In the regime of extreme events, blast-structure interaction is of a particular interest. Additionally, the naval industry has specific interest in problems involving underwater blast-structure interaction. Shallow underwater blasts from explosive charges result in a high pressure gas region expanding into ambient pressure water and a resulting shock which propagates in the immersing fluid. Ultimately, due to momentum, overexpansion of the gas bubble occurs. This overexpansion leads to the collapse of the bubble. Upon collapse, momentum again drives subsequent re-expansion and collapse until energy is completely dissipated. Concurrently, a shock in an immersing fluid will propagate from the charge and contact any immersed solid materials, resulting in a complex structural response. It is desirable to resolve the behavior of the explosive gas product, immersing fluid and any immersed solid structure. Robust computation of immersed structural response in the air-blast case has been demonstrated using the immersed method. Similar techniques are applied to the computation of underwater blast. Using an immersed isogeometric method, the structural, fluid and explosive behavior during a detonation type extreme event both underwater and in air are studied.In this work, the performance of an air-blast immersed-isogeometric pressure primitive full-energy formulation is demonstrated in three dimensions and subsequently modified for the computation of underwater blast phenomena. Initialized domains consisting of fluid materials satisfying both the ideal gas equation of state in the air-blast case and Jones-Wilkens-Lee (JWL) equations of state in the underwater blast case in a density primitive reduced-energy compressible flow formulation are evolved using an immersed method. Solid materials are introduced as immersed solids, and explosive charges are introduced as immersed fluids. The focus of this study is on the detonation of Trinitrotoluene (TNT) in air and 1,3,5-Trinitro-1,3,5-triazinane (RDX) in water.&nbsp;&nbsp;Further developments in solid residual based shock capturing are used to stabilize immersed solid domains. Significant attenuation of spurious oscillations in solid shocks has been demonstrated in previous work, and is particularly advantageous for the study of materials with complex constitutive models. Additional improvements in artificial viscosity discontinuity capturing tailored for JWL materials are shown to effectively stabilize the formulation.&nbsp;&nbsp;Expansion of explosive gas products results in under-integration as particles spread. Long-time stability of immersed detonation charges is aided through mass-preserving quadrature volume update on all immersed fluid domains, naturally implemented in the density primitive formulation. This development is coupled with solid shock capturing as well as JWL specific discontinuity capturing to form a robust framework for air and underwater blast structure computations. One dimensional water shocks and underwater detonations are demonstrated to agree with benchmark results. A collection of underwater 1D and 3D examples are provided to illustrate the performance of the new methodology.&nbsp;

Underwater and Air-Blast Structure Interaction Using the Immersed Approach

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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