Abstract
Physical models of the formation of ballistic and muzzle waves generated during an artillery shot have been developed and investigated. A promising method for assessing the degree of wear of artillery barrels is the acoustic non-contact method. However, its implementation requires separate records of the ballistic and muzzle waves. A series of physical models have been developed to assess the possibility of such a recording. A model for calculating parameters of a ballistic wave accompanying an artillery shot has been built. The proposed model features replacement of the problem of spatial axisymmetric streamlining the shell surface by the problem of plane streamlining the wedge. The model makes it possible to determine the value of the angle of inclination of the oblique shock to the direction of the oncoming flow depending on the Mach number. Calculation of pressure of the powder gases flowing from the muzzle section of the barrel behind the shell is based on the application of the law of energy conservation for compressed powder gases. This avoids solving the complex modified Lagrange problem. Calculations show that the muzzle wave pressure changes in the range (30...300) MPa. A physical model of the muzzle wave propagation at the initial stage of the outflow of powder gases from the bore was proposed. During propagation of the muzzle wave, a situation is possible at an initial stage in which this wave reaches the recording point before the ballistic wave. This situation can occur if the range angles and the wedge taper are small. This phenomenon can be avoided by appropriate angle selection. The proposed model determines the law of propagation of the muzzle wave and makes it possible to estimate the rate of its attenuation. It has been established that measuring microphones recording the actual ballistic wave can be located at distances of 50÷500 m from the barrel. The developed models are useful in practice. It is possible to estimate the initial speed of the shell and the degree of barrel wear by separate recording the ballistic and muzzle waves
Highlights
Powerful acoustic fields are formed with each artillery shot
Analysis of temporal and spectral characteristics of the recorded acoustic signals makes it possible to obtain a kind of «acoustic portrait» of the «artillery gun – shell» system using acoustic fields formed by shots [2]
The following tasks were set: – obtain a theoretical estimate of the ballistic wave parameters; – calculate the pressure of powder gases flowing from the muzzle section of the barrel after the shell to determine initial parameters of the muzzle wave; – model the process of propagation of the muzzle wave to determine its decay rate as a blast wave in order to calculate time from the time point of the shot and the distance from the gun at which this wave acquires properties of a linear acoustic wave
Summary
Powerful acoustic fields are formed with each artillery shot. These fields are mainly formed by two waves: ballistic (accompanying the shell flight) and muzzle (created by powder gases flowing out of the gun barrel under high pressure). The sonic artillery reconnaissance which has been widely used in practice for over a hundred years is based on this principle [1] Another trend that has emerged in the last decade implies the recording of ballistic and muzzle waves formed by firing at fairly short distances (less than 500 m) from a gun firing position. There are no adequate models of the formation of ballistic and blast waves and the dynamics of their behavior during the first seconds after the shot This makes it impossible to develop a pattern of arrayal of recording microphones in such a way as to avoid the superposition of acoustic signals and have a clear idea of the nature of the measured audio signals. It is necessary to estimate amplitudes of the blast waves generated during the shot
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