View Factors Calculator Model Reference

Solver Properties: View Factors Calculator

Patches and view factors are computed automatically at the beginning of the solution if they do not exist. However, they can also be generated manually using creation commands that are located in a pop-up menu that is accessed by right-clicking the View Factors Calculator solver node. The creation commands simply provide added flexibility to generate patches and view factors manually before initiating the solution.

The View Factors Calculator solver can work with overset mesh, but in the case of coincident uncoupled boundaries, both boundaries are patched and the behavior of the solver becomes inconsistent since rays can be terminated at either boundary without preference.

Verbosity

Provides additional output during the calculation of the view factors.

None

No output.

Low

Displays ray tracing progress and reciprocity convergence.

High

Displays additional progress and resource usage information.

Solver Frozen

When On, the solver does not update any quantity during an iteration. It is Off by default. This is a debugging option that can result in non-recoverable errors and wrong solutions due to missing storage. See Finite Volume Solvers Reference for details.

Number of Beams

The number of beams affects accuracy, view factor calculation time, and view factor storage requirements. A higher number of beams increases the accuracy of the view factors. However, increasing the number also increases the view factor calculation time and the memory requirements. The default number (1024) is usually a good balance between accuracy and resource use.

Maximum Reciprocity Iterations

Sets the maximum number of iterations in the reciprocity procedure. (Reciprocity is the constraint on view factors that the second part of Eqn. (1693) imposes.)

Reciprocity Tolerance

Specifies the criterion for convergence that is used in the reciprocity procedure. (Reciprocity is the constraint on view factors that the second part of Eqn. (1693) imposes.)

Update Frequency

Controls the frequency with which the solver calculates view factors. Use this property only for cases with mesh motion that results from rigid body motion.

Maximum Polygons per Voxel

Controls the resolution of the voxel mesh that is used in ray tracing. Lowering the value increases the resolution of the voxel mesh. This property generally does not need to be changed from the default value of 50. Increasing the number slightly decreases memory requirements, but can also slightly increase the calculation time.

View Factors Calculator Solver Pop-Up Menu

The following commands are accessed by right-clicking on the View Factors Calculator node.

Generate Radiation Patches

Adds radiation patches to the simulation.

Calculate View Factors

Generates the view factors. If patches do not exist, this command generates them.

Delete View Factors

Deletes all view factors in the simulation.

Display View Factor summary

Writes a summary of the view factor data in the Output window.

Export ASCII View Factors

Exports the view factor data to an ASCII file in your current working directory.

Controlling View Factor Recalculation for Rigid Body Motion

In cases where rigid body motion is present, view factors are recalculated every time-step by default. For cases where some reduction in accuracy is acceptable, you can save on computational time by recalculating the view factors less frequently. The property Update Frequency, provides this control.

The model uses the update frequency for:

• Mesh motion that results from rigid body motions. For all other cases (such as addition or removal of cells, reconstruction of interfaces, and morphing motion), the view factor solver acts as if the update frequency equaled 1. If mesh motion occurs due to rigid body motion, view factors are recalculated based on the input value of the update frequency. Within the update frequency interval, the S2S solver uses old view factors.
• Any mesh changes in a region where no radiation model is enabled or where radiation is enabled but the Radiation Transfer Option is set to None.

The update frequency is related to the time-steps, not the inner iterations for the unsteady solver. This approach represents a compromise between accuracy and the computational cost of view factor recalculation.