumferential growth of a through-wall crack in a stainless steel piping system, Part 2: The applied displacements produce bending and tensile deformation

Against the background of the technological problem of integranular stress corrosion cracking of Type 304 stainless steel Boiling Water Reactor piping systems, the stability of a circumferential through-wall crack is examined, for the case where the cracked section is at a position where the pipe enters a larger component. The paper presents a general methodology for determining the instability criterion for fixed displacement loadings, which are appropriate for an accident condition, the criterion being expressed in terms of the applied and material tearing moduli, or equivalently in terms of an effective pipe length. The methodology is applied to models which simulate bends in a piping system, and general conclusions are drawn with regards to the effect of pipe bends on crack instability.     

The stability of a circumferential crack in a pipe I. The influence of the boundary conditions imposed at the ends

The paper examines the case where a pipe of length L is built-in at one end and the other end is subject to an imposed displacement or rotation. The criterion for instability of growth of a circumferential through-wall crack is shown to depend on the pipe-end boundary conditions as well as the pipe geometry, crack size and crack location. The worst possible case is that where there is only a force, but no moment, at the pipe-end. However, this is probably an artificial situation which is unlikely to arise in practice. A pipe is more likely to be built-in at both ends, and for this situation, it is concluded that the instability criterion is the same irrespective of whether a displacement or rotation is imposed at a built-in end.     

A Modelling Study of Evolving Particle-laden Turbulent Pipe-flow

An Eulerian turbulent two phase flow model using kinetic theory of granular flows for the particle phase was developed in order to study evolving upward turbulent gas particle flows in a pipe. The model takes the feedback of the particles into account and its results agree well with experiments. Simulations show that the pipe length required for particle laden turbulent flow to become fully developed is up to five times longer than an unladen flow. To increase the understanding of the dependence of the development length on particle diameter a simple model for the expected development length was derived. It shows that the development length becomes shorter for increasing particle diameters, which agrees with simulations up to a particle diameter of 100 ??m. Thereafter the development length becomes longer again for increasing particle diameters because larger particles need a longer time to adjust to the velocity of the carrier phase.     

Dynamical stability analysis of a hose to the sky

The Stratospheric Shield was proposed as a geoengineering concept to control the Earth's climate and reverse global warming. This approach seeks to release sulphur dioxide (SO₂) aerosols in the stratosphere to decrease the amount of sunlight that reaches the surface of the Earth. It was proposed that this can be done by pumping liquefied SO₂ from the ground to the stratosphere in a 30 km long hose supported by aerostats.In this paper we evaluate the dynamic stability of a hose to the sky considering distributed supportive aerostats and an atomiser nozzle that forces a radial discharge of the fluid at the free end of the pipe. We modelled the pipe as a taut string conveying fluid using the finite element method.With a nozzle that discharges the flow straight through, we found that the pipe loses stability by buckling when the tension becomes null at least at one location along its length. This instability can be avoided by having a sufficient minimum tension T₀ throughout the whole length of the pipe. The distribution of aerostats does not influence this instability but it modifies the mode shapes and affects the complex frequencies. The atomiser discharging the flow radially at the tip of the pipe has for effect to remove the possibility of an instability; its use is thus recommended. Moreover, we showed that the Coriolis damping can be significant and that by appropriately selecting the number of aerostats as well as the dimensionless flow velocity, stability can be increased. With this in mind, a functional hose to the sky could be designed to maximise Coriolis damping and thus passively damp the motion of the pipe due to forcing from the wind.     

Turbulent Transition in the Inlet Region of a Circular Pipe

Calculated and experimental data on turbulent transition in a circular pipe are analyzed. The calculations were performed using the three-parameter turbulence model. The dependence of the distance from the inlet to the point of minimum friction during transition on the Reynolds number for fixed inlet conditions and the distribution of the turbulence parameters over the pipe length and radius are obtained. The dependence of the maximum (critical) Reynolds number, Re^*, for which there is no transition in the pipe, on the inlet intensity and scale of turbulence is found. It is suggested that Re^* depends on the inlet perturbation parameters up to Re^* = 1000, where the friction coefficients for laminar and turbulent flows coincide.     

Analysis of the stability and Hopf bifurcation of money supply delay in complex macroeconomic models

Considering the macroeconomic model of money supply, this paper carries out the corresponding extension of the complex dynamics to macroeconomic model with time delays. By setting the parameters, we discuss the effect of delay variation on system stability and Hopf bifurcation. Results of analysis show that the stability of time-delay systems has important significance with the length of time delay. When time delay is short, the stable point of the system is still in a stable region; when time delay is long, the equilibrium point of the system will go into chaos, and the Hopf bifurcation will appear in certain conditions. In this paper, using the normal form theory and center manifold theorem, the periodic solutions of the system are obtained, and the related numerical analysis are also given; this paper has important innovation-theoretical value and acts as important actual application in macroeconomic system.     

