Release

This section is only available when the check box has been selected in the physics interface section. Enter (SI unit: s) or click the button (

) to select and define a range of specific times. At each release time, rays are released with initial position and ray direction vector as defined next.

Select an : (the default) or .

For enter a value for the N (dimensionless). The default is 100. Then enter a value or expression for the ρ (dimensionless). The default is 1.

The ρ can be an expression rather than a number; the resulting ray distribution approximately has a number density that is proportional to this expression. The resulting distribution looks a bit random, and it depends on the order in which the mesh elements are numbered. The distribution is probably not exactly the same in different COMSOL Multiphysics versions, but the total number of rays released is always N.

	The Density proportional to expression must be strictly positive.

The following options can be adjusted to make the number density of rays more closely conform to the expression.

Select a between and (the default is ), which determines the integration order that is used when computing the number of rays to release within each mesh element. The higher the accuracy order, the more accurately rays will be distributed among the mesh elements.

The (default 0) must be a nonnegative integer. When the refinement factor is 0, each ray is always assigned a unique position, but the density is taken as a uniform value over each mesh element. If the refinement factor is a positive integer, the distribution of rays within each mesh element is weighted according to the density, but it is possible for some rays to occupy the same initial position. Further increasing the increases the number of evaluation points within each mesh element to reduce the probability of multiple rays occupying the same initial position.

For the rays are released from a set of positions determined by a selection of geometric entities (of arbitrary dimension) in the mesh. Given a between 1 and 5, the centers of the refined mesh elements are used. Thus, the number of positions per mesh element is refine^dim, except for pyramids, where it is (4*refine2-1)*refine/3.

Select an option from the list: (the default), , , , or (3D only).

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For a single ray is released in the specified direction. Enter coordinates for the L0 (dimensionless) based on space dimension.

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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 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 enter coordinates for the r based on space dimension. Then enter the α (SI unit: rad; default π/3).

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The 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 Nw (dimensionless). The default is 50. Then enter coordinates for the r based on space dimension.

If is selected in a 3D model, select an option from the list:

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(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 the Nθ (dimensionless) and the 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 Nw (dimensionless), which is instead derived from the relation Nw = Nθ × Nϕ + 1.

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: specify the 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 directions is Nw = 3Nθ(Nθ + 1) + 1.

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: 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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: 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.

In 3D for the you can also let the be (the default) or . For enter the components of et. This controls, for example, the orientation of the ray fan when is selected.

For , , , and , select an option from the list: (the default) or . If is selected, the initial ray direction vectors are computed using an algorithm that seeks to distribute the rays as evenly as possible in wave vector space. This algorithm will give the same initial ray directions whenever the study is run. If is selected, the initial direction of each ray is sampled from a probability distribution in wave vector space using pseudorandom numbers. The result may be the same when rerunning the study multiple times on the same computer, but the solution is likely to be different on different architectures.

For it is also possible to initialize the ray direction vector either in the global coordinate system or in a coordinate system that moves with the same velocity as the background medium. Select an option from the list: (the default) or .

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For the initial wave vector is computed with respect to a coordinate system that moves at the background velocity, so the initial ray direction might not be parallel to the vector entered in the text field if the medium is moving.

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For the initial ray direction is parallel to the vector entered in the text field as long as a ray could reasonably propagate in that direction. For example, rays cannot be released in certain directions if the background fluid is moving with a supersonic velocity.

This section is available when the check box is selected under the physics interface section.

Select a : (the default), , , , or .

When is selected, enter an initial value f0 (SI unit: Hz). The default value is 1000 Hz.

Select to create a normal distribution function, to create a log-normal distribution function, or to create a uniform distribution function. For any of these distributions, select an option from the check box: (the default) or . For sampling the mean and standard deviation may not be exactly equal to the specified values but will statistically converge as the number of rays is increased. The sets the number of values that are sampled from the distribution function at each release point.

For the or distribution enter a user-defined (default 1000 Hz) and (default 100 Hz). For the distribution enter the fmin (default 1000 Hz) and fmax (default 2000 Hz).Select to enter a list of distinct frequency values.

This section is available when the check box is selected under the physics interface section. Enter an Ψ0 (SI unit: rad). The default value is 0.

This section is available when the ray intensity is solved for in the model and is selected as the . Enter a value for the I0 (SI unit: W/m2). The default is 1000 W/m2.

This section is available when the ray intensity is solved for in the model and is selected as the . Select a . In 3D the available options are (the default), , and . In 2D the available options are (the default) and .

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For an idealized plane wave the radii of curvature would be infinite. However, because the algorithm used to compute intensity requires finite values, when is selected the initial radii of curvature are instead given an initial value that is 108 times greater than the characteristic size of the geometry.

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For an , enter the r1,0 (SI unit: m) and the r2,0 (SI unit: m). Also enter the 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

This section is available:

Enter a Psrc (SI unit: W). The default is 1 W. In 2D, instead enter the Psrc (SI unit: W/m). The default is 1 W/m.

This section is available if an Auxiliary Dependent Variable has been added to the model.

For each of the nodes added to the model, select a for the initial value of the auxiliary dependent variables and whether the initial value of the auxiliary dependent variables should be a scalar value or sampled from a distribution function.

The number of rays simulated can increase substantially and the following options are available for each added to the model.

When is selected, enter an initial value. The symbol for the initial value is the auxiliary variable name followed by a subscript 0, so for the default name rp the initial value has symbol rp0.

For the initial value of the auxiliary dependent variables, select to create a normal distribution function, to create a log-normal distribution function, or to create a uniform distribution function. For any of these distributions, select an option from the check box: (the default) or . For sampling the mean and standard deviation may not be exactly equal to the specified values but will statistically converge as the number of rays is increased. The sets the number of values that are sampled from the distribution function at each release point.

For the or distribution enter the (default 0) and (default 1). For the distribution enter the (default 0) and (default 1). Select to enter a set of numerical values directly.

By default auxiliary dependent variables are initialized after all other degrees of freedom. Select the check box to compute the initial value of the auxiliary dependent variable immediately after computing the initial wave vectors of the rays. By selecting this check box it is possible to define the initial ray direction as a function of the auxiliary dependent variables.