Pressure fluctuation signal analysis of pump based on ensemble empirical mode decomposition method

Pressure fluctuations, which are inevitable in the operation of pumps, have a strong non-stationary characteristic and contain a great deal of important information representing the operation conditions. With an axial-flow pump as an example, a new method for time-frequency analysis based on the ensemble empirical mode decomposition （EEMD） method is proposed for research on the characteristics of pressure fluctuations. First, the pressure fluctuation signals are preprocessed with the empirical mode decomposition （EMD） method, and intrinsic mode functions （IMFs） are extracted. Second, the EEMD method is used to extract more precise decomposition results, and the number of iterations is determined according to the number of IMFs produced by the EMD method. Third, correlation coefficients between IMFs produced by the EMD and EEMD methods and the original signal are calculated, and the most sensitive IMFs are chosen to analyze the frequency spectrum. Finally, the operation conditions of the pump are identified with the frequency features. The results show that, compared with the EMD method, the EEMD method can improve the time-frequency resolution and extract main vibration components from pressure fluctuation signals.

Correlation between detrended fluctuation analysis and the Lempel-Ziv complexity in nonlinear time series analysis

We study the correlation between detrended fluctuation analysis（DFA） and the Lempel-Ziv complexity（LZC） in nonlinear time series analysis in this paper.Typical dynamic systems including a logistic map and a Duffing model are investigated.Moreover,the influence of Gaussian random noise on both the DFA and LZC are analyzed.The results show a high correlation between the DFA and LZC,which can quantify the non-stationarity and the nonlinearity of the time series,respectively.With the enhancement of the random component,the exponent α and the normalized complexity index C show increasing trends.In addition,C is found to be more sensitive to the fluctuation in the nonlinear time series than α.Finally,the correlation between the DFA and LZC is applied to the extraction of vibration signals for a reciprocating compressor gas valve,and an effective fault diagnosis result is obtained.

A Correlation Coefficient Approach for Evaluation of Stiffness Degradation of Beams Under Moving Load

This paper presents a new approach using correlation and cross-correlation coefficients to evaluate the stiffness degradation of beams under moving load.The theoretical study of identifying defects by vibration methods showed that the traditional methods derived from the vibration measurement data have not met the needs of the actual issues.We show that the correlation coefficients allow us to evaluate the degree and the effectiveness of the defects on beams.At the same time,the cross-correlation model is the basis for determining the relative position of defects.The results of this study are experimentally conducted to confirm the relationship between the correlation coefficients and the existence of the defects.In particular,the manuscript shows that the sensitivity of the correlation coefficients and cross-correlation is much higher than the parameters such as changes in stiffness(EJ)and natural frequency values(Δf).This study suggests using the above parameters to evaluate the stiffness degradation of beams by vibration measurement data in practice.

Study on pick arrangement of shearer drum based on load fluctuation

According to the coal or rock cutting theory,a mechanical model and computing formula for a pick and the drum load fluctuation model were established in order to obtain relationships between pick arrangements and drum fluctuation loads,drum rotary speeds and haulage speeds.Based on a minimum load fluctuation,an optimal mathematical model was established for drum pick arrangements.The effects of pick arrangements(including punnett square,sequence,aberrance I and II)on the drum load fluctuation coefficient are discussed.The relationships between the pick arrangements of the drum with different start vanes and the cutting load fluctuation coefficient,the drum rotary speed and haulage speed were also studied.The results indicate that the punnett square arrangement has a smaller cutting load fluctuation coefficient than other forms of arrangement and the drum with the 4-start vanes has the smallest coefficient.The drum rotary speed and haulage speed are affected not only by pick arrangements,but also by the number of vanes.

