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noise

The noise utility requires the FFTW library to compute Discrete Fourier Transforms (DFTs). Building of the noise utility is skipped if the FFTW library was not found during OpenFOAM installation.

Overview​

The noise utility processes point and surface pressure data to generate:

  • Root Mean Square (RMS) pressure [Pa];
  • Sound Pressure Level (SPL) [dB];
  • Power Spectral Density (PSD) in [Pa2^2/Hz] and/or [dB/Hz]; and
  • 1/3 Octave SPL data, whereby the bins are constrained to pass through the centre frequency at 1 kHz.

Input data can be windowed using a run-time selectable model, where options include:

  • Uniform;
  • Hanning, with options including symmetry, and extended (non-zero at the end-points); and
  • window overlap.

Usage​

Command line usage:

note

Option lists are generated from noise -help in a sourced OpenFOAM environment. Run npm run refresh-help-snippets to update the snippet below.

Usage: noise [OPTIONS]
  -help  Display short help and exit

The noise utility is configured using a <case>/system/noiseDict taking the general form:

noiseModel      <modelType>

<modelType>Coeffs
{
    // Model-specific entries (see below)
    // `````````````````````````````````~

    ...

    // Common entries
    // ````````````~~

    windowModel     Hanning;

    HanningCoeffs
    {
        // Window overlap percentage
        overlapPercent  50;
        symmetric       yes;
        extended        yes;

        // Optional number of windows, default = all available
        nWindow         5;
    }

    // Input files list
    files       ("postProcessing/faceSource1/surface/patch/patch.case";)


    // Optional entries
    // ```````````````~

    // Reference density (for incompressible cases); default = 1
    rhoRef      1;

    // Number of samples in sampling window; default = 2^16 (=65536)
    N               4096;

    // Lower frequency bound; default = 25 Hz
    fl              25;

    // Upper frequency bound; default = 10000 Hz
    fu              10000;

    // Start time
    startTime       1;

    // Minimum pressure
    minPressure     0;

    // Maximum pressure
    maxPressure     100000;

    // SPL weighting; default = none
    SPLweighting    dBA;

    // Reference for dB calculation; default = 2e-5
    dBRef           2e-5;

    // Output prefix; default = ""
    outputPrefix    "source1";

    // Write options
    writeOptions
    {
        writePrmsf      yes;
        writeSPL        yes;
        writePSD        yes;
        writePSDf       yes;
        writeOctaves    yes;
    }
}

SPL Weighting​

SPL data can be weighted using the SPLweighting entry, where options include:

A weighting​

SPLweighting    dBA;

The gain is computed as:

A(f)=20log⁡10(RA(f))−20log⁡10(RA(1000)),A(f) = 20\log_{10}(R_A(f)) - 20 \log_{10}(R_A(1000)),

where

RA(f)=121942f4(f2+20.62)(f2+107.72)(f2+739.92)(f2+121942).R_A(f) = \frac{12194^2 f^4}{(f^2 + 20.6^2)\sqrt{(f^2 + 107.7^2)(f^2 + 739.9^2)}(f^2 + 12194^2)}.

B weighting​

SPLweighting    dBB;

The gain is computed as:

B(f)=20log⁡10(RB(f))−20log⁡10(RB(1000)),B(f) = 20\log_{10}(R_B(f)) - 20 \log_{10}(R_B(1000)),

where

RB(f)=121942f3(f2+20.62)(f2+158.52)(f2+121942).R_B(f) = \frac{12194^2 f^3}{(f^2 + 20.6^2)\sqrt{(f^2 + 158.5^2)}(f^2 + 12194^2)}.

C weighting​

SPLweighting    dBC;

The gain is computed as:

C(f)=20log⁡10(RC(f))−20log⁡10(RC(1000)),C(f) = 20\log_{10}(R_C(f)) - 20 \log_{10}(R_C(1000)),

where

RC(f)=121942f2(f2+20.62)(f2+121942)R_C(f) = \frac{12194^2 f^2}{(f^2 + 20.6^2)(f^2 + 12194^2)}

D weighting​

SPLweighting    dBD;

The gain is computed as:

D(f)=20log⁡10(RD(f)),D(f) = 20\log_{10}(R_D(f)),

where

RD(f)=f6.8966888496476e−5h(f)(f2+79919.29)(f2+1345600),R_D(f) = \frac{f}{6.8966888496476e-5}\sqrt{\frac{h(f)}{(f^2 + 79919.29)(f^2 + 1345600)}},

and

h(f)=(1037918.48−f2)2+1080768.16f2(9837328−f2)2+11723776f2.h(f) = \frac{(1037918.48 - f^2)^2 + 1080768.16 f^2}{(9837328 - f^2)^2 + 11723776 f^2}.

Output​

All possible data is written by default. The writeOptions sub dictionary can contains a list of boolean entries to select results individually.

// Write options
writeOptions
{
    writePrmsf      yes;
    writeSPL        yes;
    writePSD        yes;
    writePSDf       yes;
    writeOctaves    yes;
}

The plain text output files created by the pointNoise model and the surfaceNoise model's surface averaged data include a header section that provides case information, e.g. for the average surface RMS pressure:

# f [Hz] vs P(f) [Pa]
# Lower frequency: 2.50000000e+01
# Upper frequency: 5.00000000e+01
# Window model  : Hanning
# Window number : 7
# Window samples: 128
# Window overlap %: 5.00000000e+01
# dBRef         : 2.00000000e-05
# Area average  : true
# Area sum      : 8.99999982e-02
# Number of faces: 400
# f                 P(f)

Further information​

Source code

See also

Tutorials