Steepness Of Front Research Articles

The influence mechanism of leakage inductance and distributed capacitance on nanosecond pulse transformer-type trigger

The pulse trigger generator exerts a significant impact on the Marx generator’s output pulse (OP). In this paper, a pulse transformer (PT)-type trigger device is intended to give a pulse of front steepness below 30 ns, a half-width of more than 300 ns, and a magnitude of 50 kV to a 4 MV Marx generator. A steepening circuit is modeled on the output side of the PT equivalent circuit to reduce the OP front steepness, establishing the model of a closed-core PT-type trigger generator. The influence of distributed capacitance and leakage inductance (parasitic parameters) of the PT winding on the OP magnitude, triggering delay time, and front steepness are analyzed, and the design scheme of the PT is decided accordingly. Then, the pulse trigger generator model is simulated, and the trigger pulses are obtained in accordance with the design index. The OP waveforms are tested using a newly developed pulse trigger device prototype.

Simulated conformality of atomic layer deposition in lateral channels: the impact of the Knudsen number on the saturation profile characteristics.

Atomic layer deposition (ALD) is exceptionally suitable for coating complex three-dimensional structures with conformal thin films. Studies of ALD conformality in high-aspect-ratio (HAR) features typically assume free molecular flow conditions with Knudsen diffusion. However, the free molecular flow assumption might not be valid for real ALD processes. This work maps the evolution of the saturation profile characteristics in lateral high-aspect-ratio (LHAR) channels through simulations using a diffusion-reaction model for various diffusion regimes with a wide range of Knudsen numbers (106 to 10-6), from free molecular flow (Knudsen diffusion) through the transition regime to continuum flow conditions (molecular diffusion). Simulations are run for ALD reactant partial pressures spanning several orders of magnitude with the exposure time kept constant (by varying the total exposure) and with the total exposure kept constant (by varying the exposure time). In a free molecular flow, for a constant total exposure, the saturation profile characteristics are identical regardless of the LHAR channel height and the partial pressure of the reactant. Under transition regime and continuum conditions, the penetration depth decreases and the steepness of the adsorption front increases with decreasing Knudsen number. The effect of varying individual parameters on the saturation profile characteristics in some cases depends on the diffusion regime. An empirical "extended slope method" is proposed to relate the sticking coefficient to the saturation profile's characteristic slope for any Knudsen number.

The Dynamics of a Barotropic Current Impinging on an Ice Front

Abstract The vertical front of ice shelves represents a topographic barrier for barotropic currents that transport a considerable amount of heat toward the ice shelves. The blocking effect of the ice front on barotropic currents has recently been observed to substantially reduce the heat transport into the cavity beneath the Getz Ice Shelf in West Antarctica. We use an idealized numerical model to study the vorticity dynamics of an externally forced barotropic current at an ice front and the impact of ice shelf thickness, ice front steepness, and ocean stratification on the volume flux entering the cavity. Our simulations show that thicker ice shelves block a larger volume of the barotropic flow, in agreement with geostrophic theory. However, geostrophy breaks locally at the ice front, where relative vorticity and friction become essential for the flow to cross the discontinuity in water column thickness. The flow entering the cavity accelerates and induces high basal melt rates in the frontal region. Tilting the ice front, as undertaken in sigma-coordinate models, reduces this acceleration because the flow is more geostrophic. Viscous processes—typically exaggerated in low-resolution models—break the potential vorticity constraint and bring the flow deeper into the ice shelf cavity. The externally forced barotropic current can only enter the cavity if the stratification is weak, as strong vertical velocities are needed at the ice front to squeeze the water column beneath the ice shelf. If the stratification is strong, vertical velocities are suppressed and the barotropic flow is almost entirely blocked by the ice front. Significance Statement Ice shelves in West Antarctica are thinning, mostly from basal melting through oceanic heat entering the underlying ice shelf cavities. Thinning of ice shelves reduces their ability to buttress the grounded ice resting upstream, leading to sea level rise. To model the ice sheet’s contribution to sea level rise more accurately, the processes governing the oceanic heat flux into the ice shelf cavity must be articulated. This modeling study investigates the dynamics of a depth-independent current approaching the ice shelf; it corroborates previous findings on the blocking of such a current at the ice front. The amount of water that enters the cavity strongly depends on ice shelf thickness and ocean stratification. For a well-mixed ocean, the upper part of the flow can dive underneath the ice shelf and increase basal melting near the ice front. In a stratified ocean, the approaching depth-independent current is almost entirely blocked by the ice front.

