Prediction of the quasi-static pressure in confined and partially confined explosions and its application to blast response simulation of flexible structures

• This article widens the scope of internal blast in terms of partial afterburning in case of oxygen deficiency, correction of numerical simulations for accounting the afterburning energy release and developing a thermodynamic model for the prediction of the gas pressure.
• An analytic method, based on thermodynamic rules, was developed for calculating the gas pressure as a result of TNT confined explosion.
• The sensitivity of the gas pressure to the heat capacity ratio and internal energy of explosion was studied.
• The proposed approach based on using the developed gas pressure is well suited for simulation of partially confined explosions.
• The developed gas pressure was successfully applied to simulation of confined blast response of flexible structures.

The paper aims at understanding some characteristics of an interior explosion within a room with limited venting. Internal explosions may occur as a result of an ammunition storage explosion, or a charge explosion within a room in a terrorist action or a warhead explosion following its penetration into a closed space. The paper deals with one of the basic aspects of internal blast – residual blast pressure (gas pressure, quasi-static pressure). The article presents different models for the prediction of the gas pressure. The sensitivity of the gas pressure to the heat capacity ratio and internal energy of explosion is studied. It is demonstrated that the heat capacity ratio has a much stronger effect on the gas pressure than the internal energy of explosion. It is shown that a thermodynamic model based on accounting for the afterburning energy release shows best agreement with experimental data. This method takes into account the variation of the total energy released and the heat capacity ratio depending on the ratio between the charge weight divided by the confined air volume. It is demonstrated that the proposed simplified approach based on using the developed gas pressure as well as on the Bernoulli equation for the quasi-stationary phase is well suited for simulation of partially confined explosions and properly describes the pressure relief and gas outflow from the vented room. The developed gas pressure can be successfully applied to simulation of confined blast response of flexible structures. An analytical solution of the SDOF blast response of a flexible structure is implemented. It is shown that the simplified approach based on the quasi-static gas pressure properly describes the elastic-plastic shell behaviour. It shows a good agreement with test data and with a solution using pressure time history obtained by AUTODYN simulation.