Transfer Matrix Coupling
The Transfer Matrix Coupling boundary feature is used to couple two boundaries (source and destination) using a transfer matrix representation. The transfer matrix is a reduced or lumped representation of the physical domain connecting the two boundaries. Examples of applications range from modeling of diesel particulate filter (DPF) in an exhaust system using an analytical model to represent the filter, as a lumped representation of a solid structure, or simply as a lumped model for an acoustic subsystem. The feature has two options, a so-called pointwise coupling and a lumped representation.
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The pointwise option Transfer matrix, pointwise couples the velocity and pressure independently at every point on the source/destination boundaries. This options requires the source and destination boundaries to be identical (they can be rotated). This option is typically used if the system that couples the source and destination can be assumed to only depend on the local acoustic properties, for example, parallel nearly independent waveguides in a DPF.
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The lumped option Transfer matrix, lumped two-port couples the average pressure and volume flow of the source/destination boundaries. This option is valid for plane wave propagation in the system and can be applied to boundaries that have different sized/shapes as it couples average surfaces values.
Transfer Matrix Coupling
Select the transfer matrix Representation as either Transfer matrix, pointwise (the default) or Transfer matrix, lumped two-port. Enter the components of the Transfer matrix T11, T12, T21, and T22. These are complex-valued expressions, constants, analytical expressions, or data from an interpolation function. In all cases, the values will typically depend on the studied frequency parameter freq.
When the Transfer matrix, lumped two-port option is chosen, also select the Source and destination area as Use symmetries (the default) or Selected boundaries.
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For Use symmetries, select the Area multiplication factor Ascale as Automatic (the default) or enter a value for Ascale. The automatic option will analyze the geometry and look for symmetry conditions to calculate Ascale. The area scaling is necessary for computing the correct volume flow at the boundaries.
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For the Selected boundaries, the area of the source and destination boundaries are taken as they are and no multiplication factor is applied.
Orientation of Source
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog box. For information about the Orientation of Source section, see Orientation of Source and Destination in the COMSOL Multiphysics Reference Manual.
Mapping Between Source and Destination
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog box. For information about the Mapping Between Source and Destination section, see Mapping Between Source and Destination in the COMSOL Multiphysics Reference Manual.