Instantaneous Energy Density Research Articles

Analysis and Visualization of the Instantaneous Spatial Energy Density and Poynting Vector of the Wireless Power Transfer System

This study analyzes the instantaneous spatial energy density and Poynting vector in the WPT system and presents time-varying distributions and animations of this energy density and Poynting vector. First, the energy density is decoupled by two self-energy densities of each coil and the mutual energy density of the two coils. Result reveals how the energy is stored in the WPT system. Second, the Poynting vector is analyzed, and it is found that the power is transferred only in the last half period of the Poynting vector, not at every moment of the whole period. This instantaneous Poynting vector also possesses a characteristic that shows no power flow on the condition that the current phase difference equals zero. This finding is different from the energy density and indicates that the instantaneous Poynting vector can perfectly interpret how power is transferred in the WPT system. Finally, a simulation and an experiment were conducted to verify the correctness of the analysis. This study contributes to a deeper and better understanding of the intrinsic characteristics of energy storage and power flow in the WPT system, and can be referred to for WPT system design and optimization when one considers the EMC or human electromagnetic field exposure problem.

Hilbert–Huang Transform Based Transient Analysis in Voltage Source Converter Interfaced Direct Current System

Due to the rapid discharging of the dc-link capacitors, the short-circuit fault normally results in a fast-growing transient current in the voltage source converter (VSC) based dc power system. Therefore, a fast and sensitive fault detection method is required. In this article, the feasibility of Hilbert-Huang transform (HHT) for fault detection in VSC-based high-voltage direct current systems is analyzed. The instantaneous energy density level is used as the fault detection criterion, which emphasizes the fault characteristics in a predefined frequency range and suppresses the effect of steady-state ripple components. The theory of the proposed HHT-based fault detection method is presented in detail. Its effectiveness is tested on an OPAL-RT based multiterminal dc system and a point-to-point experimental dc system. A response delay within 2 ms after the fault inception is achieved. The comparison with other popular frequency-domain based fault detection methods including the wavelet transform, the short-time Fourier transform, the S transform, and the existing HHT-based analysis, using amplitude frequency coefficient as detection criterion, underlines the performance of the proposed method.

Microstructure Change in Welded TiNi Alloys

Due to the obvious change of the weld structure and the original base metal structure after laser processing, under the action of instantaneous high energy density laser beam, the weld structure is coarse and the strength, plasticity and toughness are reduced. Compared with the base metal, the microstructure of the alloy after laser welding was studied by experiment.

Ultrasonic rock microcracking characterization and classification using Hilbert–Huang transform

This study aims to set up a non-destructive method to control the quality of aggregates using ultrasonic wave acquisition and processing. Two applications are presented proving the applicability of the proposed methodology. The first is the characterization and classification of four limestone rocks from cement quarries in the northern part of Tunisia selected from different geological ages (Lower Jurassic, Upper Cretaceous, and Lower Eocene). The second application deals with assessing rock crushing-induced microcracking evolution in quarried rock from the first initial source rock mass to the final aggregate. Five stages were considered: before the blast (bench front), after the blast round (muck pile), after the primary crusher, after the secondary crusher, and after the tertiary crusher. A physico-chemical and ultrasonic characterization was performed on aggregates and core samples in order to identify their characteristics namely the crack porosity and P-wave velocity. A cluster statistical analysis was then adopted to classify the investigated samples into several groups where crack porosity is the most relevant factor in classifying their quality. In addition to measuring ultrasonic parameters such as the spatial attenuation and P-wave velocity, the ultrasonic study looks at the spectrum of the received signal (non-stationary and nonlinear signal) by measuring the instantaneous energy density with the Hilbert–Huang transform. Beyond the fact that the high negative correlation between the P-wave velocity and the instantaneous energy was identified, the methodology developed allowed to prove that the latter is a relevant factor for the classification of limestone rocks.

