基于极大似然估计的加速因子计算方法

目的在产品寿命服从参数未知指数分布的情况下,分析定时转换步加试验得到的数据,估算相关的加速因子。方法列出各应力下的寿命分布密度函数形式,通过加速因子建立各分布密度函数之间的联系,以条件概率的方式处理步加试验每一阶段开始时的累积损伤问题,以极大似然估计的方法进行参数估计。结果得出了一种新的估算加速因子的方法,计算获得了产品在所分析应力下加速因子与应力水平之间的关系。结论利用该方法能很好地处理某应力下无失效发生的情况。     

基于HHT方法的公路运输振动信号时频分析

目的分析具有非线性、非平稳特征的公路运输振动信号的时频信息。方法利用Hilbert-Huang变换算法,在对公路运输的振动信号进行EMD分解的基础上,开展Hilbert谱和各IMF的功率谱密度计算,并与常规的功率谱进行比较。结果基于IMF分量的功率谱可以克服传统Fourier功率谱计算在低频偏低、高频偏高的误差。结论基于HHT的公路运输振动信号时频分析方法是一种有效的运输振动非平稳信号分析手段。     

Suitability of ignition source “exploding wire” for determination of dust explosion characteristics in the 20-L-sphere

Several safety characteristics of dusts are determined in the 20-L-sphere (also known as SIWEK Chamber) according to international standards. Dust cloud ignition is carried out using pyrotechnical igniters. Due to various disadvantages of such igniters the need for alternative ignition sources arises again and again. An alternative could be an ignition source which is known as “exploding wire” or “fuse wire”. The paper presents test results of a comparative study between both ignition sources for the determination of the safety characteristics “Maximum Explosion Pressure” and “Maximum Rate of Explosion Pressure Rise” of five selected dusts in the 20-L-sphere. In addition to that the ignition mechanisms of both ignition sources were analyzed by high speed camera recordings and the ignition energy was determined with electric and calorimetric recordings. The paper shows results of measurements of the ignition energy of both ignition sources as well as sequences of the flame propagation.     

露天采矿爆破振动对民房破坏的旋转森林预测模型

针对爆破振动对民房破坏问题,应用因子分析及旋转森林理论,选取爆破振动幅值、主频率、主频率持续时间、灰缝强度、砖墙面积率、房屋高度、屋盖形式、圈梁构造柱、施工质量、场地条件为影响因素。建立基于因子分析的露天采矿爆破振动对民房破坏的旋转森林预测模型。利用现场实测32组爆破数据作为学习样本进行训练。采用回代估计方法进行检验,误判率为1/32。用另外12组爆破试验数据作为测试样本进行预测。结果表明,就爆破振动对民房破坏而言,灰缝强度、房屋高度、屋盖形式、圈梁构造柱及施工质量与其相关程度较高。用模型所得预测结果的误判率为1/6。     

Measurement Accuracy of the Electrosensitive Protective Device Response Time When Using the Double Penetration Method

The Double Penetration Method (DPM) method of measuring ESPD (Electrosensitive Protective Device) response time was presented by Dzwiarek (1997). Calibrating the measuring equipment is a crucial stage of the procedure. Experimental verification of theoretical predictions is also crucial. For calibration purposes, a device simulating real ESPD operation thus enabling a correct setting of the response time was designed (Dzwiarek, 1997).

Theoretical analysis has shown that measuring ESPD response time with the DPM is subject to localisation errors made in the localisation of the detection zone border, rod position measurement errors made during highspeed penetration, and time delay measurement errors. The values of all those components of the total error have been determined experimentally using the calibrating device. Measurements have been taken under conditions as close to real ones as possible proving that the total measurement error is really enclosed within the assumed limits.     

Effects of Manual Handling,Posture, and Whole Body Vibrations on Low-Back Pain

To determine the effect of occupational stress on low-back pain (LBP), a cross-sectional study has been carried out, by interviews, on workers exposed to 3 stresses: manual handling (MH, 82 women and 264 men), whole body vibrations (WBV, 274 men), and static postures (278 women). Anthropometric data, occupational stress, LBP severity and frequency, and a psychological evaluation of these groups were compared to those of a control population of 208 workers (104 men and 104 women).

The results show that 30% of the population had never suffered from LBP. Age and the body mass index of the workers were the parameters most closely associated with LBP. Women involved in MH had higher frequency and severity of LBP than their reference population. Men involved in MH or exposed to WBV had higher frequency of painful episodes than their reference population. Workers exposed to one of the stresses were on sick leave for LBP more often, and for longer periods, than workers in the reference group. The results show that individual factors are often decisive in the onset of LBP. Nevertheless, in the more serious LBP cases, occupational stress is an aggravating factor for LBP and its consequences.     

高速铁路桥梁路段地面环境振动衰减特性研究

为了解高速铁路桥梁段列车运行引起的桥下地面环境振动衰减规律,对京津城际铁路247号桥墩处高速列车桥梁段列车运行时的环境振动进行测试,通过回归分析测试数据,得到了高速铁路桥梁段列车运行时所引起的地面环境振动衰减经验公式,并对现场测试数据与其他预测公式进行比较,分析了预测公式的有效性,为高速铁路引起地面环境振动的预防和治理提供参考。     

电驱动道路车辆动力锂离子电池芯试验中的实验室安全和防护

实验室标准化试验的条件远比装车使用严酷得多,在电驱动道路车辆的动力锂离子电池试验的过程中,实验室的安全是不可忽视的问题。基于实践和探索,本文介绍了关于电池芯试验的安全和防护。     

机载设备振动条件确定方法的研究

本文以机载显控台上的显示器为例,结合GJB 150A和GJB 4239的指导,介绍了在设计阶段和生产阶段上分别通过配重和设备的振动试验测量设备安装位置的响应,分析数据并确定机载设备振动试验条件的方法。     

型式试验过程中机械振动试验方法的研究

本文以正弦振动为例,结合相应的国标指导,介绍了电工电子和(或)核仪器类产品进行型式试验过程中机械振动试验方法的研究,以考察产品能否经受住预定的振动条件,并根据经受试验不同严酷等级的能力来划分设备等级。