基于改进蚁群算法和Mann-Kendall法的涡桨发动机性能预测

针对涡桨发动机复杂、非线性的工作环境，利用层次分析（AHP）法提取发动机工作状态特征参数，考虑各特征参数对工作状态识别的影响，以特征参数加权的改进蚁群算法为基础，进行发动机同一工作状态识别、聚类，并采用Mann-Kendall法开展发动机性能预测分析。利用多台涡桨发动机性能参数飞参数据进行验证，结果表明：该方法能准确识别发动机起飞、额定工作状态，巡航以下工作状态识别准确率达84%以上；此外，发动机性能预测效率提升了近50%，而预测错误率小于10%，可以满足航空兵部队维修保障工作的实际需要。     

锯切圆柱形42CrMoA的声发射监测试验

针对锯切加工中的带锯条磨损状态未知、锯切质量下降等问题，本文研究了新试制的FTCUT双金属带锯条锯切圆柱形42CrMoA合金结构钢过程中锯切行为的变化，探讨了声发射信号与单刀锯切过程、锯齿磨损和锯切表面质量变化的关联。研究表明：锯切圆柱材料时随着锯切深度的变化，参与齿数先增大后减小，带锯条约束条件不断变化，进而影响着声发射信号幅值和锯切表面质量；基于时域分析可知锯齿磨损过程分为磨合磨损、快速磨损、稳定磨损三个阶段；基于FFT频域分析发现当频谱图出现多个主频，且第一主频幅值下降时，表明声发射信号来源比较分散，即可认定带锯条失效；基于小波包频域分析发现第7频段信号占比最高，最能反映工件表面质量的变化，其波动情况与锯切表面的微纹和波纹情况可建立一定的联系。因此，可基于声发射信号时域和频域分析判断锯齿磨损和锯切表面恶化情况，为锯齿磨损和锯切表面质量的在线监测提供一定的思路。     

On the behavior of thermospheric O1D 630.0 nm dayglow emission during counter electrojet events

This study presents the response of thermospheric O¹D 630.0 nm dayglow emission to the variability associated with equatorial Counter Electrojet (CEJ) events. The analysis based on the data from a meridian scanning Dayglow Photometer, Digital Ionosonde and Proton Precession Magnetometer over Trivandrum (8.5°N, 77°E, 0.5°dip lat.), indicates that the O¹D 630.0 nm emission behave distinctly different during the CEJ events compared to that on normal days. It has been observed that O¹D 630.0 nm emission shows enhancement during the negative excursion of the ΔH, followed by an unusual depletion during the peak CEJ time. The observed variability was found to be more pronounced in a latitudinal region of ±3° centered at around the dip equator. In addition, the emission intensities also exhibit the presence of enhanced short period oscillations of periodicity 20–30 min during the CEJ events. Analysis of the data from the collocated ionosonde revealed that the F-region electron density showed enhancement during the early phase of the CEJ and a decrease during the peak CEJ. Further, the simulation studies using a Quasi 2 dimensional ionospheric model showed that the modified plasma fountain during the CEJ can alter the plasma density at the emission centroid. The study reveals a strong dynamical coupling between the E and F-region of the dip equatorial ionosphere.     

Assessing the hydromorphological condition of the Sub-Himalayan Mahananda-Balason system using the hydromorphological quality Index

An evaluation of the hydromorphological condition of the Mahananda-Balason River system of the sub-Himalayan foothills, West Bengal, India was attempted using a multiparameter-based Hydromorphological Quality Index (HQI). After segmenting these rivers based on continuity, bed material and channel planform, a total of 18 indicators, divided into 3 subgroups Continuity (C), Planform (P), and Floodplain Morphology (FM), were quantified reach-wise and scaled upon the level of alteration (1 for highly altered and 5 for no alteration). The derived overall HQI (3.6) exhibited a moderate hydromorphological quality of the system, however, significant differences between the HQIs of confined and unconfined reaches were witnessed. Students ‘t-test and Multiple Correspondence Analysis both portrayed vast dissimilarities among the confined and unconfined reaches and the clustering was depending on their confinement. The deviations measured from the system’s mean and least altered conditions portrayed that the confined reaches with lesser human interventions were in comparatively more pristine hydromorphological conditions. Conversely, unconfined reaches showed moderate to very poor hydromorphological conditions chiefly due to intense human-induced alterations regarding urbanization, embanking and sediment extraction. Restorations on these aspects should initiate with immediate effect to avoid a shortage of riverine resources such as fluvial sediment, fish and groundwater. Overall, this methodology was found suitable for continuous monitoring of the river systems along with the precise identification of areas and aspects to be restored for upgrading the hydromorphological quality. More testing of this methodology would eventually help in validating the hydromorphological quality assessment protocol for Indian rivers.     

