Multi-objective optimisation of carbon fibre sailing yacht masts

Abstract

Modern sailing yacht masts are lightweight structures, with specic properties that are tai- lored to the requirements of the overall rig and vessel. The three key objectives of mast design which are considered in this thesis are to minimise the mass and centre of gravity (COG) height of the structure, as well as achieving a mast bend shape and magnitude which complements the geometry of the sails. These objectives are functions of the cross-sectional geometry and composite layup of the mast. Design spaces that involve composite materials are often complex, due to the large number of design variables required to specify both the shape and laminate of the structure. The size of the design space makes assessing the trade-os between objectives dicult, especially when using a systematic, trial and error based approach. Multi-objective optimisation stud- ies provide a means of assessing the trade-os between objectives to better inform design decisions. A multi-objective optimisation methodology was developed for mast design using Dassault Systemes Isight, a multi-disciplinary optimisation tool. This method considers both the shape and laminate of the mast as design variables. A nite element (FE) model of the mast is developed in ABAQUS CAE to model the geometry changes of the mast, and approximate models are used to predict the response of the FE model for the optimisation study. Optimisation of the mast problem is carried out using an archive based micro-genetic algo- rithm. The resulting Pareto sets show that to minimise the COG height or improve the bend shape of a mast there is a mass penalty. A weighted sum function approach is used to select designs based on the trade-o information and observations are made about the dierences in the designs which occur when dierent objectives are prioritised. The nal design of the mast is selected based on the importance that is assigned to each objective by the designer. The methodology is applied to the design of a TP52 mast and compared to a baseline design from Southern Spars. The optimised design achieves a mass reduction of 4.4%, while also more closely tting the desired mast bend shape and magnitude.