遗传算法在L型机头优化设计中的应用

阐述了遗传算法在L型机头设计中的应用,并编制了相应的计算软件包.讨论了L型机头流道主要参数对挤出压力分布均匀性的影响,并将本计算模块应用于工业实践.从使用效果来看,这种计算方法对于机头的设计具有实际的指导意义,具有一定的应用前景.     

对顶式内衬层生产线挤出机机头流道优化分析

采用Ansys-polyflow软件对对顶式内衬层生产线挤出机机头流道流场进行优化分析。机头流道结构直接影响挤出出口断面宽度方向胶料流速、温度、压力和剪切速率分布的均匀性。减小机头流道中部区域的阻尼,可有效解决半成品中间壁厚偏小和两边壁厚偏大的问题;增大机头流道分散角有助于优化胶料流动,有效减小出口断面宽度方向不同部位胶料流速、压力、温度和剪切速率差值。优化设计挤出机机头流道呈鱼尾状,流经流道的胶料呈压缩式层流流动,基本实现了出口断面宽度方向胶料流速、压力、温度和剪切速率分布均匀。     

鱼尾型片材机头内熔体流动的三维有限元模拟

利用ANSYS和MATLAB软件，对鱼尾型片材机头流道内熔体的速度、压力和剪切应力的分布进行三维有限元模拟和分析。通过对机头流道不同截面处熔体场量分布的模拟，探知了熔体在流道内的运动规律及特点，对口模设计具有一定的指导作用。     

发泡机头流道内PS/CO2均相体系压力场的模拟

利用有限元软件包Polyflow模拟不同条件下发泡机头流道内PS/CO2熔体的流动,获得了压力,计算出压降速率,并分析熔体温度、CO2含量、机头模口流道直径和质量流率对流道内压力和压降速率的影响。结果表明,在加工条件允许的范围内,降低熔体温度,可以显著提高机头流道中的压力和机头模口流道中的压降速率;当熔体温度一定时,机头流道中的压力和机头模口流道中的压降速率随着CO2含量的增加而降低。尤其当熔体温度为150℃,CO2质量含量由1%增加到2%时,机头模口流道中的压降速率急剧降低;减小机头模口流道直径可有效地提高机头流道内的压力和压降速率。熔体温度175℃,CO2质量含量5%、质量流率1kg/h时,模口直径由1mm减小到0.5mm,机头入口段压力由5.9MPa增大到近30MPa。     

螺旋式管材机头内熔体流动的计算机模拟

介绍了用于生产管材的螺旋机头及其主要设计方法和有限元建模方法,并用有限元软件POLYFLOW对机头内的熔体流动进行了三维模拟,分析了流道内的速度分布,压力分布和剪切速率分布,并指出了现有文献对螺旋机头的分析的某些不当之处。     

板型机头流道的有限元计算辅助设计

在板型机头中聚合物流动的有限元分析基础上,建立了一种利用有限元计算设计板型机头流道的方法,建立了流道设计原则,编制了设计计算程序,井用该方法对φ65挤出机平板机头流道进行了校验和再设计。实践表明:该机头流道经重新设计后,其内的胶料速度分布与停留时间分布有明显改善,这说明了本文所提出的板型机头流道设计方法的可行性。     

螺杆分配机头内部压力场分布的CAE分析

用ANSYS有限元软件对生产宽幅橡胶板材的螺杆分配机头流道内部的压力场进行三维模拟与分析，选择Fluid 142三维六面体单元划分网格，建立螺杆分配机头内部流道的三维有限元模型，得到在一定工艺条件下机头流道内部的压力分布。分析了阻尼块几何形状对压力分布的影响，指出阻尼块可以增加流道内原来速度和压力较高部位的流动阻力，选择合适的阻尼块高度可以使胶料的压力值逐渐趋于横向均匀。     

机头流道的计算机分析(九)

熔体在机头内的流动分析对机头设计很重要,从流动分析导出的压力、流速、流量表达式可导出流道尺寸的表达式,从而达到理论设计机头的目的。本节除继续分析熔体在流道中两维流动的简易计算方法之外,还进行了在流道内发生非平行流动情况的流动分析,这样的流道有圆锥形流道和V字形流道。全文除对机头流道进行全面的流动分析外,还给出了大多数设计公式的计算机程序,这些程序都在APPLE微机上试算过,效果良好。     

