Development of a model updating technique for nonlinear systems

Thesis Type: Doctorate

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

Approval Date: 2015




In structural dynamics, obtaining an accurate numerical model is very crucial. However there are usually discrepancies between calculated dynamic behavior from numerical models and the ones obtained experimentally, and therefore it will be necessary to update the numerical models. In real life applications, structures usually have nonlinearity, and for nonlinear structures, in order to update the numerical model, firstly nonlinearity in the structure can be identified, and then updating procedure may be applied to the linear part of the model. Application of such an approach may not be straightforward, especially for nonlinear systems having multiple nonlinearities including friction type of nonlinearity. In this thesis, a new model updating technique for nonlinear structures that have multiple nonlinearities including friction type of nonlinearity is developed. The method identifies multiple nonlinearities in the structure and simultaneously extracts the FRFs of the underlying linear system. The accuracy of the method developed is first verified by using nonlinear lumped SDOF and MDOF systems, as well as with nonlinear structure using simulated experimental data. Then, as experimental studies,method developed is applied to a real test system and finally to an engineering system (nonlinear gun barrel of a battle tank). It is shown that, the method developed can be successfully applied both to a test system and to a complex engineering problem for obtaining an accurate nonlinear model. In conclusion, the validation and application of the model updating method developed for nonlinear structures are demonstrated successfully with both simulated case studies and experimental real life applications.