双层0.618法在某力学问题中的应用

建立了一组平行移动荷载作用下,简支桥梁挠度的数学模型;利用双层0.618法搜索梁的绝对最大挠度对应的最危险截面位置以及移动荷载最不利位置,计算该位置相应的挠度得到梁的绝对最大挠度.本文算法以计算机为工具,适用于任意有限多个平行移动荷载,对于桥梁的设计计算与安全评估,有一定的实用价值.     

车桥随机振动作用下的桥梁动态影响线研究

将传统的静态影响线概念推广到动态影响线范围,研究了在车辆荷载和桥面随机不平度的作用下,简支梁桥和三跨弹性支承梁桥跨中挠度的动态影响线.基于虚拟激励法将桥面不平度转化为确定性的简谐激励,并采用精细积分法对车桥系统方程求解,获得了桥梁跨中挠度动态影响线的均值和标准差.基于 法则构造虚拟激励输出响应的确定值计算方法,获得了桥梁挠度动态影响线的确定性值域.最后通过算例分析了桥梁动态影响线的随机特性和车速与桥面不平度等级变化对桥梁动态影响线的影响,并研究了简支梁桥和弹性支承梁桥在随机振动作用下的动态影响线差异.     

箱形梁剪力滞效应的分离求解方法及参数影响分析

选取剪力滞效应引起的附加挠度为广义位移,将箱梁的剪力滞变形状态从初等梁挠曲变形状态中分离出来,作为一种独立的变形状态进行分析,运用能量变分法建立了以附加挠度为未知量的截面控制微分方程及边界条件;结合简支边界条件分别导出了集中荷载和均布荷载作用下箱梁的附加挠度和纵向应力计算公式.纵向应力分析表明:该文方法计算的应力结果和样条函数法计算的应力结果吻合良好,从而验证了其方法的正确性.挠度研究表明:剪力滞附加挠度由跨中向两侧支点递减;针对于该文算例而言,均布荷载和集中荷载作用下跨中截面的剪力滞附加挠度分别占初等梁挠度的2. 57%和3. 03%;随着高跨比和宽跨比的增大,相应箱梁跨中截面的附加挠度逐渐减小,且宽跨比对附加挠度的影响远大于高跨比的影响.     

多夹层板壳的非线性理论及应用(Ⅰ)──基本理论

本文建立了多夹层壳体小应变状态下的中转动二阶大挠度的理论,接着进行适当的简化,获得了中转动、中小转动的一阶大挠度的理论.     

基于桥梁经验数据的理论易损性曲线校准

基于理论计算或试验研究定义桥梁损伤状态建立的理论易损性曲线,通常不能将桥梁构造(包括几何性质、材料性质等)、地面运动和场地条件等因素均考虑在内.鉴于此,为更加精确地以易损性曲线的形式评估桥梁抗震性能,首先利用1994年北岭地震桥梁损伤数据建立双参数对数正态分布的经验易损性曲线;其次,给出一种多跨桥梁力学模型,定义桥墩柱转动延性值量化桥梁损伤状态,获得4种损伤状态下的理论易损性曲线;最后,以90%置信区间的经验易损性曲线对理论易损性曲线进行校准.计算结果表明:利用桥梁力学模型建立的理论易损性曲线校准后能近似吻合经验易损性曲线,且3种损伤状态阈值由SRSS优化公式得到校准.随着结构损伤知识的进展,未来可利用更详细的结构损伤过程对校准后的理论易损性曲线做二次更新,进一步提高桥梁系统风险评估的精确性,尤其是遭受强震灾害下由多座桥梁组成的高速公路网络.     

球壳轴对称弯曲问题精确的挠度微分方程及其奇异摄动解

本文提出了球壳轴对称弯曲问题精确的挠度(ω)微分方程和精确的转角(dω/da)微分方程.本文重点研究了挠度微分方程的精度,基本思路是:首先假设边缘效应时经线中面位移u=0,从而建立挠度微分方程,然后再精确地证明挠度微分方程与原来微分方程内力解答完全相同.再精确地证明边缘效应时经线中面位移u=0是精确解.本文给出了挠度微分方程的奇异摄动解,最后验算了平衡条件,证明摄动解求出的内力和外荷载是完全平衡的.这一方面表明摄动解的计算是正确的;另一方面也再二次表明挠度微分方程是精确的微分方程.新微分方程的优点是:1.新微分方程和原来微分方程精度完全相同;2.新微分方程满足的边界条件非常简单;3.新微分方程便于使用摄动解;4.新微分方程可以得到挠度(ω)和转角(dω/da)的表达式.新微分方程使球壳的计算得到很大的简化.本文采用的符号与徐芝纶《弹性力学》第二版下册相同[1].     