Assessment of active tectonics in the Siwalik basin around the Subansiri river, NE India

In this paper we evaluate the morphotectonics of the area around the Subansiri river in north-eastern India. Research focuses on understanding the impacts on areas experiencing active tectonic deformation. It also explains the variety of kinematics observed in the area from the Miocene to the present. The tectonics can explain some structures related to the extensional tectonics predominant in the region and the development of the minor and major morph structures driven by faults with different kinematics. We developed a morphotectonic evolutionary model for the area based on the morphotectonic analysis and geological mapping. Morphotectonic indices used to evaluate the tectonic activeness in this study are Mountain Front sinuosity Index, Valley Floor Width to Valley Height Ratio, Asymmetry Factor, Transverse Topographic Symmetry Factor, Mountain Front Steepness Index, Basin Shape Index and Stream Length Gradient Index. There are numerous lineaments present in the study area which are trending in NW-SE and NE-SW direction.

Experimental study of the effect of wind above irregular waves on the wave-induced load statistics

The design load from waves on offshore structures are often estimated by aid of experimental studies in wave flumes and basins. When going from open sea to laboratorial conditions a number of factors are either added or omitted such as wind above waves. The paddle-generated waves are based on a spectrum taking the indirect effect of wind into account, whereas the direct effect of wind is left out. Previous studies have focused on the direct effect of wind on waves themselves, but no investigations on the load have been made. The question is whether or not airflow separation, vortexes etc. in the wind field alter physical properties such as steepness of waves, the number of breaking waves and hereby the force; especially the in-line force. To investigate the matter, an experimental study of depth-integrated force on a circular cylinder from irregular waves both with and without wind above, was conducted. An objective, when conducting the tests, was to achieve the same significant wave height whether wind was present or not. Exceedance probability curves for wave crest height, depth-integrated force and pressure were obtained. Moreover, a more descriptive assessment of the phenomena was done by studying the average force shape of the hundred largest force events. In addition, there was applied a phase-based harmonic separation method to explore the wind's effect on the harmonic force components of higher order. The front steepness of the waves was clearly increased with the introduction of wind and further increased, when increasing the wind velocity. The introduction of wind consistently increased the number of breaking waves detected with a breaking criterion. The wave-induced load in the tail of the exceedance probability curve was only increased for some of the sea states, when wind was present. This was very dependent on the size of the crest height of the largest breaking waves. The maximum wave-induced pressure in the tail of the exceedance probability curve was on the contrary increased for all sea states, when wind was present, and it kept increasing with increasing wind velocity. For one of the sea states with increased force extrema, the averaged force shape for the hundred largest events of a case with wind revealed a shape with a spiky peak consistent with that generated from breaking waves. This was not present for the case without wind. The separated harmonic contents of the force up to fourth order also showed a tendency towards more energy at harmonic components of higher order for the case with wind.

