Interior Perforated Plate/Pair Perforated Plate
The Interior Perforated Plate and Pair Perforated Plate nodes provide the possibility of specifying the characteristic properties for a perforated plate. Add the Interior Perforated Plate node from the Interior Conditions submenu.
COMSOL Multiphysics has three Model types for calculating the transfer impedance of a perforated plate. The following options are available:
•
Thin plate (the default), the model where the losses due to heat conduction are negligible.
•
Thick plate, the model that takes the thermal effects into account.
•
Asymptotic (legacy) model, the model available in COMSOL Multiphysics version 5.2a and earlier.
A detailed description of the implemented models can be found in the Theory for the Interior Impedance Models section. The model properties are divided into two groups as shown below.
Interior Perforated Plate/Pair Perforated Plate
•
Hole diameter dh (SI unit: m). The default is 1 mm (10−3 m).
•
Plate thickness tp (SI unit: m). The default is 1.5 mm (1.5·10−3 m).
•
Area porosity σ, that is, the holes’ fraction of the boundary surface area, a dimensionless number between 0 and 1. The default is 0.1, which means 10% of the plate area consists of holes.
•
End correction to the resistance δresist and the reactance δreactt (SI unit: m). The default built-in sets δresist = δresist = 4dh/3π. Otherwise, select the user defined.
•
Hole-hole interaction fint, a dimensionless function that accounts for the influence of the porosity on the end correction. The default is the built-in Fok function (using eight terms):
.
•
Discharge coefficient (linear) , that is, a dimensionless coefficient related to the rate of the real flow through a hole to the theoretical flow. The default is 1.
Enable the Include nonlinear effects check box to include the nonlinear contribution to the resistance at high sound pressure levels. The following parameters become available:
•
Scaling factor fnl, a dimensionless. Default is 1.
•
Discharge coefficient (nonlinear) , which has the same meaning as . The default is 0.76.
Enable User-defined contribution check box to, for example, include the effects of a mean flow on the impedance. The following parameters become available:
•
User-defined resistance θ(user) , a contribution to the resistive part of the impedance, dimensionless. The default is 0.
•
User-defined resistance χ(user) , a contribution to the reactive part of the impedance, dimensionless. The default is 0.
Fluid Properties
Select the Fluid material from Boundary material (the default) or select a material from the list. If Boundary material is selected, you need to add a material to the given boundary under the Materials node.
Select the material properties either From material (the default) or User defined:
•
Density ρ (SI unit: kg/m3).
•
Speed of sound c (SI unit: m/s).
•
Dynamic viscosity μ (SI unit: Pa·s).
•
Ratio of specific heats γ (SI unit: 1). Only for the Thick plate model.
•
Heat capacity at constant pressure Cp (SI unit: J/(kg·K)). Only for the Thick plate model.
•
Thermal conductivity k (SI unit: W/(m·K)). Only for the Thick plate model.
The transfer impedance models from the list above are only valid for the perforates with round holes. For other types of perforates — with squared or slit-shaped holes — the values of some parameters can considerably differ from that of the suggested built-in perforates. It is recommended that you use the Interior Impedance/Pair Impedance condition to enter a user-defined model in such a case. The user-defined impedance can be obtained from a thermoviscous acoustic submodel (see The Thermoviscous Acoustics, Frequency Domain Interface) as demonstrated in the Acoustic Muffler with Thermoviscous Acoustic Impedance Lumping model.