A combined DEM–FEM numerical method for Shot Peening parameter optimisation

A numerical modelling approach capable of simulating Shot Peening (SP) processes of industrial interest was developed by combining the Discrete Element Method (DEM) with the Finite Element Method (FEM).In this approach, shot–shot and shot–target interactions as well as the overall shot flow were simulated efficiently using rigid body dynamics. A new algorithm to dynamically adapt the coefficient of restitution (CoR) for repeated impacts of shots on the same spot was implemented in the DEM code to take into account the effect of material hardening. Then, a parametric study was conducted using the Finite Element Method (FEM) to investigate the influence of the SP parameters on the development of residual stresses.Finally, a two-step coupling method is presented to combine the output of DEM simulation with FEM analyses to retrieve the Compressive Residual Stresses (CRS) after multiple impacts with the aim to evaluate the minimum area required to be modelled to realistically capture the field of residual stresses. A series of such coupled analyses were performed to determine the effect of peening angle and the combination of initial velocity and mass flow rate on CRS.     

配电网短路故障分析及其识别方法研究

分析了在不同中性点接地方式下单相接地和两相短路接地故障的相电压及中性点电压变化特征,结合三相短路和两相短路的故障特征,提出了完整的配电网短路故障识别方法。仿真结果表明,该方法具有采集的模拟量少、判据简单、运算简便的优点,具有一定的实用价值。     

基于UDDI的应用服务注册中心的设计

服务注册与发现技术是当前企业级应用集成系统研究的热点.基于统一表述、发现和集成(UDDI)协议的应用服务注册系统是面向服务软件体系结构的重要组件,其目的是促进企业间的服务资源共享,以及企业间跨越互联网的业务整合,UDDI协议包括服务注册系统程序接口规范和数据结构规范.应用服务注册系统采用.NET平台下的C#语言开发,适用于在线web服务交易.为了确保信息的可靠性,系统对UDDI协议作了扩展,提供了对将要发布的信息的审批机制和基于角色的用户管理.     

Synthesis of TiC/Ti–Cu composites by pressureless reactive infiltration of TiCu alloy into carbon preforms fabricated by 3D-printing

The microstructure of dense TiC/Ti–Cu composites fabricated by pressureless infiltration of TiCu alloy into porous starch derived carbon preform produced by 3D-printing has been studied. The reactive melt infiltration was carried out at 1100 °C in a flowing Ar atmosphere and resulted in formation of a composite comprised predominantly of substoichiometric TiC_x (x=0.78), binary intermetallic Ti–Cu phases and residual carbon. SEM analyses revealed a microstructure consisting of a dispersed fine-grained TiC_0.78 (∼7 μm) in a Ti–Cu matrix.     

Colloidal stability of surfactant-free radiation curable polyurethane dispersions

Radiation-curable polyurethane dispersions (UV-PUDs) are colloidal dispersions whose stability is mainly ensured by the electrostatic repulsion between the negatively charged polymer particles. In this article, particle stabilization is presented in terms of the physico-chemical characteristics of the polymer dispersion and its microstructure. The phenomenon of the colloidal destabilization at higher temperature is studied by multiple light scattering, then correlated with the evolution of the particle size distributions and the measurement of the apparent critical coagulation concentration of a salt as an indication of the energy barrier at the surface of the particles. The investigation of selected chemical parameters of the polymer on the colloidal stability aims to identify the most relevant ones with an understanding of the underlying mechanism. The study underlines that UV-PUDs constitute a waterborne polymer family with its own identity, adding complexity to the traditional radiation curing chemistry. Finally, it highlights the new perspectives offered for novel environmental-friendly products with high-end performance and extended stability and robustness.     

Delamination study of through-thickness reinforced composite laminates via two-phase interface model

A technique to enhance the strength of the composite laminates in the thickness direction consists in inserting through-thickness reinforcement, by which the potential delamination crack faces are bridged in order to increase the interlaminar fracture strength. In this paper, the composite delamination is analyzed in the context of non-linear fracture mechanics making use of the interface concept. The presence of the reinforcement fibres provides an anisotropic elastic and post-elastic mechanical response, which herein is described by an original two-phase interface model. The two phases, namely the adhesive joint (or matrix of the composite) and the reinforcement, are characterized by their own constitutive laws and coupled at the equilibrium level.     

Experimental measurements of the effective thermal conductivity of a lithium titanate (Li2TiO3) pebbles-packed bed

Tritium breeding materials, which have the ability to react with neutrons and produce tritium, are required to fuel fusion reactions. Tritium is produced inside the fusion blanket by neutron irradiation of lithium ceramics (tritium breeders). Using the lithium ceramics in form of pebbles-packed bed is a promising concept for fusion blankets, and worldwide efforts have been dedicated to its R&D. Thermal properties of lithium ceramic pebble beds have a significant impact upon the thermal performance of the fusion blanket. Specifically, the effective thermal conductivity of lithium ceramic pebble beds is important for the design and analysis of fusion blankets. The experimental apparatus of this study was designed and built based on the principles of the steady state and axial heat flow methods in order to conduct the required measurements. The objective of this study is to measure the effective thermal conductivity of a Li₂TiO₃ pebble bed as a function of the average bed temperature. The pebble bed has pebbles of 1.7–2.0 mm diameter and a packing fraction of 61%. Helium at atmospheric pressure was used as a filling gas. The experimental results showed that the effective thermal conductivity decreased from 1.40 to 0.94 W/m K with the increase of the average bed temperature from 50 to 500 °C. The results presented in this work will help to create a database of the effective thermal conductivity of Li₂TiO₃ pebble beds which can be used for the design and analysis of fusion blankets.     

蜜蜂进化型遗传算法在水库优化调度中的应用

提出了一种基于蜜蜂进化型遗传算法的水库优化调度问题的求解方法,并通过实例对蜜蜂进化型遗传算法和标准遗传算法的性能做了比较.结果表明,在进化代数相同的条件下,由于蜜蜂进化型遗传算法在配种选择算子上使用种群的最优个体作为蜂王,提高了种群收敛速度;再者,在代进化过程中引入一个随机种群,保持了群体的多样性,提高了算法的勘测能力.     

鸡羽毛角蛋白助剂的制备及其对羊毛毡缩性能的影响

利用氢氧化钠破坏羽毛角蛋白质的空间结构，使其水解，制备成可溶性蛋白质，并利用角蛋白助刑改善羊毛的毡缩性能．优选出了最佳水解工艺条件，即氢氧化钠7．5g／L，尿素6g／L，80℃溶解2．5h，固液比1：20．结果表明，角蛋白助剂结合等离子体处理能提高羊毛的防毡缩性．     

基于偏最小二乘回归与神经网络耦合的岩溶泉预报模型

本文将偏最小二乘回归与神经网络耦合，建立了泉流量预报模型。利用偏最小二乘法对影响岩溶泉流量的诸多因素进行分析，提取对因变量影响强的成分，从而克服了变量之间的多重相关性问题，降低了神经网络的输入维数。同时，利用神经网络建模可以较好地解决非线性问题。实例表明，本耦合模型的拟合和预报精度均优于独立使用偏最小二乘回归或神经网络建模的精度。