Time–frequency characteristic analysis method for track geometry irregularities based on multivariate empirical mode decomposition and Hilbert spectral analysis

The description and evaluation of track geometry irregularities are commonly performed in the distance domain or the frequency domain, and therefore one cannot simultaneously obtain precise measurements of actual frequencies and the distance locations where they appear. This paper proposes the time–frequency energy density (TFED) method to analyse the characteristics of track irregularities in the joint spatial distance–frequency plane. The proposed method describes the energy density distribution of track irregularities in the spatial distance–frequency domain based on the adaptive decomposition characteristics of the multivariate empirical mode decomposition and the time–frequency aggregation on the signal energy of the Hilbert spectrum. The mathematical relationships between the TFED and the standard deviation, as well as the power spectral density, are deduced and validated in the field data of track irregularities. The TFED method was applied to the spatial distance–frequency characteristic distribution of track irregularities and the distribution of instantaneous energy density in the sensitive wavelengths. The track geometry quality is evaluated based on the TFED, using track inspection data of actual high-speed railways.

A research on pulse power source with high instantaneous energy density for coupled mechanical ultrasonic-electrical pulse treatment

The high strength and high hard metal materials such as nickel-based superalloy have been widely used because of their excellent properties. If the gradient nanostructures are prepared on their surfaces, their properties will be further improved and their application will be expanded. In this paper, a coupled mechanical ultrasonic-electric pulse (CMUEP) treatment method is presented and its special pulse power source with high instantaneous energy density is developed. The power supply includes main circuit, gate turn-off thyristor (GTO) control circuit, switch control circuit, display circuit, etc. The CMUEP treatment of nickel-based superalloy is carried out by using this power source. The results show that grains with the average diameter of 25.8nm are prepared on Inconel 718 surface, which can further improve the properties of the high strength and high hard metal materials and broaden their application.

Fault Diagnosis Feature Extraction of Marine Rolling Bearing Based on MEMD and Pe

Cui, J.-C. and Ma, L.-J., 2019. Fault diagnosis feature extraction of marine rolling bearing based on MEMD and pe. In: Gong, D.; Zhu, H., and Liu, R. (eds.), Selected Topics in Coastal Research: Engineering, Industry, Economy, and Sustainable Development. Journal of Coastal Research, Special Issue No. 94, pp. 342–346. Coconut Creek (Florida), ISSN 0749-0208.Aiming at the modal aliasing problem of EMD method, an improved MEMD algorithm is proposed, which can greatly improve the signal-to-noise ratio of reconstructed signal and improve the modal aliasing problem. Through simulation signal analysis, the performance of MEMD method with added and subtracted noise is found. Compared with the meme and noise-added MEMD and pe methods, the optimal range of the added noise and the variance of the signal to be decomposed and the optimal number of concentrated averages are found. The signal-to-noise ratio of the reconstructed signal is continuously increased until the maximum value is applied to the gear and bearing. The analysis of the measured vibration signal of the fault shows the effectiveness of the method. The frequency of the fault feature can be clearly found from the instantaneous energy density spectrum.

Gearbox Fault Diagnosis Based on Hierarchical Instantaneous Energy Density Dispersion Entropy and Dynamic Time Warping.

The accurate fault diagnosis of gearboxes is of great significance for ensuring safe and efficient operation of rotating machinery. This paper develops a novel fault diagnosis method based on hierarchical instantaneous energy density dispersion entropy (HIEDDE) and dynamic time warping (DTW). Specifically, the instantaneous energy density (IED) analysis based on singular spectrum decomposition (SSD) and Hilbert transform (HT) is first applied to the vibration signal of gearbox to acquire the IED signal, which is designed to reinforce the fault feature of the signal. Then, the hierarchical dispersion entropy (HDE) algorithm developed in this paper is used to quantify the complexity of the IED signal to obtain the HIEDDE as fault features. Finally, the DTW algorithm is employed to recognize the fault types automatically. The validity of the two parts that make up the HIEDDE algorithm, i.e., the IED analysis for fault features enhancement and the HDE algorithm for quantifying the information of signals, is numerically verified. The proposed method recognizes the fault patterns of the experimental data of gearbox accurately and exhibits advantages over the existing methods such as multi-scale dispersion entropy (MDE) and refined composite MDE (RCMDE).

