Different hammer tips | Introduction to modal analysis | Part 5 

1.: Yes, the procedure is correct. If you want to know the damping for each resonance, this can be done using the averaged FFT. The overall damping can be determined from the time signal. 2.: The advantage of the hammer test lies in the ability to calculate a Frequency Response Function (FRF) using controlled excitation, where both input and output are known. A curve fitter can then process the measured FRF and accurately calculate resonance and damping for each mode.

@HEADacousticsInternational Thanks for the response, brother. 1: Okay, totally got it. 2: Without the hammer, we are getting the time vs. frequency data and then converting it to FFT in OriginLab, as there is only one output response. Now, with the hammer impact, we will have input data for the impact (force) and the output data we are already getting. How can we combine them into one FFT? Is there any method for this? Also the FRF would be only for force( input) or for both?

The FRF H(f) takes into account both input and output. There are multiple ways to calculate it. First, the FRF can be approximated by direct division of your input spectra I(f) and output spectra O(f): H(f) ≈ O(f)/I(f). This can however lead to instable results under certain conditions, e.g. when the input spectrum is close to zero for specific frequencies. The robust and accurate way is calculating the FRF based on the auto and cross spectra of input and output. The cross spectrum of input and output is: S_IO(f) = I(f) * O_conj(f), where O_conj is the complex conjugated output spectrum. The input auto spectrum is: S_II(f) = I(f) * I_conj(f), where I_conj is the complex conjugated input spectrum. Division of the two yields the FRF: H(f) = S_IO(f)/S_II(f). By the way, if you want to give this a try in ArtemiS SUITE, you might want to consider applying for our modal trial: www.head-acoustics.com/modal-analysis . All you need is your recorded time data, and we can provide the required software modules. 30 days free of charge.

@@HEADacousticsInternational How to request a 30 days free trial?

Keep it simple and make it clear. Danke für die sehr sehr gute Rückmeldung

É verdade, professor! hahaha Estou aqui fazendo análise modal experimental e aprendendo com os vídeos também

@@vitormateusmartini3946 Bom receber notícias suas, Dr! Quando tiver um tempo escreva contando o que está fazendo e quando ocorre a defesa!

Depends on what frequency you want to stimulate