1. A computer-implemented method of modelling the non-linear structural response of a stiffened panel, the method comprising: determining one or more intermediate boundary conditions for application to an intermediate mesh by extracting in-plane nodal forces from a linear finite element analysis of a global mesh subject to one or more global boundary conditions, wherein the one or more global boundary conditions are determined based on an out-of-plane load; performing a linear finite element analysis of the intermediate mesh subject to the one or more intermediate boundary conditions; determining one or more local boundary conditions for application to a local mesh, the one or more local boundary conditions being determined on the basis of the linear finite element analysis of the intermediate mesh and the out-of-plane load; and performing a non-linear finite element analysis of the local mesh subject to the one or more local boundary conditions; wherein the global mesh is associated with a global domain representing a real-world structure comprising the stiffened panel, the intermediate mesh is associated with an intermediate domain which is a sub-domain of the global domain, and the local mesh is associated with a local domain which is a sub-domain of the intermediate domain.