局部拉弯应力对民机蒙皮2024-T3铝合金剥蚀行为的影响

 根据弯梁法自制简易加载装置,结合电化学阻抗谱(EIS)测试方法,研究了民机蒙皮2024-T3铝合金在局部拉弯应力作用下浸泡于剥落腐蚀(EXCO)溶液中的剥蚀行为。结果表明,合金在发生剥蚀时,EIS中将出现2个时间常数。2024-T3铝合金加载试样的EIS在12 h时出现2个时间常数,而未加载试样的EIS在12~24 h之间才出现2个时间常数,且通过对比剥蚀过程中2种试样EIS的拟合数据,说明局部拉弯应力对2024-T3铝合金剥蚀的发生及发展具有促进作用。     

考虑输入饱和的多航天器系统姿轨耦合分布式协同跟踪控制

基于一致性理论,研究了多航天器系统相对轨道及姿态耦合的分布式协同控制问题。在仅有部分跟随航天器可获取领航航天器信息的情形下,针对各跟随航天器存在未建模动态以及外部环境干扰等问题,利用双曲正切函数的性质,提出了考虑输入饱和的分布式自适应协同控制律。首先,对于领航航天器具有时变状态的情形,为每个跟随航天器设计了3个滑模估计器,对领航航天器的状态进行估计。其次,针对跟随航天器间相对速度和角速度难以测量的问题,设计仅需领航航天器状态的切比雪夫神经网络自适应更新律。最后,设计考虑输入饱和的分布式自适应协同控制律保证各跟随航天器跟踪动态领航航天器。仿真结果表明了该算法的有效性、可行性。     

Polynomial networks based adaptive attitude tracking control for NSVs with input constraints and stochastic noises

This paper proposes a backstepping technique and Multi-dimensional Taylor Polynomial Networks (MTPN) based adaptive attitude tracking control strategy for Near Space Vehicles (NSVs) subjected to input constraints and stochastic input noises. Firstly, considering the control input has stochastic noises, and the attitude motion dynamical model of the NSVs is actually modeled as the Multi-Input Multi-Output (MIMO) stochastic nonlinear system form. Furthermore, the MTPN is used to estimate the unknown system uncertainties, and an auxiliary system is designed to compensate the influence of the saturation control input. Then, by using backstepping method and the output of the auxiliary system, a MTPN-based robust adaptive attitude control approach is proposed for the NSVs with saturation input nonlinearity, stochastic input noises, and system uncertainties. Stochastic Lyapunov stability theory is utilized to analysis the stability in the sense of probability of the entire closed-loop system. Additionally, by selecting appropriate parameters, the tracking errors will converge to a small neighborhood with a tunable radius. Finally, the numerical simulation results of the NSVs attitude motion show the satisfactory flight control performance under the proposed tracking control strategy.     

Investigation of straightforward impedance eduction method on single-degree-of-freedom acoustic liners

In order to address the current aircraft noise problem, the knowledge of impedance of acoustic liners subjected to high-intensity sound and grazing flow is of crucial importance to the design of high-efficiency acoustic nacelles. To this end, the present study is twofold. Firstly, the StraightForward impedance eduction Method (SFM) is evaluated by the strategy that the impedance of a liner specimen is firstly experimentally educed on a flow duct using the SFM, and then its accuracy is checked by comparing the numerical prediction with the measured wall sound pressure of the flow duct. Secondly, the effects of grazing flow and high-intensity sound on the impedance behavior of two single-layer liners are investigated based on comparisons between educed impedance and predictions by three impedance models. The performance of the SFM is validated by showing that the educed impedance leads to excellent agreement between the simulation and the measured wall sound pressure for different grazing flow Mach numbers and Sound Pressure Levels (SPLs) and over a frequency range from 3000?Hz down to 500?Hz. The grazing flow effect generally has the tendency that the acoustic resistance exhibits a slight decrease before it increases linearly with an increase in Mach, predicted successfully by the sound-vortex interaction theoretical model and the Kooi semi-empirical impedance model. However, the Goodrich semi-empirical impedance model gives only a simple linear relation of acoustic resistance starting from Mach zero. Additionally, when the SPL increases from 110 to 140?dB in the present investigation, the acoustic resistance exhibits a significant increase at all frequencies in the absence of flow; however, the resistance decreases slightly under a grazing flow of Mach 0.117. It indicates that the SPL effect can be greatly inhibited when flow is present, and the grazing flow effect can be reduced partly as well at a relatively high SPL.     

考虑状态约束的弹性高超声速飞行器自适应饱和容错控制

针对弹性高超声速飞行器跟踪控制问题进行研究,主要考虑状态约束、输入饱和、执行器故障等约束条件.首先,将弹性模态、外界干扰和模型参数不确定性归结为一类带有未知上界的系统干扰.其次,根据被动容错思想,针对速度和高度子系统分别设计抗饱和自适应容错控制器,通过引入双曲正切函数和新型屏障李雅普诺夫函数分别处理了输入饱和与状态约束...     

同轴探针对称激励矩形波导模式谱图研究

文章用输入阻抗方法探讨同轴探针中心对称激励矩形波导在多模传输时所能激发的传输模式。说明采取一定的措施,可以避免产生某些高次模式。并应用分式线性变换检测法,以精心设计的实验验证了理论分析的正确性。     

An online data driven actor-critic-disturbance guidance law for missile-target interception with input constraints

In this article, we develop an online robust actor-critic-disturbance guidance law for a missile-target interception system with limited normal acceleration capability. Firstly, the missiletarget engagement is formulated as a zero-sum pursuit-evasion game problem. The key is to seek the saddle point solution of the Hamilton Jacobi Isaacs(HJI) equation, which is generally intractable due to the nonlinearity of the problem. Then, based on the universal approximation capability of Neural Networks(N...     

多种材料双层 EFP数值仿真对比研究

以双层药型罩形成的串联爆炸成型弹丸（EFP）为研究对象，运用数值仿真软件AUTODYN，对不同材料组成的双层药型罩产生的串联EFP成型与侵彻靶板过程进行数值模拟计算。通过比较双层EFP形状、速度、长径比、动能等参数，得出内外罩材料冲击阻抗之差对于双层EFP侵彻能力的影响，其侵彻能力最强的材料组合为外钽内铝组合。     

一种航天接口芯片静电防护电路的软击穿现象

接口阻抗测试是航天产品中对产品状态是否正常来进行判断的常用方法。在航天产品应用中，通常认为接口芯片阻抗测试异常即代表该接口芯片已经失效。本文针对一种LVDS接口发送芯片由静电导致阻抗测试异常，但功能正常的现象进行分析。在元器件失效分析的基础上，定位静电损伤的位置为芯片内部静电防护电路，从而建立了对应的电路模型，对芯片静电损伤的现象进行理论分析。分析说明：该芯片在被静电打击时，其静电防护电路中一个NMOS管受损，但该电路保护了芯片的功能电路，被击穿的NMOS管等效为一个电阻，因此导致阻抗测试异常，但芯片功能电路未受损的现象，为静电软击穿现象。且可认为该芯片在受静电影响后并未失效，相关电路仍具有正常工作的能力。即阻抗异常现象并不是芯片失效的充分条件。