Research on runoff variations based on wavelet analysis and wavelet neural network model： A case study of the Heihe River drainage basin （1944-2005）

The Heihe River drainage basin is one of the endangered ecological regions of China. The shortage of water resources is the bottleneck, which constrains the sustainable development of the region. Many scholars in China have done researches concerning this problem. Based on previous researches, this paper analyzed characteristics, tendencies, and causes of annual runoff variations in the Yingluo Gorge （1944-2005） and the Zhengyi Gorge （1954-2005）, which are the boundaries of the upper reaches, the middle reaches, and the lower reaches of the Heihe River drainage basin, by wavelet analysis, wavelet neural network model, and GIS spatial analysis. The results show that： （1） annual runoff variations of the Yingluo Gorge have principal periods of 7 years and 25 years, and its increasing rate is 1.04 m^3/s.10y; （2） annual runoff variations of the Zhengyi Gorge have principal periods of 6 years and 27 years, and its decreasing rate is 2.25 m^3/s.10y; （3） prediction results show that： during 2006-2015, annual runoff variations of the Yingluo and Zhengyi gorges have ascending tendencies, and the increasing rates are respectively 2.04 m^3/s.10y and 1.61 m^3/s.10y; （4） the increase of annual runoff in the Yingluo Gorge has causal relationship with increased temperature and precipitation in the upper reaches, and the decrease of annual runoff in the Zhengyi Gorge in the past decades was mainly caused by the increased human consumption of water resources in the middle researches. The study results will provide scientific basis for making rational use and allocation schemes of water resources in the Heihe River drainage basin.

Wavelet Neural Network Based on NARMA-L2 Model for Prediction of Thermal Characteristics in a Feed System

Research of thermal characteristics has been a key issue in the development of high-speed feed system. Most of the work carried out thus far is based on the principle of directly mapping the thermal error against the temperature of critical machine elements irrespective of the operating conditions. But recent researches show that different sets of operating parameters generated significantly different error values even though the temperature of the machine elements generated was similar. As such, it is important to develop a generic thermal error model which is capable of evaluating the positioning error induced by different operating parameters. This paper ultimately aims at the development of a comprehensive prediction model that can predict the thermal characteristics under different operating conditions （feeding speed, load and preload of ballscrew） in a feed system. A novel wavelet neural network based on feedback linearization autoregressive moving averaging （NARMA-L2） model is introduced to predict the temperature rise of sensitive points and thermal positioning errors considering the different operating conditions as the model inputs. Particle swarm optimization（PSO） algorithm is brought in as the training method. According to ISO230-2 Positioning Accuracy Measurement and ISO230-3 Thermal Effect Evaluation standards, experiments under different operating conditions were carried out on a self-made quasi high-speed feed system experimental bench HUST-FS-001 by using Pt100 as temperature sensor, and the positioning errors were measured by Heidenhain linear grating scale. The experiment results show that the recommended method can be used to predict temperature rise of sensitive points and thermal positioning errors with good accuracy. The work described in this paper lays a solid foundation of thermal error prediction and compensation in a feed system based on varying operating conditions and machine tool characteristics.

Network traffic prediction by a wavelet-based combined model

Network traffic prediction models can be grouped into two types, single models and combined ones. Combined models integrate several single models and thus can improve prediction accuracy. Based on wavelet transform, grey theory, and chaos theory, this paper proposes a novel combined model, wavelet-grey-chaos （WGC）, for network traffic prediction. In the WGC model, we develop a time series decomposition method without the boundary problem by modifying the standard à trous algorithm, decompose the network traffic into two parts, the residual part and the burst part to alleviate the accumulated error problem, and employ the grey model GM（1,1） and chaos model to predict the residual part and the burst part respectively. Simulation results on real network traffic show that the WGC model does improve prediction accuracy.

