Development and Investigation of Algorithms for Modal Identification of Linear Systems with a Local Nonlinear Mechanism

Kurzfassung

Vibration testing is a crucial step within the admission process of an aircraft. Before certification, these tests are essential to validate the existing numerical models and to ensure flutter clearance to guarantee the safe operation of the system. Currently, these tests are performed within the so called Ground Vibration Test, where the aircraft is under operational-like boundary conditions and excited in a hangar with shakers to identify the modal parameters of the system. However, these procedures are very time intensive and take place during a period of aircraft development that is very time critical. To circumvent this problem, the DLR has developed a new method that promises to save time, named Taxi Vibration Test. During this process, the aircraft merely taxis over the uneven runway. The occurring vibrations are recorded by sensors. Complex algorithms are then used to identify the modal parameters. In contrast to the Ground Vibration Test where the aircraft is hung up with cords to imitate the boundary conditions, the nonlinear landing gear is involved within the system which influence the modal parameters. Since the algorithms used for this purpose are formulated for linear systems, this work addresses the problem in which various methods are developed and investigated to identify the overall nonlinear system within the Taxi Vibration Test. In doing so, a promising algorithm is presented that can identify the nonlinearity for the most part.