Lumped Port
The Lumped Port feature connects a waveguide or duct inlet/outlet to a lumped representation element. This can be an Electrical Circuit (lumped electroacoustic representation), a two-port network defined through a transfer matrix, or a lumped representation of a waveguide. Basically, it couples the end of a waveguide to an exterior system that has a given acoustic lumped representation. Several representations and sources exist to describe the lumped system. When using the lumped port representation, it is assumed that only plane pressure waves propagate in the acoustic waveguide, that is the (0,0)-modes.
Port Mode Settings
The Port Mode Settings correspond to the options set in the Port Properties and Port Mode Settings sections of the Port condition.
Port Geometry
The Port Geometry settings correspond to those set in the Port condition.
The Lumped Port condition can only be applied to connected boundaries and the boundaries should typically be coplanar. The port condition can in principle be applied to a curved continuous boundary, but care should be taken that the setup is mathematically and physically consistent.
The Lumped Port boundary conditions should in general be placed at least one waveguide diameter from other geometry features to ensure that only a pure fully developed propagating wave exists at the port. Note also that the port condition does not treat possible evanescent waves.
The geometry restriction typically has to be tightened for the Plane wave option, where no attenuation exists at the waveguide walls. In this case, the port should be placed at least two viscous wavelengths from other geometry features. This is to ensure that reflected evanescent viscous waves are fully dissipated. In this case, at the lowest frequency fmin studied in the model, place the port at a distance:
Lumped Port Properties
Select the type of lumped representation connected to the port by selecting the Connection type as Circuit, Two-port (the default), or Waveguide. The selection made here influences the settings and options in the Connection Type section (see below).
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The Circuit option is used to connect the port boundary to an Electrical Circuit interface (this requires the AC/DC module). The connection is set up by adding the External I vs. U element in the circuit model and selecting the lumped port as the Electric potential, for example, Voltage from lumped port (acpr/lport1). The feature automatically introduces a unit transformation from electric to acoustic units. The classical equivalence between the voltage V (SI units: V) and the pressure p (SI unit: Pa) as well as the current I (SI unit: A) and the volume velocity Q (SI unit: m3/s) is made.
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For the Two-port option, it is assumed that the port boundary is connected to a two-port system described through a transfer matrix T. See the Connection Type section for details.
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For the Waveguide option, it is assumed that the port boundary is extended with a waveguide of constant and identical cross section. The connection is equivalent to the two-port as the waveguide is defined through the appropriate transfer matrix T, of a waveguide. See the Connection Type section for details.
For the Two-port and the Waveguide options also select the Exterior condition as Circuit, Ideal source (the default), or Impedance. The selection made here influences what section is visible in the user interface. See below for a description of the options.
Connection Type
This section is visible if Two-port or Waveguide is selected as the Connection type.
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For Two-port, select the Two-port representation as Acoustic (the default) or Electroacoustic. The selection indicates if the transfer matrix is from acoustic to acoustic variables or from electric to acoustic variables. The first can be used to include a transfer matrix of an acoustic subsystem, for example, extracted using the Port condition. The latter should, for example, be used if the transfer matrix represents a transducer with electric inputs and acoustic outputs.
Enter expressions, for example, calling interpolation functions that depend on frequency, for the elements of the transfer matrix T11, T12, T21, and T22.
For the Acoustic option, you can choose to invert the transfer matrix (reverse its direction) by selecting Invert transfer matrix direction. This option will invert and correct the signs of the transfer matrix T behind the scene.
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For Waveguide, select the Waveguide model as Automatic (the default) or User defined. The Automatic option will use the cross-section specific characteristic impedance and fluid properties of the boundary for the waveguide model. If User defined is selected, enter values for the Wave number k, the Specific characteristic acoustic impedance Z. For both options, enter the Waveguide length L (SI unit: m) modeled with the lumped representation.
The transfer matrix T couples the inlet (1) and outlet (2) pressure p and flow rate Q, defined in the feature, according to the following usual convention:
What is inlet and outlet depends on if the port excites the system (with a source) or it is passive (with an end impedance).
Source Settings
This section is visible if Ideal source is selected as the Exterior condition.
Select the Input source as Average pressure (the default) or Volume flow. Enter values for the average pressure pav,in or the volume flow Qin. These represent ideal sources equivalent to an ideal voltage or ideal current source.
Impedance Settings
This section is visible if Impedance is selected as the Exterior condition.
In this case, the lumped port is not active and an impedance condition can be applied to terminate the lumped representation. This could, for example, be the acoustic impedance of a microphone membrane. Select the Impedance model as User defined (the default) or RCL.
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For the User defined option select the input format as an Acoustic impedance Zac (SI unit: kg/m4·s) or an Impedance Z (SI unit: Pa·s/m). If the electroacoustic representation is used for the two-port enter the Electric impedance Z (SI unit: Ω).
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The RCL option is described for the Impedance boundary condition of The Pressure Acoustics, Frequency Domain Interface.
Circuit
This section gives information about the state of coupling/connection to an Electrical Circuit interface. If the Lumped Port is not connected, the text Connect to ‘External I vs. U’ in the Electrical Circuit interface text will be displayed. Once connected, a reference with a tag to the associated External I vs. U node, in the Electrical Circuit interface, is displayed.
Excluded Edges
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog box. See Suppressing Constraints on Lower Dimensions for details.