宁波甬江大桥的大挠度非线性计算问题

研究了宁波甬江铁路大桥的大挠度非线性设计计算问题.提出了非线性方程的叠代近似算法,同时指出了如果两岸落差约5m,两岸跨度约100m计算,则桥梁中间的最大斜度将超过5%,这远远超过铁路设计允许的斜度.为此,提出了减小路轨斜度的设计方案,即铁路在两岸都有长度约1km斜度为0.5%的路基,使两岸的落差减小到约为原来落差的1/10.这样路轨在跨越甬江时,其挠度的斜度就会大大缩小,也在0.5%～0.6%之间.     

中考“数与式”考什么

"数与式"是学习初中数学的基础,也是中小学数学教学衔接的桥梁.纵观各地的中考题,对"数与式"考查的比重也不低.笔者根据自己的教学认识和探索,归纳出了"数与式"常考的几个方面,请各位同行指导.     

矩形板在横向压力和面内压缩共同作用下的后屈曲

本文从Kármán板大挠度方程出发,先用Galerkin法将横向载荷作用转化为初挠度影响,然后以挠度为摄动参数,采用直接摄动法研究简支矩形板在横向载荷与面内压缩共同作用下的后屈曲性态.本文讨论了两种面内边界条件,同时计及板初始几何缺陷的影响.计算结果与实验结果的比较表明二者是一致的.     

单向压缩简支矩形板后屈曲摄动分析

本文从Kármán板大挠度方程出发,以挠度为摄动参数,采用直接摄动法,研究了简支矩形板在单向压缩作用下的后屈曲性态.本文讨论了两种面内边界条件,同时考虑了初始挠度的影响.计算结果与实验结果的比较表明二者是一致的.本文所用的方法,没有见到有人发表过.作者认为,对于矩形板后屈曲分析,本文是比较简明的.     

A state space condition monitoring model for furnace erosion prediction and replacement

The paper develops a replacement action decision aid for a key furnace component subject to condition monitoring. A state space model is used to predict the erosion condition of the inductors in an induction furnace in which a measure of the conductance ratio (CR) is used to indirectly assess the relative condition of the inductors, and to guide replacement decisions. This study seeks to improve on this decision process by establishing the relationship between CR and the erosion condition of the inductors. To establish such a relationship, a state space model has been established and the system parameters estimated from CR data. A replacement cost model to balance at any time costly replacements with possible catastrophic failure is also proposed based upon the predicted probability of inductor erosion conditional upon all available information. The well known Kalman filter is employed to derive the predicted and updated probability of inductor erosion level conditional upon CR data to date. This is the first time the condition monitoring decision process has been modelled for real plant based upon filtering theory. The model fits the data well, gives a sensible answer to the actual problem, and is transferable to other condition monitoring contexts. Possible extensions are discussed in the paper.     

A two-stage prognosis model in condition based maintenance

We often observe in practice that the life of a piece of production equipment can be divided into two stages. The first stage is referred to as the normal working stage where no significant deviation from the normal operating state is observed. The second stage is called the failure delay period, since a defect may be initiated, and progressively develop into an actual failure, i.e., the equipment is in a defective stage but still working during this stage. With the help of condition monitoring, hidden defects already present in the equipment may be detected, but for maintenance planning purposes, the prediction of the initiation point of the second stage, and more importantly, the residual life thereafter is important. This paper reports on the development of a probability model to predict the initiation point of the second stage and the remaining life based on available condition monitoring information. The method for model parameters estimation is discussed and applied to real data.     

The decision support research of ultra-long distance pullback force computing model through the process of pipeline crossing pullback

The calculation of pullback by the analysis of strain on pipe shows that it involves many disciplines. It is hard to build a mechanical model that is very consistent with the actual working conditions and with the general applicability. After summarizing the calculation method of domestic and foreign authorities or national standards, the paper derives a set of its own formulas. Based on statistical data of actual projects, the paper develops a formula more suitable for ultra-long pullback by comparing the computing result with the actual measured drag force, that is for engineering design and site construction personnel reference. The calculated value of ultra-long pullback coincides well with the engineering value. Three components of pullback resistance, all occupy a high proportion in back-dragging load, and the contribution of the pullback load weights back Trawler changes dynamically. Thus proving that the method is a reasonable, simple, reliable and effective method to predict pipeline status, and makes a useful exploration for the research to improve the existing prediction models in the future.     

