Index: palm/trunk/SOURCE/Makefile
===================================================================
--- palm/trunk/SOURCE/Makefile	(revision 1911)
+++ palm/trunk/SOURCE/Makefile	(revision 1914)
@@ -56,4 +56,8 @@
 # Tails removed. lpm_release_set removed. calc_precipitation, impact_of_latent_heat
 # removed. 
+#
+# 1819 2016-04-06 21:05:15Z witha
+# Added wind turbine model and renamed it from wind_turbine_model to
+# wind_turbine_model_mod
 #
 # 1817 2016-04-06 15:44:20Z maronga
@@ -330,5 +334,5 @@
 	user_parin.f90 user_read_restart_data.f90 \
 	user_spectra.f90 user_statistics.f90 wall_fluxes.f90 \
-	write_3d_binary.f90 write_var_list.f90
+	wind_turbine_model_mod.f90 write_3d_binary.f90 write_var_list.f90
 
 
@@ -383,5 +387,5 @@
 check_parameters.o: modules.o mod_kinds.o land_surface_model_mod.o \
 	netcdf_interface_mod.o plant_canopy_model_mod.o pmc_interface_mod.o radiation_model_mod.o \
-	spectra_mod.o subsidence_mod.o microphysics_mod.o
+	spectra_mod.o subsidence_mod.o microphysics_mod.o wind_turbine_model_mod.o
 close_file.o: modules.o mod_kinds.o netcdf_interface_mod.o
 compute_vpt.o: modules.o mod_kinds.o
@@ -429,5 +433,6 @@
    lpm_init.o ls_forcing_mod.o netcdf_interface_mod.o plant_canopy_model_mod.o \
    radiation_model_mod.o random_function_mod.o random_generator_parallel_mod.o \
-   surface_layer_fluxes_mod.o microphysics_mod.o mod_particle_attributes.o
+   surface_layer_fluxes_mod.o microphysics_mod.o mod_particle_attributes.o \
+   wind_turbine_model_mod.o
 init_advec.o: modules.o mod_kinds.o
 init_cloud_physics.o: modules.o mod_kinds.o
@@ -486,5 +491,5 @@
 parin.o: modules.o cpulog_mod.o land_surface_model_mod.o mod_kinds.o netcdf_interface_mod.o \
    plant_canopy_model_mod.o pmc_interface_mod.o progress_bar_mod.o spectra_mod.o \
-   radiation_model_mod.o microphysics_mod.o
+   radiation_model_mod.o microphysics_mod.o wind_turbine_model_mod.o
 plant_canopy_model_mod.o: modules.o mod_kinds.o
 pmc_interface_mod.o: modules.o mod_kinds.o pmc_client_mod.o pmc_general_mod.o\
@@ -508,5 +513,5 @@
 	eqn_state_seawater.o mod_kinds.o microphysics_mod.o \
 	nudging_mod.o plant_canopy_model_mod.o production_e.o radiation_model_mod.o \
-	subsidence_mod.o user_actions.o
+	subsidence_mod.o user_actions.o wind_turbine_model_mod.o
 progress_bar_mod.o: modules.o mod_kinds.o
 radiation_model_mod.o : modules.o mod_particle_attributes.o microphysics_mod.o
@@ -536,5 +541,6 @@
 	ls_forcing_mod.o mod_kinds.o nudging_mod.o pmc_interface_mod.o production_e.o \
 	prognostic_equations.o progress_bar_mod.o radiation_model_mod.o \
-	spectra_mod.o user_actions.o surface_layer_fluxes_mod.o microphysics_mod.o
+	spectra_mod.o user_actions.o surface_layer_fluxes_mod.o microphysics_mod.o \
+        wind_turbine_model_mod.o
 time_to_string.o: mod_kinds.o
 timestep.o: modules.o cpulog_mod.o mod_kinds.o microphysics_mod.o
@@ -572,4 +578,5 @@
 user_statistics.o: modules.o mod_kinds.o netcdf_interface_mod.o user_module.o
 wall_fluxes.o: modules.o mod_kinds.o
+wind_turbine_model_mod.o: modules.o cpulog_mod.o mod_kinds.o
 write_3d_binary.o: modules.o cpulog_mod.o mod_kinds.o land_surface_model_mod.o \
 	radiation_model_mod.o random_function_mod.o random_generator_parallel_mod.o \
Index: palm/trunk/SOURCE/check_parameters.f90
===================================================================
--- palm/trunk/SOURCE/check_parameters.f90	(revision 1911)
+++ palm/trunk/SOURCE/check_parameters.f90	(revision 1914)
@@ -389,4 +389,6 @@
     USE statistics
     USE transpose_indices
+    USE wind_turbine_model_mod,                                                &
+        ONLY: wtm_check_parameters, wind_turbine
 
