Improved Methodology for Accurate Prediction of Blast Wave Clearing on a Finite Target

Abstract

Accurate estimation of blast loads on a structure requires consideration of several complex phenomena during interaction with the target surface. One such phenomenon is the clearing effect observed during the diffraction of blast waves from finite reflecting targets. A clearing wave is generated due to the pressure difference between the edge and internal locations of the target surface, which reduces the reflected impulse at the considered location on the target surface. The state of the practice relies on simplified empirical methods to predict the clearing effects, which are often inaccurate or may also be unconservative. Past analytical studies on the clearing effect have mainly focused on weak blast, where the clearing wave speed is assumed to be the ambient sound speed. In the present study, the authors propose a methodology to include the effect of clearing on reflected overpressure history for strong blasts by considering an average clearing wave speed computed using the ideal gas law. The modified approach was verified and validated with existing literature and benchmarked against numerical studies. The proposed clearing methodology was shown to address the limitations of the current state of practice. Finally, a simplified version of the proposed clearing model was presented in the form of charts that can be used to compute the reflected overpressure history, including the effect of clearing on a finite-surface rectangular target.