塑化过程螺槽中三维流场的数值模拟

采用CROSS模型表示聚氯乙烯(PVC)的黏度特征,使用POLYFLOW软件数值模拟了塑料注射成型机螺杆计量段螺槽中熔体在塑化过程的三维等温流场,求解和分析了3条参考直线、yz截面和xy截面上不同时刻螺槽中的压强场、速度场、剪切速率场和黏度场,数值计算的结果表明:在螺棱附近区域物料的剪切速率大,物料剪切稀化作用增强,物料黏度减小。并采用粒子运动轨迹示踪的方法研究了塑化过程中注塑机粒子运动轨迹。得知塑化过程中注塑机粒子运动轨迹比挤出机复杂得多,有三种典型的运动方式:一部分粒子边旋转边向负Z方向运动、另一部分粒子在旋转的同时先向负Z方向运动后向正Z方向运动,还有一部分粒子和边旋转边向正Z方向运动。     

行星式搅拌釜内高黏固液两相流的数值研究

行星式搅拌装置适用于固体颗粒与高黏度聚合物熔体的混合,搅拌釜内高黏度流体的流动状况非常复杂,实验方法很难获得搅拌釜内流场细节.利用FLUENT软件数值模拟了新型行星式搅拌釜内高黏固液两相流的流场,分析了不同转速条件下搅拌釜不同截面的速度场和浓度场.计算中采用欧拉模型,使用动网格技术,利用FLUENT的用户自定义函数确定...     

注塑成形中气体反压技术的数值模拟

针对某平板注塑成形过程,通过改变气体反压（Gas Counter Pressure,GCP）压力场,用ANSYS CFX模拟GCP技术对成形质量的影响.由模拟结果可知：在GCP压力作用下,熔体的流动形态发生明显变化.当GCP压力增大时,熔体的最大流动长度减少,且熔体流动速度和剪切应变速率呈下降的趋势.在充填时间内,GCP压力由0增加到2 MPa时,塑料熔体沿流动方向上的速度由0.52 m/s下降到0.45 m/s,熔体的最大剪切应变速率最大降低42.7%.     

折流旋转床吹脱含氨废水实验研究

应用折流式旋转床吹脱高浓度含氨废水,研究了在不同的工艺条件下,各工艺参数,如气液比、旋转填料床转速、温度等对含氨废水氨去除率的影响.研究表明:折流旋转填料床具有压降小、高传质性能,用于处理含氨废水能有效地提高氨去除率;在温度为23℃、pH为11左右,液体流量为60L/h、气体流量为160m2/h、转鼓转速为800 r/min的条件下,用旋转填料床处理含氨5 000mg/L废水的单程吹脱率可达82%;单元传质高度为36mm.     

分子动力学的聚合物流动诱导结晶取向数值模拟

聚合物的实际成型加工过程中,熔体在充填过程中不仅要受到热历史的作用,而且要受到剪切应力的作用,所以就不可避免地发生流动诱导结晶及取向现象。本文基于悬浮液理论和分子动力学方法,建立聚合物流动诱导结晶取向的数学模型,研究了剪切作用对结晶聚合物流动诱导结晶取向的影响。模型将结晶体系假设为结晶晶粒分散于无定型基质的悬浮液,通过取向张量计算取向因子,预测剪切过程中的晶相的取向行为。使用谱方法离散求解扩散方程,并计算取向分布函数和取向张量,模拟和分析了简单剪切场下结晶聚合物的流动诱导结晶取向行为。模拟结果表明,剪切强度对聚合物熔体的取向行为有着显著的影响,较高的剪切速率有助于晶区较早的完善取向。     

带微型涡轮的旋转盘腔内流场的数值仿真研究

对带有反预旋喷嘴的旋转涡轮盘腔内部流动特性进行数值仿真研究.采用Gambit2.10软件创建计算模型,采用Fluent6.1软件计算求解3个转速下(50rpm、800rpm、1300rpm)旋转盘腔内部流场的分布规律.压力速度耦合方法采用SIMPLE算法,各参数的离散采用二阶迎风格式.数值仿真结果表明:在低转速(50rpm)下,主要由进气惯性力控制流场内部结构;在过渡转速(800rpm)下,进气惯性力和旋转效应共同控制流场内部结构;在高转速(1300rpm)下,主要由旋转效应控制流场内部结构.同时得到流场内部切向速度的分布规律.     

