About the Pressure Acoustics Fluid Models

Linear Elastic with Attenuation Fluid Model

Use the linear elastic with attenuation fluid model to specify a fluid with attenuation given by an attenuation coefficient α. This results in a complex-valued wave number k. It is used to define the complex speed of sound.

There are different attenuation types to select from: attenuation coefficient Np/m, attenuation coefficient dB/m, or attenuation coefficient dB/λ. Select to define an attenuation coefficient in Np/m (nepers per meter), to define:

Select to define an attenuation coefficient in dB/m (decibel per meter), to define:

Select λ to define an attenuation coefficient in dB/λ (decibel per wavelength), to define (notice the different definition of the complex density):


	Defining a Linear Elastic with Attenuation Fluid Model

Viscous Fluid Model

The viscous model is an equivalent-fluid model that mimics the propagation of sound in a fluid including viscous losses occurring in the bulk of the fluid. The elastic fluid model with viscous losses is defined by:

where μ is the dynamic viscosity and μB is the bulk viscosity (see Ref. 4 or Ref. 6 chapter 9). This choice is only appropriate for situations where the damping takes place in free space and is not related to interaction between the fluid and a solid skeleton or a wall. These losses, in most fluids, occur over long distances or at very high frequencies.


	Defining a Viscous Fluid Model

Thermally Conducting Fluid Model

The thermally conducting model is an equivalent-fluid model that mimics the propagation of sound in a fluid including losses due to thermal conduction in the bulk. The elastic fluid model with thermal losses is defined by:

where γ is the ratio of specific heats, Cp is the specific heat at constant pressure, and k is the thermal conductivity (see Ref. 6 chapter 9). This choice is only appropriate for situations where the damping takes place in free space and is not related to interaction between the fluid and a solid skeleton or a wall.


	Defining a Thermally Conducting Fluid Model

Thermally Conducting and Viscous Fluid Model

The thermally conducting and viscous model is an equivalent-fluid model that mimics the propagation of sound in a fluid including losses due to thermal conduction and viscosity in the bulk of the fluid. The elastic fluid model with thermal and viscous losses is defined by:

where μ is the dynamic viscosity and μB is the bulk viscosity, γ is the ratio of specific heats, Cp is the specific heat at constant pressure, and k is the thermal conductivity (see Ref. 6 chapter 9). This choice is only appropriate for situations where the damping takes place in free space and is not related to interaction between the fluid and a solid skeleton or a wall.


	Defining a Thermally Conducting and Viscous Fluid Model