A numerical model to predict the powder–binder separation during micro-powder injection molding

The micro-powder injection molding (micro-PIM) process has the potential to bridge the gap between the design and manufacturing of micro-components that are often used in small and handy devices. Numerical modeling helps to analyze and overcome various difficulties of micro-PIM. In the present work, a numerical model is developed to predict the powder–binder separation (a common defect in PIM and especially severe in micro-PIM) during the injection of an alumina feedstock. A powder–binder separation criterion is proposed dealing with applied injection pressure and friction force between the powder and binder. An indirect comparison of feedstock travel time between two locations is used to validate the model. The predicted segregation from the simulated result is supported by a qualitative experimental measurement. The developed model can be used to optimize injection parameters to get a defect-free product.     

Micron-sized silica mesh for enhancing the performance of quantum dot sensitized solar cells

Three dimensional silica mesh structures are prepared through a new and simple method for enhancing the quantum dot sensitized solar cells performance and stability.Silica patterns are made on the top of the TiO₂ photoanodes and a marked improvement in light scattering properties of meshed structures is confirmed by diffuse reflectance spectroscopy measurements. This improvement enhances the current density and consequently the cells ‘efficiency. Parameters of electron transport in cells are explored by electrochemical impedance spectroscopy (EIS). According to the EIS results, silica mesh declines the recombination rate in cells in a clear way. Here more than 50% efficiency improvement is obtained in meshed structures in comparison to cells with normal TiO₂ photoanode structures. The insulated silica mesh, reduces the electrolyte's deleterious effect on the semiconductor layers and the cells’ stability is improved.     

基于虚拟现实的复杂场景加载优化算法

目前大规模场景模型生成的需求量日益增加, 现提出了一种基于区域的自动 LOD (Levels Of Details)构建算法. 该算法基于动态网格简化算法, 在游戏设计制作的过程中, 游戏开发人员会经常需要对美工部门人员提供的模型进行优化. 为了可以使模型的面数得到简化, 并且不改变模型的外观. 当今流行的 LOD技术非常擅于处理这种情况, 判断模型与摄像机的距离如果超过一定范围之后, 自动调取不同层次的模型, 当模型距离摄像机很远的情况下使用面数低的模型替换高模, 这样可以提高帧率并且降低摄像机前的三角面以及顶点数从而减少渲染压力. 一般模型的简化分为静态和动态模型的简化.大部分情况下, 程序员会让美工部门提供几套不同面数的模型或者通过模型简化工具对高模进行减面并存成多个Mesh, 并在程序运行的时候, 根据模型与摄像机的距离远近动态的替换Mesh. 这是一种静态的方法.这里将尝试使用一种动态的网格简化和LOD技术相结合的方法. 这种新型算法的大大的简化了操作流程, 美术人员只需要提供一个模型, 程序员可以使用这种方法生成量级不同的低模, 根据摄像机与模型的远近自动的调取不同精度的模型.     

高强不锈钢绞线网与ECC黏结-滑移关系模型

高强不锈钢绞线网与ECC的黏结是二者协同工作的基础，且黏结 滑移关系模型是其黏结性能的综合反映，故通过对17组51个高强不锈钢绞网增强ECC薄板试件进行单边拉拔试验，研究横向钢绞线间距、纵向钢绞线直径和相对锚固长度等因素对钢绞线网在ECC中黏结性能的影响规律。试验结果表明，横向钢绞线的设置可使黏结破坏由脆性破坏转变为延性破坏；高强不锈钢绞线网与ECC的黏结滑移曲线可分为5个阶段，分别为上升段、微降段、延性强化段、下降段和残余段。基于试验结果，对钢绞线网在ECC中的黏结破坏特征和黏结 滑移机理进行分析，在相关黏结-滑移关系模型的基础上，提出钢绞线网与ECC的黏结 滑移关系模型，并进行模型参数分析。所提模型及模型参数计算公式与试验结果吻合良好，能较好地反映钢绞线网与ECC的界面黏结滑移特征。     

Performance analysis of large-scale MIMO system for wireless backhaul network

In this paper, we present a performance analysis of large-scale multi-input multi-output (MIMO) systems for wireless backhaul networks. We focus on fully connected N nodes in a wireless meshed and multi-hop network topology. We also consider a large number of antennas at both the receiver and transmitter. We investigate the transmission schemes to support fully connected N nodes for half-duplex and full-duplex transmission, analyze the achievable ergodic sum rate among N nodes, and propose a closed-form expression of the achievable ergodic sum rate for each scheme. Furthermore, we present numerical evaluation results and compare the resuts with closed-form expressions.     

