fluid_scheme_incompressible.f90

Go to the documentation of this file.

! Copyright (c) 2020-2025, The Neko Authors
! All rights reserved.
!
! Redistribution and use in source and binary forms, with or without
! modification, are permitted provided that the following conditions
! are met:
!
!   * Redistributions of source code must retain the above copyright
!     notice, this list of conditions and the following disclaimer.
!
!   * Redistributions in binary form must reproduce the above
!     copyright notice, this list of conditions and the following
!     disclaimer in the documentation and/or other materials provided
!     with the distribution.
!
!   * Neither the name of the authors nor the names of its
!     contributors may be used to endorse or promote products derived
!     from this software without specific prior written permission.
!
! THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
! "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
! LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
! FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
! COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
! INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
! BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
! LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
! CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
! LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
! ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
! POSSIBILITY OF SUCH DAMAGE.
!
module fluid_scheme_incompressible
  use fluid_scheme_base, only : fluid_scheme_base_t
  use gather_scatter, only : gs_t, gs_op_min, gs_op_max
  use mean_sqr_flow, only : mean_sqr_flow_t
  use neko_config, only : neko_bcknd_device
  use checkpoint, only : chkp_t
  use mean_flow, only : mean_flow_t
  use num_types, only : rp, i8
  use comm
  use fluid_source_term, only: fluid_source_term_t
  use field, only : field_t
  use space, only : space_t, gll
  use dofmap, only : dofmap_t
  use zero_dirichlet, only : zero_dirichlet_t
  use krylov, only : ksp_t, krylov_solver_factory, krylov_solver_destroy, &
    ksp_max_iter
  use coefs, only: coef_t
  use usr_inflow, only : usr_inflow_t, usr_inflow_eval
  use dirichlet, only : dirichlet_t
  use field_dirichlet, only : field_dirichlet_t
  use field_dirichlet_vector, only: field_dirichlet_vector_t
  use jacobi, only : jacobi_t
  use sx_jacobi, only : sx_jacobi_t
  use device_jacobi, only : device_jacobi_t
  use hsmg, only : hsmg_t
  use phmg, only : phmg_t
  use precon, only : pc_t, precon_factory, precon_destroy
  use fluid_stats, only : fluid_stats_t
  use bc, only : bc_t
  use bc_list, only : bc_list_t
  use mesh, only : mesh_t, neko_msh_max_zlbls, neko_msh_max_zlbl_len
  use math, only : cfill, add2s2, glsum
  use device_math, only : device_cfill, device_add2s2
  use operators, only : cfl
  use logger, only : neko_log, log_size, neko_log_verbose
  use field_registry, only : neko_field_registry
  use json_utils, only : json_get, json_get_or_default, json_extract_object, &
    json_extract_item
  use json_module, only : json_file, json_core, json_value
  use scratch_registry, only : scratch_registry_t
  use user_intf, only : user_t, dummy_user_material_properties, &
    user_material_properties
  use utils, only : neko_error, neko_warning
  use field_series, only : field_series_t
  use time_step_controller, only : time_step_controller_t
  use field_math, only : field_cfill, field_add2s2
  use shear_stress, only : shear_stress_t
  use gradient_jump_penalty, only : gradient_jump_penalty_t
  use device, only : device_event_sync, device_stream_wait_event, &
       glb_cmd_queue, glb_cmd_event
  implicit none
  private
 
  type, abstract, extends(fluid_scheme_base_t) :: fluid_scheme_incompressible_t
     type(fluid_source_term_t) :: source_term
     class(ksp_t), allocatable :: ksp_vel
     class(ksp_t), allocatable :: ksp_prs
     class(pc_t), allocatable :: pc_vel
     class(pc_t), allocatable :: pc_prs
     integer :: vel_projection_dim
     integer :: pr_projection_dim
     integer :: vel_projection_activ_step
     integer :: pr_projection_activ_step
     logical :: strict_convergence
     logical :: if_gradient_jump_penalty
     type(gradient_jump_penalty_t) :: gradient_jump_penalty_u
     type(gradient_jump_penalty_t) :: gradient_jump_penalty_v
     type(gradient_jump_penalty_t) :: gradient_jump_penalty_w
     type(field_t), pointer :: u_e => null() 
     type(field_t), pointer :: v_e => null() 
     type(field_t), pointer :: w_e => null() 
 
