The Poroacoustics node defines a fluid domain with a porous material modeled in a homogenized way using a so-called equivalent fluid model. Several models exist to define the attenuation and dispersion experienced by the pressure waves as they propagate in the porous domain. The different models are described below.

Select a Poroacoustics model: Delany-Bazley-Miki (the default), Zwikker-Kosten, Attenborough, Wilson, Johnson-Champoux-Allard, Johnson-Champoux-Allard-Lafarge, Johnson-Champoux-Allard-Pride-Lafarge, Williams EDFM, or Wood.

Enter the properties of the saturating fluid that is inside of the porous material. These settings are common to most porous models. By default the Fluid material uses the Domain material.

The following properties are available based on the Poroacoustics model selected above. The default values are taken From material. For User defined enter a different value or expression.

If any other than the default Delany-Bazley-Miki is selected, the following properties are also required, depending on the selection. These material parameters are necessary as the more advanced models include the losses associated with viscosity and thermal conduction in a more or less detailed way:

In this section, enter the properties that describe the porous material. By default the Porous elastic material uses the Domain material (the material defined for the domain). Select another material as needed. For example, create your own material that contains the properties of a given porous material and refer to it here. Here you also select if you want to use a rigid frame approximation or a limp frame approximation for the porous material (where applicable). The poroacoustic model defines complex-valued frequency-dependent expressions for both the bulk modulus and the equivalent density.

Based on the Poroacoustics model selected, enter the following settings for the porous matrix.

The Delany-Bazley-Miki model is an empirical model used to describe fibrous materials such as rockwool or glass fiber. The model can be used for materials with a porosity, εp, close to one. For Delany-Bazley-Miki, the Flow resistivity Rf (SI unit: Pa·s/m2) uses values From material. For User defined, enter a value or expression.

Select an option from the Constants list: Delany-Bazley (the default), Miki, Qunli, Mechel, glass fiber, low X, Mechel, glass fiber, high X, Mechel, rock fiber, low X, Mechel, rock fiber, high X, Komatsu, Modified Champoux and Allard, or User defined. For User defined enter values in the C1 to C8 fields. The models are empirical and based on fitting to measured data. This means the models have different regions of applicability with respect to the flow resistivity Rf, the frequency f, the material type, and the parameter X defined as

All the models are applicable for materials with a porosity εp close to 1. The model informations are listed in Table 2-2. See also Ref. 23 and the relevant section in About the Poroacoustics Models for further details.

The Zwikker-Kosten model is a two-parameter semiempirical model. It is one of the earliest equivalent fluid models for porous materials. The model assumes that the pores are cylinder-like with an effective hydraulic radius Hr. See Ref. 15 and About the Poroacoustics Models for further details.

For Zwikker-Kosten, select a Porous matrix approximation: Rigid (the default) or Limp. Then based on your choice, the default value for each of the following parameters is taken From material. For User defined, enter another value or expression.

The Attenborough model is also based on the cylindrical-like pore assumption. It is a so-called four-parameter semiempirical model. The model is an extension of the Zwikker-Kosten model and has two additional input parameters. It accounts for the tortuosity (high frequency limit) , which is related to the orientation of the pores relative to the propagation direction. The hydraulic diameter of the pores is replaced by an expression that included the flow resistivity Rf and a fitting parameter b (this parameter is related to the anisotropy of the pore distribution). See Ref. 9, Ref. 16, and About the Poroacoustics Models for details.

For Attenborough, select a Porous matrix approximation: Rigid (the default) or Limp. Then based on your choice, the default value for most of the following parameters is taken From material. For User defined, enter another value or expression.

The Wilson model is a generalization of the semianalytical models for porous materials with constant cross section and parallel pores. This model is intended to match the middle frequency behavior of a porous material. See Ref. 17, Ref. 9, Ref. 18, and About the Poroacoustics Models for further details.

For Wilson, select a Porous matrix approximation: Rigid (the default) or Limp. Then based on your choice, the default value for the following parameters is taken From material. For User defined, enter another value or expression.

The Johnson-Champoux-Allard (or JCA model) is a five-parameter semiempirical model for describing a large range of porous materials with rigid (or limp) frames. As input, the model requires the viscous Lv and thermal Lth characteristic lengths (sometimes denoted Λ and Λ'). These replace the hydraulic radius used in simpler models and account for the thermal and viscous losses that appear at the acoustic boundary layer at pore walls. See About the Poroacoustics Models for details.

For Johnson-Champoux-Allard, select a Porous matrix approximation: Rigid (the default) or Limp. Then based on your choice, the default value for most of the following parameters is taken From material. For User defined, enter another value or expression.

The Johnson-Champoux-Allard-Lafarge (or JCAL model) is an extension to the JCA model. It introduces corrections to the bulk modulus thermal behavior at low frequencies which is not captured by the JCA model. It introduces the static thermal permeability parameter and, thus, has one more parameter than the JCA model. It is a six-parameter semiempirical model. See Ref. 13, Ref. 9, and About the Poroacoustics Models for further details.

For Johnson-Champoux-Allard-Lafarge, the settings are the same as for Johnson-Champoux-Allard with the addition of the Static thermal permeability (SI unit: m2) setting.

The Johnson-Champoux-Allard-Pride-Lafarge (or JCAPL model) further extends the JCAL models by introducing a static viscous τ0 and thermal τ'0 tortuosity.

For Johnson-Champoux-Allard-Pride-Lafarge, the settings are the same as for Johnson-Champoux-Allard plus these additional parameters:

Williams EDFM is an effective density fluid model (EDFM) used to model the propagation of acoustic waves in sediments. The model assumes that the bulk and shear moduli of the frame of the porous material are negligible, meaning that the porous frame is limp. See Ref. 24 and About the Poroacoustics Models for further details.

The Porous Matrix Properties (the properties for the sediment) for Williams EDFM have the default values taken From material. For User defined, enter another value or expression:

The Wood model is used for a fluid mixture or a fluid suspension (solid inclusions completely surrounded by fluid). The Woods formula for the sound velocity is determined by using the effective bulk modulus of the suspension and the volume average density. As the Williams EDFM, this model gives effective values for the mixture. This model is exact for low frequencies, when the wavelength is much larger than the size of the inclusions. See Ref. 25 and About the Poroacoustics Models for further details.

The Porous Matrix Properties (the properties for the inclusions) for the Wood model are entered in the Inclusion properties table. For each Inclusion (any number of inclusions can be added, the number is automatically incremented) enter the Volume fraction, the Bulk modulus, and the Density. Add a new row (inclusion) by clicking the plus sign below the table. The table may be saved or loaded from a file.