关于黄锡恺、郑文纬主编的机械原理教材中几个问题的讨论

本文对黄、郑二教授主编的机械原理教材中一些不正确、不确切或不利于教学的内容和提法提出了意见,供教材的编者及有关学者讨论、参考和指正。     

双曲薄壳稳定性的分析

弹性稳定理论分析的结果表明,当周边约束的影响可不考虑时,一般双曲薄壳的临界内力可按下式决定：式中：Ｔｅ－壳体在θ向的单位长度截面上的计算（压）内力;－壳体中曲面沿截面走向的曲率半径;δ－壳体厚度．Ｅ－材料弹性模数,μ－巴桑比数． 周边约束影响可不予考虑的条件如下：式中ｌｅ为壳体在θ向的跨度． 文中在分析了若干个在其中边界约束的影响必须于以考虑的例子,并将结果与已知结果作了比较． 最后,作者建议采用材料正切弹性模数的近似表达式,以便将分析结果,推广到弹塑性范围,并提出了结构计算中的实用公式．     

孔隙压力对微裂隙低渗透介质变形的影响实验研究

应力敏感作用对低渗透储层的渗流有重要的影响。为了明确微裂隙低渗透储层的应力敏感特征,首先分析了储层的变形机理;然后通过改变孔隙压力实验,模拟测定微裂隙低渗透储层的应力敏感特征;最后分析了应力敏感对生产的影响。研究表明:超低渗透研究区微裂隙比较发育,使其储层砂岩具有应力敏感特征;渗透率模数能够较好的描述研究区的介质变形特征;孔隙压力降低,超低渗透岩心渗透率下降幅度远远高于其它各类储层岩心,表明油藏开发过程中,超低渗储层介质变形非常严重。随着生产压差增大,超低渗介质变形油藏单井产能随之增加,油井开采过程中,选择合理的生产压差是减小介质变形对油井产能造成伤害的关键。     

齿轮模数的现场测绘

齿轮模数是齿轮几何尺寸计算的重要参数．对于损坏齿轮，生产现场要求准确、快速地确定其模数，以便及时配制．经过严密计算和实践验证，用公法线长度测绘法确定齿轮模数可满足要求．     

基元模数与组合多面体外接球半径的几何关系

网壳结构作为曲面形的网格结构,兼有杆系结构和薄壳结构的固有特性。随机法组合多面体球面网壳结构在国内还很少见,既没有理论作指导,更没有实际经验可以借鉴。在这种情况下,提出的组合多面体理论和组合多面体变体理论,为随机法单层球面网壳的几何构型设计提供了依据。随机法组合多单层球面网壳的半径与其组成单元的基元模数、单元中正五边形的边长存在着一定的几何关系,了解基元模数与组合多面体外接球半径之间的关系,对随机法组合多面体各参数的计算有着非常重要的意义。     

Classification using wavelet packet decomposition and support vector machine for digital modulations

To make the modulation classification system more suitable for signals in a wide range of signal to noise rate （SNR）, a feature extraction method based on signal wavelet packet transform modulus maxima matrix （WPTMMM） and a novel support vector machine fuzzy network （SVMFN） classifier is presented. The WPTMMM feature extraction method has less computational complexity, more stability, and has the preferable advantage of robust with the time parallel moving and white noise. Further, the SVMFN uses a new definition of fuzzy density that incorporates accuracy and uncertainty of the classifiers to improve recognition reliability to classify nine digital modulation types （i.e. 2ASK, 2FSK, 2PSK, 4ASK, 4FSK, 4PSK, 16QAM, MSK, and OQPSK）. Computer simulation shows that the proposed scheme has the advantages of high accuracy and reliability （success rates are over 98% when SNR is not lower than 0dB）, and it adapts to engineering applications.     

An Improved Grid Security Infrastructure by Trusted Computing

Current delegation mechanism of grid security infrastructure （GSI） can＇t satisfy the requirement of dynamic, distributed and practical security in grid virtual organization. To improve this situation, a TC-enabled GSI is discussed in this paper. With TC-enabled GSI, a practical delegation solution is proposed in this paper through enforcing fine granularity policy over distributed platforms with the emerging trusted computing technologies. Here trusted platform module is treated as a tamper-resistance module to improve grid security infrastructure. With the implement of Project Daonity, it is demonstrated that the solution could gain dynamic and distributed security in grid environment.     

Estimation of Single-fibre Tensile Properties from the Bundle Tensile Curve of Polyester Fibres

Fibre bundle tensile curves can be used to characterise fibre processing properties and end-use performance directly and to predict single-fibre properties in theory. In this paper, the tensile behaviour of polyester fibre-bundles has been analysed in characteristic values and diagramming. The characteristic distributions which include the symmetry distribution on right part, SRBS‘(e), on left part, SLBS‘(e) and the curve on base-line modification, MBS‘(e),based on the modulus distribution, BS‘(e), as well as thefrequency density function of broken fibres, B‘(e), havebeen derived from the tail of bundle tensile curves. Thetheoretical and measured results show that the mostimportant curves are MRS‘(e) and B‘(e) and can be usedto estimate the breaking-extension distribution of singlefibres. Especially for MRS‘(e), the modulus distributioncan accurately characterize single-fibre tensile propertiesand is no limitation as the calculation of B‘(e) because thebundle specific stress Y(e) of no fibre breaking at extensione should be found at first.     

Experimental Study on Pull-out Behavior of Different Geotextiles

The pullout testing of geosynthetics is essential for studying interface interaction in the soil-reinforcement system. In this paper, a new method for testing interface properties of geotextiles is proposed. The interface frictional characters of two kinds of geotextiles (woven and needle-punched nonwoven) are investigated through pullout test.Nonwoven specimen has more wide variety of displacement along length than that of woven under the same pressure because of their different exteusibility. The greater the elongation and deformation of specimens, the more evident the variations of displacement along reinforcement from front to pullout end. The greater the normal pressure, the smaller the displacement of every position along length with the same pullout load. The study focuses on the effects of the tensile modulus and the difference of pullout response between woven and nonwoven geotextiles.     

韩国古建筑实例的基本尺度取值规律探析

通过对部分韩国古建筑实例测绘数据的分析，探索其营造尺复原值，并提出一种尺度规律的推定结果：存在一种基本模数，控制建筑的面阔、进深和高度各项基本尺度．