A holistic microclimate model

Relaxation

To avoid numerical oscillations during the initialisation phase, ENVI-met can “relax” the results of the TKE-e equation system.
This means that the new results of the equation are only partly used to obtain the solution.

The principle mathematical formulation is

X(new,relaxed)=X(new)*relax+X(old)*(1-relax)

where X is the variable (TKE or e in this case) and relax is the relaxation factor ranging from 1.0 to 0.0.
For a relaxation factor of 1.0 the new result X(new) will be taken as a final result of the calculation. For relaxation factors below 1.0, the old value X(old) will be mixed with the new result to a certain extend, e.g. 30% for relax =0.7.
This method ensures, that short-time numerical oscillations will not crash the complete system.

ENVI-met realises, if problems with the TKE-e equation system occur and dynamically adjusts the relaxation factor until the problem is solved or a factor of 0.1 is reached.

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