Numerical analysis of pulsating heat pipe based on separated flow model

The examination on the operating mechanism of a pulsating heat pipe (PHP) using visualization revealed that the working fluid in the PHP oscillated to the axial direction by the contraction and expansion of vapor plugs. This contraction and expansion is due to the formation and extinction of bubbles in the evaporating and condensing section, respectively. In this paper, a theoretical model of PHP was presented. The theoretical model was based on the separated flow model with two liquid slugs and three vapor plugs. The results show that the diameter, surface tension and charge ratio of working fluid have significant effects on the performance of the PHP. The following conclusions were obtained. The periodic oscillations of liquid slugs and vapor plugs were obtained under specified parameters. When the hydraulic diameter of the PHP was increased to d=3mm, the frequency of oscillation decreased. By increasing the charging ratio from 40 to 60 by volume ratio, the pressure difference between the evaporating section and condensing section increased, the amplitude of oscillation reduced, and the oscillation frequency decreased. The working fluid with higher surface tension resulted in an increase in the amplitude and frequency of oscillation. Also the average temperature of vapor plugs decreased.     

多声道超声流量计在弯管段安装的适应性研究

针对在不具备直管段安装条件时,如何合理地选取多声道超声流量计的声道数量、测量断面及安装角度,本文从数学建模、误差分析、数值计算仿真与试验分析等方面,对DN400多声道超声流量计在弯管中的适应性进行了综合研究.利用高斯-雅克比数值积分法,给出了试验数据处理与数值仿真的数学模型,并分析了模型误差及横流的影响,提出利用双断面测量可减小横流的影响,并在数值仿真和试验中得到了验证.通过对声道数量、测量断面、安装角度进行数值仿真和试验表明,安装角度对低流速测量影响显著,最佳安装角应为0°;高流速测量应选用双断面,可根据测量精度的要求选用8声道或18声道.仿真结果与试验结果得到了很好的吻合,为进一步指导试验奠定了理论基础.     

基于SolidWorks的圆管弯头对水流的影响分析

文章对弯管轴线上水的流速进行数值计算,分析弯头曲率及半径对管内水流的影响。结果表瞻选用弯管,当首选小曲率渐弯管;折管的折角越小,为其设置大曲率半径弯头的必要性越大。     

利用LS-DYNA的微尺度球面-平面接触模型力学行为有限元分析

球面-平面接触模型是研究接触问题的基础.首先,分析了LS-DYNA有限元接触算法的基础理论,然后利用LS-DYNA有限元分析软件,分析了微尺度球面-平面接触模型的力学行为.研究表明,微尺度球面与平面以不同接触深度接触时,接触应力场以球面顶部位置为中心,呈圆形分布在接触位置区域,并且随着接触深度增加,合应力明显增大.接触过程中首先在基体表层产生弹性变形,然后进入塑性变形,并随接触深度增加,塑性变形区进一步扩大.比较接触区域不同位置的接触应力,在接触区域底部、中下部接触应力最大,而在上部、中上部的接触应力要小.随着接触深度的加深,局部发生以塑性变形为主的变形,材料失效,接触区域各位置的接触应力反而变小,且大致相同.     

An alternative mathematical model of vane anemometers based on the balance of power

Anemometers based on the exchange of momentum between the flow and rotating measuring element comprise an important class of instruments used in flow metrology, especially in meteorological and ventilation measurements. In these instruments, overvaluation of the measured average velocity, caused by the inertia of their rotors, takes place. To analyse this phenomenon and the dynamics of the measurement process, as well as to estimate and minimize the measurement uncertainty, it is required to be acquainted with the mathematical model of the anemometer. In this study, the model of the vane anemometer based on the equation of motion of its rotor available in the literature is analysed, and a new model based on the power balance is proposed. Model testing and a comparison of both models has also been performed.     