Hail impact responses and residual tensile properties of CFRP T-joints

Hail impact is a major challenge encountered by aircraft in flight, and thus is a key concern in the design of damage-tolerant composite T-joints in aviation. The study uses the Z-pinning technique(the pre-hole insertion technology) in combination with fillets of two radiuses to manufacture four types of Carbon Fiber Reinforced Polymers(CFRP) T-joints. The T-joints are then subjected to hail impact tests at two energy levels, as well as post-impact quasi-static tensile tests.The results show tha...     

高空来流条件下航空发动机双旋流燃烧室点火特性数值模拟

为深入了解真实航空发动机燃烧室极端条件下点火性能，在自有CFD平台上对不同高空来流条件下典型航空发动机双旋流燃烧室点火过程进行了数值模拟。为保证模拟精度，对模型包括全部气膜冷却小孔在内的所有精细结构均进行了完全仿真，并完整再现了燃烧室内从燃油雾化到点火燃烧全过程。结果表明3种高空来流条件下单次点火均失败。点火过程显示高温燃气越过旋流杯中心向上回流区扩张是点火的关键时空区域，在此时补充点火可推动火焰顺利传播到整个主燃区。对8km和6km两种状态分别增加点火次数到3次和5次后最终点火成功，结果表明前者着火极限油气比约为0.057，后者为0.038~0.042。     

船用多级轴流压气机低工况扩稳优化研究—“航海专刊”

对某型船用九级轴流压气机，为了探讨减少可转导叶列数的可行性，并提升低工况喘振裕度，本文通过数值模拟方法研究通流布局优化对压气机低工况稳定性的影响。通过特性分析和详细流场分析，结论表明，一维关键参数选取对最佳可转导叶控制策略影响较大，本文优化部分级关键参数，不仅减少了可转导叶列数，而且提升了低转速下的喘振裕度，在75%转速下喘振裕度提升了2.27%，在70%转速下喘振裕度提升了3.3%。     

Selective thermal emission and infrared camouflage based on layered media

Infrared camouflage based on artificial thermal metasurfaces has recently attracted significant attention. By eliminating thermal radiation differences between the object and the background, it is possible to hide a given object from infrared detection. Infrared camouflage is an important element that increases the survivability of aircraft and missiles, by reducing target susceptibility to infrared guided threats. Herein, a simple and practicable design is theoretically presented based on a multilayer film for infrared stealth, with distinctive advantages of scalability, flexible fabrication, and structural simplicity. The multilayer medium consists of silicon substrate, carbon layer and zinc sulfide film, the optical properties of which are determined by transfer matrix method. By locally changing the thickness of the coating film, the spatial tunability and continuity in thermal emission are demonstrated. A continuous change of emissive power is further obtained and consequently implemented to achieve thermal camouflage functionality. In addition, other functionalities, like thermal illusion and thermal coding, are demonstrated by thickness-engineered multilayer films.     