     type(mean_flow_t) :: mean
     type(fluid_stats_t) :: stats
     type(mean_sqr_flow_t) :: mean_sqr
     logical :: forced_flow_rate = .false. 
 
     character(len=:), allocatable :: nut_field_name
 
     integer(kind=i8) :: glb_n_points
     integer(kind=i8) :: glb_unique_points
     type(scratch_registry_t) :: scratch
   contains
     procedure, pass(this) :: init_base => fluid_scheme_init_base
     procedure, pass(this) :: scheme_free => fluid_scheme_free
     procedure, pass(this) :: validate => fluid_scheme_validate
     procedure, pass(this) :: bc_apply_vel => fluid_scheme_bc_apply_vel
     procedure, pass(this) :: bc_apply_prs => fluid_scheme_bc_apply_prs
     procedure, pass(this) :: compute_cfl => fluid_compute_cfl
     procedure, pass(this) :: set_material_properties => &
       fluid_scheme_set_material_properties
 
     procedure, pass(this) :: update_material_properties => &
       fluid_scheme_update_material_properties
     procedure, nopass :: solver_factory => fluid_scheme_solver_factory
     procedure, pass(this) :: precon_factory_ => fluid_scheme_precon_factory
  end type fluid_scheme_incompressible_t
  type, abstract, extends(fluid_scheme_base_t) :: fluid_scheme_incompressible_t …
 
  interface
 
     module subroutine fluid_scheme_factory(object, type_name)
       class(fluid_scheme_base_t), intent(inout), allocatable :: object
       character(len=*) :: type_name
     end subroutine fluid_scheme_factory
  end interface
 
  public :: fluid_scheme_incompressible_t, fluid_scheme_factory
 
contains
 
  subroutine fluid_scheme_init_base(this, msh, lx, params, scheme, user, &
    kspv_init)
    implicit none
    class(fluid_scheme_incompressible_t), target, intent(inout) :: this
    type(mesh_t), target, intent(inout) :: msh
    integer, intent(in) :: lx
    character(len=*), intent(in) :: scheme
    type(json_file), target, intent(inout) :: params
    type(user_t), target, intent(in) :: user
    logical, intent(in) :: kspv_init
    type(dirichlet_t) :: bdry_mask
    character(len=LOG_SIZE) :: log_buf
    real(kind=rp), allocatable :: real_vec(:)
    real(kind=rp) :: real_val, kappa, b, z0
    logical :: logical_val
    integer :: integer_val, ierr
    type(json_file) :: wm_json
    character(len=:), allocatable :: string_val1, string_val2
    real(kind=rp) :: gjp_param_a, gjp_param_b
 
    !
    ! SEM simulation fundamentals
    !
 
    this%msh => msh
 
    if (msh%gdim .eq. 2) then
       call this%Xh%init(gll, lx, lx)
    else
       call this%Xh%init(gll, lx, lx, lx)
    end if
 
    call this%dm_Xh%init(msh, this%Xh)
 
    call this%gs_Xh%init(this%dm_Xh)
 
    call this%c_Xh%init(this%gs_Xh)
 
    ! Local scratch registry
    this%scratch = scratch_registry_t(this%dm_Xh, 10, 2)
 
    !
    ! First section of fluid log
    !
 
    call neko_log%section('Fluid')
    write(log_buf, '(A, A)') 'Type       : ', trim(scheme)
    call neko_log%message(log_buf)
 
    !
    ! Material properties
    !
    call this%set_material_properties(params, user)
 
