桅杆结构随机风振的离散分析法

风致振动是桅杆结构安全性的控制因素。由于这种结构存在频谱密集的动力特性,不适合采用振型迭加法进行分析。为此本文引入一种新的频域方法计算桅杆结构随机风振响应。基于随机振动的离散分析理论,推导出白噪声激励下结构动力响应的递推公式。经过对风荷载这种有色噪声进行白噪声滤波,桅杆结构的风致振动描述为白噪声激励下的随机振动。于是离散分析理论适用,推导出桅杆结构随机风振响应的递推公式。采用线性化模型时,该方法绝对收敛。计算结果表明,当桅杆结构处于正常使用状态时,采用离散分析理论可以得到满意的精度。

空间钢框架结构弹塑性稳定的综合离散分析法

本文采用综合离散化分析方法进行空间钢框架结构的弹塑性稳定计算。该方法既采用了有限元法处理离散结构的便利,又通过力学途径来减少所需求解的未知量。算例结果表明,本文方法不仅有很高的计算精度,且省时省空间,是一种空间钢框架结构稳定分析的实用方法。

随机风荷载作用下桅杆结构响应矩计算的离散分析法

整体考虑纤绳的空间振动以及纤绳、杆身的相互影响 ,推导出桅杆结构在随机风荷载作用下的非线性振动方程 ;在此基础上采用随机振动的离散分析理论 ,推导出结构响应均值和方差的递推式。由于结构的非线性特征 ,矩方程中包含位移的高阶矩 ,递推方程式不闭合。引入 Gauss闭合假定 ,将响应的高阶矩用均值和方差表示 ,递推方程式成为响应均值和方差的非线性方程 ,可以迭代求解。该方法计算效率高 ,收敛快。算例表明 ,该方法计算结果与 Monte Carlo模拟结果符合较好。

周转轮系的离散分析法

目前 ,复杂周转轮系的功率流分析、传动比和啮合效率的计算既困难又繁复 ,而应用离散分析法可以改变这一局面。本文首先介绍了离散图的画法 ,然后应用离散图和反映基本周转轮系特性的方程式 ,对一个复杂的周转轮系进行了分析 ,列出线性方程组并求解。应用表明 ,离散分析法简明直观 。

基于离散元的散状物料运动轨迹分析

采用离散元分析法分析散状物料的运动轨迹,解决或改善物料搬运过程中产生的冲击、磨损、堵塞、跑偏、粉尘等问题,提高设备的可靠性和使用率,改善人员工作环境,具有经济性和环保性等特点。

高速主轴—夹具—刀具系统动态特性分析

基于导纳耦合分析法,建立高速轴—夹具—刀具系统模型,得到不同转速下刀具端点处的频响函数,并采用半离散分析法,对变刚度铣削加工过程的稳定性进行分析,研究主轴转速对铣削稳定性的影响。结果表明,考虑轴承变刚度的影响,在高速情况下铣削加工稳定曲线向低转速方向偏移,且临界铣削深度明显降低。

一类变形双重介质渗流模型解的存在性分析

以Warren-Root模型为基础,引入分形参数和压缩系数,考虑了压力对具有分形特征的渗透率和孔隙度的影响,验证了变形双重介质分形油藏非线性渗流数学模型。利用离散泛函分析方法,引入不动点原理,就该模型一般形式的差分方程探讨了其解的存在性。研究认为:分形几何理论及方法在正确认识复杂非均质油藏及应力敏感地层油气藏方面具有独到优势。

希尔波特变换法解调干涉条纹的相位

叙述了希尔波特变换法解调相位的原理 ,提出了仅从一幅光载频干涉条纹获取物体表面的全部相位信息 ,再由最小二乘法原理 ,迭代出信息的相位 ,并讨论了条纹相位的算法 。

