Mitigating end effects of EMD using non-equidistance grey model

Aiming at mitigating end effects of empirical mode decomposition （EMD）, a new approach motivated by the non- equidistance grey model （NGM） termed as NGM（1,1） is proposed. Other than trapezoid formulas, the cubic Hermite spline is put forward to improve the accuracy of derivative to the accumulated generating operation （AGO） series. Hopefully, it is worth stressing that the proposed NGM（1,1） model is particularly useful for predicting uncertainty data. Qualitative and quantitative comparisons between the proposed approach and other well-known algorithms are carried out through computer simulations on synthetic as well as natural signals. Simulation results demonstrate the proposed method can reduce end effects and improve the decomposition results of EMD.

Optimization of the End Effect of Hilbert-Huang transform(HHT)

In fault diagnosis of rotating machinery, Hil- bert-Huang transform （HHT） is often used to extract the fault characteristic signal and analyze decomposition results in time-frequency domain. However, end effect occurs in HHT, which leads to a series of problems such as modal aliasing and false IMF （Intrinsic Mode Func- tion）. To counter such problems in HHT, a new method is put forward to process signal by combining the general- ized regression neural network （GRNN） with the bound- ary local characteristic-scale continuation （BLCC）. Firstly, the improved EMD （Empirical Mode Decompo- sition） method is used to inhibit the end effect problem that appeared in conventional EMD. Secondly, the gen- erated IMF components are used in HHT. Simulation and measurement experiment for the cases of time domain, frequency domain and related parameters of Hilbert- Huang spectrum show that the method described here can restrain the end effect compared with the results obtained through mirror continuation, as the absolute percentage of the maximum mean of the beginning end point offset and the terminal point offset are reduced from 30.113% and 27.603% to 0.510% and 6.039% respectively, thus reducing the modal aliasing, and eliminating the false IMF components of HHT. The proposed method caneffectively inhibit end effect, reduce modal aliasing and false IMF components, and show the real structure of signal components accuratelX.

Performance Analysis of Nested-loop Secondary Linear Doubly-fed Machine Considering End Effects

Nested-loop secondary linear doubly-fed machine(NLS-LDFM) is a novel linear machine evolved from rotary brushless doubly-fed induction machine, which has a good application prospect in linear metro. In order to analyze the performance of NLS-LDFM, the mechanism and action rules of end effects are investigated in this paper. Firstly, the mechanism of static and dynamic end effects is analyzed in aspect of direct coupling, winding asymmetry and transient secondary current. Furthermore, based on the winding theory for short primary linear machines, the machine parameters are established qualitatively considering pulsating magnetic field of NLS-LDFM. Finally, the NLS-LDFM performance analysis is supplemented by the finite element algorithm(FEA) simulation and experiments under different operating conditions.

A new method to reduce end effect of linear induction motor

A new method to compensate the end effect of a linear induction motor （LIM） in low-speed maglev vehicles is proposed. With this method, the motors are close to each other so that the front motor＇s exit-end magnetic field extends into the next motor＇s entry zone. As a result, the motor＇s magnetic field traveling wave become continuous and the end effect of short primary LIMs is greatly weakened. In the analysis of the air-gap magnetic field distribution, the LIM is assumedly divided into two identical motors vcith the distances of 20, 40, 60, and gO ram. The results show that the air-gap magnetic field is still continuous within these distances due to LIM＇s end effect. As the distance between two motors increases, the distortion of the air-gap magnetic field becomes more severe. Then, we investigate the relationship between the secondary speed and the thrust in three cases, i.e., a single LIM, two motors divided with 72 mm with pole pitch corrected, and two motors divided with 60 mm without the pole pitch being corrected. We find that the thrust has a small decrease when the speed increases, which means that the magnetic field is already continuous and its amplitude is approximately a constant. Furthermore, the thrust loss of case 3 is more than that of case 2, which indicates that the pole pitch correction is effective.

Researches on End Effects of Permanent Magnet Electromagnetic Launchers

Brushless DC linear motors have considerable advantages of simpler structure,higher efficiency,higher thrust density and so on.They are well suited for many domains such as electromagnetic launch and launch-assist,but it is inevitable that there exist longitudinal end effects in the mover of the motor caused by longitudinal discontinuities.The serious trouble caused by longitudinal end effects is the thrust ripple.Firstly,by using the method of finite element simulation,this paper studies the distribution of magnetic field and energy in the end region when the mover is in different positions in the range of a polar pitch and discusses the effective methods of reducing the longitudinal end effects.Then the law of the influence of different mover length on the longitudinal end effects has been studied by using analytic methods,and the influences of the mover length and its end geometry shape on the longitudinal end effects have been verified for the test model by using the method of finite element simulation.