 
@@ -1057,6 +1059,10 @@
 
 !
+!-- If wind turbine model is used, perform additional checks
+    IF ( wind_turbine )  CALL wtm_check_parameters
+!
 !-- When radiation model is used, peform addtional checks
     IF ( radiation )  CALL radiation_check_parameters
+
 
     IF ( .NOT. ( loop_optimization == 'cache'  .OR.                            &
Index: palm/trunk/SOURCE/init_3d_model.f90
===================================================================
--- palm/trunk/SOURCE/init_3d_model.f90	(revision 1911)
+++ palm/trunk/SOURCE/init_3d_model.f90	(revision 1914)
@@ -37,4 +37,7 @@
 ! nzb_2d replaced by nzb_u|v_inner
 ! 
+! 1839 2016-04-07 18:48:14Z witha
+! Renamed calls for wind turbine model
+!
 ! 1833 2016-04-07 14:23:03Z raasch
 ! initialization of spectra quantities moved to spectra_mod
@@ -50,4 +53,7 @@
 ! icloud_scheme replaced by microphysics_*
 !
+! 1819 2016-04-06 21:05:15Z witha
+! Added initialization of the wind turbine model
+! 
 ! 1817 2016-04-06 15:44:20Z maronga
 ! Renamed lsm calls.
@@ -331,4 +337,7 @@
    
     USE transpose_indices 
+
+    USE wind_turbine_model_mod,                                                &
+        ONLY:  wtm_init, wtm_init_arrays, wind_turbine
 
     IMPLICIT NONE
@@ -688,4 +697,10 @@
 
 !
+!-- Allocate wind turbine model arrays
+    IF ( wind_turbine )  THEN
+       CALL wtm_init_arrays
+    ENDIF
+
+!
 !-- Allocate arrays containing the RK coefficient for calculation of 
 !-- perturbation pressure and turbulent fluxes. At this point values are
@@ -1675,4 +1690,13 @@
        CALL location_message( 'finished', .TRUE. )
     ENDIF
+    
+!
+!-- If required, initialize quantities needed for the wind turbine model
+    IF ( wind_turbine )  THEN
+       CALL location_message( 'initializing wind turbine model', .FALSE. )
+       CALL wtm_init
+       CALL location_message( 'finished', .TRUE. )
+    ENDIF
+
 
 !
Index: palm/trunk/SOURCE/package_parin.f90
===================================================================
--- palm/trunk/SOURCE/package_parin.f90	(revision 1911)
+++ palm/trunk/SOURCE/package_parin.f90	(revision 1914)
@@ -28,4 +28,7 @@
 ! Initialization of aerosols added.
 !
+! 1839 2016-04-07 18:48:14Z witha
+! Reading of &wind_turbine_par moved to wind_turbine_model_mod
+! 
 ! 1833 2016-04-07 14:23:03Z raasch
 ! reading of spectra_par moved to spectra_mod
@@ -41,4 +44,7 @@
 ! +collision_algorithm
 ! Tails removed.
+
+! 1819 2016-04-06 21:05:15Z witha
+! Added namelist for wind turbine model
 !
 ! 1817 2016-04-06 15:44:20Z maronga
Index: palm/trunk/SOURCE/parin.f90
===================================================================
--- palm/trunk/SOURCE/parin.f90	(revision 1911)
+++ palm/trunk/SOURCE/parin.f90	(revision 1914)
@@ -27,4 +27,7 @@
 ! 1849 2016-04-08 11:33:18Z hoffmann
 ! Adapted for modularization of microphysics
+!
+! 1839 2016-04-07 18:48:14Z witha
+! Added call to wind turbine model for reading of &wind_turbine_par
 !
 ! 1833 2016-04-07 14:23:03Z raasch
@@ -259,4 +262,7 @@
     USE statistics,                                                            &
         ONLY:  hom, hom_sum, pr_palm, region, statistic_regions
+
+    USE wind_turbine_model_mod,                                                &
+        ONLY:  wtm_parin
 
