Design of composite cylindrical shells to meet given cross sectional stiffness properties

This paper examines the design of 4-ply composite cylindrical shells to meet given cross-sectional stiffness properties from both analytical and computational perspectives. This problem has many similarities to the design of composite helicopter rotor blades, namely that the structure is designed to meet given cross-sectional stiffness values, that the design space for the unsimplified problem is discrete, and that the objective function may be non-linear and non-convex. Ignoring stacking sequence effects reduced the dimensionality of the design space. A discrete search of this reduced design space was then performed, which showed that the problem became convex if stacking sequence is ignored. This allows deterministic optimisation methods to be used, which is considerably more computationally efficient than stochastic methods. The response of a single objective function to the design variables was highly non-linear. By contrast, a linear approximation very closely modelled the response of each individual target variable (e.g. EA, EI, GJ) to the design variables (e.g. shell radius, ply thicknesses). The problem was therefore reformulated into a number of simultaneous linear equations that are easily solved by matrix methods, thus allowing an optimum to be located with a minimum number of computationally expensive finite element analyses.