    !
    ! Turbulence modelling and variable material properties
    !
    if (params%valid_path('case.fluid.nut_field')) then
       call json_get(params, 'case.fluid.nut_field', this%nut_field_name)
       this%variable_material_properties = .true.
    else
       this%nut_field_name = ""
    end if
 
    ! Fill mu and rho field with the physical value
 
    call this%mu_field%init(this%dm_Xh, "mu")
    call this%rho_field%init(this%dm_Xh, "rho")
    call field_cfill(this%mu_field, this%mu, this%mu_field%size())
    call field_cfill(this%rho_field, this%rho, this%mu_field%size())
 
    ! Since mu, rho is a field, and the none-stress simulation fetches
    ! data from the host arrays, we need to mirror the constant
    ! material properties on the host
    if (neko_bcknd_device .eq. 1) then
       call cfill(this%mu_field%x, this%mu, this%mu_field%size())
       call cfill(this%rho_field%x, this%rho, this%rho_field%size())
    end if
 
 
    ! Projection spaces
    call json_get_or_default(params, &
      'case.fluid.velocity_solver.projection_space_size', &
      this%vel_projection_dim, 20)
    call json_get_or_default(params, &
      'case.fluid.pressure_solver.projection_space_size', &
      this%pr_projection_dim, 20)
    call json_get_or_default(params, &
      'case.fluid.velocity_solver.projection_hold_steps', &
      this%vel_projection_activ_step, 5)
    call json_get_or_default(params, &
      'case.fluid.pressure_solver.projection_hold_steps', &
      this%pr_projection_activ_step, 5)
 
 
    call json_get_or_default(params, 'case.fluid.freeze', this%freeze, .false.)
 
    if (params%valid_path("case.fluid.flow_rate_force")) then
       this%forced_flow_rate = .true.
    end if
 
 
    if (lx .lt. 10) then
       write(log_buf, '(A, I1)') 'Poly order : ', lx-1
    else if (lx .ge. 10) then
       write(log_buf, '(A, I2)') 'Poly order : ', lx-1
    else
       write(log_buf, '(A, I3)') 'Poly order : ', lx-1
    end if
    call neko_log%message(log_buf)
    this%glb_n_points = int(this%msh%glb_nelv, i8)*int(this%Xh%lxyz, i8)
    this%glb_unique_points = int(glsum(this%c_Xh%mult, this%dm_Xh%size()), i8)
 
    write(log_buf, '(A, I0)') 'GLL points : ', this%glb_n_points
    call neko_log%message(log_buf)
    write(log_buf, '(A, I0)') 'Unique pts.: ', this%glb_unique_points
    call neko_log%message(log_buf)
 
    write(log_buf, '(A,ES13.6)') 'rho        :', this%rho
    call neko_log%message(log_buf)
    write(log_buf, '(A,ES13.6)') 'mu         :', this%mu
    call neko_log%message(log_buf)
 
    call json_get(params, 'case.numerics.dealias', logical_val)
    write(log_buf, '(A, L1)') 'Dealias    : ', logical_val
    call neko_log%message(log_buf)
 
    write(log_buf, '(A, L1)') 'LES        : ', this%variable_material_properties
    call neko_log%message(log_buf)
 
    call json_get_or_default(params, 'case.output_boundary', logical_val, &
      .false.)
    write(log_buf, '(A, L1)') 'Save bdry  : ', logical_val
    call neko_log%message(log_buf)
 
    !
    ! Setup right-hand side fields.
    !
    allocate(this%f_x)
    allocate(this%f_y)
    allocate(this%f_z)
    call this%f_x%init(this%dm_Xh, fld_name = "fluid_rhs_x")
    call this%f_y%init(this%dm_Xh, fld_name = "fluid_rhs_y")
    call this%f_z%init(this%dm_Xh, fld_name = "fluid_rhs_z")
 
