Partial safety factor approach to the design of submarine pressure hulls using nonlinear finite element analysis

A framework for the design of submarine pressure hulls using nonlinear finite element (FE) analysis is presented in order to improve upon the conventional analytical–empirical design procedure. A numerical methodology is established that allows the collapse pressure of a hull to be predicted with controlled accuracy. The methodology is characterized by quasi-static incremental analysis, including material and geometric nonlinearities, of FE models constructed from shell elements. The numerical methodology is used with ANSYS to predict the results of 47 collapse experiments on small-scale ring-stiffened cylinders representative of submarine hulls. A probabilistic analysis is applied to the experimental–numerical comparisons in order to estimate the accuracy of the FE methodology and derive a partial safety factor (PSF) for design. It is demonstrated that a high level of accuracy, within 10% with 95% confidence, can be achieved if the prescribed FE methodology is followed. Furthermore, it is shown that the PSF for design does not need to be very large, even if a high degree of statistical confidence is built in. The designer can be 99.5% confident that the FE error has been accounted for by dividing the predicted collapse pressure by a PSF=1.134.

► FE pressure hull collapse predictions are accurate within 10% with 95% confidence.
► FE predictions improve when perturbing defects or damage exist in the hull.
► Partial safety factor of 1.134 gives 99.5% confidence that error is accounted for.