Dependence of discharge, channel area, and flow velocity on river stage and a refutation of Manning’s equation

ABSTRACT Field data reveal how the discharge (Q), channel area (A), and average water velocity (Vavg) of natural streams functionally depend on the effective stage (h) above channel bottom. A graphical technique allows the level that corresponds to a dry channel, denoted “h0,” to be determined, permitting the dependent variables Q, A, and Vavg to all be expressed as simple functions of h, equal to hL– h0, where hL is the local stage that is typically reported relative to an arbitrary, site-specific datum. Once h0 is known, plots of log Q, log A, and log Vavg versus log h can be constructed using available data. These plots define strong, nearly linear trends for which the slopes (1) quantify the power relationships among these variables; (2) show that Vavg varies nearly linearly with h, unlike behaviors assumed in the Chezy and Manning equations; (3) distinguish the individual contributions of A and Vavg to discharge, which is their product; (4) provide quantitative means with which to compare different sites; and (5) offer new insights into the character and dynamics of natural streams.

Влияние предыонизации на микроканальную структуру искрового разряда в воздухе в промежутке острие-плоскость

The initial phase of a spark discharge in the gap between the pin (cathode) and a plane 1.5 mm long in atmospheric pressure air under conditions of preliminary photoionization by an auxiliary discharge was investigated by the method of shadow photography. In the absence of preionization, the discharge from the first nanoseconds after breakdown is an aggregate of a large number of micron-diameter channels. It was found that the electron concentration resulting from preionization, estimated at 108  109 cm-3, increases the degree of uniformity of the discharge channel in the near-cathode region; however, in the near-anode region, the channel remains microstructured. Within the framework of the mechanism of microstructure formation due to the instability of the ionization wave front, a criterion for the formation of a uniform discharge is obtained and an explanation of the results obtained is presented.

Investigation of short-channel design on performance optimization effect of Hall thruster with large height-radius ratio

In this study, the neutral gas distribution and steady-state discharge under different discharge channel lengths were studied via numerical simulations. The results show that the channel with a length of 22 mm has the advantage of comprehensive discharge performance. At this time, the magnetic field intensity at the anode surface is 10% of the peak magnetic field intensity. Further analysis shows that the high-gas-density zone moves outward due to the shortening of the channel length, which optimizes the matching between the gas flow field and the magnetic field, and thus increases the ionization rate. The outward movement of the main ionization zone also reduces the ion loss on the wall surface. Thus, the propellant utilization efficiency can reach a maximum of 96.8%. Moreover, the plasma potential in the main ionization zone will decrease with the shortening of the channel. The excessively short channel will greatly reduce the voltage utilization efficiency. The thrust is reduced to a minimum of 46.1 mN. Meanwhile, because the anode surface is excessively close to the main ionization zone, the discharge reliability is also difficult to guarantee. It was proved that the performance of Hall thrusters can be optimized by shortening the discharge channel appropriately, and the specific design scheme of short channel of HEP-1350PM was defined, which serves as a reference for the optimization design of Hall thruster with large height-radius ratio. The short-channel design also helps to reduce the thruster axial dimension, further consolidating the advantages of lightweight and large thrust-to-weight ratio of the Hall thruster with large height-radius ratio.

High-current arc discharge in air

Computational model of high-current pulsed arc discharge in air is proposed. This is, in general, two-dimensional model with taking into account gas dynamics of the discharge channel, real air thermodynamics in a wide range of pressure and temperature, electrodynamics of the discharge including pinch effect, and radiation. The developed model was applied to simulate the electric discharge in air for the currents of 1 - 250 kA and characteristic rise times in 13 - 25 µs, and results of calculations were compared with experimental ones. It was concluded that most of characteristics of the discharge are predicted well. Namely, arc column radius and shock wave position agree well with experimental data for all current amplitudes and rise times considered. Radial distributions of temperature and electron density also satisfactorily agree with experimental data. It was found that pinch effect should be considered for currents higher than 100 kA.