粉体粒度对松装粉体孔隙度影响的计算机模拟研究

本文应用离散元分析法(DEM),综合分析粉体颗粒受到的重力、分子力、接触力、摩擦力等多种力的作用,建立松装粉体颗粒的数学模型。使用计算机模拟技术对粉体颗粒的堆积过程进行仿真。利用回归分析得到堆积松装粉体孔隙度随着粉体颗粒粒径的减小而逐渐增大的关系。并对比分析了计算机仿真与实际验证实验的共同点和差异产生的原因,提出了可能的解决方案。

文丘里粉体喷射器内部颗粒运动特性的联合仿真

采用计算流体力学-离散单元法(CFD-DEM)耦合方法,对文丘里粉体喷射器内部5种不同粒径球形颗粒组成的颗粒群的气力输送过程进行数值模拟;分析颗粒的运动轨迹,发现部分颗粒在吸收室的底部聚集,颗粒在文丘里喷射器内部的运动集中分布在输送管道的中下部位,小尺寸颗粒速度较快,颗粒尺寸越大,颗粒与颗粒碰撞次数越多,颗粒与壁面碰撞次数越少;采用离散单元法-有限单元分析(DEM-FEA)耦合方法对颗粒与壁面碰撞引起的壁面应力变化进行分析。结果表明,喷射器在喷嘴出口处附近和吸收室底部出现应力峰值。

Continuum and Discrete Element Coupling Approach to Analyzing Seismic Responses of a Slope Covered by Deposits

Numerical analyses of earthquake effects on the deformation, stability, and load transfer of a slope covered by deposits are traditionally based on the assumption that the slope is a continuum. It would be problematic, however, to extend these approaches to the simulation of the slide, collapse and disintegration of the deposits under seismic loading. Contrary to this, a discrete element method （DEM） provides a means to consider large displacement and rotation of the non-continuum. To take the advantages of both methods of continuum and non- continuum analyses, seismic responses of a slope covered by deposits are studied by coupling a twodimensional （a-D） finite difference method and a 2-D DEM, with the bedrock being modelled by the finite difference grids and the deposits being represented by disks. A smooth transition across the boundaries of the continuous/discontinuous domains is obtained by imposing the compatibility condition and equilibrium condition along their interfaces. In the course of computation, the same time-step value is chosen for both continuous and discontinuous domains. The free-field boundaries are adopted for lateral grids of bedrock domain to eliminate the radiation damping effect. When the static equilibrium under gravity load is obtained, dynamic calculation begins under excitation of the seismic wave input from the continuum model bottom. In this way, responses to the earthquake of a slope covered by deposits are analyzed dynamically. Combined with field monitoring data, deformation and stability of the slope are discussed. The effects of the relevant parameters of spectrum characteristic, duration, andpeak acceleration of seismic waves are further investigated and explained from the simulations.

Kinematic analysis of geosynthetics-reinforced steep slopes with curved sloping surfaces and under earthquake regions

A procedure of kinematic analysis is presented in this study to assess the reinforcement force of geosynthetics required under seismic loadings, particularly for steep slopes which are hardly able to maintain its stability. Note that curved sloping surfaces widely exist in natural slopes, but existing literatures were mainly focusing on a planar surface in theoretical derivation, due to complicated calculations. Moreover, the non-uniform soil properties cannot be accounted for in conventional upper bound analysis. Pseudo-dynamic approach is used to represent horizontal and vertical accelerations which vary with time and space. In an effort to resolve the above problems, the discretization technique is developed to generate a discretized failure mechanism, decomposing the whole failure block into various components. An elementary analysis permits calculations of rates of work done by external and internal forces. Finally, the upper bound solution of the required reinforcement force is formulated based on the work rate-based balance equation. A parametric study is carried out to give insights on the implication of influential factors on the performance of geosynthetic-reinforced steep slopes.

Dispersion penalty analysis gor VSR-1 optical links

This paper presents an approach to calculate dispersion penalty for VSR-1 optical links.Based on parameters of a specific VSR-1 link,dispersion penalties are computed for various modal dispersion bandwidths respectively.The worst-case eye closure is expressed numerically by using the signal waveform at time 0,and the signal waveform is obtained in frequency domain through FFT algorithm.By this approach,the dispersion penalty is determined by the shape of transfer functions of the various components in the links.To simplify the derivation of multimode fiber link transfer function,a Gaussian form of normalized impulse response is used.This calculation approach can be used to estimate the worst-case dispersion penalty of VSR-1 links in the link budget analysis.

