Optimisation of parametric equations for shock transmission through surface ships from underwater explosions

Elder, D 2006, Optimisation of parametric equations for shock transmission through surface ships from underwater explosions, Masters by Research, Aerospace, Mechanical and Manufacturing Engineering, RMIT University.


Document type: Thesis
Collection: Theses

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Title Optimisation of parametric equations for shock transmission through surface ships from underwater explosions
Author(s) Elder, D
Year 2006
Abstract Currently shock effects on surface ships can be determined by full scale shock trials, Finite Element Analysis or semi empirical methods that reduce the analytical problem to a limited number of degrees of freedom and include hull configurations, construction methods and materials in an empirical way to determine any debilitating effects that an explosion may have on the ship. This research has been undertaken to better understand the effect of hull shape on surface ships' shock response to external underwater explosions (UNDEX). The study is within the semi empirical method category of computations. A set of simple closed-form equations has been developed that accurately predicts the magnitude of dynamic excitation of different 2- D rigid-hull shapes subject to far-field UNDEX events. This research was primarily focused on the affects of 2-D rigid hull shapes and their contribu tion to global ship motions. A section of the thesis, "T-Joint", considers the exacerbating affects that shock wave propagation has on a typical Glass Reinforced Polymer (GRP) laminated ship T-Joint with respect to its strength and the transmission of the shock to the adjacent bulkhead. The hull motion parametric equations developed in this research are compared against computational fluid structure interaction predictions obtained from non-linear, explicit finite Element (FE) simulations using -the LS-Dyna code. The equations are shown to predict the vertical acceleration and velocity of four basic hull shapes to within approximately ±15% of the - FE model results. Addition error estimates obtained for sensitivity analyses, predicted that the LS-Dyna simulations were accurate to within ±11 % when compared to real UNDEX events. The resultant error of the closed-form solutions compared to real UNDEX events is the summation of the two error estimates at ±26%. A number of different GRP T-Joint geometries were r anked with respect to their capability of withstanding UNDEX shock loading, the study included three basic geometries, allowing for the affects of non-monolithic construction due to jointing methods and material strain rate considerations. The study concluded that two of the joint geometries: the 45° chamfered and the 40 mm fillet preformed significantly better that the 22.5° chamfered geometry.
Degree Masters by Research
Institution RMIT University
School, Department or Centre Aerospace, Mechanical and Manufacturing Engineering
Keyword(s) Finite element
shock
UNDEX
underwater explosions
composite bonded joints
GRP
ship hull
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