单向阀三维动态流场稳定性仿真研究

对单向阀自激振动机理进行研究,采用线性分析方法提出了单向阀的临界稳定曲线。应用泵阀仿真软件PumpLinx的动网格技术,开展了单向阀三维动态流场仿真分析,数值研究了不同工作压力、不同质量流量条件下的单向阀动态稳定特性。结果表明:在某一工作压力条件下,小流量时单向阀工作不稳定,会形成周期性的阀门颤振,随着质量流量增大,单向阀动态稳定性增强;当质量流量足够大时,单向阀工作稳定,单向阀保持稳定开度工作;质量流量一定时,工作压力降低,单向阀动态稳定性增强。单向阀三维动态流场仿真结果与线性稳定性结论相一致,从三维动态流场角度验证了单向阀自激振动机理及线性稳定性分析方法的有效性。     

Robust adaptive fault-tolerant control of a tandem coaxial ducted fan aircraft with actuator saturation

This paper is concerned with the robust adaptive fault-tolerant control of a tandem coaxial ducted fan aircraft under system uncertainty, mismatched disturbance, and actuator saturation. For the proposed aircraft, comprehensive controllability analysis is performed to evaluate the controllability of each state as well as the margin to reject mismatched disturbance without any knowledge of the controller. Mismatched disturbance attenuation is ensured through a structured H-infinity controller tuned by a non-smooth optimization algorithm. Embedded with the H-infinity controller, an adaptive control law is proposed in order to mitigate matched system uncertainty and actuator fault. Input saturation is also considered by the modified reference model. Numerical simulation of the novel ducted fan aircraft is provided to illustrate the effectiveness of the proposed method. The simulation results reveal that the proposed adaptive controller achieves better transient response and more robust performance than classic Model Reference Adaptive Control (MRAC) method, even with serious actuator saturation.     

转子-支承耦合结构的模型修正研究

在转子-支承耦合结构的动力学分析过程中,结构模态参数计算结果与实验测试结果往往存在较大差异。针对此问题,应用优化算法对结构动力学模型进行修正,使计算模型能更准确地反映结构特性。建立由梁单元、盘单元、弹性支承单元组成的结构动力学有限元模型;选择优化目标函数、设计参数,并对各参数进行灵敏度分析。应用粒子群算法对选取的设计参数进行优化,得到最优模型。利用转子-滚动轴承实验器进行验证,结果表明,方法能够有效地实现转子-支承耦合结构的动力学模型修正,修正后模型更接近实际结构。     

一种四元数矩阵建模的彩色图像质量评价方法

针对彩色图像的质量评估问题,提出了一种基于四元数矩阵模型的图像质量评价方法。利用四元数矩阵对彩色图像建模,构造出图像的四元数矩阵模型;对矩阵进行奇异值分解,得到一组奇异值向量;计算标准图像与失真图像对应奇异值向量间的欧式距离,获得失真映射图谱;由失真图谱计算两幅图像间的全局误差,作为失真图像的质量评价结果。通过对几组不同类型失真图像的评价测试,结果表明,方法对图像质量的客观评价结果与主观感知有较高的一致性,并且能够从失真映射图谱判定图像的失真类型。     

一种基于稀疏分解的微多普勒频率估计算法

目标微动特性和微多普勒特征分析在真假目标识别方面发挥了重要作用。由于微动目标雷达同波具有非线性、多分量性等特征,需要相应的具有高分辨力、低交叉项、大的动态范围的分析工具,才能较好地揭示目标微多普勒特征。稀疏分解方法中的匹配追踪（MP）具有频域高分辨能力,对于信号细微特征提取具有很好的效果。研究了基于匹配追踪的微多普勒频率估计问题,该方法可以准确提取出目标微多普勒频率,为后续的目标识别提供了重要的依据。-     

