基于ANSYS Workbench的输液管道系统振动控制仿真研究

以折弯式管道为例研究了输液管道系统的振动控制。首先,建立了输液管道系统的运动方程,但由于方程在离散过程中结构矩阵和流体矩阵的数值计算量过大,在计算过程中常出现溢出错误,因此使用模态缩减法简化矩阵以便于进行计算;其次,在高频振荡流体载荷的作用下,利用ANSYS Workbench的双向隐式迭代法计算管道系统的动力学特性;最后,建立带有节流孔板的管道系统有限元模型,研究了节流孔板对系统振动的抑制作用。计算结果表明节流孔板对输液管道系统的振动控制是非常有效的。     

Vibration analysis of compressor piping system with fluid pulsation

A piping system connected to a rotary compressor is an essential component for refrigerant transport in air-conditioning systems. The vibration of the pipes has been thought to be generated only by the mechanical forces due to the compressor operation. In this study, the fluid pulsation in the pipe is considered to be a source of the vibration, as well as the mechanical forces by the compressor operation. The mechanical force was first identified experimentally using measured acceleration signals over the shell. The calculation of the fluid force resulting from the pulsating fluid in the pipe was then derived theoretically. The estimation used the pressure pulsation signal in the pipe measured by a pressure transducer. Both sources of the vibration were finally applied to the finite element model of the piping system. Conclusively, the prediction of the vibration response to both sources showed better agreement with the experimental results than prediction considering only the mechanical force. Therefore the theoretical process deriving the fluid force was valid.     

冲击气流作用下放空管道流固耦合动力学分析

为了解决某装气站放空管线排气放空时引起的管路振动问题,建立流固耦合三维动力有限元模型,采用瞬态时间历程分析方法对放空管道进行冲击气流下管道动力响应仿真分析。其中管道内流体分别选择氮气和液化气,建立现有管道流固耦合三维动力有限元模型;进行2种流体介质下管道结构动力响应对比。通过研究管道在冲击气流作用下的振动机理和振动特性,从管道结构入手提出了该放空管道振动控制的措施,给出了减振方案。建立减振方案中管道的流固耦合动力有限元模型,进行仿真分析并与原方案计算结果进行了对比,发现管道系统的振动得到大幅度的降低,验证了所提出的减振方案可以对管道振动进行合理有效的控制,确保了管道振动幅度在安全裕度内。     

Bending-torsional instability of a viscoelastic cantilevered pipe conveying pulsating fluid with an inclined terminal nozzle

In the present study, dynamic stability of a viscoelastic cantilevered pipe conveying fluid which fluctuates harmonically about a mean flow velocity is considered; while the fluid flow is exhausted through an inclined end nozzle. The Euler-Bernoulli beam theory is used to model the pipe and fluid flow effects are modelled as a distributed load along the pipe which contains the inertia, Coriolis, centrifugal and induced pulsating fluid flow forces. Moreover, the end nozzle is modelled as a follower force which couples bending vibrations with torsional ones. The extended Hamilton's principle and the Galerkin method are used to derive the bending-torsional equations of motion. The coupled equations of motion are solved using Runge-Kutta algorithm with adaptive time step and the instability boundary is determined using the Floquet theory. Numerical results present effects of some parameters such as fluid flow fluctuation, bending-to-torsional rigidity ratio, nozzle inclination angle, nozzle mass and viscoelastic material on the stability margin of the system and some conclusions are drawn.     

复杂管道应力分析中的支吊架布置方法

针对核电厂复杂管道系统应力分析中支吊架布置设计,基于有限元分析,以管道应力分析的专业计算软件为平台,对其进行了大量的数值模拟计算。总结了管道应力分析中支吊架布置过程和方法,并以设计实例验证了该方法的可靠性和有效性。     

印刷滚体非牛顿流体弹流动压性能的有限元分析

印刷滚体间的接触是一个带有共性的主要技术问题,对于非牛顿性质的流体,本文介绍了一种研究这种软层接触问题的分析模型。应用加辽金加权残留方法和虚功原理分别得到了关于压力和变形的控制方程。用有限元方法求得了问题的数值解,与测试数据相比较,结果具有一定的一致性。     

