Displacement field denoising for high-temperature digital image correlation using principal component analysis

Principal component analysis (PCA) was extended to minimize the noise effect in digital image correlation (DIC) measurement under a high-temperature atmosphere environment. First, the principle of PCA was introduced, and the singular vectors and singular values for each component of the displacement fields from DIC were obtained. Then, the simulated high-temperature speckle images were developed to investigate the influences of noise on the DIC method under a high-temperature environment. Finally, the displacement fields of several special conditions were extracted from the simulated speckle images and experimental images; the effects of noise on the PCA were also analyzed.     

Numerical simulation of prestrain history effect on ductile crack growth in mismatched welded joints

Pipe reeling may lead to plastic pre‐deformation (prestrain) around existing cracks in components; therefore, investigating whether this process accelerates or counteracts ductile crack growth, especially for strength mismatched welded joints, is warranted. This study focused on the effect of prestrain history on ductile crack growth in mismatched welded joints. A single‐edge‐notched tension specimen was selected for numerical study, and the crack was assumed to have existed before a prestrain history was applied. Crack growth resistance curves for plane strain and mode I crack growth under large‐scale yielding conditions have been computed using the complete Gurson model. Meanwhile, symmetrical and non‐symmetrical prestrain cycle modes with different loading levels were applied to the overmatched specimens. The outcome demonstrated that the mismatch ratio (the ratio between the yield stress of the weld metal and base metal) showed a significant effect on fracture resistance regardless of the stage at which the prestrain cycle loading was located. By contrast, the processing of the crack growth was weakened by the increase of prestrain values, and the symmetrical prestrain cycle resulted in greater plastic damage than the non‐symmetrical prestrain cycle did. However, the initial crack length had a non‐significant effect on the ductile fracture considering the prestrain and mismatch effects.     

Modelling and joint monitoring of input and output of systems with arbitrary order autoregressive disturbance

Considerable studies have been done on modelling and joint monitoring of input and output of systems with autoregressive moving average (ARMA) disturbance. Most of these studies focus on systems with ARMA (1, 1) disturbance. However, many kinds of systems are not conform to ARMA(1, 1) disturbance. Motivated by the fact that an autoregressive (AR) model with high order can be implemented to approximate the stationary ARMA model at any precision, a new generic model and a joint monitoring scheme of systems with arbitrary order AR(p) disturbance are developed. A minimum mean squared error (MMSE) controller with arbitrary order AR disturbance is designed to reduce the system variability. The mathematical expectation and average run length of MMSE-controlled outputs are derived. A new joint chart for monitoring the input and output simultaneously is explored. Two out-of-control rules for the joint monitoring chart are developed. The monitoring performances of the input chart, the output chart and the joint monitoring chart are also discussed. The results of simulation experiments and case studies validate the effectiveness of the developed model and joint monitoring chart.     

柔性关节空间机械臂奇异摄动自抗扰控制仿真研究

针对不同重力环境条件下考虑摩擦、关节刚度非线性与外扰影响的柔性关节空间机械臂的控制问题,提出了一种基于奇异摄动理论的自抗扰控制方法。首先建立了柔性关节空间机械臂在地面重力和空间微重力环境下的动力学模型;然后采用奇异摄动法将系统模型分为快变子系统和慢变子系统,针对快变子系统设计速度反馈控制律来抑制柔性关节的振动,针对慢变子系统设计加入前馈补偿的自抗扰控制器(ADRC)来抵抗系统的内外扰动,并对系统进行了稳定性分析;最后对设计的控制器进行了仿真验证与对比研究。仿真结果表明,采用该方法,在不同重力环境下柔性关节空间机械臂均能实现很好的轨迹跟踪和抖振抑制,且能有效抵抗内外扰动,系统具有鲁棒性。     

