Improving the accuracy of the n-dB method for determining damping of non-lightly damped systems

Accuracy and robustness of four basic single degree of freedom methods for determining the modal parameters of non-lightly damped systems

“…Most commonly n ¼3 dB, but smaller values may be used, see [5,8,14], and here n ¼{1 dB, 3 dB}. The performance of…”

“…In order to calculate F, two additional frequencies are required, one lower and one upper with respect to the modal frequency, designated G l /mS and G u /mS , respectively. There are two damping estimators; these could be referred to as ''approximate'' and ''exact'' (as denoted in [14]) as they have their historical origins in the development of damping measurement applied to lightly damped systems [7,14]. However, in some cases it will be seen that applying the ''approximate'' estimator is more accurate than applying the ''exact'' one.…”

“…[14] they are applied to the spectral magnitude), but are defined here so that they may be applied to different methods and spectra. Two of the measurement methods used here define G l /mS and G u /mS from a threshold relative to the peak response, and the definition Table 1 Summary of the four measurement methods and their variations used to measure modal frequency and damping, when applied to quadrature corrected spectrum (Q), along with a summary of the notation used for the frequency (G) and damping (F) operators.…”

“…The dual-damping model used here has been previously applied [1,14]. Here it is extended to the three response parameters.…”

“…The current authors have studied and improved the obtainable accuracy of modal measurements made using a commonly applied method based on the spectral magnitude. This was achieved by correcting the inaccurate measured value itself [14], although this technique is outside the scope of this paper.…”