Near-Field Pressure Directivity Of Cylindrical Underwater Explosions and Semi-Empirical Modeling

In this study, the near-field pressure dynamics of cylindrical explosives in underwater explosions are systematically investigated using computational modeling and empirical validation. A three dimensional finite element model based on the Arbitrary Lagrangian-Eulerian (ALE) algorithm is developed to simulate detonation processes in infinite water domains, with model accuracy confirmed through comparisons against experimental data. Focusing on the poorly understood extreme near-field region, the influence of explosive geometric parameters (length-to-diameter ratio, L/D) and detonation asymmetry on pressure distribution is analyzed. Key findings reveal that in the extreme near-field, peak pressure is initially more pronounced in the axial direction, but transitions to radial dominance with increasing standoff distance, a behavior that is more pronounced in high-L/D configurations (e.g., L/D = 5 exhibits a 44.4% slower axial-to-radial transition than L/D = 3). Non-central detonations of cylindrical explosives introduce significant pressure directivity, enhancing local peak pressures by up to 26.9% and inducing deviations from axisymmetric wavefronts. To characterize these effects, a semi-empirical engineering model integrating explosive mass loss and centroid trajectory is proposed, complemented by a scaling law regression method to quantify directional intensity. Specifically, this framework provides directional upper and lower bounds for peak pressure in the extreme near-field by coupling time-resolved mass consumption with dynamic centroid migration, and serves as an engineering tool for preliminary assessment of pressure directivity under cylindrical charge UNDEX loading.