Application of SN-EMD in Mode Feature Extraction of Ship Radiated Noise

Due to the randomness of added noise, noise-assisted versions based on EMD (empirical mode decomposition) usually cause new “mode mixing” problem. In addition, these algorithms also have problems such as high time-consuming and large recovering error. For the reasons, a new method SN-EMD (Selective Noise-assisted EMD) is put forward in this paper. It determines whether to add noise as assistance by judging whether there is high frequency intermittent component contained in the signal or not. The new method was proved to have the optimal performance by comparing the performance parameters for evaluating the decomposition. In this paper, SN-EMD was used to decompose ship radiated noise. On account of the differences in the original information contained in each mode of radiated noise signals from different ship, we selected the first three modes for processing. Average instantaneous frequency, center frequency, energy density, and energy distribution ratio were extracted as mode feature of ship targets for classification and recognition. Spatial distribution of the feature quantities in three-dimensional space verified similarity of the same target and separability of different targets.

Relativistic longitudinal self-compression of ultrashort time-domain hollow Gaussian pulses in plasma

We report a study on dynamical evolution of the ultrashort time-domain dark hollow Gaussian (TDHG) pulses beyond the slowly varying envelope approximation in homogenous plasma. Using the complex-source-point model, an analytical formula is proposed for describing TDHG pulses based on the oscillating electric dipoles, which is the exact solution of the Maxwell’s equations. The numerical simulations show the relativistic longitudinal self-compression (RSC) due to the relativistic mass variation of moving electrons. The influences of plasma oscillation frequency and collision effect on dynamics of the TDHG pulses in plasma have been considered. Furthermore, we analyze the evolution of instantaneous energy density of the TDHG pulses on axis as well as the off axis condition.

Wearable Sensor-Based Human Activity Recognition Method with Multi-Features Extracted from Hilbert-Huang Transform.

Wearable sensors-based human activity recognition introduces many useful applications and services in health care, rehabilitation training, elderly monitoring and many other areas of human interaction. Existing works in this field mainly focus on recognizing activities by using traditional features extracted from Fourier transform (FT) or wavelet transform (WT). However, these signal processing approaches are suitable for a linear signal but not for a nonlinear signal. In this paper, we investigate the characteristics of the Hilbert-Huang transform (HHT) for dealing with activity data with properties such as nonlinearity and non-stationarity. A multi-features extraction method based on HHT is then proposed to improve the effect of activity recognition. The extracted multi-features include instantaneous amplitude (IA) and instantaneous frequency (IF) by means of empirical mode decomposition (EMD), as well as instantaneous energy density (IE) and marginal spectrum (MS) derived from Hilbert spectral analysis. Experimental studies are performed to verify the proposed approach by using the PAMAP2 dataset from the University of California, Irvine for wearable sensors-based activity recognition. Moreover, the effect of combining multi-features vs. a single-feature are investigated and discussed in the scenario of a dependent subject. The experimental results show that multi-features combination can further improve the performance measures. Finally, we test the effect of multi-features combination in the scenario of an independent subject. Our experimental results show that we achieve four performance indexes: recall, precision, F-measure, and accuracy to 0.9337, 0.9417, 0.9353, and 0.9377 respectively, which are all better than the achievements of related works.

