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Title: A feasibility study on applying real-time dynamic substructuring to a nonlinear landing gear fuselage system
Author: Terkovics, Nándor
ISNI:       0000 0004 5917 120X
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2014
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Aircraft nose landing gear must be tested for shimmy oscillations experimentally. Current test methods consider the landing gear as stand alone systems without the possibility of accounting for the dynamics of the fuselage which they are attached to. This means that all possible interaction between them is ignored during the experiment which, if the interaction for specific conditions is significant, might reduce the reliability of the test results. On the other hand, conducting a full scale experiment on the aircraft would be impractical due to size and related costs. In this thesis the nonlinear interaction between the nose landing gear and the airframe is explored and the feasibility of the real-time dynamic substructuring test method to this particular system is discussed. Due to the nonlinearities involved, the applied method in the majority of this work is bifurcation analysis. First, a coupled nose landing gear-fuselage model is developed. It is a simplified two degree-of-freedom nose landing gear model coupled to the lateral component of the fuselage motion at the attachment point. By means of one- and two-parameter bifurcation diagrams it is demonstrated how the presence of fuselage dynamics may influence the behaviour of the landing gear - and vice versa, how the vibrations of the gear affect the dynamics of the fuselage - when key parameters of the system are varied. It is found that dynamic interaction between the two subsystems is possible. How significant this interaction is strongly depends on the characteristics of the fuselage dynamics. Owing to this interaction the application of the real-time dynamic substructuring method on the model is reasonable and, hence, its feasibility is explored numerically and analytically. In a substructuring test part of the system is kept as the physical test specimen while the remainder is simulated numerically. The numerical and physical substructures are connected via a transfer system (an actuator) and the interface is controlled in real-time to ensure that the dynamic behaviour of the substructured system replicates with high accuracy that of the system being emulated. The main challenge in a substructuring test is the delay arising from the response time of the actuator. The effect of the delay is analysed in terms of the proposed test configuration, which consists of the fuselage as the numerical model and the nose landing gear as the physical substructure; the latter is also represented by a simplified two degree-of-freedom model. It is found that the substructured system is extremely sensitive to the delay. In order to reduce the sensitivity, without modifying structural parameters, the numerical model is extended by an additional compliance, and the influence of this on the sensitivity is studied. By careful adjustment of the additional compliance, the robustness of the test can be improved; however, the accuracy may then be compromised.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available