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.     

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     

锯齿型螺旋翅片管束传热与阻力性能的分析研究

对气流横掠锯齿型螺旋翅片管管束的对流传热进行了试验研究，并通过了工业试验验证，得出了相应的传热和阻力系数的数学关联式，可供设计计算使用。     

Supramolecular Nanofibers from Collagen-Mimetic Peptides Bearing Various Aromatic Groups at N-Termini via Hierarchical Self-Assembly

Self-assembly of artificial peptides has been widely studied for constructing nanostructured materials, with numerous potential applications in the nanobiotechnology field. Herein, we report the synthesis and hierarchical self-assembly of collagen-mimetic peptides (CMPs) bearing various aromatic groups at the N-termini, including 2-naphthyl, 1-naphtyl, anthracenyl, and pyrenyl groups, into nanofibers. The CMPs (R-(GPO)_n: n > 4) formed a triple helix structure in water at 4 °C, as confirmed via CD analyses, and their conformations were more stable with increasing hydrophobicity of the terminal aromatic group and peptide chain length. The resulting pre-organized triple helical CMPs showed diverse self-assembly into highly ordered nanofibers, reflecting their slight differences in hydrophobic/hydrophilic balance and configuration of aromatic templates. TEM analysis demonstrated that 2Np-CMP_n (n = 6 and 7) and Py-CMP₆ provided well-developed natural collagen-like nanofibers and An-CMP_n (n = 5–7) self-assembled into rod-like micelle fibers. On the other hand, 2Np-CMP₅ and 1Np-CMP₆ were unable to form nanofibers under the same conditions. Furthermore, the Py-CMP₆ nanofiber was found to encapsulate a guest hydrophobic molecule, Nile red, and exhibited unique emission behavior based on the specific nanostructure. In addition to the ability of CMPs to bind small molecules, their controlled self-assembly enables their versatile utilization in drug delivery and wavelength-conversion nanomaterials.     

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。