shiftedPBCs Subroutine

  subroutine shiftedPBCs
      ! Nudge the flow in a region near the outlet
      use modglobal, only : ib, itot, ie, jb, je, kb, ke, xh, ds, dyi, xlen, rk3step, dt, pi
      use modfields, only : u0, v0, w0, u0av, up, vp, wp, vm
      use decomp_2d, only : zstart

      integer :: i, j, k, ig
      real :: vs, RHS, rk3coef

      if (ds > 0) then
      rk3coef = dt / (4. - dble(rk3step))
      do i = ib,ie
         ig = i + zstart(1) - 1 ! global i position
         if (ig > int(itot/2)) then
            do j = jb,je
               do k = kb,ke
                  vs = 0.5 * pi * ds / (0.5*xlen) * u0av(k) * sin(pi*(xh(ig)-xh(int(itot/2))) / (0.5*xlen))
                  up(i,j,k) = up(i,j,k) - vs * (u0(i,j,k) - u0(i,j-1,k)) * dyi
                  vp(i,j,k) = vp(i,j,k) - vs * (v0(i,j,k) - v0(i,j-1,k)) * dyi
                  wp(i,j,k) = wp(i,j,k) - vs * (w0(i,j,k) - w0(i,j-1,k)) * dyi
               end do
            end do
         end if
      end do

      end if

   end subroutine shiftedPBCs