grans_obj_PrepareSolverFields Subroutine

    subroutine grans_obj_PrepareSolverFields(this)
      !> Prepares fields used by the GRANS solver.
      implicit none
      class(grans_obj), intent(inout) :: this                                  !! GRANS solver
      ! Work variables
      character(len=str64) :: filename
      logical              :: overwrite

      call this%parser%Get('Fields write file',  filename)
      call this%parser%Get('Fields overwrite ',  overwrite, default=.true.)

      ! Initialize fields container
      call this%fields%Initialize(this%block,this%parallel)

      ! Set IO parameters
      call this%fields%SetWriteFileName(filename)
      call this%fields%SetOverwrite(overwrite)

      ! Add each field to main container.
      ! This will allocate the underlying arrays
      ! and facilitate IO.

      if (this%use_RP .or. this%use_IB) then
        call this%fields%Add('rhs',  0,this%rhs    )
        call this%fields%Add('ibS',  0, this%ibS   )
        call this%fields%Add('ibVF', 0, this%ibVF  )
        call this%fields%Add('ibF1', 1, this%ibF(1))
        call this%fields%Add('ibF2', 2, this%ibF(2))
        call this%fields%Add('ibF3', 3, this%ibF(3))
        call this%fields%Add('ibN1', 1, this%ibN(1))
        call this%fields%Add('ibN2', 2, this%ibN(2))
        call this%fields%Add('ibN3', 3, this%ibN(3))

        ! Intialize IB vol frac and ibS
        this%ibVF%cell = 0.0_wp
        this%ibS%cell  = 0.0_wp
      end if

      ! Initialize particle vol frac
      call this%fields%Add('PVF', 0,this%PVF  )
      this%PVF%cell  = 0.0_wp

      return
    end subroutine grans_obj_PrepareSolverFields