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。     

基于流体动力学的弯管应力有限元分析

由直管弯制而成的弯管几何形状和结构复杂,在流体作用下受力复杂,准确的应力分析是进行强度计算和弯管设计的重要前提。使用ANSYS流体-固体有限元分析软件,建立了管内流体动力学分析和弯管结构应力三维分析模型,利用两种不同物理环境的转换,得出了弯管在流体不均匀压力作用下的应力分布,讨论了流量、弯管加工缺陷对弯管应力的影响。     

Computer simulations of the dynamic behavior of three point bend specimens

Computer simulations of the mechanical behavior of a three point bend specimen with a quarter notch under impact load are performed. Two cases with different load application points at the side and at the middle of the specimen are considered. An elastic-plastic von Mises material model is chosen. Three phases such as impact, bouncing and bending phases are found to be identified during the period from the moment of impact to the estimated time for crack initiation. The quasi static case is compared with the above two cases. It is clearly shown that no plastic deformation near the crack tip is appeared at the impact phase. However, it is confirmed that the plastic zone near the crack tip emerges in the second phase and the plastic hinge has been formed in the third phase i.e., at the end of which a quasi static state is reached.     

Dynamic behavior of cracked pipe conveying fluid with moving mass based on timoshenko beam theory

In this paper we studied about the effect of the open crack and the moving mass on the dynamic behavior of simply supported pipe conveying fluid. The equation of motion is derived by using Lagrange’s equation and analyzed by numerical method. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments i.e. the crack is modeled as a rotational spring. The influences of the crack severity, the position of the crack, the moving mass and its velocity, the velocity of fluid, and the coupling of these factors on the vibration mode, the frequency, and the mid-span displacement of the simply supported pipe are depicted.     

基于Agent的映射的情感劝说行为产生模型

针对既有研究中对基于Agent的情感劝说过程中的动态变化因素量化不足的现状,将情感引入基于Agent的劝说行为产生模型.首先定义基于Agent的情感映射,结合层次分析法和Agent个性参数,建立基于个性化高斯混合模型(P-GMM)的Agent"个性—心情"映射模型;利用三维心情空间(PAD)和OCC模型,通过距离归一化...     

Effect of bend angle on plastic loads of pipe bends under internal pressure and in-plane bending

This paper quantifies the effect of a bend angle of a pipe bend on plastic loads, via small strain and large strain finite element (FE) limit analyses using elastic–perfectly plastic materials. To consider the effect of the attached straight pipe, two limiting cases are considered. One case corresponds to the pipe bend without the attached straight pipe, and the other to that with a sufficiently long attached straight pipe. For the former case, the FE results suggest that the limit load is not affected by the bend angle for both in-plane bending and internal pressure. For the latter case, however, the bend angle affects plastic loads. An interesting finding is that the plastic load smoothly changes from the limit load of the straight pipe when the bend angle approaches zero to the plastic load of the 90 pipe bend when the bend angle approaches 90. Based on such observations, closed-form plastic load solutions are proposed for the pipe bend with an arbitrary bend angle under in-plane bending and internal pressure.     

Dynamic behavior of lifting pipe with equivalent model under mining vessel heave motion

The lifting pipe is a key component of deep sea mining whose dynamic response directly affects the safety of the lifting operation. The objective of this paper was to investigate the effects of heave motion and sailing velocity of mining vessel and the buffer mass on the dynamic response of lifting pipe. First, an equivalent model of the lifting pipe was established, and the natural frequency and dynamic response of the lifting pipe equivalent model were determined with consideration of the wave action by the method of separated variables. Secondly, the reliability of the equivalent model was verified by simulating a 5000 m stepped pipe with OrcaFlex software. Then the dynamic displacement, axial tension, axial stress of the lifting pipe under different sea conditions and sailing velocities were studied, and the main factors affecting the dynamic response of the pipe described. By comparing the simulation results of actual and equivalent models, the equivalent model can be used to analyze the longitudinal vibration characteristics of the lifting pipe. The sailing velocity of the mining vessel has little effect on the dynamic response of the lifting pipe, but the surface wave has a significant effect.

     

基于负压波分析的油管检漏技术研究

通过对负压波产生、流体参数测量及波形模式识别原理的分析,阐述了采用负压波分析的方法对油管泄漏进行检测和诊断的可行性,并提出了与负压波分析相结合的上下文无关文法,最后举例说明了这种方法的实际应用。     

基于数字散斑相关法的弯管残余应力测量系统

为了测量圆形管件在弯曲后产生的残余应力的情况,提出了一种新的基于数字散斑相关法(DSCM)的残余应力测量方法并且搭建了对应的测量系统.利用该系统对90.弯管外圆弯曲处的残余应力进行了测量.使用电测法作为参考,验证了基于数字散斑相关法的测量方法能够有效测定弯管内残余应力的值.实验结果表明,该方法在保证一定的测量精度的同时能够大幅度地提高测量效率,为进一步研究残余应力对弯管工艺的影响提供了基础.     