Effects of signal modulation and coloured cross-correlation of coloured noises on the diffusion of a harmonic oscillator

The diffusion in a harmonic oscillator driven by coloured noises ξ（t） and η（t） with coloured cross-correlation in which one of the noises is modulated by a biased periodic signal is investigated. The exact expression of diffusion coefficient d as a function of noise parameter, signal parameter, and oscillator frequency is derived. The findings in this paper are as follows. 1） The curves of d versus noise intensity D and d versus noises cross-correlation time z3 exist as two different phases. The transition between the two phases arises from the change of the cross-correlation coefficient A of the two Ornstein-Uhlenbeck （O-U） noises. 2） Changing the value of T3, the curves of d versus Q, the intensity of colored noise that is modulated by the signal, can transform from a phase having a minimum to a monotonic phase. 3） Changing the value of signal amplitude A, d versus Q curves can transform from a phase having a minimum to a monotonic phase. The above-mentioned results demonstrate that a like noise-induced transition appears in the model.

EFFECT OF EMPIRICAL COEFFICIENTS ON SIMULATION IN TWO-SCALE SECOND-ORDER MOMENT PARTICLE-PHASE TURBULENCE MODEL

A two-scale second-order moment two-phase turbulence model accounting for inter-particle collision is developed, based on the concept of particle large-scale fluctuation due to turbulence and particle small-scale fluctuation due to collision. The proposed model is used to simulate gas-particle downer reactor flows. The computational results of both particle volume fraction and mean velocity are in agreement with the experimental results. After analyzing effects of empirical coefficient on prediction results, we can come to a conclusion that, inside the limit range of empirical coefficient, the predictions do not reveal a large sensitivity to the empirical coefficient in the downer reactor, but a relatively great change of the constants has important effect on the prediction.

钢桁梁断面形式对公铁两用桥上列车气动特性影响

钢桁梁断面形式的不同可能会改变桥上列车的气动力,进而影响桥上列车运行安全性和舒适性。为此,以某千米级公铁两用悬索桥为工程为背景,通过风洞试验对三种常用钢桁梁断面形式的桥上列车进行测力、测压试验。研究结果表明,当单列车位于三种钢桁梁断面形式上的上游时,列车的阻力、升力系数无明显差异,而单列车位于下游时,列车的阻力、升力系数有较大的区别;在双车状态下,由于迎风侧列车的遮挡作用,改变了不同钢桁梁断面形式下列车的流场,使得钢桁梁断面形式对背风侧列车影响较小。无论列车位于上游、下游,其三种钢桁梁断面形式下列车的阻力系数、升力系数随风攻角的变化趋势一致。当列车位于上游时,其三种钢桁梁断面形式上列车顶部和底部圆弧过渡段都出现不同程度的流动分离,使得其列车平均风压系数不同;当列车位于下游时,三种钢桁梁断面形式上列车平均风压系数变化趋势一致,说明钢桁梁断面形式对下游列车的平均风压影响较小。列车位于上、下游时,其脉动风压系数会有显著的差异,其脉动风压系数的大小受腹杆布置形式的影响要比梁高的不同更为显著。本文研究结果可为大跨钢桁梁桥的断面形式选取提供参考和依据。

周期性脉动源对风力机功率的影响

针对WindPACT1.5 MW机组,通过大涡模拟探究风轮5°仰角时周期性脉动源(仰角、塔影效应、偏航、风剪切)对风力机总功率的影响,并结合逆叶素动量理论,进一步分析功率与升力系数之间的联系。结果表明,仰角、塔影效应加仰角与偏航加仰角均使得风力机总功率产生“3P”的波动规律,而风剪切加仰角使得总功率产生“锯齿状”的高频率波动规律,其中偏航是总功率损失的主要因素,塔影效应是功率波动的主要因素,且发现升力系数波动规律与功率单周期内的波动规律相似。

