Axisymmetric finite element models have been developed for the simulation of negative discharges in air without and with the presence of dielectrics. The models are based on the hydrodynamic drift-diffusion approximation. A set of continuity equations accounting for the movement, generation and loss of charge carriers (electrons, positive and negative ions) is coupled with Poisson's equation to take into account the effect of space and surface charges on the electric field. The model of a negative corona discharge (without dielectric barriers) in a needle-plane geometry is analysed first. The results obtained show good agreement with experimental observations for various Trichel pulse characteristics. With dielectric barriers introduced into the discharge system, the surface discharge exhibits some similarities and differences to the corona case. The model studies the dynamics of volume charge generation, electric field variations and charge accumulation over the dielectric surface. The predicted surface charge density is consistent with experimental results obtained from the Pockels experiment in terms of distribution form and magnitude.
A unified collision avoidance system is proposed to improve the efficiency and safety of marine transport, namely maritime avoidance navigation, totally integrated system (MANTIS). The principle behind its operation is to remove the difficulties and uncertainties involved in marine navigation through a system structure that makes marine transport deterministic rather than uncertain. Fundamental to its operation is a strategic interactive expert system that can determine safe and efficient navigation routes for all vessels as part of journey planning and en route collision avoidance. An important requirement is to take account of non-navigable areas, collision regulations, ship characteristics, sea state and sensor accuracy during evaluation. An outline of the MANTIS infrastructure is given, followed by a description of the vessel management system (VMES). Simulation results exemplify the significance of the system for future exploitation.
This paper studies the feasibility of applying the electro-optical Pockels technique to measure surface discharge at a solid-liquid insulation interface. The principle of the method is based on the Pockels characteristic of the Bismuth Silicon Oxide (BSO) sensing crystal. The presence of surface charge induces an electric field across the crystal which in turn linearly changes the polarisation state of the incoming polarised light. This change in the light polarisation state can be deduced from the recorded light intensity and hence surface charge density can be calculated. The distribution of charge generated from a needle electrode immersed in mineral oil under two cycles of AC voltage was measured and results are compared with those obtained in gas and gas-liquid structures.
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