Spectral attenuation report

When you solve a flow or coupled transient analysis, you can request the creation of spectral attenuation graphs to simulate noise reduction or acoustic wave propagation.

The spectral attenuation, SA, is a function of frequency, f, and is given by this equation:

Where:

• Pem(f) is the complex number of the fast Fourier transform of the emitted pressure at frequency f.

• Pre(f) is the complex number of the fast Fourier transform of the received pressure at frequency f.

• Pre*(f) is the complex conjugate of Pre(f).

To create the spectral attenuation graphs, you need to select the Spectral Attenuation check box that is located in the Report dialog box when the Type is set to Between Regions.

Note:

To create a spectral attenuation report, you must select constant time steps, because the software calculates the discrete frequencies using the time step value it assumes to be constant. To select constant time steps, select Constant from the Time Step Option list on the Transient Setup page in the Solution dialog box to let the software calculate the discrete frequencies.

Pressure as function of time	Pressure as function of frequency
Spectral attenuation as function of frequency

After the solve, the software saves the following graphs in the run directory:

• The emitted and received pressures as functions of time in flowsppsig.png.

• The fast Fourier transform of the emitted and received pressures as functions of frequency in flowsppspec.png.

• The spectral attenuation as a function of frequency in flowspatt.png.

The [simulation name]-[solution name].GroupReport.htm and GroupReport.csv files contain the tabulated data.

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