Release from Boundary
Use the Release from Boundary node to determine how to release rays on an interior or exterior boundary in a specific direction.
The Nonlocal Accumulator subnode is available from the context menu (right-click the parent node) or from the Physics toolbar, Attributes menu.
See Release for information on the following sections: Release Times, Initial Ray Frequency, Initial Phase, Initial Intensity, Total Source Power, and Initial Value of Auxiliary Dependent Variables.
Coordinate System Selection
It is possible to specify the initial ray direction in terms of the global coordinates or in another coordinate system defined for the model Component. Select an option from the Coordinate system list. By default Global coordinate system is selected. If other coordinate systems are defined, they can also be selected from the list. When specifying the initial ray direction (see the Ray Direction Vector section), direction components can be specified using the basis vectors of whichever coordinate system has been selected from the list.
When a coordinate system other than Global coordinate system is selected from the Coordinate system list, arrows will appear in the Graphics window to indicate the orientation of the basis vectors of the coordinate system on the selected boundaries.
Initial Position
Select an Initial position: Uniform distribution (the default for 2D components) Projected plane grid (the default for 3D components), Mesh based, or Density. Mesh based and Density have the same settings as described for the Release node.
For 2D components, if Uniform distribution is selected, enter the Number of rays per release N (dimensionless). The union of the selected boundaries is divided into N segments of approximately equal length, and a ray is placed in the middle of each segment.
For 3D components, if Projected plane grid is selected, enter the Number of rays per release N (dimensionless). The rays are distributed on a plane grid in planes that are approximately tangential to the selected boundaries (for a plane boundary, you get a uniform distribution).
Ray Direction Vector
Select an option from the Ray direction vector list: Expression (the default), Hemispherical, Conical, or Lambertian (3D only).
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For Expression, a single ray is released in the specified direction. Enter coordinates for the Ray direction vector L0 (dimensionless) based on space dimension. Select the Specify tangential and normal vector components check box to specify the initial direction using a coordinate system based on the directions tangential and normal to the surface (t1, t2, n).
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For Hemispherical, a number of rays are released at each point, sampled from a hemispherical distribution in wave vector space. Enter the Number of rays in wave vector space Nw (dimensionless). The default is 50. Then enter coordinates for the Hemisphere axis r based on space dimension. Select the Specify tangential and normal vector components check box to specify the hemisphere axis using a coordinate system based on the directions tangential and normal to the surface (t1, t2, n).
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For Conical, a number of rays are released at each point, sampled from a conical distribution in wave vector space. Enter the Number of rays in wave vector space Nw (dimensionless). The default is 50. Then enter coordinates for the Cone axis r based on space dimension. Then enter the Cone angle α (SI unit: rad). The default is π/3 radians. Select the Specify tangential and normal vector components check box to specify the cone axis using a coordinate system based on the directions tangential and normal to the surface (t1, t2, n).
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The Lambertian option is only available in 3D. A number of rays are released at each point, sampled from a hemisphere in wave vector space with probability density based on the cosine law. Enter the Number of rays in wave vector space Nw (dimensionless). The default is 50. Then enter coordinates for the Hemisphere axis r based on space dimension. Select the Specify tangential and normal vector components check box to specify the hemisphere axis using a coordinate system based on the directions tangential and normal to the surface (t1, t2, n)
When the Specify tangential and normal vector components check box is selected, arrows indicating the normal direction on the selected boundaries will appear in the Graphics window.
Note that the normal direction may be opposite the built-in variable for the boundary normal (for example, nx, ny, and nz) to ensure that a positive value causes rays to be released into the simulation domain. This often occurs when the release is applied to exterior boundaries.
When the normal direction used by the Release from Boundary feature is opposite the normal vector defined by the geometry, the tangential directions are similarly inverted to ensure that the boundary coordinate system is right handed.
If Conical is selected in a 3D model, select an option from the Conical distribution list:
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Uniform density (the default): rays are released with polar angles from 0 to the specified cone angle. The rays are distributed in wave vector space so that each ray subtends approximately the same solid angle.
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Specify polar and azimuthal distributions: specify the Number of polar angles Nθ (dimensionless) and the Number of azimuthal angles Nφ (dimensionless). Rays are released at uniformly distributed polar angles from 0 to the specified cone angle. A single axial ray (θ = 0) is also released. For each value of the polar angle, rays are released at uniformly distributed azimuthal angles from 0 to 2π. Unlike other options for specifying the conical distribution, it is not necessary to directly specify the Number of rays in wave vector space Nw (dimensionless), which is instead derived from the relation Nw = Nθ × Nφ + 1.
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Hexapolar: specify the Number of polar angles Nθ (dimensionless). In this distribution, for each release point, one ray will be released along the cone axis. Six rays are released at an angle α/Nθ from the cone axis, then 12 rays at an angle of 2α/Nθ, and so on. The total number of ray directions in the distribution is Nw = 3Nθ(Nθ + 1) + 1.
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Flat: rays are released in a flat fan shape within the specified angle.
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Marginal rays only: the rays are all released at an angle α with respect to the cone axis. The rays are released at uniformly distributed azimuthal angles from 0 to 2π.
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Marginal and axial rays only: the rays are all released at an angle α with respect to the cone axis, except for one ray which is released along the cone axis. The marginal rays are released at uniformly distributed azimuthal angles from 0 to 2π.
The available Conical distribution options are illustrated in Figure 8-1.
In 3D for the Conical distribution you can also let the Transverse direction be Automatic (the default) or User defined. For User defined enter the components of et. This controls, for example, the orientation of the ray fan when Flat is selected.
For Hemispherical, Conical, and Lambertian, select an option from the Sampling from Distribution list: Deterministic (the default) or Random. If Deterministic is selected, the initial ray direction vectors are computed using the same algorithm, which seeks to distribute the rays as evenly as possible in wave vector space, whenever the study is run. If Random is selected, the initial direction of each ray is sampled from a probability distribution in wave vector space using pseudorandom numbers.
Initial Radii of Curvature
This section is available when the ray intensity is solved for in the model and Expression is selected as the Ray direction vector. Select a Wavefront shape. In 3D the available options are From surface curvature (the default), Plane wave, Spherical wave, and Ellipsoid. In 2D the available options are Plane wave (the default) and Cylindrical wave.
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For a Spherical wave or Cylindrical wave, enter the Initial radius of curvature r0 (SI unit: m).
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For an Ellipsoid (3D only), enter the Initial radius of curvature, 1 r1,0 (SI unit: m) and the Initial radius of curvature, 2 r2,0 (SI unit: m). Also enter the Initial principal curvature direction, 1 e1,0 (dimensionless).
For spherical and cylindrical waves the Initial radius of curvature must be nonzero. To release a ray such that the initial wavefront radius of curvature is zero, instead select a different option such as Conical from the Ray direction vector list.
Principal Radii of Curvature