Robust extension of the simple sea-surface irradiance model to handle cloudy conditions for the global ocean using satellite remote sensing data

Sea-surface solar radiation (abbreviated as photosynthetically available radiation, PAR) in the visible wavelength (400–700 nm) is an essential parameter to estimate marine primary productivity and understanding phytoplankton dynamics, upper ocean physics and biogeochemical processes. Although many remote-sensing models were developed to estimate daily PAR (DPAR) from ocean colour data, these models often produce biases in the DPAR products under cloudy-sky and complex atmospheric conditions due to the lack of parameterization to deal with the cloud cover conditions and insufficient in-situ DPAR data. This study presents an Extended Sea-surface Solar Irradiance Model (ESSIM) for estimating DPAR over the global ocean. The ESSIM uses the direct and diffuse components from the Simple sea-surface Solar Irradiance Model (SSIM) along with a new parameter to handle cloudy conditions. The ESSIM produced DPAR products with greater accuracy under both clear and cloudy conditions. Its performance was tested on the time-series MODIS-Aqua images and compared with the concurrent in-situ data and the results from two global models. Results showed that the DPAR values produced by ESSIM agree with in-situ data better than the global models for all-sky conditions (with a mean relative error of 11.267 %; a root mean square error of 5.563 Em^?2day^?1; and a mean net bias of 2.917 Em^?2day^?1). The ESSIM performed slightly better than the SSIM for clear conditions and the Frouin's Operational Algorithm (FOA) for all-sky conditions. As the new parameterization accounts for cloudy conditions, the ESSIM produced more accurate results for cloud cover conditions across latitudes (up to 60°). The time-series Level-3 binned MODIS-Aqua data (global gridded) also demonstrated that the ESSIM improved the accuracy of DPAR products and produced spatially and temporally consistent DPAR products over the global ocean regardless of the seasons and sky conditions.     

Nightside 135.6 nm emission enhancements of mid/low latitudes during geomagnetic storms as observed by the ionosphere PhotoMeter (IPM) on the Chinese meteorological satellite FY-3D

IPM has detected nightside 135.6 nm emission enhancements over a wide latitude range, from the sub-auroral latitudes to the equatorial regions during geomagnetic storms. Our work, presented in this paper, uses the data of IPM to understand these 135.6 nm emission enhancements during of geomagnetic storms and studies the variations of total electron content (TEC) and the F₂ layer peak electron density (NmF2) in the region of enhanced emissions. Middle and low latitude emission enhancements are presented during several medium storms in 2018. The variations of both the integrated electron content (IEC) derived from the nighttime OI 135.6 nm emission by IPM and TEC from the International GNSS Service (IGS) relative to the daily mean of magnetically quiet days of per each latitude bin (30°≦geographic latitude < 40°, 15°≦geographic latitude < 30°, 0°≦geographic latitude < 15°, ?15°≦geographic latitude < 0°, ?30°≦geographic latitude < -15°, ?40°≦geographic latitude < -30°) are investigated and show that on magnetically storm day, IEC by IPM always increases, while TEC from IGC may increase or decrease. Even if both increase, the increase of IEC is greater than that of TEC. From the comparison of IEC and TEC during magnetic storms, it can be seen that the enhancement of the nighttime 135.6 nm emissions is not entirely due to the ionospheric change. The time of IEC enhancements at each latitude bin is in good agreement, which mainly corresponds to the main phase time of the geomagnetic storm event and lasts until the recovery phase. The available ground-based ionosonde stations provide the values of NmF2 which match the 135.6 nm emissions measured by IPM in space and time. The variations of NmF2 squared can characterize the variations of the OI 135.6 nm emissions caused by O⁺ ions and electrons radiative recombination. The study results show that the OI 135.6 nm emission enhancements caused by O⁺ ions and electrons radiative recombination (where NmF2 squared increases) are obviously a contribution to the measured 135.6 nm emission enhancements by IPM. The contribution accounts for at least one of all contributions to the measured 135.6 nm emission enhancements by IPM. However, where the NmF2 squared provided by ionosonde decrease or change little (where the OI 135.6 nm emissions cause by O⁺ ions and electrons radiative recombination also decrease or change little), the emission enhancements measured by IPM at storm-time appear to come from the contributions of other mechanisms, such as energetic neutral atoms precipitation, or the mutual neutralization emission (O+ + O-→2O + h? (135.6 nm)) which also occupies a certain proportion in 135.6 nm airglow emission at night.