The characteristics of shock wave loads from air blast near the water surface

Blasts near the water surface are one of the major threats to ships. Experiments were carried out to study the load characteristics of the shock wave on the water surface with TNT/RDX(40/60) explosives. Three typical scaled burst heights were used: contact burst, near-surface blast, and air blast. In the experiments, overpressures in air and water were obtained, and high-speed photographic was used to record the explosion images. A numerical simulation method based on a five-equation model was used to study further the explosion phenomenon and the loading characteristic of shock waves on the water surface. The numerical simulation results are in good agreement with the experimental results. The results show significant differences among contact bursts, near-surface blasts, and air blasts. In the contact burst, the detonation products drive the water surface directly, creating a hemispherical cavity, and the water at the edge of the cavity is squeezed upwards, forming a hollow water column. In the near-surface blast, the collision of the detonation products with the water surface is relatively weak, and the shock wave on the water surface mainly propagates outwards as Mach waves along the water surface. In the air blast, there are clear regular and irregular reflection zones of the shock wave on the water surface. Under the same yield conditions, the overpressure on the water surface of the contact burst is lower than that of the near-surface blast, but the pressure in the water is more stressful. Therefore, the water surface can no longer be considered a rigid plane. The formulas of overpressure and positive pressure duration of shock wave on the water surface within the range of 0.5～4.0 m/kg^1/3 in the contact burst and the near-surface blast were obtained through data fitting, which provides a reference for shock wave loading calculation and analysis.