Evaluation of protective structures designed to withstand explosions regularly involves full scale testing to create the specified conditions of Airblast.
The energy distribution from an explosive charge detonated on the ground surface has been investigated to better understand why the airblast wave generated contains considerably less than 20 percent of the available detonation energy. An illustration of this for surface burst TNT is shown in the following figure:
For a surface detonation, energy is expended in the following manner: 1. Crater formation, 2. Generation of various seismic waves, 3. Fireball heat, 4. Airblast shock wave compression of the air and 5. The Airblast shock wave energy based on the following equation for energy flux: E = [1/(ρU)]∫P2dt, where ρ is the density, U is the shock velocity and P is the incident overpressure.
The first four of these energy elements are “wasted” as they do not participate in the shock wave loading of subject protective structures.
The energy balance from surface detonations has been quantitatively determined by evaluating the aforementioned 5 forms of energy.
