mod_particle_advect.t

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!> Tracer for advected particles moving with fluid flows
!> By Jannis Teunissen, Bart Ripperda, Oliver Porth, and Fabio Bacchini (2017-2020)
module mod_particle_advect
  use mod_particle_base
 
  private
 
  public :: advect_init
  public :: advect_create_particles
  integer, parameter :: Euler = 1, rk4=2, ark4=3
 
  ! Variables
  public :: vp, rhop
 
contains
 
  subroutine advect_init()
    use mod_global_parameters
    integer :: idir
 
    ngridvars=0
    allocate(vp(ndir))
    do idir = 1, ndir
      vp(idir) = idir
    end do
    ngridvars=ngridvars+ndir
    if(ndefpayload>0) then
      rhop=vp(ndir)+1
      ngridvars=ngridvars+ndefpayload
    end if
 
    particles_fill_gridvars => advect_fill_gridvars
 
    if (associated(particles_define_additional_gridvars)) then
      call particles_define_additional_gridvars(ngridvars)
    end if
 
    select case(integrator_type_particles)
    case('Euler','euler')
      integrator = euler
    case('RK4','Rk4','rk4')
      integrator = rk4
    case('ARK4','ARk4','Ark4','ark4')
      integrator = ark4
    case default
      integrator = ark4
    end select
 
    particles_integrate  => advect_integrate_particles
 
  end subroutine advect_init
 
  subroutine advect_create_particles()
    ! initialise the particles
    use mod_global_parameters
    use mod_usr_methods, only: usr_create_particles, usr_update_payload, usr_check_particle
 
    integer          :: n, idir, igrid, ipe_particle, nparticles_local
    double precision :: x(3, num_particles)
    double precision :: v(3, num_particles)
    double precision :: q(num_particles)
    double precision :: m(num_particles)
    double precision :: rrd(num_particles,ndir)
    double precision :: w(ixg^t,1:nw)
    double precision :: defpayload(ndefpayload)
    double precision :: usrpayload(nusrpayload)
    logical          :: follow(num_particles), check
 
    follow = .false.
    x      = 0.0d0
 
    if (mype==0) then
      if (.not. associated(usr_create_particles)) then
        ! Randomly distributed
        do idir=1,ndir
          do n = 1, num_particles
            rrd(n,idir) = rng%unif_01()
          end do
        end do
        do n=1, num_particles
          {^d&x(^d,n) = xprobmin^d + rrd(n,^d) * (xprobmax^d - xprobmin^d)\}
        end do
      else
        call usr_create_particles(num_particles, x, v, q, m, follow)
      end if
    end if
 
    call mpi_bcast(x,3*num_particles,mpi_double_precision,0,icomm,ierrmpi)
    call mpi_bcast(follow,num_particles,mpi_logical,0,icomm,ierrmpi)
 
    nparticles_local = 0
 
    do n=1,num_particles
      call find_particle_ipe(x(:,n),igrid,ipe_particle)
      particle(n)%igrid  = igrid
      particle(n)%ipe    = ipe_particle
 
      if(ipe_particle == mype) then
        check = .true.
 
        ! Check for user-defined modifications or rejection conditions
        if (associated(usr_check_particle)) call usr_check_particle(igrid, x(:,n), v(:,n), q(n), m(n), follow(n), check)
        if (check) then
          call push_particle_into_particles_on_mype(n)
        else
          cycle
        end if
 
        nparticles_local = nparticles_local + 1
 
        allocate(particle(n)%self)
        particle(n)%self%follow = follow(n)
        particle(n)%self%index  = n
        particle(n)%self%time   = global_time
        particle(n)%self%dt     = 0.0d0
        particle(n)%self%x      = 0.d0
        particle(n)%self%x(:)   = x(:,n)
        w=ps(igrid)%w
        call phys_to_primitive(ixg^ll,ixg^ll,w,ps(igrid)%x)
        do idir=1,ndir
          call interpolate_var(igrid,ixg^ll,ixm^ll,&
               w(ixg^t,iw_mom(idir)),ps(igrid)%x,x(:,n),v(idir,n))
        end do
        particle(n)%self%u(:) = 0.d0
        particle(n)%self%u(1:ndir) = v(1:ndir,n)
 
