Probabilistic Approach to Predict Cracking in Lightly Reinforced Microconcrete Panels

The ultimate strength of structures made of brittle materials—such as microconcrete—strongly depends on microstructural defects, the structure size, and the loading pattern. Probabilistic approaches allow one to take account of such dependencies. By using a Weibull model, cracking of ferrocement panels is analyzed. Provided the behavior of the reinforcement remains elastic, it is shown that the Weibull parameters identified on unreinforced microconcrete samples tested in flexure may be used to predict multiple cracking in ferrocement panels tested in tension. A key aspect of the analysis is related to the understanding and modeling of the stress heterogeneity effect on the local failure probability of unreinforced as well as reinforced microconcrete by the use of a so-called Weibull stress.     

网格门户下基于GSI的MyProxy Login实现

Globus项目通过网格安全基础设施GSI(GridSecurityInfrastructure)来提供网格计算环境中的安全认证和安全通信能力,该文通过基于GSI的安全技术分析和对Gridport下MyProxylogin实现原理的研究,并与普通登录方式进行比较,说明Gridportlogin利用MyProxy解决用户代理问题将更安全、高效。     

基于经济模型的Web区分服务模型的设计与实现

Web区分服务研究已经成为电子商务应用中的重要课题,基本思想是为高优先级用户提供更好的服务。该文基于经济模型给出另一种形式的Web区分服务,并用来解决IDCWebhosting中用户资源的优化配置。     

双盘悬臂转子轴承系统松动碰摩耦合故障分析

针对考虑松动-碰摩耦合故障的双盘悬臂立式转子-轴承系统，建立了该系统的力学模型和有限元模型，并基于非线性有限元方法和接触理论研究了松动刚度和碰摩间隙两个重要参数对系统动力学特性的影响。通过对在不同松动刚度和不同碰摩间隙时系统动力学特性的研究分析，发现转静件碰摩能够减小松动引起的低频振动，支座松动产生的碰摩具有明显的方向性，从而得出转子系统中诊断松动-碰摩耦合故障的依据。     

磁悬浮轴承-转子系统的分岔与混沌特性

研究磁悬浮轴承-转子系统主共振情形时的非线性动力学行为。由Taylor级数展开得到非线性电磁力的表达式。用Lung-Kutta法计算系统的运动响应。借助Poincare影射和Lyapunov指数对系统的运动形态进行分析。结果发现了在主共振情形下系统中由环面破裂产生的混沌现象及之后的由倍周期分岔导致的混沌现象。     

Improved single neuron controller for multivariable stochastic systems with non-Gaussianities and unmodeled dynamics

In this paper, a new adaptive control approach is presented for multivariate nonlinear non-Gaussian systems with unknown models. A more general and systematic statistical measure, called (h,?)$(h,?)$-entropy, is adopted here to characterize the uncertainty of the considered systems. By using the “sliding window” technique, the non-parameter estimate of the (h,?)$(h,?)$-entropy is formulated. Then, the improved neuron based controllers are developed for multivariate nonlinear non-Gaussian systems by minimizing the entropies of the tracking errors in closed loops. The condition to guarantee the strictly decreasing entropy of tracking error is presented. Moreover, the convergence in the mean-square sense has been analyzed for all the weights in the neural controllers. Finally, the comparative simulation results are presented to show that the performance of the proposed algorithm is superior to that of PID control strategy.     

矿车车体减振特性分析

建立了矿车车体振动的力学及数学模型，运用控制理论分析了车体对阶跃激励的响应特性，得到了车体振幅变化规律及矿车振动力学模型中阻尼系数与车体振幅之间的关系，从而提出在矿车上安装干摩擦阻尼器，以增大系统的阻尼系数，减小车体的振幅。通过建立Simulink仿真模型，对具有不同阻尼系数的矿车车体的振动过程进行了动态模拟，从而证明增大阻尼系数可以减小车体的振幅。     

多级离心压缩机无叶扩压器内气动性能的数值研究

对某多级离心压缩机的气动性能进行了整级CFD数值模拟,重点研究并比较了级间与级后无叶扩压器内的气动特点。计算方法基于Jameson格式,湍流模型选择Spalart-Allmaras模型。结果表明,在多级离心压缩机中,无叶扩压器的性能对整个机组的总体性能影响很大。级间与级后无叶扩压器内的能量损失都很高,但后者以摩擦损失为主,而前者由于受其下游弯道的影响,流动发生分离,因而其能量损失来源于摩擦与分离的共同作用。     

模板的加工

介绍了某军工产品模板加工的基准选择、精度控制、装卡方式、刀具选用等.