基于聚光集热和脉动风压的定日镜群模拟研究

太阳辐射量和风荷载会直接影响光热电站的持续发电量。文章根据新疆哈密地区中电淖毛湖光热电站的实际环境情况,建立定日镜群的三维数值模型,对不同季节太阳辐射和迎风仰角下镜群的受热情况及流场特性开展数值模拟,分析获得风在不同入射角下镜面耀斑分布情况和脉动风压系数。结果表明:模拟所得镜群阻力系数和升力系数与相关研究结果较为吻合,验证了所建模型的有效性;不同季节下耀斑的分布规律较为相似,主要取决于太阳方向角的变化;随着风入射角的增大,镜群的尾流区域呈先减小后增大趋势;由于定日镜镜群中的尾流可有效抑制风压,结合镜群的排布方式保证内部的稳定性,其中,正五边形定日镜的中心处保持较低的脉动风压,极大提高了镜面受力均衡性。

树脂基复合材料摩擦噪声特性研究

树脂基复合材料被广泛应用于多种制动系统中,但其在摩擦过程中易产生严重的环境噪声污染.通过摩擦试验和有限元模拟方法,总结了不同试验条件下摩擦系数、摩擦力波动系数以及摩擦噪声有效声压级的变化规律,分析了摩擦噪声与摩擦界面稳定性之间的关系,揭示了酚醛树脂基复合材料摩擦噪声的产生机理,同时研究了温度对其摩擦学性能及摩擦噪声行为的影响.结果表明:摩擦系数和摩擦力波动系数随载荷、相对滑动速度以及温度的改变呈现出不同的变化趋势,摩擦噪声的有效声压级与摩擦力波动系数正相关,且噪声的自功率谱与摩擦界面振动自功率谱相吻合.摩擦噪声的产生归因于接触界面的不稳定振动,研究结果为树脂基复合材料摩擦噪声的控制及发生机理提供了一定的理论基础.

温度梯度铁电材料热释电性质的微观机制研究

在平均场近似的理论框架下,采用拓展的横场伊辛模型理论,引入分布函数描述材料内部的量子起伏效应和温度梯度导致的铁电畸变,探讨影响温度梯度铁电材料热释电性质的微观机制。研究表明量子起伏效应和铁电畸变是影响铁电材料热释电性质的两个重要因素。随着量子起伏效应的增强,热释电系数峰值逐渐下降,但对热释电峰值出现的位置影响并不显著;铁电畸变的存在,大大提高了材料热释电系数的峰值;温度梯度铁电材料内第一层级发生相变的时刻是影响材料热释电峰出现的最显著的因素。

公路货物运输量统计测算方法综述

为全面总结公路货物运输量统计测算问题的研究进展,根据在统计过程中是否对货车运输装载和运输路径进行分离处理,分为“集计”和“非集计”测算,对各方法的优缺点进行了评述,并归纳了官方公路货物运输量统计测算方法发展的历史阶段。研究表明:计量经济和基于车型、车轴、路网结构的估算方法属于“集计”测算,是以某一特定类型的车辆群体为单位,通过建立模型将货车流量整体化,将运输载荷平均化后测算总量的方法。抽样调查法属于“非集计”测算,是以每一个车辆样本为单位,建立模型测算总量的方法。我国公路货物运输量统计测算经历了四个历史阶段,即计划经济体制下的全面调查、市场经济条件下的抽样调查、信息化背景下的抽样调查和有限数据下的融合调查,即将迎来多源异构大数据与统计数据的融合应用阶段,未来研究方向将聚焦在打破统计“数据孤岛”,开发大数据处理新工具,构建多重抽样框等方面。