AN ESTIMATION OF FUZZY RELIABILITY OF DISTINCT ELEMENT METHOD IN PREDICTION OF SURFACE SUBSIDENCE DUE TO COAL MINING

The quantitative evaluation of errors involved in a particular numerical modelling is of prime importance for the effectiveness and reliability of the method. Errors in Distinct Element Modelling are generated mainly through three resources as simplification of physical model, determination of parameters and boundary conditions. A measure of errors which represent the degree of numerical solution 'close to true value' is proposed through fuzzy probability in this paper. The main objective of this paper is to estimate the reliability of Distinct Element Method in rock engineering practice by varying the parameters and boundary conditions. The accumulation laws of standard errors induced by improper determination of parameters and boundary conditions are discussed in delails. Furthermore, numerical experiments are given to illustrate the estimation of fuzzy reliability. Example shows that fuzzy reliability falls between 75%-98% when the relative standard errors of input data is under 10 %.

Solitary Solution of Discrete mKdV Equation by Homotopy Analysis Method

In this paper, we apply homotopy analysis method to solve discrete mKdV equation and successfully obtain the bell-shaped solitary solution to mKdV equation. Comparison between our solution and the exact solution shows that homotopy analysis method is effective and validity in solving hybrid nonlinear problems, including solitary solution of difference-differential equation.

离散单元法在平高2号高架大桥岸坡变形模拟中的应用

本文采用离散元位移分析法对百色至罗村口公路平高2号高架大桥坡岸边坡变形情况进行模拟分析,得到施工期及蓄水期坡岸变形数据,经过对比分析,为该桥坡岸边坡的稳定性评价及加固方式的选择提供合理的建议。

Estimation of active earth pressure based on pseudo-dynamic approach and discretization technique

A method combining the pseudo-dynamic approach and discretization technique is carried out for computing the active earth pressure.Instead of using a presupposed failure mechanism,discretization technique is introduced to generate the potential failure surface,which is applicable to the case that soil strength parameters have spatial variability.For the purpose of analyzing the effect of earthquake,pseudo-dynamic approach is adopted to introduce the seismic forces,which can take into account the dynamic properties of seismic acceleration.A new type of micro-element is used to calculate the rate of work of external forces and the rate of internal energy dissipation.The analytical expression of seismic active earth pressure coefficient is deduced in the light of upper bound theorem and the corresponding upper bound solutions are obtained through numerical optimization.The method is validated by comparing the results of this paper with those reported in literatures.The parametric analysis is finally presented to further expound the effect of diverse parameters on active earth pressure under non-uniform soil.

Numerical Solution of Klein-Gordon Equation on Manifold Using DEC

In physics,the Klein-Gordon equation describes the motion of a quantum scalar or pseudoscalar field.Itis important to find actual values of its solutions in general timespace manifold.The paper deals with description ofdiscrete exterior calculus method for solving this equation numerically on space manifold and the time.The analysis ofstable condition and error for this method is also accomplished.

A POSTERIORI ERROR ANALYSIS FOR A FULLY DISCRETE DISCONTINUOUS GALERKIN APPROXIMATION TO A KIND OF REACTIVE TRANSPORT PROBLEMS

In order to obtain an expected numerical solution, a fully discrete discontinuous Galerkin method is applied to a kind of reactive transport problems in two dimension. That is to say, the space variable is discretized with the symmetric interior penalty Calerkin method （SIPG）, and the time variable is done with the backward Euler method. Making use of the duality technique, hp approximation properties and the interpolation theory, a residual-type a posteriori error estimation is achieved, which can be used for adaptivity. Compared with the analyses of semi-discretization, the current presentation is more challenging and more significant.