Numerical study of implosion of shell structures
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ORIGINAL PAPER
Numerical study of implosion of shell structures Y. W. Kwon1 · S. Sugimoto2 Received: 25 July 2020 / Accepted: 17 August 2020 / Published online: 30 September 2020 © This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply [2020] 2020
Abstract To better understand the implosion and the resultant shock wave, a series of numerical modeling and simulations were undertaken for the buckling and collapse of spherical and cylindrical shell structures. The shells were assumed to be made of steel, aluminum, and laminated fibrous composites, respectively. First, the buckling was examined for the shell structures subjected to external pressure loading without any contact with fluid media. Both static and dynamic buckling was studied. For the dynamic buckling, the speed of collapse was controlled to investigate its effect on the buckling characteristics such as buckling mode. This was achieved by decreasing the internal pressure at different rates as the structures were subjected to a constant external pressure. Then, the full implosion process associated with the collapse of shell structures was modelled and studied to understand the shock wave propagation radiated from the collapsing shell structures. The structures were initially subjected to an external water pressure equivalent to a specified water depth. Then, the collapse speed of the shells was controlled, too. Finally, the effect of an initial defect on the buckling and implosion of cylindrical shells was examined. The numerical study compared the implosion characteristics resulting from spherical and cylindrical shells, different material properties, and various controlled collapse speeds. The results suggested that there were optimal parameters which generate the maximum peak pressure during the implosion process. Keywords Implosion · Buckling · Shock wave · Metals and composites · Initial defect
1 Introduction When a structure buckles suddenly under a high external water pressure, the collapsing structure produces shock waves propagating back into the surrounding water. The resultant shock wave can be detrimental to any neighboring structure. As a result, research has been conducted to understand and predict the implosion process. A sudden collapse of a cavity (or bubble) also produces high shock wave back into the surrounding water medium. Therefore, much research has been also conducted for the collapsing bubbles. When a structure has very negligible
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Y. W. Kwon [email protected] S. Sugimoto [email protected]
1
Department of Mechanical and Aerospace Engineering, Naval Postgraduate School, Monterey, CA 93943, USA
2
Naval Platform and Signature Research Division, Structure and Material Research Section, Naval Systems Research Center, Acquisition, Technology and Logistics Agency, Tokyo, 1530061, Japan
strength and stiffness, its collapse can be approximated as the collapse of a bubble of the equivalent geometric shape. Thus, the bubble collapse can be considered as
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