基于VSG的并网变流器LADRC策略研究北大核心

针对复杂工作环境下并网变流器容易受到外界干扰,传统控制策略控制效果不理想的问题,提出了一种基于虚拟同步发电机(Virtual Synchronous Generator, VSG)的并网变流器线性自抗扰控制(Linear Active Disturbance Rejection Controller, LADRC)策略。建立了三相并网变流器的数学模型,分析了VSG控制的基本原理;根据并网变流器详细建模设计了双闭环LADRC控制器;通过MATLAB/Simulink仿真,对基于VSG的PI控制和基于VSG的LADRC控制在改变有功功率和改变网侧电压的工况下变流器运行情况进行了对比分析。仿真结果表明,基于VSG的LADRC略鲁棒性更好、抗干扰性更强。     

基于改进型自抗扰控制的永磁同步电机伺服控制

目的 解决传统包装机械存在的包装速度慢、包装质量堪忧等问题,满足包装机械的高效率、高精度等要求,提高食品包装的自动化水平和包装企业的经济效益。方法 对具有较大潜力的永磁同步电机,进行控制器和控制方法的研究与改进,并最终选定自抗扰控制器,对自抗扰控制器中非光滑函数fal进行改进得到连续平滑的tal函数,使其减小在原点周围的颤振,并且基于tal函数重新设计非线性状态误差反馈率和扩张状态观测器,以取得对永磁同步电机更好的控制效果。结果 仿真表明,tal函数比fal函数具有更好的平滑性和连续性。基于改进型自抗扰控制的永磁同步电机具有更好的动态性能、稳态精度、抗扰能力和跟踪能力。结论 文中优化后的永磁同步电机伺服控制系统,适用于高精度、负载变动频繁的场合,能够有效地提高包装自动化水平,满足高效率、高精度的包装行业要求。     

基于自抗扰技术的高超声速飞行器控制系统设计

高超声速飞行器在飞行过程中超燃冲压发动机对攻角及侧滑角有较严格的要求,为实现对攻角及侧滑角的精确控制,文章采用自抗扰控制技术设计了高超声速飞行器的攻角自动驾驶仪;首先建立高超声速飞行器控制系统的数学模型,然后采用扩张状态观测器对受扰对象的状态和干扰进行观测,并对状态误差采用非线性反馈,对观测的干扰进行补偿,从而实现对干扰的快速抑制和对指令的精确跟踪,最后仿真表明所设计的自动驾驶仪满足性能要求,验证了该方法的正确性。     

一种联合收获机脱粒滚筒转速的鲁棒预测控制

联合收获机的轴流式脱粒滚筒转速系统具有强非线性、不确定、滞后、大干扰等特点,以收获机的行走速度和喂入量为控制量,滚筒转速为被控量,建立闭环控制系统,设计时变的鲁棒稳定控制器.在频域内基于比例微分校正技术补偿无级变速传动的滞后环节影响;基于近似模型预测的连续预测控制律保证了大范围工作的控制系统性能;同时,设计收敛的非线性...     

DRNN-ADRC异步电机直接转矩控制系统研究

由于经典PID控制器自身所固有的缺陷,在异步电机直接转矩控制(DTC)调速中不能满足大范围高精度的调速要求.采用自抗扰控制器(ADRC)作为速度调节器,并借助对角递归神经网络(DRNN)进行参数整定,构成了新的异步电机直接转矩控制调速系统.仿真结果表明:对于异步电机直接转矩控制系统,基于对角递归神经网络整定的自抗扰控制...     

全光纤安防系统模式识别及混合编程

介绍了全光纤监控预警系统及其模式识别算法。利用小波包分解对信号提取各频段内信号分量能量谱作为特征向量;应用速度与精度均非常出色的RBF神经网络实现信号分类,提高网络泛化能力。利用MATLAB引擎、组件对象模型(COM)两种混合编程方法实现将MATLAB算法程序集成到VC编写的系统平台中。使用文本文件存取网络数据,克服了MATLAB无法编译神经网络工具箱函数的缺陷,并从操作复杂度、执行时间、消耗内存等方面对两种方式进行对比,最终选定组件对象模型作为系统应用方案。