Prediction of Al(OH)_3 fluidized roasting temperature based on wavelet neural network

The recycle fluidization roasting in alumina production was studied and a temperature forecast model was established based on wavelet neural network that had a momentum item and an adjustable learning rate. By analyzing the roasting process, coal gas flux, aluminium hydroxide feeding and oxygen content were ascertained as the main parameters for the forecast model. The order and delay time of each parameter in the model were deduced by F test method. With 400 groups of sample data (sampled with the period of 1.5 min) for its training, a wavelet neural network model was acquired that had a structure of {7 211}, i.e., seven nodes in the input layer, twenty-one nodes in the hidden layer and one node in the output layer. Testing on the prediction accuracy of the model shows that as the absolute error ±5.0 ℃ is adopted, the single-step prediction accuracy can achieve 90% and within 6 steps the multi-step forecast result of model for temperature is receivable.

Self-Constructing Neural Network Modeling and Control of an AGV

Tracking precision of pre-planned trajectories is essential for an auto-guided vehicle (AGV). The purpose of this paper is to design a self-constructing wavelet neural network (SCWNN) method for dynamical modeling and control of a 2-DOF AGV. In control systems of AGVs, kinematical models have been preferred in recent research documents. However, in this paper, to enhance the trajectory tracking performance through including the AGV’s inertial effects in the control system, a learned dynamical model is replaced to the kinematical kind. As the base of a control system, the mathematical models are not preferred due to modeling uncertainties and exogenous inputs. Therefore, adaptive dynamic and control models of AGV are proposed using a four-layer SCWNN system comprising of the input, wavelet, product, and output layers. By use of the SCWNN, a robust controller against uncertainties is developed, which yields the perfect convergence of AGV to reference trajectories. Owing to the adaptive structure, the number of nodes in the layers is adjusted in online and thus the computational burden of the neural network methods is decreased. Using software simulations, the tracking performance of the proposed control system is assessed.

基于神经网络模型的朝阳市生猪价格预测

选取2020年1月至2023年6月朝阳市生猪日价格和猪饲料中豆粕的日价格作为研究数据,分别建立BP神经网络模型和小波神经网络模型对朝阳市生猪价格进行预测.将前160周的价格数据作为BP神经网络模型和小波神经网络模型训练集数据,161~180周的价格数据作为预测数据,通过图形显示预测值和实际值变化,计算2种神经网格模型的平均绝对误差和均方根误差.通过误差比较分析得出,在朝阳市生猪价格波动领域,小波神经网络模型优于BP神经网络模型,建议推广应用.

基于自适应小波回声神经网络的光纤陀螺测角仪温度误差补偿技术

基于光纤陀螺的测角仪可以实现对各项角运动参数的一体化动态精密测量,但在实际应用中,光纤陀螺测角仪受到温度变化的影响,导致测量精度下降。针对这一问题,本文提出了一种基于自适应小波回声神经网络的光纤陀螺测角仪温度误差补偿技术。为了提高温度误差建模的进度,提高传统神经网络的逼近能力,通过自适应前向线性预测滤波器对建模用测角仪温度漂移数据进行预处理,并采用自适应小波回声神经网络建立温度漂移模型,能够避免传统神经网络结构设计的盲目性和局部最优等问题,增强了网络学习能力和泛化能力,并利用自适应律代替神经网络梯度进行网络训练,提升神经网络的逼近精度和收敛速度。实验结果表明,该模型可以提高光纤陀螺测角仪的测量精度和环境适应性,为光纤陀螺测角仪的性能优化和实际应用提供了可靠的技术支撑。

基于自回归小波神经网络的机械臂自适应滑模控制

针对机械臂存在模型不确定和未知扰动的问题,提出一种动力学模型参数分块逼近的神经网络非奇异终端滑模(nonsingular terminal sliding mode, NTSM)控制方法.为加快系统跟踪误差的收敛速度,避免传统终端滑模存在的奇异性问题,采用一种非奇异终端滑模面.利用多组自回归小波神经网络(self-recurrent wavelet neural network, SRWNN)分块逼近系统未知的动力学模型参数,并采用自适应更新律调整权重.通过积分控制项补偿SRWNN的逼近误差,并使用Lyapunov稳定性理论证明了系统稳定性.使用MATLAB进行仿真分析,分块SRWNN滑模控制与滑模控制、整体SRWNN滑模控制相比,关节角度跟踪误差的平均稳态误差分别降低了31.9%、76.5%,表明此方法是一种可靠、有效的轨迹跟踪控制方法.