 
@@ -504,4 +510,9 @@
 
 !
+!--       Check if wind turbine model is used and read &wind_turbine_par if
+!--       required
+          CALL wtm_parin
+
+!
 !--       Read user-defined variables
           CALL user_parin
Index: palm/trunk/SOURCE/prognostic_equations.f90
===================================================================
--- palm/trunk/SOURCE/prognostic_equations.f90	(revision 1911)
+++ palm/trunk/SOURCE/prognostic_equations.f90	(revision 1914)
@@ -28,8 +28,6 @@
 ! Module renamed (removed _mod)
 ! 
-! 
 ! 1850 2016-04-08 13:29:27Z maronga
 ! Module renamed
-! 
 ! 
 ! 1826 2016-04-07 12:01:39Z maronga
@@ -38,4 +36,7 @@
 ! 1822 2016-04-07 07:49:42Z hoffmann
 ! Kessler microphysics scheme moved to microphysics.
+
+! 1819 2016-04-06 21:05:15Z witha
+! Added calls for wind turbine model
 !
 ! 1757 2016-02-22 15:49:32Z maronga
@@ -313,4 +314,7 @@
         ONLY:  user_actions
 
+    USE wind_turbine_model_mod,                                                &
+        ONLY:  wind_turbine, wtm_tendencies
+
 
     PRIVATE
@@ -428,4 +432,8 @@
              IF ( nudging )  CALL nudge( i, j, simulated_time, 'u' )
 
+!
+!--          Forces by wind turbines
+             IF ( wind_turbine )  CALL wtm_tendencies( i, j, 1 )
+
              CALL user_actions( i, j, 'u-tendency' )
 !
@@ -487,4 +495,8 @@
              IF ( nudging )  CALL nudge( i, j, simulated_time, 'v' )
 
+!
+!--          Forces by wind turbines
+             IF ( wind_turbine )  CALL wtm_tendencies( i, j, 2 )
+
              CALL user_actions( i, j, 'v-tendency' )
 !
@@ -543,4 +555,8 @@
 !--       Drag by plant canopy
           IF ( plant_canopy )  CALL pcm_tendency( i, j, 3 )
+
+!
+!--       Forces by wind turbines
+          IF ( wind_turbine )  CALL wtm_tendencies( i, j, 3 )
 
           CALL user_actions( i, j, 'w-tendency' )
@@ -1011,4 +1027,8 @@
     IF ( nudging )  CALL nudge( simulated_time, 'u' )
 
+!
+!-- Forces by wind turbines
+    IF ( wind_turbine )  CALL wtm_tendencies( 1 )
+
     CALL user_actions( 'u-tendency' )
 
@@ -1087,4 +1107,8 @@
     IF ( nudging )  CALL nudge( simulated_time, 'v' )
 
+!
+!-- Forces by wind turbines
+    IF ( wind_turbine )  CALL wtm_tendencies( 2 )
+
     CALL user_actions( 'v-tendency' )
 
@@ -1158,4 +1182,8 @@
 !-- Drag by plant canopy
     IF ( plant_canopy )  CALL pcm_tendency( 3 )
+
+!
+!-- Forces by wind turbines
+    IF ( wind_turbine )  CALL wtm_tendencies( 3 )
 
     CALL user_actions( 'w-tendency' )
@@ -1847,4 +1875,8 @@
     IF ( nudging )  CALL nudge( simulated_time, 'u' )
 
+!
+!-- Forces by wind turbines
+    IF ( wind_turbine )  CALL wtm_tendencies( 1 )
+
     CALL user_actions( 'u-tendency' )
 
@@ -1914,4 +1946,8 @@
     IF ( nudging )  CALL nudge( simulated_time, 'v' )
 
+!
+!-- Forces by wind turbines
+    IF ( wind_turbine )  CALL wtm_tendencies( 2 )
+
     CALL user_actions( 'v-tendency' )
 
