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Response of the ultra high performance concrete under dynamic compressive loading
Get PDFUltra high performance concrete is a modern cementitious material which exhibits excellent mechanical properties such as damage tolerance, fracture toughness and durability. These features make this materials suitable for wide range of applications where is the material subjected to different modes of loading and different loading rates.This paper deals with measurement of the Ultra high performance concrete reinforced with steel fibres in quasi-static compression mode of deformation and two elevated strain rates using split Hopkinson pressure bar. The results of the measurement show high increase of the mechanical properties with elevated strain rate
Heat Transfer in the Solid Cathode of a Hollow Cathode Plasma Torch
Get PDFAfter recalling the working principle of hollow cathode plasma torches, we evaluate the heat flux profile on the cathodic arc root. This evaluation takes into account the physics of the cathode sheath. Particular attention is devoted to electron emission from the cold copper cathode. This heat flux profile is then used as a moving boundary condition to obtain the temperature field in the solid cathode with a heat conduction study, with the aim of discussing the problem of its erosion
Two-dimensional Axisymmetric Modeling of the Magnetic Field for High-voltage Gas Circuit Breakers
Get PDFHigh fidelity numerical analyses of high-voltage gas circuit breakers have been conducted at Hitachi Energy Research with an in-house CFD-based arc simulation tool. The tool extends the capability of a commercial flow solver (ANSYS Fluent) to represent physical phenomena at play in a high voltage circuit breaker during a breaking operation, such as magnetostatics, polymeric and metal evaporation, and arc-network interaction. This work describes the implementation of the Biot-Savart law for computing the magnetic field generated by an electric arc under the magnetostatic approximation and in two--dimensional axisymmetric conditions. The implementation is compared to the reference one based on the magnetic vector potential formulation of the Amp`ere’s law in the Coulomb gauge. The limitations of the two formulations are discussed and their numerical accuracy compared
Research on Discharge Characteristics in Ultra-high Pressure Gases (Supercritical Fluids): A Brief Review
Get PDFThis paper provides a review of the research on discharge characteristics in ultra high pressure gases (supercritical fluids) and discusses different applications in various fields. Followed by a summary on the investigations performed on the application of supercritical fluids for power switching purposes. A brief overview of the open research questions related to characterization of ultra high pressure switching arcs concludes the paper
Molecular Dynamic Simulation of the Effect of Initial Surface Temperature on Arc Erosion Due to Ion Bombardment
Get PDFThis study focuses on the effects of initial surface temperature on arc erosion caused by ion bombardment. The simulation results show that higher surface temperature leads to a greater number of lost Cu atoms and an increased size of the erosion crater. This is due to the ability of the incident ions to have a greater sputtering yield at higher temperatures. Moreover, the Cu atoms tend to agglomerate and form clusters after ion bombardment while leaving the surface
Influence of Gas Temperature on Gaseous Products Generated by Coplanar Barrier Discharge in Air and N2/O2 Mixtures
Get PDFAbsolute densities of gaseous products generated by coplanar dielectric barrier discharge in N2/O2 mixtures and in ambient air were determined by UV optical absorption spectroscopy (OAS). Ozone (O3) and nitrogen oxides (N2O, NO2 and N2O5) were identified as the stable products of the discharge. It was found that the actual product composition strongly depends on the gas temperature. At low input power with the low gas temperature, O3 density was high and the NO2 density was very low. When the input power increased and the gas temperature also increased, then O3 disappeared, while NO2 density started to increase steeply
Design of Autonomous Position and Secondary Estimation of Atmospheric Parameters Sensor Using Low-cost GNSS
Get PDFThe article focuses on the design and implementation of a Low-cost GNSS device for autonomous position monitoring and for determining parameters of the atmosphere. The first part is dedicated to the specification of individual components and their combination into several devices. The primary part includes a test of these GNSS devices and the parameters of data collection. This is followed by a quality test of these collected datasets, in several graphs is shown device capabilities. Also, we can see some problems with components, but we were able to specify what causes them. The final part deals with positioning and determining atmospheric parameters by G-Nut software with the selected GNSS sensor
Study on the settlement law of tunnel in diatomite stratum based on Strain Softening model
Get PDFNowadays, there is no precedent for building a high-speed railway in diatomite area. Due to the complex structure and poor mechanical properties of diatomite as well as the lack of relevant engineering experience, more attention has been paid to the proper constitutive model of the tunnel in diatomite layer using the numerical calculation method, while the traditional Elastoplastic calculation model is the most used yet. Therefore, relying on the Feifengshan tunnel, through FLAC3D software as well as the on-site monitoring, the analysis of the settlement law about tunnelling in diatomite stratum is carried out based on different constitutive models. The research results show that diatomite has obvious strain-softening characteristics. The calculated surface settlement and vault settlement based on the Strain Softening model was greater than that based on the Mohr Coulomb model. When compared with the on-site monitoring data, it was found that the Strain Softening model would more accurately show the settlement law of the tunnel in diatomite and has better applicability in the diatomite area. The above-mentioned research results may provide some references for the construction and design of tunnels in similar strata in the future
Preparation of the composite asphalt material and its performance in road rehabilitation
Get PDFAsphalt materials have a very wide range of applications in roads, but with the increase of traffic pressure and the intensification of cracking and rutting in traditional asphalt pavements, there is an urgent need to further improve the performance of asphalt materials. In this paper, composite asphalt materials containing 10%, 20%, and 30% trinidad lake asphalt (TLA) and 0%, 2%, 3%, and 4% styrene-butadiene rubber (SBR) were prepared. Their basic properties and the properties of the mixes used for road rehabilitation were analyzed. It was found that the addition of TLA and SBR caused a decrease in the penetration degree of the material, but significantly increased the softening point of the material, TLA was detrimental to the ductility of the material, and SBR could improve the ductility. From the analysis of the performance of road rehabilitation mixes, the comprehensive performance of 20% TLA+3% SBR was good, its dynamic stability reached 3,712.66 times/mm, its water stability was also good, and its stiffness modulus was 3,332.64 MPa. The results prove the improvement of TLA and SBR for asphalt performance, and this method can be applied in practical projects
Experimental Study of Arc Erosion in Gas-blasting and Free-burning Conditions in High-voltage Circuit Breakers
Get PDFArc erosion behavior depends on varieties of factors, such as the shape and material of contacts, the gas type and the pressure filled in the chamber. In this contribution, experimental research on the gas-blasting and free-burning conditions was carried out in a model circuit breaker to investigate the gas blowing effect on the mass loss of arcing contacts. SF6 was filled in the chamber and copper-tungsten was used as the contact material. Three different peak current amplitudes (5/20/35kA) were selected, and the average mass loss of plug contact was measured after five consecutive arcing tests. The erosion physical process between arc root and contact material is extremely complex. The mass loss was estimated with four different indexes, which include integral of current squared, thermal stress, transferred electric charge and arc energy. It has been found that the arc energy can be used to represent the degree of arc erosion to relate the gas-blasting and free-burning conditions