Identification of localized nonlinearity for dynamic analysis of structures

Download
2013
Aykan, Murat
Most engineering structures include nonlinearity to some degree. Depending on the dynamic conditions and level of external forcing, sometimes a linear structure assumption may be justified. However, design requirements of sophisticated structures such as satellites, stabilized weapon systems and radars may require nonlinear behavior to be considered for better performance. Therefore, it is very important to successfully detect, localize and parametrically identify nonlinearity in such cases. In engineering applications, the location of nonlinearity and its type may not be always known in advance. Furthermore, as the structure will be excited from only a few coordinates, the frequency response function matrices will not be complete. In order to parametrically identify more than one type of nonlinearity which may co-exist at the same location with the above mentioned limitations, a method is proposed where restoring force surface plots are used which are evaluated by describing function inversion. Then, by reformulating this method, a second method is proposed which can directly evaluate the total describing function of more than one type of nonlinearity which may co-exist at the same location without using any linear frequency response function matrix. It is also aimed in this study to use the nonlinearity localization formulations for damage localization purposes. The validation of the methods developed in this study is demonstrated with case studies based on simulated experiments, as well as real experiments with nonlinear structures and it is concluded that the methods are very promising to be used in engineering structures.

Suggestions

Parametric identification of nonlinearity in structural systems using describing function inversion
Aykan, Murat; Özgüven, Hasan Nevzat (Elsevier BV, 2013-10-01)
Most engineering structures include nonlinearity to some degree. Depending on the dynamic conditions and level of external forcing, sometimes a linear structure assumption may be justified. However, design requirements of sophisticated structures such as satellites may require nonlinear behavior to be considered for better performance. Therefore, it is very important to successfully detect, localize and parametrically identify nonlinearity in such cases. In engineering applications, the location of nonlinea...
Development and comparative evaluation of a new structural modification method in application to aircraft structures
Köksal, Sertaç; Özgüven, Hasan Nevzat; Department of Mechanical Engineering (2006)
In the development of engineering products, it is necessary to predict dynamic properties of the modified structures. Achieving such predictions by using the structural properties of the original structure and information on the modifications is commonly referred to as structural modification analysis. In this thesis, Özgüven’s Structural Modification Method and Sherman-Morrison Method are selected as exact methods for structural modifications to predict the dynamics of a locally modified structure. Also, a...
Identification of nonlinearities in structural dynamics by using artificial neural networks and optimization
Koyuncu, Anıl; Özgüven, Hasan Nevzat; Ciğeroğlu, Ender; Department of Mechanical Engineering (2013)
Many real life engineering structures exhibit nonlinear behavior in practice. Although there are sophisticated methods including the effect of nonlinearities on dynamic response of structures in literature, uncertainties about nonlinear elements make further investigation necessary for modeling nonlinearity, and this is usually achieved by using experimental data taken from real systems. Therefore, identification of nonlinearities -determining location, type and parameters of the nonlinear elements- is crit...
Investigation of model updating techniques and their applications to aircraft structures
Kozak, Mustafa Tuğrul; Özgüven, Hasan Nevzat; Department of Mechanical Engineering (2006)
Mathematical models that are built in order to simulate the behavior of structures, most often, tend to respond differently than the actual structures in their initial state. In order to use the mathematical models and their computational outputs instead of testing the real structure under every possible case, it is mandatory to have a mathematical model that reflects the characteristics of the actual structure in the best possible way. In this thesis, the so called model updating techniques used for updati...
Structural coupling of two nonlinear structures
Tepe, Çağrı; Ciğeroğlu, Ender; Department of Mechanical Engineering (2018)
In mechanical design, modelling and analysis of a complex structure can be simplified with dividing the structure into substructures; therefore, any change in the structure can be addressed easily which is referred as “structural coupling”. Utilization of proper coupling techniques, it is possible to understand the behavior of the whole structure by considering the behavior of its substructures. For linear structures, coupling is a common technique; however, in most of the engineering structures, nonlineari...
Citation Formats
M. Aykan, “Identification of localized nonlinearity for dynamic analysis of structures,” Ph.D. - Doctoral Program, Middle East Technical University, 2013.