The effect of fabric structure on the bursting characteristics of warp-knitted surgical mesh

Abstract

Surgical mesh is a porous fabric that is mainly produced from polymeric monofilaments using the warp-knitting method. Surgical mesh is used for healing hernia. Among the mechanical properties of the mesh, tensile and bursting strength have special significance. In this research, warp-knitted surgical meshes with five structures have been produced using polypropylene monofilament, and the effect of the fabric structure on the bursting characteristics of them has been investigated. All the meshes exhibited supraphysiologic bursting strength. quasi-Sandfly mesh demonstrated the highest, while quasi-Marqussite mesh exhibited the least bursting characteristics. The increase in the bursting characteristics of the meshes is attributed to the increase in the areal density and decrease in the porosity of them. Moreover, conformity between the bursting and tensile properties of them in bias direction has been observed. Overall, quasi-Marqussite mesh was proposed as the most desirable mesh in terms of porosity, weight, and bursting characteristics.     

某型发动机自反馈调节阀动态仿真分析

基于FLUENT软件提供的计算方法和物理模型，利用动网格技术及用户自定义函数（User-define Function，UDF），对发动机预燃室调节阀的自反馈调节过程进行动态数值模拟，并分析阻尼参数对调节效果的影响。结果表明：自反馈机构可实现对不同压力扰动的及时响应，具有稳定流量的效果，改变阻尼参数可对调节响应速度和流量稳定性进行优化，其中摩擦力对调节影响最显著。     

纤维金属层板铆接剩余强度影响因素研究

为研究单搭铆接接头中纤维金属层板耦合损伤行为，运用金属硬化Johnson-Cook失效准则、纤维增强复合材料三维Hashin损伤准则、脱层B-K失效理论以及刚度退化失效准则建立了纤维金属层板铆接渐进失效模型，并结合实验验证了模型的合理性。考察了单搭铆接二次弯曲效应、层板铝合金体积分数、预紧力、层板孔边距对纤维金属层板铆接强度和失效模式的影响，为提高纤维金属层板铆接剩余强度提供可靠建议。分析结果表明：二次弯曲效应加速损伤发生，从而降低层板铆接强度，其中偏心加载可以削弱二次弯曲效应，更好地提高铆接强度；层板铝合金体积分数的增大能够提高层板铆接强度，但当体积分数大于50%时层板铆接比刚度和比强度反而下降；预紧力的增加能够提高层板铆接强度和增强层板损伤抗力；随着孔边距的递增，铆接剩余强度有所提高，破坏模式由灾难性拉断失效模式逐渐转化为理想的挤压失效模式，但当孔边距达到一定数值时，铆接强度不再明显提高，而失效模式也维持为挤压破坏。     

基于网格曲面形状修改的柔性件装配偏差分析

柔性件装配偏差有限元分析方法中的敏感度矩阵来源于产品的理论数学模型，而理论数学模型与实际模型之间存在一定的外形差异，会产生很大的分析误差。针对该问题，提出了一种装配偏差分析的改进方法，即根据产品理论外形和误差源数据，运用网格曲面变形方法获取逼近零件实际形状的数学模型，代替理论数学模型进行装配偏差分析。开展了金属薄板的装配回弹试验以及飞机壁板件的装配偏差分析计算，使用仿真、试验及测量等手段获取了各类偏差分析结果，并进行比较。数据表明，装配偏差分析误差可减小到5%以内。     

网状结构织物制备与应用研究进展

为深入拓展网状结构织物在实际工程中的应用,分别介绍了近年来机织网状结构织物、针织网状结构织物和编织网状结构织物的应用基础和制备方法。从纤维原材料、织物组织结构和织物后整理方面重点阐述了网状结构织物的力学性能和仿真模拟的研究进展。针对网状结构织物应用领域的不断扩大,进一步探索了网状结构织物的力学性能,增强网状结构织物的动态模拟,提高网类材料的使用寿命、减少能耗,以使网状结构织物的性能和使用效果逐渐提升。结合当前科技发展趋势,预测网状结构织物将会在海洋、建筑、航空航天等领域方向有更深入的发展,期望为网状结构织物产品的研发提供参考。