Modelling and Analysis Capabilities for Lightweight Masts

Abstract : This study was undertaken to address modelling and analysis capabilities for metallic and composite mast structures, required by DREA in their effort to investigate lightweight masts for the Halifax Class frigate, as part of midlife refit. The study focussed on three main areas. First, a review of finite element formulations for composite shell structures was performed to provide an understanding of the kinematic theories, failure and damage mechanisms, and element types that can be suitably used for composite mast structures. Next, an overview of metallic and composite mast structures used world-wide was undertaken to identify various mast configurations and finally, the design and development of a prototype mast analysis software (MAST AS) was implemented. It was shown that finite elements based on the Equivalent Single Layer (ESL) theories, such as the classical laminate plate (CLPT) and first order shear deformation theory (FSDT) can provide reasonable approximations of global response quantities, such as natural frequencies, buckling loads, strain energy and global displacements. On the other hand, higher order ESL theories or layerwise theories would be required to compute detailed stresses at cutouts, connections and other critical locations. It was also shown that for better accuracy of modelling damage in composites, it is necessary to use progressive failure concepts. There are four main types of masts, namely, polemasts (stayed and unstayed), tripod, lattice, and enclosed masts used on naval ships. The polemast, the simplest form of mast, is found on naval ships, including some auxiliary Canadian vessels. The lattice mast is by far the most common type found on Canadian as well as other navy ships. The tripod mast, which has the advantage of requiring smaller space for installation (compared to the lattice mast) is found mainly on ships of the US Navy but not Canadian ships.