The reliability analysis of welded structure with embedded cracks by using three dimensional stochastic FEM

In this paper, the reliability of welded structure with an embedded elliptical crack was calculated by using three dimensional stochastic finite element method. This method has overcome the shortcomings of conservative results in safety assessment with deterministic fracture mechanics method. The calculation of reliability was based on three dimensional perturbation stochastic finite element program which was developed by ourselves. The effects of variables (such as fracture toughness K IC , load P, the ratio of minor axis to major axis a/c) on the structure reliability were also discussed. The calculation results indicate that among the three variables (K IC ,P, a/c) , the fracture toughness K IC has the greatest effect on the structure reliability. The next is external load P. The ratio of the a/c has lower effect on structure reliability than both K IC and P . The method has put forward a new way for safety assessment of welded structure with embedded elliptical cracks.

边坡稳定可靠性的随机有限元分析

摘要:随机有限元法可以处理土性参数的变异性和空间相关性。对二阶摄动随机有限元法的摄动理论和程序进行了研究,提出了偏导矩阵的组集方法,采用正态分布随机变量的正交变换法来提高计算效率。考虑土性参数随机场作用和土性指标之间的互相关性,建立边坡局部抗剪和总体稳定性可靠度的随机有限元分析模型,对某实际土坡进行了可靠度计算,计算结果较为符合实际。

基于三维随机有限元法的含缺陷焊接结构可靠性分析

采用随机有限单元法对含浅表面和深表面裂纹焊接结构的可靠性进行了计算。该方法克服了传统的确定性断裂力学在结构的安全评定中结果偏于保守的缺点。在结构可靠性计算中 ,采用自行编制的基于摄动理论的三维随机有限元程序 ,就焊接残余应力对结构可靠性的影响进行了计算 ,并讨论了断裂韧度、外载荷、裂纹尺寸三个随机变量的变异对结构可靠性的影响。计算结果表明 ,焊接残余应力对结构的可靠性有较大影响 ,无论结构中是否有残余应力 ,上述三个随机变量中 ,断裂韧度的变异对结构的可靠性影响最大 ,其次是外载荷 ,裂纹尺寸的变异对结构的可靠性影响较前两者都小。

桥梁结构固有频率的统计特征

运用摄动法随机有限元导出随机参数桥梁结构本征值问题的基本列式。结构的基本设计变量按局部平均随机场理论离散。一个具有随机质量密度和截面直径的简支梁算例验证了本文方法的正确性。最后假设主缆弹性模量和质量密度、主梁质量密度等为随机参数，计算了主跨８８８ｍ虎门大学自振频率的统计特征，并对有关随机变量作参数分析，讨论其对悬索桥固有振动特性的影响。

钻压波动对轨迹影响的摄动随机有限元分析

井眼轨迹形成过程中,影响轨迹的许多因素都难于精确测量或精确描述,这些不确定因素对井眼轨迹综合作用是随机的、不确定的。借助随机有限元方法和摄动方程初步分析了钻压波动对井眼轨迹的影响。该法首先利用泰勒级数展开,将随机函数表示成确定性部分和随机部分之和,然后对随机参数空间离散化,把随机场转化为随机向量,在假定参数的扰动是微小的情况下,利用中心二阶摄动法,将有限元控制方程转化为一组递归方程。一次求解此方程即可确定随机变量对位移场的影响。