Comparison of finite element reliability methods

The spectral stochastic finite element method (SSFEM) aims at constructing a probabilistic representation of the response of a mechanical system, whose material properties are random fields. The response quantities, e.g. the nodal displacements, are represented by a polynomial series expansion in terms of standard normal random variables. This expansion is usually post-processed to obtain the second-order statistical moments of the response quantities. However, in the literature, the SSFEM has also been suggested as a method for reliability analysis. No careful examination of this potential has been made yet. In this paper, the SSFEM is considered in conjunction with the first-order reliability method (FORM) and with importance sampling for finite element reliability analysis. This approach is compared with the direct coupling of a FORM reliability code and a finite element code. The two procedures are applied to the reliability analysis of the settlement of a foundation lying on a randomly heterogeneous soil layer. The results are used to make a comprehensive comparison of the two methods in terms of their relative accuracies and efficiencies.     

三种新型流量计在醋酸装置中的应用

阐述了阿牛巴、超声波、电磁等3种流量计的性能特点、选用原则和安装要点。重点分析了低压甲醇羰基化生产醋酸装置中的各种介质的特点如强腐蚀性、两相流、低电导率等,根据不同介质的特点和工艺要求选用不同类型的流量计,并且总结了这些流量计替代原有孔板、涡街、涡轮流量计的实际使用情况以及经验教训。     

无线随钻测量技术的应用现状与发展趋势

目前,无线随钻测量技术是石油工程技术发展的一个主要方向。详细介绍了无线随钻测量仪器的传输方式、国内外无线随钻测量技术的主要进展和应用现状,指出了国内外无线随钻测量仪器的优缺点和应用范围,分析了无线随钻测量技术的发展趋势,并提出我国应在借鉴国外先进的无线随钻测量技术的基础上,研制具有自主知识产权的无线随钻测量仪器,以加快我国无线随钻测量技术的发展,缩短与国际先进水平的差距。     

高速电路中地电流的影响及其对策

从理论上分析了产生地电流干扰的原因，从而在实践上提出了一些经常被忽略，却是行之有效的方法来减小地电流的干扰，设计出高质量的电路。     

不同磁场作用对AZ31镁合金的凝固组织的影响

镁合金是具有优越性能的金属材料,镁合金的加工是目前国内外正在深入进行研究的新课题.实验发现在镁合金的凝固过程中施加低频或静态磁场都能细化晶粒,但静磁场得到的细化效果要优于低频交流磁场,同时随磁感应强度的增加,静磁场细化晶粒的效果明显提高;在静磁场条件下晶界共晶体组织的厚度明显减小,同时在晶内出现了大量细小块状化合物,这有利于改善镁合金的综合性能.     

Extremes of random fields over arbitrary domains with application to concrete rupture stresses

To find the exact probability distribution of the global maximum or minimum of a random field within a bounded domain is a pending problem even for Gaussian fields. Except for very special examples of fields, recourse must be taken to approximate reasoning or asymptotic considerations to be judged with respect to accuracy by simulations. In this paper, the problem is addressed through a functional equation that leads to the definition of a class of distribution functions that depend solely on process or field characteristics and domain quantities that can be calculated explicitly. This distribution function class is studied for Gaussian processes in earlier works by the author and it has been obtained explicitly for Gaussian fields on rectangular domains in the plane. Simulation studies show that rather good predictions are obtained for sufficiently smooth wide band Gaussian processes and fields. In this paper, the distribution function is obtained in general for Gaussian fields over arbitrary bounded domains with piecewise continuous and differentiable boundaries, and as in earlier works the distribution function is tested against empirical distribution functions obtained by simulation of sample functions of a smooth approximately Gaussian field, herein called a broken line Hino field. For completeness this particular field type is defined in appendix a and appendix b. The paper concludes with a statistical application on data for plain concrete tensile strength.     

电力系统微机型产品的电磁兼容设计

从分析电力系统中电磁干扰的来源、传输途径入手，对应用于电力系统的微机型产品设计中的电磁兼容问题进行了较为系统的探讨，并提出了行有效的解决措施。     

高层天台移动通信天线电磁辐射影响水平探讨

移动通信基站在高层建筑天台架设的定向天线，对周围环境的电磁辐射影响水平的监测进行分析，探讨高层建筑天台电磁辐射环境的污染防治对策。     

非对称型外差激光探针

本文描述用于检测微振动的非对称型外差激光探针系统及实验结果。实验数据表明,系统检测灵敏度为1×10~(-4)nm/(Hz)~1/2将本系统用于检测薄膜电路在交变电热下的微振动以及表面波聚焦换能器的辐射声场分布,得到满意的结果。     

电磁铸造液柱高度数学模型的建立及应用

为了研究熔体金属电磁立柱成形能力并计算电磁作用下的液注高度,从电磁铸造立柱成形的基本原理出发,建立了电磁场作用下金属立柱成形时液柱高度数学模型,并试验验证了模型的准确性.利用液柱高度数学模型对铝、钢、锡铅合金等金属的电磁铸造可行性,以及电力参数对液柱高度的影响进行研究.结果表明:铝电磁无模成形能力最强,而钢及锡铅合金电磁无模成形能力则基本相同;钢及锡铅合金电磁立柱成形所需的磁感强度约为0.08～0.10 T,而铝则只需约0.04T.