INVESTIGATION OF DECOUPLING TECHNIQUES FOR LINEAR AND NONLINEAR SYSTEMS


Thesis Type: Doctorate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Mechanical Engineering, Turkey

Approval Date: 2018

Student: TANER KALAYCIOĞLU

Supervisor: HASAN NEVZAT ÖZGÜVEN

Abstract:

Structural coupling methods are widely used in predicting dynamics of coupled systems. In this study, the reverse problem, i.e. predicting the dynamic behavior of a particular subsystem from the knowledge of the dynamics of the overall system and of all the other subsystems, is studied. This problem arises when a substructure cannot be measured separately, but only when coupled to neighboring substructures. The dynamic decoupling problem of coupled linear structures is well investigated in literature. However, decoupling of coupled structures that include a nonlinear element such as clearance, friction and nonlinear stiffness still remains untouched. In this thesis, firstly, decoupling techniques for coupled linear structures are investigated. Two new methods for decoupling of coupled linear systems are introduced and their performances were compared to those of the best decoupling methods known in literature. Then, the dynamic decoupling problem of coupled nonlinear structures is considered for the first time. A method is developed for calculating FRFs of a substructure decoupled from a coupled nonlinear structure involving any type of nonlinearity that can be modelled as a single nonlinear element. Depending on where the nonlinear element is, i.e., either in the known or unknown substructure, or at the connection, the formulation differs. Firstly, applications of the method are demonstrated on nonlinear lumped parameter systems using simulated experimental data. Then, real-life applicability of the proposed method is shown through two nonlinear experimental test structures. Finally, the method is applied on a real-life engineering problem in order to demonstrate its performance.