Study on accelerated life tests for main shaft bearings in wind turbines

Journal of Mechanical Science and Technology - This paper focused on a 2.1 MW wind turbine main shaft bearing as the research object and analyzed its reliability under actual working conditions for...     

Optical design of a static solar concentrator using Fresnel lenses

We present an optical design for a static solar concentrator for a photovoltaic cell (SCPV). The concentrator consists of two Fresnel lenses, one concave and one convex. The SCPV was designed and optimized using ray-tracing computer simulations. The performance of the SCPV was demonstrated using two settings: static mode and periodic mode with passive bi-yearly angle adjustments. Even without an active tracking system, the SCPV achieved an average Concentration ratio (CR) in the range of 1.94-2.86. The CR was distributed non-uniformly throughout the year, and the value and season of the highest CR were different for the two settings. The optimal mode for SCPV use can be chosen by balancing specific preferences regarding the target season for peak performance, maximum average CR, and maintenance frequency.

     

Study on validation for accelerated life tests of pneumatic cylinders based on the test results of normal use conditions

This paper presents a validation method for Accelerated life tests (ALTs) of pneumatic cylinders. Two ALTs using each temperature and pressure stress were performed. Weibull analyses for these ALTs and their combination data were conducted. The comparison analysis was carried out between predictions based on ALTs and results obtained from normal use conditions. In other words, the validation of ALTs was conducted by applying hypothesis tests and confidence intervals for Weibull parameters. Finally, the Weibull shape parameter, the acceleration index of pressure, the activation energy for temperature, and the life cycles (B ₁₀ and characteristic) under normal use conditions for pneumatic cylinders were obtained.     

Heat loss investigation from spherical cavity receiver of solar concentrator

The heat losses are mainly affects on the performance of cavity receiver of solar concentrator. In this paper, the experimental and numerical study is carried out for different heat losses from spherical cavity receiver of 0.385 m cavity diameter and 0.154 m opening diameter. The total and convection losses are studied experimentally to no wind and wind conditions for the temperature range of 150 °C to 300 °C at 0°, 30°, 45°, 60° and 90° inclination angle of cavity receiver. The experimental set up mainly consists of copper tube material cavity receiver wrapped with nichrome heating coil to heat the cavity and insulated with glasswool insulation. The numerical analysis was carried out with Fluent Computational fluid dynamics (CFD) software, to study connective heat losses for no wind condition only. The numerical results are compared with experimental results and found good agreement with maximum deviation of 12 %. The effect of inclination angle of cavity receiver on total losses & convection losses shows that as the inclination angle increases from 0o to 90o, both losses decreased due to decreased in convective zone into the cavity receiver. The effect of operating temperature of cavity shows that as the temperature of cavity receiver increases, the total and convective losses goes on increasing. The effect of external wind at 2 m/s and 4 m/s in two directions (side-on wind and head-on wind) is also studied experimentally for total and convective heat losses. The result shows that the heat losses are higher for head-on wind condition compared to side-on wind and no wind condition at all inclination angle of cavity receiver. The present results are also compared to the convective losses obtained from the correlations of Stine & Mcdonald and M. Prakash. The convective loss from these correlations shows nearest prediction to both experimental and numerical results.

     

Friction machine for accelerated wear tests of frictional rolling elements

The construction of a friction machine for accelerated tests of friction rolling elements for frictional torque and wear. A study of the influence of rolling resistance force, rotational speed, and external load on the wear of samples has been carried out. A regression mathematical model that makes it possible to predict the amount of wear on the components of the friction pair under loading conditions has been obtained.     

碟式太阳能聚光器镜面组件设计及制造工艺

介绍了三种碟式太阳能聚光器及其镜面组件的结构形式,针对西航公司自主研发的20k W/25k W斯特林太阳能热发电系统,设计了其聚光器镜面组件,进行了在9级风和自重条件下镜面组件的刚度模拟计算,介绍了镜面组件的制造工艺及关键技术,通过太阳光聚光试验,光斑直径可以达到15cm,表明所设计的镜面组件可以实现聚光要求。     

槽式太阳能聚光器支架结构的拓扑优化设计

槽式太阳能聚光器支架结构是太阳能热发电系统中聚光器组的主要承载部件,为了在产品设计阶段寻求最佳设计方案,运用有限元软件Hyperworks中的Optistruct模块,以柔顺度为目标,以体积为约束条件,对单工况下的支架结构进行优化设计.根据拓扑优化的结果并结合生产经验,设计出新结构,最后用ABAQUS软件对新结构进行有限元分析.结果表明,优化后的支架性能在多方面均有所提高,对提高产品质量、缩短设计周期有重要作用,一定程度上也减少了企业的生产成本,为企业带来一定的经济效益.     