    ! Initialize the source term
    call this%source_term%init(this%f_x, this%f_y, this%f_z, this%c_Xh, user)
    call this%source_term%add(params, 'case.fluid.source_terms')
 
    ! Initialize velocity solver
    if (kspv_init) then
       call neko_log%section("Velocity solver")
       call json_get_or_default(params, &
         'case.fluid.velocity_solver.max_iterations', &
         integer_val, ksp_max_iter)
       call json_get(params, 'case.fluid.velocity_solver.type', string_val1)
       call json_get(params, 'case.fluid.velocity_solver.preconditioner', &
         string_val2)
       call json_get(params, 'case.fluid.velocity_solver.absolute_tolerance', &
         real_val)
       call json_get_or_default(params, &
         'case.fluid.velocity_solver.monitor', &
         logical_val, .false.)
 
       call neko_log%message('Type       : ('// trim(string_val1) // &
         ', ' // trim(string_val2) // ')')
 
       write(log_buf, '(A,ES13.6)') 'Abs tol    :', real_val
       call neko_log%message(log_buf)
       call this%solver_factory(this%ksp_vel, this%dm_Xh%size(), &
         string_val1, integer_val, real_val, logical_val)
       call this%precon_factory_(this%pc_vel, this%ksp_vel, &
         this%c_Xh, this%dm_Xh, this%gs_Xh, this%bcs_vel, string_val2)
       call neko_log%end_section()
    end if
 
    ! Strict convergence for the velocity solver
    call json_get_or_default(params, 'case.fluid.strict_convergence', &
      this%strict_convergence, .false.)
 
    ! Assign velocity fields
    call neko_field_registry%add_field(this%dm_Xh, 'u')
    call neko_field_registry%add_field(this%dm_Xh, 'v')
    call neko_field_registry%add_field(this%dm_Xh, 'w')
    this%u => neko_field_registry%get_field('u')
    this%v => neko_field_registry%get_field('v')
    this%w => neko_field_registry%get_field('w')
 
    !! Initialize time-lag fields
    call this%ulag%init(this%u, 2)
    call this%vlag%init(this%v, 2)
    call this%wlag%init(this%w, 2)
 
    ! Initiate gradient jump penalty
    call json_get_or_default(params, &
      'case.fluid.gradient_jump_penalty.enabled',&
      this%if_gradient_jump_penalty, .false.)
 
    if (this%if_gradient_jump_penalty .eqv. .true.) then
       if ((this%dm_Xh%xh%lx - 1) .eq. 1) then
          call json_get_or_default(params, &
            'case.fluid.gradient_jump_penalty.tau',&
            gjp_param_a, 0.02_rp)
          gjp_param_b = 0.0_rp
       else
          call json_get_or_default(params, &
            'case.fluid.gradient_jump_penalty.scaling_factor',&
            gjp_param_a, 0.8_rp)
          call json_get_or_default(params, &
            'case.fluid.gradient_jump_penalty.scaling_exponent',&
            gjp_param_b, 4.0_rp)
       end if
       call this%gradient_jump_penalty_u%init(params, this%dm_Xh, this%c_Xh, &
         gjp_param_a, gjp_param_b)
       call this%gradient_jump_penalty_v%init(params, this%dm_Xh, this%c_Xh, &
         gjp_param_a, gjp_param_b)
       call this%gradient_jump_penalty_w%init(params, this%dm_Xh, this%c_Xh, &
         gjp_param_a, gjp_param_b)
    end if
 
    call neko_field_registry%add_field(this%dm_Xh, 'u_e')
    call neko_field_registry%add_field(this%dm_Xh, 'v_e')
    call neko_field_registry%add_field(this%dm_Xh, 'w_e')
    this%u_e => neko_field_registry%get_field('u_e')
    this%v_e => neko_field_registry%get_field('v_e')
    this%w_e => neko_field_registry%get_field('w_e')
 
    call neko_log%end_section()
 
  subroutine fluid_scheme_init_base(this, msh, lx, params, scheme, user, & …
  end subroutine fluid_scheme_init_base
 
  subroutine fluid_scheme_free(this)
    class(fluid_scheme_incompressible_t), intent(inout) :: this
 