Experimental determination of time lag due to phase shift on a flexible pipe conveying fluid

A finite element model of a flexible tube conveying fluid is developed in MATLAB^© based on the principle of virtual work, using a three-node isoparametric beam element. Finite element equations are formulated by applying Galerkin technique on the coupled equations of pipe conveying fluid. The present element developed is capable to model three-dimensional flexible tubes by including curved geometry, effects of damping, velocity and gyroscopic effects. The external excitation applied at the middle of the tube in the lateral direction produced a time lag between the lateral responses, which were measured at two equidistant points from the excitation point. This is due to the Coriolis effect, and the same is simulated using the developed code. An experiment, supported with a robust error analysis, is also conducted on a straight polyurethane tube conveying water, subjected to a sinusoidal excitation at the center between the clamped supports. The measured time responses are compared with the numerical values predicted by the code. The time lags for both cases are obtained from the temporal shift along the time axis, between the zero crossing points of the time–response curves. The results obtained agreed well. The code can be used to predict the time lag, which is correlated to the mass flow rate. The proposed method will help to design Coriolis mass flow meters for existing pipelines, without altering the system.     

Finite element analysis of fluid flows with moving boundary

The objective of the present study is to analyze the fluid flow with moving boundary using a finite element method. The algorithm uses a fractional step approach that can be used to solve low-speed flow with large density changes due to intense temperature gradients. The explicit Lax-Wendroff scheme is applied to nonlinear convective terms in the momentum equations to prevent checkerboard pressure oscillations. The ALE (Arbitrary Lagrangian Eulerian) method is adopted for moving grids. The numerical algorithm in the present study is validated for two-dimensional unsteady flow in a driven cavity and a natural convection problem. To extend the present numerical method to engine simulations, a piston-driven intake flow with moving boundary is also simulated. The density, temperature and axial velocity profiles are calculated for the three-dimensional unsteady piston-driven intake flow with density changes due to high inlet fluid temperatures using the present algorithm. The calculated results are in good agreement with other numerical and experimental ones.     

面内开/闭弯载荷作用下压力管道弯头的塑性载荷研究

采用弹塑性有限元分析技术，将材料简化为理想弹塑性，同时考虑几何非线性影响，针对不同厚径比t／rm、相对弯曲半径R／rm和弯曲模式下有直管连接弯头的弹塑性行为进行了系统分析，在此基础上分别建立了便于工程应用的无缺陷弯头在开、闭弯作用下的塑性载荷估算式。试验研究表明本文建立的面内开／闭弯塑性载荷估算式能够满足工程实际需要。     

The vibration of an artery-like tube conveying pulsatile fluid flow

A hybrid method for investigating pulsatile fluid flow in a long, thin, artery-like tube subjected to external excitations is presented. The non-linear partial differential equations governing the motion of the system, which incorporate the influence of circumferential strains, are solved by a combination of a finite element method, a finite difference method and a method of characteristics with interpolation. An initially axially stretched elastic tube conveying pulsating fluid, simply supported at both ends, is modelled to assess the effect of external harmonic excitation on the dynamic responses of the tube and the fluid flow. The results agree well with new experimental data. Comparison of the predicted results with those of a decoupled model demonstrates that it is necessary to consider the mechanism of fluid-structure interaction fully in the study of initially stretched cylindrical tubes conveying pulsatile fluid flow. An analysis of these coupling effects is presented for Womersley numbers alpha = 2.81 and 3.97 and a mean flow Reynolds number Re = 875.     

