1. A method of designing a structure, the method comprising: a. generating a first set of candidate designs in a first optimisation process, each candidate design comprising a set of M design variables associated with an M-dimensional design space; b. selecting a subset of the first set of candidate designs; c. using the selected subset of candidate designs to define an N-dimensional design space defined by N design variables, N being less than M; and d. generating a second set of one or more candidate designs in a second optimisation process, each candidate design comprising a set of N design variables associated with the N-dimensional design space.