A novel sine wave modulation method of pulse current during double wire MIG welding

As a highly efficient welding method that guarantees good weld quality, double wire pulse welding has broken the neck bottle of single wire welding in terms of weld speed and tackled such problems as undercut and hump during single wire high-speed welding. During double wire welding, double current waveform modulation is a key that affects weld quality and efficiency. Based on single wire sine wave modulation, this paper proposes a new double wire sine wave modulation method. Front and back wire pulse currents with the same peak value and basic current variation amplitude were obtained by performing sine wave modulation on ordinary double current pulse waveform. An in-depth analysis was made in terms of the energy distribution coefficient m, amplitude coefficient k, and the negative half-cycle sine wave pulse number Nn to discuss how double wire sine wave modulation affects weld seam imaging quality. Experimental results show that with the application of sine wave modulation, double wire pulse welding can effectively enhance instantaneous energy density and broaden the energy variation range between pulse current base value and peak value. Also, enhancing weld speed appropriately helps to improve weld quality and efficiency to a great extent.

Stress field analysis of the single pulse discharge machining insulating alumina ceramics with high instantaneous energy density

Insulating alumina ceramics have been widely used recent years due to their good properties. However, it shows low efficiency, high cost, and poor surface integrity when machining them with the traditional machining methods. A new method which employs the high instantaneous energy density for electric discharge machining of insulating alumina ceramics based on the assisting electrode is presented. The process uses the high voltage, large capacitor and high discharge energy, the high energy stored in the capacitor can be discharged to the tool electrode, assisting electrode, ceramic workpiece, and discharge gap in a very short time, so the process is able to effectively machine insulating alumina ceramics. Thermal-stress coupled analysis of the single pulse discharge is performed. The effects of dielectric, peak voltage, and capacitance on the stress field and the stress removed zone on the insulating alumina ceramics have been investigated.

Bearing damage classification using instantaneous energy density

A methodology is proposed for classification of type of defect in a bearing using vibration data. Hilbert-Huang Transform (HHT) is used to obtain Instantaneous energy density (IE) values corresponding to interaction of rolling elements and the defect. IE values are treated as a time series and autocorrelation coefficients (ACs) with varying lags are calculated. Based on the ACs, a Defect Occurrence Index (DOI) is proposed to rank the possibility of a type of bearing damage. Based on the DOI, an adaptive filtering process is used to filter the maximum IE corresponding to the peaks generated during the defect interaction. The main feature of the present approach involves capturing the phenomenon of amplitude modulation (using the approach of autocorrelation) for an inner race defect and uses its absence in the case of outer race defect to distinguish between the inner and outer race defects. Statistical techniques (Chi-square test and Coefficient of variation (CV)) on the filtered IE are used for damage type identification. A new parameter, Defect Severity Value (DSV), is proposed for assessment of the severity of the bearing defect. The proposed methodology is validated on simulated outer/inner race defect, and on two different vibration datasets obtained from seeded defect experiments. The proposed methodology helps uniquely identify the bearing damage.

An Adaptive Ultrasonic Backscattered Signal Processing Technique for Accurate Object Localization Based on the Instantaneous Energy Density Level

An Adaptive Ultrasonic Backscattered Signal Processing Technique for Accurate Object Localization Based on the Instantaneous Energy Density Level

Transient Signal Detection Method Based on Partial Instantaneous Energy Density Level

为实现低信噪比条件下的水声瞬态信号检测，该文提出子波检测和局部瞬时能量密度级双重降噪方法。该双重降噪方法通过自适应选取含有用信号的某阶固有模态函数(IMF)，计算Hilbert能量谱并进行局部积分，滤除子波检测残留下来的带外噪声。此外，结合宽度-包络联合检测机制，构造了水声瞬态信号局部瞬时能量密度检测器。湖试数据处理结果表明，局部瞬时能量密度检测器可有效降噪并在低信噪比条件下提取瞬态信号，较传统能量检测器具有更好的检测性能。

