Future high-speed flight vehicles will be exposed to extreme environments with aerodynamic heating, static, and dynamic loading. The resulting structural response can exhibit significant nonlinear deformation. As a consequence, detailed simulations of long portions of the vehicle's trajectory must be performed to account for path-dependent structural response. Recent developments in nonlinear reduced-order models (ROMs) have demonstrated orders-of-magnitude reductions in computation time for acoustic response prediction simulations. These models are relatively insensitive to small imperfections. Conversely, the generalized finite element method (GFEM) provides a framework to model local effects such as stress risers and cracks without geometric dependency on the finite element (FE) mesh. A more general version of the GFEM, with numerically-built enrichment functions provides a multi-scale modeling capability through a simple, direct coupling of global and local FE models. Replacing the component FE model with a ROM will allow for efficient computation of dynamic response while providing the necessary information to drive local, solid analyses which can zoom in on regions containing stress risers, as deemed necessary. This paper describes the coupling of these two approaches (ROM/GFEM).
NomenclatureA i jk r = cubic stiffness coefficients B i j r = quadratic stiffness coefficients E = Young's Modulus f f f = external force vector G = energy release rate H 1 (ω α )= first order Hilbert space defined on ω α K K K = linear stiffness matrix K I , K II , K III = mode 1,2 and 3 stress intensity factors K K K1 1 1, , , K K K2 2 2 = quadratic and cubic stiffness matrices L αi = enrichment function defined on ω α M M M = mass matrix M = number of patches x x x belongs to m α = number of enrichment functions used for node α N = number of degrees-of-freedom in FE model n = number of modes q q q = vector of modal coordinates S GFEM = generalized FE approximation space t = time u u u = displacement field u u u hp = FE approximation of u u u w w w = displacement vector x x x = point in space α = index of node in FE mesh Γ Γ Γ = modal damping matrix θ θ θ = nonlinear function vector θ = angle along crack front Λ Λ Λ = modal stiffness matrix ν = Poisson's ratio Ψ Ψ Ψ = mode shape matrix ϕ α = FE partition of unity function φ αi = generalized FE shape function χ α = local approximation space on ω α Ω = solid, FE domain ω α = set of elements connected to node α