@@ -1976,4 +2012,8 @@
 !-- Drag by plant canopy
     IF ( plant_canopy )  CALL pcm_tendency( 3 )
+
+!
+!-- Forces by wind turbines
+    IF ( wind_turbine )  CALL wtm_tendencies( 3 )
 
     CALL user_actions( 'w-tendency' )
Index: palm/trunk/SOURCE/time_integration.f90
===================================================================
--- palm/trunk/SOURCE/time_integration.f90	(revision 1911)
+++ palm/trunk/SOURCE/time_integration.f90	(revision 1914)
@@ -42,4 +42,7 @@
 ! 1822 2016-04-07 07:49:42Z hoffmann
 ! icloud_scheme replaced by microphysics_*
+!
+! 1819 2016-04-06 21:05:15Z witha
+! Added call for wind turbine model and moved it
 !
 ! 1808 2016-04-05 19:44:00Z raasch
@@ -316,4 +319,7 @@
         ONLY:  user_actions
 
+    USE wind_turbine_model_mod,                                                &
+        ONLY:  wind_turbine, wtm_forces
+
     IMPLICIT NONE
 
@@ -405,4 +411,16 @@
        CALL user_actions( 'before_timestep' )
 
+!
+!--    Calculate forces by wind turbines
+       IF ( wind_turbine )  THEN
+
+          CALL cpu_log( log_point(55), 'wind_turbine', 'start' )
+
+          CALL wtm_forces
+
+          CALL cpu_log( log_point(55), 'wind_turbine', 'stop' )
+
+       ENDIF       
+       
 !
 !--    Start of intermediate step loop
Index: palm/trunk/SOURCE/wind_turbine_model_mod.f90
===================================================================
--- palm/trunk/SOURCE/wind_turbine_model_mod.f90	(revision 1914)
+++ palm/trunk/SOURCE/wind_turbine_model_mod.f90	(revision 1914)
@@ -0,0 +1,2528 @@
+!> @file wind_turbine_model_mod.f90
+!------------------------------------------------------------------------------!
+! This file is part of PALM.
+!
+! PALM 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.
+!
+! PALM 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
+! PALM. If not, see <http://www.gnu.org/licenses/>.
+!
+! Copyright 1997-2016 Leibniz Universitaet Hannover
+!------------------------------------------------------------------------------!
+!
+! Current revisions:
+! -----------------
+! 
+! 
+! Former revisions:
+! -----------------
+! $Id$
+!
+! 1912 2016-05-26 13:03:07Z witha
+! Added subroutine wtm_check_parameters
+! Renamed wtm_read_tables to wtm_read_blade_tables
+! Review of Pitch and Speed Control
+!
+! 1864 2016-04-14 17:23:11Z witha
+! Definition of PRIVATE and PUBLIC variables and functions
+! Relocation of some variables from module to the subroutines
+! Added subroutines wtm_speed_control and wtm_init_speed_control
+! Airfoil tables are now read from the input folder 
+!
+! 1843 2016-04-08 08:20:19Z witha
+! Bugfix and revision in reading mechanism
+! 
+! 1839 2016-04-07 18:48:14Z witha
+! Added subroutine for parin, renamed subroutines, witha
+! Added subroutine wtm_read_tables, changes on parin, lvo
+! 
+! 1820 2016-04-06 21:08:26Z witha
+! Initial revision
+! 
+!
+! Description:
+! ------------
+!> This module calculates the effect of wind turbines on the flow fields. The
+!> initial version contains only the advanced actuator disk with rotation method
+!> (ADM-R).
+!> The wind turbines include the tower effect, can be yawed and tilted.
+!> The wind turbine model includes controllers for rotational speed, pitch and
+!> yaw.
+!> Currently some specifications of the NREL 5 MW reference turbine
+!> are hardcoded whereas most input data comes from separate files (currently
+!> external, planned to be included as namelist which will be read in
+!> automatically).
+!>
+!> @todo Revise code according to PALM Coding Standard