        ! Compute default and user-defined payloads
        allocate(particle(n)%payload(npayload))
        if(ndefpayload>0) then
          call advect_update_payload(igrid,x(:,n),v(:,n),q(n),m(n),defpayload,ndefpayload,0.d0)
          particle(n)%payload(1:ndefpayload)=defpayload
        end if
        if (associated(usr_update_payload)) then
          call usr_update_payload(igrid,x(:,n),v(:,n),q(n),m(n),usrpayload,nusrpayload,0.d0)
          particle(n)%payload(ndefpayload+1:npayload)=usrpayload
        end if
      end if
 
    end do
 
    call mpi_allreduce(nparticles_local,nparticles,1,mpi_integer,mpi_sum,icomm,ierrmpi)
 
  end subroutine advect_create_particles
 
  subroutine advect_fill_gridvars
    use mod_global_parameters
 
    integer                                   :: igrid, iigrid, idir
    double precision, dimension(ixG^T,1:nw)   :: w
 
    ! Fill fluid velocity only
    do iigrid=1,igridstail; igrid=igrids(iigrid);
      gridvars(igrid)%w(ixg^t,1:ngridvars) = 0.0d0
      w(ixg^t,1:nw) = ps(igrid)%w(ixg^t,1:nw)
      call phys_to_primitive(ixg^ll,ixg^ll,w,ps(igrid)%x)
      gridvars(igrid)%w(ixg^t,vp(:)) = w(ixg^t,iw_mom(:))
      gridvars(igrid)%w(ixg^t,rhop) = w(ixg^t,iw_rho)
    end do
 
  end subroutine advect_fill_gridvars
 
  subroutine advect_integrate_particles(end_time)
    ! this solves dx/dt=v for particles
    use mod_odeint
    use mod_global_parameters
    use mod_usr_methods, only: usr_create_particles, usr_update_payload
    double precision, intent(in) :: end_time
 
    double precision, dimension(1:ndir) :: v, x
    double precision                 :: defpayload(ndefpayload)
    double precision                 :: usrpayload(nusrpayload)
    double precision                 :: tloc, tlocnew, dt_p, h1, tk
    double precision, dimension(1:ndir) :: yk, k1, k2, k3, k4
    double precision,parameter       :: eps=1.0d-6, hmin=1.0d-8
    integer                          :: ipart, iipart, igrid
    integer                          :: nok, nbad, ierror
 
    do iipart=1,nparticles_active_on_mype
      ipart                   = particles_active_on_mype(iipart);
      igrid                   = particle(ipart)%igrid
      igrid_working           = igrid
      dt_p                    = advect_get_particle_dt(particle(ipart), end_time)
      particle(ipart)%self%dt = dt_p
 
      tloc                    = particle(ipart)%self%time
      x(1:ndir)               = particle(ipart)%self%x(1:ndir)
      tlocnew                 = tloc+dt_p
 
      ! Position update
      select case (integrator)
      case (euler) 
        ! Simple forward Euler 
        call derivs_advect(tloc,x,v)
        particle(ipart)%self%x(1:ndir) = particle(ipart)%self%x(1:ndir) + dt_p * v(1:ndir)
 
      case (rk4)
        ! Runge-Kutta order 4
        tk = tloc
        yk = x
        call derivs_advect(tk,yk,k1)
        tk = tloc + dt_p/2.d0
        yk = x + dt_p*k1/2.d0
        call derivs_advect(tk,yk,k2)
        tk = tloc + dt_p/2.d0
        yk = x + dt_p*k2/2.d0
        call derivs_advect(tk,yk,k3)
        tk = tloc + dt_p
        yk = x + dt_p*k3
        call derivs_advect(tloc,yk,k4)
        x = x + dt_p/6.d0*(k1 + 2.d0*k2 + 2.d0*k3 + k4)
      
      case (ark4)
        ! Adaptive stepwidth RK4:
        h1 = dt_p/2.0d0
        call odeint(x,ndir,tloc,tlocnew,eps,h1,hmin,nok,nbad,derivs_advect,rkqs,ierror)
  
        if (ierror /= 0) then
          print *, "odeint returned error code", ierror
          print *, "1 means hmin too small, 2 means MAXSTP exceeded"
          print *, "Having a problem with particle", iipart
        end if
      end select
      particle(ipart)%self%x(1:ndir) = x(1:ndir)
 
      ! Velocity update
      call get_vec_advect(igrid,x,tlocnew,v,vp(1),vp(ndir))
      particle(ipart)%self%u(1:ndir) = v(1:ndir)
 
