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calc_dt_kernel.f90
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!Crown Copyright 2012 AWE.
!
! This file is part of CloverLeaf.
!
! CloverLeaf is free software: you can redistribute it and/or modify it under
! the terms of the GNU General Public License as published by the
! Free Software Foundation, either version 3 of the License, or (at your option)
! any later version.
!
! CloverLeaf is distributed in the hope that it will be useful, but
! WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
! FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
! details.
!
! You should have received a copy of the GNU General Public License along with
! CloverLeaf. If not, see http://www.gnu.org/licenses/.
!> @brief Fortran timestep kernel
!> @author Wayne Gaudin
!> @details Calculates the minimum timestep on the mesh chunk based on the CFL
!> condition, the velocity gradient and the velocity divergence. A safety
!> factor is used to ensure numerical stability.
MODULE calc_dt_kernel_module
CONTAINS
SUBROUTINE calc_dt_kernel(x_min,x_max,y_min,y_max, &
g_small,g_big,dtmin, &
dtc_safe, &
dtu_safe, &
dtv_safe, &
dtdiv_safe, &
xarea, &
yarea, &
cellx, &
celly, &
celldx, &
celldy, &
volume, &
density0, &
energy0, &
pressure, &
viscosity, &
soundspeed, &
xvel0,yvel0, &
dt_min, &
dt_min_val, &
dtl_control, &
xl_pos, &
yl_pos, &
jldt, &
kldt, &
small)
IMPLICIT NONE
INTEGER :: x_min,x_max,y_min,y_max
REAL(KIND=8) :: g_small,g_big,dtmin,dt_min_val
REAL(KIND=8) :: dtc_safe,dtu_safe,dtv_safe,dtdiv_safe
REAL(KIND=8), DIMENSION(x_min-2:x_max+3,y_min-2:y_max+2) :: xarea
REAL(KIND=8), DIMENSION(x_min-2:x_max+2,y_min-2:y_max+3) :: yarea
REAL(KIND=8), DIMENSION(x_min-2:x_max+2) :: cellx
REAL(KIND=8), DIMENSION(y_min-2:y_max+2) :: celly
REAL(KIND=8), DIMENSION(x_min-2:x_max+2) :: celldx
REAL(KIND=8), DIMENSION(y_min-2:y_max+2) :: celldy
REAL(KIND=8), DIMENSION(x_min-2:x_max+2,y_min-2:y_max+2) :: volume
REAL(KIND=8), DIMENSION(x_min-2:x_max+2,y_min-2:y_max+2) :: density0
REAL(KIND=8), DIMENSION(x_min-2:x_max+2,y_min-2:y_max+2) :: energy0
REAL(KIND=8), DIMENSION(x_min-2:x_max+2,y_min-2:y_max+2) :: pressure
REAL(KIND=8), DIMENSION(x_min-2:x_max+2,y_min-2:y_max+2) :: viscosity
REAL(KIND=8), DIMENSION(x_min-2:x_max+2,y_min-2:y_max+2) :: soundspeed
REAL(KIND=8), DIMENSION(x_min-2:x_max+3,y_min-2:y_max+3) :: xvel0,yvel0
REAL(KIND=8), DIMENSION(x_min-2:x_max+3,y_min-2:y_max+3) :: dt_min
INTEGER :: dtl_control
REAL(KIND=8) :: xl_pos,yl_pos
INTEGER :: jldt,kldt
INTEGER :: small
INTEGER :: j,k
REAL(KIND=8) :: div,dsx,dsy,dtut,dtvt,dtct,dtdivt,cc,dv1,dv2,jk_control
!$OMP PARALLEL
small=0
dt_min_val = g_big
jk_control=1.1
!$OMP DO PRIVATE(dsx,dsy,cc,dv1,dv2,div,dtct,dtut,dtvt,dtdivt)
DO k=y_min,y_max
DO j=x_min,x_max
dsx=celldx(j)
dsy=celldy(k)
cc=soundspeed(j,k)**2
cc=cc+2.0*viscosity(j,k)/density0(j,k)
cc=MAX(SQRT(cc),g_small)
dtct=dtc_safe*MIN(dsx,dsy)/cc
div=0.0
dv1=(xvel0(j ,k)+xvel0(j ,k+1))*xarea(j ,k)
dv2=(xvel0(j+1,k)+xvel0(j+1,k+1))*xarea(j+1,k)
div=div+dv2-dv1
dtut=dtu_safe*2.0*volume(j,k)/MAX(ABS(dv1),ABS(dv2),g_small*volume(j,k))
dv1=(yvel0(j,k )+yvel0(j+1,k ))*yarea(j,k )
dv2=(yvel0(j,k+1)+yvel0(j+1,k+1))*yarea(j,k+1)
div=div+dv2-dv1
dtvt=dtv_safe*2.0*volume(j,k)/MAX(ABS(dv1),ABS(dv2),g_small*volume(j,k))
div=div/(2.0*volume(j,k))
IF(div.LT.-g_small)THEN
dtdivt=dtdiv_safe*(-1.0/div)
ELSE
dtdivt=g_big
ENDIF
dt_min(j,k)=MIN(dtct,dtut,dtvt,dtdivt)
ENDDO
ENDDO
!$OMP END DO
!$OMP DO REDUCTION(MIN : dt_min_val)
DO k=y_min,y_max
DO j=x_min,x_max
IF(dt_min(j,k).LT.dt_min_val) dt_min_val=dt_min(j,k)
ENDDO
ENDDO
!$OMP END DO
!$OMP END PARALLEL
! Extract the mimimum timestep information
dtl_control=10.01*(jk_control-INT(jk_control))
jk_control=jk_control-(jk_control-INT(jk_control))
jldt=MOD(INT(jk_control),x_max)
kldt=1+(jk_control/x_max)
xl_pos=cellx(jldt)
yl_pos=celly(kldt)
IF(dt_min_val.LT.dtmin) small=1
IF(small.NE.0)THEN
WRITE(0,*) 'Timestep information:'
WRITE(0,*) 'j, k : ',jldt,kldt
WRITE(0,*) 'x, y : ',cellx(jldt),celly(kldt)
WRITE(0,*) 'timestep : ',dt_min_val
WRITE(0,*) 'Cell velocities;'
WRITE(0,*) xvel0(jldt ,kldt ),yvel0(jldt ,kldt )
WRITE(0,*) xvel0(jldt+1,kldt ),yvel0(jldt+1,kldt )
WRITE(0,*) xvel0(jldt+1,kldt+1),yvel0(jldt+1,kldt+1)
WRITE(0,*) xvel0(jldt ,kldt+1),yvel0(jldt ,kldt+1)
WRITE(0,*) 'density, energy, pressure, soundspeed '
WRITE(0,*) density0(jldt,kldt),energy0(jldt,kldt),pressure(jldt,kldt),soundspeed(jldt,kldt)
ENDIF
END SUBROUTINE calc_dt_kernel
END MODULE calc_dt_kernel_module