Transient Dynamic Analysis For Double Shell Structures Subjected To Underwater Explosion

Underwater contact explosion means explosions with short chargingdistance and severe damage effect. Recently, with the improvement ofprecision guided weapons, the risk increases that a serving vessel surfersfrom underwater contact explosion. In order to protect the vessels fromthe risk, many countries are dedicated to developing novel structuralforms. However, the current numerical simulation methods have severaldeficiencies, since the underwater explosion is with complicate process,various loads types and strong nonlinearity. Therefore, the numericalsimulation method of underwater contact explosion is studied andexplosion resisting performances of different structural forms areanalyzed.Based on the finite difference scheme of Navier-Stokes equations,the dynamic response of underwater bubbles is numerically simulated. Ahigh accuracy numerical method is realized to define the free surfaceboundaries with severe deformation. An innovative outer boundarycondition is proposed to improve the numerical efficiency, which was low in the past applications. The method simplified the pressure distributionof the far field with potential theory. The method is proved to be of highefficiency and accuracy. Good agreement is obtained between numericalresults, Rayleigh-Plesset equation and experiments. Finally, the dynamicresponse of several explosive bubbles in the vicinity of a rigid boundaryis simulated and the influence of the charging parameters upon jetparameters is analyzed.A calculation process is proposed to simulate the dynamic responseof double-shell structures subjected to both explosive wave and jet impact,using Msc.Dytran finite element solver. First of all, the jet impact processis simulated separately in order to obtain the impact pressure distributionover time and space. The impact pressure is then applied to the explosivewave fluid-structure-interaction model by a Dytran user-subroutine.Besides, the user-subroutine defines the load condition of the inner shellwhen material failure occurs on the outer shell. The contact effectbetween the two shells is also considered. The formerly proposed processis then applied to calculate the explosion resisting performances ofI-shape/Y-shape double-shell structures in batches. The influence ofstructural design parameters upon explosion resisting performance isanalyzed and Y-shape is proved to be superior to I-shape. Finally, threefailure modes of a grillage structure are concluded based on the simulation of this structural form subjected to serial jet impact loads.