测压管道系统频响函数及对风效应的影响

利用管道测压试验,确定不同长度测压管的频率响应函数。在此基础上,研究不考虑管道系统修正时,测压管道长度对平屋面风压系数和结构风振响应均方根和极值的影响规律。研究结果表明：短管对脉动风压有放大效应,长管则呈现缩小效应;当管道长度较大时,风压信号衰减十分显著,尤其在高频位置;管道长度对风振响应的影响小于屋面风压系数,误差影响规律差别较大;测压管道长度对风压系数和风振响应计算误差的影响呈现振荡特性,100cm左右管道长度引起的误差相对较小,对于大多数管道长度,均需要进行风压管道修正。     

并联管道耗散模型的理论研究

多通道测压管路是获得实验模型表面多个邻近测点平均风压时程的必要测量系统．其测量结果对于计算结构风振响应具有重要意义。为了准确地计算多通道测压管路系统的频率响应函数，本基于电路传输线理论，推导了可用于并联管道的耗散模型，进一步完善了原先只能用于串联管道的耗散模型．为今后深入分析多通道测压管路系统打下了理论基础。接着利用并联管道的耗散模型与Bergh—Tijdeman方程对几组不同管路系统的频率响应函数进行了计算，并将两个方程的计算结果与实验值进行比较，结果表明两个方程计算的结果完全一致，并与实验值吻合得很好。中进一步指出较之递归式的Bergh-Tijdeman方程，非递归式的耗散模型运用起来更加方便。     

小波递归最小二乘语音自适应增强

针对语音自适应增强的递归最小二乘算法必须已知参考信号的约束条件,将小波技术引入RLS算法中,提出了一种语音自适应增强算法—小波递归最小二乘算法(WRLS)。无需参考输入和输入信号的延时量,而是用小波分解、合成技术初估期望信号,以此获得先验误差;再用RLS算法求解滤波器权系数修正量;同时采用"块"和"符号"技术减少权系数修正的运算量,提高算法的收敛速度。仿真实验表明该算法的增强效果明显优于谱减法和小波增强法。     

紊流积分尺度对CAARC模型表面风压特性的影响

常规风洞不能较好模拟紊流积分尺度,造成模型缩尺比与积分尺度不匹配。采用两种缩尺比CAARC(Commonwealth Advisory Aeronautical Research Council)模型在相应缩尺比的B类风场中进行同步测压试验,研究紊流积分尺度对平均风压系数、脉动风压均方根系数、脉动风压功率谱、风压水平和竖向相关系数、以及风压竖向相干函数的影响。结果表明：平均风压系数受紊流积分尺度影响较小,而脉动风压均方根系数随L■/D的减小而减小,且脉动风压均方根系数偏小程度随L■/D偏小程度的增大而增大;迎风面驻点的脉动风压功率谱,在低频区间,由准定常效应控制,基本保持一致,在高频区间,其衰减速度快于脉动风速功率谱,且衰减速度随紊流积分尺度的减小而加快;紊流积分尺度越小,宽面迎风时侧面与背面的脉动风压功率谱越大,迎风面外缘点和背面的漩涡脱落特征更明显;在迎风面,脉动风压水平相关系数和竖向相关系数随着L■/D的减小而减小;在侧面,宽面迎风时脉动风压水平和竖向相关系数随着L■/D的减小而增大,窄面迎风时脉动风压水平相关系数随着L■/D的减小而减小,测点距离较近时,竖向相关系数随着L■/D...     

