空间环境分子污染对航天器的影响

空间环境分子污染对航天器的影响,是目前高可靠性、长寿命航天器在设计时非常重要的问题之一。通过对国外航天器在轨飞行过程中所发生的分子污染现象的总结,从分子污染的来源、形成过程、与原子氧和紫外辐射等其他空间环境因素间的反应、对航天器敏感表面特性的影响等方面,对分子污染效应做了详细的介绍。并指出,材料的真空放气产物和原子氧剥蚀产物在航天器表面的沉积,是分子污染的主要来源。而在原子氧和紫外辐射的作用下,污染层会发生氧化、固结、暗化等现象,使其外观和成分发生了不同程度的变化,从而对航天器敏感表面的光、电、热控等性能带来了很大程度的影响。     

半潜入喷管收敛段碳/酚醛材料烧蚀特性

采用流固热耦合数值方法,以及Abaqus的ALE（arbitrary Lagrangian-Eulerian,任意拉格朗日欧拉方法）自适应网格技术,对位于半潜入喷管收敛段的碳/酚醛的烧蚀现象进行了预估,与试验结果进行了对比分析。结果表明:在收敛段,Al/Al₂O₃液滴或颗粒对材料的传热烧蚀起到了关键作用,当气流与材料表面平行时,液滴或颗粒的影响很小;从碳/酚醛热分解角度出发,基于完全碳化即被剥蚀的假设,基本能够预估碳/酚醛材料的烧蚀特征,烧蚀速率大约为0.3 mm/s;后效碳化对材料碳化过程的影响明显,发动机工作期间,分解层的厚度大约为2.0 mm,考虑后效作用,分解层厚度可能会增加至4.0 mm左右;与喉衬接触的材料区域,喉衬的传热会明显加剧材料的碳化过程。      

可磨耗封严涂层的冲蚀磨损特性及模型

抗冲蚀性是可磨耗封严涂层最重要的性能。在自制的真空自由落砂试样旋转式冲蚀磨损试验机上对几种中温封严涂层的冲蚀磨损特性及机理进行了研究。实验结果表明,冲蚀失重与冲蚀时间具有良好的线性关系;在60°时冲蚀率最大;冲蚀率与冲蚀速度有幂函数关系,速度指数随冲蚀角度增大而增大;90°冲蚀时,涂层的冲蚀机理为冲击粒子在涂层表面冲击挤压,产生凹坑和凹坑边缘凸起的唇片,随后的冲蚀使唇片流失;粒子的不断冲击使表层金属相松动,导致呈颗粒状剥落。30°冲蚀时涂层的冲蚀机理为切削、犁削并有孔洞、非金属相贯通效应。在此基础上提出了封严涂层的冲蚀磨损模型。     

Integration of artificial intelligence with meta classifiers for the gully erosion susceptibility assessment in Hinglo river basin,Eastern India

The main aim of this study is to evaluate the gully erosion susceptibility coupling the artificial intelligence and machine learning ensemble approaches. In the present study, the multilayer perceptron neural network (MLP) was used as the base classifier and the hybrid ensemble machine learning methods i.e. Bagging and Dagging were used as the functional classifiers. The Hinglo river basin, an important tributary of the Ajay River was selected as the study area, consists with the parts of Chhotonagpur plateau and Rarh lateritic region. The study area is facing the gully erosion problems which are interrupted the growth of the agriculture. The gully erosion susceptibility maps (GESMs), prepared by MLP, MLP-Bagging and MLP-Dagging were classified into four classes such as low, moderate, high and very high susceptibility classes with the help of natural break method (NBM) in GIS environment. The very high susceptibility class covered 19.41% (MLP), 13.52% (MLP-Bagging) and 15.30% (MLP-Dagging) areas of the basin. For the evaluation and comparison of the models, receiver operating characteristics (ROC), accuracy, mean absolute error (MAE) and root mean square error (RMSE) were applied. Overall, all the gully erosion susceptibility models were performed as excellent. Integration of hybrid ensemble models with MLP has increase the accuracy of the MLP models. Among these models MLP-Dagging has achieved the highest accuracy in compare to the other models. The importance of the selected factors in the present study was assessed by the Relief-F method. The results show that the soil type factor has the highest predictive performance. Sensitivity analysis also showed soil type as most important factor. The gully erosion susceptibility maps (GESMs) are considered as the efficient tool which could be used to take the necessary steps for mitigating and controlling the soil erosion problem and sustainable environmental management and development.     