利用格壁安装角对栅格舵展开折叠压心控制的工程方法研究探索

随着技术的发展，在工程设计中，对于巡航迎角下栅格舵导弹的展开与折叠的压心变化控制对于控制系统来说尤为重要。本文创新性的首次提出利用栅格舵的内壁单元的偏转，即相对于水平面的夹角来实现在设计点下的压心控制。由于设计过程需要多次迭代，本文利用计算在所关注的设计点处对展开折叠压心进行了验证，创造性的利用了等效代替的方法提出了一种新型的计算折叠状态压心的快速工程方法。     

Single track and single layer formation in selective laser melting of niobium solid solution alloy

Selective laser melting (SLM) was employed to fabricate Nb-37Ti-13Cr-2Al-1Si (at%) alloy, using pre-alloyed powders prepared by plasma rotating electrode processing (PREP). A series of single tracks and single layers under different processing parameters was manufactured to evaluate the processing feasibility by SLM, including laser power, scanning speed, and hatch distance. Results showed that continuous single tracks could be fabricated using proper laser powers and scanning velocities. Both the width of a single track and its penetration depth into a substrate increased with an increase of the linear laser beam energy density (LED), i.e., an increase of the laser power and a decrease of the scanning speed. Nb, Ti, Si, Cr, and Al elements distributed heterogeneously over the melt pool in the form of swirl-like patterns. An excess of the hatch distance was not able to interconnect neighboring tracks. Under improper processing parameters, a balling phenomenon occurred, but could be eliminated with an increased LED. This work testified the SLM-processing feasibility of Nb-based alloy and promoted the application of SLM to the manufacture of niobium-based alloys.     

Noise analysis of continuous GPS coordinate time series for CMONOC

The Crustal Movement Observation Network of China (CMONOC) is one of the major scientific infrastructures, mainly using Global Positioning System (GPS) measurements, to monitor crustal deformation in the Chinese mainland. In this paper, decade-long coordinate time series of 26 continuous GPS sites of CMONOC are analyzed for their noise content using maximum likelihood estimation (MLE). We study the noise properties of continuous GPS time series of CMONOC for the unfiltered, filtered solutions and also the common mode signals in terms of power law plus white noise model. In the spatial filtering, we remove for every time series a common mode error that was estimated from a modified stacking of position residuals from other sites within ∼1000 km of the selected site. We find that the common mode signal in our network has a combination of spatially correlated flicker noise and a common white noise with large spatial extent. We demonstrate that for the unfiltered solutions of CMONOC continuous GPS sites the main colored noise is a flicker process, with a mean spectral index of ∼1. For the filtered solutions, the main colored noise is a general power law process, indicating that a major number of the filtered regional solutions have a combination of noise sources or local effects. The velocity uncertainties from CMONOC continuous GPS coordinate time series may be underestimated by factors of 8–16 if a pure white noise model is assumed. In addition, using a white plus flicker noise model, the median values of velocity errors for the unfiltered solutions are 0.16 (north), 0.17 (east) and 0.58 (vertical) mm/yr, and the median values for the filtered solutions are 0.09 (north), 0.10 (east) and 0.40 (vertical) mm/yr.     

复合材料缠绕气瓶可靠性验证技术

根据航天器用复合材料气瓶高可靠性特点,对复合材料气瓶的可靠性进行了分析,气瓶的失效模式主要为泄漏和爆破,影响因素分别为疲劳寿命和承压能力,其中疲劳寿命主要受内衬影响,而承压能力主要由复合层性能决定。最后对气瓶的可靠性试验进行了描述,举例说明了气瓶的可靠度试验验证方法。     

对我国结构性生产过剩及其调整的认识

我国近年来经济发展中出现的生产过剩不同于资本主义国家经济危机时的相对过剩，而是我国经济发展中的结构性生产过剩，具有过渡的性质。这一现象的出现对传统经济理论具有挑战意义。本文试图对我国目前出现的结构性生产过剩的原因作出探讨，并对其调整提出对策。