FDS Source: Issue #14221, Disallow inconsistent backings

Author: mcgratta

Manuals/FDS_User_Guide/FDS_User_Guide.tex

@@ -2428,7 +2428,9 @@ \subsection{Thermal Properties}
 \subsection{Back Side Boundary Conditions}
 \label{info:BACKING}
 
-There are several options for defining the back surface boundary condition of a thermally-thick obstruction. The default, \ct{BACKING='EXPOSED'} on the \ct{SURF} line, assumes that the back side is exposed to the thermal environment behind the solid\footnote{Prior to FDS, the boundary condition \ct{BACKING='EXPOSED'} was limited to zero or one cell thick solids. This restriction no longer applies.}. FDS calculates the heat transfer through the solid into the space behind the wall and vis versa. This heat conduction calculation in the solid is based on the \ct{THICKNESS} of the material layers specified on the \ct{SURF} line, not the dimension of the \ct{OBST} or other solid that the \ct{SURF} is applied to. For example, when modeling a steel plate that is 5~mm thick, if the \ct{OBST} is approximated as a zero-cell thick sheet because 5~mm is less than half the grid dimension of 5~cm, then FDS will still compute the heat transfer through a 5~mm thick plate of steel. If a \ct{SURF} with \ct{BACKING='EXPOSED'} is applied to the surface of a solid whose dimension in the normal direction is at least one gas phase grid cell length greater than \ct{THICKNESS}, FDS will then ignore \ct{BACKING='EXPOSED'} and apply \ct{BACKING='VOID'} instead. This latter boundary condition is described below.
+There are several options for defining the back surface boundary condition of a thermally-thick obstruction. The default, \ct{BACKING='EXPOSED'} on the \ct{SURF} line, assumes that the back side is exposed to the thermal environment behind the solid. FDS calculates the heat transfer through the solid into the space behind the wall and vis versa. This heat conduction calculation in the solid is based on the \ct{THICKNESS} of the material layers specified on the \ct{SURF} line, not the dimension of the \ct{OBST} or other solid that the \ct{SURF} is applied to. For example, when modeling a steel plate that is 5~mm thick, if the \ct{OBST} is approximated as a zero-cell thick sheet because 5~mm is less than half the grid dimension of 5~cm, then FDS will still compute the heat transfer through a 5~mm thick plate of steel. If a \ct{SURF} with \ct{BACKING='EXPOSED'} is applied to the surface of a solid whose dimension in the normal direction is at least one gas phase grid cell length greater than \ct{THICKNESS}, FDS will then ignore \ct{BACKING='EXPOSED'} and apply \ct{BACKING='VOID'} instead. This latter boundary condition is described below.
+
+If a \ct{VENT} is applied to a thermally-thick obstruction, the \ct{SURF_ID} associated with this \ct{VENT} must describe a thermally-thick solid as well; that is, the \ct{SURF} line must have a \ct{MATL_ID}.
 
 An alternative back side boundary condition, \ct{BACKING='INSULATED'}, assumes that the solid backs up to a perfectly insulated material, in which case no heat is lost to the back side. Use of this condition means specifying properties of the inner insulating material is not necessary because it is assumed to be perfectly insulated.
 
@@ -14079,6 +14081,7 @@ \chapter{Error Codes}
 375  \> \ct{OBST ... is VARIABLE_THICKNESS or HT3D and needs a MATL_ID.} \> Section~\ref{info:HT3D_Limitations}  \\
 376  \> \ct{Meshes must have the same y/z bounds for TUNNEL_PRECONDITIONER.} \> Section~\ref{tunnel_solver}  \\
 377  \> \ct{SURF ... IMPINGING JET model requires ...} \> Section~\ref{info:impinging_jet}  \\
+378  \> \ct{SURF ... cannot be applied to a thermally-thick solid.} \> Section~\ref{info:BACKING}  \\
      \>                                                                               \>                                     \\
 381  \> \ct{Need more spectral band limits.} \> Section~\ref{info:RADI_Wide_Band}  \\
 382  \> \ct{Spectral band limits should be given in ascending order.} \> Section~\ref{info:RADI_Wide_Band}  \\

Source/init.f90

@@ -3752,6 +3752,7 @@ SUBROUTINE FIND_WALL_BACK_INDICES(NM)
 
 DO IW=1,M%N_EXTERNAL_WALL_CELLS+M%N_INTERNAL_WALL_CELLS
    CALL FIND_WALL_BACK_INDEX(NM,IW)
+   IF (STOP_STATUS/=NO_STOP) RETURN
 ENDDO
 
 ! Search all neighboring meshes for 3-D WALL cells. Add index and surface information from these to M%OMESH(NOM)%WALL_RECV_BUFFER
@@ -4039,11 +4040,15 @@ SUBROUTINE FIND_WALL_BACK_INDEX(NM,IW)
    ! Determine if the back face is found
 
    IF ((.NOT.OM%CELL(IC)%SOLID .AND. OM%CELL(IC)%WALL_INDEX(IOR)>0) .OR. NOM==0) THEN ! the back wall face is found
-   !  IF (NOM>0 .AND. SF%BACKING/=EXPOSED) RETURN  ! No need to assign back cell information for anything but exposed backing
       ONE_D%BACK_INDEX = OM%CELL(IC)%WALL_INDEX(IOR)
       ONE_D%BACK_MESH  = NOM
       ONE_D%BACK_SURF  = OM%CELL(IC)%SURF_INDEX(IOR)
       IF (NOM>0) THEN
+         IF (SURFACE(ONE_D%BACK_SURF)%THERMAL_BC_INDEX/=THERMALLY_THICK) THEN
+            WRITE(MESSAGE,'(3A)') 'ERROR(378): SURF ',TRIM(SURFACE(ONE_D%BACK_SURF)%ID),&
+                                  ' cannot be applied to a thermally-thick solid.'
+            CALL SHUTDOWN(MESSAGE,PROCESS_0_ONLY=.FALSE.) ; RETURN
+         ENDIF
          OS => M%OMESH(NOM)%WALL_RECV_BUFFER
          IF (.NOT.ALLOCATED(OS%ITEM_INDEX)) THEN
             OS%N_ITEMS_DIM = 50

Source/main.f90

@@ -2090,6 +2090,8 @@ SUBROUTINE INITIALIZE_BACK_WALL_EXCHANGE
    CALL FIND_WALL_BACK_INDICES(NM)
 ENDDO
 
+CALL STOP_CHECK(1)
+
 ! Adjust the thickness and internal noding of HT3D surfaces
 
 DO NM=LOWER_MESH_INDEX,UPPER_MESH_INDEX

Verification/WUI/dragon_5a.fds

@@ -15,7 +15,7 @@
 &OBST XB=-0.30, 0.00,-0.10, 0.10,2.25,2.25, SURF_ID='STEEL SHEET' /
 &OBST XB=-0.10, 0.00,-0.10, 0.10,2.10,2.10, SURF_ID='STEEL SHEET' /
 
-&OBST XB=-0.30,-0.10,-0.10, 0.10,0.90,1.00, SURF_IDS='BLOWER','STEEL SHEET','STEEL SHEET' /
+&OBST XB=-0.30,-0.10,-0.10, 0.10,0.90,1.00, SURF_IDS='BLOWER','INERT','INERT' /
 &SURF ID='BLOWER', VEL=-3.0, COLOR='BLUE' /
 
 &VENT MB='XMIN', SURF_ID='OPEN' /