Uncharted islands of chatter instability in milling

This paper provides conclusive evidence that isolated islands of chatter vibration can exist in milling processes. Investigations show these islands are induced by the tool helix angle and act to separate regions of period-doubling and quasi-periodic behavior. Modeling efforts develop an analytical force model with three piecewise continuous regions of cutting that describe helix angle tools. Theoretical results examine the asymptotic stability trends for several different radial immersions and helix angles. In addition, new results are shown through the implementation of a temporal finite element analysis approach for delay equations written in the form of a state space model. Predictions are validated by a series of experimental tests that confirm the isolated island phenomenon.     

盾构施工前向地质探测技术及系统方案设计

将探地雷达应用于直径为6.34 m的法国FCB(Fives Cail Babcock)盾构前向探测中,通过对刀盘进行机械改造以及采用无线和有线联合传输信息的方式,盾尾控制室可实时获取挖掘面前方地质图像。根据各种典型地质类型、障碍物及其相应的雷达图像建立盾构前向探测分析系统,通过分析当前施工地质的雷达图像,实现对挖掘面前方地质状况的解释和识别,为安全准确地进行盾构施工提供依据。理论分析和试验表明,利用该前向探测技术实现地质的超前探测是完全可行的,具有一定的创新性和工程应用价值。     

实体单元焊点模型在前纵梁碰撞仿真中的应用

为了提高碰撞仿真中汽车前纵梁焊点的模拟精度,应用LS-DYNA软件,建立了壳单元模拟母材、单个实体单元模拟焊核和热影响区的焊点模型。母材材料特性及焊点失效参数分别通过板材拉伸试验及焊点杯形拉伸试验获得。采用数值KSⅡ试验对该焊点模型在母材网格不同偏置情况下的内力进行了研究。基于经验证的纵梁有限元模型对前纵梁碰撞进行了仿...     

The reduction of NO with H2 over Ru/MgO

Ruthenium supported on magnesia was found to be a highly active and selective catalyst for the reduction of NO to N₂ with H₂. The adsorption of NO on Ru/MgO was studied at room temperature by applying frontal chromatography with a mixture of 2610 ppm NO in He. Subsequently, temperature‐programmed desorption (TPD) and temperature‐programmed surface reaction (TPSR) experiments in H₂ were performed. The adsorption of NO was observed to occur partly dissociatively as indicated by the formation of molecular nitrogen. The TPD spectrum exhibited a minor NO peak at 340 K indicating additional molecular adsorption of NO during the exposure to NO at room temperature, and two N₂ peaks at 480 K and 625 K, respectively. The latter data are in good agreement with previous results with Ru(0001) single‐crystal samples, where the interaction with NH₃ was found to lead to two N₂ thermal desorption states with a maximum coverage of atomic nitrogen of about 0.38. Heating up the catalyst after saturation with NO at room temperature in a H₂ atmosphere revealed the self‐accelerated formation of NH₃ after partial desorption of N₂, whereby sites for reaction with H₂ become available. As a consequence, the observed high selectivity towards N₂ under steady‐state reduction conditions is ascribed to the presence of a saturated N+O coadsorbate layer resulting in an enhanced rate of N₂ desorption from this layer and a very low steady‐state coverage of atomic hydrogen. The formation of H₂O by reduction of adsorbed atomic oxygen is the slow step of the overall reaction which determines the minimum temperature required for full conversion of NO. This revised version was published online in July 2006 with corrections to the Cover Date.     

A multi-frontal parallel algorithm for coupled thermo–hydro–mechanical analysis of deforming porous media

In this paper, a multi-frontal parallel algorithm is developed to solve fully coupled heat, water and gas flow in deformable porous media. The mathematical model makes use of the modified effective stress concept together with the capillary pressure relationship and takes phase change and latent heat transfer into account. The chosen macroscopic field variables are displacement, capillary pressure, gas pressure and temperature. The parallel program is developed on a cluster of workstations. The PVM (Parallel Virtual Machine) system is used to handle communications among networked workstations. The multi-frontal method has advantages such as numbering of the finite element mesh in an arbitrary manner, simple programming organization, smaller core requirements and shorter computation times. An implementation of this parallel method on workstations is discussed. The speedup and efficiency of this method is demonstrated and compared with a general domain decomposition method based on band matrix methods by numerical examples. © 1998 John Wiley & Sons, Ltd.     

Polymer blends by self-propagating frontal polymerization

The use of self-propagating frontal polymerization to produce polymer blends has been investigated. A homogeneous solution of monomer, polymer (of a second monomer), and initiator is initially heated at a specific location to start a polymerization front that propagates along the system. The obtained polymerization reaction is very fast compared with diffusion, so that the two types of macromolecules remain homogeneously distributed, as in the original monomer/polymer solution. In the case of two incompatible polymers, the system has no time to reach the equilibrium condition where phase separation occurs and a polymer blend is obtained in the form of a metastable solution. Applications to two incompatible pairs (methyl methacrylate-styrene and methyl methacrylate-methacrylic acid) are discussed. Moreover, it has been found that the presence of inert polymer in the initial mixture improves the process performance, leading to more stable propagation fronts, lower front temperatures, and higher monomer conversions. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2695–2702, 1998     

引水式电站恒前池水位控制系统的稳定分析

根据引水式电站恒前池水位控制系统的控制原理和相应的水力联系,建立了弹性水击情况下的水轮机调节系统的数学模型,对该调节系统进行了稳定分析,求出了连续系统和离散系统的稳定边界方程,分析比较了连续系统和离散系统的稳定域以及调节对象主要参数对调节系统稳定域的影响.