    !
    ! Free everything related to field_dirichlet BCs
    !
 
    call this%Xh%free()
 
    if (allocated(this%ksp_vel)) then
       call krylov_solver_destroy(this%ksp_vel)
       deallocate(this%ksp_vel)
    end if
 
    if (allocated(this%ksp_prs)) then
       call krylov_solver_destroy(this%ksp_prs)
       deallocate(this%ksp_prs)
    end if
 
    if (allocated(this%pc_vel)) then
       call precon_destroy(this%pc_vel)
       deallocate(this%pc_vel)
    end if
 
    if (allocated(this%pc_prs)) then
       call precon_destroy(this%pc_prs)
       deallocate(this%pc_prs)
    end if
 
    call this%source_term%free()
 
    call this%gs_Xh%free()
 
    call this%c_Xh%free()
 
    call this%scratch%free()
 
    nullify(this%u)
    nullify(this%v)
    nullify(this%w)
    nullify(this%p)
 
    if (this%variable_material_properties) then
       nullify(this%u_e)
       nullify(this%v_e)
       nullify(this%w_e)
    end if
 
    call this%ulag%free()
    call this%vlag%free()
    call this%wlag%free()
 
 
    if (associated(this%f_x)) then
       call this%f_x%free()
    end if
 
    if (associated(this%f_y)) then
       call this%f_y%free()
    end if
 
    if (associated(this%f_z)) then
       call this%f_z%free()
    end if
 
    nullify(this%f_x)
    nullify(this%f_y)
    nullify(this%f_z)
 
    call this%rho_field%free()
    call this%mu_field%free()
 
    ! Free gradient jump penalty
    if (this%if_gradient_jump_penalty .eqv. .true.) then
       call this%gradient_jump_penalty_u%free()
       call this%gradient_jump_penalty_v%free()
       call this%gradient_jump_penalty_w%free()
    end if
 
  subroutine fluid_scheme_free(this) …
  end subroutine fluid_scheme_free
 
  subroutine fluid_scheme_validate(this)
    class(fluid_scheme_incompressible_t), target, intent(inout) :: this
    ! Variables for retrieving json parameters
    logical :: logical_val
 
    if ( (.not. associated(this%u)) .or. &
      (.not. associated(this%v)) .or. &
      (.not. associated(this%w)) .or. &
      (.not. associated(this%p))) then
       call neko_error('Fields are not registered')
    end if
 
    if ( (.not. allocated(this%u%x)) .or. &
      (.not. allocated(this%v%x)) .or. &
      (.not. allocated(this%w%x)) .or. &
      (.not. allocated(this%p%x))) then
       call neko_error('Fields are not allocated')
    end if
 
    if (.not. allocated(this%ksp_vel)) then
       call neko_error('No Krylov solver for velocity defined')
    end if
 
    if (.not. allocated(this%ksp_prs)) then
       call neko_error('No Krylov solver for pressure defined')
    end if
 
    !
    ! Setup checkpoint structure (if everything is fine)
    !
    call this%chkp%init(this%u, this%v, this%w, this%p)
 
  subroutine fluid_scheme_validate(this) …
  end subroutine fluid_scheme_validate
 
  subroutine fluid_scheme_bc_apply_vel(this, t, tstep, strong)
    class(fluid_scheme_incompressible_t), intent(inout) :: this
    real(kind=rp), intent(in) :: t
    integer, intent(in) :: tstep
    logical, intent(in) :: strong
 
    call this%bcs_vel%apply_vector(&
      this%u%x, this%v%x, this%w%x, this%dm_Xh%size(), t, tstep, strong)
    call this%gs_Xh%op(this%u, gs_op_min, glb_cmd_event)
    call this%gs_Xh%op(this%v, gs_op_min, glb_cmd_event)
    call this%gs_Xh%op(this%w, gs_op_min, glb_cmd_event)
    if (neko_bcknd_device .eq. 1) then
       call device_stream_wait_event(glb_cmd_queue, glb_cmd_event, 0)
    end if
 
