时域分析技术在机械设备故障诊断中的应用

低速重载的一些机械设备,由于频率较低,故受振动诊断分析仪器功能的限制,频谱分析方法效果不太理想。经过现场的长期监测及诊断分析,几个典型案例说明了对于低速重载的机械设备,时域分析是最有效的故障诊断方法之一。     

SPV50Q高强钢焊接接头在湿H2S环境下的开裂敏感性研究

具有较高强度和良好韧性的SPV50Q钢常用于制造液化石油气(liquefied petroleum gas,LPG)球罐,球罐通过焊接制造后一般不经过焊后热处理,因此在焊接接头处将有焊接残余应力存在.服役经历和现场检测表明,较高H2S浓度和焊接残余应力将会导致材料产生环境失效如氢鼓泡(hydrogen blistering,HB)或氢致开裂(hydrogen-induced cracking,HIC)、硫化物应力腐蚀开裂(sulfide stress corrosion cracking,SSCC)以及应力诱导氢致开裂(stress-oriented hydrogen induced cracking,SOHIC).文中通过1×10-6s-1的慢应变速率拉伸试验,对手工电弧焊焊接的SPV50Q焊接接头在不同浓度H2S水溶液中的开裂敏感性以及开裂特征进行研究.试验结果表明,SSCC和HIC发生在靠近焊接接头热影响区的母材上,不同温度下的焊后热处理将降低材料的应力腐蚀开裂敏感性,实施正确焊后热处理可提高SPV50Q焊接接头抵抗SSCC或HIC能力,而不降低钢的力学性能尤其是韧性.     

On the computation of the slow dynamics of nonlinear modes of mechanical systems

A novel method for the numerical prediction of the slowly varying dynamics of nonlinear mechanical systems has been developed. The method is restricted to the regime of an isolated nonlinear mode and consists of a two-step procedure: In the first step, a multiharmonic analysis of the autonomous system is performed to directly compute the amplitude-dependent characteristics of the considered nonlinear mode. In the second step, these modal properties are used to construct a two-dimensional reduced order model (ROM) that facilitates the efficient computation of steady-state and unsteady dynamics provided that nonlinear modal interactions are absent.The proposed methodology is applied to several nonlinear mechanical systems ranging form single degree-of-freedom to Finite Element models. Unsteady vibration phenomena such as approaching behavior towards an equilibrium point or limit cycles, and resonance passages are studied regarding the effect of various nonlinearities such as cubic springs, unilateral contact and friction. It is found that the proposed ROM facilitates very fast and accurate analysis of the slow dynamics of nonlinear systems. Moreover, the ROM concept offers a huge parameter space including additional linear damping, stiffness and near-resonant forcing.     

Improved fuel properties of whole table olive stones via pyrolytic processing

This paper describes the thermochemical transformation of residual whole olive stones from the industrial production of pitted and stuffed table olives by using a rotary reactor. This experimental investigation describes the chemical, physical and fuel properties of the resulting solids and liquids obtained in the temperature range between 200 °C and 900 °C. Optimum torrefaction conditions, intended to maximize mass and energy yields, were obtained at 278 °C and resulted in a solid product with 68 wt% volatile matter, 29 wt% fixed carbon, 58 wt% elemental carbon, 0.55 O/C ratio, 23.4 MJ/kg of HHV, 11.25 GJ/m³ apparent energy density for an energy yield of 89%. The carbonized solids obtained at temperatures between 500 °C and 900 °C exhibited LHV and apparent energy density up to 57–66% higher than the original biomass. The carbonization process generates a condensable liquid that represents 50–53 wt% of the original biomass and contains between 57 and 61 wt% water and 39–43 wt% organic products. The carbon content (up to 25 wt%) and heating value (HHV and LHV up to 5.2 MJ/kg and 2.8 MJ/kg, respectively) of this liquid is limited. A model has been tested and a series of equations have been produced which allow us to predict the chemical and energy properties of the solid fraction derived from the torrefaction and carbonization process. This model has found linear correlations between the solid yield and elemental/proximate composition of the solids, and exponential correlations between solid and energy yields.     

缓变参数计算机测控系统的按位判断滤波法

本文针对缓变参数计算机测控系统中，被测参数变化缓慢的特点，提出一种按位判断数字滤波法，并对此进行了数学分析和计算机仿真实验。     

北京FEL电子束时间分辨能谱仪的控制及慢扫描系统

叙述了北京ＦＥＬ谱仪中的控制与扫描系统的基本功能以及用于偏转电子束的慢慢转线圈的磁分析及其微秒脉冲电流源性能。     

Modelling the &Vdot;O2 kinetic response to heavy intensity exercise in children

The purpose of this study was to apply a series of mathematical models in order to investigate the nature of the kinetic response to heavy intensity exercise with children and identify a suitable model with which to estimate parameters of the response. Sixty two children (35 male, 27 female aged 10?–?15 years) completed four transitions from baseline pedalling to 40% of the difference between their previously determined anaerobic threshold and peak [Vdot]O₂ on an electronically braked cycle ergometer. Initially three models were fitted to the averaged response profiles following the end of phase 1, and their residuals compared; 1, a single exponential with a delay term; 2, an exponential and linear term with independent delays; and 3, a double exponential with independent delays. Up to 95% of the response profiles were better fitted by either model 2 or 3 (p?<?0.05), and model 3 was a statistically better fit (p?<?0.05) than model 2 in 77% of cases. Residual inspection confirmed the superior fit by model 3. A fourth model which consisted of a single exponential with a delay term was fitted within the phase 2 fitting window. Estimated parameters (A₁ and τ₁), using model 4 were not significantly different from model 3, and model 4 was identified as the model of choice due to the wide confidence intervals in τ₂ and A₂ using model 3. It was concluded that the nature of the response to heavy intensity exercise in children is similar to that previously reported with adults and that the response should be modelled accordingly.     

基于慢变流理论的管网泄漏检测模型的建立

提出一种基于慢变流理论的给水管网泄漏诊断与定位模型,即首先对管网施加随时间缓慢变化的压力激励,如果管网中存在泄漏,随着压力的不同泄漏程度也不一样,进而影响到管网中其他节点压力和管段流量等参数的变化;依据系统辨识反问题分析方法,实时监测管网监测点处的状态参数,运用贝叶斯算法对模型的预测参数——泄漏位置和泄漏量的概率值大小进行寻优,寻找模型计算值与测量值之间吻合程度最好的预测参数,得到最可能的泄漏位置与泄漏量。通过对算例管网的计算结果表明,采用该模型能够对漏失点和漏失量进行满足概率要求的准确诊断。     

基于SFA和GLCM的影像特征提取方法

针对遥感影像中同类样本差异性较大的缺点,提出一种基于SFA和灰度共生矩阵(GLCM)的遥感影像特征提取方法。对原始图像进行SFA变换,利用SFA的生物视觉特性消除图像中的同类差异性,对变换得到的图像进行GLCM计算,获得基于SFA和GLCM的新型特征。实验结果证明,SFA预处理能降低遥感影像的同类差异性,提高特征的可区分性,其效果优于传统的GLCM特征提取方法。     

Some Tauberian theorems for the weighted mean methods of summability

In this paper, we introduce the concept of the weighted generator sequence and prove that certain conditions in terms of weighted generator sequences are Tauberian conditions for the weighted mean summability method.