机械设备流固耦合动力分析的有效方法

提出流固耦合动力分析的新方法。该法通过结构动力学的有限元求解方程和Newmark法,导出了新的迭代公式。流场的动压力使弹性体的动态特性变为载荷非线性问题;同时,固体位移场的变形作用使流场成为可变域流场。这些问题都可用本法得以解决。文中给出算例和工程应用实例。数值解结果表明,该法收敛速度快,效率高,克服了耦合问题的求解困难。     

On the vibrations of three-dimensional angled piping systems conveying fluid

The vibrations of three dimensional angled pipe systems conveying fluid are studied by using the finite element method. Extended Hamilton's principle is applied to derive the equations of motion. The characteristics matries consisting of inertia, stiffness, and Coriolis terms are derived by variational method, in which the effects of the internal flow velocity and pressure are considered. The change of dynamic characteristics of the piping system due to the variation of flow velocity, pressure and the geometry of the system is investigated. As a result, it can be found that the natural frequency of the system decreases generally as the flow velocity and pressure increase and that the tendency is more significant as the geometry of the system is similar to the straight pipe.     

Combined heat transfer of radiation and forced convection flow of participating gases in a three-dimensional recess

This research work presents a numerical investigation of three-dimensional combined convection-radiation heat transfer over a recess including two inclined steps in a horizontal duct. To simulate the inclined surface boundaries, the blocked off method is employed for both fluid mechanic and radiation problems. The fluid is treated as a gray, absorbing, emitting and scattering medium. In numerical solution of the governing equations including conservation of mass, momentum and energy, the three-dimensional Cartesian coordinate system is used. These equations are solved numerically using the CFD techniques to obtain the temperature and velocity fields. Discretized forms of the governing equations are obtained by the finite volume method and solved using the SIMPLE algorithm. Since the gas is considered as a radiating medium, all of the convection, conduction and radiation terms are presented in the energy equation. For computation of radiative term in energy equation, the radiative transfer equation (RTE) is solved numerically by the discrete ordinates method (DOM) to find the divergence of radiative heat flux distribution inside the radiating medium. The effects of radiation-conduction parameter, optical thickness and albedo coefficient on heat transfer behavior of the system are presented. Comparison of numerical results with the available data published in open literature shows a good agreement.     

Numerical model for thermal hydraulic analysis in cable-in-conduit-conductors

The issue of quench is related to safety operation of large-scale superconducting magnet system fabricated by cable-in-conduit conductor. A numerical method is presented to simulate the thermal hydraulic quench characteristics in the superconducting Tokamak magnet system. One-dimensional fluid dynamic equations for supercritical helium and the equation of heat conduction for the conduit are used to describe the thermal hydraulic characteristics in the cable-in-conduit conductor, The high heat transfer approximation between supercritical helium and superconducting strands is taken into account due to strong heating induced flow of supercritical helium, The fully implicit time integration of upwind scheme for finite volume method is utilized to discretize the equations on the staggered mesh, The scheme of a new adaptive mesh is proposed for the moving boundary problem and the time term is discretized by the-implicit scheme, It remarkably reduces the CPU time by local linearization of coefficient and the compressible storage of the large sparse matrix of discretized equations. The discretized equations are solved by the IMSL The numerical implement is discussed in detail, The validation of this method is demonstrated by comparison of the numerical results with those of the SARUMAN and the QUENCHER and experimental measurements.     

Calculation of Stribeck curves for (water) lubricated journal bearings

This paper describes a mixed elastohydrodynamic lubrication (EHL) model for finite length elastic journal bearings. The finite element method was employed to discretise the coupled system of 2D–3D Reynolds-structure equations and to compute Stribeck curves at constant load. As underrelaxation strategies have been found to be insufficient for an iterative solution of this problem, artificial dynamics have been added to the numerical structure equations in order to solve for stationary solutions of the fluid–structure problem. An ideal plastic asperity contact model together with an effective film thickness formulation according to Chengwei and Linqing was employed in order to compute the contact pressure in mixed lubrication. The method presented in this paper is applied to a typical water lubricated journal bearing problem. Computed Stribeck curves are presented and the numerical performance of the method is evaluated.     

