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1.
《中国航空学报》2021,34(1):350-363
This paper presents a review of the various methods for the stationary non-Gaussian random vibration control. Random vibration tests can be divided, according to the number of exciters, in single-shaker tests and multiple-shaker tests. In the stationary non-Gaussian random vibration test, the time and frequency domain characteristics of the responses should be controlled independently and simultaneously. Skewness and kurtosis are usually selected as the non-Gaussian time control references (targets) while power spectral density is the frequency domain control procedure before it recalls the concepts of non-Gaussianity. Then, the generation of a one frame stationary non-Gaussian random signal for both the single and multiple shakers are reviewed. The commonly used methods for the single non-Gaussian random signal generation in the random vibration test are memoryless nonlinear transformation, phase modification and Filtered Poisson process. For the multiple-shaker case, the sequential phase modification and memoryless nonlinear transformation are used to generate one frame coupled multi-channel non-Gaussian random signal. In order to obtain a stationary and consecutive dynamic input, the time domain randomization procedure is introduced with high computational efficiency and its influences on the skewness and kurtosis are analyzed. Finally, two existing problems in the non-Gaussian random vibration control are addressed. 相似文献
2.
孔隙率对复合材料性能有很大影响。针对高孔隙率复合材料超声表征不足问题,本文把超声功率谱特征和非线性特征应用于表征高孔隙石英酚醛复合材料的孔隙率,即在频域上对比研究孔隙对基波幅值的衰减及谐波幅值的滋生的影响。结果表明:二者均能有效表征高孔隙复合材料的孔隙率。基于频域基波分析的超声功率谱特征参量测量容易,随孔隙增加呈递减变化,在孔隙率较低时具有一定优势;基于谐波分析的超声二阶非线性特征参量,随孔隙增加呈递增变化,对高孔隙率表征更具优势。 相似文献
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针对多旋转关节空间太阳能电站(Space Solar Power Station, SSPS),提出一种环形拓扑的电力系统架构。基于功率分层准则对SSPS电力拓扑架构进行设计,提出U1~U7共7个层级、母线电压5000V、功率等级为MW的太阳能电站电力系统。针对分层架构中多太阳电池阵子阵并联(U6层),提出分层功率平衡统一控制策略,对MPPT控制、MPPT控制+稳定直流母线电压混合控制、MPPT算法+下垂稳定直流母线电压混合控制三种控制方法开展仿真分析。结果表明,提出的基于虚拟阻抗的下垂控制策略可以有效调节、分配功率,解决了空间发电站母线电压无法稳定的问题。 相似文献
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《中国航空学报》2016,(1):268-273
It is well-known that the application of ultrasound during liquid to solid transitions for alloys can refine the solidification microstructure and thus improves the mechanical properties. How-ever, most published work focuses on single phase dendritic growth, whereas little has been con-ducted on the multiphase alloys with complicated phase transformations during solidification. In this work, the solidification process of ternary Cu40Sn45Sb15 alloy was realized within intensive ultra-sonic field with a resonant frequency of 20 kHz and ultrasound power from 0 W to 1000 W. The ultrasound refines the size of the primary e(Cu3Sn) intermetallic compound by two orders of mag-nitudes. If the ultrasound power increases to 1000 W, g(Cu6Sn5) phase nucleates and grows directly from parent liquid phase without the occurrence of peri-eutectic reaction on the top of the alloy sam-ple where the ultrasound intensity is sufficiently high. These microstructural variations lead to the enhancement of compressive strength and elasticity modulus of ternary Cu40Sn45Sb15 alloy. 相似文献