FDS Source: Issue firemodels#9520. Throw an ERROR if BURN_AWAY is app…

…lied inconsistently.

Manuals/FDS_User_Guide/FDS_User_Guide.tex

@@ -3003,10 +3003,10 @@ \subsubsection{Special topic: Making Fuels Disappear}
 If a combustible solid is to disappear from the simulation once it is consumed, set {\ct BURN\_AWAY=T} on the {\ct SURF} line that is applied to the {\ct OBST}. The solid object disappears from the calculation cell by cell as the mass contained within each solid cell is consumed either by the pyrolysis reactions or by the prescribed HRR. The following issues should be kept in mind when using {\ct BURN\_AWAY}:
 \begin{itemize}
 \item Use {\ct BURN\_AWAY} cautiously. If an object has the potential of burning away, a significant amount of extra memory has to be set aside to store additional information for newly exposed surfaces.
-\item If {\ct BURN\_AWAY} is prescribed, the {\ct SURF} should be applied to the entire object, not just a face of the object because it is unclear how to handle edges of solid obstructions that have different {\ct SURF\_ID}s on different faces.
 \item The heat conduction into an {\ct OBST} that can {\ct BURN\_AWAY} is limited to 1-D. On the {\ct SURF} line, specify the {\ct THICKNESS} to be approximately that of a single cell, and also set {\ct BACKING='VOID'}. It is assumed that the solid is relatively well-insulated and that the in-depth temperature profile drops off relatively quickly at the surface. When a cell is removed, the newly exposed surface is initially at ambient temperature but heats up quickly at the surface.
 \item If the volume of the obstruction changes because it has to conform to the uniform mesh, FDS does {\em not} adjust the burning rate to account for this as it does with various quantities associated with areas, like {\ct HRRPUA}.
-\item A parameter called {\ct BULK\_DENSITY} (kg/m$^3$) can be applied to the {\ct OBST} rather than the {\ct SURF} line. This parameter is used to determine the {\em combustible} mass of the solid object. The calculation uses the user-specified object dimensions, not those of the mesh-adjusted object. This parameter over-rides all other parameters from which a combustible mass would be calculated. Note that without a {\ct BULK\_DENSITY} specified, the total amount of mass burned will depend upon the grid resolution. The use of the {\ct BULK\_DENSITY} parameter ensures a specific fuel mass per unit volume that is independent of the grid resolution. Note that in the event that the solid phase reaction involves the production of solid residue (like char or ash), the {\ct BULK\_DENSITY} refers to the mass of the solid that is converted to gas upon reaction.
+\item A parameter called {\ct BULK\_DENSITY} (kg/m$^3$) can be specified on the {\ct OBST} line to designate the {\em combustible} mass of the solid object. The calculation uses the user-specified object dimensions, not those of the mesh-adjusted object. This parameter over-rides all other parameters with which a combustible mass would be calculated. Note that without a {\ct BULK\_DENSITY} specified, the total amount of mass burned will depend upon the grid resolution. The use of the {\ct BULK\_DENSITY} parameter ensures a specific fuel mass per unit volume that is independent of the grid resolution. Note that in the event that the solid phase reaction involves the production of solid residue (like char or ash), the {\ct BULK\_DENSITY} refers to the mass of the solid that is converted to gas upon reaction.
+\item If {\ct BURN\_AWAY} is prescribed on a {\ct SURF} line, that single {\ct SURF\_ID} should be applied to the entire {\ct OBST}, not to specific faces, because it is unclear how to remove solid obstructions that have different {\ct SURF\_ID}s on different faces. An exception to this rule is where a {\ct BULK\_DENSITY} is applied to the {\ct OBST}, in which case the {\ct OBST} will disappear when the mass of fuel designated by {\ct BULK\_DENSITY} is consumed rather than that of any particular face.
 \item To compensate for the inaccurate obstruction area, an additional parameter {\ct AREA\_MULTIPLIER} can be added on the {\ct SURF} line. It will multiply all mass and energy fluxes with a user-specified factor. Check that the {\ct BURN\_AWAY} works as expected if these two features are combined.
 \item The mass of the object is based on the densities of all material components ({\ct MATL}), but it is only consumed by mass fluxes of the {\em known} species. If the sum of the gaseous yields is less than one, it will take longer to consume the mass.
 \end{itemize}

Source/read.f90

@@ -10162,6 +10162,18 @@ SUBROUTINE READ_OBST
                OB%BULK_DENSITY = BULK_DENSITY
                IF (BULK_DENSITY > 0._EB) OB%MASS = OB%BULK_DENSITY*(OB%X2-OB%X1)*(OB%Y2-OB%Y1)*(OB%Z2-OB%Z1)
 
+               ! Check for inconsistencies in specification of BUL_DENSITY
+
+               IF (OB%CONSUMABLE .AND. OB%BULK_DENSITY <= 0._EB) THEN
+                  DO IOR=-2,3
+                     IF (IOR==0) CYCLE
+                     IF (OB%SURF_INDEX(IOR)/=OB%SURF_INDEX(-3)) THEN
+                        WRITE(MESSAGE,'(A,A,A)')  'ERROR: OBST ',TRIM(OB%ID),' needs a BULK_DENSITY if it is to BURN_AWAY'
+                        CALL SHUTDOWN(MESSAGE,PROCESS_0_ONLY=.FALSE.) ; RETURN
+                     ENDIF
+                  ENDDO
+               ENDIF
+
                ! Make obstruction invisible if it's within a finer mesh
 
                DO NOM=1,NM-1