Using the Bidirectionally Coupled Ray Tracing Study
The Bidirectionally coupled ray tracing study step is a dedicated study step for ray heating and similar applications. It functions like a Ray tracing study step for the degrees of freedom defined by the Geometrical Optics interface but computes all other degrees of freedom using a Stationary solver. In addition to the settings that are available for the Ray tracing study step, it is possible to specify a Number of iterations. The default value is 5. If the Bidirectionally coupled ray tracing study step is used with The Ray Heating Interface, the following iterative solver loop is automatically set up to compute the ray trajectories and temperature:
1
Solve for the temperature field, assuming that the rays do not generate any heat source.
2
Using the value of the temperature computed during the previous step, compute the ray trajectories and any heat sources that occur due to the attenuation of rays in an absorbing medium.
3
Using the heat source computed in the previous step, compute the temperature field.
4
Alternate between steps 2 and 3 for the specified Number of iterations. Alternatively, the sequence can end when a specified variable converges to within a specified tolerance.
The result of the iterative solver loop is that the heat source generated by the attenuation of rays is taken into account when computing the temperature. If the refractive index of the medium is a expressed as a function of the temperature, then the temperature dependence of the refractive index is taken into account when computing the ray trajectories. Thus, a bidirectional coupling is automatically set up between the two physics interfaces.
It is possible to extend this bidirectional coupling to include other physical effects. For example, the addition of the Solid Mechanics interface and the Thermal Expansion and Temperature Coupling Multiphysics nodes.
To account for thermal expansion or other types of structural deformation while tracing the rays, use a Moving Mesh (ALE) interface to model the mesh deformation or, for structural mechanics models, select the Include geometric nonlinearity check box in the study step Study Settings section (requires the Structural Mechanics Module, MEMS Module, or Acoustics Module).
In the COMSOL Multiphysics Reference Manual:
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Bidirectionally Coupled Ray Tracing
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Studies and Solvers