Sub-domain and slope problems in LSET models

[alips123]

Hi everyone,
I hope you are doing well. I am facing with some unintentional weird things in a simple model I have created.
I have modeled a slope area of veg, an at the end, there is a building on a inert horizontal area. I have used subdomains to use multi mesh processing method.
I am seeing two possible potential problems in my model.
First: when I am using subdomains, however, I have not defined any gap between domains and they are continuous but I am seeing a little gap. Can it affect results? Am I doing something wrong?
Second: When I am using &GEOM for creating a sloped area, at the end, even first, of the slope, vegetation fell down to the least z of the defined domain. What is more interesting is that fire propagates vertically down. It isn't correct, is it? How can I solve this too?

I upload a pic to show where the problem is:
https://ibb.co/x8tfHm2n

[marcosvanella]

Hi @alips123, can you post your input file?

[alips123]

Sure. Here you are:

&HEAD CHID='wui_validation', TITLE='WUI Fire Scenario/

&MISC LEVEL_SET_MODE=4 / ! Assume terrain image for DEM; in practice, use external tool for MESH XB from DEM

&TIME T_END=3000 / ! Up to
&SPEC ID='CELLULOSE', C=2.28, H=6.34, O=2.44 / ! For grass/shrubs level set, but custom

&REAC FUEL='CELLULOSE', HEAT_OF_COMBUSTION=15600., CO_YIELD=0.004, SOOT_YIELD=0.01 /

&WIND V0=3 /

&SPEC ID='WATER VAPOR'
CONDUCTIVITY = 0.026 ! W/m·K at 300 K (approximate)
VISCOSITY = 1.0E-5 ! kg/m·s
DIFFUSIVITY = 2.6E-5 ! m²/s
PRIMITIVE = .TRUE. ! FDS recognizes as built-in/

&MESH IJK=10,38,20 , XB= 0.0, 10.0, -1 , 37, 0.0, 20.0 /
&MESH IJK=10,38,20 , XB=10.0, 20.0, -1 , 37, 0.0, 20.0 /
&MESH IJK=10,38,20 , XB=20.0, 30.0, -1 , 37, 0.0, 20.0 /
&MESH IJK=10,38,20 , XB=30.0, 40.0, -1 , 37, 0.0, 20.0 /

&MESH IJK=10,38,20 , XB= 0.0, 10.0, 37 , 75, 0.0, 20.0 /
&MESH IJK=10,38,20 , XB=10.0, 20.0, 37 , 75, 0.0, 20.0 /
&MESH IJK=20,76,40 , XB=20.0, 30.0, 37 , 75, 0.0, 20.0 /
&MESH IJK=20,76,40 , XB=30.0, 40.0, 37 , 75, 0.0, 20.0 /

!====
! CHAR AND ASH – REQUIRED FOR PYROLYSIS
!====
&MATL ID='CHAR'
DENSITY = 300.0,
SPECIFIC_HEAT = 2.04,
CONDUCTIVITY = 0.052,
EMISSIVITY = 0.95/

&MATL ID='ASH'
DENSITY = 67
SPECIFIC_HEAT = 1.96
CONDUCTIVITY = 0.1
EMISSIVITY = 0.95/

&PART ID='brands'
DRAG_LAW='DISK'
SURF_ID='firebrand'
COLOR='ORANGE'
PROP_ID='disk image'
SAMPLING_FACTOR=1
QUANTITIES='PARTICLE WEIGHTING FACTOR','PARTICLE TEMPERATURE'/

&SURF ID = 'firebrand'
MATL_ID = 'CHAR'
THICKNESS = 0.0005
LENGTH = 0.005
WIDTH = 0.005
GEOMETRY = 'CARTESIAN'
TMP_INNER = 1000./

