Medium Properties

Use the node to specify the speed of sound and density of the medium. This node is created by default and includes all of the selected domains for the physics interface.

Pressure Acoustics Model

If the ray intensity or power is computed in the model, select an option from the list: (the default), , , , or . This section determines which additional fluid properties can be specified in this section.

The c (Si unit: m/s) is always required. By default it uses values . For enter a value or expression. The default is 343 m/s.

If the ray intensity or power is solved for, both the density and the speed of sound are required to compute the transmittance and reflectance at boundaries between different media. The default ρ (SI unit: kg/m3) uses values . For , enter a value or expression. The default is 1.2 kg/m3.

Additional inputs are shown in this section depending on the option selected from the list:

•

If is selected, absorption by the medium is neglected, so no other inputs are required.

•

If is selected, select an option from the list. The default is .

For enter a value or expression for the α (SI unit: Np/m). The default is 0. Note that this is the attenuation coefficient of the pressure amplitude rather than the intensity. The ray intensity (neglecting wavefront curvature terms) actually scales as I(x) = I0exp(−2αx), where x is the propagation distance.

For enter a value or expression for the m (SI unit: Np/m). The default is 0. Neglecting curvature terms, the ray intensity decreases as I(x) = I0exp(−mx).


	In most room acoustics references the attenuation coefficient given is the intensity attenuation coefficient m. When setting up models it is important to know which definition is used and choose between the preceding two options accordingly.

For , enter a value or expression for the α’ (SI unit: dB/m). The default is 0.

For , enter a value or expression for the α(λ) (SI unit: dB). The default is 0.

•

For enter the following in the section:

T (SI unit: K, default 293.15 K)

pA (SI unit: Pa, default 1 atm)

φw (dimensionless, default 0)

By default, these model inputs are all , but they can also be taken from a .

•

For enter the following in the section:

T (SI unit: K, default 293.15 K)

Sp (dimensionless, default 35)

D (SI unit: m, default 0)

By default, these model inputs are all , but they can also be taken from a . Also, in the section, enter a value or expression for the pH (dimensionless). The default is 8.


	The Practical salinity is defined on the Practical Salinity Scale. It represents a specific way of measuring salinity through electric conductivity. Practical salinity is a unitless quantity, although it can be thought of as given in units of g/kg. The default value for the Practical salinity Sp is 35. For details, see Ref. 22.

•

If is selected, specify the following material properties. By default, all fluid properties take default values . Choose to enter a value or expression for the:

ρ (SI unit: kg/m3). The default is 1.2 kg/m3.

Cp (SI unit: J/(kg·K)). The default value is 1005.4 J/(kg·K).

γ (dimensionless). The default value is 1.4.

k (SI unit: W/(m·K)). The default value is 0.0257 W/(m·K). For ray acoustics, the thermal conductivity is assumed to be isotropic.

μ (SI unit: Pa·s). The default value is 0.0181 mPa·s.

μB (SI unit: Pa·s). The default is 0.

To define the attenuation coefficient or another medium property as a function of ray properties such as the ray frequency or intensity, the ray variable must be enclosed in the noenv() operator. For example, to use the ray frequency rac.f in an expression for the speed of sound, it must be included as part of the expression noenv(rac.f).


	Attenuation Within Domains