磁致伸缩纵向导波管道检测数值建模与分析

检测模型是磁致伸缩纵向导波检测技术发展的基石。现有磁致伸缩纵向导波检测模型存在不包含接收过程和不包含静态磁场计算等不足,难以满足设计优化接收传感器、增强导波检测信号等方面的研究需求。因此,以磁致伸缩纵向导波管道检测为背景,分析激励和接收过程中的控制方程,在此基础上建立了包括激励过程、声场传播和接收过程的有限元模型。分别采用仿真和实验分析了接收线圈的提离效应,仿真和实验结果吻合较好,验证了该数值模型的正确性。     

Finite element analysis on the V-die coining bend process of steel metal

An elasto-plastic incremental finite element computer code based on an updated Lagrangian formulation was developed to simulate the V-die coining bend process of sheet metal under the plane-strain condition. A modified Coulomb’s friction law was introduced to treat the alternation of the sliding–sticking state of friction at the contact interface. The r-minimum method was used to treat the elastic–plastic stress state and to solve contact problems at the tool–metal interface. V-bends of sheet metals are classified according to the number of contact points of the sheet with the bending die, and include air bends, bottoming bends, and coining bends. The former has three contact points with the bending die at the punch top and die shoulders, and there have been many experimental and analytical research works reported on it. The latter two are in contact at a greater number of points. To clarify the bending characteristics, it is necessary to fully understand the process and stress state in the bent part. The experiment was performed to validate the theoretical formulation and to support the development of the computer code. Simulation was performed on the punch load of the coining bend and the bend angle of the bent part after unloading. Calculated sheet geometries and the forming force agree well with the experimental data. The simulation clearly demonstrates the efficiency of the code to simulate V-die coining bend processes that proceed under contact history.     

Pro/ENGINEER管道特征在空调管路设计中的应用及弯管尺寸标注方法

根据数控弯管机矢量弯管原理,利用Pro/ENGINEER管道特征对空调器管路进行3D建模以及2D投影图转换,并结合数控弯管机的弯管程序特性,提出一种合理的弯管尺寸标注方式,以便于生产过程中程序的编制及零件的检验,减少试弯次数,从而实现空调器管件的生产效率提高及生产成本降低.     

分布种群的遗传算法收敛性证明

基于分布种群的遗传算法(DPGA)是一种高级的最有保留遗传算法(EGA),高级遗传算法目前应用很广,其一般数学定义和收敛性证明没有一般性结果。针对基于分布种群的遗传算法(DPGA)首先给出其特点,然后提出抽象的数学定义,最后利用DPGA运行的并行性在其子空间用马尔可夫链理论分别进行遗传操作的数学分析,从而在全局范围内给出DPGA两种实现方式的收敛性证明。     

基于CAE的QX1060车轮结构性能分析

以轻型车QX1060铝合金车轮为研究对象,详细叙述了车轮的设计过程。首先确定了车轮零件的类型和相关基本参数,然后运用UG软件对车轮零件进行三维建模。在ANSYS软件中,利用92号单元建立其有限元模型,分别就车轮承受胎压载荷、径向载荷、周向载荷、侧向载荷的工况进行模拟计算,得出了不同工况下车轮的应力和变形的大小和分布。计算结果表明,对车轮的有限元仿真分析是实现其设计的有效手段。     

基于马尔可夫模型的NCS可靠性分析

基于传统可靠性理论的研究,提出了一种Markov模型的网络控制系统可靠性评估方法及其建模过程.该方法通过详细分析工业网络控制系统的特殊性,构建网络控制系统的可靠性状态图,以推导系统的查普曼-科尔莫戈罗夫(Chapman-Kolmoqorov)方程,得到工业网络控制系统的可靠度模型,为网络控制系统进一步应用于国民经济众多领域奠定基础.