Wave Tail Research Articles

Evaluation principle and method of horizontal grounding electrode based on time‐varying impedance

The length of the horizontal grounding electrode is usually extended to decrease the impulse grounding resistance. In this paper, the mechanism for influencing the effective length is revealed by studying the dispersal process of a horizontal electrode and a method for determining the length is proposed. Firstly, the impulse current and the response voltage are measured at different positions. The results are used to analyse the time-varying characteristics of the impedance in the dispersal process, the mechanism and the factors influencing the effective length. Furthermore, the current propagation process is divided into a wave head process and a wave tail process. The variation rule and influencing factors of the transient impedance are determined. The wave head impedance acts as a dynamic process from the injection impedance to the wave tail impedance, and the injection impedance is not affected by the length of the grounding electrode. The wave tail impedance is constant and is equal to the DC steady-state impedance. It is proposed that the effective length is caused by two different dispersal processes and it is obtained when the tail impedance is equal to the impulse grounding resistance. These results are highly significant for optimizing the grounding device.

Global stability of travelling waves for a class of monostable epidemic models

We study the stability of travelling wave solutions for a monostable reaction-diffusion system which describes the spatial spread of a class of bacterial and viral in man-environment diseases. Mathematically we prove the global stability of traveling wave solutions with any admissible wave speed (including the critical wave speed) for the system, and compute numerically the critical wave speed and solutions of the cauchy problem with given initial functions close to the travelling waves at the wave tail for some reaction functions to show the global stability of traveling wave solutions with noncritical wave speed and critical wave speed, respectively.

Fast and Effective Technique in Evaluation of Lightning Impulse Voltage Parameters

This paper presents an approach for the waveform parameter evaluation of lightning impulse voltage in high voltage tests according to the IEC standards. Such waveform parameters are composed of peak voltage (Up), front time (T1), time to half (T2), and the overshoot rate (Be). An artificial neural network with a back-propagation learning algorithm was applied to determine a base curve and its parameters from 14 points along the recorded waveform between 20% of the peak voltage on the wave front part to 40% of the peak voltage on the wave tail part. The 29 waveforms recommended by the standard were used in the training process of the development of the network model, and some experimental cases were also utilized for verification of the proposed method. It is found that the waveform parameters evaluated by the proposed approach are in the tolerances of the standard requirements. Maximum absolute deviations of Up, T1, T2, and Be are 0.06%, 2.00%, 0.12%, and 0.79%, respectively. Due to that no iteration process in the proposed approach is required, the efficiency in calculation process is significantly faster than the standard recommended approach.

Karakterisasi dari Properti Larutan Garam dengan Range Finder Ultrasonik Menggunakan Metode Transformasi Fourier

In this paper we characterize the saline solution using Range Finder Ultrasonic (RFU). RFU is one kind of ultrasonic transducer that requires air as a transmission medium and commonly are used to determine distances. The advantages of this transducer are cheap and common in local market. Since it uses air as medium, the signal which is produced by transducer are easy to shape shift and has a very long noise tail wave. This phenomenon was seen in previous studies, when the transducer position was slightly shifted, the shape of the echo signal became very different. In this paper, we modified the input signal from the technique in the previous paper to improve the echo signal. Some modification of trigger signal from transmitter models were done, then calculate the echo signal to ensure the signal have smallest Signal to Noise Ratio (SNR) and noise tail wave. Furthermore, we did filtering process from echo signal and calculating using Fourier Transform which are performed to obtain accurate echo signal information of 40 KHz frequency. The results of this experiment is an improvement in the average error of calibration curve 0.1224221 (Vrms) and 0.14383881 (Vpeak). While the average error of the results of the normalization of the magnitude Fourier Transform of 40 KHz frequency is equal to 0.096973114.

Accumulative effect of partial discharges at impulse voltage wave tail

This study describes a technique for evaluating partial discharges at fast impulse voltages. Fast transient voltages are increasingly present in power equipment and industrial environments due to the ubiquitous application of power electronics switching devices. Special attention should be paid to the dangers caused by the accumulative effect of repetitive impulse voltages on electrical insulation. This study describes a method of analysing partial discharges occurring during impulse voltage stimuli. A repetitive train of pulses is applied to a dielectric specimen and the accumulated PD pattern is obtained. This study focuses on the reverse discharges which occur during the tail part of the impulse voltage waveform acquired in time-resolved mode. Investigations of the partial discharges in the wave tail can potentially lead to greater degradation of the insulation due to the formation of longer, repetitive sequence occurring along the decaying impulse voltage tail. Experiments were performed which investigated the influence of rise time, fall time and peak voltage on discharge pattern reshaping, intensity and time to inception on the tail. In the future, such an approach might be further developed for diagnostic applications and for extended factory tests.