基于子带处理与相关系数的风电机组功率异常波动检测

风电机组功率的周期性异常波动容易引起电网的低频振荡,威胁电网安全;而风电机组功率信号是一种非线性、非平稳信号,其异常波动频率存在不确定性,为异常波动特征的提取与检测带来困难。为此,文章提出一种基于子带处理与相关系数的风电机组功率异常波动检测方法。其首先将原始功率信号通过高通滤波器去除趋势项,然后采用子带处理滤波器组进行信号分解,得到一系列子带信号;将去除趋势项后的功率信号与各子带信号分别计算互相关系数,并根据互相关系数实现周期性异常波动所在子带的定位及子带筛选;基于筛选所得子带信号进行信号重构得到高信噪比重构信号;采用峰值检波与自相关分析相结合的检测方法,识别重构信号中特定幅值周期性异常波动发生时段,从而达到风电机组功率信号周期性异常波动检测的目的。现场数据测试结果表明,对于0.06 Hz、0.32 Hz等不同频率的功率周期性异常波动,该方法能够准确识别其所在子带及特征。

蜂巢状有源配电网中多端口能量枢纽控制策略

作为一种适应高比例分布式新能源接入的新型配电网架构,蜂巢状有源配电网利用多端口能量枢纽(multi-port energy hub,MEH)可实现多微电网/配网单元间功率的互联互济,如MEH中包含储能设备,可以进一步提升新能源利用率和电网可靠性。文中提出一种含储能的MEH及其分层协调控制策略。上层控制根据储能系统的荷电状态和配电网运行状态协调控制储能变流器与各并网端口变流器之间的功率分配,使得MEH在平抑新能源波动、配网故障恢复等运行模式下均能够对内部储能系统进行能量管理。下层控制通过将储能变流器有功功率的微分值反馈至储能系统控制环路进行补偿,提高储能变流器输入/输出有功功率响应速度。文中设计了MEH控制系统关键参数,利用MATLAB/Simulink对MEH在配电系统中的应用进行仿真。不同工况下的仿真对比验证了所提分层协调控制策略的有效性,证明该策略能够延长储能系统工作时间,提高储能系统有功功率变化率,减小直流母线的电压波动。

基于Python的网络舆情对恒瑞医药股价波动的关联性研究

移动互联时代下网络舆情对股价波动的影响成为金融市场不可忽视的因素。这里选取恒瑞医药作为研究对象,运用Python爬虫技术获取舆情信息与股价数据、情感词语料库负面词汇构建舆情评分系统,通过皮尔森相关系数实证分析了上市公司网络舆情对股价的影响。研究结果表明:(1)网络舆情与股价波动有弱正相关关系,属于上市公司股价波动的一个相关因素;(2)上市公司的舆情控制管理对股价波动有一定积极作用;(3)随着互联网的发展、新媒体信息的广泛传播,网络舆情对金融市场的影响日益重要。

创业板涨跌幅限制放宽政策对股价波动率的影响

为评估创业板涨跌幅限制放宽至20%对股价波动的影响,本文选取2020年1月1日至2021年12月31日创业板和深证主板个股的日交易数据,采用双重差分法研究得出创业板股价波动性显著加剧的结论。接着采取变异系数法比较该政策对不同行业股价波动的影响差异,研究发现:作为周期性板块的计算机、汽车和有色金属行业股价波动上升,而农林牧渔和医药生物行业因其高防御性,价格波动减缓;短期中农林牧渔业股价波动小幅上升,医药生物板块中期的价格变异系数变化幅度最大,计算机和有色金属在中长期因市场利好股价波动远高于其余三个行业,汽车板块在长期呈现高景气,股价波动增势明显。