DECAY RATE OF SAINT-VENANT END EFFECTS FOR PLANE DEFORMATIONS OF PIEZOELECTRIC-PIEZOMAGNETIC SANDWICH STRUCTURES

This paper is concerned with the decay of Saint-Venant end effects for plane deformations of piezoelectric （PE）-piezomagnetic （PM） sandwich structures, where a PM layer is located between two PE layers with the same material properties or reversely. The end of the sandwich structure is subjected to a set of self-equilibrated magneto-electro-elastic loads. The upper and lower surfaces of the sandwich structure axe mechanically free, electrically open or shorted as well as magnetically open or shorted. Firstly the constitutive equations of PE mate- rials and PM materials for plane strain are given and normalized. Secondly, the simplified state space approach is employed to arrange the constitutive equations into differential equations in a matrix form. Finally, by using the transfer matrix method, the characteristic equations for eigen- values or decay rates axe derived. Based on the obtained characteristic equations, the decay rates for the PE-PM-PE and PM-PE-PM sandwich structures are calculated. The influences of the electromagnetic boundary conditions, material properties of PE layers and volume fraction on the decay rates are discussed in detail.

Visualization study on fluid distribution and end effects in core flow experiments with low-field mri method

Core flow experiment is an important means of simulation experiments to evaluate the effect of displacing agent, but conventionally the internal characteristics in the core cannot be intuitively observed, and then some important information can not be directly acquired by experiments. In this paper, a visualization method was used to detect the water-flooding process by using an improved low field nuclear magnetic resonance imaging（MRI） device, and the images describing the distribution of oil and water were collected. The experimental results show that the distribution of oil and water can be visually detected in an appropriate range of core porosity, and the end effect in many mechanics experiments is found to exist also in natural core flow test, and the influence range is about 0.004 m from the end of a 0.05752 m length natural core. The results also indicate that MRI is an effective tool to study the real time fluid distribution in natural core.

Realizing profits immediately:disposition effect of open-end fund investors in China

This paper explores the disposition effect, the tendency of investors to hold losing investments too long and sell winning investments too soon, by analyzing a unique data set that consists of the buying and selling positions of open-end fund investors in China. Results show that investors' buying and selling behaviors are significantly affected by fund performance. The reasons that lie behind such results are mainly related to the non-persistence of fund performance. When fund performance is non-persistent, investors are not clear about the future returns on funds. So, investors, especially individual investors, would have to realize the profits on hand immediately. Meanwhile, fund investors are highly sensitive to fund age and loading fees, but not sensitive to management fees charged by funds when they buy or sell fund shares.

Study of Reducing Non-Ideal Effects Based on TiN Sensitive Electrode with Front-End Offset Circuit

The structure of the extended gate ion sensitive field effect transistor (EGISFET) is similar to the structure of the ion sensitive field effect transistor (ISFET).Moreover,the non-ideal effect of EGISFET is the main impediment to development of commercial processes for sensitive devices.It is necessary to promote the stability and reliability of the devices by employing calibration circuits and the better fabrication conditions.The temporal drift exists in the entire measurement experiment. Furthermore,in this study we can reduce the temporal drift effect which influences the stability of the TiN sensitive electrode with the differential front-end offset circuit.The measurement system combines with shifting circuit,differential and instrument amplifiers.We employ the calibration circuit to compare with the variations of the output voltage,and expectably improve the stability and reliability of the TiN sensitive electrode by the novel calibration circuit.

Study on the squeezing effect of open-ended pipe piles

During the installation of a pipe pile,the soil around the pile will be squeezed out. This paper deals with this squeezing effect of open-ended pipe piles using the cylindrical cavity expansion theory. The characteristics of soil with different tension and compression moduli and dilation are involved by applying the elastic theory with different moduli and logarithmic strain. The closed-form solutions of the radius of the plastic region,the displacement of the boundary between the plastic region and the elastic region and the expansion pressure on the external surface of the pipe piles are obtained. When obtaining these solutions,the soil plug in the open-ended pipe pile is considered by employing an incremental filling ratio to quantify the degree of soil plugging. Moreover,the effects of the ratio of tension and compression moduli,angle of dilation and incremental filling ratio on the radius of the plastic region and the expansion pressure on the external surface of the pipe pile are investigated. The parametric analyses show that it is necessary and important to consider the difference between the tension modulus and compression modulus,dilation angle and incremental filling ratio for studying the squeezing effect of open-ended pipe pile installation. It is concluded that the analytical solutions presented in this paper are suitable for studying the squeezing effect of open-ended pipe piles.

