基于FEM-DEM的大米破碎仿真初探

提出了大米破碎仿真的一个整体框架,该框架将抽样裂纹检测、含裂纹大米的有限元建模和仿真、大米的离散元建模和仿真以及碾米机的参数修改结合在一起,构成了一个有序的统一体。研究了基于扩展有限元的大米破碎仿真,并以松粳9号糙米为例进行了裂纹扩展仿真。仿真结果表明,上述框架和裂纹扩展仿真技术可以应用在碾米机的结构设计和工艺参数确定中,并对类似颗粒物加工机械的设计和应用有一定的参考意义。     

基于离散元法的糙米碾白过程仿真初探

碾白是谷物加工中重要的加工工序,为了研究该过程中糙米的破碎率,基于离散元方法,以EDEM软件为平台,对糙米碾白进行离散元仿真。仿真糙米颗粒破碎,通过离散单元法的Hertz-Mindlin黏结模型,用"黏结键"将更小的球形颗粒黏结在一起,当颗粒受力达到其破碎强度时,"黏结键"断裂,从而可以有效模拟糙米的破碎。通过对糙米碾白仿真,得出糙米的动力属性和破碎率都较符合实际情况。     

基于EDEM的猴魁茶叶充填过程仿真研究

为解决猴魁茶叶包装劳动强度大、效率低等问题,课题组设计了一款适用于猴魁茶叶的自动化充填系统。运用EDEM离散元仿真软件对猴魁茶叶的充填过程进行仿真模拟,观察充填过程中茶叶姿态的变化规律,以验证设计的合理性;并以堆积角、平均速率及平均挤压力作为评价指标,探究不同结构参数对茶叶充填性能的影响规律。结果表明：载具转速对茶叶充填性能影响最为显著,转速越大,茶叶的堆积角、速度及内部挤压力越大。课题组的研究可为后续装置研究与参数化设计提供参考。     

微型胶囊在模拟肠道中的受力模型及流固耦合仿真

对胶囊在黏性液体环境下的受力进行了理论分析,研究了不同尺寸头部分别为圆形、椭圆形的磁驱胶囊在肠道环境中流固耦合作用下的动力特性。采用COMSOL分析了肠道动力黏度、肠道尺寸、胶囊外形3因素对胶囊运动受力影响,肠道壁模型基于力学性能相近原则,采用超弹性固体材料。进行了多因素、多水平的数值模拟试验。结果显示:在同水平的动力黏度和肠道内壁尺寸参数下,椭圆形较圆形胶囊的头部压力平均降低了12.8%。     

基于UDF动网格的钢索管式刮板输送机气固两相流数值研究

钢索管式刮板输送机在进行物料输送时,由于刮板的高速运动使管内形成了负压效应,空气进入和物料混合使物料呈现一定的流态化现象,有利于提高输送机的输送效率。由于刮板输送机模型的复杂性,本研究基于FLUENT中UDF动网格技术使刮板边界实现了在跑道形流道内运动的情况,成功获取了输送管内部空气相流场的运行情况,然后在此基础上进行了气固两相流的数值模拟,获得了颗粒和空气的运行参数和体积分布云图。     

纤维与气流耦合的数值模拟

结合纤维的本构方程与气流控制方程,建立二维的纤维与气流耦合方程。采用相容时间积分与迭代耦合算法,对纤维在喷气织机主喷嘴中拉伸弯曲运动特性、纤维受力情况以及与壁面接触时的微观运动特性进行研究。结果表明:纤维在气流的作用下会产生拉伸弯曲变形,呈现正弦或者余弦形式波动;纤维在自由端的弯曲变形效果比在约束端的明显;纤维受到气流作用时,最大应力值往往发生在纤维弯曲部位以及与壁面相接触的部位。     

CFD simulation of ozone gas flow for controlling Sitophilus zeamais in rice grains

Ozone gas (O₃) is a prominent alternative for the integrated pest management of stored products. The present study fitted a computational fluid dynamics (CFD) model to elucidate the ozone gas flow dynamics in an aeration system, at a lethal concentration for Sitophilus zeamais Mots in rice grains. First, an experiment was carried out to understand the flow of ozone gas (2.2 mg L⁻¹; 2 L min⁻¹) in a cylindrical PVC column filled with 4 kg of rice grains. The ozone gas concentration was monitored every 12 h, at a point immediately above the grains. The gas flow was modeled using the CFD technique. The parameters used to feed the model and adjust it to the experimental data were the mass transfer coefficient and ozone-rice grain reaction constant. Then, a simulation of ozone gas injection in a silo with a static capacity of 69.6 tons of rice was performed. In the ozone gas injection experiment, 100% of insect mortality was observed on the sixth day, when the O₃ concentration reached 0.1 mg L⁻¹. In this case, the mass transfer coefficient was 0.55 m s⁻¹, and the reaction constant was 0.78 s⁻¹. At the concentration of 0.8 mg L⁻¹, it is possible to treat 69.6 tons of rice grains within 9 days.     