雷暴冲击风作用下高层建筑风压频域特性

为研究雷暴冲击风作用下高层建筑风压的频域特性,采用冲击射流装置模拟雷暴冲击风,对矩形高层建筑模型进行测压试验。根据试验数据,对模型表面的脉动风压系数功率谱、水平和竖向相关系数、水平及竖向相干函数进行了详细分析,讨论了模型所在径向位置对脉动风压频域特性的影响。结果表明:各径向位置处模型迎风面的脉动风压功率谱与来流脉动风速谱基本一致;侧面与背风面脉动风压的能量主要集中在旋涡脱落频率处;风压相关性随测点间距离的增大而减小;迎风面风压的水平和竖向相干性均较强,脉动风压同步性较好;侧面测点风压水平相干性在折减频率小于0.2时较为显著,竖向相干性在整个频率范围内相对较好;背风面测点风压的水平和竖向相干性在折减频率小于0.1时较好,随着折减频率增大,相干性迅速减弱;迎、背风面中心测点风压在折减频率0.06附近存在较强的水平相干性,相位角相差180°左右,脉动风压呈现相反的相位特征。     

Kriging-POD法在预测大跨屋盖风荷载中的应用研究

结合POD (Proper Orthogonal Decomposition)技术与Kriging法,提出用于空间数据插值的POD-Kriging方法;基于大跨屋盖结构表面风压的数据,实现了对风压的空间重构与预测。预测的平均风压系数、脉动风压系数、脉动风压的时域与频域特性与风洞实验结果吻合良好。表明该文提出的预测方法在大跨结构表面风压的预测是可行的。     

小振幅振动屋盖风压特性研究

风荷载作用下,大跨度屋盖通常会出现不同频率的小振幅振动。为描述这类小振幅振动屋盖的风荷载分布情况,采用准定常理论,构造基于时间离散的准定常风压统计方法,并由此给出相应的平均风压统计表达式。采用计算流体力学方法,对不同振动频率的屋盖进行风压分布模拟,结合准定常风压统计方法分析屋盖表面平均风压和脉动风压分布特性,并与相关风洞试验数据进行对比。研究结果表明:对于二阶振型振动的小振幅平屋盖,在不同振动频率条件下,屋盖表面平均风压的分布与静态平屋盖的形态接近;而脉动风压的特性与静态平屋盖的情况差别较大。     

基于窄带滤波及分组DTFT的科氏流量计信号处理方法

提出了一种用于科氏流量计的数字信号处理方法：利用椭圆滤波器滤除左右两路信号中的谐波,再对滤波后的信号进行修正的自适应陷波滤波并测量信号基频,跟踪频率变化;采用计及负频率影响的分组DTFT递推算法测量两路信号的相位差。仿真分析表明,所提出的方法具有很好的跟踪效果且计算简单,可用于科氏流量计的实时信号处理。     

基于递归分析的微裂纹缺陷超声检测技术研究

为准确检测金属构件微裂纹缺陷,采用超声脉冲反射法对金属试块进行检测,并提取超声背散射信号进行分析。通过对背散射信号进行简单的建模,说明其组成要素。由于背散射信号的非线性特征,缺陷回波信号会对系统的递归特性产生影响;在此基础上提出了基于递归分析的方法分别对含人工微裂纹缺陷金属试块的无缺陷区、单裂纹区及双裂纹区背散射信号进行检测研究;通过合理的参数选择,对采样信号进行递归分析并绘制递归图;对比含缺陷信号与无缺陷信号,发现前者会在递归图中产生明显的白色交叉条纹带。使用递归定量分析进一步研究了含缺陷背散射信号的递归特征量。结果表明多种特征量对缺陷回波信号比较敏感,其中递归率(RR)和捕获时间(TT)在缺陷位置有明显的特征。     

均值对随机场POD分解影响机理

基于POD方法的理论基础与数学矩阵分析,通过引入随机场均值的相关矩阵及对均值相关矩阵的POD分解,阐述均值对随机场完整信号和脉动信号POD分解的影响机理。以双曲冷却塔模型和闭口箱梁模型的断面风压场POD分解实例,分析风压均值的影响,并验证上述理论解释的合理性。尽管随机场均值并不影响POD方法对随机场的分解和重建过程,但两种信号分解得到的各阶参数如本征值、本征模态及主坐标都只是所采用信号特性的反映而不能相互混淆。以完整信号分解得到的各阶参数都将受到随机场均值的影响,尤其是低阶参数。由于实际使用中对随机场的信号均值和脉动信号多分别对待,因此在POD分解中应使用脉动信号构建相关矩阵以完全反映脉动信号的特性,从而避免信号均值的影响。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。