双螺杆挤出机流场数值模拟中流道进出口边界条件的探讨

在对双螺杆挤出机流场的数值模拟中,流道进出口边界条件的设置一直是一个颇具争议的问题。由于事先无法获得计算域进出口平面上的真实边界条件,研究人员在进行双螺杆挤出机的流场分析时,大都采用放松边界条件。为了考察放松边界条件对双螺杆挤出机流场数值模拟结果的影响,本文采用聚合物流动分析软件POLYFLOW,在流量恒定的前提下对双螺杆挤出机流道进出口给定三种不同分布形式的速度边界条件,对其流场进行了数值模拟。数值计算结果表明,在体积流量恒定的条件下,流道进出口不同分布形式的速度边界条件对流场的影响主要集中在进出口附近区域,但对离进出口边界较远的流场影响很小。一般而言,当计算域所对应的螺杆较长时,可以忽略流道进出口的放松边界条件所引起的误差;当计算域较短时,不宜直接采用放松边界条件,而应根据螺杆的实际构型．在计算域的进出口增加适当长度的发展段。     

Ω形双螺杆泵流场仿真与实验研究

研究螺杆转子转动过程中的流场变化有助于对双螺杆泵运行参数的优化。采用计算流体力学(CFD)方法,对双螺杆泵流场进行三维瞬态动网格仿真分析。针对Ω形双螺杆泵,建立内流场数值模型,通过仿真得到一个转动周期内泵内压力分布,同时研究了不同粘度下泵外特性的变化规律。仿真结果表明,泵内压力由吸入端到排出端逐级增大,与容积腔推挤增压规律相吻合;在吸入端容积腔截面和螺杆啮合缝隙内均存在负压,且由于泄露的原因,密封腔两端的压力分布并非完全一致,存在轻微差异;流量随着压差的增大而呈近似线性下降趋势,粘度越大,流量受压差的影响就越小;泵效随压差的变化曲线呈抛物线形,达到峰值后先逐渐减小,最后趋于平稳。实验结果与仿真一致,证明了仿真方法的有效性。     

电潜离心泵内流场及外特性的数值模拟分析

针对目前油田使用的两种不同叶导轮结构的电潜离心泵,包括传统径向流泵和聚驱用混向流泵,采用计算流体动力学(CFD)研究方法,建立电泵内流场的数值仿真,在流量80～200m³/d范围内,研究泵输送不同运动黏度为1～40mm²/s介质时特性差异。在介质黏度为1和40mm²/s,流量为80～180m³/d工况下,使用FLUENT软件选用标准k-ε湍流模型和SIMPLE算法进行求解,分析两种泵在不同工况下的内部流场变化规律,通过流场分析探究叶轮结构对泵外特性的影响机制。仿真得到泵的扬程、效率曲线,发现泵性能出现变化的工况点与叶轮内流场分析结果相对应,并根据泵叶轮的内流场分布和泵的性能曲线分析两种泵所适用的工况。结果表明,径向流泵适用于大流量和高黏度工况,混向流泵适用于较低流量和中低黏度工况,为不同工况下泵的选择及泵的优化提供理论依据。     

旋转固体发动机燃烧室-喷管两相流数值仿真

针对旋转引起的固体发动机内弹道性能和热防护性能变化影响发动机推力性能,从旋转对发动机内部燃气流动影响出发,用Reynolds时均N-S方程、Reynolds应力方程湍流模型(RSM)和颗粒随机轨道模型,在FLUENT软件上对不同旋转转速的固体发动机燃烧室-喷管内气-固两相流动进行了一体化数值仿真,比较了有无旋转两种状态下的流场结构,研究了转速对流场结构和发动机热结构的影响,并进一步研究了发动机的工作特性.仿真结果表明,发动机旋转使燃烧室内部流场结构发生显著变化,流场结构呈组合涡形式,粒子严重偏离发动机对称轴,导致燃烧室压强升高,推进剂燃速增大,发动机工作时间变短,热防护环境恶化,工作性能降低.这些变化随转速的增加呈现加剧趋势.研究结果为发动机设计提供了一定的技术支持.     

Optimization of magnetic field assisted EDM using the continuous ACO algorithm

In this paper, a rotary tool with rotary magnetic field has been used to better flushing of the debris from the machining zone in electrical discharge machining (EDM) process. Two adaptive neuro-fuzzy inference system (ANFIS) models have been designed to correlate the EDM parameters to material removal rate (MRR) and surface roughness (SR) using the data generated based on experimental observations. Then continuous ant colony optimization (CACO) technique has been used to select the best process parameters for maximum MRR and specified SR. Here, the process parameters are magnetic field intensity, rotational speed and product of current and pulse on-time. Also, ANFIS models of MRR and SR are the objective and constraint functions for CACO, respectively. Experimental trials divided into three main regimes of low energy, the middle energy and the high energy. Results showed that the CACO technique which used the ANFIS models as objective and constrain functions can successfully optimize the input conditions of the magnetic field assisted rotary EDM process.     

Vibration characteristics of a rotating blade with localized damage including the effects of shear deformation and rotary inertia

The flexural vibration characteristics of a uniform rotating bar with localized zones of damage are studied by using a finite element analysis. The effects of shear deformation and rotary inertia have been taken into consideration. The influences of parameters such as the extent, position of damage and rotational speed on the frequencies of oscillation of the blade are discussed. It is observed that the presence of damage has a marked effect on the natural frequencies. A flaw in the beam near the tip of the blade has substantial effects on the frequencies as rotational speed increases. As the rotary inertia and shear deformation parameters increase, the frequencies increase for all damage parameters.     

