Deployment of SMP Miura-ori sheet and its application: Aerodynamic drag and RCS reduction

Origami, such as Miura-ori, is the art of folding two-dimensional materials into complex, elaborate, and multifunctional three-dimensional objects. In this paper, SMP MO sheet are prepared, and the accuracy of deployable process is verified by experiments. The folding and deployable process of SMP MO sheet is divided into 4 stages, and each stage is described in detail. The stiffness of smart deployable stage is characterized by an exponential decline at the beginning and a gradual decrease to 0, and this is similar to the theoretical shear equivalent modulus in the Y direction. The effects of various parameters on strain and stress are also explored. The purpose of studying these mechanical characteristics is to provide driving force reference in application; In terms of application, the flow field and electromagnetic characteristics of MO sheet in different directions are studied. The aerodynamic drag and RCS reduction of MO unit cell and graded MO sheet during the deployable process are evaluated. When the dihedral fold angle is about 45°, the RCS reduction and drag reduction characteristics of MO sheet are relatively optimal, which is most beneficial to morphing aircraft.     

基于边界层燃烧方法的宽速域飞行器内流道减阻研究

为了降低宽速域飞行器的内流阻力，基于边界层燃烧方法，分析了系列进口马赫数条件下二维扩散段总阻力中摩阻和压阻的特性，研究了不同进口马赫数下摩阻和压阻分量对总减阻的贡献、燃烧影响区域和壁面热流密度，探讨了喷射参数对减阻效果的影响，探索了边界层燃烧方法在典型混压式进气道中的减阻应用。结果表明，随着进口马赫数的增加，总阻力中摩阻分量随之增加；边界层燃烧对摩阻和压阻减阻的机理有所不同，壁面附近流场特性变化使得摩擦系数减小，燃烧局部增压对壁面产生的增推效果使得压力系数减小；从总内阻减阻百分比看，在相同燃料/空气当量比下，低马赫数工况下边界层燃烧减阻效果不如高马赫数工况，且在低马赫数工况下，喷嘴附近壁面热流密度会显著增加；在本文所研究的参数范围内，摩阻和压阻对当量油气比更为敏感，而对喷射方向和喷射速度不敏感。     

TC4-DT钛合金线性摩擦焊接头组织特征及其形成机制

研究TC4-DT损伤容限型钛合金线性摩擦焊(linear friction welding,LFW)接头的组织特征及形成机制。利用光镜和扫描电镜对接头各区域微观组织进行表征,利用显微硬度计测试接头的显微硬度分布。结果表明:接头焊缝区(WZ)发生动态再结晶,焊接过程中WZ温度超过β转变点,焊后快冷的条件下发生了β→α′及β→α两种相变并析出了大量α′马氏体以及二次层片α;TC4-DT钛合金母材(BM)组织具有较高的变形抗力,使得接头形成的热力影响区(TMAZ)较窄。TMAZ内组织在强烈的热力耦合作用下拉长变形并破碎,焊后快冷的条件下析出少量α′马氏体及大量二次层片α;毗邻TMAZ的热影响区(HAZ)基本保留了BM不同位向的α集束的组织特征,但受热的影响α集束内α/β相界两侧元素相互扩散,层间β消耗,初生α长大;WZ组织的细晶强化和第二相强化,TMAZ组织的应变强化和第二相强化,以及HAZ内α相的长大使得接头上述区域显微硬度均高于BM。     

Compact wideband FSS-absorber-based low-RCS reflectarray antenna

This paper presents a method to realize compact broadband low-RCS Reflect Array(RA) antenna based on a Frequency Selective Surface(FSS) absorber and a reflective metasurface.Such an FSS absorber consists of a resistance-loaded lossy layer and an FSS layer, which is utilized to reach an absorption-transmission response. The bottom reflective metasurface works as a phase array, reshaping the quasi-sphere wave from the feeding antenna into the quasi-plane wave. As a demonstration, the low-RCS RA an...     

