A mechanism informed neural network for predicting machining deformation of annular parts

Controlling machining deformation of annular parts is crucial for ensuring the performance of high value products and equipment. For example, during manufacturing of critical parts in aircrafts and spacecrafts, accurate prediction of machining deformation is the basis for guiding the formulation of deformation control strategies. However, due to the complexity of the machining deformation of annular parts, existing methods still have limitations in accurate prediction. To this end, this paper proposes a mechanism informed neural network (MINN) to predict machining deformation of annular parts. MINN is realized by establishing the dual sub-networks structure and using enhanced loss functions with the consideration of the deformation mechanism model characteristics of annular parts. The deformation was decomposed into the axisymmetric portion and the non-axisymmetric portion according to the deformation superposition principle, and modeled separately based on the thin-shell theory and Fourier series. Experiment results showed that the proposed method could predict the machining deformation of annular parts more accurately and stably with a small amount of training data, compared with previous methods.     

基于NB分类器重访概率预测的Web缓存替换策略

Web缓存是用来解决网络访问延迟和网络拥塞问题，缓存替换策略直接影响缓存的命中率。为此，提出一种朴素贝叶斯（NB）分类器重访概率预测的Web缓存替换策略；根据用户之前访问日志，通过分区操作提取多项特征来表示每次访问的对象，并构建特征数据集；训练NB分类器，用来确定缓存中对象被再次访问的概率，为对象分配权重；结合LRU策略来合理删除一些对象。仿真结果表明，提出的策略在保证较高命中率的同时有效降低了执行时间。     

Machine fault diagnosis with small sample based on variational information constrained generative adversarial network

In actual engineering scenarios, limited fault data leads to insufficient model training and over-fitting, which negatively affects the diagnostic performance of intelligent diagnostic models. To solve the problem, this paper proposes a variational information constrained generative adversarial network (VICGAN) for effective machine fault diagnosis. Firstly, by incorporating the encoder into the discriminator to map the deep features, an improved generative adversarial network with stronger data synthesis capability is established. Secondly, to promote the stable training of the model and guarantee better convergence, a variational information constraint technique is utilized, which constrains the input signals and deep features of the discriminator using the information bottleneck method. In addition, a representation matching module is added to impose restrictions on the generator, avoiding the mode collapse problem and boosting the sample diversity. Two rolling bearing datasets are utilized to verify the effectiveness and stability of the presented network, which demonstrates that the presented network has an admirable ability in processing fault diagnosis with few samples, and performs better than state-of-the-art approaches.     

低压环境下航空电缆材料燃烧特性的研究

在高高原实验室(61 kPa、4 290 m)和广汉实验室(96 kPa、520 m),分别开展常低压条件下FXL型航空电缆的对比燃烧实验。通过热辐射加热箱、烟密度及成分测试仪和氧指数仪等设备,测量点燃时间、烟密度、质量损失速率和CO、CO2及O2等浓度变化。实验结果表明:在96 kPa和61 kPa两种实验环境下,低压下最小点燃时间及温度的数值更大,两者的温度和时间差分别为15℃和4.8 s;烟密度曲线快速升高后趋于平衡,61 kPa条件下的发烟量小于96 kPa;O2体积浓度随着加热时间先下降后升高,而CO2的变化趋势相反。在61 kPa条件下,CO曲线会出现双峰现象且更明显;随着氧浓度增加,质量损失速率加快且呈线性关系;压力因素对燃烧影响减弱且燃烧持续时间差值变小。研究结果揭示了低压环境对航空电缆的燃烧影响,为增强航空安全提供参考。     

The physicochemical and fire extinguishing performance of aqueous film-forming foams based on a class of short-chain fluorinated surfactants

Aqueous film-forming foams (AFFFs) are an important for fire extinguishing, and their key ingredient is fluorinated surfactant. In recent years, traditional long-chain fluorinated surfactants have been banned by most countries because of their persistence, bio-accumulation and toxicity. Therefore, increased attention has been paid to the research and development of short-chain fluorinated surfactants. As is well known, the introduction of hydrophilic or hydrophobic groups in a surfactant affects its surface activity, and therefore, the fire extinguishing performance of AFFFs. In this work, a series of short-chain fluorosurfactant-based AFFFs with different hydrophobic chain lengths were prepared. The physicochemical performance of mixed systems (fluorinated surfactant plus sodium hexanesulfonate), including surface activity, spreading ability, foam expansion, drainage time, and the fire extinguishing and burn-back performance of AFFFs were studied. The results show that the critical micelle concentration (CMC) and the surface tension (γ_CMC) at the CMC of mixed systems at 25°C are lower than 7.68 mmol/L and 16.51 mN/m, respectively. For mixed systems, the average spreading rate is more than 1.09 cm/s, the foam expansion is over 7.1, and the drainage time is greater than 3.28 min. The fire extinguishing time of AFFFs on fuels is less than 51 s while the burn-back time is more than 15.18 min. The results imply a potential application prospect of the short-chain fluorinated surfactants in AFFFs.     

