钻孔攻牙自动上螺丝机设计

主要介绍一款为铜柱钻孔、攻牙、上螺丝的自动加工、装配一体化机器设计.通过对一体机的生产、制造、设计等系统阐述、分析,以及试生产达到的预期效果,对产品组装、装配需用到的钻孔、攻牙、上螺丝等工序的自动化改造有实际借鉴意义.     

A mathematical model with experiments of single effect absorption heat pump using LiBr–H2O

A mathematical model of a single effect, LiBr–H₂O absorption heat pump operated at steady conditions is presented. This model took into consideration of crosscurrent flow of fluids for heat and mass exchangers, two-dimensional distribution of temperature and concentration fields, local values of heat and mass transfer coefficients, thermal parameter dependent physical properties of working fluids and operation limits due to the danger of the LiBr aqueous solution hydrates and crystallization. Improvements of the calculation method make this simulation much more convenient and efficient. An improved absorber experiment set-up and a complete absorption heat pump were built and tested for further study. It was found that the mass flux of vapor increased with the increase of absorber pressure, coolant flow rate, spray density of LiBr solution and decrease of coolant and input temperature of solution. And the vapor mass flux increased almost linearly with the increase of absorber pressure. Results derived from this model show agreement within 7% with experimental values.     

预应力钢绞线张拉数据偏差分析及对策

针对案例中预应力钢绞线张拉数据的偏差问题,通过详尽的原因分析,计算出预应力损失并复测钢绞线的有效预应力,肯定了该批预应力构件的合理性和使用性能,避免了大量的经济损失和工期损失,为解决类似工程问题提供了科学参考。     

感应电机转子故障特征在交直交变频器中的传播

为研究感应电机转子故障特征在交直交变频器中的传播规律,在感应电机由交直交变频器驱动的系统中,利用逆变器和整流器的开关函数,对感应电机发生转子断条故障时的逆变器直流侧电流和整流器交流侧电流进行了解析分析,发现了对应的故障特征频率分量。分别在感应电机转子一根断条和转子两根断条的情况进行试验,试验结果也证明了理论分析的正确性,这为从变频器的整流器交流侧诊断感应电机转子故障提供了理论依据。     

地下水年度用水计划编制技术探讨

编制和实施地下水年度用水计划,是实现地下水精细化管理的基础。分析探讨了编制地下水年度用水计划的原则、程序、年度计划开采量的确定方法以及发生特殊干旱和突发事件等情况时,对地下水年度用水计划进行调整的原则要求。地下水年度用水计划的编制应充分考虑区域地下水开发利用总量控制指标、预测的来年水资源状况、上年度的地下水用水状况以及经济社会发展需求等因素。     

Synthesis and characterization of La2Ti2O7 employed for photocatalytic degradation of reactive red 22 dyestuff in aqueous solution

Perovskite structured La₂Ti₂O₇ catalyst prepared by polymerized complex method was characterized and examined the photocatalytic activity by decomposing an azo dyestuff, Reactive Red 22, in aqueous solutions under UV irradiation. La₂Ti₂O₇ powders prepared by polymerized complex method exhibit higher surface areas, better homogeneity and are more sensitive to solution than those prepared by solid-state method. The first derivatives of UV–vis DRS patterns confirmed the complete crystallization of La₂Ti₂O₇ sintered at temperatures higher than 900 °C. The effects of sintering temperature of catalyst and solution pH of photocatalytic reaction were studied. The photocatalytic decomposition of Reactive Red 22 per unit surface area was found to be higher for experiments using La₂Ti₂O₇ than using TiO₂. However, the electron–hole recombination was found to be more obvious for La₂Ti₂O₇ than for TiO₂ because the network of metal cations constructed within La₂Ti₂O₇ enhances the mobility of photogenerated electrons and holes.     

Stability of first and high order iterative learning control with data dropouts

This paper presents a stability analysis of the iterative learning control (ILC) problem for discrete-time systems when the plants are subject to output measurement data dropouts. It is assumed that data dropout occurs during the data transfers from the plant to the ILC controller, resulting in what is called intermittent ILC. Using the super-vector approach for ILC, the expectation of output error is used to develop conditions for stability of the first order ILC and high order ILC processes. Through the theoretical analysis, it is shown that the convergence of the intermittent ILC is guaranteed although some measurements are missing. The analysis is also supported by numerical examples.     

高速铁路箱梁用高性能混凝土的试验研究

采用L9(34)正交分析表,选取胶凝材料用量、粉煤灰掺量、矿粉掺量和水胶比四个因素,每个因素选取三个水平,分别对铁路箱梁C50配合比的10,28 d强度进行了正交分析。结果表明:对于10 d强度,粉煤灰的影响系数要高于水胶比和胶凝材料用量,矿粉影响系数最小;对于28 d强度,影响系数最大的是水胶比,其次是胶凝材料用量,影响系数最小的是矿粉用量。根据正交分析结果并结合实际工程需要,设计出满足标准和施工要求的配合比。     

GH169合金疲劳与蠕变裂纹萌生及扩展的微观动态物理过程研究

研究了镍基高温合金GH169的疲劳,疲劳蠕变复合作用下裂纹萌生、扩展的微观动态物理过程,结果表明,高温疲劳裂纹在滑移带与晶界相交处萌生,以晶内驻留滑移带处微裂纹连接方式扩展。疲劳蠕变复合作用下裂纹在垂直于应力轴方向的晶界处萌生,以晶界滑动方式扩展。疲劳蠕变复合作用使裂纹扩展方式由切变型转变为止应变型。晶粒大小对疲劳/蠕变复合作用下材料断裂寿命的影响远大于第二相的作用。晶粒越小,其断裂寿命越长。