Modelling statistics of sonic boom parameters in turbulent media using nonlinear parabolic equation

Over the past decade, plans to develop a new generation of supersonic passenger aircrafts have spurred interest in sonic boom propagation in the atmosphere. New designs are focused on reducing its loudness on the ground. Sonic boom waves are affected by propagation in turbulence of the planetary boundary layer occurring in few kilometers above the ground. Therefore, sonic boom wave parameters such as peak pressure and rise time, as well as corresponding noise levels, become random, which requires statistical characterization. Theoretical analysis of the effects of the presence of turbulent layer is frequently based on one-way model equations of different complexity, of which the basic equation is the nonlinear parabolic Khokhlov-Zabolotskaya-Kuznetsov-type (KZK) equation. Here, sonic boom propagation through homogeneous isotropic turbulence is simulated using the KZK equation. Classical N-waves with different amplitudes and several examples of low-boom waveforms are considered as input waveforms at the entrance to turbulent layer. Statistical data of the peak pressure, shock front steepness, and perceived loudness metric are analyzed. It is shown than unless sonic boom amplitude exceeds a certain threshold, perceived loudness variability is mainly determined by waveform spectral components at mid-range frequencies around 100 Hz. [Work supported by RSF-18-72-00196 and ANR-10-LABX-0060/ANR-16-IDEX-0005.]

Revisiting the Power Law Characteristics of the Plastic Shock Front under Shock Loading.

Under uniaxial shock compression, the steepness of the plastic shock front usually exhibits power law characteristics with the Hugoniot pressure, also known as the "Swegle-Grady law." In this Letter, we show that the Swegle-Grady law can be described better by a third power law rather than the classical fourth power law at the strain rate between 10^{5}-10^{7} s^{-1}. A simple dislocation-based continuum model is developed, which reproduced the third power law and revealed very good agreement with recent experiments of multiple types of metals quantitatively. New insights into this unusual macroscopic phenomenon are presented through quantifying the connection between the macroscopic mechanical response and the collective dynamics of dislocation assembles. It is found that the Swegle-Grady law results from the particular stress dependence of the plasticity behaviors, and that the difference between the third power scaling and the classical fourth power scaling results from different shock dissipative actions.

Экспериментальное исследование путей повышения эффективности импульсного дефектографирования для контроля состояния обмоток высоковольтных трансформаторов

The energy efficiency and reliability of electric power systems depends in many respects on the condition of high-voltage transformer equipment. Defective condition of one transformer unit is often the cause of a sudden emergency stoppage of the entire technological chain of an integral production process. To prevent such situations, an efficient technology for monitoring the condition of transformer windings is necessary. Standard methods show poor efficiency in detection of winding defects at their early development stages. An approach to a winding defect diagnosing methodology based on the use of a nanosecond probing pulse with a steep front is proposed. It is shown that by probing the windings with a pulse of 100 ns duration and a front of about 20 ns it is possible to reveal both mechanical and electrical defects. Experiments performed on a power transformer physical model have shown that the proposed method has the necessary sensitivity to minor changes in capacitive elements caused by defects at their initial development stage. It has been established that the nanosecond pulse method sensitivity increases significantly with decreasing the probing pulse duration and increasing its front steepness.

Numerical Simulation of a Nonlinear Parabolic Equation for Analyzing The Perceived Loudness Statistics of Sonic Boom Wave after Propagation Through Atmospheric Turbulent Layer

Soniс boom propagation in the atmospheric turbulent layer, represented by a model of homogeneous isotropic turbulence, is investigated numerically in two-dimensional geometry using a KZK-type nonlinear parabolic equation for an inhomogeneous moving medium with relaxation. The mean value, standard deviation, and cumulative probabilities of the sonic boom amplitude, shock front steepness, and the Perceived Loudness Mark VII metric of subjective loudness of an impulse noise are analyzed at different propagation distances traveled by the sonic boom wave in the turbulent layer and for different initial amplitudes of the wave.