Homogeneous Boiling Explosion Condition: From an Energy Point of View

When a liquid undergoes boiling by homogeneous nucleation during non-equilibrium heating is very important as the characteristics of the system before and after the occurrence of homogeneous boiling explosion is significantly different. In the present study, we studied homogeneous boiling explosion condition from an energy point of view: how much energy is required to boil the liquid by homogeneous nucleation from a given initial temperature. As a representative one, water heating at atmospheric pressure has been considered under three different heating conditions namely; i) linear heating at the boundary ii) high heat flux pulse heating and iii) liquid contact with high temperature surface. The analytical formulations for cumulative energy distribution in the liquid under various liquid heating conditions have been derived and the cumulative energy density within the liquid are calculated. It has been found that the instantaneous cumulative energy density very near to the liquid boundary is several times higher than that corresponding to the thermal penetration depth for all liquid heating cases. The present study shows that, the cumulative energy density at the boiling explosion over a characteristic liquid cluster being equal to the size of a critical embryo is independent of the heating parameter and for a given initial condition, it has been found to be almost constant for all liquid heating conditions. However, the cumulative energy density at the boiling explosion decreases as the liquid initial temperature increases for all liquid heating cases. The obtained results are compared with other numerical results reported in the literature for water subjected to uniform volumetric heating at atmospheric pressure.

Heavy quark energy loss far from equilibrium in a strongly coupled collision

Abstract We compute and study the drag force acting on a heavy quark propagating through the matter produced in the collision of two sheets of energy in a strongly coupled gauge theory that can be analyzed holographically. Although this matter is initially far from equilibrium, we find that the equilibrium expression for heavy quark energy loss in a homogeneous strongly coupled plasma with the same instantaneous energy density or pressure as that at the location of the quark describes many qualitative features of our results. One interesting exception is that there is a time delay after the initial collision before the heavy quark energy loss becomes significant. At later times, once a liquid plasma described by viscous hydrodynamics has formed, expressions based upon assuming instantaneous homogeneity and equilibrium provide a semi-quantitative description of our results — as long as the rapidity of the heavy quark is not too large. For a heavy quark with large rapidity, the gradients in the velocity of the hydrodynamic fluid result in qualitative consequences for the ‘drag’ force acting on the quark. In certain circumstances, the force required to drag the quark through the plasma can point opposite to the velocity of the quark, meaning that the force that the plasma exerts on a quark moving through it acts in the same direction as its velocity. And, generically, the force includes a component perpendicular to the direction of motion of the quark. Our results support a straightforward approach to modeling the drag on, and energy loss of, heavy quarks with modest rapidity in heavy ion collisions, both before and after the quark-gluon plasma hydrodynamizes, and provide cautionary lessons at higher rapidity.

Modal Power Flow Analysis of a Damaged Orthotropic Plate

The effect of the change of structural integrity to the change of the reactive power flow of a vibrating structure at resonance is explored both analytically and numerically. When an undamped structure undergoes free vibration at one of its natural frequencies, the reactive component is of modal pattern and it can be used as a new modal signature. The reactive power flow in this case can thus be termed as modal power flow. The instantaneous energy density associated with the vibration mode consists of a static component and a dynamic component, related to the mean total and Lagrangian energy densities, respectively. The modal power flow is relevant to the latter but independent of the former. The inverse problem of detecting structural damage due to the identification of variation of modal power flow pattern is investigated. Modal power flow of an orthotropic composite plate with a region of reduced stiffness in the plate is analyzed. Numerical tests show that the proposed method is effective for detection of the damage and the modal power flow is more sensitive to the change of plate stiffness than the strain mode shape in the test cases.

Instantaneous electric energy and electric power dissipation in dispersive media

We derive the instantaneous densities of electric energy and electric power dissipation in lossless and lossy dispersive media for a time-harmonic electric field. The instantaneous quantities are decomposed into DC and AC components, some of which are shown to be independent of the dispersion of dielectric constants. The AC component of the instantaneous energy density can be used to visualize propagation of electromagnetic waves through complex 3D structures.