Medium Properties
Use the Medium Properties 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
This section is available if the ray intensity or power is computed in the model. Select an option from the Fluid model list: Linear elastic (the default), Linear elastic with attenuation, or Thermally conducting and viscous. This section determines which additional fluid properties can be specified in the Medium Properties section below.
Medium Properties
The default Speed of sound c (Si unit: m/s) uses values From material. For User defined enter a value or expression. The default is 343 m/s.
If the ray intensity or power is solved for, the following edit fields are available, depending on the option selected from the Fluid model list in the Pressure Acoustics Model section:
•
If Linear elastic is selected, specify the Density ρ (SI unit: kg/m3). The default density uses values From material. For User defined enter a value or expression. The default is 1.2 kg/m3.
The definition of the attenuation coefficient implemented in the Ray Acoustics interface results in an intensity that scales as I(x) = I0exp(−2αx), where x is the distance traveled (this is not including terms based on curvature) and I0 is the initial intensity. The factor 2α is sometimes referred to as the intensity absorption coefficient. In most room acoustics references this value is called the attenuation constant m. When setting up models it is important to know which definition is used and possibly divide the input data with 2, as α = m/2.
•
If Linear elastic with attenuation is selected, specify the Density ρ (SI unit: kg/m3). The default density uses values From material. For User defined enter a value or expression. The default is 1.2 kg/m3. Enter a value or expression for the Attenuation coefficient α (SI unit: 1/m). Do not confuse this coefficient with the attenuation constant m most often defined in room acoustics (also known as the intensity attenuation coefficient). The two are related through 2α = m.
•
For Ocean attenuation enter the following:
-
Temperature T (SI unit: K) in the Model Inputs section. This can be User defined or taken from the Common model input. For User defined the default is 293.15 K.
-
Practical salinity Sp (dimensionless) in the Model Inputs section. This can be User defined or taken from the Common model input. For User defined the default is 0.
-
Depth D (SI unit: m) in the Model Inputs section. This can be User defined or taken from the Common model input. For User defined the default is 0.
-
pH-value pH (dimensionless). The default is 8.
•
For Atmosphere attenuation enter the following:
-
Temperature T (SI unit: K) in the Model Inputs section. This can be User defined or taken from the Common model input. For User defined the default is 293.15 K.
-
Absolute pressure pA (SI unit: Pa) in the Model Inputs section. This can be User defined or taken from the Common model input. For User defined the default is 1 atm.
-
Relative humidity φ (dimensionless) in the Model Inputs section. This can be User defined or taken from the Common model input. For User defined the default is 0.
•
If Thermally conducting and viscous is selected, specify the following material properties. By default, all fluid properties take default values From material. Choose User defined to enter a value or expression for the:
-
Density ρ (SI unit: kg/m3). The default is 1.2 kg/m3.
-
Heat capacity at constant pressure Cp (SI unit: J/(kg·K)). The default value is 1005.4 J/(kg·K).
-
Ratio of specific heats γ (dimensionless). The default value is 1.4.
-
Thermal conductivity 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.
-
Dynamic viscosity μ (SI unit: Pa·s). The default value is 0.0181 mPa·s.
-
Bulk viscosity 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