Wave Front Steepness and Influence on Horizontal Deck Impact Loads

In design storm sea states, wave-in-deck forces need to be analysed for fixed and floating offshore platforms. Due to the complex physics of wave impact phenomena, numerical analyses should be complemented by model test data. With a large statistical variability, such experiments usually involve running many 3-h storm realisations. Efforts are being done to establish efficient procedures and still obtain improved statistical accuracy, by means of an initial simplified screening based on parameters derived from the incident wave record only. Here, we investigate the vertical rise velocity of the incident wave elevation at a fixed point in space, which indirectly measures both the local slope and the near-surface orbital velocity. A derived simple deck slamming model is also suggested, to support the check of the physical basis of the approach. Correlation against data from a GBS wave-in-deck model test is used for checking this model. The results show that, although there is a significant random scatter in the measured impact forces, especially in the local slamming forces but also in the global forces, there is a correlation to the rise velocity. Comparisons to the simple load model also show promising results when seen on background of the complex physics and random scatter of the impact problem.

Stepwise Development of a Positive Long Spark in the Air

A spark discharge is modelled in a long air gap of atmospheric pressure at a positive voltage with a long front duration, excluding the quasi-continuous development of the leader. It is shown that, with a front steepness of less than 30 kV/μs, an ionization wave moves in the gap, whose speed is 2 orders of magnitude slower than the speed of streamers in the streamer zone of the leader. The electric field behind the front of such a wave along the entire length of the formed primary channel is kept within 20–25 kV/cm, providing an electron density of 1011 cm–3 for hundreds of microseconds. The state of the gas in the primary channel changes dramatically with the propagation of a disturbing field effect of a nanosecond in duration. The disturbance range to the head of the primary channel initiates the development of a streamer flash from this head with the initial velocity of ~109 cm/s, which leads to a sharp increase in the brightness of the radiation from the channel. The reason for the amplification of radiation is the active production of electronically excited particles. The gas temperature in the channel does not exceed 1000 K. According to characteristics such as the gas temperature, longitudinal electric field, and electron density, the channel in the step phase of the development of a long spark differs fundamentally from the leader’s channel, which is able to exist and develop only in the quasi-continuous phase.

Энергосберегающая методика изучения физической модели высоковольтного инвертора на основе электронно-лучевого клапана

The schemes of inverters applied in static reactive power compensators (SRPC) are as a rule developed with the use of power semiconductor devices (PSD); however, attempts to develop industry-grade prototypes of high-voltage inverters on the basis of serially produced vacuum-tube devices (VTD) are also made. High-voltage electron beam valves (EBV), which feature—owing to beam recovery at the anode — the minimum possible voltage drop across the anode-cathode section in the conductive state among the VTDs and a high steepness of the impulse front and trailing edges in comparison with PSDs, seem to be promising for such applications. An EBV was simulated in the EWB circuit engineering computer program environment to determine the minimum permissible load resistance at which the EBV has the maximum electrical efficiency up to 0.99. To determine whether it is advisable to construct such inverters, it is necessary to conduct not only theoretical, but also experimental investigations on physical models using dedicated test benches. A high-voltage energy-saving bench for testing EBVs operating within the SRPC circuit in an inverter mode has been developed. The bench takes power supply from the 3x380 V, 50 Hz network. The bench comprises a three-phase high-voltage transformer, using which the power supply voltage can be increased to a 40 kV level. This voltage is rectified according to the Larionov bridge scheme, and, owing to an artificial midpoint, the 0 to +20 kV and 0 to -20 kV voltages with the maximum current up to 1 A are obtained. The voltage amplitude can be smoothly varied using a three-phase electromechanical regulator installed in the high-voltage transformer primary winding. A 50 Hz sine-wave voltage is produced in the inverter mode by means of pulse-width modulation (PWM) with a clock frequency smoothly variable in the 1...3 kHz range and is applied to a water equivalent of load. To increase the bench power level during the test and achieve energy saving, a gating logic device (GLD) was introduced, which allows the EBV control system to operate in an intermittent PWM generation mode. The GLD produces pulses using which three cycles of a 50 Hz sine-wave voltage (with the total duration equal to 60 ms) repeating at approximately 1.2 s intervals are generated. The use of the GLD producing packs of control pulses makes it possible to study the EBV operation modes on the bench at a short-term power of up to 200 kW in pulse-periodic mode, which is significantly (by 10.20 times) higher than the average power of the bench constant-voltage network power supply source. The GLD output voltage waveforms and the load voltage and current front and trailing edge waveforms are given.

