modelling vibration of a crane that I described as a mdof with mass stiffness and damping. Now I need to find the damping. I attempted Rayleigh approach but did not get far as I only have one damping ratio for the single decay curve.
It depends what you need to have in result. If you investigate overall response by first mode, then MDOF is not needed at all. Otherwise, if you have to analyse response at every natural mode, you need FRF. Firstly, try to assign damping inversely proportion to natural frequencies and with such values so that to approximate your overall decay curve.
Hi Alex
You are absolutely right - with an overall decay curve you have too little data to get very far.
Feel free to take a look here for some ramblings of mine regarding damping.
http://qringtech.com/2014/06/22/designed-damping-types-mechanisms-application-limitation/
You may want also to look at previous discussions on damping here on RG - it is a recurring theme, e.g..
https://www.researchgate.net/post/How_can_i_calculate_the_elastic_stiffness_and_effective_damping_of_high_damper_bearing_isolater_in_sap_or_csi
https://www.researchgate.net/post/How_we_can_measure_damping_coefficient_for_any_material_by_simple_way
https://www.researchgate.net/post/How_can_we_find_the_eigenvectors_and_eigenvalues_when_have_unknow_values_in_damping_matrix
https://www.researchgate.net/post/What_is_the_relation_between_bending_damping_and_torsion_damping_of_a_circular_beam
Hope this helps
Claes
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