+!> @todo Implement ADM and ALM turbine models
+!> @todo Generate header information
+!> @todo Implement parameter checks and error messages
+!> @todo Revise and add code documentation
+!> @todo Output turbine parameters as timeseries
+!> @todo Include additional output variables
+!> @todo Revise smearing the forces for turbines in yaw
+!> @todo Revise nacelle and tower parameterization
+!> @todo Allow different turbine types in one simulation
+!
+!------------------------------------------------------------------------------!
+ MODULE wind_turbine_model_mod
+
+    USE arrays_3d,                                                             &
+        ONLY:  dd2zu, tend, u, v, w, zu, zw
+
+    USE constants
+
+    USE control_parameters,                                                    &
+        ONLY:  dt_3d, dz, message_string, simulated_time
+
+    USE cpulog,                                                                &
+        ONLY:  cpu_log, log_point_s
+
+    USE grid_variables,                                                        &
+        ONLY:  ddx, dx, ddy, dy
+
+    USE indices,                                                               &
+        ONLY:  nbgp, nx, nxl, nxlg, nxr, nxrg, ny, nyn, nyng, nys, nysg, nz,   &
+               nzb, nzb_u_inner, nzb_v_inner, nzb_w_inner, nzt
+
+    USE kinds
+
+    USE pegrid
+
+
+    IMPLICIT NONE
+
+    PRIVATE
+
+    LOGICAL ::  wind_turbine=.FALSE.   !< switch for use of wind turbine model
+
+!
+!-- Variables specified in the namelist wind_turbine_par
+
+    INTEGER(iwp) ::  nairfoils = 8   !< number of airfoils of the used turbine model (for ADM-R and ALM)
+    INTEGER(iwp) ::  nturbines = 1   !< number of turbines
+
+    LOGICAL ::  pitch_control = .FALSE.   !< switch for use of pitch controller
+    LOGICAL ::  speed_control = .FALSE.   !< switch for use of speed controller
+    LOGICAL ::  yaw_control   = .FALSE.   !< switch for use of yaw controller
+
+    REAL(wp) ::  segment_length  = 1.0_wp          !< length of the segments, the rotor area is divided into
+                                                   !< (in tangential direction, as factor of MIN(dx,dy,dz))
+    REAL(wp) ::  segment_width   = 0.5_wp          !< width of the segments, the rotor area is divided into
+                                                   !< (in radial direction, as factor of MIN(dx,dy,dz))
+    REAL(wp) ::  time_turbine_on = 0.0_wp          !< time at which turbines are started
+    REAL(wp) ::  tilt            = 0.0_wp          !< vertical tilt of the rotor [degree] ( positive = backwards )
+
+    REAL(wp), DIMENSION(1:100) ::  dtow             = 0.0_wp  !< tower diameter [m]
+    REAL(wp), DIMENSION(1:100) ::  omega_rot        = 0.0_wp  !< inital or constant rotor speed [rad/s]
+    REAL(wp), DIMENSION(1:100) ::  phi_yaw          = 0.0_wp  !< yaw angle [degree] ( clockwise, 0 = facing west )
+    REAL(wp), DIMENSION(1:100) ::  pitch_add        = 0.0_wp  !< constant pitch angle
+    REAL(wp), DIMENSION(1:100) ::  rcx        = 9999999.9_wp  !< position of hub in x-direction
+    REAL(wp), DIMENSION(1:100) ::  rcy        = 9999999.9_wp  !< position of hub in y-direction
+    REAL(wp), DIMENSION(1:100) ::  rcz        = 9999999.9_wp  !< position of hub in z-direction
+    REAL(wp), DIMENSION(1:100) ::  rnac             = 0.0_wp  !< nacelle diameter [m]
+    REAL(wp), DIMENSION(1:100) ::  rr              = 63.0_wp  !< rotor radius [m]