      ! Time update
      particle(ipart)%self%time = tlocnew
 
      ! Update payload
      if(ndefpayload>0) then
        call advect_update_payload(igrid,x,v,0.d0,0.d0,defpayload,ndefpayload,tlocnew)
        particle(ipart)%payload(1:ndefpayload) = defpayload
      end if
      if (associated(usr_update_payload)) then
        call usr_update_payload(igrid,x,v,0.d0,0.d0,usrpayload,nusrpayload,tlocnew)
        particle(ipart)%payload(ndefpayload+1:npayload) = usrpayload
      end if
 
    end do
 
  end subroutine advect_integrate_particles
 
  !> Payload update
  subroutine advect_update_payload(igrid,xpart,upart,qpart,mpart,mypayload,mynpayload,particle_time)
    use mod_global_parameters
    integer, intent(in)           :: igrid,mynpayload
    double precision, intent(in)  :: xpart(1:ndir),upart(1:ndir),qpart,mpart,particle_time
    double precision, intent(out) :: mypayload(mynpayload)
    double precision              :: rho, rho1, rho2, td
 
    td = (particle_time - global_time) / dt
 
    ! Payload 1 is density
    if (mynpayload > 0 ) then
      if (time_advance) then
        call interpolate_var(igrid,ixg^ll,ixm^ll,gridvars(igrid)%wold(ixg^t,rhop),ps(igrid)%x,xpart,rho1)
        call interpolate_var(igrid,ixg^ll,ixm^ll,gridvars(igrid)%w(ixg^t,rhop),ps(igrid)%x,xpart,rho2)
        rho = rho1 * (1.0d0 - td) + rho2 * td
      else
        call interpolate_var(igrid,ixg^ll,ixm^ll,gridvars(igrid)%w(ixg^t,rhop),ps(igrid)%x,xpart,rho)
      end if
      mypayload(1) = rho * w_convert_factor(1)
    end if
 
  end subroutine advect_update_payload
 
  subroutine derivs_advect(t_s,x,dxdt)
    use mod_global_parameters
    use mod_geometry
    double precision :: t_s, x(ndir)
    double precision :: dxdt(ndir)
 
    double precision :: v(ndir)
 
    call get_vec_advect(igrid_working,x,t_s,v,vp(1),vp(ndir))
    select case (coordinate)
    case (cylindrical)
      v(phi_) = v(phi_)/x(r_)
    case (spherical)
      v(2) = v(2)/x(1)
      v(3) = v(3)/(x(1)*sin(x(2)))
    end select
    dxdt(:) = v(:)
 
  end subroutine derivs_advect
 
  function advect_get_particle_dt(partp, end_time) result(dt_p)
    use mod_global_parameters
    type(particle_ptr), intent(in) :: partp
    double precision, intent(in)   :: end_time
    double precision               :: dt_p
    integer                        :: ipart, iipart, idims
    double precision               :: v(1:ndir),dtdims(1:ndim)
 
    if (const_dt_particles > 0) then
      dt_p = const_dt_particles
      return
    end if
 
    ! make sure we step only one cell at a time:
    call derivs_advect(partp%self%time,partp%self%x,v)
    do idims=1,ndim
      dtdims(idims)=minval(ps(partp%igrid)%ds(ixm^t,idims))/(max(abs(v(idims)),smalldouble))
    end do
 
    dt_p = particles_cfl*minval(dtdims)
 
    ! Make sure we do not advance beyond end_time
    call limit_dt_endtime(end_time - partp%self%time, dt_p)
 
  end function advect_get_particle_dt
 
  subroutine get_vec_advect(igrid,x,tloc,var,ibeg,iend)
    use mod_global_parameters
 
    integer,intent(in)                                   :: igrid, ibeg, iend
    double precision,dimension(ndir), intent(in)         :: x
    double precision, intent(in)                         :: tloc
    double precision,dimension(iend-ibeg+1), intent(out) :: var
    double precision,dimension(iend-ibeg+1)              :: e1, e2
    integer                                              :: ivar, iloc
    double precision                                     :: td
 
    if(.not.time_advance) then
      do ivar=ibeg,iend
        iloc = ivar-ibeg+1
        call interpolate_var(igrid,ixg^ll,ixm^ll,gridvars(igrid)%w(ixg^t,ivar),ps(igrid)%x(ixg^t,1:ndim),x,var(iloc))
      end do
    else
      td = (tloc - global_time) / dt
      do ivar=ibeg,iend
        iloc = ivar-ibeg+1
        call interpolate_var(igrid,ixg^ll,ixm^ll,gridvars(igrid)%wold(ixg^t,ivar),ps(igrid)%x(ixg^t,1:ndim),x,e1(iloc))
        call interpolate_var(igrid,ixg^ll,ixm^ll,gridvars(igrid)%w(ixg^t,ivar),ps(igrid)%x(ixg^t,1:ndim),x,e2(iloc))
        var(iloc) = e1(iloc) * (1.0d0 - td) + e2(iloc) * td
      end do
    end if
 
  end subroutine get_vec_advect
 
end module mod_particle_advect