Prescribed Acoustic Fields
The Prescribed Acoustic Fields condition makes it possible to prescribe one or more of the dependent variables at a boundary. When specifying (constraining) the dependent variables for the linearized Euler equations, it is necessary to not underconstrain the system. Typically, this requires defining both the density and pressure, defining the velocity, or defining all three at the same time. Add this node from the Prescribed Conditions submenu.
For systems that can be assumed isentropic, where the acoustic changes in the entropy are zero, enter an expression for the pressure p_user and the density p_user/lef.c0^2. This corresponds to the classical relation . This is also achieved using the Pressure (Isentropic) condition.
Prescribed Values for Acoustic Variables
By default no checkboxes are selected. Click to select the following checkboxes as needed.
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Prescribed density ρp (SI unit: kg/m3).
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Prescribed velocity (SI unit: m/s). If this checkbox is selected, choose one or more of these additional checkboxes: Prescribed in x direction upx, Prescribed in y direction upy, or Prescribed in z direction upz (for 3D components); or Prescribed in r direction upr and Prescribed in z direction upz (for 2D axisymmetric components).
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Prescribed pressure pp (SI unit: Pa).
Constraint Settings
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog.
Excluded Edges/Points
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog. See Suppressing Constraints on Lower Dimensions for details.