基于改进EMD-LSTM的混凝土坝变形预测模型

针对混凝土坝变形监测数据的非线性和复杂性等特征,为提高混凝土坝变形预测的精度,提出了一种基于改进经验模态分解(EMD)法和长短期记忆(LSTM)神经网络的混凝土坝变形预测模型。该模型采用小波阈值方法对EMD法分解的高频分量进行优化处理,在去除数据噪声的同时,尽可能保留原始数据的特征信息,并运用LSTM神经网络对处理后的数据进行时序预测。实例验证结果表明,该模型能够准确模拟坝体变形过程,具有较高的预测精度。

基于改进WNN的作战飞机维修保障能力评估方法

针对现有作战飞机维修保障能力评估中评估结果误差较大、不确定性较高等问题,提出一种基于改进小波神经网络的飞机维修保障能力评估方法。依据IPO&E模型建立飞机维修保障能力评估指标体系;利用麻雀搜索算法提高小波神经网络的收敛稳定性与评估准确性;基于分级量化理论对原始数据进行处理,并开展作战飞机维修保障能力评估。算例分析表明,所提方法的评估结果与收集到的维修保障能力评估数据仅有2.4%误差,稳定性优于其他神经网络,可为作战飞机维修保障能力评估提供可行方法。

基于整体退火遗传小波网络的计量终端可靠性预测

为了解决小波神经网络初值敏感性及收敛稳定性问题,以提高计量终端软件可靠性预测建模的效率及准确性。文章完善了整体退火遗传算法(WAGA),并验证了其具有极强的整体收敛和全局优化能力,利用其全局寻优能力,优化小波神经网络(WNN)的参数,提出基于整体退火遗传小波神经网络(WAGA-WNN)的建模方法;用该方法建立计量终端的软件可靠性预测模型。实验结果表明,该方法可以解决小波神经网络初值敏感性及收敛稳定性难题,建立的软件可靠性预测模型效率和准确度较高。

基于行波法的配网混合线路故障定位研究

为实现配网混合线路故障的精准定位,提出了一种行波极性判断与单端故障定位提取相结合的方法.首先,基于小波变换模极大值的方法,计算不同区段的行波电流极性,确定故障点所在的区间;接着,仿真计算故障区间内的行波波速,并基于小波变换提取波头时间,实现混合线路的故障定位;最后,在10kV动模试验平台搭建混合线路故障模型,开展不同影响因素的定位精度研究.研究结果表明:当采样频率和故障初相角增加时,定位精度也会逐步增加;故障区段为电力电缆时,定位精度优于架空线路的故障区段;该方法可精准地实现故障定位,具有一定的推广意义.

基于EWT和NeuralProphet-MLP的蜂窝网络流量长期预测方法

蜂窝网络流量长期预测对网络扩展和优化具有重要意义,针对长期预测中数据可用性低以及非线性等弊端所带来的诸多挑战,提出一种基于分解的分频预测模型。分别采用NeuralProphet模型和多层感知机对分解出的低频分量和中高频分量进行预测,最后对各分量预测结果进行逆经验小波变换得到最终结果。在真实的蜂窝网络流量数据集上进行验证,结果表明所提方法相较于传统预测模型在准确度上有较大提升,具有较好的应用价值。

小波降噪及改进遗传算法的BP神经网络在基坑变形中的组合应用

以某市人民医院基坑工程为例,针对实测数据建立实测数据结合BP神经网络预测模型,小波降噪结合BP神经网络模型和小波降噪结合改进遗传算法优化的BP神经网络模型,并利用误差分析理论对基坑变形数据预测效果评价。结果表明:对比3种模型实际处理、预测数据能力,实测数据结合BP神经网络模型预测精度在1%-4%之间,小波降噪结合BP神经网络模型预测精度1%-2%之间,小波降噪结合改进遗传算法优化的BP神经网络模型预测精度在1%以内,小波降噪结合改进遗传算法优化的BP神经网络模型的预测准确率最高。针对基坑变形监测,小波降噪结合改进遗传算法优化的BP神经网络模型具有更高预测精度,可为类似工程提供实际参考。

