I have a fixed-fixed I beam , I need to extract experimentally its Rayleigh damping coefficients using a trivial and effective setup. I have done the modal analysis using ANSYA 22R1
Mohamed A M Salem Rayleigh damping is a rather artificial kind of damping. The major advantage is the fact that the normal modes simultaneously diagonalize the mass, stiffness and damping matrix. Usually, two natural frequencies are used to determine the Rayleigh parameter \alpha and \beta.
Nils Wagner
appreciated for your concern, I need to know the most trivial technique to measure it experimentally for such structure case
Mohamed A M Salem You might use https://github.com/sdypy/sdypy-EMA to extract modal damping information from the FRFs of your experimental modal analysis. Good luck.
The simplest, and most time consuming method, is just to extract the half power badwidth and calculate the Q values or loss factos eta for each mode. This will work for separate modes and becomes difficult when the modes overlap significanlty.
A second fast method is to measure the structural reverberation of the modes driven by an impact or a pull of some sort. This method gives the loss factor or Q in given frequency bands as an ensemble average. It is much used in room acoustics as the 3D room have a rather high modal density, at least above a given frequency.
On structures it may be a bit more tricky. Fairly wide bands needs to be used, like octave bands, as the filters needs to be faster than the modes in the object tested in its time response, unless you will get the RT of the filter not the object.
A third method is the power injection method. I do not know the details there, nor have I used it. But I know it is a possibility.
A fourth method is to do a modal analysis and extract the modal parameters there, already mentioned above.
Hi
I’d say, it is a tough nut to crack as Rayleigh damping is not based on any known physical damping mechanisms, ie it is a purely mathematical construct and thus, hard to make meaningful tests on.
As suggested by other authors, one can measure damping using a variety of methods, some standardisEd, other not. Then, damping has to be translated from one mechanism to the other, which can only be done at resonance.
Hope this helps
Claes
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