MODELING AND METHODOLOGY OF EVALUATION OF ENGINEERING SITUATION IN RIVER BREAKDOWN OF SEREDNYODNIPROVSKA HES

The article deals with the process of parameters estimation of the flood zone at the dam break or its destruction, and a scale of possible destruction caused by possible emergencies. Modeling is carried out for the time of approach of the breakthrough wave to a given distance, the height of the breakthrough wave, the time of discharge of the reservoir, the duration of the passage of the wave at a predetermined distance for buildings and structures in the area of shock wave. The example is done for the dam of the Middle Dnieper hydroelectric power station. A technique for modeling a hazardous situation related to the consequences of a breakthrough of the dam at the Middle Dnieper Hydropower Plant has been developed. The prediction and simulation is based on the phenomenological parameters of the Kamyansky reservoir.The simulation of the assessment of the engineering environment for the dam of the Serednyodniprovska hydroelectric power station was carried out using the parameters of flooding of the terrain. Parameters used - the possible maximum depth of flooding, the width of flooding and the rate of water flow at the break of the dam, the time of arrival of the wave front, the crest and tail of the break wave, maximal flow dams, wave heights above water level above domestic flow. As a result, the maximum flooded area was estimated.Based on the use of dam and reservoir characteristics and the use of appropriate formulas for calculating emergency factors and using modeling using ArcGIS, the possible topographic consequences of the breakthrough of the dam in the city Kamianske and the locations of industrial enterprises in its vicinity were obtained. The latter enables rescue services to promptly assess the threat of an emergency in the event of an emergency, to have an idea of the consequences in order to take preemptive measures to prevent the occurrence of an emergency.

Experimental Research on Lightning Disturbance Characteristics of 10-kV Fusion Voltage Transformer Intelligent Component Acquisition Port

In the lightning impulse test, the 10 kV fusion voltage transformer intelligent component acquisition port often suffers from functional failure or breakdown. In this paper, experimental measurement and inversion calculation were used to study the electromagnetic disturbance level of smart component acquisition port. During the inversion calculation, the applicability of the dual exponential function model, Heidler function model, and impulse function model as the primary source for describing the lightning impulse device were compared and analyzed. The results show that the double exponential model was used as the calculation source of the primary side lightning waveform, and the inversion calculation results were in good agreement with the actual measurement. In addition, the effects of the primary side lightning voltage peak, wave head, and wave tail parameters on the maximum amplitude of the disturbance waveform calculated by inversion are discussed and analyzed. Based on the analysis results, a sufficient inversion calculation parameter was proposed to estimate the disturbance level of the intelligent component acquisition port. Finally, the measured results were compared and discussed with the IEC 61439 assessment level, and it was suggested that the assessment level of fusion equipment should be modified.

Insulation characteristics of GIS bus with conductive protrusion attached to the high-voltage electrode under lightning impulses with different wavefront times

The wavefront time T f of lightning impulse plays an important role in the detection of insulation defects in metal enclosed gas insulated switchgear (GIS). Usually, a rod-plane electrode system with different geometric parameters is adopted to simulate local field enhancements in GIS. But, for GIS, the defects may occur on the high-voltage electrode which can not be properly simulated by a rod-plane electrode. To research the influence of waveform parameters on actual defects in GIS, cylinder-plane, coaxial cylinder, and basin-type insulator with a conductive protrusion, were used in this study. A generating system of double-exponential impulses with wavefront times in the range of 0.08 to 15 μs and wave tail times of approximately 50 μs was used to simulate different impulse test waveforms based on a fully enclosed oil-immersed Marx generator. The results show that for the cylinder-plane gap with a protrusion, when the gap distance of the needle tip to the plane is constant, increasing the length of the needle decreases the 50% breakdown voltage. Comparing with the insulation characteristics of rod-plane gap, the U 50 %-T f curves of the cylinder-plane electrode with needle defects thereafter no longer show a U shape as the rod-plane electrode, but increase with an increase in the wavefront time. The difference can be explained by the shielding effect of the cylinder electrode on the defect, which changes the electric field distribution of the gap. The U 50 %-T f curves of GIS bus with different voltage levels and basin-type insulator with surface conductive defect also show the similar increase trend. For V-t characteristics of GIS bus with different voltage levels, we find that the higher the voltage level, the more obvious the trend of the V-t characteristic bathtub curve.

