Underwater implosion pressure pulse interactions with submerged plates

Abstract

An experimental and analytical investigation is conducted to study the underwater interaction of implosion pressure pulses with large plates. Two plates with stiffnesses significantly apart are investigated experimentally in a large-diameter pressure vessel for their Fluid-Structure Interaction (FSI) phenomena during proximal implosions of thin metallic shells. High-speed photography, in conjunction with 3D Digital Image Correlation (DIC) measurements, is employed to obtain full-field displacements of the plates. Local dynamic pressure histories are also simultaneously recorded to investigate the incident, reflected and transmitted fluid pressures across the plates during dynamic loading. The lesser stiffness plate showed higher deflection, allowed a weaker reflected pressure pulse and allowed a stronger transmitted pressure pulse as compared to the higher stiffness plate. The peak deflections of the plates occurred during the underpressure phase of the implosion event. Four analytical modeling iterations with increasing complexities starting from Taylor's FSI model are considered to assess the response of water backed plates to dynamic pressure pulse loadings. Each iteration is analyzed individually in an experimental context to understand its role as a building block in a final analytical model. The final model developed is based on the classical plate-bending equation and fluid velocity corrected for ‘afterflow’ effects and performed better than Taylor's original model in predicting pressure-time history of the plates’ reflected pressure and transmitted pressure. The plates’ mid-point deflection profiles are also better predicted using this model. Furthermore, the model showed that the response of a plate during a dynamic implosion pressure pulse interaction is weakly dependent on its bending stiffness. Instead, it is observed that for a large plate, its areal mass density is the dominant factor in determining the reflected pressure, the transmitted pressure and the plate mid-point deflection profiles.