On the effectiveness of ventilation to mitigate the damage of spherical chambers subjected to confined trinitrotoluene detonations

Abstract

This article presents a comparative study on the effectiveness of ventilation to mitigate blasting effects on chambers subjected to confined detonations of high explosives. The pressure time-history that acts on the chamber walls is described by three components: (1) the first shock wave, (2) the train of re-reflected shock waves, and (3) the gas pressure. The radial response of spherical chambers is described by the radial breathing mode and modeled by an equivalent single degree of freedom system. The three pressure components are considered for the calculation of the maximum ductility ratio, which is obtained from the numerical solution of the single degree of freedom chamber response. It is assumed that openings reduce the gas pressure but they have an insignificant effect on shock waves. The dynamic response of fully and partially confined chambers are calculated and compared. Results show that intermediate/small openings (less than 10% of the surface of the chamber) are ineffective to mitigate the chamber response and damage. The vibratory response of the chamber is susceptible to elastic or plastic resonance but it is not considerably modified by the long-term gas pressure because of its high radial breathing mode frequency, allowing concluding that ventilation is ineffective to reduce the maximum response of spherical chambers subjected to internal high explosive explosion.

On the effectiveness of ventilation to mitigate the damage of spherical membrane vessels subjected to internal detonations

“…These high natural frequencies are in the same order of magnitude of the reverberation frequency associated with secondary re-reflected shock waves (SWs), which are generated when an internal detonation of a high explosive (HE) occurs inside a fully confined (FC) blast chamber. Therefore, spherical chambers may experience resonant responses due to multiple re-reflected shock waves (Buzukov, 1980;Hernandez, 2016;Hernandez et al, 2019;Zhdan, 1981).…”

“…It also assumes that the pressure components (first shock wave, re-reflected shock waves, and the gas pressure) can be modeled by a transient uniform radial pressure, which acts synchronically on the entire chamber wall. The solution of the SDOF system considering a perfect elastic-plastic response was analyzed by Hernandez et al (2019), concluding that all pressure components contribute significantly to the chamber response. The secondary re-reflected shock waves can increase the peak response of spherical chambers up to 85% when elastic or plastic resonance occurs.…”

“…The secondary re-reflected shock waves can increase the peak response of spherical chambers up to 85% when elastic or plastic resonance occurs. In fact, chamber resonance was observed when re-reflected secondary shock waves coincide with a positive radial velocity of the camber wall (Hernandez et al, 2019), which increases the work that is done by blast pressure and the internal energy absorbed by the chamber. The gas pressure component can also increase the chamber response, particularly when ductile chambers are analyzed.…”

“…The gas pressure component can also increase the chamber response, particularly when ductile chambers are analyzed. Previous studies found that the gas pressure component could increase the ductility ratio up to 40% (when the chamber shows a ductility ratio of 5 associated with the first shock wave only; Hernandez et al, 2019). Thus, it is inaccurate to assume that the first shock wave plays a dominant role and ignores the effect of other pressure components such as simplified approaches suggest (Baker and Allen, 1958;Dong et al, 2012).…”

“…Thus, it is inaccurate to assume that the first shock wave plays a dominant role and ignores the effect of other pressure components such as simplified approaches suggest (Baker and Allen, 1958;Dong et al, 2012). It was also demonstrated by Hernandez et al (2019) that because the gas pressure is not released quick enough, spherical chambers can rapidly reach the peak response. As a result, the gas pressure cannot be significantly relieved by a relatively small vent on the chamber (10%-20% of the total chamber surface area), implying that small ventilation could be ineffective in mitigating the damage of spherical chambers.…”