Early observation of modal parameter changes by an enhanced frequency evaluation algorithm

Abstract

By monitoring the vibration response of mechanical or civil engineering systems, the modal parameter changes due to materials or geometrical properties can be observed. Fine frequency shift identification is decisive to determine particularly small changes and thereby small cracks or damages. This paper firstly presents some existing methods to accurately find the frequency values. All these methods show non-linear, relevant errors in interpretation. Afterward a simple method is proposed, consisting in iterative decreasing of the number of samples from the original signal, performing a standard frequency analysis for each truncated signal and finally overlapping of achieved spectra. Thus, the resulted spectrum has a much fine resolution due to the important addition of spectral lines. In this way a more accurate identification of frequencies is possible. In fact, the relevant frequency is accomplished under a lobe shape. In the peak position of this lobe the best frequency value can be clearly identified. With the help of these more accurate frequency values, modal analysis becomes more reliable and efficient.