用ABAQUS软件处理管土相互作用中的接触面问题

采用ABAQUS软件处理管土相互作用中的接触面问题，利用ABAQUS软件中的主控-从属接触算法，使管道和海床形成一个接触对；并且建立了管土系统有限单元模型．海床土体分别采用非线性弹性模型、多孔弹性模型、Ramberg-Osgood塑性模型对管土系统进行计算通过分析计算，得到了管道沉降量与管重间的关系，以及由于管道沉陷而形成的土体楔形，土体楔形的存在，增加了管道的稳定性．计算结果和有关试验结果相符合，说明采用该软件进行管土相互作用问题分析是可行的．     

基于交叉型双气室空气互联悬架的全地形车侧倾特性研究

设计了一种采用囊式空气弹簧的交叉型双气室空气互联悬架 (PIS 悬架),并应用于侧翻事故发生率极高的全地形车上. 建立了交叉型双气室气体耦合 AMEsim 模型与全地形车整车动力学 ADAMS/Car 模型,通过将前者模型中的空气弹簧弹性力作为整车动力学模型的输入变量,将后者模型中的空气弹簧压缩伸张位移作为气体耦合模型的输入变量,建立了完整的机械-气体耦合多自由度动力学联合仿真模型. 通过 J 型弯高速典型仿真实验对搭载 PIS 悬架、双气室非互联悬架 (UN-PIS 悬架) 和普通螺旋弹簧悬架 (HS 悬架) 的全地形车进行侧倾特性对比研究. 研究结果显示,PIS 悬架若关闭互联管路,则会形成 UN-PIS 非互联状态,使悬架刚度瞬间大幅上升,平顺性瞬间变差,而具有相同垂向刚度的 PIS 悬架与 HS 悬架,前者能够提供更多的侧倾角刚度. 研究了气路系统 中影响动态侧倾特性的相关因子,包括连接管路管长、管径、附加气室容积. 研究表明,互联管路管长越小,越有利于提升全地形车侧倾特性,存在临界管径,管径小于或大于该值时,均会小幅度提升侧倾特性,附加气室容积越小,侧倾角刚度越大,为 PIS 悬架气路系统设计提供理论依据.      

Analysis of nonlinear dynamic stability of liquid-converying pipes

Nonlinearly dynamic stability of flexible liquid-conveying pipe in fluid structure interaction was analyzed by using modal disassembling technique. The effects of Poisson, Junction and Friction couplings in the wave-flowing-vibration system on the pipe dynamic stability were included in the analytical model constituted by four nonlinear differential equations. An analyzing example of cantilevered pipe was done to illustrate the dynamic stability characteristics of the pipe in the full coupling mechanisms, and the phase curves related to the first four modal motions were drawn. The results show that the dynamic stable characteristics of the pipe are very complicated in the complete coupling mechanisms, and the kinds of the singularity points corresponding to the various modal motions are different. Foundation items: the National Natural Science Foundation of China (50079007); the Hydraulic Science Foundation of China Hydraulic Ministry (SZ9830); the Natural Science Foundation of Yunnan Provicce (98E003G) Biographies: ZHANG Li-xiang (1959−) HUANG Wen-hu (1926−)     

Entropy generation of radial rotation convective channels

The exchange of heat between two fluids is established by radial rotating pipe or a channel. The hotter fluid flows through the pipe, while the cold fluid is ambient air. Total length of pipe is made up of multiple sections of different shape and position in relation to the common axis of rotation. In such heat exchanger the hydraulic and thermal irreversibility of the hotter and colder fluid occur. Therefore, the total entropy generated within the radial rotating pipe consists of the total entropy of hotter and colder fluid, taking into account all the hydraulic and thermal irreversibility of both fluids. Finding a mathematical model of the total generated entropy is based on coupled mathematical expressions that combine hydraulic and thermal effects of both fluids with the complex geometry of the radial rotating pipe. Mathematical model follows the each section of the pipe and establishes the function between the sections, so the total generated entropy is different from section to section of the pipe. In one section of the pipe thermal irreversibility may dominate over the hydraulic irreversibility, while in another section of the pipe the situation may be reverse. In this paper, continuous analytic functions that connect sections of pipe in geometric meaning are associated with functions that describe the thermo-hydraulic effects of hotter and colder fluid. In this way, the total generated entropy of the radial rotating pipe is a continuous analytic function of any complex geometry of the rotating pipe. The above method of establishing a relationship between the continuous function of entropy with the complex geometry of the rotating pipe enables indirect monitoring of unnecessary hydraulic and thermal losses of both fluids. Therefore, continuous analytic functions of generated entropy enable analysis of hydraulic and thermal irreversibility of individual sections of pipe, as well as the possibility of improving the thermal–hydraulic performance of the rotating pipe consisting of n sections. Analytical modeling enabled establishing of a mathematical model of the total generated entropy in a radial rotating pipe, while the generated entropy of models with radial rotating pipe were determined by experimental testing, with comparisons of the achieved results.     

