均匀分布的线性近似贝叶斯估计

本文利用线性贝叶斯方法估计均匀分布R(-θ,θ)的未知参数,提出了θ的线性近似贝叶斯估计(LABE),LABE具有封闭解析解的形式且便于使用.数值模拟表明本文提出的LABE与普通的贝叶斯估计(BE)很接近,其中BE由数值积分得到,我们也使用了所谓的强力算法来获得BE.进一步,我们比较了LABE与Lindley近似.在均...     

基于参数估计线性回归模型选择的研究

关于线性回归模型选择 ,[1 ]中介绍了许多方法 ,他们均基于残差平方和下建立的选择准则 .本文试基于参数估计的理论给出一种方法 ,从参数估计的优良性质上来说 ,我们认为是合理的 .同时给出了计算方法及应用实例 .     

A new criterion for occurrence of strick-slip motion in drive mechanism

This paper, using Karnopp's model of friction force and phase plane method, studies the stick-slip motion of the flexble drive mechanism. It is explained that a sudden drop of friction force is the essential source of stick-slip motion when the sliding is impending. A new criterion for occurrence of stick-slip motion is established. The stick-slip region and the stable region in a parameter plane are separated by a critical parameter curve. Moreover, for the stick-slip motion of the flexible drive mechanism without viscous damping, a parameter expression is obtained. The results may be used in design of the flexible drive mechanism.     

弹性压应力波下直杆动力失稳的机理的判据

基于应力波理论和失稳瞬间能量的转换和守恒,导出了一个直杆动力分岔失稳的准则：（1）直杆在发生分岔失稳的瞬间所释放出的压缩变形能等于屈曲所需变形能与屈曲动能之和;（2）在上述能量转换过程中,能量对时间的变化率服从守恒定律。应用临界条件（1）推导出的直杆动力失稳的控制方程和杆端边界条件以及连续条件,与应用哈密顿原理推导的结果完全相同,但不足以构成求解直杆动力失稳问题的完备定解条件,导出包含两个特征参数的一对特征方程。从而建立了求解直杆动力失稳模态和两个特征参数（临界力参数和失稳惯性项指数参数即动力特征参数）的较严密理论方法。     

Fatigue criteria for integrity assessment of long-span steel bridge with health monitoring

A structural health assessment (SHA) methodology is developed using data acquired from structural health monitoring (SHM) system installed on long-span bridges. A set of fatigue criteria has been proposed for pre-determining the global state of the bridge structure failure due to fatigue. This involves finding the threshold of fatigue initiation, below which the rate of fatigue damage may be undetectable under current technology or it is economically unfeasible. The state-of-art for large structures corresponds to the initiation of macro-cracks caused by the accumulation of damage generated by actual service loads for the case of bridges. In what follows, consideration is given to developing fatigue crack growth criterion based on the concept of the continuum damage mechanics (CDM). Fatigue accumulative is included in the model where a fatigue limit for multi-axial stress state is considered. The proposed criterion advocates the evolution of micro-crack growth up to the stage of macro-crack formulation. Considered are the loading histories that correspond to normal traffic loading for highways and railways, incidental or accident loadings such as those caused by typhoons and effective environmental loadings. The potential sites of damage are determined are discussed. The proposed criterion is applied to analyze the fatigue damage of the Tsing Ma Bridge with online strain history data acquired by the SHM system that is permanently installed in the bridge.     

Dual-parameter elastic-plastic fracture criterion of metals and alloys in the plane strain case

In recent years, some investigators discussed the applicability of the HRR theory for engineering materials based on the results of numerical analyses and experimental studies. In the present paper, the finite element method is employed to analyze the crack tip fields of the engineering elastic-plastic material with a variety of geometry configurations of cracked specimens from elastic state to intensely general yielded state in the plane strain case. The results indicate that the HRR theory loses its validity of application for engineering elastic-plastic materials in the plane strain case. The reasons for this are analyzed. A dual-parameter fracture criterion is suggested for this case.     

A nonlocal theory for brittle fracture

In this paper, a nonlocal theory of fracture for brittle materials has been systematically developed, which is composed of the nonlocal elastic stress fields of Griffith cracks of mode-I, II and III, the asymptotic forms of the stress fields at the neighborhood of the crack tips, and the maximum tensile stress criterion for brittle fracture. As an application of the theory, the fracture criteria of cracks of mode-I, II, III and mixed mode I–II, I–III are given in detail and compared with some experimental data and the theoretical results of minimum strain energy density factor.     

Optimal Slewing of a Flexible Spacecraft

An optimal slewing program is designed within the class of Euler rotations for a spacecraft with elastic elements. The mathematical model constructed accounts for an arbitrary number of partial modes of elastic vibrations. An optimal reorientation problem is formulated using a nontraditional performance criterion, which minimizes the dynamic overloads of the elastic elements in relative motion. An algorithm for solving the corresponding nonlinear boundary-value problem is developed and implemented in a software package of FORTRAN-programs. A neural network is generated in the space of slew parameters; it may be trained during a preflight period. Known radial basis functions are used to model the process of fast in-flight computation of the optimal reorientation program