In addition to the ship shock trial simulation work conducted by the SVCL staff, doctoral and graduate students from the Mechanical Engineering Department here at the Naval Postgraduate School have extensively researched the underwater shock phenomena and its damaging effects.
Investigations have included computer modeling and simulation, biomechanical specimen testing, explosive model testing and vibration panel testing, in both the classified and unclassified formats. Some of the past thesis topics include:
Creating a virtual shock environment by use of a computer to model the ship structure and the surrounding fluid presents a valuable design tool and an attractive alternative to life fire testing. Continuing work in this area examines the accuracy of shock simulation using the shock trials conducted on USS WINSTON S. CHURCHILL (DDG 81) in 2001. Specifically, all three explosions that DDG 81 was subjected to have been simulated and the resulting predictions compared with actual shock trial data. The effects of the fluid volume size, mesh density, mesh quality, and shot location have been investigated in depth. Findings from the research conducted on the DDG 53 and DDG 81 shock trials are being applied to the predictions currently being generated for the forthcoming LPD 17 shock trials.
Ship survivability is a complex issue. For a ship to remain a viable warfighting asset followingdamage resulting from enemy munitions such as mines or torpedoes, the ship’s crew must remain sufficiently uninjured to be capable of employing the ship’s weapons systems. Sophisticated computer simulations of human response, such as those made possible by the Articulated Total Body (ATB) Model, may be used to estimate injury potentials, and thus crew survivability, during underwater explosion events. With this goal in mind, accelerometer data and video footage recorded during live fire testing were used to generate and validate ATB models for both a seated and a standing Hybrid III Anthropomorphic Test Device (ATD). Subsequently, these models were used to estimate the biodynamic response and injury potentials for both male and female human subjects in a vessel subjected to underwater explosion events. This established a method for evaluating crew survivability for a given underwater explosion induced deck excitation.
The whipping of surface ships refers to the low frequency vibration of its hull girder. This whipping phenomenon is caused by the gas bubble oscillation from an underwater explosion or from the impact of large waves in certain ship hull forms. Our work focuses on the whipping that occurs following an underwater explosion, an event which consists of two primary types of loading, the initial shockwave and subsequent gas bubble oscillations. Both the bubble oscillation frequency and the fundamental frequency of a hull girder have been found to coexist in the low frequency range. Therefore, the bubble oscillation can further excite the low frequency motion, or whipping, of a ship’s hull. A comparative whipping response study of the full ship finite element model of a DDG-51 Class destroyer and its corresponding beam model has been conducted using the Hicks bubble algorithm in the Underwater Shock Analysis (USA) code. Simulation whipping results of the full ship model subjected to various charge geometries are being investigated.