Dynamics of a partially confined,discharging, cantilever pipe with reverse external flow

The potential for fluid-elastic instability of hanging cantilevered pipes subjected to simultaneous internal and external axial flows is investigated. Such systems may lose stability by amplified oscillations (flutter) or buckling (static divergence). The system of interest is a flexible tubular cantilever hanging concentrically within a rigid outer tube of larger diameter. Flow inside the cantilever is directed from the clamped end to the free end. Upon exiting the cantilever, the fluid flows in the opposite direction in the annular region between the outer tube and the cantilever. The rigid outer tube is of variable length and it can cover part of the length of the cantilever. This system has applications in brine production and salt-cavern hydrocarbon storage. A linear model is derived based on the work of Paidoussis, Luu and Prabhakar; the presence of the shorter outer rigid tube is taken into account in a simplified way. Series solutions are obtained using a Galerkin method with Euler–Bernoulli beam eigenfunctions as comparison functions. Experimental results are presented and compared with the theoretical model. Additional computations are performed to quantify the effect of confinement (i.e. the narrowness of the annular region) on the cantilever stability, as well as the effect of confined-flow length, for both the short laboratory-sized system and long brine-string-like systems. An increase in these parameters gives rise to flutter for short systems, or a succession of flutter and divergence for long systems. In addition, the effect of the system length is investigated. Increasing length results in asymptotic behaviour, with both the critical flow-velocity and associated frequency reaching limiting values. Sufficiently long systems lose stability by divergence rather than flutter.     

ANALYSIS OF NONLINEAR DYNAMIC STABILITY OF LIQUID-CONVEYING PIPES

Nonlinearly dynamic stability of flexible liquid-conveying pipe in fluid structure interaction was analyzed by using modal disassembling technique . The effects of Poisson . Junction and Friction couplings in the wave-flowing-vibration system on the pipe dynamic stability were included in the analytical model constituted by four nonlinear differential equations . An analyzing example of cantilevered pipe was done to illustrate the dynamic stability characteristics of the pipe in the full coupling mechanisms , and the phase curves related to the first four modal motions were drawn . The results show that the dynamic stable characteristics of the pipe are very complicated in the complete coupling mechanisms, and the kinds of the singularity points corresponding to the various modal motions are different.     

三参量固体模型粘弹性输流管道的动力特性分析

推导了三参量固体模型粘弹性输流管道的振动微分方程 ,计算了在不同无量纲松弛系数和弹性常数比下管道的无量纲临界流速和无量纲自振复频率 ,并给出了前三阶复频率与流速的关系 .计算结果表明 ,质量比、无量纲松弛系数及无量纲弹性常数比对输流管道的动力特性均有影响 .     

An inverse dispersed multiphase flow model for liquid production rate determination

The aim of this study is to develop a model for the determination of the superficial velocities in horizontal and slightly inclined oil–water pipe flow conditions by using pressure gradient and mixture density information. In this article an inverse model is suggested for a dispersion of oil in water and of water in oil. This approach permits to select dispersed flow conditions from a set of experimental data, and uses a new hybrid model for the effective viscosity. A set of 310 oil–water experimental data points collected on an experimental set-up of length L = 15 m and diameter D = 8.28 cm at various (slight) orientations is used to validate the inverse method. The comparison between model reconstructions and measured flow velocities show a reasonable agreement.     

分布式运动约束下悬臂输液管的参数共振研究

输液管道结构在航空、航天、机械、海洋、水利和核电等工程领域都有广泛应用,其稳定性、振动与安全评估备受关注.针对具有分布式运动约束悬臂输液管的非线性动力学模型,分别采用立方非线性弹簧和修正三线性弹簧来模拟运动约束的作用力,研究了管道在脉动内流激励下的参数共振行为.首先,从输液管系统的非线性控制方程出发,利用Galerkin方法进行离散化;然后,由Floquet理论得出线性系统在失稳前两个不同平均流速下脉动幅值和脉动频率变化时的共振参数区域;最后,考虑系统的几何非线性项和分布式非线性运动约束力的影响,求解了管道的非线性动力学响应,讨论了非线性项及运动约束力对管道参数共振行为的影响.研究结果表明,系统非线性共振响应的参数区域与线性系统的共振参数区域是一致的,分布式运动约束力对发生参数共振时管道的位移响应有显著影响;立方非线性弹簧和修正三线性弹簧模型所预测的分岔路径存有较大差异,但都可诱发管道在一定的参数激励下出现混沌运动.