Numerical simulation for heat transfer and velocity field characteristics of two-phase flow systems in axially rotating horizontal cans

Volume of fluid (VOF) element method coupled with a finite volume (FV) discretization technique was used to simulate two-dimensional, transient, two-phase flow patterns (air–water and air–food material) in an axially rotating horizontal can for rotational speeds of 10–160 rpm. Rotational Reynolds number ranged from 1700 to 27200 and 0.88 to 14.1 for water and food phases, respectively. FV solution was performed on a moving mesh system representing the can motion in on-axis axial rotation with respect to an inertial-fixed frame. Since the two-phase flow pattern prediction was an important aspect of modeling fluid mixing and improved heat transfer in canning process, reliable time- and spatially-dependent flow pattern maps were given to identify the rotational effects on two-phase flow characteristics and to determine flow patterns prevailing at different rotational speeds. Single-phase and food-phase flow computations with the corresponding flow patterns were also provided for a direct comparison with air–water results to further determine the physical limitations of the rotational effects. Numerical results demonstrated that two-phase flow patterns were significantly influenced by increasing rotational speeds leading to distinguishable flow patterns in terms of air–liquid (water/food material) interface characteristics and associated headspace air bubble movement through the liquid phase.     

气固分离称重料仓的设计与模拟分析

针对当前通用型称重料仓工艺烦琐和设备复杂的问题,以大豆为例,运用模块化集成设计理念,采用理论分析与仿真模拟相结合的方法,设计开发了一套集卸料器与料仓于一体的气固分离称重料仓。采用Solidworks三维建模软件将设备各部分构件建模,运用计算流体力学及离散项模型对气固分离称重料仓的关键结构进行分析。结果表明,设计的气固分离称重料仓在完成称重卸料的同时可分离轻杂,简化了称重卸料过程,新增的蝶阀模块可根据料仓内的物料量动态调整进出仓过程。综上,设计的气固分离称重料仓可用于气力输送大豆的称重卸料。     

基于数字图像处理技术糙出白率和碾白率检测

通过扫描获取不同碾白时间下的大米图像,提取大米图像信息,分析大米图像信息与糙出白率和碾白率之间的相关性。结果表明:B平均值同糙出白率、H平均值同碾白率的相关系数较高,分别为-0.984 6、-0.986 1;然后建立B平均值同糙出白率、H平均值同碾白率的回归方程,分别为y=-0.302 5x+135.733,R2=0.965 6;y=-0.132 9x+105.401,R2=0.968 9。用建立的回归方程预测糙米糙出白率和碾白率,通过F检验和t检验表明,预测的糙出白率和碾白率与实际检测值是一致的.     

Modelling non-Newtonian two-phase flow in conventional and helical-holding tubes

Summary The research described in this communication was undertaken to test the hypothesis that the fluid mechanics and heat-transfer aspects involved in aseptic processing could be modelled. In order to do this, a finite difference FORTRAN program (using the fourth-order, four-stage explicit Runge–Kutta method) was written by the authors to compute the velocity of fluid elements and particles during fully 3-dimensional flow in conventional and helical-holding tubes. The effect of particles on the fluid-flow field and the interaction between particles was taken into account during the modelling. Simulation results showed that an increase in specific gravity, tube diameter or coil diameter resulted in an increase in the residence time of the particles, while an increase in the flow rate decreased the residence time of the particles. An increase in the particle diameter or the flow rate narrowed the Residence Time Distribution (RTD) of the particles, while an increase in specific gravity or the tube diameter increased the RTD of the particles.     

基于PSO的BP-PID碾米机组控制系统优化

针对当前碾米机组之间流量稳定性差,单机效率低、碾白不均衡或过碾致碎米增加等问题,提出了基于粒子群算法(PSO)优化BP-PID控制的碾米机组控制系统;运用多机协同优化技术,通过调控在线碾米单机的碾除糠粉比例及其匹配的运行参数实现流量平衡控制;通过BP神经网络训练PID控制器的参数建立碾米机组调控数学模型,并引入PSO对BP神经网络的性能进行优化。仿真试验表明,经PSO优化的控制系统的响应速度更快,其稳态精度有所提高,且具有良好的控制效果。