Bidirectionally Coupled Ray Tracing Study Step
The Bidirectionally Coupled Ray Tracing study step is a dedicated study step for ray heating and similar applications.
It should only be used if all of the following criteria are met:
1
Rays are being traced.
2
Some other field, such as temperature or structural displacement, is solved for in a domain where the rays are being traced.
3
All fields, apart from the ray paths themselves, are stationary.
4
The ray paths are affected by the field being solved for. This could include rays interacting with a deformed geometry, or a refractive index that depends on the values of field variables like strain or temperature.
5
The rays generate enough heat to significantly affect one of the fields being solved for in the domain, usually temperature.
If condition 4 is not satisfied, instead use a Stationary study step for the fields, followed by a Ray Tracing study step for the rays.
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 temperature computed during the previous step, compute the ray paths and any heat sources that occur due to ray attenuation 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, or specify a Global variable whose convergence will be used to terminate the loop.
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. By including a thermo-optic dispersion model, such as the Temperature-dependent Sellmeier model, the temperature in turn affects the ray paths. Thus, a bidirectional coupling is established between the two physics interfaces.
Like any COMSOL Multiphysics simulation, it is possible to extend this bidirectional coupling to include other physical effects. For example, to include structural deformation due to thermal stress, add the Solid Mechanics interface and the Thermal Expansion Multiphysics coupling.
Thermally Induced Focal Shift in High-Power Laser Focusing Systems: Application Library path Ray_Optics_Module/Structural_Thermal_Optical_Performance_Analysis/thermally_induced_focal_shift
In the COMSOL Multiphysics Reference Manual:
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Bidirectionally Coupled Ray Tracing
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Studies and Solvers