Forecasting the viability of friction pairs in accelerated tests

In order to simulate on a laboratory model the processes of friction and wear in a crane brake under conditions of rapidly-repeated loading, the scale factor must be taken into account. A method is described for obtaining scale coefficients for the transfer from a full-size to a model system on the basis of similarity theory and dimensional analysis. The validity of the coefficients has been confirmed experimentally and the accuracy of the simulation estimated.     

Lifetime estimation of harmonic reducer for manufacturing robot using accelerated life test

We present a calibrated accelerated life test to predict the operational lifetime of newly manufactured harmonic reducers for robots. To this end, a framework based on torque as the accelerating stress is proposed, and a step-stress test is performed to determine the highest stress level. Furthermore, the failure mode and corresponding failure mechanisms of the primary components of the harmonic reducer, and the effect of stress due to the applied load are analyzed. Accordingly, the lifetime of the harmonic reducer under its rated condition is estimated by extrapolating the acceleration test data at three stress levels and analyzing the same using statistical methods. The results obtained include such measures of reliability as the shape and scale parameters of the Weibull distribution, acceleration index for torque, and various estimates of the harmonic reducer’s lifetime.

     

Prediction of remaining useful life under different conditions using accelerated life testing data

Prognostics methods model the degradation of system performance and predict remaining useful life using degradation data measured during service. However, obtaining degradation data from in-service systems in practice is either difficult or expensive. Therefore, accelerated life testing (ALT) is instead frequently performed for validating designs using considerably heavy loads. This work discusses the methods and effectiveness of utilizing ALT degradation data for the prognostics of a system. Depending on the degradation model and loading conditions, four different ways of utilizing ALT data for prognostics are discussed. A similar transformation method used in ALT is adopted to convert accelerated loading conditions to field loading conditions. To demonstrate the proposed approach, synthetic data are generated for crack growth under accelerated loading conditions; these data are used for training a neural network model or identifying model parameters in a particle filter. The applied example shows that the use of ALT data increases the accuracy of prognostics in the early stages in all four cases and compensates for the problem posed by data insufficiency through the proposed method.     

Using nonparametric goodness-of-fit tests to validate accelerated failure time models

The construction of a reliability function from the results of accelerated failure time (AFT) models is considered. The constructed AFT models are verified by analyzing a sample of residuals. The fit of the residual sample to the baseline probability distribution is tested using modified nonparametric goodness-of-fit tests. In the absence of censoring in tests, it is proposed to use previously constructed models of distribution of statistics for testing composite hypotheses. In the case of censoring of type I or II, distributions of the goodness-of-fit test statistics are found by statistical modeling.     

橡胶减振元件加速寿命试验的仿真研究

针对橡胶减振元件疲劳寿命试验时间较长的问题,采用计算机仿真开展了加速寿命试验研究。利用CATIA和ABAQUS软件分别建立了橡胶减振元件的三维实体及有限元模型,采用二参数的Mooney-Rivilin模型模拟橡胶材料。通过模态分析,结合橡胶减振元件的工作状态,确定了试验系统的极限加载频率。施加3种不同的随时间变化的位移载荷,对橡胶减振元件进行了瞬态动力学分析,获得了其应力分布,从而确定了易于发生疲劳破坏的危险部位。提取橡胶减振元件危险部位的应变值,利用Manson-Coffin关系,根据橡胶材料的应变幅-疲劳寿命关系曲线,确定了3种加载条件下橡胶减振元件的破坏周期。研究结果表明,在同样的累积损伤、疲劳破坏模型条件下,通过合理提高加载频率和加载等级,可以大大缩短橡胶减振元件的疲劳寿命试验周期。     