注射合模机立柱应力分析和结构改进

针对某注射合模机立柱螺纹根部开裂问题,采用ANSYS Workbench建立单根立柱有限元模型,对某三梁四柱式注射合模机进行强度分析,得到立柱与螺母啮合处的应力大小和分布。在轴向载荷作用下,应力峰值出现在立柱与螺母啮合的第一个螺纹处,其中轴向应力分量最大;若在立柱与螺母啮合的第一个螺纹处进行圆弧过渡,可有效降低应力集中;与无圆弧半径比较,当过渡圆弧半径r=7 mm时,最大von Mises等效应力下降46%。     

Numerical modeling of laser sintering of two-component powder mixtures

The process of direct sintering of metal powders induced by laser radiation is investigated. A two-component mix of powders consisting of low- and high-melting components is considered. The model is based on a self-consistent nonlinear equation of continuity for volume fractions of low- and high-melting components of the mixture and on the equation of energy transfer in the melt-powder mixture system. It includes the motion of hard particles due to shrinkage associated with the changed density of the powder mixture and with convective fluxes caused by the forces of surface stress and gravitation. The liquid flow is determined by the Darcy law of filtration. The effect of the finite width of the region of phase transition of the high-melting powder has been detected. The rate of melting zone expansion is shown to depend on both the parameters of laser radiation (beam power) and on the physical characteristics of the substance of particles, and to grow with the increase in penetrability or phase transition heat. A diagram of the evolution quality of the melting front is obtained, by which it is possible to predict the solution behavior depending on the parameters of the powder mixture (penetrability and melting heat).     

Effects of Curvature and Stenosis-Like Narrowing on Wall Shear Stress in a Coronary Artery Model with Phasic Flow

To gain insight into the details of intracoronary flow we have used computational fluid dynamic techniques to determine the velocity and wall shear stress distributions in both steady- and phasic-flow models of a curved coronary artery with several degrees of stenosis. The steady-flow Reynolds number was 500 and the peak phasic flow Reynolds number was 700. Without stenosis and at 25% (area) stenosis wall shear stress and velocities are higher at the outer wall than the inner wall but retain the same direction as the superimposed flow. At higher stenoses laminar flow separation occurs and the inner wall is exposed to shear stresses that vary widely, both temporally and spatially.     

螺杆转速与挤出量的非线性校正控制及实现

根据交联电缆生产工艺的要求提出了挤塑机螺杆转速与挤出量的非线性校正控制算法,并对控制算法进行了详细的分析和描述。     

Influence of shear deformation and rotary inertia on nonlinear free vibration of a beam with pinned ends

The method of multiple scales is used to analyze the nonlinear vibrations of a beam with pinned ends. The formulation incorporates the effects of the transverse shear deformation as well as the rotary inertia on the large amplitude vibration behaviour. A uniformly valid higher second-order perturbation solution is obtained. The predictions of nonlinear frequencies at different beam parameters are given. The influences of shear and rotary inertia are significant in the case of moderately thick and short beams undergoing large amplitude vibrations.     

回转窑煅烧带温度控制器的设计与仿真

针对传统的回转窑煅烧带温度PID控制系统存在温度稳定性差、无法在线调整PID参数等问题,文章提出了一种采用模糊自整定PID参数控制方式设计回转窑煅烧带温度控制器的方案,介绍了该控制器的结构、设计步骤及回转窑煅烧过程系统的建模等,并采用Matlab中的Simulink模糊工具箱对模糊自整定PID温度控制器进行了仿真。仿真结果表明,该控制方法无超调量、调节时间短,能够实现参数的在线自调整。实际应用也证明了该控制方法的优越性。     

Hybrid algorithms for the twin–screw extrusion configuration problem

The twin-screw configuration problem (TSCP) arises in the context of polymer processing, where twin-screw extruders are used to prepare polymer blends, compounds or composites. The goal of the TSCP is to define the configuration of a screw from a given set of screw elements. The TSCP can be seen as a sequencing problem as the order of the screw elements on the screw axis has to be defined. It is also inherently a multi-objective problem since processing has to optimize various conflicting parameters related to the degree of mixing, shear rate, or mechanical energy input among others. In this article, we develop hybrid algorithms to tackle the bi-objective TSCP. The hybrid algorithms combine different local search procedures, including Pareto local search and two phase local search algorithms, with two different population-based algorithms, namely a multi-objective evolutionary algorithm and a multi-objective ant colony optimization algorithm. The experimental evaluation of these approaches shows that the best hybrid designs, combining Pareto local search with a multi-objective ant colony optimization approach, outperform the best algorithms that have been previously proposed for the TSCP.