+    REAL(wp), DIMENSION(1:100) ::  turb_cd_nacelle = 0.85_wp  !< drag coefficient for nacelle
+    REAL(wp), DIMENSION(1:100) ::  turb_cd_tower    = 1.2_wp  !< drag coefficient for tower
+
+!
+!-- Variables specified in the namelist for speed controller
+!-- Default values are from the NREL 5MW research turbine (Jonkman, 2008)
+
+    REAL(wp) ::  rated_power    = 5296610.0_wp    !< rated turbine power [W]
+    REAL(wp) ::  gear_ratio     = 97.0_wp         !< Gear ratio from rotor to generator
+    REAL(wp) ::  inertia_rot    = 34784179.0_wp   !< Inertia of the rotor [kg/m2]
+    REAL(wp) ::  inertia_gen    = 534.116_wp      !< Inertia of the generator [kg/m2]
+    REAL(wp) ::  gen_eff        = 0.944_wp        !< Electric efficiency of the generator
+    REAL(wp) ::  gear_eff       = 1.0_wp          !< Loss between rotor and generator
+    REAL(wp) ::  air_dens       = 1.225_wp        !< Air density to convert to W [kg/m3]
+    REAL(wp) ::  rated_genspeed = 121.6805_wp     !< Rated generator speed [rad/s]
+    REAL(wp) ::  max_torque_gen = 47402.91_wp     !< Maximum of the generator torque [Nm]
+    REAL(wp) ::  slope2         = 2.332287_wp     !< Slope constant for region 2
+    REAL(wp) ::  min_reg2       = 91.21091_wp     !< Lower generator speed boundary of region 2 [rad/s]
+    REAL(wp) ::  min_reg15      = 70.16224_wp     !< Lower generator speed boundary of region 1.5 [rad/s]
+    REAL(wp) ::  max_trq_rate   = 15000.0_wp      !< Max generator torque increase [Nm/s]
+    REAL(wp) ::  pitch_rate     = 8.0_wp          !< Max pitch rate [degree/s]
+
+
+!
+!-- Variables specified in the namelist for yaw control
+
+    REAL(wp) ::  yaw_speed = 0.005236_wp   !< speed of the yaw actuator [rad/s]
+    REAL(wp) ::  max_miss = 0.08726_wp     !< maximum tolerated yaw missalignment [rad]
+    REAL(wp) ::  min_miss = 0.008726_wp    !< minimum yaw missalignment for which the actuator stops [rad]
+
+!
+!-- Set flag for output files TURBINE_PARAMETERS
+    TYPE file_status
+       LOGICAL ::  opened, opened_before
+    END TYPE file_status
+    
+    TYPE(file_status), DIMENSION(500) :: openfile_turb_mod =                   &
+                                         file_status(.FALSE.,.FALSE.)
+
+!
+!-- Variables for initialization of the turbine model
+
+    INTEGER(iwp) ::  inot         !< turbine loop index (turbine id)
+    INTEGER(iwp) ::  nsegs_max    !< maximum number of segments (all turbines, required for allocation of arrays)
+    INTEGER(iwp) ::  nrings_max   !< maximum number of rings (all turbines, required for allocation of arrays)
+    INTEGER(iwp) ::  ring         !< ring loop index (ring number)
+    INTEGER(iwp) ::  rr_int       !<
+    INTEGER(iwp) ::  upper_end    !<
+
+    INTEGER(iwp), DIMENSION(1) ::  lct   !<
+
+    INTEGER(iwp), DIMENSION(:), ALLOCATABLE ::  i_hub     !< index belonging to x-position of the turbine
+    INTEGER(iwp), DIMENSION(:), ALLOCATABLE ::  i_smear   !< index defining the area for the smearing of the forces (x-direction)
+    INTEGER(iwp), DIMENSION(:), ALLOCATABLE ::  j_hub     !< index belonging to y-position of the turbine
+    INTEGER(iwp), DIMENSION(:), ALLOCATABLE ::  j_smear   !< index defining the area for the smearing of the forces (y-direction)
+    INTEGER(iwp), DIMENSION(:), ALLOCATABLE ::  k_hub     !< index belonging to hub height
+    INTEGER(iwp), DIMENSION(:), ALLOCATABLE ::  k_smear   !< index defining the area for the smearing of the forces (z-direction)
+    INTEGER(iwp), DIMENSION(:), ALLOCATABLE ::  nrings    !< number of rings per turbine
