竖流沉淀池内流态及影响因素模拟分析

为了研究了城市污水处理厂沉淀池速度场和质量浓度场,利用改进的RNG(重整化群)k-e紊流模型和Mixture混合模型,FLUNENT15.0软件对沉淀池进行仿真。结果表明:1)在竖流沉淀池距池底2~3米处池壁位置和污泥斗上部会形成两个明显的涡流,已经沉淀的颗粒在涡流的作用下重新进入沉淀池中;2)中心筒的污水遇到锥形挡板以后会有一部分重新进入到中心筒中,减轻了下降的污水对沉淀区的冲击;3)通过改变入流速度进行模拟对比,发现入流速度由0.3m/s增加到0.8m/s,清水区深度由池深的五分之四减小为二分之一,继续增加到1m/s,清水区消失,出水浓度达到0.3%,失去了沉淀效果。在保证出水水质的前提下沉淀池能承受的最大入流速度为0.86m/s.入流密度由1050 kg/m^3增加到1250 kg/m^3,沉淀区厚度由2m减小为1.5m,沉淀效果增强。试验结果验证了上述仿真结果可靠,对竖流式沉淀池工程设计具有一定的指导意义。     

双螺杆挤出机模具过渡和稳流段流场的数值模拟

采用Carreau模型描述熔体的黏度特征,使用POLYFLOW软件数值模拟了异向旋转双螺杆挤出机模具过渡和稳流段的三维等温流场。在不同的工艺参数下,分析比较了模具过渡和稳流段内的速度场、压强场、剪切速率场、剪切应力场以及黏度场。结果表明在模具过渡和稳流段内,螺杆的旋转是该聚合物熔体流变性能的最大影响因素,螺杆头对高黏度熔体的影响范围不大,只限于螺杆头的周围;进入稳流段后,在稳流段作用下熔体的流动逐渐变得稳定均匀;在本文讨论的转速和流量范围内,转速和流量的增加,分别会在不同的区域使熔体受到的剪切速率和剪切应力明显地增大。研究结果为某企业设计双螺杆模具和优化工艺条件提供理论依据。     

压电风扇振动方程和速度场的数值分析

通过ANSYS建立压电风扇的简化模型,对压电风扇进行模态分析,得出1阶模态下的共振频率为51.19 Hz;通过瞬态分析得出风扇上给定点的最大振动位移和振动特性,拟合出压电风扇处于最大位移时的振动曲线;得出压电风扇在整个工作过程的振动函数方程;通过此运动方程编写用户自定义函数（User Defined Function,UDF）在FLUENT中计算出压电风扇周围最大速度为1.94 m/s,沿流道长度方向上的速度约为0.73 m/s.     

内循环厌氧反应器CFD气液两相流模拟研究

内循环反应器的设计关键是流体在内部可以形成稳定的内循环流动,而表观气速是影响内循环形成的关键因素。采用标准k-ε湍流模型和欧拉-欧拉双流体模型,对内循环厌氧反应器内的气-液两相流体的流动规律进行了三维非稳态数值模拟研究。考察了不同表观气速对反应器内流体力学行为的影响。模拟结果表明:当表观气速较小(0.003 m/s)时,内循环无法形成;当表观气速在0.006 m/s至0.01 m/s范围内逐渐增大时,反应器内循环过程越容易形成,反应器的实际容积越能得到充分利用,且随着表观气速的增大,反应器内液相及气相轴向速度不断增大,轴向气含率逐渐增加;而气相去除率却呈现先上升后下降趋势;当表观气速增大至0.02 m/s时,部分气体由液体出口排除,影响反应器效率及出水稳定性。     

多层金字塔夹芯结构在冲击载荷作用下的动态响应

金属材料点阵夹芯结构能量吸收效率较高,为得到多层金字塔点阵夹芯结构在冲击载荷作用下的动态响应,利用Patran建立多层金字塔点阵夹芯结构在冲击载荷作用下的数值模拟模型,通过Dytran计算分析质量为25 kg的钢板以30 m/s, 60 m/s和90 m/s的速度冲击时模型的应力、应变、变形以及变形能,研究随着冲量的增加,模型的应力、应变、变形和变形能的变化规律.     

飞机起落架收放系统运动模拟

使用三维设计软件CATIA模拟了起落架收放系统的运动规律,消除了各零件之间的干涉现象.用软件计算了关键部位的速度和加速度随时间曲线和机轮上3点的运动轨迹,最后计算了各运动件的扫过体积.计算结果表明,收起和放下的过程并不完全对称,机轮的最大速度值为0.019m/s,缓冲支柱下表面的最大速度为0.031m/s,机轮的最大加速度值为11m/s2,缓冲支柱下表面的最大速度为14m/s2,收起过程的最大速度更大.在系统所有零件中,机轮扫过体积最大.     