片材机头内聚合物熔体流动的模拟分析

利用ANSYS和MATLAB软件,对缩放型片材机头中熔体的速度、压力和剪切应力的分布进行三维有限元模拟和分析。通过对机头流道不同截面处熔体场量分布的模拟,探知了熔体在流道内的运动规律及特点。     

胎面双复合挤出机机头流道压力分布三维有限元分析

采用ANSYS有限元分析软件对胎面双复合挤出机头流道内部的压力场进行模拟和分析。通过选取合适的单元形式及恰当的划分网格单元 ,建立胎面双复合挤出机头的三维有限元模型 ,得到在一定工艺条件下机头内部流道的压力分布情况并分析其原因。     

Maximum entropy estimation of the bubble size distribution in fluidized beds

This work presents a new methodology, based on the maximum entropy method, to obtain bubble characteristics in fluidized beds. The probability distributions (PDF) of bubble pierced length and velocity are obtained applying the maximum entropy principle to experimental measurements. In addition, the bubble diameter distribution has been inferred from experimental pierced length measurements. This method is applied to characterize bubbles in fluidized beds for the first time and the most general bubble geometry, a truncated spheroid, is considered. The distance between probes, s, which is the minimum pierced length that is possible to measure accurately using intrusive probes, has been introduced as a constraint in the derivation of the size distribution equation.The maximum entropy method is applied to experimental measurements of bubble characteristics carried out using optical and pressure probes in a three-dimensional fluidized bed of Geldart B particles. Results on bubble size obtained from pressure and optical probes are very similar, although optical probes provide more local information and can be used at any position in the bed. The maximum entropy principle has been found to be a simple method that offers many advantages over other methods applied before for size distribution modeling in fluidized beds.     

A feasibility study of scattered-light photoelasticity in the determination of the side pressure distribution of the pressed powder bed

A method for the determination of the side pressure distribution of the pressed powder bed by the scattered-light photoelastic technique has been proposed. A cylindrical container made of photoelastic-sensitive material was used as a die, the powder in which was pressed uniaxially. The stress distribution in the wall of the container was measured by the scattered-light photoelastic method. The stress distribution at the inner surface of the container wall was obtained by extrapolation, and the pressure components of the powder bed at the powder—container interface were evaluated from the stress. The existence of a maximum of the side pressure near the surface of the powder bed is suggested.     

Evaluation of force—displacement measurements during one-sided powder compaction in a die — the influence of friction with the die wall and of the diameter of punches and die on upper and lower punch pressure

On an instrumented single-punch press, working at an overall rate of 30 strokes per minute, the influence of diameter of punches and die on upper and lower punch pressure, measured during the densification of a powder with an initial height of 8.0 mm, has been investigated.The upper punch pressure necessary to effect a certain state of density, proved to decrease with increasing diameter, whereas the lower punch pressure proved to be independent of the diameter. The upper punch pressure differences, found for diameters ranging from 11 to 17 mm, could not be accounted for by differences in the actual speed of compaction between the individual force displacement measurements and it could be concluded that these pressure differences were exclusively due to an influence of the diameter on the process of compaction.By using a number of hyportheses concerning friction with the die wall, it was possible to derive a mathematical model for the pressure distribution on the upper punch which qualitatively agreed with the experimental results.     

钢制压力容器焊接残余应力测试分析

应用小孔释放法对系列钢制压力容器手弧焊接接头的焊接残余应力进行测试 ,讨论了焊接残余应力的分布规律及其相关影响因素 ,对加载法消除焊接残余应力的效果进行了初步的验证。结果表明 ,焊接接头的应力不均匀性和不确定性是影响钢制压力容器安全性的关键 ,采用加载法可以有效地改善这种非均匀应力分布状况。     

空气管道出口处的负压问题

空气管道出口处负压现象的发现,打破了传统的空气管道终端压力分布理论,改变了人们长期形成的风机出口管道终端不会出现负压的观念.在阐明风机全压基本概念及其用途的基础上,着重从条件和原因方面,分析管道出口处出现负压的机理,并得出几点重要的结论.     

