Research Of Inversion Method Of Detonation Products Physical Parameters Based On Modified Method Of Characteristics

Equation of state (EOS) of detonation products is one of the most important equations in explosion mechanics, and it describes the relationship between pressure, density and temperature (internal energy) of detonation product. After explosive is detonated, detonation products expand isentropically. Detonation products parameters can be described with isentropic unloading relationship which is derived with EOS and thermodynamic entropy equation. Therefore, the research on detonation products parameters (EOS of detonation products and its coefficients) is of importance. Currently, there are many methods to measure coefficients of EOS of detonation products. However, most of them are suitable for measurement of ideal explosive, for example, standard cylinder test, and they are not appropriate for measurement of non-ideal explosive, because detonaton parameters of non-ideal explosive are affected by influence factor such as explosive charge, additive, and explosive particle size. This paper introduces an inversion method to solve detonation product parameters with modified method of characteristics. The inversion method includes experiment and numerical inversion.In applying the inversion method, detonation product parameters along isentropic unload condition, including pressure, density and sound velocity, can be solved. Main content of this paper is stated as follow(1) This paper proposed an improved continuous resistance probe which can be used to measure propagation of detonation wave and shock wave. Commercial continuous resistance probe has some problems in detonation velocity measurement that the commercial probe is easily disturbed in detonation velocity measurement, and theoretical analysis is performed on the problems. On the basis of the analysis results, an improved continuous resistance probe is produced. The improved probe has excellent capability of resisting clutter interference and reliability in experiments. The measured results are of high accuracy. The improved probe and commercial probe differ in working principle. The improved probe can work in two manners: ionized layer behind detonation wave and external pressure. Therefore, the improved can measure not only detonation wave but also shock wave in other mediums. The application range of the improved probe is much wider than the commercial one. The improved probe is used to measure detonation wave and underwater shock wave in this paper.(2) A modified method of characteristics was introduced and was applied to numerical calculation of one-dimensional spherical explosive underwater explosion. The compatible equations of the modified method have explicit entropy terms which change along particle trace line, and it indicates the modified method is much more appropriate to isentropic flow problem, for example, underwater explosion problem. Combined with shock Hugoniot relation with characteristics equations, the modified method can be used to solve discontinuity shock wave without introducing artificial viscosity. Therefore calculated shock wave is more objective. The modified method is applied to simulation of underwater explosion of spherical explosive. The calculated results are coincident with experiment data, and the comparison results verify the reliability and accuracy of the modified method. This paper also compares and analyses some commonly used EOSs of water. Some EOSs of water which are suitable for underwater explosion calculation are selected. The paper also analyse the influence of y on sound velocity in EOS of water, and proposes a relation which can judge reasonable range of EOS of water parameters.(3) An inversion method to solve physical parameters of detonation product was proposed. The inversion method can be described in two stages. In first stage, underwater shock wave is as known condition. Based on the modified method and inverse difference schemes, gas-water interface can be inversed. In second stage, on the basis of the calculated gas-water interface and self-simulation solution, detonation product parameters including pressure, density and sound velocity of detonation products are calculated with the modified method and parameter optimization method. In appling the inversion method, detonation products parameters of several explosives are solved, and the inversion parameters have a good precision in high pressuer and medium pressure region, which demonstrate the inversion method is feasible and reliable.