Frequency-dependent physical quantities

All material properties and source amplitudes are frequency-dependent physical quantities, such as in the functions:

• add_volume_material!
• add_surface_material!
• add_sound_source!

There are three ways to specify them:

1. Function

It takes a real frequency value in Hz as its argument and returns some value that can be complex or not:

# traditional function
function c(f)
    return 343.0 + 0.5im * f^2/1000
end

# function in assignment form
rho(f) = 1.2 + 0.01im*f

# anonymous function
f -> 343.0 + 0.05 * sqrt(f)

add_volume_material!(s, physical_group=1, density=c, speed_of_sound=rho)

2. Constant

A plain scalar value (complex or not). Numav will treat it as uniform across all frequencies:

add_sound_source!(s, coordinates=[0.0, 0.0, 0.0], pressure=0.1)

3. Tabulated file (path string)

A String containing the path to a plain-text CSV-like file with three columns: frequency, real, and imag. Numav reads the table and interpolates between the provided data points at each required frequency step. There is no header row.

  0, 1, 2
 25, 1, 2
 50, 5, 1
 75, 3, 2
100, 1, 0

add_sound_source!(s, physical_group=1, pressure="data/pressure.txt")

The file format rules are:

• Three columns separated by commas: frequency (Hz), real part, imaginary part.
• No header row.
• For purely real quantities (e.g. density), set the imag column to 0.