GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 2.1 GNGTS 2024 2. The standard deviation of the distribution of azimuths where is maximized angle, , θ 0 across all the vibration periods is smaller than 20°. RESULTS With the proposed methodology, we identified 175 out of 456 (38%) directive events that exhibits a clear azimuthal pattern and frequency dependence, representing the signature of source directivity. Comparison with the previous analysis in FAS shows that the directivity analysis carried out in SA extends to wider bands and that the directivity peak itself, defined by the value of , is always higher than the corresponding peak in SA. For directivity modelling, we focus on the spectral trend of the parameter, which experimentally showed a curve that can be fitted with a Gaussian distribution, with the maximum value of , and the corresponding period called . Since according to Colavitti et al. (2022) depends on the magnitude and the amplitude of is proportional to the “strength” of the directivity, we need to normalize the parametrization curve for (period of the peak of the directivity) and (the peak itself). The normalized curves are shown in Figure 1 and represent on average a Gaussian-like pattern with non-negligible variability. We decided to adopt a fit model based on a Gaussian distribution of order 1 which is defined by the following equation: [3] = 1 * (− 10 ( )− 1 ( ) 1 ) 2 where represents the function to parametrize with respect to the parameter (where ), is the amplitude, the median value along and is a coefficient that = 10 1 1 1 controls the width of the gaussian distribution bell. Figure 1 shows the fit according to the first-order Gaussian constraining the model with and . In this way, is = 1 10 = 0 1 equal to 0.8229, which is the value for the median curve considering all the events.