    call this%bcs_vel%apply_vector(&
      this%u%x, this%v%x, this%w%x, this%dm_Xh%size(), t, tstep, strong)
    call this%gs_Xh%op(this%u, gs_op_max, glb_cmd_event)
    call this%gs_Xh%op(this%v, gs_op_max, glb_cmd_event)
    call this%gs_Xh%op(this%w, gs_op_max, glb_cmd_event)
    if (neko_bcknd_device .eq. 1) then
       call device_stream_wait_event(glb_cmd_queue, glb_cmd_event, 0)
    end if
 
  subroutine fluid_scheme_bc_apply_vel(this, t, tstep, strong) …
  end subroutine fluid_scheme_bc_apply_vel
 
  subroutine fluid_scheme_bc_apply_prs(this, t, tstep)
    class(fluid_scheme_incompressible_t), intent(inout) :: this
    real(kind=rp), intent(in) :: t
    integer, intent(in) :: tstep
 
    call this%bcs_prs%apply(this%p, t, tstep)
    call this%gs_Xh%op(this%p,gs_op_min, glb_cmd_event)
    if (neko_bcknd_device .eq. 1) then
       call device_stream_wait_event(glb_cmd_queue, glb_cmd_event, 0)
    end if
 
    call this%bcs_prs%apply(this%p, t, tstep)
    call this%gs_Xh%op(this%p,gs_op_max, glb_cmd_event)
    if (neko_bcknd_device .eq. 1) then
       call device_stream_wait_event(glb_cmd_queue, glb_cmd_event, 0)
    end if
 
 
  subroutine fluid_scheme_bc_apply_prs(this, t, tstep) …
  end subroutine fluid_scheme_bc_apply_prs
 
  subroutine fluid_scheme_solver_factory(ksp, n, solver, &
    max_iter, abstol, monitor)
    class(ksp_t), allocatable, target, intent(inout) :: ksp
    integer, intent(in), value :: n
    character(len=*), intent(in) :: solver
    integer, intent(in) :: max_iter
    real(kind=rp), intent(in) :: abstol
    logical, intent(in) :: monitor
 
    call krylov_solver_factory(ksp, n, solver, max_iter, abstol, &
      monitor = monitor)
 
  subroutine fluid_scheme_solver_factory(ksp, n, solver, & …
  end subroutine fluid_scheme_solver_factory
 
  subroutine fluid_scheme_precon_factory(this, pc, ksp, coef, dof, gs, bclst, &
    pctype)
    class(fluid_scheme_incompressible_t), intent(inout) :: this
    class(pc_t), allocatable, target, intent(inout) :: pc
    class(ksp_t), target, intent(inout) :: ksp
    type(coef_t), target, intent(in) :: coef
    type(dofmap_t), target, intent(in) :: dof
    type(gs_t), target, intent(inout) :: gs
    type(bc_list_t), target, intent(inout) :: bclst
    character(len=*) :: pctype
 
    call precon_factory(pc, pctype)
 
    select type (pcp => pc)
    type is (jacobi_t)
       call pcp%init(coef, dof, gs)
    type is (sx_jacobi_t)
       call pcp%init(coef, dof, gs)
    type is (device_jacobi_t)
       call pcp%init(coef, dof, gs)
    type is (hsmg_t)
       if (len_trim(pctype) .gt. 4) then
          if (index(pctype, '+') .eq. 5) then
             call pcp%init(dof%msh, dof%Xh, coef, dof, gs, bclst, &
               trim(pctype(6:)))
          else
             call neko_error('Unknown coarse grid solver')
          end if
       else
          call pcp%init(dof%msh, dof%Xh, coef, dof, gs, bclst)
       end if
    type is (phmg_t)
       call pcp%init(dof%msh, dof%Xh, coef, dof, gs, bclst)
    end select
 
