Cavity Dynamics and the Development of a Non-Explosive Ship Shock Testing System
Dr. Georges Chahine, Dynaflow, Inc.

Abstract:
Development of a non-explosive shock testing facility called “DockShock” is conducted by a team comprising BAE Systems, Anteon, and DYNAFLOW. The system uses an array of directed energy pressure sources.  Two concepts are being investigated: an aluminum-water electrochemical source involving oxidation of aluminum in water, and an electromechanical source involving electromagnetically driven plates accelerated into the water to create the desired pressure pulse.  Feasibility studies demonstrated that both types of sources can be designed to result in the generation of the high pressures needed to reproduce a shock load comparable to that due to an underwater explosion.  Both concepts are presently being expanded to reproduce the full load history and the full particle velocity history due to an UNDEX including UNDEX bubble after-flow.  In both concepts, as in the actual UNDEX experiment, and probably in any other alternative concept, the very high local accelerations imparted to the water to achieve the required loads, result in the formation of a cavity at each source location.  The dynamics of these cavities and their interactions in the case of a bank of sources, contribute to the loads delivered to the tested ship and could either interfere with the source objectives or be harnessed to achieve the full UNDEX cycle shock testing objective.  In this paper we address this cavity dynamics aspect of the problem using a numerical tool, 3DYNAFS©, that has been validated for Navy UNDEX bubble studies, and which is expanded here to include cavitation of highly accelerated/decelerated bodies.  3DYNAFS© enabled us to model formation of the cavities, their dynamics and interactions and the resulting loads on the target for both types of alternative shock testing concepts.  Scaling laws for the case of the electro-mechanical concept were derived, which would provide guidance for the design of large scale systems that can recover the full load history. Proper selection of the size and acceleration function could achieve a loading which comprises both shock and bubble effects.

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