Merge pull request #15711 from cxp484/master

FDS Manuals User: Add CVODE_ORDER parameter description.

Author: cxp484

Manuals/FDS_User_Guide/FDS_User_Guide.tex

@@ -5645,10 +5645,12 @@ \subsection{Chemical Time Integration}
 \item \ct{MIN_EQUIV_RATIO}=0.0
 \item \ct{MAX_EQUIV_RATIO}=20.0
 \item \ct{DO_CHEM_LOAD_BALANCE}=T
+\item \ct{CVODE_ORDER}=0
 \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 does not 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.
+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. The parameter \ct{CVODE_ORDER} controls the order of discretization when solving the ODE system. By default (0), CVODE dynamically selects an order between 1 and 5. For very stiff problems, the user may specify a lower order (1 or 2) to improve stability, at the cost of slower performance because CVODE will take much smaller internal substeps.
+
 User can modify the default values of any or all of these parameters as needed using the following line in the FDS input file:
 \begin{lstlisting}
 &COMB
@@ -11966,7 +11968,7 @@ \chapter{Alphabetical List of Input Parameters}
 
 % ignore namelist/keyword combinations
 % ignorenamelistkw: /BNDF/DEBUG
-% ignorenamelistkw: /COMB/CVODE_ORDER, /COMB/FUEL_ID_FOR_AFT, /COMB/USE_MIXED_ZN_AFT_TMP
+% ignorenamelistkw: /COMB/FUEL_ID_FOR_AFT, /COMB/USE_MIXED_ZN_AFT_TMP
 % ignorenamelistkw: /DEVC/ELEM_ID, /DEVC/STATISTICS
 % ignorenamelistkw: /DUMP/MMS_TIMER, /DUMP/TURB_INIT_CLOCK, /DUMP/GET_CUTCELLS_VERBOSE, /DUMP/WRITE_CVODE_SUBSTEPS
 % ignorenamelistkw: /HVAC/DEBUG
@@ -12108,6 +12110,7 @@ \section{\texorpdfstring{{\tt COMB}}{COMB} (General Combustion Parameters)}
 \endhead
 \ct{CHECK_REALIZABILITY}                         & Logical    & Section~\ref{info:chem_integration}          &           & \ct{F}              \\ \hline
 \ct{COMPUTE_ADIABATIC_FLAME_TEMPERATURE}         & Logical    & Section~\ref{info:extinction}                &           & \ct{F}              \\ \hline
+\ct{CVODE_ORDER}                                 & Integer    & Section~\ref{info:chem_integration}          &           & 0                   \\ \hline
 \ct{DO_CHEM_LOAD_BALANCE}                        & Logical    & Section~\ref{info:chem_integration}          &           & \ct{F}              \\ \hline
 \ct{EQUIV_RATIO_CHECK}                           & Logical    & Section~\ref{info:chem_integration}          &           & \ct{T}              \\ \hline
 \ct{EXTINCTION_MODEL}                            & Character  & Section~\ref{info:extinction}                &           &                     \\ \hline