CFD simulation of DC-discharge in airflow

The main purpose of this work is to simulate a dynamics of DC discharge in a subsonic airflow. The calculations were performed in the FlowVision 3.12.01 software package. The single-fluid model (MHD approach) of equilibrium plasma was used while the initial discharge channel was set manually. Cylindrical coaxially arranged electrodes were located in the central part of the calculation area, in the core of the airflow. A 5A DC discharge at atmospheric pressure was considered, as well as a simple model of a re-breakdown between parts of discharge filament. In this work, three-dimensional distributions of temperature and current density were obtained during an evolution of discharge in a flow. Discharge channel extension by the airflow and partial channel decay after the re-breakdown process were shown.

Synchrotron mechanism of X-ray and gamma-ray emissions in lightning and spark discharges

X-ray and γ-ray emissions observed in lightning and long sparks are usually connected with the bremsstrahlung of high-energy runaway electrons. Here, an alternative physical mechanism for producing X-ray and gamma-ray emissions caused by the polarization current and associated electromagnetic field moving with relativistic velocity along a curved discharge channel has been proposed. The existence of fast electromagnetic surface waves propagating along the lightning discharge channel at a speed close to the speed of light in vacuum is shown. The possibility of the production of microwave, X-ray and gamma-ray emissions by a polarization current pulse moving along a curved path via synchrotron radiation mechanism is pointed out. The existence of long tails in the power spectrum is shown, which explains observations of photon energies in the range of 10–100 MeV in the terrestrial gamma-ray flashes, as well as measured power spectrum of laboratory spark discharge.

Small Hall Effect Thruster with 3D Printed Discharge Channel: Design and Thrust Measurements

This paper presents the design and performance of the UAH-78AM, a low-power small Hall effect thruster. The goal of this work is to assess the feasibility of using low-cost 3D printing to create functioning Hall thrusters, and study how 3D printing can expand the design space. The thruster features a 3D printed discharge channel with embedded propellant distributor. Multiple materials were tested including ABS, ULTEM, and glazed ceramic. Thrust measurements were obtained at the NASA Glenn Research Center. Measured thrust ranged from 17.2–30.4 mN over a discharge power of 280 W to 520 W with an anode ISP range of 870–1450 s. The thruster has a similar performance range to conventional thrusters at the same power levels. However, the polymer ABS and ULTEM materials have low temperature limits which made sustained operation difficult.

Research on the Influence of Typical Soil Parameters on Critical Breakdown Field Strength and Residual Resistivity Based on Discharge Topography

Partial discharge of soil occurs when a lightning current enters the ground, and the strength of partial discharge is closely related to the magnitude of its critical breakdown field strength. Therefore, how to accurately obtain the variation law of the typical soil critical breakdown field strength and residual resistivity is the key to realizing the safe operation of the grounding devices and cables in the ground. This paper first selects a variety of typical soils to study the influence of various factors on the morphology of the discharge channel, and then studies the calculation methods of the soil critical breakdown field strength and residual resistivity under the introduction of different discharge channel morphologies and structures, and further discusses the reason why typical soil media factors have a small impact on the critical breakdown field. The experimental results show that under the same conditions, the critical breakdown field strengths of different soils from small to large are sand soil, loam soil and Yellow cinnamon soil. The largest ratio of residual resistivity to initial resistivity of the three soils is sand soil.

Large-Scale Field Test Study on Failure Mechanism of Non-Cohesive Landslide Dam by Overtopping

In recent years, landslide lake disasters occur frequently in southwest mountainous areas of China. Considering the influence of dam size and discharge channel location, three large-scale field tests were carried out in a natural river to study the failure process and mechanism of non-cohesive soil landslide dam, and the process and mechanism of non-cohesive landslide dam breach were analyzed. The results show that the dam size and discharge channel location have a significant influence on the breach mechanism of the landslide dam. The dam failure process can be divided into three stages: the initiation stage, the development stage and the failure stage. When the discharge channel is located close to the bank, the width of the breach is smaller, and the volume of the residual dam body is larger. The more stable the dam body is, the longer the breach process time is, and the smaller the peak discharge is. This study can provide a scientific reference for the emergency disposal and risk assessment of landslide dam.