Fig nbsp xA The measured
Fig. 6. The measured signal of ABT 702 1: (a) acceleration with time and (b) the receptance frequency response functions.Figure optionsDownload full-size imageDownload as PowerPoint slide
5.1. Case 1: modal parameters estimation using reconstructed signal when the structure is in air
Fig. 7. Magnitude and phase angle plotted against the frequency of the new reconstructed signal when the structure is in air.Figure optionsDownload full-size imageDownload as PowerPoint slide
The estimated frequencies are 15.39, 16.93 and 23.60 Hz, and the damping ratios are 0.0069, 0.0009 and 0.0039. The following section consists of a study of the changes of these three expected-order modal parameters with a 6 × 6 Hankel matrix for the ERA.
5.2. Case 2: modal parameters estimation using reconstructed signal when the structure is in still water
To study the performance of the structure in water and ensure the comparability of modal parameters to that obtained in air, the simplest way is to place the structure in still water (with a water depth equal to 1.2 m) and excite the structure using the same method and in the same direction, which also includes using the same sensors for data collection. Fig. 8 shows the measured signal of the same sensor and its frequency performance when the structure is in still water based on the excitation of a hammer.