高分辨率详查相机窗口热门/防护门的发展概况

相机窗口热门／防护门是航天相机的关键部件。文章概要介绍了高分辨率详查相机窗口热门 ／防护门在相机中的作用以及国内外的发展情况和近期态势。     

直升机砂尘环境试验风洞的温度控制及仿真

 直升机砂尘环境试验风洞内部的热负荷变化范围较大,高低热负荷工况下需要采取不同的调温措施,为了简便地解决其温度控制难题,在对其温度变化进行动态特性分析与建模的基础上,提出了一种引入风速协调因子的砂尘环境试验风洞温度控制策略,并对其控制效果进行了仿真研究,仿真结果表明这一控制策略能在不同的热负荷条件下有效协调加热与制冷两种作用相反的控制措施,并将风洞内的温度控制在要求范围内。     

温度畸变发生器的设计与实验

介绍了航空发动机温度畸变试验装置设计技术与研制方法,主要设备及设计技术指标,以及用A型涡轮喷气发动机B型涡轮风扇发动机调试和对比试验结果。调试试验结果表明:温度畸变发生器主要技术指标满足发动机进口温度畸变的需求,该装置具有高的工作可靠性、可控性和稳定性。      

航空发动机高温升燃烧室贫油熄火及冒烟性能研究

高温升燃烧室头部燃烧组织方案设计,以改善高温升燃烧室的贫油熄火边界及冒烟性能。该方案的特点是采用了三旋流器以及双油路复合式喷嘴,设计的主燃区油气分布相当均匀,而回流区内的油气分布是局部富油的。以常规双旋流器+双油路压力雾化喷嘴(旋流杯)燃烧室作为一个基准方案,在相同的进口实验条件下与本研究方案进行了贫油熄火和出口冒烟性能的比较。实验表明,本研究方案与常规的双旋流杯设计方案相比燃烧稳定性好及出口冒烟改善。      

Method for denoising and reconstructing radar HRRP using modified sparse auto-encoder

A high resolution range profile (HRRP) is a summation vector of the sub-echoes of the target scattering points acquired by a wide-band radar. Generally, HRRPs obtained in a non-cooperative complex electromagnetic environment are contaminated by strong noise. Effective pre-processing of the HRRP data can greatly improve the accuracy of target recognition. In this paper, a denoising and reconstruction method for HRRP is proposed based on a Modified Sparse Auto-Encoder, which is a representative non-linear model. To better reconstruct the HRRP, a sparse constraint is added to the proposed model and the sparse coefficient is calculated based on the intrinsic dimension of HRRP. The denoising of the HRRP is performed by adding random noise to the input HRRP data during the training process and fine-tuning the weight matrix through singular-value decomposition. The results of simulations showed that the proposed method can both reconstruct the signal with fidelity and suppress noise effectively, significantly outperforming other methods, especially in low Signal-to-Noise Ratio conditions.     

称重法低温介质流量校验系统方案研究

液体火箭发动机试验中，流量测量的准确度至关重要。不同于常温流量测量，低温推进剂的流量测量有其特殊性。介绍了称重法低温介质流量校验原理、方法及方案，对流入法排出气体及流出法增压气体流量简略计算公式进行了推导；针对低温容器气枕换热传质特点，对气枕平均温度的一致性进行了讨论。得出了流入法排出气体流量一致性较好、采用流入法可以使低温流量计检定准确度更高的结论。     

蒙皮材料对浮空器热特性影响的研究

分析临近空间浮空器热特性的影响因素,并建立临近空间浮空器热特性的数学模型,采用Fortran语言编写程序,对蒙皮材料热辐射特性对浮空器热特性的影响进行了研究.结果表明,选用短波吸收率较低且长波辐射发射率较高的蒙皮材料时,氦气平均温度的昼夜差值较低,浮空器热性能越好.夜晚蒙皮温差随长波辐射发射率的增加而增加;而白天随短波辐射吸收率的增加而增加,在长波辐射发射率较大时,其对蒙皮温差的影响不大,然而长波辐射发射率比较小时,蒙皮温差会非常大,蒙皮温差的峰值出现于黎明和黄昏时段这两个时段.     

快变换交流方波埋弧焊电源研制

设计了一种双逆变电路结构的快变换交流方波埋弧焊电源,该电源由全桥型一次逆变电路和半桥型二次逆变电路组成.二次逆变电路由续流耦合电感、小功率电压尖峰吸收保护逆变回馈电路、IGBT半桥电路构成.一次逆变电路采用了电压、电流双闭环控制,二次逆变电路采用“临界共同导通”的控制策略,并对其电路换向过程进行了分析.试验结果表明,这种交流方波埋弧焊电源在电流换向过程中换向速度快且无过零死区时间,保证了电弧稳定性,具有良好的工程应用前景.     

Performance analysis of variable speed tail rotors with Gurney flaps

Gurney Flaps (GFs) are used for improving the performance of variable speed tail rotors. A validated analytical helicopter model able to predict the main and tail rotor power is utilized. The fixed height GF has substantially small influence on the tail rotor power in hover and low to medium speed forward flight, and can obtain significant power reduction in high speed flight. This ability can be enhanced by decreasing the tail rotor speed. With the deployment of GF, the collective pitch of the tail rotor decreases, and the maximum tail rotor thrust increases. The GF can compensate the reduction of the maximum thrust by the decrease in the tail rotor speed. The GF with a height of 5% of the chord length can almost remedy 50% of the thrust reduction introduced by decreasing 10% of the tail rotor speed. With the increase of GF height, the maximum thrust generated by the tail rotor increases. The GF with larger height can cause the increase in the tail rotor power in hover and low to medium speed flight. The retractable GF can obtain more power savings than the fixed height GF. However, the benefit is substantially small even in high speed flight. Considering the side effects introduced by the active GF, the fixed height GF may be more preferable. The mechanism for the retractable GF to generate more tail rotor thrust is to increase the lift in advancing side due to the higher dynamic pressure.     

A deformation model of flexible,HAMR objects for accurate propagation under perturbations and the self-shadowing effects

A new type of space debris in near geosynchronous orbit (GEO) was recently discovered and later identified as exhibiting unique characteristics associated with high area-to-mass ratio (HAMR) objects, such as high rotation rates and high reflection properties. Observations have shown that this debris type is very sensitive to environmental disturbances, particularly solar radiation pressure, due to the fact that its motion depends on the actual effective area, orientation of that effective area, reflection properties and the area-to-mass ratio of the object is not stable over time. Previous investigations have modelled this type of debris as rigid bodies (constant area-to-mass ratios) or discrete deformed body; however, these simplifications will lead to inaccurate long term orbital predictions. This paper proposes a simple yet reliable model of a thin, deformable membrane based on multibody dynamics. The membrane is modelled as a series of flat plates, connected through joints, representing the flexibility of the membrane itself. The mass of the membrane, albeit low, is taken into account through lump masses at the joints. The attitude and orbital motion of this flexible membrane model is then propagated near GEO to predict its orbital evolution under the perturbations of solar radiation pressure, Earth’s gravity field (J₂), third body gravitational fields (the Sun and Moon) and self-shadowing. These results are then compared to those obtained for two rigid body models (cannonball and flat rigid plate). In addition, Monte Carlo simulations of the flexible model by varying initial attitude and deformation angle (different shape) are investigated and compared with the two rigid models (cannonball and flat rigid plate) over a period of 100?days. The numerical results demonstrate that cannonball and rigid flat plate are not appropriate to capture the true dynamical evolution of these objects, at the cost of increased computational time.