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Thin plate (the default), the model where the losses due to heat conduction are negligible.
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Thick plate, the model that takes the thermal effects into account.
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Asymptotic (legacy) model, the model available in COMSOL Multiphysics version 5.2a and earlier.
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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.
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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.
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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):
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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.
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Discharge coefficient (nonlinear) , which has the same meaning as . The default is 0.76.
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User-defined resistance θ(user) , a contribution to the resistive part of the impedance, dimensionless. The default is 0.
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User-defined resistance χ(user) , a contribution to the reactive part of the impedance, dimensionless. The default is 0.
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Speed of sound c (SI unit: m/s).
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Dynamic viscosity μ (SI unit: Pa·s).
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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.
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