1 Copyright © 2012 by ASME Proceedings of the Internoise 2012/ASME NCAD meeting August 19-22, 2012, New York City, NY, USA IN12-586 CHARACTERIZATION OF THE PRESSURE WAVE EMITTED FROM IMPLOSION OF SUBMERGED CYLINDRICAL SHELL STRUCTURES Michael D. Shields Ph.D. Weidlinger Associates, Inc. New York, NY, USA shields@wai.com Pawel Woelke Ph.D. Weidlinger Associates, Inc. New York, NY, USA woelke@wai.com Najib N. Abboud Ph.D. Weidlinger Associates, Inc. New York, NY, USA abboud@wai.com ABSTRACT Buckling of submerged cylindrical shells is a sudden and rapid implosion which emits a high pressure pulse that may be damaging to nearby structures. The characteristics of this pressure pulse are dictated by various parameters defining the shell structure such as the length to diameter ratio, shell thickness, material, and the existence and configuration of internal stiffeners. This study examines, through the use of high fidelity coupled fluid-structure finite element computations, the impact of various structural parameters on the resulting pressure wave emanating from the implosion. The results demonstrate that certain structural configurations produce pressure waves with higher peak pressure and impulse thereby enhancing the potential for damage to nearby structures. INTRODUCTION The implosion phenomenon is the result of structural instability (either elastic or inelastic) of an enclosed volume with relatively low internal pressure subjected to large external hydrostatic pressure. This instability, when it occurs, very rapid and can result in a complete inward collapse of the structure. Engineers must be concerned with implosion when designing or analyzing any enclosed structure that is expected to withstand large external pressure. This environment may arise for example in deep sea applications such as off-shore oil drilling, sea exploration, or deep sea naval exercises as well as in certain hydraulic systems. Although design standards are in place to aid designers in avoiding such a catastrophic failure (e.g. [1], [2]), these codes do not necessarily cover some of the extreme environments (such as underwater shock) that may be encountered in the applications listed above. The problem of implosion extends beyond the structural collapse itself (and the potential payload loss that may result) because an implosion event may also result in a violent shock- type pressure wave emanating from the implosion in the surrounding fluid. This pressure wave has the potential to damage nearby structures. The objective of this work is to begin characterizing this emitted pressure wave in terms of specific structural characteristics using high fidelity fluid- structure finite element calculations. The most common implodable volumes are cylinders and spheres [3] although an externally pressurized closed volume of any shape will be vulnerable to implosion [4]. The study presented in this work focuses specifically on the characteristics of the fluid response resulting from implosion of two unstiffened cylindrical shell structures with differing length, diameter, and shell thickness and represents a small sample of a much larger effort to characterize the fluid response for a generalized set of structural parameters. IMPLOSION BEHAVIOR FOR CYLINDERS Structural Behavior Implosion of an unstiffened cylindrical structure generally results from one of two possible failure mechanisms: elastic buckling or plastic buckling. The elastic buckling pressure, ݍ  , for unstiffened cylinders has been studied exhaustively and can be predicted with reasonable accuracy using the equation presented by Timoshenko and Gere [5]: