A Method for the Geometrically Nonlinear Computation of Maneuver Loads in Preliminary Design of Jet Transports

Kurzfassung

For conventional jet transports with low and moderate aspect ratio wings, linear structural methods are applied for the computation of static and dynamic loads. High Aspect Ratio Wings (HARW) will be indispensable for future civil transport aircraft to significantly increase efficiency; however, they introduce complexity in the design process due to the higher flexibility and demand (geometrically) nonlinear methods for the accurate computation of loads, especially when aerodynamic forces are calculated by high fidelity methods (CFD). As hundreds or thousands of load cases are typically computed in the loads and optimization process, a fast and robust structural method is required that captures nonlinearities due to geometrically large deflections. Regarding appropriate structural methods, the extended modal approach, which is based on higher order (mainly quadratic and cubic) mode components is eligible because it combines simplicity with accuracy. A drawback, however, is the complex computation the higher order mode components in pre processing. In this work, a new approach for the calculation of the higher order mode components is proposed which uses the nonlinear relationships between strains (or curvatures) and displacements from a geometrically exact beam theory (GEBT). The idea is to take the curvatures of a structural mode shape and to integrate them using successively simplified compatibility equations. In his way, the higher order mode components are directly obtained, and the costly pre-processing step with a series of nonlinear static simulations is circumvented. The method is applied to the computation of higher order mode components for a condensed structural (loads) model typically used in iterative loads and structural optimization processes.