机身/发动机数控组件测试系统的研制

针对国内尚未拥有机身/发动机数控组件维修、测试能力的现状,并结合该组件当前故障率,提出一种基于虚拟仪器技术的维修测试平台。该平台以GPIB仪器、VXI模块为依托完成硬件设计,利用labview驱动模块实现对各类测试仪器的控制,并进一步完成软件设计。针对此平台进行误差分析的结果表明：该系统测试精度较高,参数误差均在性能指标范围内,能够满足机身/发动机数控组件的维修测试需求。     

27. 5 kV 电缆金属护层雷击特性的建模与仿真

基于行波理论,通过仿真计算不同分段情况下27.5 kV电缆分布式参数等效模型上雷电流波传播的速度,对比验证模型的准确性。通过理论计算确定金属护层装设护层保护器的必要性和护层保护器装设在首端的合理性。在此基础上,采用仿真软件研究雷电流波经接触网入侵电缆线芯时电缆长度、金属护层末端接地电阻和线芯末端阻抗对金属护层雷击感应电压的影响。结果表明,长度约为800 m的电缆其金属护层雷击感应电压最大值的平均值最小;接地电阻在2.5～3Ω内时,电缆金属护层雷击感应电压最大值的平均值最小,且均低于25 kV,当接地电阻超过5Ω时,外护套冲击耐受电压小于电缆金属护层雷击感应电压最大值,可导致外护套击穿;当接有较大容性阻抗或电缆末端短路,外护套冲击耐受电压远小于金属护层雷击感应电压,而接有较大感性阻抗或电缆末端开路时,金属护层雷击感应电压低于外护套冲击耐受电压。     

轮轨材料/硬度匹配研究进展与展望

车轮与钢轨硬度是影响轮轨磨损的主要因素之一,合理的轮轨材料与硬度匹配对于减轻轮轨磨损、延长服役寿命具有十分关键的作用。当前我国铁路运营过程中存在2种硬度钢轨匹配4种硬度车轮的现象,材料匹配行为复杂。针对铁路轮轨材料和硬度的选用与匹配,至今尚无统一合理的规定与标准。从轮轨材料硬度出发,首先分析了国内外轮轨材料发展与硬度匹配的使用现状,发现不同国家和地区轮轨材料硬度的选用存在较大差异。具体表现为:日本新干线使用的车轮硬度远高于钢轨(H_R/H_W<1),欧洲高速铁路上H_R/H_W值接近1,而中国高速铁路系统中,轮轨种类多,硬度区间大。其次,总结了轮轨硬度匹配研究进展,明确材料硬度和轨轮硬度比(H_R/H_W)对磨损与滚动接触疲劳损伤都具有显著影响,但并没有形成统一的结论,且以往的材料选用经验并不完全适用于当前的铁路系统。然后,针对现阶段轮轨材料与硬度匹配研究,探讨了材料加工硬化、合金钢微观组织、表面热处理工艺、复杂服役环境与车轮运行参数等因素的潜在影响。最后,提出...     

A Method of Applying Flight Data to Evaluate Landing Operation Performance

Abstract

Pilots’ operation has an important effect on flight safety and performance, particularly in the final landing stage when pilots need to deal with complicated operations. This study aims to determine the potential value of flight data and develop a method of evaluating a pilot’s performance during landing phase based on flight quick access recorder (QAR) data from the perspective of risk assessment. First, a Landing Operation Performance Evaluation Model was developed based on risk evaluation principles. Three landing parameters, which are touchdown distance, touchdown vertical acceleration and touchdown pitch angle, were selected as indicators to evaluate the pilots’ landing operation performance in this model. Second, the flight landing operation performance evaluation system (FLOPES) was set up based on the evaluation model. Test results showed that FLOPES can accomplish all calculation flow of operation performance evaluation. Finally, it concluded that this method is a more accurate and effective way for evaluating the landing operation performance of a flight. It could be as a practical tool for airlines to manage landing risk quantitatively and to provide a more practical support for improving training and design in aviation.Practitioner summary: This study aims to determine the potential value of flight data and to develop a method of evaluating pilot’s landing operation performance from the risk evaluation perspective. Test results showed that this method is effective and could be as a practical tool for airlines to manage landing risk and improve training.Abbreviations:QAR: Quick Access Recorder; FLOPES: Flight Landing Operation Performance Evaluation System; ICAO: International Civil Aviation Organization; IATA: International Air Transport Association; SMS: Safety Management System; CAAC: Civil Aviation Administration of China; FOQA: Flight Operations Quality Assurance; VBA: Visual Basic for Applications     

Three classes of binary linear codes with good parameters

Three classes of linear codes with good parameters are constructed in this paper. The length, dimension and minimum distance for each class of linear codes are also investigated by means of the well-known Kloosterman sums over finite fields. It is interesting to note that the constructed three classes of linear codes possess good parameters and some of them are shown to be optimal.