Wind Load Characteristics of Wind Barriers Induced by High-Speed Trains Based on Field Measurements

This paper focuses on field measurements and analyses of train-generated wind loads on wind barriers (3.0 m height and porosity 0%) with respect to different running speeds of the CRH380A EMU vehicle. Multi-resolution analysis was conducted to identify the pressure distribution in different frequency bands. Results showed that the wind pressure on the wind barrier caused by train-induced wind had two significant impacts with opposite directions, which were the “head wave” and “tail wave”. The peak wind pressure on the wind barrier was approximately proportional to the square of the speed of the train, and the peak wind pressure decreased rapidly along the wind barrier height from the bottom of the wind barrier. The maximum wind pressure occurred at the rail surface height. Furthermore, results of the multi-resolution analysis illustrated that the energy of the frequency band from 0 to 2.44 Hz accounted for 94% of the total energy. This indicated that the low-frequency range component of the wind pressure dominated the design of the wind barrier. The frequency of pulse excitation of train-induced wind loads may overlap with the natural frequency of barriers, and may lead to fatigue failure due to cyclic loads generated by the repeated passage of high-speed trains. In addition, the speed of the train had a negligible effect on the energy distribution of the wind pressure in the frequency domain, while the extreme pressure increased slightly with the increase of the speed of the train.

Transition of regular wave fronts to irregular wave fronts in gravity-driven thin films over topography

This article contributes to an understanding of the pathway from regular to chaotic traveling wave fronts over periodically undulated inclines in thin films. In order to investigate the transition from regular to chaotic waves, we used various undulation forms and varied the Reynolds number and the inclination angle in the measurements. Thereby, we revealed the first partially chaotic waves on a gravity-driven thin film channel flow. The wave is subdivided into: (i) the chaotic wave front and (ii) a regular wave tail. The area of the chaotic part can be increased by increasing the inertia of the system. Various phenomena on the flow were revealed: (a) bubble formation, (b) fingering, (c) splashes, and (d) pinch-offs. Our investigation leads to the conclusion that wave breaking over obstacles is a necessary condition for the transition from regular to chaotic wave fronts.

Effects of impulse waveform parameters on the breakdown characteristics of nano-TiO<inf>2</inf> modified transformer oil

Statistical results have shown that the waveforms of impulses invading power transformers differ from those of the standard impulse voltage recommended by the IEC Standard. However, the effect of such differences on the modification effect of nano-modified transformer oil has rarely been studied. The present work therefore experimentally investigated the effects of impulse waveform parameters on the breakdown characteristics of nano-TiO 2 modified transformer oil (NMTO). We determined the breakdown characteristics of NMTO with different nano-particle concentrations, and compared the breakdown characteristics under both standard impulse voltage and non-standard impulse voltage. Specifically, the influence of the wave front time and wave tail time of the applied voltage on the breakdown characteristics of NMTO were experimentally identified. Finally, mechanisms of observed phenomena were analyzed. Test results indicate that both the waveform parameters and polarity have important effects on the modification effect of NMTO. Such effects are attributed to the migration of positive particles and charged nano-particles.

Complexity Analysis on the Aerodynamic Performance of the Mega High-Speed Train Caused by the Wind Barrier on the Embankment

With the world development of high-speed railways and increasing speeds, aerodynamic forces and moments acting on trains have been increased further, making trains stay at a “floated” state. Under a strong crosswind, the aerodynamic performance of a train on the embankment is greatly deteriorated; lift force and horizontal force borne by trains will be increased quickly; trains may suffer derailing or overturning more easily compared with the flat ground; train derailing will take place when the case is serious. All of these phenomena have brought risks to people’s life and properties. Hence, the paper establishes an aerodynamic model about a high-speed train passing an air barrier, computes aerodynamic forces and moments, and analyzes pulsating pressures on the train surface as well as those of unsteady flow fields around the train. Computational results indicate that when the train passed the embankment air barrier, the head wave of air pressure full wave is more than the tail wave; the absolute value of negative wave is more than that of the positive wave, which is more obvious in the head train. When the train is passing the air barrier, pressure pulsation values at head train points are more than those at other points, while pressure changes most violently at the train bottom, and pressure values close to the air barrier are more than those points far from the air barrier. Pressure values at the cross section 1 were larger than those of other points. Pressure values at measurement points of the tail train ranked the second place, with the maximum negative pressure of 1253 Pa. Pressure change amplitudes and maximum negative pressure on the train surface are increased quickly, while pressure peak values on the high-speed train surface are in direct ratio to the running speed. With the increased speed of the high-speed train, when it is running in the embankment air barrier, the aerodynamic force and moment borne by each train body are increased sharply, while the head train suffers the most obvious influences of aerodynamic effects.