    call ksp%set_pc(pc)
 
  subroutine fluid_scheme_precon_factory(this, pc, ksp, coef, dof, gs, bclst, & …
  end subroutine fluid_scheme_precon_factory
 
  function fluid_compute_cfl(this, dt) result(c)
    class(fluid_scheme_incompressible_t), intent(in) :: this
    real(kind=rp), intent(in) :: dt
    real(kind=rp) :: c
 
    c = cfl(dt, this%u%x, this%v%x, this%w%x, &
      this%Xh, this%c_Xh, this%msh%nelv, this%msh%gdim)
 
  function fluid_compute_cfl(this, dt) result(c) …
  end function fluid_compute_cfl
 
 
  subroutine fluid_scheme_update_material_properties(this)
    class(fluid_scheme_incompressible_t), intent(inout) :: this
    type(field_t), pointer :: nut
    integer :: n
 
    this%mu_field = this%mu
    if (this%variable_material_properties) then
       nut => neko_field_registry%get_field(this%nut_field_name)
       n = nut%size()
       call field_add2s2(this%mu_field, nut, this%rho, n)
    end if
  subroutine fluid_scheme_update_material_properties(this) …
  end subroutine fluid_scheme_update_material_properties
 
  subroutine fluid_scheme_set_material_properties(this, params, user)
    class(fluid_scheme_incompressible_t), intent(inout) :: this
    type(json_file), intent(inout) :: params
    type(user_t), target, intent(in) :: user
    character(len=LOG_SIZE) :: log_buf
    ! A local pointer that is needed to make Intel happy
    procedure(user_material_properties), pointer :: dummy_mp_ptr
    logical :: nondimensional
    real(kind=rp) :: dummy_lambda, dummy_cp
 
    dummy_mp_ptr => dummy_user_material_properties
 
    if (.not. associated(user%material_properties, dummy_mp_ptr)) then
 
       write(log_buf, '(A)') "Material properties must be set in the user&
         & file!"
       call neko_log%message(log_buf)
       call user%material_properties(0.0_rp, 0, this%rho, this%mu, &
         dummy_cp, dummy_lambda, params)
    else
       ! Incorrect user input
       if (params%valid_path('case.fluid.Re') .and. &
         (params%valid_path('case.fluid.mu') .or. &
         params%valid_path('case.fluid.rho'))) then
          call neko_error("To set the material properties for the fluid,&
            & either provide Re OR mu and rho in the case file.")
 
          ! Non-dimensional case
       else if (params%valid_path('case.fluid.Re')) then
 
          write(log_buf, '(A)') 'Non-dimensional fluid material properties &
            & input.'
          call neko_log%message(log_buf, lvl = neko_log_verbose)
          write(log_buf, '(A)') 'Density will be set to 1, dynamic viscosity to&
            & 1/Re.'
          call neko_log%message(log_buf, lvl = neko_log_verbose)
 
          ! Read Re into mu for further manipulation.
          call json_get(params, 'case.fluid.Re', this%mu)
          write(log_buf, '(A)') 'Read non-dimensional material properties'
          call neko_log%message(log_buf)
          write(log_buf, '(A,ES13.6)') 'Re         :', this%mu
          call neko_log%message(log_buf)
 
          ! Set rho to 1 since the setup is non-dimensional.
          this%rho = 1.0_rp
          ! Invert the Re to get viscosity.
          this%mu = 1.0_rp/this%mu
          ! Dimensional case
       else
          call json_get(params, 'case.fluid.mu', this%mu)
          call json_get(params, 'case.fluid.rho', this%rho)
       end if
 
    end if
  subroutine fluid_scheme_set_material_properties(this, params, user) …
  end subroutine fluid_scheme_set_material_properties
 
end module fluid_scheme_incompressible