Влияние параметров барьера и приложенного напряжения на характеристики импульсного поверхностного разряда

The results from an experimental study of impulse surface discharge occurring in an electrode system containing a dielectric plate are presented. On one of its sides, the plate had a corona-producing electrode made of 50 mm thick copper foil grounded through a current shunt for measuring the discharge current. On its other side, the plate had a high-voltage electrode, to which the voltage from a pulse generator was applied. The article presents the results from measurements of the initial voltage and the sizes of the surface discharge area in air when applying single voltage pulses with different pulse front steepness in the range 0,1–3,4 kV/ms and amplitude in the range 7–15 kV. The measurements were carried out for different dielectric barrier materials with the e values from 2 to 35. The dielectric barrier thickness was 0,9–1,8 mm. The study results have shown that the initial surface discharge ignition voltage depends essentially on the voltage pulse parameters, whereas the barrier characteristics have a weaker effect on this voltage. It has been determined that the discharge has different discharge zone length and different structure depending on the dielectric barrier properties and applied voltage parameters. The streamer zone sizes decrease with increasing the barrier material e value at the same voltage pulse steepness and increase with increasing the steepness for each barrier material. The data obtained for a wide range of external conditions can be used in numerical modeling of discharge.

Nonlinear deformation and run-up of single tsunami waves of positive polarity: numerical simulations and analytical predictions

Abstract. The estimate of an individual wave run-up is especially important for tsunami warning and risk assessment, as it allows for evaluating the inundation area. Here, as a model of tsunamis, we use the long single wave of positive polarity. The period of such a wave is rather long, which makes it different from the famous Korteweg–de Vries soliton. This wave nonlinearly deforms during its propagation in the ocean, which results in a steep wave front formation. Situations in which waves approach the coast with a steep front are often observed during large tsunamis, e.g. the 2004 Indian Ocean and 2011 Tohoku tsunamis. Here we study the nonlinear deformation and run-up of long single waves of positive polarity in the conjoined water basin, which consists of the constant depth section and a plane beach. The work is performed numerically and analytically in the framework of the nonlinear shallow-water theory. Analytically, wave propagation along the constant depth section and its run up on a beach are considered independently without taking into account wave interaction with the toe of the bottom slope. The propagation along the bottom of constant depth is described by the Riemann wave, while the wave run-up on a plane beach is calculated using rigorous analytical solutions of the nonlinear shallow-water theory following the Carrier–Greenspan approach. Numerically, we use the finite-volume method with the second-order UNO2 reconstruction in space and the third-order Runge–Kutta scheme with locally adaptive time steps. During wave propagation along the constant depth section, the wave becomes asymmetric with a steep wave front. It is shown that the maximum run-up height depends on the front steepness of the incoming wave approaching the toe of the bottom slope. The corresponding formula for maximum run-up height, which takes into account the wave front steepness, is proposed.

Transient Electromagnetic Pulse Emanation in Digital Systems in the Mode of Pulsed Excitation of the Printed Connector Elements

Specific features of the formation of transient electromagnetic pulse emanation fields induced by the pulsed excitation of printed elements are discussed. The field formation affects the electromagnetic compatibility of digital signal processing devices. It is shown that printed conductors in complex-layout boards with a specific geometrical configuration can work as electromagnetic emitters. It has been established that the video pulse length, clock frequency, and code sequence alternation phase determine the spectral behavior of a digital signal, which may coincide with the eigenfrequencies of printed emitters, in particular, forming a mode of excitation on the self-oscillations when decreasing video pulse length or front steepness. The results of investigations of potentially emitting printed element prototypes are reported.