计及边端效应的直线式移相变压器等效电路分析

直线式移相变压器是一种新型移相变压器,具有绕组结构简单、易于模块化和可任意角度移相的优点。其直线型结构导致变压器存在边端效应,进而导致气隙磁场产生畸变。为了计算出边端效应产生的影响,该文从直线式移相变压器的磁场进行深入分析,并建立计及边端效应的等效电路模型。首先,基于一维场理论对直线式移相变压器进行数学分析,根据场路复功率相等的原则,推导出等效电路二次侧参数,并计算出边端效应修正系数;然后,根据边端效应的分析结果和直线感应电机的等效电路拓扑建立计及边端效应的等效电路模型;最后,通过直线式移相变压器的二维有限元仿真模型和小功率样机的实验,验证了建模方法的合理性和等效电路模型的准确性。

结构参数对环形线性感应电磁泵性能的影响分析

环形线性感应电磁泵(ALIP)是液态金属反应堆中泵送冷却剂的关键驱动设备。在电磁泵的设计和分析中,结构参数是影响电磁泵输出性能的重要因素。为了进一步研究环形线性感应电磁泵结构设计参数对输出性能的影响,首先利用有限元分析软件建立考虑端部效应和环形导电管道影响的环形线性感应电磁泵仿真模型,然后基于模型计算分析了不同齿槽比、流道高度和管道壁厚度对电磁泵的磁密分布、电磁力密度分布和输出电磁力的影响,最后进一步对比分析了不同结构参数下环形线性感应电磁泵的输出特性和效率,研究结果为环形线性感应电磁泵的结构参数优化提供了参考依据。

考虑空穴效应的连杆小头摩擦副润滑特性与冲击影响研究

为改善连杆小头轴承润滑及活塞销冲击特性,基于粗糙峰接触理论、平均流量模型及弹流润滑理论,以某高压共轨4缸柴油机为研究对象,运用AVL EXCITE Power Unit软件搭建混合润滑活塞连杆组多体动力学模型,研究了考虑空穴条件下不同转速对连杆小头摩擦副润滑及冲击特性的影响规律。研究结果表明:标定功率转速2400 r/min下,在做功时刻1080°后峰值油膜压力达到最大值197.1 MPa,最小油膜厚度达到最小值1.8μm,而润滑油填充率在整个发动机循环过程中均低于0.12。在怠速800 r/min、最大扭矩转速1600 r/min、标定功率转速2400 r/min下,进气、压缩、做功、排气4个冲程过程中,空穴区域由连杆小头轴承下半区转移至上半区、再转移至下半区。转速升高会导致峰值油膜压力增大,最小油膜厚度减小,粗糙接触压力增大,活塞销Z向速度峰值加大,对连杆小头轴承冲击加重,在缸内最高燃烧压力时刻,800 r/min,1600 r/min,2400 r/min下的平均润滑油填充率均值为0.84,0.70,0.69,因润滑油填充率随转速的升高而降低,空穴程度加重。

基于模糊扩展卡尔曼的直线感应电机无速度传感器控制

直线感应电机(linear induction motor,LIM)可实现无接触、无摩擦的直线运动,具有爬坡强、横断面小、低噪音等优势,在中低速磁悬浮与城市轨道交通中被广泛应用。其中,基于观测器的电机无速度传感器矢量控制方法,是解决速度传感器成本高、可靠性低、维护难等问题的有效途径。针对LIM速度辨识受系统内外扰动影响导致观测精度下降问题,提出基于模糊扩张卡尔曼滤波(Fuzzy Extended Kalman Filter,FEKF)的速度观测方法,提高观测器鲁棒性。首先在αβ坐标系下建立考虑动态边端效应的LIM数学模型,利用LIM的实时电流和电压作为输入信号,以电流、磁链和速度作为状态变量,推导出基于扩展卡尔曼滤波(extended kalman filter,EKF)观测器电机状态空间方程的离散模型,利用EKF对LIM的速度和磁链进行在线观测,并用于实现LIM的矢量控制。其次,为提高EKF的噪声协方差矩阵Q对LIM系统内外扰动的鲁棒性,引入模糊控制方法对矩阵Q进行自适应调整,实现速度与磁链的估计精度。具体通过计算系统理论残差与实际残差的偏离程度得到噪声调节因子,实时调整噪声协方差矩阵Q,并在下一周期更新模糊扩展卡尔曼的反馈增益矩阵,提高对速度与磁链的估计精度。之后对系统的能观性与FEKF的收敛性进行分析,探明矩阵Q中各参数的边界及整定规律。最后通过仿真和硬件在环实验验证所提FEKF优化算法的有效性,结果表明FEKF能有效提高对LIM速度辨识准确性,实现LIM无速度传感器矢量控制。

