In the two opposite limits Zi → ∞ and Zi → 0, this boundary condition is identical to the Sound Hard Boundary (Wall) condition and the Sound Soft Boundary condition, respectively.
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COMSOL Multiphysics supports the use of the rayl unit when specifying a value of the impedance (1 rayl = 1 Pa·s/m). Two variants exist: [rayl] and [rayl_cgs]. The latter is the definition of the unit in the cgs unit system. Notice that inconsistent definitions give: 1[rayl_cgs] = 10[rayl] = 10[Pa*s/m].
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On an impedance boundary, postprocessing variables exist to evaluate the equivalent absorption coefficient. They are the absorption coefficient for normal incidence acpr.imp1.alpha_n and for random incidence acpr.imp1.alpha_ran (here given for the impedance feature imp1).
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Notice that the Impedance boundary condition cannot directly be combined with a source like Normal Acceleration. In cases where such a behavior is desired, modeling a source impedance, this can be achieved by coupling the boundary to an Electrical Circuit model. See, for example, the Lumped Loudspeaker Driver model under Electroacoustic Transducers in the Application Library.
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Generic 711 Coupler — An Occluded Ear-Canal Simulator: Application Library path Acoustics_Module/Tutorials,_Thermoviscous_Acoustics/generic_711_coupler
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Ratio of specific heats γ (SI unit: 1).
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Thermal conductivity k (SI unit: W/(m·K)).
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Dynamic viscosity μ (SI unit: Pa·s).
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Open Pipe: Application Library path Acoustics_Module/Verification_Examples/open_pipe
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For Automatic, the angle of incidence is set to 50o behind the scenes. This angle gives an on average value, valid for random incidence, and is useful when modeling closed spaces like rooms.
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For User defined, enter the Wave direction ek, the default is the surface normal. If a Background Pressure Field feature is present you can, for example, use the wave direction components: acpr.bpf1.kdirx, acpr.bpf1.kdiry, and acpr.bpf1.kdirz (here in 3D, use the appropriate tag).
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