Hydrodynamic loads on axisymmetric bodies with casings in translation
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Date
2017
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University of New Brunswick
Abstract
A comprehensive study was performed of hydrodynamic forces and moments on submarine hull geometries with casings in steady translation using an enhanced database consisting of experimental and computational results. The objective was to develop a hydrodynamic load estimation method that allows for the rapid simulation of the performance characteristics of underwater vehicles. This is an important step in determining the safe operating envelope of submarines.
Accurate potential flow and viscous flow results of the geometries of interest were performed at varying incidence and orientation angles. The simulations were verified by a mesh refinement study and validated against analytical solutions and experimental data. Potential flow was found to be a useful predictor of the effects of geometric asymmetric on the out-of-plane and in-plane force distributions and moments. The viscous simulations showed that casings, and hull asymmetries in general, have significant effects on the separation lines, surface pressure distributions, and wake topologies. These effects caused large variations in the in-plane loads and introduced out-of-plane loads. Increasing the casing width produced the largest changes in the in-plane and out-of-plane loads and wake topology.
Previous models were found to be unsuitable for the prediction of the in-plane loads on hulls with casings mainly due to their reliance on slender body theory. An alternative model was developed, which combined potential flow with viscous contributions to obtain the hydrodynamic impulse. The tail plane impulse, and therefore the hydrodynamic force, could be approximated with the first nine Fourier modes of the orientation angle. The hydrodynamic moment predictions were found to be accurate. The model was found to have difficulty in predicting the in-plane moment for small asymmetries such as a narrow casing.