砖混历史建筑改造中的自支撑施工方法

针对砖混历史建筑改造中经常需要拆除木楼面代之以钢筋混凝土楼面,而拆除木楼板、木梁等构件后既有墙体可能会产生因失去侧向支撑而失稳或在风荷载作用下破坏的问题,通过合理安排拆除木楼面的次序,实现用拟拆除的木楼面及屋盖作为墙体在施工期间的水平支撑,保证墙体在施工过程中的安全,在施工到楼板位置时将其拆除,保证墙体的安全,减小施工成本,提高经济效益.     

一类排队服务系统的最优控制策略研究

建立一个双阈值排队服务模型, 用来协调顾客的等待时间和服务系统的运行成本. 采用一种精细的概率分解方法获得瞬态和稳态队长的概率分布性质; 再根据系统稳态性能指标, 建立系统营运利润函数, 并设计一种针对双离散变量函数的全局优化收索算法来研究最优控制策略; 进一步的数值实验揭示出双重阈值策略的优越性.     

65米射电望远镜副面调整系统姿态精度监测与回零策略

上海天文台65米射电望远镜的副面调整机构为Stewart型并联机器人,为了及时发现该并联机器人因机械磨损或误差累积造成的精度下降问题,使用倾角传感器对并联机器人动平台姿态进行检测,求得动平台姿念均方根误差并将其与设计指标进行比较,从而用户可以判断是否需要进行维修或回零操作.为了提高并联机器人的易维护性,设计了光电传感器回零和磁尺(磁致伸缩位移传感器)回零两种回零方式,分析了两种回零方式以及通过回零操作对光电传感器和磁尺精度进行检测的原理.总结了该并联机器人需要进行回零操作的不同状况,并给出了相应的回零控制策略.实验证明本文提出的回零控制策略是解决并联机器人回零问题的一种有效方法.     

The effect of partial substitution of Ti with Zr, Cr or V in the Mg35Ti10Ni55 electrode alloy on its electrochemical performance

In this paper, Zr, Cr and V were selected as the partial substitution elements for Ti to form Mg₃₅Ti₅M₅Ni₅₅ quaternary alloys prepared by means of mechanical alloying on the basis of the ternary Mg₃₅Ti₁₀Ni₅₅ electrode alloy previously studied by the authors. It is found that all the three quaternary alloys possess an amorphous main phase and exhibit improved cycling stability than the original ternary Mg₃₅Ti₁₀Ni₅₅. The Zr-substituted alloy has also a higher discharge capacity. X-ray photoelectron spectroscopy (XPS) surface analysis reveals that on the surface of each alloy a multi-component oxide composite film is formed, which is more compact and corrosion resistant than the Mg(OH)₂ film and the (TiO₂)_x(NiO)_y(Mg(OH)₂)_z composite films reported previously. Auger electron spectroscopy (AES) analysis shows that the substituting elements tend to reduce the thickness of the passivation films. The thickness of composite oxide film on the alloys is in the following order: Mg₃₅Ti₁₀Ni₅₅>Mg₃₅Ti₅V₅Ni₅₅>Mg₃₅Ti₅Zr₅Ni₅₅>Mg₃₅Ti₅Cr₅Ni₅₅. The result agrees well with that of the polarization resistances (R_P) values obtained from the electrochemical impedance spectroscopy (EIS) Nyquist diagrams. It demonstrates that the thicker the passivation film is, the higher the R_P is and the more difficultly the charge transfer reaction proceeds. Anodic polarization curves indicate that the addition of Cr and Zr decreases effectively the corrosion current. However, the corrosion of the electrode alloys in the electrolyte is still high and proceeds constantly as the corrosion current remains almost constant during further cycles.     

X65管线钢裂纹分析

某热轧厂近期生产的X65管线钢在用户使用过程中出现较严重的横向裂纹,为此,通过对X65管线钢的金相组织观察和强度、延伸率、冲击韧性测试,分析了该钢组织结构和性能。结果表明,微观组织无明显偏析,连铸工艺参数选择不当是X65出现裂纹的主要原因。     

Multiresolution Visualization of Higher Order Adaptive Finite Element Simulations

h –p–adaptive projection with respect to any prescribed threshold value for the visual error. This projection can then be processed by various local rendering methods, e.g. color coding of data or isosurface extraction. Especially for color coding purposes modern texture capabilities are used to directly render higher polynomial data by superposition of polynomial basis function textures and final color look-up tables. Numerical experiments from CFD clearly demonstrate the applicability and efficiency of our approach. Received September 25, 2001; revised March 31, 2003 Published online: May 26, 2003 The authors acknowledge the valuable hints of the anonymous referees.     

烟气脱硫系统配置的优化

为降低烟气脱硫系统投资和运行消耗，依据烟气脱硫系统技术和现代设计技术的最新发展，结合扬州发电厂200MW机组烟气脱硫工程，提出根据目标对象特点运用优化设计、可靠性工程进行烟气脱硫系统配置优化的方法，在经济性和可靠性2个方面给出符合烟气脱硫系统固有特点的分析计算模型，据此模型可构筑基于精确定量分析的烟气脱硫设计平台，达到合理地配置烟气脱硫系数，以最低的投资和运行消耗实现系统目标。     

Numerical integration of singular integrands using low-discrepancy sequences

We investigate quasi-Monte Carlo integration for functions on thes-dimensional unit cube having point singularities. Error bounds are proved and the theoretical results are verified by computations using Halton, Sobol’ and Niederreiter sequences. Supported by the Austrian Science Foundation (Project 10223-PHY).     

Discrete least-squares technique for eigenvalues. Part I: The one-dimensional case

A discrete least-squares technique for computing the eigenvalues of differential equations is presented. The eigenvalue approximations are obtained in two steps. Firstly, initial approximations of the desired eigenvalues are computed by solving a quadratic matrix eigenvalue problem resulting from the least-squares method applied to the equation under consideration. Secondly, these initial approximations, being of sufficient accuracy in some cases, are improved by using the Gauss-Newton method. Results from numerical experiments are reported that show great efficiency of the proposed technique in solving both regular and singular one-dimensional problems. The high flexibility of the technique enables one to use also the multidomain approach and the trial functions not satisfying any of the prescribed boundary conditions.     

On the existence and convergence of the solution of PML equations

In this article we study the mesh termination method in computational scattering theory known as the method of Perfectly Matched Layer (PML). This method is based on the idea of surrounding the scatterer and its immediate vicinity with a fictitious absorbing non-reflecting layer to damp the echoes coming from the mesh termination surface. The method can be formulated equivalently as a complex stretching of the exterior domain. The article is devoted to the existence and convergence questions of the solutions of the resulting equations. We show that with a special choice of the fictitious absorbing coefficient, the PML equations are solvable for all wave numbers, and as the PML layer is made thicker, the PML solution converge exponentially towards the actual scattering solution. The proofs are based on boundary integral methods and a new type of near-field version of the radiation condition, called here the double surface radiation condition. Partly supported by the Finnish Academy, project 37692.