腐蚀应力加速寿命试验条件下滚动轴承的可靠性评估

为了缩短轴承可靠性评估试验时间,用逆幂律Weibull加速寿命试验方法分析了腐蚀条件下滚动轴承的可靠性。用加权最小二乘法和极大似然法给出了评估模型参数的点估计,结合信息矩阵法给出了评估模型参数及轴承平均寿命、可靠度、可靠寿命等可靠性指标的区间估计。解决了常见轴承可靠性评估中只有可靠性指标点估计而缺少区间估计的问题,使评估结果更加全面。分析了具体实例,基于Akaike信息准则(AIC)、贝叶斯信息准则(BIC)原理,用最佳模型给出了腐蚀条件下轴承的可靠性评估结果。计算结果表明所提方法具有较高的评估精度,且当腐蚀应力提高1倍时,轴承的平均寿命缩短8.75%,可靠度减小16.83%。     

航天电连接器步进应力加速寿命试验研究

航天电连接器具有可靠性高、寿命长的特点,为解决其接触可靠性评估问题,通过分析其接触失效机理,指出在温度应力下的接触失效物理模型为Arrhenius方程,接触寿命服从两参数的Weibull布,并在此基础上建立了接触可靠性统计模型;研究了航天电连接器步进应力加速寿命试验方法,利用极大似然估计和Nelson累积失效模型,提出...     

非恒定应力加速寿命试验方法及其应用研究

通过对加速寿命试验的研究,进一步深入探讨了符合实际试验条件的非恒定应力下的加速寿命试验的过程,提出了其加速寿命试验模型和数据处理方法,借助软件完成了对非恒定应力加速寿命试验的寿命-应力模型的建立和寿命数据的处理及优化.并通过了某电加热器的实例验证了此模型和计算的合理有效.     

快速漩流浓缩仪用于多种农药残留分析

介绍快速漩流浓缩仪装置的结构、工作原理、各种参数对回收率的影响以及在多种农药残留分析技术中的应用     

Instrumentation for urologic laser surgery

Carbon dioxide, neodymium:yttrium-aluminum-garnet, ruby, and argon lasers are the only commercially available lasers with wavelengths suitable for laser surgery. Consequently, researchers have attempted to make the tool fit the clinical need. A pediatric #6 bronchoscope was fitted to a carbon dioxide laser endoscopic coupler to form a modified cystoscopic laser delivery system. This instrument was able to vaporize small condylomata of the distal male urethra. However, the restricted visibility of this crude adaptation represents an inferior solution compared with the endless possibilities of sophisticated fiberoptic technology. Future prospects in infrared optical fiber technology portend a breakthrough for transurethral carbon dioxide laser surgery. Adapting the Nd:YAG laser for urologic surgery is attractive because it can be easily incorporated into conventional cystoscopes. The argon laser's capacity to absorb blood and traverse water suggests future importance for transurethral surgery. Investigation is needed to develop a surgical laser adaptable to both open and transurethral urologic surgery.     

采用线性累积模型的变换形式分析步加试验

对用于分析步进应力加速寿命试验的累积损伤模型进行时间变换,保留模型对数据拟合的灵活性的同时简化了数学计算。为了比较模型的拟合性,对仿真数据进行了卡方拟合优度检验。     

基于定时测试的综合应力加速寿命试验方案优化设计

针对定时测试综合应力加速寿命试验设计问题,就恒定应力加速寿命试验方法,根据所提出的加速寿命试验方案优化设计的准则和方法,以产品在正常工作应力水平时寿命估计值的方差最小为目标,在确定了每个应力水平组合下定时测试时间获取方式后,以各加速因子的试验应力水平、各次试验的试样分配比例及各次试验的截尾时间为设计变量,应用极大似然估计理论,建立了定时测试综合应力加速寿命试验方案优化设计的数学模型.对航天电连接器的定时测试综合应力加速寿命试验方案优化设计的结果表明,经过优化以后的定时测试试验方案不仅可以提高试验数据的估计精度、减少试验次数,而且还可以在相同置信度下减少试验所需的样本数量,并能够缩短试验时间.     

Instrumentation for 500 kHz Uigh-Resolution Chronoamperometry

ABSTRACT

An interactive, computer-controlled system for ligh-speed chronoamperometry was developed. The system consists of a digital potential-stepenerator with 12-bit resolution, coupled to a data retrieval circuit. This circuit includes a 12-bit malog-to-digital converter which operates at a speed of 500 kHz (2 μs/conversion), and a 76t-word memory. Alter a start signal from the computer, the xternal system is self-supporting in the cquisition and storage of current data from an lectrochemical cell. It allows for accurate recording of highly transient currents.