计算机辅助模拟注射模充模过程

在注射成形过程中 ,塑料熔体的流动状况是决定塑件质量的重要因素 ,运用注射成形流动模拟软件可以准确模拟塑料熔体的整个充模过程 ,优化塑料熔件的流动场 ,以找到最合适的浇注系统及尺寸。     

Moldflow在光驱托盘模具设计中的应用

为制造出高质量高精度的模具,以某光驱托盘为研究对象,利用Moldflow MPI 6.0的填充、流动以及冷却-流动-翘曲分析模块对熔体在模具中的流动行为进行数值模拟.制品采用Pro/ENGINEER建模并进行自动网格划分.网格采用Fusion格式,尺寸为3 mm.根据模拟出的熔体流动前沿的推进速度、填充过程中的温度和压力变化、制品冷却时间等流动行为和工艺参数,确定最佳成型方案.示例表明该方法能基本满足产品的质量要求.     

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。     

聚苯乙烯熔体通过矩形收缩口模的研究

在回顾了文献工作的基础上,本文使用Carreau本构方程模拟聚苯乙烯熔体的流变特性,用基于控制容积法的SIMPLEC算法求解二维流体力学基本方程,研究了聚苯乙烯熔体在矩形收缩口模中的不可压、非等温、稳态流动,获得了速度、压力、粘度、应力和温度的分布。计算结果可用于高分子注射过程中的口模设计。     

Simulation of the filling process in molding components with micro channels

In micro molding of components with micro features, the ability for the polymer melt to flow into the micro channels is a crucial factor for successful molding. In this case, the molded volume is about the same as the conventional molding. The penetration distance into the microstructure depends on the flow rate and the cooling rate of the micro features, which is function of the geometric dimensions. In this study, a simplified model was established to estimate the injection distance into the micro channels of a mold insert. The effect of the mold temperature, injection rate, and micro channel dimension on the filling distance was investigated based on the model. The filling distance increases dramatically with respect to the increase of the channel width. In molding of components with micro features as those analyzed in this study, decrease of the part thickness could enhance the filling in the micro features.The authors would like to thank for the financial support from National Science Council in Republic of China under the contract number of NSC 91-2212-E006-131.     

有限单元法在塑料注射充模流动模拟中的应用

对塑料熔体注射成型充模流动过程的流变方程进行了熔体充模过程流变方程参数基于3维有限单元法的数值求解研究,得到基于形函数的压力刚度矩阵、温度刚度矩阵的方程式,进而得出压力场、速度场、温度场数值解的方程式。据此完成了注射熔体流动充模过程由M atlab编程实现的有限元分析本体程序。用具体的注射成型塑料制品作为检验实例,用2种不同的塑料进行注射成型模拟,其结果与国际著名的M old flow商品化软件和文献数据进行比较,表明本研究的设计软件算法正确、程序运行速度快。     

Visualizing analysis for weld line forming in micro injection molding by experimental method

In micro injection molding, the melt flow behavior is important for the final product quality. However, the current process monitoring and measurement technology are not adequate enough to provide a direct analysis access. In the presented study, a glass insert mold designed for performing the direct visual analysis for melt flow phenomena in micro injection molding is introduced. The micro tensile specimen with 0.1 × 0.4 mm² (depth × width) cross section dimension is chosen as the objective part. The correlation between processing parameters (injection pressure, injection speed, mold temperature) and flow behavior was investigated and analyzed. The results show that the injection pressure put an obvious effect on the filling speed through micro cavity. Injection speed can influence the filling time dramatically also. Higher mold temperature brings positive influence with the flowing speed, due to the lower viscosity of polymers in higher mold temperature.     

基于控制参数化的注塑工业过程最优反馈控制方法

本文针对一类典型的注塑工业过程系统, 研究了注塑填充过程中产生的熔体流动速度最优跟踪控制问题, 提出了一种基于控制参数化的计算最优反馈控制器设计方法以实现注塑过程中熔融聚合物流动前沿位移的最优跟 踪控制, 进而达到改善注塑零件性能的高效生产目标. 首先, 面向注塑工艺复杂生产过程建立了动态过程系统数学 模型, 提出了注塑机内部熔融聚合物流动前沿位置的动态最优跟踪控制问题; 其次, 设计了一种多级反馈控制律, 通 过控制参数化方法将控制反馈核进行了参数化表示, 将控制器设计问题转化为一序列最优参数决策问题; 然后, 通 过状态灵敏度方程分析方法, 求解出了目标函数及约束条件关于决策变量参数梯度信息的显式表达式, 并基于所提 供的梯度信息结合序列二次规划算法进行了高效优化迭代求解; 最后, 通过实验仿真验证了本文所提出的最优反 馈控制器设计方法的可行性和有效性.     