电弧加热器铜污染组分效应发射光谱定量研究

电弧加热器是研究飞行器气动热防护问题的重要地面试验平台，其采用电极放电加热获得高温气体的方式，会产生铜蒸汽粒子，并随同进入地面试验模拟的等离子体气流，产生电弧风洞地面试验铜污染组分效应。本研究利用发射光谱诊断技术，发展了一套电弧加热器高温流场组分在线诊断测量系统，开展对10 MW高焓叠片式电弧加热器铜电极烧蚀的在线测量，获得了铜原子浓度的实时测量结果。基于所选铜原子谱线，开展了对电弧加热器起弧过程和稳定工作过程的测量，同时分析了管式电极和环形电极下电极烧蚀的情况。研究结果表明：起弧瞬间，电极烧蚀较明显，管式电极的铜原子峰值浓度要明显高于环形电极；稳定工作后，环形电极铜原子烧蚀量迅速下降，并保持在一个较低水平（<10^-6），管式电极仍然存在较高、不稳定的烧蚀，显示管式电极的烧蚀量要明显高于环形电极，且管式电极烧蚀量随着电弧加热器运行电流的增加而增加。基于该测量结果，建立了判定电极失效的直接判据，并用于保障电弧加热器运行安全。为研究电弧加热器电极烧蚀及地面试验铜污染组分效应提供了非接触式测量手段，目前，该测量系统已经作为电弧加热器的常规测试手段，提供电弧加热器高温气流的在线诊断。     

基于均匀设计的钛合金化铣工艺研究与应用

化学铣切是一种能使表面形状复杂、加工精度要求高的零件达到加工要求的表面处理方法.简要介绍了钛合金化学铣切的工艺方法,阐述了化学铣切的反应机理,并在均匀设计试验的基础上讨论了化学铣切温度和溶液配方对钛合金产品化学铣切质量的影响.通过实验数据回归分析确定了最优的化学铣切工艺方案,分析表明验证结果与理论是相符的,可应用于实际生产.     

防热复合材料抗粒子侵蚀特性研究

研究了含钨Ｃ／Ｃ复合材料、细编穿刺Ｃ／Ｃ复合材料等防热材料抗粒子侵蚀性能及其形貌特征。针对试验结果,探讨了目前侵蚀性能试验存在的问题。指出不同种类的防热复合材料在不同试验条件下表现出不同的抗粒子侵蚀机理和形貌特征,以侵蚀系数Ｃｎ值表征不同防热材料抗粒子侵蚀能力的大小具有不直观性。     

Creating Habitable Zones, at all Scales, from Planets to Mud Micro-Habitats, on Earth and on Mars

The factors that create a habitable planet are considered at all scales, from planetary inventories to micro-habitats in soft sediments and intangibles such as habitat linkage. The possibility of habitability first comes about during accretion, as a product of the processes of impact and volatile inventory history. To create habitability water is essential, not only for life but to aid the continual tectonic reworking and erosion that supply key redox contrasts and biochemical substrates to sustain habitability. Mud or soft sediment may be a biochemical prerequisite, to provide accessible substrate and protection. Once life begins, the habitat is widened by the activity of life, both by its management of the greenhouse and by partitioning reductants (e.g. dead organic matter) and oxidants (including waste products). Potential Martian habitats are discussed: by comparison with Earth there are many potential environmental settings on Mars in which life may once have occurred, or may even continue to exist. The long-term evolution of habitability in the Solar System is considered.     

电弧推力器流场的数值计算

在流体计算软件fluent的微分方程中加入电磁项,可以计算电磁场作用下的流场。本文介绍了电弧推力器的理论模型,计算了电弧流场,并将计算结果和试验数据进行比较。分析了欧姆加热对提高工质气体比冲、降低推进剂消耗的作用,并根据流场温度分布,估计了电弧对电极的热烧蚀情况,提出了相应的解决方案。     

粒子云侵蚀的机理分析

本文用图示法表达了粒子云侵蚀/烧蚀问题中各环节之间的联系和各种耦合作用。然后简要地分析了几个主要环节:粒子在激波层中破碎、减速和汽化,高速运动的粒子撞击物面引起的侵蚀,侵蚀过程中多粒子的互相影响,以及粒子云环境中表面气动加热的增量。