基于国产FPGA及DAC的任意波形发生器的设计

任意波形发生器作为测试测量设备的一种重要仪器,在航空航天的测量与控制技术领域中得到了广泛应用;当前市场成熟任意波形发生器产品多为国外产品或者国内厂商基于国外FPGA和DAC研制的产品;为了打破技术垄断,提高国产任意波形发生器的自主技术保障能力,研制基于国产芯片的任意波形发生器愈发重要;随着国产芯片设计技术提升,国产FPGA和DAC的性能显著提高,并得到了广泛应用;PXI总线作为当前仪器领域的主要总线类型之一,可以满足大部分测试仪器的通讯要求;基于国产FPGA和DAC器件,从硬件设计和软件设计两个方面出发,成功研制了一款采样率为100 MSa/s的 PXI总线任意波形发生器模块,实现了43 MHz信号输出,通过实验测试了模块的功能和性能,完全满足模块指标要求,充分证明了国产芯片在工程设计中的性能特性。     

气球轨迹法测风和风廓线雷达测风的对比分析

文章在介绍了气球轨迹法测风和风廓线雷达测风各自原理的基础上，重点分析、探讨了二者间的差异，以及采用风廓线雷达测风的优势与发展风廓线雷达的意义。     

Survey on methods of increasing the efficiency of extended state disturbance observers

This survey presents various methods of improving the overall estimation quality in the class of extended state observers (ESO), which estimate not only the conventional states of the system, but the acting disturbance as well. This type of observers is crucial in forming the active disturbance rejection control structure (ADRC), where the precision of online perturbation reconstruction and cancellation directly influences the robustness of the closed-loop control system. Various aspects of the observer-based disturbance estimation/rejection loop are covered by this work and divided into three categories, related with observer: structure, tuning, and working conditions. The survey is dedicated to researchers and practitioners who are interested in increasing the efficiency of their ADRC-based governing schemes.     

面向微组装单元的数字孪生同步方法及系统实现

为了解决微组装生产线数字化转型面临的数据处理难和设备信息化控制难的问题,设计了微组装生产线单元数字孪生系统架构,提出一种基于实时生产数据的四维融合模型孪生同步方法,从行为实时映射、状态实时映射和动作实时映射的角度对孪生同步进行了诠释,并对其关键技术——多源异构数据分类、清洗与解析和实时数据驱动四维融合孪生模型进行了详细...     

Fatigue damage in SiC/CAS composites

While ceramic-matrix composites exhibit none of the fatigue mechanisms that are familiar in metals and polymers, they are, nevertheless, susceptible to reduced working performance under cyclic loading. The main source of this deterioration is the matrix cracking which occurs at low strain levels in brittle/brittle systems where the fibres and matrix possess different stiffnesses. As a result of this cracking, the apparent elastic modulus and Poisson's ratio of the composite change with cycling or with strain in complex fashions that may cause serious difficulties for designers. In this paper, we present an analysis of cracking during repeated tension and flexural loading of a Nicalon SiC fibre-reinforced calcium aluminosilicate glass-ceramic composite. The changing fatigue response is interpreted in relation to microstructural information obtained by edge replication and to acoustic emission analysis. The damage which occurs in tension and flexural fatigue of unidirectional and cross-plied composites is of a similar nature, and it appears that the relationship between stiffness and crack density is similar for samples damaged in fatigue and monotonic loading.     

嵌入层叠混沌策略的随机粒子群算法

鉴于求解复杂问题时粒子群优化算法易出现早熟收敛的问题,通过引入轨迹扰动因子,提出随机粒子群进化迭代方程.该方程在统计行为中保证粒子向特定的收敛中心逼近,但对“旧址”的依赖性呈现出随机特性,从而使粒子群的快速跳转和迁移成为可能,避免过早落入局部陷阱.同时该进化方程还利用层叠混沌策略和对称极值扰动策略进一步增强算法的局部收敛性和全局搜索性.实验表明,由上述进化方程和改进策略构成的随机混沌粒子群算法具有鲁棒性较强、收敛速度较快和精度较高等优势,性能优于其他同源粒子群算法.     

