A novel PEM fuel cell remaining useful life prediction method based on singular spectrum analysis and deep Gaussian processes

Accurate remaining useful life (RUL) prediction of proton exchange membrane fuel cells (PEMFCs) can assess the reliability of fuel cells to determine the occurrence of failures and mitigate their operational risk. However, is it quite challenging to design a high-precision prediction method because the implicit degradation details of PEMFCs are difficult to learn well from the measurement data with high-frequency noise. Recognizing this, a novel RUL prediction method based on singular spectrum analysis (SSA) and deep Gaussian process (DGP) is proposed in this paper. The SSA-based method is firstly employed to preprocess the measurement data, which can strengthen the effective information of PEMFC degradation data at the same time remove the noise and spikes that interfere with degradation prediction. As a deep structural model, DGP has strong feature learning ability which can represent the nonlinear details of degradation data and give more accurate prediction results. At the same time, it serves as a probabilistic model that can provide the confidence interval to enhance reliability of RUL prediction. The effectiveness of the proposed method is evaluated by experimental data of the PEMFCs under steady-state conditions, and the results show that the SSA-DGP method has higher accuracy and reliability than conventional methods.     

基于粒子群优化的超声共振谱法测量材料弹性常数

超声共振谱法是一种基于材料样品的自由共振频率,再反推其弹性常数的高精度材料力学属性求取方法,该方法在高Q值(品质因素)固体材料的弹性常数计算方面应用广泛。然而对于具有较高黏弹性阻尼的材料来说,受共振谱线平缓、共振频率提取困难等影响,该方法的应用存在一定困难。建立了关于弹性常数的贝叶斯模型,结合粒子群优化(PSO)的全局搜索能力,寻找弹性常数的最大后验概率密度点,最终实现材料的弹性估计。测量了皮质骨模拟材料的弹性常数,与传统方法相比较,基于PSO的超声共振谱方法对弹性常数初始值不敏感,可用于高阻尼材料弹性常数的测量。     

Processing map and hot deformation behavior of Ta-particle reinforced TiAl composite

The hot deformation behavior of a Ta-particle reinforced TiAl composite was studied. Ti–48Al–2Cr–2Nb– 0.2W(at.%)/20vol.%Ta metal matrix composite was fabricated by spark plasma sintering. The deformation behavior was investigated by hot compression tests at the temperature ranging from 1050 to 1200 °C and the strain rate ranging from 1×10⁻³ to 1 s⁻¹. The constitutive equation containing true strain variables was established. The values of activation energy Q under different strain degrees are between 240 and 280 kJ/mol, which are lower than that of pure TiAl. Based on dynamic material modeling, the processing maps at various strain degrees were established, and the optimized parameters for hot working are 1050–1100 °C and 0.005–0.01 s⁻¹. The microstructural evolution during deformation was characterized, which indicated that the dynamic recrystallization plays an important role in this process.     

基于热电效应的高效环控系统

部分空间科学实验对环境温度有较高的要求，环境温度高于或低于空间科学系统能够提供的热沉温度，需要有可靠有效的加温降温处理措施。使用可靠性强的热电制冷片作为制冷制热方式和气液换热器二次换热来实现环境温度控制的需求，并对不同流体温度制冷制热效果进行分析，结果表明流体温度和目标温度差越小，热电制冷制热的效果越好。在环境温度制冷工况中，热电单元数量随电流增加先减少后增加，在制热工况中则单调递减，设计中需按照制冷工况进行热电单元数量的确定。当流体温度接近制冷制热的目标温度时，会出现整个系统总效率优于热电系统效率的区间。通过对热电单元和气液换热器的组合系统的性能计算，提供一种适于热电环控系统的计算方法和部件选型思路，对空间站环控系统的设计有重要参考意义。     

Effects of yttrium on wettability and interactions between molten superalloy and SiO2-based ceramic core

In order to obtain high-quality superalloy castings, the wettability and interactions between superalloy melts with various Y contents and SiO₂-based ceramic cores were investigated at 1823 K. The results indicated that the wettability and interface reactions were affected by the content of Y in the alloy. For the alloys with Y content less than 0.011 wt%, no Y-oxide was found at the interface, but HfO₂, Al₂O₃ and ZrO₂ phases were formed, and the wetting angle dropped slightly. However, different Y-oxides precipitated at the alloy-ceramic interface for the alloys with Y content more than 0.017 wt%, and the wetting angle dropped sharply. When the content of Y was 0.017 and 0.025 wt%, Al₂O₃, Y₃Al₂(AlO₄)₃, HfO₂ and ZrO₂ phases were formed at the interface. When the content of Y was 0.1 wt%, YAlO₃, Y₃Al₅O₁₂, Y₄Al₂O₉, HfO₂ and ZrO₂ phases were formed. The formation of different reaction products was mainly caused by the change of Y activity (a_Y) in the alloy. The reaction between Y and SiO₂ could improve the wettability of the system apparently.     