基于SCADA告警数据的电网故障类型判断方法

为了提高电网故障诊断效果,提出基于SCADA告警数据的电网故障类型判断方法。构建引入动量项、自适应学习率的改进小波神经网络故障识别模型,采用提升小波对元器件两端线路数正序信号进行分裂、预估、调整等过程分解,获取不同尺度正序信号输入神经网络,输出结果即为细化的电网故障类型。实验结果表明,分解尺度为3时,故障录波信号均方误差最小,小波神经网络性能更稳定。该方法根据相间两相电流突变量情况判断故障类型及故障相,可精准判断电网故障类型及故障原因。

基于改进小波神经网络的新型PMSM速度控制

采用传统PI控制策略的永磁同步电机调速系统无法兼顾良好的动态响应性能与抗扰动能力,且在实际应用中参数整定繁琐。为改善以上问题,对速度环设计一种改进型小波神经网络PI控制器,该控制器基于自适应学习速率的梯度下降法并引入惯性项在线更新网络参数,通过权重因子扩大PI参数输出范围,以增强控制器性能;为消除电流环比例参数对速度环的影响,设计无差拍电流预测控制器,进一步提升系统动态响应性能。仿真结果表明,上述控制方案能够实现速度环PI参数在线自整定,明显提升系统动态响应性能,且具有良好的抗扰动能力。

基于Kmeans算法的配电房防汛预测模型研究

为了避免配电房受强降雨影响出现被淹情况,提出基于Kmeans算法的配电房防汛预测模型。构建预测指标体系,筛选预测指标,基于Kmeans算法获取指标数据,将预测日预测指标数据和积水深度数据作为样本数据,构建配电房水淹风险预测模型对样本数据进行训练,获取积水深度值预测结果,与风险划分标准对比得到被淹风险程度,实现配电房防汛预测。实验证明,应用设计方法进行预测的CH指数大于0.9,积水深度预测结果与实际结果之间的皮尔逊相关系数达到0.9以上,说明提出的预测模型准确度高。

基于交通小区短时交通生成预测的城市道路网短时动态交通预测研究

城市道路周边用地性质的不同导致短时发生和吸引交通量的差异,直接影响城市道路网上的交通流。论文对城市路网中各地块的发生和吸引交通量进行短时预测,将预测的交通量通过动态交通分配到城市路网中,以此实现城市路网短时动态交通预测。将单一的BP神经网络模型为对比模型,对模型进行训练及参数标定,并检验模型的预测效果。实验结果表明,论文所提的预测方法与BP神经网络相比,预测精度最高可提升84.28%。

6kV高压电动机故障智能诊断方法

针对6 kV高压电动机故障智能诊断方法存在错诊率较高和诊断响应时间较长的问题,提出6k V高压电动机故障智能诊断方法。利用无线传感器采集电动机运行数据,利用降噪自编码网络模型对数据去噪处理,利用小波包分析技术获取数据小波包能量熵信息,提取数据特征,根据计算故障特征频率,诊断电动机故障类型,以完成6 kV高压电动机故障智能诊断。实验证明,该设计方法错诊率在1%以内,能在1s内完成故障诊断,具有良好的应用前景。

新能源配电网低碳运行长期负荷预测研究

为解决新能源配电网持续低碳运行时的长期负荷预测难度问题。提出利用多时间尺度分析法获取电力负荷数据的小波尺度,选取多个尺度进行分析获取的初步长期负荷数据,采用指数平滑法对获取的初步长期负荷数据进行平滑处理。通过对平滑处理后长期负荷数据的累加累减以及还原,构建一阶微分方程,利用灰色关联方法实现配电网低碳运行长期负荷预测。结果表明,所提方法的预测结果接近电力负荷实际值,预测误差始终低于0.3 MW,且在配电网不同时期的预测误差范围均较小。