Coating deposition regularity depended on orientation difference in PS-PVD plasma jet

The YSZ coatings are prepared by the plasma spray-physical vapor deposition (PS-PVD) technology based on a specific experimental design. The structure, thickness and growth angle of YSZ coatings on the entire circumferential surface of the cylindrical sample are studied. The results indicated that the structure, thickness and deflection growth angle of YSZ coatings are related to the orientation of deposition location. The numerical simulation of the multiphase mixed fluid near the substrate is carried out and the deposition regularity and mechanism of YSZ coatings prepared by PS-PVD is deduced. The growth rate is related to the local characteristics of the plasma flow field, and is directly proportional to the field pressure and inversely proportional to the field velocity. The growth angle of the coating is generally affected by the flow direction of the plasma jet. Especially, the normal component of velocity vector, V_norm, mainly affects the speed at which the coating grows vertically upwards. The tangential component of velocity vector, V_tan, determines the degree that the coating growth direction deviates from the vertical direction. When V_tan ≠ 0, the coating forms a fine column with a certain deflection angle and finally develops into an oblique columnar structure.     

载人地月混合轨道一次脉冲应急返回轨道分析

对于载人地月转移任务，应急返回轨道是航天员安全返回地球的保障。针对载人混合轨道地月转移对安全性要求高的特点，基于载人地月混合轨道，提出了3种一次脉冲的应急返回轨道，即直接返回、即刻机动绕月返回及绕月后机动返回等模式。研究了不同时刻发生故障后，利用3种应急模式返回地球的转移时间和速度增量等特性，研究了载人地月转移全过程出现故障后的应急方式，总结了3种应急模式的应用特点及优劣，可为载人月球探测任务顶层任务分析与设计提供参考。     

Efficient prediction of ground noise from helicopters and parametric studies based on acoustic mapping

Based on the acoustic mapping, a prediction model for the ground noise radiated from an in-flight helicopter is established. For the enhancement of calculation efficiency, a high-efficiency second-level acoustic radiation model capable of taking the influence of atmosphere absorption on noise into account is first developed by the combination of the point-source idea and the rotor noise radiation characteristics. The comparison between the present model and the direct computation method of noise is done and the high efficiency of the model is validated. Rotor free-wake analysis method and Ffowcs Williams-Hawkings (FW-H) equation are applied to the aerodynamics and noise prediction in the present model. Secondly, a database of noise spheres with the characteristic parameters of advance ratio and tip-path-plane angle is established by the helicopter trim model together with a parametric modeling approach. Furthermore, based on acoustic mapping, a method of rapid simulation for the ground noise radiated from an in-flight helicopter is developed. The noise footprint for AH-1 rotor is then calculated and the influence of some parameters including advance ratio and flight path angle on ground noise is deeply analyzed using the developed model. The results suggest that with the increase of advance ratio and flight path angle, the peak noise levels on the ground first increase and then decrease, in the meantime, the maximum Sound Exposure Level (SEL) noise on the ground shifts toward the advancing side of rotor. Besides, through the analysis of the effects of longitudinal forces on miss-distance and rotor Blade-Vortex Interaction (BVI) noise in descent flight, some meaningful results for reducing the BVI noise on the ground are obtained.     

鸭翼/边条对融合体型机身大攻角气动特性影响

通过对融合体型机身进行表面测压和PIV(Particle Image Velocimetry)流动显示实验,研究了大攻角下鸭翼/边条对机身气动特性的影响规律.结果表明:加装鸭翼后攻角小于50°时机头区流动变化不大,超过50°攻角后,机头区法向力显著下降,并且随着攻角增加受影响区域向头部方向扩大;加装鸭翼致使鸭翼区截面法向力大幅增加.加装边条改善了边条区流动,边条涡对机头涡产生有利诱导,增大了边条区法向力.加装边条/鸭翼时,对机头区及鸭翼区流场的影响由鸭翼起主控作用,对边条区流场的影响由边条起主控作用.     

自适应滤波在动态推力测量中的应用

动态推力测量过程中的干扰信号频谱经常与有用信号重叠,经典的模拟滤波或数字滤     

真空模拟环境下液体推进剂蒸发特性的试验研究

为研究液体推进剂在真空环境下的蒸发特性,建立了真空环境模拟试验系统。对水、饱和盐水、煤油、酒精和凝胶模拟液等工质进行了蒸发特性试验。通过控制系统实时采集了真空舱的真空度和工质温度。试验中观察到了明显的闪蒸现象。由于闪蒸的存在,工质蒸发过程非常剧烈。最后分析了不同工质在真空环境下的蒸发特性,给出了部分工质的闪蒸参数。     

基于相位重构的相位编码信号脉内特征分析

基于希尔伯特变换,提出了一种相位编码信号相位无模糊重构的脉内特征分析方法。该方法一方面利用魏格纳-威利变换对信号进行降噪处理,改善了在低信噪比下相位编码信号脉内特征识别和提取能力;另一方面对重构相位进行多阶差分处理来提高识别精度。仿真结果验证了该方法的正确性和有效性。     

雷达敌我识别系统干扰方法分析

敌我识别系统在现代战争中具有极为重要的作用。简述了雷达敌我识别的工作原理,讨论了对雷达敌我识别的干扰方法,着重对噪声压制和应答机占据两种方法的干扰效果进行了分析。     

未知测量噪声分布下的多目标跟踪算法

 粒子概率假设密度滤波(SMC-PHDF)在进行粒子更新时需要知道测量噪声的概率分布以计算似然函数,这使得SMC-PHDF依赖于测量噪声的概率模型。针对这一点不足,提出一种未知测量噪声分布下的多目标跟踪算法——基于风险评估的概率假设密度滤波(RE-PHDF)。该算法在SMC-PHDF进行概率假设密度(PHD)粒子更新时采用风险函数计算每个PHD粒子的风险值,并通过一个风险评估函数评估每个PHD粒子,然后用评估后的结果更新粒子的权值。由于粒子更新时避免了在多维测量空间中计算似然函数,算法不仅不依赖于测量噪声的概率分布,还可以节省大量计算时间。仿真结果表明：和SMC-PHDF相比,RE-PHDF在未知的复杂测量噪声环境下具有更高的鲁棒性和稳定性;同时,在两种算法跟踪精度接近的情况下,所提算法节省了50%的运行时间。     

一种基于有限元/边界元耦合方法的管道进口声传播及声辐射模型

本文发展了一种基于有限元和边界元耦合方法的管道进口声传播及声辐射计算模型。该模型将整个声场分为内部有限域和外部无界域,分别用有限元和边界元方法求解控制方程,在二者之间的界面上使用具有物理意义的声阻抗参数进行匹配,并通过一种快速迭代方法实现全声场求解。这种迭代方法可以保证有限元刚度矩阵等带宽以及对称的特性不被破坏,有助于提高计算效率。该模型先得到了Levine and Schwinger标准解的检验,进而在无流动情况下对于简化的航发短舱进口管道模型进行了噪声辐射现象的数值模拟,最后基于计算结果分析了声衬对远场声辐射的影响。