基于EMD算法的光栅莫尔条纹信号去噪方法研究

针对计量光栅莫尔条纹信号的质量问题,提出了基于经验模态分解（EMD）算法对非平稳光栅莫尔条纹信号模型的去噪方法。建立非平稳的光栅时变信号模型,利用EMD算法不需要定义滤波器参数的自适应性优点,对添加不同噪声的多组光栅信号模型进行了滤波分析的仿真实验,其信噪比和均方根误差两项指标优于均值滤波、小波阈值去噪方法。对两路正余弦理想信号添加高次谐波分量,通过对比EMD算法抑制高次谐波前后的李萨如图形,验证了该方法在去噪过程中对光栅莫尔条纹信号正弦性误差补偿的良好效果。     

Testing Transverse Sensitivity of Linear Single-Axis Pendulous Accelerometer with Double Turntable Centrifuge

Current ISO standard methods for testing transverse sensitivity of accelerometers are vibration-based. They have difficulties in producing low-frequency vibration for various reasons. This paper introduces a double turntable centrifuge (DTC) to test the accelerometer transverse sensitivity at low frequencies (from 0.01 to 10 Hz). The proposed method can avoid limitations of traditional vibration-based schemes for transverse sensitivity test. In this paper, a theoretical analysis of the method is followed by a presentation of the experimental set-up, and the measurement procedure of a linear single-axis pendulous accelerometer. According to the theoretical analysis and experimental results, it is practicable to test the low-frequency transverse sensitivity with a DTC. The method proposed here can test accelerometer transverse sensitivity at low-frequency with large amplitudes (up to 700 m/s²), and directly measure the angle of the transverse sensitivity with high resolution. It can be a supplement to the standard methods for testing accelerometer transverse sensitivity at low-frequency.     

Carbon black reinforced C8 ether linked bismaleimide toughened electrically conducting epoxy nanocomposites

The present work deals with the toughening of brittle epoxy matrix with C8 ether linked bismaleimide (C8 e-BMI) and then study the reinforcing effect of carbon black (CB) in enhancing the conducting properties of insulating epoxy matrix. The Fourier transform infrared spectroscopy (FTIR) and Raman analysis indicate the formation of strong covalent bonds between CB and C8 e-BMI/epoxy matrix. The X-ray diffraction (XRD) and Field Emission Scanning Electron Microscope (FESEM) analysis indicate the event of phase separation in 5 wt% CB loaded epoxy C8 e-BMI nanocomposites. The impact strength increased up to 5 wt% of CB loading with particle pull and crack deflection to be driving mechanism for enhancing the toughness of the nanocomposite and beyond 5 wt% the impact strength started to decrease due to aggregation of CB. The dynamic mechanical analysis (DMA) also indicates the toughness of the nanocomposites was improved with 5 wt% of CB loading due to the phase segregation between epoxy and C8 e-BMI in the presence of CB. The electrical conductivity was also increased with 5 wt% of CB due to classical conduction by ohmic chain contact.     

圆分度角测量检定中的分段内插测量法

圆分度角用排列互比法测量时,一般选用较大的测量间隔角。为了测出大间隔角范围内的小角度偏差,提出了分段内插测量法。由于组成间隔角的两角位置的偏差已由排列互比法测出,因此可作为控制点。通过和小角度陪检工具的连续比较,消减陪检工具角度偏差的影响,得到间隔角范围内的小角度偏差。分段内插测量法是排列互比法的扩展与补充。     

薄壁结构高温随机振动疲劳寿命估算方法

为了研究涡轮转子叶片在高温环境中气流激振力作用下随机振动疲劳失效机理,从基础研究出发,采用薄壁板件为研究对象。基于高温试验台与振动台联合试验,结合数值仿真,得到了不同温度和不同振动量级组合下试验件根部与颈部的轴向动应力响应规律。基于疲劳累积损伤理论,采用改进的雨流计数法预估试验件的疲劳寿命。通过高温随机振动试验,同时参照常温随机振动试验,获得试验件在实际工况下的应力、应变、频率等动力学响应和寿命数据,并对各个试验组的响应与寿命进行数据统计,仿真与试验结果比较发现:数值仿真对试验件破坏位置判断准确,应力响应误差在5.6%以内,频率响应相差1%左右,疲劳寿命相差28.6%以内,证明了高温条件下随机振动疲劳分析方法是有效的而且精确的。     

CCD自准直仪示值漂移的自校准系统

数显式自准直仪使用时,气流等环境条件的影响以及仪器本身发热等原因都会引起示值的漂移和跳动,使测量误差增大、测量结果不能回零。采用增加一块固定反光镜作为参考镜,它与工作反光镜以自准直仪进行差动,组成自校准系统,可以有效地进行消减。仅用工作反光镜时2h内的漂移量为0.03″,经自校准系统后为0.01″;样本标准偏差为0.091 1″,经自校准后为0.057 4″。差动式反光镜自校准系统可以显著减小CCD自准直仪的示值漂移,对减小示值跳动也具有一定作用。且无论是对环境条件还是仪器本身原因引起的漂移和跳动都是有效的。     

故障预测与健康管理系统建模技术研究

简要介绍了PHM系统建模的主要方法,并依据飞机特征,给出飞机PHM系统分层体系模型,提出了基于数据的飞机典型部件液压泵PHM系统的建模方法,通过试验对该方法进行了验证.     

Ablative property and mechanism of SiC-CuxSiy modified C/C-ZrC composites prepared by a rapid method

A rapid method was developed to fabricate C/C-ZrC-SiC-Cu_xSi_y composites with low open porosity by precursor infiltration and pyrolysis combining with pressure assisted reactive melt infiltration. Dominant phases of ZrC and SiC with scattered Cu_xSi_y inclusions were present in continuous infiltrated matrix, in which the dimension of submicron ZrC particles displayed gradient change. At ablation test, the heat absorbing effect of Cu_xSi_y-phase and formation of protective ZrO₂-SiO₂ cover enhanced the ablative property of composites for short-time ablation, causing ablation rates of 30 s ablation reached 1.7 ± 0.1 µm/s and 1.3 ± 0.1 mg/s, respectively. As ablation time extends to 60 s, the massive consumption of Si-phase damaged the integrity of surface oxide cover, but the partial melted ZrO₂ improved the viscosity and self-healing ability of ZrO₂-SiO₂ mixture, protecting substrate from further erosion. Thus, ablation rates were increased and decreased to 3.8 ± 0.2 µm/s and 1.2 ± 0.1 mg/s, respectively.     

Reducing pitch error of a linear motion system actuated by a permanent magnet open face linear motor

When using iron-core open face linear motors, the magnetic attraction between the forcer and the magnet track is about 5–7 times higher than the maximum motor force. The magnetic attraction can be used in a motor-preloaded-bearing concept, e.g. to preload aerostatic or hydrostatic bearings. Based on this concept a high-precision grinding tool machine that moves on aerostatic bearings has been successfully introduced. However, the attraction force also creates an inherent pitch moment and resulting position dependent, periodic pitch error motion due to finite bearing stiffness. A method to model and reduce the resulting pitch error is presented. In experiments the overall pitch was reduced by a factor of 3.