基于QAR数据的民航客机对称发动机差异监控模型和算法

从某型民航客机发动机机队管理的实际出发,利用HOLT双参数指数平滑方法,建立基于机载QAR数据的对称发动机性能参数的差异监控模型,并给出实现对称发动机差异监控的算法。算例分析表明模型和算法能有效地识别发动机运行状态,并能预测发动机故障征兆,使发动机排故端口提前,且方法简单易于实现。     

A prognosis model for wear prediction based on oil-based monitoring

This paper reports on the development of a wear prediction model based on stochastic filtering and hidden Markov theory. It is assumed that observations at discrete time points are available such as metal concentrations from oil-based monitoring, which are related to the true underlying state of the system which is unobservable. The system state is represented by a generic term of wear which is modelled by a continuous hidden Markov Chain using a Beta distribution. We formulated a recursive model to predict the current and future system state given past observed monitoring information to date. The model is useful to wear-based monitoring such as oil analysis. Numerical examples are presented in the paper based on simulated and real data.     

Dynamic monitoring and control of software project effort based on an effort buffer

The improvement to the monitoring and control efficiency of software project effort is a challenge for project management research. We propose to overcome this challenge through the use of a model for the buffer determination and monitoring of software project effort. This software project effort buffer was originally determined on the basis of a risk management factor analysis with total consideration for project managers’ risk preference. The effort buffer was next allocated to different stages according to the buffer allocation cardinal. An effort deviation monitoring and control model was then established based on the grey prediction model, including the establishment of a deviation monitoring and control model, a simulation test of the accuracy and the deviation prediction algorithm flow chart. The method system was eventually applied to an actual project and compared with the actual project data. The results show that the relative error test accuracy of the proposed model is qualified according to the test standard of the grey model, signifying that it could be used for the prediction of effort deviation and decision-making. The proposed model could use the dynamic control system to monitor and control software project effort in an effective manner.     

Optimal observation of controlled elastic vibrations of a beam in the presence of measurement errors

The problem of constructing of an optimal operation for restoring the state of controlled elastic vibrations of a beam in the presence of measurement errors is investigated. By the method of separation of variables, the problem is reduced to an observation problem with an actual output signal for an infinite system of ordinary differential equations. For each harmonic, a universal optimal operation that restores the deflection of the beam from equilibrium and the velocities of all points of the beam is constructed by amplifying the ideal part of the signal produced by the system.     

Analysis of nanoindentation experiments by means of atomic force microscopy

Nanoindentation is quite a common method for local material characterization. Values for hardness and Young's modulus can be determined directly from the recorded data. Essential for the correct determination of the material parameters is the precise measurement of the actual indentation depth of the indenter. The indenter measures the current depth by means of a Wheatstone bridge which correlates the indentation depth to a change in voltage. A possible tool for the verification of the recorded indentation depths is Atomic Force Microscopy (AFM). AFM is able to scan an area of indents for almost any surface. The deflection of the tip is measured by a laser spot reflected from the surface of the cantilever. The difference in height between the surface and the indent can directly be read off from the plotted image. However, using an AFM only allows us to measure the depth of the permanent indentation depth after unloading the indenter. Nevertheless, correlation between the remaining indentation depths measured by the explained methods allows for a first assessment of the correctness of the online recorded depth-data by the nanoindenter. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

非等距时序灰色预测模型及其在岩石锚碇承载力分析中的应用

在许多桥梁工程中,锚碇岩石边坡的承载力和稳定性对整个桥梁工程的稳定和正常运营起着至关重要的作用.利用推广的非等间距灰色预测理论模拟了虎门大桥锚碇隧洞拉拔力试验中拉拔力与相应山体位移间的关系,并用所得到的非等距灰色预测模型预测了山体位移,结果表明,非等间距灰色预测模型的预测精度令人满意.研究结果对桥梁工程安全施工和岩石工程预测预报有重要理论意义和工程价值.