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Abstract

Do semi-empirical equations written in FORTRAN have a place in submarine design in the age of digital twins, genetic algorithms and coupled multi-physics simulations? Submarine programmes do not have the opportunity to build a prototype, due to the cost and time required to design and build a submarine the first boat manufactured is the first of class. As a consequence, submarine designs tend to be conservative and incremental in their development. The basic analytical design equations for UK submarine pressure hulls were developed in the 1960s, and coded into FORTRAN in the 1970s. These equations have been proven by model scale testing and physical trials and by continued operation of the current and previous classes of UK submarine. Over the last six years QinetiQ have worked closely with the UK Ministry of Defence (MOD) to migrate these semi-empirical equations written in FORTRAN from obsolete HPUX based hardware to modern PC based systems with new graphical and command line user interfaces. These tools have been verified against the legacy code, updated to reflect the current UK structural design standards and fully documented. These updates have provided a modern, intuitive and supported user interface to the legacy equations, enabling their continued use. The new interfaces have also enabled the equations written in FORTRAN to be linked to modern tools such as Isight for process automation and optimisation. This enables a design of experiment (DoE) or optimisation studies with ten thousand iterations to be run within a week using a known, trusted and well understood toolset. The migration and updates to these legacy tools have enabled them to be used in a way that would never have been considered when they were developed. The new approach enables a much wider exploration of the design space, and the ability to understand the sensitivity of the design to a given parameter. The capability has supported the development of a suite of automated Finite Element tools in Abaqus CAE Finite Element (FE) software, which automate and standardise the building and analysis of submarine pressure hull compartments. The ability to quickly and easily verify the FE analysis against the analytical tools for known cases has accelerated the development and confidence in the standardised FE process and by expanding the range of designs compared has started to identify the limitations of the analytical tools. Coupling the analytical and FE tools together using Isight enables a potentially powerful parametric design tool, which can quickly run large numbers of low fidelity analytical solutions to identify potential solutions for further evaluation using linear and non-linear FE analysis which could form the basis for a digital twin of the submarine structure for use to support the platform through life.

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