Analysis of Negative Differential Resistance and Energy Consumption at Transient Surge Response against Winter Lightning for MOVs, ABDs, and TSSs

Abstract surge protective components (SPCs) such as metal oxide varistors (MOVs), avalanche breakdown diodes (ABDs), and thyristor surge suppressors (TSSs) have been widely used in low-voltage power distribution systems, in main AC power lines inside of appliances, electrical, and electronic systems, or signaling and telecommunication lines in ICT equipment to protect them against lightning surges. The maximum transient clamping voltage and surge-handling capability are important parameters to determine the ability of the SPCs. They are determined by the negative differential resistance, which depends on the steepness and wave-tail of the applied lightning surge waveform, especially characterized by winter lightning. The transient surge responses of SPCs were analyzed, and the mechanisms of negative differential resistance were clarified. Negative differential resistance was caused by the lead wire inductance in MOVs, the positive temperature coefficient of breakdown voltage in ABDs, the dependence on temperature of the Auger recombination, and the carrier mobility in TSSs. Clamping voltage and surge-handling capability designs considering inductance in the lead wire and the dependence on temperature during self-heating are important to apply to SPCs so that they can withstand high energy winter lightning with a long wave tail.

Interaction of phase singularities on the spiral wave tail: reconsideration of capturing the excitable gap.

The action mechanism of stimulation toward spiral waves (SWs) owing to the complex excitation patterns that occur just after point stimulation has not yet been experimentally clarified. This study sought to test our hypothesis that the effect of capturing excitable gap of SWs by stimulation can also be explained as the interaction of original phase singularity (PS) and PSs induced by the stimulation on the wave tail (WT) of the original SW. Phase variance analysis was used to quantitatively analyze the postshock PS trajectories. In a two-dimensional subepicardial layer of Langendorff-perfused rabbit hearts, optical mapping was used to record the excitation pattern during stimulation. After a SW was induced by S1-S2 shock, single biphasic point stimulation S3 was applied. In 70 of the S1-S2-S3 stimulation episodes applied on 6 hearts, the original PS was clearly observed just before the S3 point stimulation in 37 episodes. Pairwise PSs were newly induced by the S3 in 20 episodes. The original PS collided with the newly induced PSs in 16 episodes; otherwise, they did not interact with the original PS. SW shift occurred most efficiently when the S3 shock was applied at the relative refractory period, and PS shifted in the direction of the WT. In conclusion, quantitative tracking of PS clarified that stimulation in desirable conditions induces pairwise PSs on WT and that the collision of PSs causes SW shift along the WT. The results of this study indicate the importance of the interaction of shock-induced excitation with the WT for effective stimulation. NEW & NOTEWORTHY The quantitative analysis of spiral wave dynamics during stimulation clarified the action mechanism of capturing the excitable gap, i.e., the induction of pairwise phase singularities on the wave tail and spiral wave shift along the wave tail as a result of these interactions. The importance of the wave tail for effective stimulation was revealed.

Experimental Research about Shock Wave in a 1+1/2 Counter-Rotating Turbine

To investigate the internal distribution regularities of shock wave structure in 1+1/2 counter-rotating turbine, numerical simulation and experimental research about the shock wave structure were conducted by using the schlieren apparatus under different working conditions.From the point of the unsteady results, the unsteady effect has few influence on the flow field of high pressure guide vane, but the wake of the high pressure guide leaves periodically sweeps through the front edge of the high pressure blade and there presents strong unsteady effect on flow field of high pressure rotor. Because of periodic influence of external wake and shock wave, the unsteadiness of flow in low pressure rotor is still strong but not that drastic compared to the high pressure rotor. 50% height section of the blade of the three types of blades are extracted respectively to make plane cascades which are conducted blowing experiments in supersonic wind tunnel. The final photograph were analyzed by comparing with the CFD results. Results show that with the increase of expansion ratio, the wave structures in blade channel move toward the exit and the caudal interference between the outer tail wave and is strengthened gradually.

