Release from Exterior Field Calculation

	This feature is only available in 3D.

Use a node to launch rays with an initial intensity and phase distribution matching the exterior field solved for in another study.

	To add this feature, either the ray intensity or power must be solved for. Select an appropriate option from the Intensity computation list in the physics interface Intensity Computation section.

The node can be used for multiscale acoustics modeling. First, the Pressure Acoustics, Frequency Domain interface should be used to compute the near-field acoustic pressure distribution, such as the first few wavelengths surrounding a speaker or another source. The node should be added to this instance of the Pressure Acoustics, Frequency Domain interface, and → ∞. should be selected from the list. Because the near-field calculation is solving for the instantaneous pressure amplitude in individual waves, the Nyquist criterion must be fulfilled. Typically this requires 10 linear elements or 5 second-order elements per wavelength.

Then, in the same model component or a different component, the Ray Acoustics interface can be used to extend the exterior field over an arbitrarily large number of wavelengths, because the ray tracing approach does not require a finite element mesh fine enough to resolve individual oscillations of the acoustic pressure field.

The node is only available in 3D. However, the exterior field function it uses to initialize the ray intensity and phase can be defined either in a 3D model component or a 2D axisymmetric model component. If the previous model component was a 2D axisymmetric component, the intensity distribution of released rays will also be assumed to be axisymmetric.

See Release for information on the section and the optional section.

Select an option from the list: (the default) or .

Enter based on space dimension (qx,0, qy,0, and qz,0) for the ray positions or click the button (

) to select and define a range of specific coordinates.

If is selected, the number of initial coordinates entered for each space dimension must be equal, and the total number of rays released is equal to the length of one of the lists of initial coordinates. If is selected, the total number of rays released is equal to the product of the lengths of each list of initial coordinates.

In the section, you can click the

and

buttons to visualize the ray release positions. Clicking will cause a point to appear in the Graphics window for every release position. Clicking will cause a bounding box to appear, indicating the spatial extents of the released rays.

Select an option from the list: (the default), , or .

•

For a number of rays are released at each point, sampled from a spherical distribution in wave vector space. Enter the Nw (dimensionless). The default is 50.

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For a number of rays are released at each point, sampled from a hemispherical distribution in wave vector space. Enter the Nw (dimensionless). The default is 50. Then select an option from the list: or . For enter coordinates for the r based on space dimension.

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For a number of rays are released at each point, sampled from a conical distribution in wave vector space. Enter the Nw (dimensionless). The default is 50. Then select an option from the list: or . For enter coordinates for the r based on space dimension. Then enter the α (SI unit: rad). The default is π/3 radians.

Note that unlike the Release from Grid feature, the options and are not available here. In addition, if is selected, the cone must be isotropic. This is because each ray is assumed to subtend approximately the same solid angle, so direction distributions that give unequal weight to some directions (like ) or options with no direction distribution at all (like ) cannot initialize the ray intensity and power in a consistent and physically meaningful way.

Enter an expression for the . The default expression is pext. This expression must match the variable name in a corresponding node.

Use the settings in this section to orient the ray source. This allows, for example, the release of rays from a speaker to be modeled with the speaker oriented in many different directions, while only solving for the exterior field once.

Enter the . The labels Z-X-Z indicate the order in which rotation about the different axes is performed. First, the local coordinate system of the exterior field is rotated about its Z-axis by the angle α. Then it is rotated about its X-axis (which is now at an angle α to the global x-axis) by the angle β. Finally, this local coordinate system is rotated about its new Z-axis by the angle γ. All three inputs are plane angles (SI unit: rad) with default values of 0.

This section is only shown if the check box is cleared in the physics interface section.

The check box is selected by default. While this check box is selected and the node is active, the frequency of released rays will be determined by the or study in the section of the solver settings. Usually, this previous study was used to solve for the exterior field using the Pressure Acoustics, Frequency Domain interface.

While this check box is selected and the node is active, the frequency specified in the Ray Properties node is ignored.