基于有限元--离散元耦合的粒子阻尼减振研究

在侧挂构型发射任务中，中心承力筒与卫星直接连接，其动力学特性对卫星的振动响应有直接影响。首先分析中心承力筒的模态特性，据此完成粒子阻尼器的结构参数设计。随后，使用有限元--离散元耦合仿真方法，确定了阻尼器填充粒子的最佳直径和阻尼器最佳安装位置。仿真结果表明，该方案下星箭界面减振效果可达40%。最后，使用最优粒子阻尼参数开展水平激励实验。实验结果表明，与未安装粒子阻尼器相比，中心承力筒+粒子阻尼器组合体的减振效果可达35%以上，与仿真结果一致。     

Experimental and numerical investigation on opposing plasma synthetic jet for drag reduction

Experimental and numerical studies are carried out to validate the potential of opposing Plasma Synthetic Jet (PSJ) for drag reduction for a hemisphere. Firstly, flow field changes of opposing PSJ are analyzed by comparing the experimental schlieren images and simulation results in a supersonic free stream of Mach number 3. As PSJ is a kind of unsteady pulsed jet, the shock standoff distance increases initially and then decreases under the control of PSJ, which corresponds to the change of the strength of PSJ. Accordingly, the amount of drag reduction of the hemisphere increases initially and then decreases. It is found that there is a short period of “drag rise” during the formation of PSJ before the drag reduction, which is induced by the generation of normal shock waves and the area difference of the cavity wall of PSJ Actuator (PSJA). Secondly, the effects of five parameters, including exit diameter, discharge energy of PSJA, Mach number, static pressure of incoming flow and angle of attack, on drag reduction of opposing PSJ were studied in detail by using numerical method. It is found that the Maximum Pressure Ratio (MPR) has a significant impact on the average drag reduction for a configuration-determined PSJA. For the configuration selected in this study, the flow field of opposing PSJ shows typical Short Penetration Mode (SPM) in a control cycle of PSJ when the MPR is less than 0.89. However, the flow field shows typical Long Penetration Mode (LPM) at some time when the MPR is bigger than 0.89. Relatively better drag reduction is achieved in this case.     

捷联惯组空间八点减振IMU组合设计CSCD

为了研究捷联惯组空间八点减振IMU组合的力学性能及其在抑制线角耦合方面的作用,采用NX三维建模及ANSYS仿真分析工具对IMU组合的刚度、减振器的线角频率、减振性能方面进行了充分的理论验证。同时,推导出平衡机的调平原理,通过调平使IMU弹性中心与质心重合,然后对惯组进行振动试验,观察其减振性能及三向陀螺角速度输出值。结果表明,经理论分析该IMU组合模态为875.7Hz,具备足够的刚度;减振器线角频率差值在50Hz以上,具有较高的离散度。经试验验证,该IMU组合调平小于0.1mm时,减振效率不低于42%,三向陀螺角速度输出不大于11(°)/s,具有较好的力学环境适应性与极高的角速度输出特性。     

Design and analysis of a novel hybrid cooling method of high-speed high-power permanent magnet assisted synchronous reluctance starter/generator in aviation applications

To improve the heat dissipation performance, this paper proposes a novel hybrid cooling method for high-speed high-power Permanent Magnet assisted Synchronous Reluctance Starter/Generator (PMaSynR S/G) in aerospace applications. The hybrid cooling structure with oil circulation in the housing, oil spray at winding ends and rotor end surface is firstly proposed for the PMaSynR S/G. Then the accurate loss calculation of the PMaSynR S/G is proposed, which includes air gap friction loss under oil spray cooling, copper loss, stator and rotor core loss, permanent magnet eddy current loss and bearing loss. The parameter sensitivity analysis of the hybrid cooling structure is proposed, while the equivalent thermal network model of the PMaSynR S/G is established considering the uneven spraying at the winding ends. Finally, the effectiveness of the proposed hybrid cooling method is demonstrated on a 40 kW/24000 r/min PMaSynR S/G experimental platform.     

基于智能差分算法的摩擦力补偿方法研究

针对光电平台低速转动时，受摩擦力影响较大，使得速度跟随曲线出现“死区”现象，导致跟踪性能明显下降这一问题，提出了一种基于智能差分进化算法和Lurge摩擦模型的摩擦力补偿控制方法。通过采集记录光电转台正、反向匀速运动时的摩擦力大小，建立转台不同速度和摩擦力之间的对应关系。通过最小二乘法对摩擦模型静态参数进行分段拟合，采用智能差分进化算法辨识摩擦模型动态参数，并基于反馈的速度信息和获得的摩擦模型等效为摩擦补偿力矩输入到电流环控制输入端，实现平台平稳低速运行。实验结果表明：摩擦力补偿后速度响应误差由补偿前的±0.1°/s减小到±0.04 °/s，提出方法效果显著。