Maternal behaviour in response to predation threats in a vulnerable lizard from Patagonia, Argentina

AbstractClimatic and ecological conditions can determine the existence and degree of parental care. In species that live in cold‐temperate environments and exhibit high reproductive effort it is expected that parental care would have greater selective value. In this study, we aimed to detect maternal behavioural responses to predation threats in the lizard Phymaturus spectabilis from cold‐climate environments of Patagonia, Argentina. Seventeen females with their offspring each were exposed to four treatments in the laboratory: first a treatment with no stimulus, and then in a random order a carnivorous sympatric lizard, a conspecific male and a simulated flight of a museum mount of a raptor. We analysed the occurrence of 11 specific behaviours. Two clearly different parental responses occurred. In the presence of the raptor, mothers stayed near the offspring and remained motionless longer than in the other treatments. Their freezing response is consistent with their cryptic coloration and this species may rely on this strategy to avoid raptor predation. In contrast, in the presence of the predator lizard, mothers presented higher frequencies of flights, tail waves and head bobs. Head bobs are commonly interpreted as dissuasive signals to the predator to discourage attack. The behaviours observed in P. spectabilis together with similar behaviours observed in congeneric species would suggest the existence of a common pattern of parental care related to the high reproductive investment in Phymaturus.

Heart rate dependency of JT interval sections

BackgroundLittle experience exists with the heart rate correction of J-Tpeak and Tpeak-Tend intervals. MethodsIn a population of 176 female and 176 male healthy subjects aged 32.3±9.8 and 33.1±8.4years, respectively, curve-linear and linear relationship to heart rate was investigated for different sections of the JT interval defined by the proportions of the area under the vector magnitude of the reconstructed 3D vectorcardiographic loop. ResultsThe duration of the JT sub-section between approximately just before the T peak and almost the T end was found heart rate independent. Most of the JT heart rate dependency relates to the beginning of the interval. The duration of the terminal T wave tail is only weakly heart rate dependent. ConclusionsThe Tpeak-Tend is only minimally heart rate dependent and in studies not showing substantial heart rate changes does not need to be heart rate corrected. For any correction formula that has linear additive properties, heart rate correction of JT and JTpeak intervals is practically the same as of the QT interval. However, this does not apply to the formulas in the form of Int/RRa since they do not have linear additive properties.

A Proposal of Front Hairstyles in Wedding Updos

This study has investigated front hairstyles in wedding updos and found the following: First, front hairstyles were analyzed in terms of parting, technique and angle. In parting, a bang parting gives the face a small, cute appearance while ‘all-back’ creates a modern and elegant image. A side parting is able to create diverse styles depending on hair length, while a center part makes the face look small. Lastly, a natural parting is helpful in creating a natural and refined look. According to a study on front hairstyles by technique, technique was frequently used in side and center parting. In side hairstyles depending on angle, the facial image can be adjusted or improved by creating an illusion of the shape of face or eyes. Second, according to analysis on basic front hairstyles, it is possible to create diverse images such as an elegant and modern image and a young image with different front hairstyles. The applied front hairstyles by technique are divided into all-back & bang, side and center. Applied design has been created by making the top and golden part voluminous with diverse techniques (tail, C-curl & S-curl, volume). The front hairstyles were created through a model, using diverse techniques (tail, C & S-curl wave, volume) in all-back & bang and side. In terms of the limitations of this study, the shape of the face in addition to parting, technique and angle has influence on front hairstyles. Therefore, there should be further objective, scientific study on changes in front hairstyles by face shape.

토중방전에 따른 접지봉의 과도적인 전기적 특성의 분석

This paper presents experimental results of the effect of impulse current spreading from a ground rod installed in sand. Transient characteristics of ground rod associated with electrical discharges in soil were studied and dynamic voltage-current, resistance-time and conventional ground resistance characteristic curves were analyzed. As a consequence, a significant decrease in ground resistance was observed during the impulse current spreading in soil. The phenomenon is caused by the electrical discharges around the tip of ground rod. Time-lags to soil ionization are lengthened with increasing the current magnitude and the electrical breakdown appears at the wave tail of impulse voltage. The conventional ground resistance is exponentially decreased with impulse current. When electrical breakdown occurs in soil, on the voltage-current curves the overheating instability development appears the negative differential resistance (dU/dt〈0).

습한 토양의 임펄스방전특성

This paper presents the experimental results related to soil ionization and electrical breakdown in a concentric hemispherical electrode system under lightning impulse voltages. Dynamic voltage-current and impedance-time characteristics of soil ionization were measured and analyzed. Also the electrical breakdowns of the soil gap were investigated. The time-lag to the peak current corresponds to the soil ionization propagation. The time of ionization propagation in wet sand is found to decrease with increasing the impulse currents. A drastic decrease in ground resistance was observed during the impulse current spreading in sand. The electrical breakdown appears at the wave tail of impulse voltage and results in a wide scatter in V-t curves. The voltage-current curves have a fan-like shape attributed to ionization processes which result in increasing current and decreasing voltage.