The following topics related to perforated materials in an acoustic analysis are available:
Several equivalent fluid models are available to approximate the perforated material with a rigid skeleton.
The equivalent fluid model uses the wave equation with complex effective density and velocity.
Define an equivalent fluid model via the
TB,PERF,,,,TBOPT command. The
following table shows the valid TBOPT values and the
input parameters (input via TBDATA) necessary for defining each
equivalent fluid model:
Table 5.1: Equivalent Fluid Models of Perforated Material
TBOPT
| Model | Input Parameters (TBDATA) | |||||
|---|---|---|---|---|---|---|---|
| JCA | Johnson-Champoux-Allard |
| |||||
| DLB | Delany-Bazley | Fluid Resistivity σ (0.01 < f/σ <1.00) | |||||
| MIKI | Miki | Fluid Resistivity σ (f/σ < 1.00) | |||||
| ZPRO | Complex Impedance and Propagating Constant |
| |||||
| CDV | Complex Density and Velocity |
|
For more information on how to define the above parameters for each equivalent fluid model, see Equivalent Fluid Model of Perforated Media in the Material Reference.
These additional parameters should be defined for the Johnson-Champoux-Allard model:
Via the MP command: dynamic (shear) viscosity η, thermal conductivity κ, heat coefficient at a constant pressure Cp, and heat coefficient at a constant volume Cv
Static reference pressure P0 input as element real constant PREF
When the Johnson-Champoux-Allard model is defined with all ten inputs, it has better numerical accuracy than the Delany-Bazley model and the Miki model, which require only one input parameter.
In the absence of multiple parameters, except for fluid resistivity, either the Delany-Bazley or Miki model can be a viable option for predicting the properties of a perforated material. The working range of the Delany-Bazley model limits it to 0.01 < f/σ <1.00 (where f is the frequency), while the Miki model extends to f/σ < 0.01 for low frequencies.
For general damping material problems (depending on the availability of parameters), use the Complex Impedance and Propagating Constant (ZPRO) model or the Complex Density and Velocity (CDV) model.
To define a frequency-dependent equivalent fluid model of the perforated material, use these commands:
TB,PERF,,,,TBOPT |
TBFIELD,FREQ,Value |
TBDATA,,C1,C2,C3,C4,C5 |
| (Repeat TBFIELD and TBDATA for each frequency, as needed.) |
The equivalent fluid model of perforated materials supports full harmonic acoustic analysis only.
Example 5.4: Defining a Frequency-Dependent Johnson-Champoux-Allard Model
mp,dens,1,1.21 ! mass density mp,sonc,1,343 ! sound speed mp,visc,1,1.827e-5 ! dynamic viscosity mp,kxx,1,0.0257 ! thermal conductivity mp,cvh,1,718 ! heat coefficient at a constant volume per mass mp,c,1,1005 ! heat coefficient at a constant pressure per mass tb,perf,1,,,jca ! JCA model tbfield,freq,f1 ! table at f1 tbdata,1,sig1,phi1,alp1,vis1,thr1 ! JCA parameters at f1 tbfield,freq,f2 ! table at f2 tbdata,1,sig2,phi2,alp2,vis2,thr2 ! JCA parameters at f2
Example 5.5: Defining a Frequency-Dependent Complex Effective Density and Sound Speed Model
mp,dens,1,1.21 ! mass density mp,sonc,1,343 ! sound speed tb,perf,1,,,cdv ! complex effective density and velocity model tbfield,freq,f1 ! table at f1 tbdata,1,denr1,deni1,cr1,ci1 ! complex density and velocity at f1 tbfield,freq,f2 ! table at f2 tbdata,1,denr2,deni2,cr2,ci2 ! complex density and velocity at f2
For more information, see Equivalent Fluid of Perforated Materials in the Theory Reference.
Trimming the perforated structures to a transfer admittance matrix is an alternative that avoids a dense mesh and offers excellent numerical accuracy. For more information, see Trim Element with Transfer Admittance Matrix.
The mixed displacement and pressure (u-P) formulation is used to solve the poroelastic acoustic problem. The poroelastic acoustic material models a perforated material with a flexible skeleton.
To specify poroelastic acoustic elements, define the acoustic element type (ET) with KEYOPT(2) = 7.
Define the poroelastic acoustic material via the TB,PERF,,,,PORO command, and specify the following parameters via TBDATA:
| Fluid resistivity |
| Porosity |
| Tortuosity |
| Viscous characteristic length |
| Thermal characteristic length |
| Bulk density of solid phase of the poroelasic material |
| Loss factor of elasticity moduli |
| Loss factor of shear moduli |
| Biot's coefficient |
| Bulk modulus of the elastic solid frame |
For more information on how to define the above parameters, see Poroelastic Acoustic Material in the Material Reference.
These additional parameters should also be defined for the poroelastic acoustic problem:
Via the MP command: dynamic (shear) viscosity η, thermal conductivity κ, heat coefficient at a constant pressure Cp, heat coefficient at a constant volume Cv, isotropic elastic moduli, shear moduli, and Poisson's ratio
Static reference pressure P0 input as element real constant PREF
To define a frequency-dependent poroelastic material, use these commands:
| TB,PERF,,,,PORO |
TBFIELD,FREQ,Value |
TBDATA,1,C1,C2,C3,C4,C5,C6 |
TBDATA,7,C7,C8,C9,C10 |
| (Repeat TBFIELD and TBDATA for each frequency, as needed.) |
The poroelastic material model supports full harmonic acoustic analysis only.
Example 5.6: Defining a Frequency-Dependent Poroelastic Material Model
mp,dens,1,1.21 ! Mass density mp,sonc,1,343 ! Sound speed mp,visc,1,1.827e-5 ! Dynamic viscosity mp,kxx,1,0.0257 ! Thermal conductivity mp,cvh,1,718 ! Heat coefficient at a constant volume per mass mp,c,1,1005 ! Heat coefficient at a constant pressure per mass mp,ex,1,ex0 ! Young’s modulus mp,gxy,1,gxy0 ! Shear modulus mp,nuxy,1,nuxy0 ! Poisson’s ratio ! tb,perf,1,,,poro ! Poroelastic model tbfield,freq,f1 ! Table at f1 tbdata,1,sig1,phi1,alp1,vis1,thr1,rhos1 ! Poroelastic parameters at f1 tbdata,7,dampE1,dampN1,BiotC1,Ks1 tbfield,freq,f2 ! Table at f2 tbdata,1,sig2,phi2,alp2,vis2,thr2,rhos2 ! Poroelastic parameters at f2 tbdata,7,dampE2,dampN2,BiotC2,Ks2
For more information, see Poroelastic Acoustics in the Theory Reference.