This conference paper was submitted for presentation at the NAFEMS World Congress 2025, held in Salzburg, Austria from May 19–22, 2025.

Abstract

Since multiple years, the Airbus Test Center Bremen successfully performs aircraft physics Virtual Testing (VT). The approach of VT by means of computer simulations of physics-based models has been applied for all major aircraft development programmes of the last years since the Airbus A380. In the given context and for the questions of interest, flexible multibody simulation (MBS) has been identified as one of the preferred simulation methods. Compared to Finite Element Model (FEM) simulations, the application of enforced displacement data as well as distributed airloads on flexible bodies can be challenging in MBS, especially if the model and the applied boundary conditions are to be kept separate from each other. In FEM simulations, the different model components are generally assembled by means of include statements immediately before solving, hence providing an ideal separation between the structural definition of the considered product and the applied boundary conditions. Whereas in MBS simulations, besides the definition of the mechanism under consideration, also the applied loads and displacements are generally merged into the model and defined inside the model. In consequence, this requires updates of the complete model in case of updated boundary conditions and easily leads to an undesirable high number of model variants and/or models which are cramped with boundary conditions. The paper describes the selected approach to maintain the separation of model and boundary conditions by means of user subroutines for application of loads and enforced displacements. It gives an overview of the different approaches for application of different representations of airloads on different representations of flexible bodies. It focuses on the approaches for application of lumped force vectors on flexible bodies based on 1D beam elements by scaled, triangular sets of modal forces as well as flexible bodies based on 2D shell elements by distribution via rigid body elements. Besides that it introduces an approach for application of enforced displacements originating from linear FEM calculations under approximation of geometric nonlinearity.