The effect of wet foam stability on the microstructure and strength of porous ceramics

Wet foam stability is of prime importance in fabricating porous ceramics with the desired microstructure and mechanical properties. In this research, wet foams were fabricated via direct foaming after separately adding an anionic surfactant (TLS) and a cationic surfactant (DTAC) into alumina slurries with a copolymer of isobutylene and maleic anhydride (PIBM) as both the dispersant and the gelling agent. The foam stability was evaluated by a stability analyzer. The bubble size rapidly increased in the wet foam with TLS as the foam stabilizer and many large bubbles appeared within 60 min. The wet foam containing DTAC was very stable. Cationic DTAC increased the hydrophobicity of alumina particles by interacting with the anionic PIBM adsorbed on the particles. The hydrophobically modified particles acted as the foam stabilizer and enhanced the wet foam stability. Furthermore, the fast gelling speed of the slurry containing DTAC also enhanced the wet foam stability. The average cell size of the ceramic with 82.9% porosity from the wet foam with TLS was 188 µm and the compressive strength was 9.7 MPa. The counterparts from the wet foam with DTAC were 54 µm of average cell size and 18.1 MPa of compressive strength. The superior stability of wet foam brought about a smaller cell size and higher strength of the resultant ceramic.     

考虑C-SiO2反应的新型硅基材料烧蚀分析模型

硅基复合材料是一种重要的烧蚀热防护材料,在综合考虑了碳-二氧化硅反应、碳的氧化、熔融二氧化硅的流失与蒸发等物理化学反应的基础上,建立了硅基复合材料的新型烧蚀分析模型。首先,利用质量守恒原理、化学平衡定律以及饱和蒸气压方程推导了包含碳-二氧化硅反应在内的壁面气体组分质量分数方程组,然后基于方程组的解计算出不同温度压力下,硅基复合材料烧蚀过程中碳与二氧化硅反应的量占碳消耗总量的比值,进而建立了包含碳-二氧化硅反应的硅基材料烧蚀的质量守恒和能量守恒模型。利用建立的模型计算了不同工况下材料的烧蚀速度,模拟结果与实验值吻合良好,与未考虑碳-二氧化硅反应的前人最新模型相比,平均误差可由10%减小至3%。最后,针对树脂含量对硅基复合材料烧蚀性能的影响进行了研究,结果表明树脂含量约0.5时烧蚀性能最佳。     

Relative Attitude and Position Estimation for Spacecraft from Multiple Geometric Features

This paper investigates the pose and motion estimation problem using single camera measurement for spacecraft. The leader spacecraft of three-dimensional shape is observed by a calibrated camera fixed on the follower spacecraft. Based on dual numbers, an integrated observation model is proposed based on a combination of multiple geometric features including points, lines and circles, which can improve the robustness and accuracy of the estimation algorithm. A six-degree-of-freedom relative motion model is proposed by using the dual quaternion representation, in which the rotation-translation coupling effect due to the points deviating from the center of the mass is described. Employing the proposed observation model and dynamics model, an Extended Kalman Filter is presented to estimate the relative state between the two spacecraft. Numerical simulations are performed to evaluate the proposed approaches, showing the convergence of relative estimation errors and superior estimation performance.     

Novel phenolic impregnated 3-D Fine-woven pierced carbon fabric composites: Microstructure and ablation behavior

The processing, microstructure and ablative properties of novel phenolic impregnated 3-D Fine-woven pierced carbon fabric ablator (PICA) with different bulk density were investigated. The density of PICA material ranges from 0.352 to 0.701 g/cm³ that having uniform resin distribution within the fibrous substrate. An oxyacetylene torch was used to explore the ablative characteristics in terms of linear/mass ablation rate and microscopic pattern of ablation. Surface and in-depth temperatures during ablation were measured by using optical pyrometers and thermocouples. The experimental results showed that the linear ablation rate varied between 0.019 and 0.036 mm/s and the mass ablation rate increased from 0.045 to 0.061 g/s for the tested PICA composites. It suggests that the PICA composites with lower density may significantly contribute to improving the thermal insulation and ablative properties.