图版法判别碳酸盐岩洞穴储层有效性

塔中地区下奥陶统碳酸盐岩地层发育岩溶洞穴,充填作用强弱不等,洞穴的有效性受到严重影响。针对此问题,根据既有资料建立了不同类型洞穴储层的交会图版,对洞穴储层进行有效性评价,从而为生产测试提供指导,极大地提高了经济效益。该方法在塔中地区取得了良好的效果。     

Non-isothermal flow of a molten polymer in a coat-hanger die

The non-isothermal flow of a power-law fluid in a coal-hanger flat die is studied. Equilibrium and thermal equations are solved by using an iterative finite difference method. The pressure distribution, the flow lines, the residence time distribution, the temperature distribution, and the flow uniformity at the end of the die are obtained, with a stress on the effect of thermal regulation and of temperature dependence of the viscosity.     

双螺杆技术在发射药制造中的应用

通过塑化成型试验,找出双螺杆机塑化成型的工艺规律,用正交试验确定工艺参数。用极差分析方法分析了溶剂比、模具形式、螺杆组合方式、模具水温、螺杆水温对产品密度、机头压力和扭矩的影响。结果表明,模具形式对产品密度影响最大,溶剂比对机头压力影响最大,螺杆组合方式对主机扭矩影响最为显著。分析了螺杆转速对机头压力和加料频率对扭矩的作用关系,为双螺杆技术在连续化、自动化发射药生产线中的工程化应用提供了依据。     

Optimization‐based design of polymer sheeting dies using generalized Newtonian fluid models

A polymer sheeting die design methodology is presented, which integrates finite element flow simulations, numerical optimization, and design sensitivity analyses to compute die cavity geometries capable of giving a near‐uniform exit velocity. This work extends earlier die design methods to include generalized Newtonian fluid (GNF) models that represent the shear‐thinning behavior of polymer melt. Melt flow computations and design sensitivity analyses are provided using the generalized Hele‐Shaw flow approximation with isothermal power‐law, Carreau‐Yasuda, Cross, Ellis, and Bingham fluid models. The nonlinear equations for die cavity pressure are solved using the Newton‐Raphson iteration method and design sensitivities are derived with the adjoint variable method. The die design method is applied to an industrial coat hanger die, in which a design parameterization is defined that allows for an arbitrary gap height distribution in the manifold of the die. In addition, die performance is assessed and compared for power‐law and Carreau‐Yasuda fluid flow over a range of die operating conditions. Pareto optimal die designs are also considered in this study. POLYM. ENG. SCI., 45:953–965, 2005. © 2005 Society of Plastics Engineers     

Fluid mechanics analysis of a two-dimensional pultrusion die inlet

Fluid mechanics plays an important role in many manufacturing processes including the pultrusion of composite materials. The analysis of fluid mechanics problems generally involves determination of quantities such as pressure and velocity. During the pultrusion process, the short, tapered inlet region of the pultrusion die experiences a significant amount of fluid resin pressure rise. The quality of a pultruded product can be affected by the amount of pressure rise in the pultrusion die inlet. Void formation can be suppressed and good fiber “wet out” achieved by a sufficiently high pressure rise in the pultrusion die inlet region. In this study the change in fluid resin pressure rise as a function of die entrance geometry is investigated by developing a finite element model based on the assumptions of Darcy's law for flow in porous media. The momentum equations are combined with the continuity equation to save computational time and memory. A Galerkin weighted residual based finite element method is developed to solve the resulting equation. This model is capable of predicting the pressure rise in the tapered inlet region of the pultrusion die as well as the straight portion of the die. By varying the size of the preform plates the thickness of the fiber/resin matrix approaching the die inlet can be varied. The finite element model predicts the impact of changing the preform plate size on the fluid resin pressure rise in the pultrusion die. The effect of varying the wedge angle for a linearly tapered die inlet region is also studied using this model. The results in this work can be useful for designing a pultrusion die system.