An evaluation of measured and predicted air blast parameters from partially confined blast waves

Abstract

Understanding the physical mechanisms by which blast waves interact with their surroundings is paramount to protecting the safety of armed service personnel and equipment. This study evaluates and discusses modern technology used in blast pressure measurement as it relates to primary blast injuries such as traumatic brain injury. Factors influencing primary blast injury were established as peak overpressure, impulse, number, and frequency of shock impacts based on a literature review. A simulated confined-corridor breaching environment was used to establish the potential for variability in these key parameters depending on location in a confined blast environment. Wearable blast pressure monitors were compared experimentally to not only laboratory grade pressure transducers but also simulated and empirically modeled blast pressure and impulse predictions at scaled distances between 3.1 and $13.6\,\hbox {m/kg}^{1/3}$ from 100-g and 200-g suspended Composition C-4 detonations partially confined by the ground. surface ground reflection. Each measurement and predictive technique is detailed and comparatively summarized. Average deviation from the mean in collected pressure and impulse data ranged between 10 and 15%. The disparity in the measured data was lowest in the static pressure range where mild traumatic brain injury is reported to occur.

Appendix: Blast parameter plots and selected waveforms

Fig. 10

Blast parameter data from the 100-g and 200-g C4 detonations suspended and measured at 1 m above the ground

Fig. 11

Selected static overpressure and static impulse waveforms over the initial positive pressure phase at 2, 4, and 6 m from the suspended 200-g C4 detonation

Fig. 12

Selected reflected overpressure and reflected impulse waveforms over the initial positive pressure phase at 2, 4, and 6 m from the suspended 200-g C4 detonation

Fig. 13

Simulation convergence test plots for static overpressure and impulse at double ($5\,\hbox {mm} \times 5\,\hbox {mm}$) and half ($20\,\hbox {mm} \times 20\,\hbox {mm}$) of the measurement resolution

Figure 10 shows graphical representations of the blast parameter data collected from this study for visualization of the data dispersion. A relative mass equivalency factor to trinitrotoluene of 1.35 was used to calculate Kingery–Bulmash parameters for C4. C4 product expansion was simulated using a Jones–Wilkins–Lee equation of state [41]. Impulse was calculated for all measurement distances by discrete integration of measured pressure data over the duration of the initial positive pressure pulse produced by the blast, including the ground-reflected shock wave. Gross positive impulse calculated automatically by the Blast Gauge over the entire 20-ms record duration is shown for comparison to manually calculated positive phase impulse. Figures 11 and 12 show selected overpressure and impulse waveforms for the static and reflected orientations, respectively, produced from the raw unprocessed outputs of each measurement system over the initial positive pressure phase.

Convergence testing of the simulations was conducted for the 200-g C4 charge at the 2-m measurement distance where the magnitude and rate of applied pressure is the most rapid. Convergence testing was conducted at double and half the Euler grid resolutions of $10\,\hbox {mm} \times 10\,\hbox {mm}$. Static overpressure showed convergence between 64.4 and 72 kPa, and static impulse converged between 39.2 and $40.6\,\hbox {kPa}\cdot \hbox {ms}$. Convergence test results and plots are shown in Fig. 13.