Use the Exterior Field Calculation node to apply the source boundaries for the exterior field transformation set up by the Helmholtz-Kirchhoff integral. You also specify a name for the acoustic exterior field variable (default name is
pext) used in subsequent postprocessing. The feature allows the calculation and visualization of the pressure field outside the computational domain at any distance including amplitude and phase. Note that when a
Background Pressure Field is present, the feature only operates on the scattered field variables and is thus also well suited for analyzing the results of a scattering problem.
Enter an Exterior field variable name for the exterior field acoustic pressure field (the default is
pext).
Select the Symmetry type that applies to the problem. The symmetry type and subsequent settings should match the conditions used in the underlying acoustics problem, for example, if using
Symmetry or the
Periodic Condition.
For each of these planes, select the type for the condition to be applied in the x =
x0,
y =
y0, or
z =
z0 planes. Select the type of condition:
Off (the default),
Symmetry/Infinite sound hard boundary, or
Antisymmetric/Infinite sound soft boundary. Then enter the value for the plane location
x0,
y0, or
z0 (the default is 0 m). This allows an offset of the infinite condition planes along the main coordinate axes.
Note that the Sector symmetry option cannot be combined with an infinite baffle (symmetry plane) used in many transducer models. For this type of setup use the
Sector symmetry with one symmetry plane option.
The option Use polynomial-preserving recovery for the normal gradient on interior boundaries is selected per default on interior boundaries. This means that the exterior field feature automatically uses the polynomial-preserving recovery operator
ppr() to get an enhanced evaluation of the normal derivative of the pressure. This increases the precision of the exterior field calculation. If you click to clear this check box this removes all instances of the operator from the equations.
The option Reverse normal direction on interior boundaries allows reversing the normal used in the Helmholtz-Kirchhoff integral. To get the correct phase the normal has to point inward. Typically, if the exterior field is calculated in an interior boundary to the physics (not a boundary next to a PML), the normals will point outward and the option should be used.