聚合物全三维非稳态非等温多相分层流动成型过程的理论模型和数值模拟

基于聚合物多组分成型技术的工程背景,建立了全三维非稳态非等温多相分层充模流动的理论模型。在综合分析了该理论模型产生数值解的不稳定及发散的主要原因基础上,提出了求解理论模型的稳定快速收敛的数值算法。采用罚函数法,以及速度场分析、温度场分析和流体体积分数分析相分离等方法来降低对计算机的CPU和存储能力的需求,而通过SUPG法、罚函数法和P1+/P1三维单元实现有限元数值分析的稳定性。并基于罚函数法和SUPG法,推导出求解N-S方程、能量方程和全三维多相分层流动成型移动前沿界面和分层界面追踪方程的有限元数值模型,并探讨了全三维非稳态非等温多相分层流动移动前沿界面和分层界面重构技术。最后揭示了粘性包围和界面不稳定的产生机理。     

Thermoelastohydrodynamic analysis of the static performance of tilting-pad journal bearings with the Newton–Raphson method

Thermoelastohydrodynamic lubrication (TEHD) analysis is presented to investigate the static performance of tilting-pad journal bearings. A completely numerical solution is obtained. The Newton–Raphson method is employed to predict the bearing characteristics of the hydrodynamic pressure, the eccentricity and the pad attitude angles simultaneously. For the temperature calculation, three-dimensional (3D) energy equations for the fluid under each pad and 3D heat transfer equations for the pads are solved using a sequential sweeping method. The elastic deformation and thermal expansion of each pad are calculated with the 20-node isoparametric finite element method. It is found that the Newton–Raphson method is a smart and efficient method. The results show that the elastic deformation due to the hydrodynamic pressure and the influence of the temperature elevation play an important role in the calculated bearing system.     

基于粘弹本构模型的注射成型充填过程模拟研究

为反映聚合物粘弹属性对注塑产品质量的影响,基于粘弹本构模型,对三维薄壁制件的注射成型充填过程进行了数值模拟研究。针对三维薄壁件,经合理简化假设,建立了其充填成型过程的数学模型,采用不可压缩Leonov粘弹本构模型。采用有限元/有限差分法来求解压力场和温度场,采用控制体积法来实现前沿界面跟踪,采用4阶龙格-库塔方法求解弹性应变张量。以一薄壁圆盘为例,对其注射充填过程中的充填时间及压力、剪切应力和第一法向应力差分布进行了数值模拟。模拟结果与前人的实验结果吻合较好,说明了本文建立的模型和数值方法的有效性及可靠性。     

板式脉动热管强化传热方法研究

为了研究板式脉动热管的传热性能强化的方法,对原型和改进型两种不同板式脉动热管传热特性进行数值分析比较。基于VOF方法建立板式脉动热管汽液两相流动及相变传热三维非稳态数学模型,仿真得到不同加热功率条件下热管内流型演化和温度分布。仿真结果表明,改进型脉动热管在高功率阶段,整体等效热阻小于原型。     

Numerical simulation of fully developed flow and heat transfer characteristics in a curved tube with pulsating pressure gradient

Characteristics of fluid flow and convective heat transfer of a pulsating flow in a curved tube have been investigated numerically. The tube wall is assumed to be maintained at a uniform temperature peripherally in a fully developed pulsating flow region. The temperature and flow distributions over a cross-section of a curved tube with the associated velocity field need to be studied in detail. This problem is of particular interest in the design of Stirling engine heat exchangers and in understanding the blood flow in the aorta. The time-dependent, elliptic governing equations are solved, employing finite volume technique. The periodic steady state results are obtained for various governing dimensionless parameters, such as Womersley number, pulsation amplitude ration, curvature ratio and Reynolds number. The numerical results indicate that the phase difference between the pressure gradient and averaged axial velocity increases gradually up to π/2 as Womersley number increases. However, this phase difference is almost independent of the amplitude ratio of pulsation. It is also found that the secondary flow patterns are strongly affected by the curvature ratio and Reynolds number. These, in turn, give a strong influence on the convective heat transfer from the pipe wall to the pulsating flow. The results obtained lead to a better understanding of the underlying physical process and also provide input that may be used to design the relevant system. The numerical approach is discussed in detail, and the aspects that must be included for an accurate simulation are discussed.