TiC-Ni系高温自润滑金属陶瓷的研究

本文利用中频热压烧结法制备了TiC-Ni、TiC-Ni-Mo和TiC-Ni-MO-WC3种高温自润滑性金属陶瓷材料。栓-盘摩擦磨损试验结果表明,TiC-Ni-Mo金属陶瓷的高温自润滑性最好,其在600℃时的摩擦系数为0.19,磨损率为1.14×10~(-14)m~3/N·m,偶件(材料W18Cr4V,HRC62)的磨损率为0.069×10~(-14)m~3/N·m。作者指出,这类材料的高温自润滑性与其摩擦表面上生成的氧化膜的组成和结构相关。此外,本文还就Mo、WC对材料物理机械性能的影响进行了探讨。     

Series solutions for steady unsaturated flow in irregular porous domains

For the most part, analytical solutions for steady unsaturated infiltration have been restricted to infinite and semi-infinite seepage geometries, using the quasi-linear approximation for the hydraulic conductivity. We provide analytical series methods to solve the steady quasi-linear flow equations, in finite irregular seepage geometries. Unlike the classical approach, the series method has been modified, to cater for arbitrary boundary geometry and surface recharge distributions. The matrix flux potential and the stream function both satisfy the same governing partial differential equation, and the stream function formulation is used to estimate the series coefficients. For a finite vadose zone, the stream function solution does not uniquely determine the matrix flux potential, when flux boundary conditions are used. Consequently, the stream function solution applies to a range of moisture distributions, for given infiltration and evapotranspiration rates through the surface.     

Structural first failure times under non-Gaussian stochastic behavior

An analytical moment-based method for calculating structural first failure times under non-Gaussian stochastic behavior is proposed.In the method,a power series that constants can be obtained from response moments (skewness,kurtosis,etc.) is used firstly to map a non-Gaussian structural response into a standard Gaussian process,then mean up-crossing rates,mean clump size and the initial passage probability of a critical barrier level by the original structural response are estimated,and finally,the formula for calculating first failure times is established on the assumption that corrected up-crossing rates are independent.An analysis of a nonlinear single-degree-of-freedom dynamical system excited by a Gaussian model of load not only demonstrates the usage of the proposed method but also shows the accuracy and efficiency of the proposed method by comparisons between the present method and other methods such as Monte Carlo simulation and the traditional Ganssian model.     

A Galerkin Approach for Power Spectrum Determination of Nonlinear Oscillators

A numerical method to estimate spectral properties of nonlinear oscillators with random input is presented. The stationary system response is expanded into a trigonometric Fourier series. A set of nonlinear algebraic equations, solved by Newtons method, leads to the determination of the unknown Fourier series coefficients of single samples of the response process. For cubic polynomial nonlinearities, closed-form expressions are used to find the nonlinear terms at each step of the solution scheme. Further, a simple procedure yields an approximation of an arbitrary nonlinearity by a cubic polynomial. Power spectral density estimates for the response process are constructed by averaging the square modulus of the computed Fourier coefficients over various samples or by means of well-established smoothing techniques of spectral analysis. Two applications are presented illustrating the effectiveness of the method as compared to statistical linearization and digital Monte-Carlo simulation.     

Nonlinear Coherence in Multivariate Research: Invariants and the Reconstruction of Attractors

First, some linear techniques in multivariate time-series analysis in EEG research are reviewed to highlight the problem of estimating the dimensionality of the state space (embedding dimension), the reconstruction of an attractor, and the evaluation of invariant properties of the attractor. The traditional linear techniques included the usual spectral and cospectral measures of power, phase, and coherence to which stepwise discriminant analysis was applied for canonical representation of the attractor. Then, some traditional nonlinear techniques of attractor reconstruction and dimensional analysis which use the time-lagged univariate approach of Ruelle and Takens (Takens, 1981) are reviewed. Next, updates and multivariate generalizations that use singular-value decomposition (Broomhead & King, 1986) are reviewed. Finally, Stewart's (1995, 1996) multivariate generalization of the method of false nearest neighbors (Abarbanel, Brown, Sidorowich, & Tsimring, 1993; Kennel, Brown, & Abarbanel, 1992) is reviewed. These are particularly relevant for evaluating multivariate coherence in research on the complex cooperative dynamical systems found in neuroscience, psychology, and social science when time series of sufficient length are investigated.     

理想导体中具有两个松弛时间的电磁热弹性波

研究处于均布磁场中的理想导体的二维电磁热弹性耦合问题，引入势函数使控制方程转化为3个偏微分方程．运用Laplace变换和Fourier变换得到该问题在变换域内的精确表达式，再通过级数展开和Laplace逆变换法求得在时间较短时的逆变换，得到时间-空间域内问题的解．运用此方法研究了表面受到热冲击的半无限空间问题．给出了电磁热弹性波、膨胀波和横向波传播的速度，并通过数值计算，给出了各个场量的分布图．所得结论与已有的结论一致．     

On a Discrete Fourier Series Solution to Static Problem for Conical Shells of Circumferentially Varying Thickness

An approach is developed to solve the two-dimensional boundary-value problems of the stress-strain state of conical shells with circumferentially varying thickness. The approach employs discrete Fourier series to separate variables and make the problem one-dimensional. The one-dimensional boundary-value problem is solved by the stable discrete-orthogonalization method. The results obtained are presented as plots and tables __________ Translated from Prikladnaya Mekhanika, Vol. 41, No. 9, pp. 26–37, September 2005.     

EXACT ANALYSIS OF WAVE PROPAGATION IN AN INFINITE RECTANGULAR BEAM

The Fourier series method was extended for the exact analysis of wave propagation in an infinite rectangular beam. Initially, by solving the three-dimensional elastodynamic equations a general analytic solution was derived for wave motion within the beam. And then for the beam with stress-free boundaries, the propagation characteristics of elastic waves were presented. This accurate wave propagation model lays a solid foundation of simultaneous control of coupled waves in the beam.     

环形板与扇形板弯曲问题的级数解

由板的基本方程,将位移和荷载沿环向展开为傅里叶级数,可得用傅里叶级数及多项式表示的环形板和直边简支的扇形板的级数解.还用富里叶级数处理沿径向分段连续荷载的问题.     

基于支持向量回归机的陀螺漂移预测模型

为了预测某导弹陀螺漂移趋势,以该陀螺漂移角速度时间序列为对象,建立了基于支持向量回归机的预测模型。针对该预测模型的特点,提出了支持向量预选取的模型优化方法。基于ε不敏感损失函数的支持向量回归机具有稀疏性,其结构由支持向量决定。因此从训练样本集中预选出有可能成为支持向量的样本,精简样本规模是提高该类支持向量回归机训练和预测效率的有效方法。针对该类支持向量回归机从分类和回归两个角度分析了支持向量的几何特征,提出了核函数空间免疫聚类的支持向量预选取方法并用于某导弹陀螺漂移预测模型的数据预处理。仿真结果表明优化后的预测模型运算量小、建模速度快,精度高。