Влияние крутизны фронта импульса напряжения на электрическую прочность полимеров

AbstractWe have studied the effect of the leading edge steepness of a high-voltage pulse front on the dielectric strength of 3-μm-thick polyethylene terephthalate film. It is found that its breakdown electric field strength increases logarithmically from 550 to 700 MV/m upon an increase in the voltage growth rate (pulse front steepness) from 2 to 70 GV/s. It is shown that the experimental data can be described using the concept of the ionization mechanism of polymer breakdown, which is not associated with the evolution of impact ionization in polymers, and accounting for the decrease in the overvoltage coefficient in a polymer dielectric upon an increase in the pulse front steepness.

Effect of the Voltage Pulse Front Steepness on the Electric Strength of Polymers

We have studied the effect of the leading edge steepness of a high-voltage pulse front on the dielectric strength of 3-μm-thick polyethylene terephthalate film. It is found that its breakdown electric field strength increases logarithmically from 550 to 700 MV/m upon an increase in the voltage growth rate (pulse front steepness) from 2 to 70 GV/s. It is shown that the experimental data can be described using the concept of the ionization mechanism of polymer breakdown, which is not associated with the evolution of impact ionization in polymers, and accounting for the decrease in the overvoltage coefficient in a polymer dielectric upon an increase in the pulse front steepness.

Impact Pressure Distribution on a Monopile Structure Excited by Irregular Breaking Wave

Abstract The problem of impact pressure distribution on a monopole structure excited by irregular breaking waves is investigated. The analysis is performed by applying a numerical model that combines potential flow model with a Navier-Stokes/VOF solution. The temporal pressure distribution is analysed for two breaking wave cases characterized by the significant difference in the steepness of the wave front. The peak impact pressures are observed in the region below the overturning wave jet where the pressure increases rapidly resulting in a peak value of the slamming coefficient equal to Cs=2π. The vertical load distribution provided by the derived model is more realistic than a rectangular shape distribution applied in engineering practice. This is because the vertical load distribution strongly depends on breaking wave shape and it is difficult to uniquely approximate such a load distribution by a rectangle.

Influence of pulse front steepness on vacuum flashover characteristics

Studying flashover characteristics in vacuum environment is extremely significant for designing reliable insulation structures. The waveform of applied voltage excitations greatly affects the flashover process. In this study, the influence of nanosecond pulse front steepness on flashover process in vacuum is investigated. Firstly, flashover experiments with nanosecond pulses are conducted. Nanosecond pulses with different front steepness are generated and used to trigger flashovers on sample surface. The relationship between pulse front steepness and flashover voltage is studied. Meanwhile, a particle-in-cell with Monte Carlo collision (PIC-MCC) two-dimensional self-sustaining discharge model based on secondary electron emission avalanche (SEEA) scheme is established. The distribution of charged particles, electric field and their evolution during flashover process are presented. Furthermore, pulses with various rising steepness are applied to the model. The multiplication and propagation of charged particles in different pulse waveform conditions are studied. In all conditions, two stages during flashover process can be obviously distinguished based on charged particle number evolution which divides the overall flashover delay time into two parts. By analyzing the voltage development in these two time slots, the quasi-linear relationship between pulse front steepness and flashover voltage in nanosecond pulse flashover in vacuum is explained.

Modeling of Return Strokes With Their Initiation Processes Under Consideration

We developed an engineering return-stroke model specifically for studying the effects of return-stroke initiation processes. In the model, two current waves with identical wave shapes propagate upward and downward at two independent speeds from a height-variable return-stroke initiation point. Using that model and several results recently observed on the lightning return-stroke initiation processes, we have studied the electromagnetic fields produced by a return stroke at a horizontal distance from the strike termination point. It is shown that, depending on the front steepness of the current waveform, the presence of the downward return-stroke current wave may result in a visible initial peak in the rising portion of the return-stroke-produced field waveforms. A larger initiation height appears to result in an initial field peak with a larger amplitude, and also longer duration time. Moreover, a larger downward return-stroke speed tends to produce a sharper initial field peak.