Application of lattice Boltzmann method in free surface flow simulation of micro injection molding

The filling flow in micro injection molding was simulated by using the lattice Boltzmann method (LBM). A tracking algorithm for free surface to handle the complex interaction between gas and liquid phases in LBM was used for the free surface advancement. The temperature field in the filling flow is also analyzed by combining the thermal lattice Boltzmann model and the free surface method. To simulate the fluid flow of polymer melt with a high Prandtl number and high viscosity, a modified lattice Boltzmann scheme was adopted by introducing a free parameter in the thermal diffusion equation to overcome the restriction of the thermal relaxation time. The filling flow simulation of micro injection molding was successfully performed in the study.     

Influence of processing parameters on micro injection molded weld line mechanical properties of polypropylene (PP)

As a hot fabrication technology for micro scale parts, micro injection molding is receiving increasing market attention. Improving mechanical properties of micro parts should be an important issue in the micro injection molding process. The relation between weld line strength in micro injection molding parts and processing parameters is investigated. A visual mold with variotherm unit is designed and constructed, in which the micro tensile specimen with weld line are prepared. Polypropylene (PP) is used as the research material in this study, and six processing parameters were chosen as investigating factors, which were melt temperature, mold temperature, injection pressure, packing pressure, ejection temperature and injection speed. In order to achieve optimized processing parameters and their order of significance, Taguchi experiment method was applied in this presented study. The prediction formulation of the strength of micro weld line was built up by multiple regression analysis based on Chebyshev orthogonal polynomial. The results showed the influencing significance order of parameters from strong to week separately are mold temperature, melt temperature, injection speed, ejection temperature, packing pressure and injection pressure. And the tolerance of micro weld line prediction formulation was found to be lower than 21% through confirmation experiments.     

The effect of injection molding PMMA microfluidic chips thickness uniformity on the thermal bonding ratio of chips

Injection molding PMMA microfluidic chips can significantly improve the efficiency of chips forming. However, due to the coexistence of macro and micro effects in the injection molding process, the thickness uniformity of molding substrates is poor, which will seriously affect the thermal bonding quality of chips. In this paper, the effect of injection molding PMMA microfluidic chips thickness uniformity on the thermal bonding ratio and the quality of micro-channels was studied by experiments and simulations. The results show that when the following three conditions were satisfied during injection molding process, chips bonding ratio reaches to 93.9?% and the distortions of micro-channels caused by thermal bonding were acceptable. Firstly, the cover plates flatness error is smaller than 50–60?μm and substrates flatness error is smaller than 80–90?μm. Secondly, the maximum thickness difference of stack chips (cover plate stack with substrate) is smaller than 70–80?μm. Thirdly, chips thickness of the middle is larger than that of the two ends along their length direction and chips thickness distribute evenly along their width direction. These conclusions can be used for the parameters selection and moulds design during injection molding process of PMMA microfluidic chips.     

Air-Flow-Based Single-Cell Dispensing System

We discuss a design and fabrication approach to increase the success rate of single-cell dispensing. Two pairs of capacitance sensors are placed in a biochip to detect the flow velocity of cells and air pressure is applied to eject cells by synchronizing the timing. A comprehensive design theory, which takes into account the back-pressure caused by the air pressure, the response time of the system, the sensor properties and the delay of the dispensing from the air pressure, is developed in order to minimize the disturbance of the system and maximize the throughput of the ejection system. Then, the system theoretically has a capability to eject 3 cells/s and the maximum flow velocity is 10 mm/s. The novelty of the system is that the biochip is disposable, which is unlike the conventional mechanical inkjet system; because the biochip is low cost and disposable this prevents contamination and means the drive system is reusable. Finally, we succeeded in automatic dispensing of a single polystyrene bead (100 μm) from a biochip to a culture well atmosphere using the developed cell ejection system with a success rate of 50%. Furthermore, we also succeeded in single swine oocyte dispensing by using the developed system.     

LCD后背板的注射成型参数正交优化设计

针对注射成型过程中最常见的制件翘曲问题,尝试以LCD后背板为研究对象,对影响薄壳塑件翘曲变形的因素(如模具温度、熔体温度、注射时间、保压压力、保压时间、冷却时间)进行分析,以正交实验法找出最佳工艺参数组合,通过极差分析,确定实现低翘曲变形的最优方案为:模具温度85℃,注射时间0.6s,保压压力100%。