直升机液冷/蒸发制冷联合系统关键部件试验性能

现代军用直升机经常执行特殊飞行任务，其机载电子设备具有功率大、瞬间振荡、高热通量等特点，使得环控系统的冷却需求呈指数上升趋势，进而制约着直升机的巡航功能和战斗性能的提升。针对直升机机载大功率电子设备的冷却需求，结合制冷剂、冷却液循环等子系统，搭建地面稳态试验台，针对蒸发器、冷凝器等关键部件进行了地面稳态试验。研究过程采用仿真与试验相结合的方法，开展了制冷循环中蒸发器、冷凝器等关键部件稳态仿真计算，且完成了蒸发器、冷凝器的换热性能试验研究，对所建立的仿真模型进行了有效性校核与参数修正。上述研究可为后续直升机液冷/蒸发制冷系统的关键部件设计提供一定的参考。     

特种车辆舱室送风系统布局仿真优化

特种车辆由于其功能特殊性和封闭性，无法像民用车辆一样利用窗户的开闭来控制舱室通风，长时间驾驶特种车辆，驾驶舱面临空间小、冷源少、热负荷大、缺乏新鲜空气等问题，且外部环境条件复杂。这就要求特种车辆舱室送风系统精细设计，满足人员和多个装置的热舒适和热控需求，因此有必要基于特殊车辆的驾驶舱特点，合理布局并优化通风系统，保证整舱热要求。为了让座舱送风与舱内热源热交换尽量完全，带出更多的热量，首先针对某型特种车辆，建立了典型舱室和乘员的三维物理模型和仿真模型。针对10种送风模式进行了详细的气流组织仿真优化分析，获得了特种车辆舱室多物理场。气流组织优化是从风口形式和送风口位置两方面进行，风口形式优化中提出多种风口组合形式，分别进行仿真。以设备温控、人员热舒适和空气龄等为目标，利用评价函数对仿真结果进行评价，对10种类型的送风工况进行了仿真。从仿真结果中，以上述多优化目标为依据，进一步开展了针对初步优选的送风形式的风口位置优化。在风口形式优化结果的基础上，采用遗传算法，将位置参数设为优化参数，选取两个评估函数作为优化的目标函数，并将头足温差等约束条件设置到优化模型中，对仿真结果进行筛选和逆优化研究，最终得到最优风口位置，完成气流组织优化。研究对于全密封特种车辆的有限空间热舒适性和空气质量研究具有一定意义。     

Enhancement of the room-temperature hydrogen sensing performance of MoO3 nanoribbons annealed in a reducing gas

Uniform-sized orthorhombic MoO₃ nanoribbons were synthesized by a simple hydrothermal method at 240 °C. The nanoribbons grew along the [001] orientation, with average length, width and thickness of approximately 20 μm, 270 nm and 90 nm, respectively. The obtained nanoribbons were further annealed in a hydrogen atmosphere at different temperatures to modify their surface states. The treatment of the nanoribbons at 300 °C significantly elevated the concentration of non-stoichiometric Mo⁵⁺ to 24.7%, much larger than the original concentration (∼14.8%). A positive relationship was found between the non-stoichiometric Mo⁵⁺, chemisorbed oxygen ion and sensor response. The sensor based on the MoO₃ nanoribbons treated at 300 °C exhibited a faster response time of approximately 10.9 s, and a higher sensor response of 17.3 towards 1000 ppm H₂, compared with the results of original tests (∼21 s and ∼5.7, respectively), indicating the significantly improved gas sensing performance of the treated MoO₃. Meanwhile, the sensor also exhibited excellent repeatability and selectivity toward hydrogen gas. The enhancement of the hydrogen gas sensing performance of treated MoO₃ nanoribbons was attributed to the more effective adjustment of the width of the depletion region on the nanoribbon surface and the height of the potential barrier at the junctions, induced by the interaction between hydrogen molecules and higher-concentration oxygen ions. Our research implied that the gas sensing performance of nanostructured metal oxides could be successfully enhanced through annealing in the reducing gas.     

Effect of energy transfer and local crystal field perturbation on the thermometric sensitivity of Ga-Tb-Eu ternary emission system

A series of optical thermometers based on Eu³⁺/Tb³⁺ doped Y₃Ga₅O₁₂ with self-excited GaO₆ group phosphors were designed through controllable energy transfer and local crystal field perturbation simulated using the density-functional theory approach and related structures. Color-tunable properties of the phosphors could be achieved through controllable energy transfer. In addition, the thermometers exhibited superb temperature sensitive properties. Over the entire temperature range (298.15–598.15 K), maximum values of the absolute sensitivity and relative sensitivity are 0.028 K^?1 and 7.03 %K^?1, respectively. Meanwhile, the thermometer has outstanding resolution (ΔT = 0.0043 K) and repeatability (98.37%).