Using the Random Decrement Technique on Short Records with Varying Signal-to-Noise Ratios

Quantifying mass changes with ambient vibration measurements

“…To track weak non-linear modal behaviour, the short-time random decrement technique (ST-RDT), a time-domain equivalent of the short-time Fourier transform [22] and an expansion on the conventional random decrement technique (RDT) [20], has been developed. In the conventional RDT, as with many time-domain OMA methods, the properties of the dynamic system are assumed to be constant over the length of the data set and therefore a longer data set will result in more accurate modal estimates [23][24][25]. However, in the case of weak non-linear modal behaviour, analysing long periods of data may mask variations in the modal parameters of the system.…”

“…A key di↵erence between real-world structures and the experiment presented in the previous structures is that it is rare for the excitation force to be constant. A non-continuous excitation force will lower the signal-to-noise ratio of the signal, which for the conventional RDT has been shown to increase the error in the modal estimates [25]. This increased error in the modal estimates is likely to occur for the ST-RDT and may necessitate the use of a longer window of data.…”

Modal identification with uncertainty quantification of large‐scale civil structures via a hybrid operation modal analysis framework

“…Moreover, the RDT can correlate the modal properties with structural vibration amplitudes by adopting different triggering conditions for the same response and thus is widely used to detect structural amplitude dependency or nonlinearity 16,17 . In contrast, the NExT is equivalent to a specific RDT having a trigger window containing the full range of structural amplitudes of selected responses, thus resulting in missing the amplitude‐dependent information 18 . On the other hand, the RDT usually requires a long enough response measurement duration to obtain reliable RDS since a sufficient number of segments are needed for its sample averaging step, while the NExT can realize this with a relatively short response duration 1,19 .…”

“…16,17 In contrast, the NExT is equivalent to a specific RDT having a trigger window containing the full range of structural amplitudes of selected responses, thus resulting in missing the amplitude-dependent information. 18 On the other hand, the RDT usually requires a long enough response measurement duration to obtain reliable RDS since a sufficient number of segments are needed for its sample averaging step, while the NExT can realize this with a relatively short response duration. 1,19 Thus, the NExT-driven method is typically used to evaluate the time-variant features of large-scale structures subjected to extreme events by applying it to each short time window and sliding the time window to traverse the measured data.…”