Incident Pressure Field
The Incident Pressure Field node is a subnode to all nonreflecting boundary conditions (plane, cylindrical, spherical wave radiation, and matched boundary). From the Physics toolbar, add to Matched Boundary, Plane Wave Radiation, Spherical Wave Radiation, or Cylindrical Wave Radiation nodes. Four options exist for the Pressure Field Type. They are Plane Wave, Cylindrical Wave, Spherical Wave, and User Defined (the only option for transient simulations).
Plane Wave
If the incident pressure field pi is a predefined plane wave, it is of the type:
where p0 is the wave amplitude, k is the wave vector with amplitude ks = ω/c and wave direction vector ek, and x is the location on the boundary.
Cylindrical Wave
If the incident pressure field pi is a predefined cylindrical wave, it is of the type:
where p0 is the amplitude given at the reference distance rref = 0.548/ks (the distance where the Hankel function is one), ks = ω/c is the wavenumber, is the Hankel function of the second kind (representing an outgoing cylindrical wave), rs is the distance from the source axis, esa is the direction of the source axis, x0 is a point on the source axis, and x is the location on the boundary.
Spherical Wave
If the incident pressure field pi is a predefined spherical wave (only for 2D axisymmetric and 3D), it is of the type:
where p0 is the amplitude given at the reference distance of 1 m, ks = ω/c is the wavenumber, rs is the distance from the source, x0 is the source location of the spherical wave, and x is the location on the boundary.
For both the cylindrical and the spherical wave options the source and/or source axis should be located outside the computational domain where the radiation condition is applied. The fields should be incident on the radiation boundary.
Transient Interface User Defined
If you are in the Pressure Acoustics, Transient interface the incident pressure field is only of the user-defined type. In this case the incident pressure field needs to be defined as a traveling wave of the form
where ω is the angular frequency and k is the wave vector. The function f is any function, for example, a sine function. This is a requirement for the radiation boundary condition to work properly.
Incident Pressure Field
From the Incident pressure field type list, select Plane wave (the default), Cylindrical Wave, Spherical Wave, or User Defined to define the incident pressure field type.
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For Plane Wave enter a Pressure amplitude p0 (SI unit: Pa), the Speed of Sound c (SI unit: m/s) of the medium defining the incident wave, and the Wave direction ek (SI unit: m).
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For Cylindrical Wave enter a Pressure amplitude at reference distance p0 (SI unit: Pa), the Speed of Sound c (SI unit: m/s) of the medium defining the incident wave, a Source Location x0 (SI unit: m), and a Source Axis esa (the vector need no to be normalized).
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For Spherical Wave enter a Pressure amplitude at reference distance p0 (SI unit: Pa), the Speed of Sound c (SI unit: m/s) of the medium defining the incident wave, and a Source Location x0 (SI unit: m).
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If User defined is selected enter the expression for the Incident pressure field pi (SI unit: Pa) as a function of space.
When calculating, for example, a transfer function use the defined variable acpr.p_i for the incident field value. This variable contains phase information which can be difficult to asses otherwise.