血糖变异系数与2型糖尿病周围神经病变的相关性分析

目的探讨2型糖尿病(T2DM)住院患者的临床资料及持续葡萄糖监测系统(CGM)收集的血糖数据与糖尿病周围神经病变(DPN)的相关性及风险预测价值。方法收集安徽医科大学第一附属医院的97例T2DM患者的临床资料,并通过CGM记录血糖情况,计算平均血糖、血糖变异系数(CV)、血糖标准差(SD)、24 h平均血糖波动幅度(MAGE)、日间血糖平均绝对差(MODD)及葡萄糖正常目标范围内时间(TIR)。将入组患者分为无DPN(NDPN)组(n=49)和DPN组(n=48)。分析2组临床资料及CGM相关指标;采用二元Logistic回归分析探讨CGM相关指标与DPN发生风险的相关性;采用受试者工作特征(ROC)曲线分析CV对DPN发生的预测价值。结果DPN组年龄、收缩压、血小板(PLT)与NDPN组比较,差异有统计学意义(P<0.05)。CGM相关数据分析结果提示,2组CV、SD、MAGE、MODD比较,差异有统计学意义(P<0.05)。二元Logistic回归分析结果显示,CV高是发生T2DM周围神经病变的危险因素(P<0.05)。ROC曲线的曲线下面积为0.714(95%CI:0.613~0.814,P<0.001),截断值为45.80%,敏感度为66.70%,特异度为65.30%。结论NDPN组和DPN组年龄、收缩压、PLT、CV、SD、MAGE、MODD有显著差异,CV是DPN发生的影响因素,对于DPN的发生具有较好的预测价值。

Research on Leak Location Method of Water Supply Pipeline Based on MVMD

At present,the leakage rate of the water distribution network in China is still high,and the waste of water resources caused by water distribution network leakage is quite serious every year.Therefore,the location of pipeline leakage is of great significance for saving water resources and reducing economic losses.Acoustic emission technology is the most widely used pipeline leak location technology.The traditional non-stationary random signal de-noising method mainly relies on the estimation of noise parameters,ignoring periodic noise and components unrelated to pipeline leakage.Aiming at the above problems,this paper proposes a leak location method for water supply pipelines based on a multivariate variational mode decomposition algorithm.This method combines the two parameters of the energy loss coefficient and the correlation coefficient between adjacent modes,and adaptively determines the decomposition mode number K according to the characteristics of the signal itself.According to the correlation coefficient,the effective component is selected to reconstruct the signal and the cross-correlation time delay is estimated to determine the location of the pipeline leakage point.The experimental results show that this method has higher accuracy than the cross-correlation method based on VMD and the cross-correlation method based on EMD,and the average relative positioning error is less than 2.2%.

利用线谱声强干涉起伏相关系数估计波导不变量

针对低信噪比时难以利用低频分析记录谱中宽带连续谱条纹状干涉图样提取波导不变量的问题,提出了一种利用线谱声强干涉起伏相关系数估计波导不变量方法。该方法根据参考线谱声强干涉起伏与经过尺度伸缩变换的线谱声强干涉起伏之间存在的正比关系包含波导不变量这一事实,构造线谱声强干涉起伏相关系数以实现波导不变量估计。讨论在声源相对水听器径向和非径向2种运动模型下,将原始采样时刻代换为新的采样时刻,得到重采样后的线谱声强干涉起伏;利用相关系数表示重采样后的参考线谱声强干涉起伏与经过尺度伸缩变换后的线谱声强干涉起伏之间的相似程度,得到不同波导不变量搜索值下的相关系数,其峰值对应的搜索结果就是波导不变量真值。仿真实验和实测数据处理结果表明,所提方法能有效实现波导不变量估计。

蘑菇形悬挑屋盖风洞试验研究

以海口“雨林之心”项目为背景,针对其蘑菇形悬挑屋盖,采用1∶40大比例尺刚性模型,开展了大型风洞试验,得到其平均风压系数和脉动风压系数,并以此分析了该结构屋盖的风压分布规律以及脉动风特性;进而给出屋盖的分块体型系数,可直接用于屋盖结构抗风设计;最后就地形对风荷载的影响进行分析。试验结果表明:该蘑菇形悬挑屋盖在风荷载作用下整体受到向上的风吸作用;3个建筑间存在较强的相互影响作用;屋盖悬挑边缘位置在来流的直接撞击下,对风荷载较为敏感,呈现为较大的风压变化梯度和较大的脉动风压;A、C建筑处于迎风侧时,由于山坡对流场的影响,悬挑迎风侧的风荷载相较B建筑更不利。针对以上问题,在设计时应重点关注。