A Long Short-Term Memory Networks Based Method for Force Reconstruction With Interval Uncertainties
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摘要: 针对传统神经网络在处理时间依赖性动态过程和含噪数据时的不稳定性问题,提出了一种基于长短期记忆网络动态力重构方法. 测量响应信号经噪声污染后,被归一化为输入变量;而归一化的动态载荷则作为输出变量. 长短期记忆网络的实现方法被采用. 为了提高网络的泛化能力,不同类型的动力响应和原始载荷被定义为每个时刻的样本结构. 考虑区间不确定性,在传统配点法的基础上调整配点策略得到逐维法,在研究某一维度不确定性变量时固定其他维度,可以高精度地解决区间变量相互独立的不确定性载荷识别问题. 最后,采用数值算例与传统神经网络(BP神经网络)对比,表征长短期记忆网络在含噪数据的处理上更为稳定,设计试验证实了对于时间依赖性的数据,该方法的有效性和可行性.Abstract: In response to the instability issues of traditional neural networks in handling time-dependent dynamic processes and noisy data, a dynamic force reconstruction method based on long short-term memory (LSTM) networks was proposed. The measured response signals, contaminated by noise, were normalized as input variables, while the normalized dynamic loads as output variables. The implementation approach of LSTM networks was adopted. To enhance the network's generalization ability, various types of dynamic responses and original loads were defined as sample structures at each time step. In view of interval uncertainty, the point distribution strategy results were adjusted to build the dimension-wise method (DWM) based on the traditional point distribution methods, to get precise resolution of uncertainty load identification with independent interval variables in the investigation of uncertainty variables in a specific dimension through fixation of others. Finally, by numerical examples and a comparison with traditional neural networks (back-propagation neural networks), the LSTM neural network was proved to be more stable in handling noisy data. An experimental design validates the effectiveness and feasibility of this method for time-dependent data.
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表 1 悬臂板材料参数
Table 1. Cantilever plate structure material parameters
material property symbol specific value Young’s modulus E/GPa 210 Poisson’s ratio ν 0.3 density ρ/(kg/m3) 7 800 表 2 神经网络训练集与测试集载荷
Table 2. The expressions of actual dynamic forces of training sets and test sets
condition actual dynamic force expression training set sample 1 F=100sin(20πt)+50sin(10πt) sample 2 F=300sin(40πt2) sample 3 F=300e-4tsin(20πt) sample 4 F=350e-6tsin(50πt2) sample 5 F=250e-10t test set - F=200sin(20πt) 表 3 不同传感器布局下力重构的总相对误差
Table 3. Relative errors of force reconstruction with different sensor layouts
sensor selection relative error/% 1, 2, 3, 4, 5, 6 8.79 1, 2, 3, 4 7.89 1, 2, 3 13.75 1, 4, 6, 9 8.05 1, 3, 6, 7 9.12 1, 6, 7, 9 8.92 表 4 初始样本和含噪样本回归的LSTM架构概要
Table 4. Summary of the LSTM architecture for initial and noise affected data regression
layer(type) number of parameters (original data) number of parameters (noise affected data) sequence input layer 20 60 Bi-LSTM layer 100(hidden layer unit) 128(hidden layer unit) fully connected layer 300 300 dropout layer 0.2(probability) 0.8(probability) fully connected layer 1(response) 1(response) regression layer - - 表 5 不同噪声条件下利用LSTM网络和BP神经网络进行力重构的相对误差
Table 5. Relative errors of force reconstruction by LSTM and BP under noisy conditions
SNR of additive noise LSTM/% BP/% 20 8.78 26.29 20, 30 18.00 41.43 20, 30, 40 18.31 41.39 表 6 不同工况下的动态载荷识别总相对误差
Table 6. Total relative errors of dynamic load recognition under different operating conditions
state temperature/℃ frequency/Hz relative error/% post-impact 60 3 3.98 pre-impact 100 5 4.44 post-impact 150 1 4.72 -
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