STUDY OF THE EFFECT OF MASS DISTRIBUTION, PATH OF ENERGY AND DYNAMIC COUPLING ON COMBINED COHERENCE (A NON-LINEARITY DETECTION METHOD)
Suresh Babu Chennagowni · OhioLink ETD Center (Ohio Library and Information Network) · 2006
Almost all practical systems are non-linear to some extent with the non-linearity being caused by one or a combination of factors.If the system is non-linear, errors are introduced in the data analysis and are observed during the modal tests of a structure.For example, high forcing levels may cause the frequency response function estimates to show non-coherent behavior over certain frequency bands.A new coherence function (Combined Coherence) provides a method to separate the effects of structural nonlinearities and the digital signal processing errors.Thomas Roscher [1] applied the combined coherence formulation to theoretical data generated from a lumped parameter (M, K, C) with static coupling.The results showed improvement in the combined coherence function over the ordinary coherence, but when Doug Coombs [2] applied combined coherence to a real world structure, it did not show improvement.In this thesis, as an extension of previous work, study is done on theoretical data generated from a lumped mass model with dynamic coupling.The effects of mass distribution, spatial density, forcing level, location of forcing function, path of energy and the dynamic coupling on the combined coherence are studied.The testing cases include SIMO and MIMO cases for a MDOF simulink model with a cubic hardening type of nonlinearity applied at different locations.Combined Coherence is calculated for a non-linear model and effects on the combined coherence are studied for the following cases.• Effect of varying the force input