An experimental investigation of clearing effects in near-field and above-ground explosions

When employing a risk management strategy for the storage of ammunition and explosives, as opposed to strictly adhering to established Quantity-Distances (QD), quantifying the effects of explosions is paramount. Practitioners, however, often face significant challenges in accurately predicting the resulting blast loading on Exposed Sites (ES). One major challenge lies in addressing the diffraction of the blast waves around the free edges of the impinged surface of the ES, which generates a pressure relief wave, thereby diminishing the reflected impulse. This phenomenon is known as blast wave clearing. The Hudson method, developed in 1955, is a first-principles approach to account for clearing effects by deriving pressure relief waveforms using the Sommerfeld diffraction theory. This method has been extensively validated through mid- and far-field experiments with surface charge open-arena blast tests. Recent comparisons with computational fluid dynamics (CFD) analyses have demonstrated the potential for extending the Hudson method to near-field and above-ground explosions. The former requires adjusting the pressure relief wave speed, as opposed to considering the constant ambient sound speed. For the later, when a target is located above the triple-point-path, two pressure relief waveforms are considered, corresponding to the incident and the ground-reflected waves that arrive separately at the target. This paper will investigate experimentally the clearing effects in near-field and above-ground explosions, and explore the application of the Hudson method to these scenarios.