Event driven algorithms applied to a high energy ball mill simulation

In the physics community, event driven molecular dynamics simulations have been successfully applied to typical physical topics, such as granular gases. In contrast, in the engineering sciences, event driven algorithms have not become as popular, even though they can be far more efficient for special systems. In this paper, we present an event driven simulation of a high energy ball mill, where the motion and energy transfer of the grinding balls during operation are simulated. Stable numerical algorithms for collision detection and collision response are developed and several possible pitfalls are discussed. Furthermore, an improved event list handling technique and a specialized space subdivision method is presented. The performance of the partitioning is demonstrated by experiments. It is shown that the scaling rules usually applied are oversimplified. A new way of scaling the process parameters to obtain a higher production yield using iso-impact diagrams is presented.     

An Experimental Investigation on the Fabrication and Testing of Mechanical Properties of Aluminum-Silica Gel Metal Matrix Composite

A metal matrix composite (MMC) was fabricated using Al as the base metal which was reinforced by a ceramic material silica gel. This article shows detail fabrication stages in the production of MMC. The properties were considered with regard to the saturation point of the reinforcement of silica gel into the metal matrix of Al-Si alloy which was found out experimentally. Here the improvement of the mechanical properties of Al-silica gel MMC composite were studied with respect to that of pure Al-Si alloy. Different tests were conducted to show the results. Conventional ingot metallurgy with infiltration technique using vortex method had been employed in the fabrication process. The test results show that there are improvements by 17.14%, 13.46%, 11.48%, and 18.18% on compressive strength, impact strength, Brinell hardness value, and Rockwell hardness no respectively of Al-silica gel MMC over the pure Al-Si alloy.     

Screw dislocations interacting with a partially debonded interface in cylindrically anisotropic composites

Interaction between screw dislocations and a partially debonded interface in cylindrically anisotropic composites subjected to uniform stress at infinity is investigated in this paper. Using Muskhelishvili’s complex variable method, the closed forms of complex potentials are obtained for a screw dislocation and a screw dislocation dipole located inside either matrix or inhomogeneity. Explicit expressions of stress intensity factors at the crack tips, image forces and image torques acting on dislocation or the center of dipole are provided. The results show that the crack and dislocation geometry combination plays an important role in the interaction between screw dislocations and interface crack. Furthermore, it is found that the anisotropy of solids may change the shielding and anti-shielding effects arising from screw dislocations and the equilibrium position of screw dislocations. The presented solutions are valid for anisotropic, orthotropic or isotropic composites and can be reduced to some novel or previously known results.     

Automatic Detection of Steel Bali＇s Surface Flaws Based on Image Processing

A new method to detect steel bali＇s surface flaws is presented based on computer techniques of image processing and pattern recognition. The steel bali＇s surface flaws is the primary factor causing bearing failure. The high efficient and precision detections for the surface flaws of steel ball can be conducted by the presented method, including spot, abrasion, burn, scratch and crack, etc. The design of main components of the detecting system is described in detail including auto-matic feeding mechanism, automatic spreading mechanism of steel ball＇ s surface, optical system of microscope, image acquisition system, image processing system. The whole automatic system is controlled by an industrial control computer, which can carry out the recognition of flaws of steel bali＇s surface effectively.     

模糊最小包含球支持向量机

为提高支持向量机的模式分类性能,综合模糊支持向量机和球形支持向量机等方法,提出一种模糊最小包含球(FMEB)支持向量机,对于模式分类问题,通过引入模糊隶属度,寻找2个分别包含二类模式的同心最小包含球,使类间间隔最大化,同时二类模式类内分布最小化,从而增强泛化性和鲁棒性。实验结果证明FMEB的模式分类性能优于其他方法。     

基于逆向解耦的球磨机系统的PID控制

球磨机系统是一个典型的多变量大时延非线性系统,各个控制量间存在严重的耦合,所以直接对其进行PID控制有些困难.针对上述问题,先利用逆向解耦构造出逆向解耦控制器,将原系统分解成两个单入单出的系统.然后利用基于内模控制的PID控制器参数整定的方法,可以直接获得PID控制器的各个参数,并且在模型失配的情况下进行了仿真研究.结果表明:逆向解耦简便实用,较传统解耦有一定优越性,所整定的PID参数有良好的调节品质,且具有很强的鲁棒性.     

中储式钢球磨制粉系统节能及智能控制方法

本文针对巴陵石化热电事业部9号炉中储式钢球磨制粉系统的特点,采用神经网络技术建立制粉系统的运行工况模型,并通过非线性优化技术确定使制粉单耗最低的运行参数;在此基础上,采用模仿人操作行为的智能控制技术对整个制粉系统进行自动控制,确保制粉系统运行在最佳的工况上。实际应用表明,通过对制粉系统的智能控制,对降低磨制粉单耗和锅炉飞灰含碳量,提高煤粉均匀性指数,有良好效果。     

Exothermic reaction characteristics of continuously ball-milled Al/Ni powder compacts

Self-propagating reactions in compacted pellets of continuously low-energy ball-milled aluminium (Al) and nickel (Ni) powders at a composition corresponding to AlNi₃ were investigated. The formation of a bi-modal structure with nanoscale lamellae of Al and Ni surrounding thicker Ni layers was observed. The milled powder sizes decreased for milling durations longer than 4 h, but the pellet green densities remained mostly constant for longer than 2 h of milling. The ignited pellets observed using high-speed optical and infrared imaging revealed that the thermal wave velocity, maximum reaction temperature, ignition initiation duration and ignition temperature decreased with increasing milling times due to solid-state diffusion. X-Ray Diffraction (XRD) analysis after ignition tests showed that the AlNi₃ amount increased with milling time. Thermal analysis using interrupted Differential Scanning Calorimetry (DSC) in combination with XRD revealed that the ball-milled pellets have similarities to nanoscale magnetron sputtered multilayer foils in terms of phase formation sequence and exothermic peak shifts.     

Characterization of Se88Te12 nanostructured chalcogenide prepared by ball milling

The present work deals with the structural and optical studies of Se₈₈Te₁₂ chalcogenide nanoparticles prepared by ball milling. Polycrystalline Se₈₈Te₁₂ chalcogenide prepared by melt quenching was used as a starting material. The ball milling was performed in a Laboratory 8000 M-Mixer/Mill (SPEX) mill using hardened steel balls and a vial with a ball-to-powder weight ratio of 10:1. After various times of milling, a small amount of material was taken from the container to be characterized by Transmission Electron Microscopy and optical measurements in thin film form within the wavelength region 400-1000 nm. Optical absorption measurements indicate that the absorption mechanism is due to direct transition. It has been observed that the optical band gap increases with the increase of milling time. The results are interpreted in terms of the change in concentration of localized states due to the shift in Fermi level.     

基于螺旋理论的Delta并联机器人自由度分析

螺旋理论以其几何概念清楚,物理意义明确,表达形式简单等优势,常被用于分析机构的自由度。按照传统的G-K(Grubler-Kutzbach)公式,能较容易地计算出串联机构的自由度,而对于一些特殊机构,尤其是含有闭环子链的复杂并联机构,往往无法便捷、正确地求解其自由度。为解决以上问题,以一种拓扑结构为[3-R(4S)1-RUPU]+R型的Delta并联机器人为研究对象,对其4S闭环子链进行了等效运动副螺旋系的求解,并判别了机构的局部自由度以及公共约束;利用修正的G-K公式,分别对原机构和等效后的机构进行了自由度的验证。结果表明:两种情形下的自由度数均为4,且自由度的性质为3平移1旋转,与实际设计相符。