About the Pressure Acoustics Fluid Models

Use the user-defined attenuation fluid model to specify an attenuation defined through an attenuation coefficient α. The attenuation can be an analytical expression or given by measurement data imported using an interpolation function. This results in a complex-valued wave number k. This defines 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):

	User-Defined Attenuation 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). 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.

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.

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.