The Slit, Circular duct, Rectangular duct, and Equilateral triangular duct models are applicable as long as the cross-section dimension is much smaller then the wavelength and the boundary layer thickness is smaller than the wavelength. The cross-section parameter can be a slowly varying function of space. These are known as a low reduced frequency (LRF) model.
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Speed of sound c (SI unit: m/s)
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Ratio of specific heats γ (SI unit: 1). In many liquids the value of γ is close to 1, the exact value can be derived from the expression where the (isobaric) coefficient of thermal expansion αp and the isothermal compressibility βT is used.
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Dynamic viscosity μ (SI unit: Pa·s)
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Thermal conductivity k (SI unit: W/(m·K))
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For Slit enter the slit Height h (SI unit: m). Use this model in narrow slit domains to include the damping and attenuation that occurs here because of the losses in the viscous and thermal boundary layer.
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For Circular duct enter the duct Radius a (SI unit: m). This model is useful for modeling the damping and attenuation that occurs when acoustic waves propagate in all tubing systems of small cross-section dimensions.
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For Rectangular duct enter the duct Side lengths W and H (SI unit: m). Use this model for waveguides and ducts with a rectangular cross section. Also see Advanced Physics Options for additional settings.
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For Equilateral triangular duct enter the duct Side length d (SI unit: m). Use this model for waveguides and ducts with an equilateral triangular cross section.
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For User defined enter the value for the Complex wave number kc (SI unit: rad/m) and (specific characteristic) Complex acoustic impedance Zc (SI unit: Pa·s/m). These values can be used to model the propagation in ducts of arbitrary cross sections.
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To determine the complex propagation constants for a waveguide, of arbitrary cross section, use The Thermoviscous Acoustics, Boundary Mode Interface. Apply it on the cross-section geometry of the waveguide. The interface solves for the propagating modes and includes all losses in detail. The complex wave number kc is then given by the plane wave mode solved for. This is the variable tabm.kn. The predefined variable tabm.Zc gives the (lumped) specific characteristic complex impedance Zc. Search for the mode nearest to the (lossless) plane wave mode.
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