Dielectric breakdown properties of Al-air mixtures

In order to investigate the influence of aluminum vapor on the breakdown performance of air,this paper makes a study of the dielectric breakdown characteristics of Al-air mixture in the temperature range of 300-5000 K at atmospheric pressure.A Boltzmann analysis method is used to deal with the electron energy distribution function(EEDF),the reduced ionization coefficients(α/N),the reduced attachment coefficients(η/N)and the critical reduced breakdown strength((E/N)cr)so as to explore the influence of temperature and mixing ratio on the dielectric breakdown properties.In the temperature range of 300-2000 K,the property of the mixture is mainly determined by the mixing proportion of aluminum vapor because the composition of particles remains unchanged.In the temperature range of 2000-2500 K,the decomposition of Al2O_(2)leads to the increase of aluminum oxides and NO,and a rise in the percentage of highenergy electrons as well as the increment ofα/N.Also,the joint action of O_(2)and NO makesη/N increase first and then decrease,and(E/N)crgoes down to a smaller temperature range.An increase in the proportion of aluminum vapor causes(E/N)crto decrease in the low-temperature region and to increase in the high-temperature region,which will reduce the transition between these two temperature regions.

Research on active arc-ignition technology as a possible residual-energy-release strategy in electromagnetic rail launch

In order to solve the problem of the original residual energy release strategy being unsuitable for high-energy and fast-firing electromagnetic rail launch,this work has explored the applicability of active arc-ignition technology(AAT).The results obtained from the comparison of launching experiments show that AAT has no influence on the acceleration of the armature and is capable of quickly releasing the residual energy.Based on the theory of magnetohydrodynamics,this work has also made numerical simulation of the muzzle arc,analyzed the influence of AAT on the muzzle arc flow field,electromagnetic(EM)field and temperature field,and evaluated the performance of AAT according to the projectile initial disturbance,the EM impact on guidance devices and the rail ablation.The results show that AAT is now one of the most practicable strategies for residual energy release.

Delamination failure analysis of G10 insulator in electromagnetic rail launcher

The electromagnetic(EM)rail launcher G10 insulator is prone to delamination damage during launch,which affects the service life of the insulator.Through the secondary development of ABAQUS®commercial finite‐element software,an EM‐structure coupling launch dynamics model considering projectile‐barrel coupling is established.The simulation indicates that the transverse swing of the projectile changes in a sine‐like law,and the time of the upper half wave corresponds to the pulse width of the impact force pulse waveform.The stress concentration occurs on the inner surface of the insulator where the contact‐impact occurs,resulting in impact damage.The midline of the insulator inner surface bears a large compressive strain under the action of pre‐tightening force,and the insulator is compressed oscillatingly under the influence of the timevarying load of the rail during launch.Under the condition of repeated launch,the launch package repeatedly impacts the insulator,and the alternating load of the rail is cyclically loaded on the insulator with impact damage,which will cause the compression fatigue of the insulator and the expansion of impact damage crack.They are the main reasons for the delamination failure of insulator,and the experimental analysis is carried out.This study provides a method to study the delamination failure mechanism of the insulator,and provides guidance for improving the life of the insulator.

Theoretical model of lithium iron phosphate power battery under high-rate discharging for electromagnetic launch

Due to the large error of the traditional battery theoretical model during large-rate discharge for electromagnetic launch,the Shepherd derivative model considering the factors of the pulse cycle condition,temperature,and life is proposed by the Naval University of Engineering.The discharge rate of traditional lithium-ion batteries does not exceed 10C,while that for electromagnetic launch reaches 60C.The continuous pulse cycle condition of ultra-large discharging rate causes many unique electrochemical reactions inside the cells.The traditional model cannot accurately describe the discharge characteristics of the battery.The accurate battery theoretical model is an important basis for system efficiency calculation,precise discharge control,and remaining capacity prediction.To this purpose,an experimental platform for electromagnetic launch is built,and discharge characteristics of the battery under different rate,temperature,and life decay are measured.Through the experimental test and analysis,the reason that the traditional model cannot accurately characterize the large-rate discharge process is analyzed.And a novel battery theoretical model is designed with the help of genetic algorithm,which is integrated with the electromagnetic launch topology.Numerical simulation is compared with the experimental results,which verifies the modeling accuracy for the large-rate discharge.On this basis,a variety of discharge conditions are applied to test the applicability of the model,resulting in better results.Finally,with the continuous cycle-pulse condition in the electromagnetic launch system,the stability and accuracy of the model are confirmed.