Impact of shape representation schemes used in discrete element modelling of particle packing

In different computer models, shape is represented using different methodologies, to varying degrees of precision. This paper examines two approaches to shape representation, and their effects on accuracy in the context of cylindrical particle packing. Two discrete element method (DEM) based software packages are used. A X-ray CT scan of a packed bed provides the experimental measurements for comparison. Eight sphere-composite representations of the same cylindrical pellet were tested. Two of these gave results that quantitatively follow experimental measurements. A range of factors that in theory could affect accuracy of the simulation results are examined, including edge roundedness, surface roughness and restitutional behaviour as a function of sphere-composite representations. The conclusion is that, for packing at least, matching the object's overall shape and dimensions is not enough. Only when a high enough resolution is applied to corners and edges, could the sphere-composite approach possibly match the experimental data quantitatively.     

Constructing developable surfaces by wrapping cones and cylinders

We model developable surfaces by wrapping a planar figure around cones and cylinders. Complicated developables can be constructed by successive mappings using cones and cylinders of different sizes and shapes. We also propose an intuitive control mechanism, which allows a user to select an arbitrary point on the planar figure and move it to a new position. Numerical techniques are then used to find a cone or cylinder that produces the required mapping. Several examples demonstrate the effectiveness of our technique.     

二级剪叉式液压升降机液压缸布置方式研究

分析了二级剪叉式液压升降机的三种主要布置方式,以及液压缸倾斜布置时的三种液压缸安装位置方案。对于其中的一种方案,应用虚位移原理计算求解液压缸推力,并以液压缸推力最小为目标建立优化设计数学模型,通过MATLAB软件得到液压缸推力最小时的液压缸安装位置。通过研究液压缸布置方式,提高了二级剪叉式液压升降机的设计效率和传动质量。     

碳纤维缠绕复合材料在潜水外压容器上的应用

在铝合金圆筒体外以浸渍树脂碳纤维进行缠绕复合增强，增强后的筒体耐静水外压能力大幅度提高；整体缠绕的全复合材料筒体，在耐静水外压能力及减轻自身重量方面也获得了明显的效果。此外，在铝合金细长圆管的外壁复合缠绕碳纤维，能有效地提高圆管对轴向压载荷的抗失稳与抗屈曲破坏能力。     

日产PD6型柴油机气缸穴蚀原因浅析及对策

本文分析日产车用PDG型柴油机的结构特点及其缸套穴蚀的形成原因、危害和检查与判断方法,并提出在使用中应采取的预防措施。     

Heat induced transition of a stable vortex street

A combined numerical and experimental investigation is presented showing the effect of heat on the stability of a horizontal vortex street for Re_D=75 and Ri_D between 1 and 2. Detailed 2D-HiRes PV experiments are compared with 2D numerical results. The results show that an early transition to 3D of the vortex street takes place for Ri_D>1. Furthermore, the location at which the 2D wake becomes essentially 3D turns out to be dependent on Ri_D. For an increasing addition of heat (increasing Ri_D), this location is shifted into the direction of the cylinder. By applying 3D measuring techniques, such as 3D-PTV and 3D visualisation techniques, the transition process and the behaviour downstream of the transition point are investigated.     

建议气瓶充装前增加气瓶音响检查项目

高压无缝钢瓶的充装前检查 ,在现有的标准或规程中是没有音响检查这一项内容的 ,只有在气瓶定期检验时 ,根据国家标准GB 130 0 4— 1999《钢质无缝气瓶定期检验与评定》中有音响检查的要求 ,但气瓶定期检验周期为二至五年。有关资料表明 ,当氧气瓶中进入海水或其他腐蚀物 ,则该瓶使用半年至一年后 ,瓶体被腐蚀处的剩余壁厚不到 2mm ,这样的气瓶如混入充装站 ,在充装过程中就很有可能发生事故。所以 ,只在气瓶定期检验中才进行一次音响检查 ,已经不能满足气瓶充装安全生产的需要。气瓶充装前的音响检查 ,可引用GB 130 0 4—1999《钢质无缝…     

两个同心施转圆柱间的Taylor问题

本文推导了在修正双极坐标系下的Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程和讨论了它的基本流的扰动解     

一种发动机气缸体气孔缺陷分析及改进

以一种发动机气缸体气孔缺陷问题为例,通过合理优化浇注系统,更改局部结构,提高排气能力等方面提出解决思路,最终将气缸体的气孔缺陷率降至较低水平。     

CY4102BZQ柴油机机体模态分析

以东风朝阳柴油机厂最新开发的CY4102BZQ柴油机机体为研究对象，利用Pro／E三维软件和I-DEAS有限元软件建立了结构的实体模型和有限元模型，进行了机体的模态分析计算，获得了机体的基本振型和相关频率。应用模态试验验证了模型的精确程度，从而提出合理的改进方案。