Modeling two-fluid response of thin elastic shells

The interaction between a weak external shock wave and a thin elastic cylindrical shell filled with and submerged into fluids with different properties is considered. The interest in investigating such a system is largely driven by the need for an accurate assessment of the performance of a number of industrial systems in extreme conditions of operations, with offshore, chemical, aerospace and nuclear industries being examples. The interaction is simulated using a semi-analytical approach based on combining the analytical techniques of mathematical physics with finite-difference approximations, and a number of effects of practical interest are observed, some for the first time. Specifically, it is demonstrated that four different interaction scenarios are possible, depending on the ratio of the acoustic speeds in the internal and external fluids, zeta. The case of zeta=1 is the previously addressed scenario of two identical fluids. When zeta>1, the situation changes dramatically because the internal pressure wave propagates faster than the external one, and as a result, not one but two high-magnitude wavefronts are observed in the external fluid. The case of zeta<1 is even more interesting, with the possibility of two sub-scenarios: one where the classical 'reflection-focusing' sequence is observed inside the shell, and one where not one but two focusings are seen, one before and one after the reflection of the internal wave from the shell surface. The effect of placing rigid co-axial cores of various radii inside the shell on the hydrodynamic fields is discussed as well. Copyright (C) 2010 John Wiley & Sons, Ltd.