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FDS User Guide: CVODE section minor modification. #13848

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FDS User Guide: CVODE section minor modification. #13848

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2 changes: 1 addition & 1 deletion Manuals/FDS_User_Guide/FDS_User_Guide.tex
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Expand Up @@ -5522,7 +5522,7 @@ \subsection{Chemical Time Integration}
\item \ct{MAX_EQUIV_RATIO}=20.0
\item \ct{DO_CHEM_LOAD_BALANCE}=T
\end{itemize}
The parameter \ct{FINITE_RATE_MIN_TEMP} defines the minimum temperature (in ~$^\circ$C) above which chemistry calculation will be performed. CVODE allows specification of relative and absolute tolerances at the species-level using the \ct{ODE_REL_ERROR} and \ct{ODE_ABS_ERROR} parameters in the \ct{SPEC} input line. These tolerances can also be set globally in the \ct{COMB} input line, with species-level settings taking precedence. Currently, CVODE doen't allow relative tolerance at the species level. The minimum concentration of a species is determined as the product of \ct{ODE_REL_ERROR} and \ct{ZZ_MIN_GLOBAL}. Concentrations below this threshold are treated as zero.
The parameter \ct{FINITE_RATE_MIN_TEMP} defines the minimum temperature (in ~$^\circ$C) above which chemistry calculation will be performed. CVODE allows specification of relative and absolute tolerances at the species-level using the \ct{ODE_REL_ERROR} and \ct{ODE_ABS_ERROR} parameters in the \ct{SPEC} input line. These tolerances can also be set globally in the \ct{COMB} input line, with species-level settings taking precedence. Currently, CVODE doesn't allow relative tolerance at the species level. The minimum concentration of a species is determined as the product of \ct{ODE_REL_ERROR} and \ct{ZZ_MIN_GLOBAL}. Concentrations below this threshold are treated as zero.

Additional optional parameters include \ct{EQUIV_RATIO_CHECK}, \ct{MIN_EQUIV_RATIO}, and \ct{MAX_EQUIV_RATIO}. When \ct{EQUIV_RATIO_CHECK} is enabled (set to true), the chemistry calculation is performed only for those cells for which equivalence ratio is within the specified \ct{MIN_EQUIV_RATIO} and \ct{MAX_EQUIV_RATIO} limits, reducing computational time. Enabling \ct{DO_CHEM_LOAD_BALANCE} significantly accelerates chemistry calculations by distributing the computational load evenly across all MPI processes.
User can modify the default values of any or all of these parameters as needed using the following line in the FDS input file:
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