&SURF ID='GRASS', VEG_LSET_SIGMA=4100, VEG_LSET_SURF_LOAD=3, VEG_LSET_ROS_00=0.06, VEG_LSET_CHAR_FRACTION =0.3, VEG_LSET_HT=1, COLOR= 'GREEN' , DRAG_COEFFICIENT=1, VEG_LSET_ROS_FIXED=T/

!&SURF ID='GRASS', VEG_LSET_FUEL_INDEX=5 , VEG_LSET_SURF_LOAD=10, VEG_LSET_HT=1, VEG_LSET_ROS_00=0.06, DRAG_COEFFICIENT=1, COLOR= 'GREEN'/

&GEOM ID='terrain', SURF_ID='GRASS','INERT', IS_TERRAIN=T,
VERTS= 40,0,0,
5, 0.0,0.0,
0,0,0,
0,70,7,
40,70,7,
FACES=2,4,3,2,
2,5,4,1,
2,1,5,2 /

&SURF ID='IGN_GRASS', VEG_LSET_FUEL_INDEX=5, VEG_LSET_IGNITE_TIME=0. , COLOR='RED'/
&VENT XB=4.5,5.5,-1,1,0,0, SURF_ID='IGN_GRASS' , GEOM=T/

&VENT XB=0.0,39.5,70,75.0, 7,7, SURF_ID='INERT' , IOR=3 /

&VENT MB='XMIN', SURF_ID='OPEN' /
&VENT MB='XMAX', SURF_ID='OPEN' /
&VENT MB='YMIN', SURF_ID='OPEN' /
&VENT MB='YMAX', SURF_ID='OPEN' /
&VENT MB='ZMAX', SURF_ID='OPEN' /

&SURF ID = 'TREE_SURF'
MATL_ID = 'TREE_DRY'
MOISTURE_FRACTION = 0.3
SURFACE_VOLUME_RATIO = 8000.
LENGTH = 0.1
GEOMETRY = 'CYLINDRICAL' /

&MATL ID='TREE_DRY', DENSITY=1000., CONDUCTIVITY=2, SPECIFIC_HEAT=2.5 , N_REACTIONS=1, A(1) = 1.89E10,
E(1) = 1.51E5,
N_S(1) = 1.0,
MATL_ID(1,1) = 'CHAR',
NU_MATL(1,1) = 0.18,
SPEC_ID(1,1) ='CELLULOSE',
NU_SPEC(1,1) = 0.82,
HEAT_OF_REACTION(1) = 416.,
HEAT_OF_COMBUSTION(1,1)= 14516. /

&MATL ID = 'MOISTURE'
DENSITY = 1000.
CONDUCTIVITY = 0.1
SPECIFIC_HEAT= 4.184
N_REACTIONS = 1
REFERENCE_TEMPERATURE = 100.
NU_SPEC = 1.0
SPEC_ID = 'WATER VAPOR'
HEAT_OF_REACTION= 2500. /

&TAIL/

[marcosvanella]

Drop the VENT line &VENT XB=0.0,39.5,70,75.0, 7,7, SURF_ID='INERT' , IOR=3 / (only ignitor vents can be used with GEOM, otherwise you set the boundary conditions through the SURF_ID of each triangle), and swap your &GEOM line by this one:

&GEOM ID='terrain', SURF_ID='GRASS','INERT', IS_TERRAIN=T
VERTS= 40,0,0,
5, 0.0,0.0,
0,0,0,
0,70,7,
40,70,7,
40,75,7,
0,75,7,
FACES=2,4,3,1,
      2,5,4,1,
      2,1,5,1,
      5,6,7,2,
      5,7,4,2
 /

Note I added the inert region at the end directly on the terrain through the last two VERTS and FACES. You can place your building obstacles on top, like I did in the picture attached with a line &OBST XB=25,35,71,74,7,12 /.

You can place the particles in the domain using INIT lines, see section 15.4.1 Basic Geometry and Boundary Conditions for solid particles.

[alips123]

Sorry for late reply. I was really busy didn't let me to reply sooner.
Appreciate for help.

Regards,