Research On The Physical Mechanism Of Bipolar Narrow Pulse Discharge Process And Inversion Of Its Physical Parameter

For Narrow bipolar event(NBE)of lightning strong electromagnetic pulse signal,based on the lightning VHF signal and broadband electric field detection data,the empirical mode decomposition Pearson correlation method is used to obtain accurate three-dimensional positioning data,combined with even The two frequency bands of high frequency and broadband electric field screen the NBE pulse and make statistics on its characteristics,simulate its electromagnetic field waveform and deeply analyze the discharge process.The research content of this paper mainly includes the following aspects:(1)Establish a GP model based on the positive streamer system,study the rapid breakdown mechanism of NBE,discuss and analyze the influence of GP model configuration parameters,and discuss the length of the NBE discharge channel,and reconstruct it by changing the stop condition of the streamer tip development of the GP model,Under the fast breakdown characteristics,the microphysical processes such as the electric field change on the axis of the conical streamer system and the charge change at the tip of the streamer are analyzed,and the development scale of the positive streamer and the current channel length of the NBE discharge event are discussed.The selection range of the input parameters of the discharge channel is provided for the NBE pulse work;(2)Construct the current inversion method of NBE pulse discharge channel using the particle swarm optimization algorithm to invert the three models,and discuss the influence of the growth factor of the MTLEI model and the decay factor of the MTLK model on the fitting effect.Fitting and inversion of characteristic parameters such as current peak value and channel scale in the bipolar narrow pulse discharge channel,and statistical analysis of the physical parameters of the bipolar narrow pulse obtained by fitting different transmission line models;(3)Based on three engineering models including TL model,MTLEI model and MTLK model,the channel currents of 24 cases of bipolar narrow pulse events were inverted and analyzed respectively;In the TL model and the MTLK model of the thermal breakdown mechanism,compared with the TL model(the peak current is 94.3 k A,the current channel length is 491.1 m,and the current velocity is 1.68×10~8 m/s),the MTLK model(the peak current is 120 k A,The length of the current channel is 678 m,and the current velocity is 2.05×10~8 m/s)considering the energy loss in the current transmission process,which is more realistic;while the MTLEI model based on the relative escape avalanche breakdown mechanism of the quasi-electrostatic field,compared with the other two A transmission line model,which shows that there is a long-term exponentially increasing current intensity(185.8-837.5 k A)with height in the narrower discharge channel.The electric dipole moments obtained by the inversion of the three transmission line models range from 100 to 800 C m,and the NBEs occurring at higher places usually have larger electric dipole moments.Obviously,the above three transmission line models can fit narrow bipolar pulses well,and these findings are of great significance for studying the real physical discharge process of NBE pulses.