Modeling and analysis of a geometrically nonlinear joined wing under thrust force

The joined-wing aircraft is an alternative configuration compared to general cantilevered configuration because of its superiority. In the present work, an efficient modeling method for flexible joined wing is proposed. The fully intrinsic formulation is applied for the geometrically nonlinear effect and the static indeterminacy of joined wing is addressed based on the force method. To avoid mathematically over-determined problem, an orientation compatibility condition with profound physical meaning is established and subsequently a strict mathematical proof is given for the existence and uniqueness of rotation. By adopting Peters finite inflow theory, the unsteady aerodynamic model for joined wing is built up. The joined-wing aeroelastic model is eventually represented by a set of differential-algebraic equations. Following validation studies show that although the displacements and rotations are excluded, contributing to higher computing speed than the mixed formulation, the numerical accuracy of present method is close to mixed formulation and superior to the incremental method. Finally, the static aeroelastic analysis for a planar joined wing under a thrust force at wingtip is implemented within flutter boundary. Results show that the thrust force can lead to an axial compressive load in front wing and the co-existing solutions are revealed because of the buckling of front wing when the thrust force exceeds a threshold value. Further studies indicate that although either solution path is possible theoretically, the "upward-bending solution" is a more likely practical solution for the planar joined wing.