基于EMD-LSTM多变量输入的极端海况预报模型

极端海况是多种外界因素共同作用的结果,传统单变量波浪预报模型无法考虑多变量的影响,因此构建EMD-LSTM多变量输入模型来预报极端海况。以浮标数据作为分析数据集,利用改进的EMD算法消除变量端点效应和时序非平稳性的影响,运用多变量输入模型对其进行预测分析。结果表明:多变量复合模型可对极端海况实现有效提前预警,输入层引入波高、风速和阵风3个关键因子后模型预报性能最佳,比对均方根误差和纳什效率系数可知多变量输入的预报性能较单变量有显著提升。

Extended Anode Effect for Tube Inner Coating of Non-Conductive Ceramics by Pulsed Coaxial Magnetron Plasma

For uniform tube inner coating of non-conductive thin films, the double-ended coaxial magnetron pulsed plasma (DCMPP) method was investigated. In this study, coating of TiN and TiO2 was performed. It was clearly shown that the extended anode effect was strongly influenced by the electric resistance of the coated thin films on the inner surface of an insulator tube. Additionally, high frequency (100 kHz) was better for relatively high plasma density. On the other hand, in the case of titanium oxide deposition, negative ion productions drastically decrease the deposition rate and the shifting velocity of plasma main position for coated TiO2 films.

EMD端点效应问题解决方法的研究

经验模态分解(EMD)是近年来兴起的一种非平稳信号处理方法,但在分解过程中因产生端点效应而造成分解结果严重失真。因此,研究了一种自适应波形匹配延拓法的改进方法,该方法根据信号端部不同特点确定延拓点并进行延拓,从而解决端点效应问题。实验结果表明,改进的自适应波形匹配延拓法能避免信号EMD分解失真。将改进的自适应波形匹配延拓法的EMD结合小波软阈值去噪方法用于处理加噪超声仿真信号,得到的信噪比比小波软阈值法处理后的信噪比高33.78%,说明该方法在非线性、非平稳信号处理方面有一定优势。

关节镜下前交叉韧带重建术中保留残端与不保留残端治疗前交叉韧带损伤患者的效果

目的:比较关节镜下前交叉韧带(anterior cruciate ligament,ACL)重建术中保留残端与不保留残端治疗ACL损伤患者的效果。方法:选取2021年2月—2022年6月中国人民武装警察部队广东省总队医院收治的102例ACL损伤患者。根据随机数表法将其分为对照组与研究组,各51例。两组均给予关节镜下ACL重建术,对照组给予不保留残端,研究组给予保留残端。比较两组术前和术后3个月、6个月膝关节功能、膝关节活动度、本体感觉功能、韧带损伤程度。结果:术前和术后3个月、6个月,两组Lysholm评分比较,差异无统计学意义(P>0.05)。术前和术后3个月、6个月,两组膝关节活动度比较,差异无统计学意义(P>0.05)。术后3个月、6个月,研究组被动活动察觉阈值和被动角度均低于对照组,差异有统计学意义(P<0.05)。术前和术后3个月、6个月,两组国际膝关节文献委员会膝关节评估表(the international knee documentation committee knee uation form,IKDC评分)评分比较,差异无统计学意义(P>0.05)。结论:关节镜下ACL重建术中保留残端与不保留残端都能够对ACL损伤患者进行有效的治疗,但ACL损伤患者保留残端可更为显著地改善本体感觉功能。

基于SVRM极值延拓的EMD端点效应抑制方法

以满足船舶机械设备故障实时在线快速诊断为牵引,针对经验模态分解(empirical mode decomposition,EMD)的端点效应问题,深入研究支持向量回归机(support vector regression machine,SVRM)延拓参数对延拓性能的影响,提出一种EMD极值快速延拓算法。研究端点效应的产生机理及影响,分析典型端点效应处理方法的优点及局限性;阐述SVRM预测基本原理,提出以信号极值尺度设置延拓长度与样本数量的方法;以信号极值点数值和时刻值为样本,提出一种基于SVRM的极值预测延拓方法。仿真结果表明:该方法可显著提高EMD的分解精度及运算效率,可为拓展EMD技术在舰船装备实时监测与智能诊断中的应用提供支撑。

软土地基电动化学加固法的试验研究

针对软土地基电动化学加固方法的相关机理和对土体性质变化的影响规律,提出了金属电极端部效应对电极的工作性能产生不利影响,讨论了土体强度的增长机制,并通过大尺寸模型试验和现场试验,验证所提出概念的正确性,结合现场试验获取了土体含水率、黏聚力、内摩擦角实测数据,探究了电动化学加固对土体物理力学和化学性能的影响。利用电动化学灌浆加固技术对珠海地区的软基进行了加固,结果表明,应用电动化学灌浆加固技术可以有效降低软土的含水率和改变软土的塑性,加固后软土的平均抗剪强度提高了3倍以上,软土的流动性显著降低。该方法能耗低、施工工期短、不需要大型施工设备、现场易于操作;灌入的化学浆液以及发生化学反应后生成的盐和沉淀物对周围环境无污染。