+    INTEGER(iwp), DIMENSION(:), ALLOCATABLE ::  nsegs_total !< total number of segments per turbine 
+
+    INTEGER(iwp), DIMENSION(:,:), ALLOCATABLE ::  nsegs   !< number of segments per ring and turbine
+
+!
+!-  parameters for the smearing from the rotor to the cartesian grid   
+    REAL(wp) ::  pol_a            !< parameter for the polynomial smearing fct
+    REAL(wp) ::  pol_b            !< parameter for the polynomial smearing fct
+    REAL(wp) ::  delta_t_factor   !< 
+    REAL(wp) ::  eps_factor       !<  
+    REAL(wp) ::  eps_min          !< 
+    REAL(wp) ::  eps_min2         !< 
+    REAL(wp) ::  sqrt_arg         !< 
+
+!
+!-- Variables for the calculation of lift and drag coefficients
+    REAL(wp), DIMENSION(:), ALLOCATABLE  ::  ard     !< 
+    REAL(wp), DIMENSION(:), ALLOCATABLE  ::  crd     !< 
+    REAL(wp), DIMENSION(:), ALLOCATABLE  ::  delta_r !< radial segment length
+    REAL(wp), DIMENSION(:), ALLOCATABLE  ::  lrd     !<
+    
+    REAL(wp) ::  accu_cl_cd_tab = 0.1_wp  !< Accuracy of the interpolation of 
+                                          !< the lift and drag coeff [deg] 
+
+    REAL(wp), DIMENSION(:,:), ALLOCATABLE :: turb_cd_tab   !< table of the blade drag coefficient
+    REAL(wp), DIMENSION(:,:), ALLOCATABLE :: turb_cl_tab   !< table of the blade lift coefficient
+
+    REAL(wp), DIMENSION(:,:,:), ALLOCATABLE ::  nac_cd_surf  !< 3d field of the tower drag coefficient 
+    REAL(wp), DIMENSION(:,:,:), ALLOCATABLE ::  tow_cd_surf  !< 3d field of the nacelle drag coefficient
+
+!
+!-- Variables for the calculation of the forces
+     
+    REAL(wp) ::  cur_r                       !< 
+    REAL(wp) ::  delta_t                     !<  tangential segment length
+    REAL(wp) ::  phi_rotor                   !< 
+    REAL(wp) ::  pre_factor                  !<  
+    REAL(wp) ::  torque_seg                  !< 
+    REAL(wp) ::  u_int_l                     !< 
+    REAL(wp) ::  u_int_u                     !< 
+    REAL(wp) ::  u_rot                       !< 
+    REAL(wp) ::  v_int_l                     !< 
+    REAL(wp) ::  v_int_u                     !< 
+    REAL(wp) ::  w_int_l                     !< 
+    REAL(wp) ::  w_int_u                     !<
+!
+!-  Tendencies from the nacelle and tower thrust
+    REAL(wp) ::  tend_nac_x = 0.0_wp  !< 
+    REAL(wp) ::  tend_tow_x = 0.0_wp  !< 
+    REAL(wp) ::  tend_nac_y = 0.0_wp  !< 
+    REAL(wp) ::  tend_tow_y = 0.0_wp  !<
+
+    REAL(wp), DIMENSION(:), ALLOCATABLE ::  alpha_attack !< 
+    REAL(wp), DIMENSION(:), ALLOCATABLE ::  chord        !< 
+    REAL(wp), DIMENSION(:), ALLOCATABLE ::  omega_gen    !< curr. generator speed
+    REAL(wp), DIMENSION(:), ALLOCATABLE ::  phi_rel      !< 
+    REAL(wp), DIMENSION(:), ALLOCATABLE ::  pitch_add_old!<
+    REAL(wp), DIMENSION(:), ALLOCATABLE ::  torque_total !<
+    REAL(wp), DIMENSION(:), ALLOCATABLE ::  thrust_rotor !<
+    REAL(wp), DIMENSION(:), ALLOCATABLE ::  turb_cl      !< 
+    REAL(wp), DIMENSION(:), ALLOCATABLE ::  turb_cd      !< 
+    REAL(wp), DIMENSION(:), ALLOCATABLE ::  vrel         !< 
+    REAL(wp), DIMENSION(:), ALLOCATABLE ::  vtheta       !< 
+
+    REAL(wp), DIMENSION(:,:), ALLOCATABLE ::  rbx, rby, rbz     !< coordinates of the blade elements
+    REAL(wp), DIMENSION(:,:), ALLOCATABLE ::  rotx, roty, rotz  !< normal vectors to the rotor coordinates
+
+!
+!-  Fields for the interpolation of velocities on the rotor grid
+    REAL(wp), DIMENSION(:,:,:), ALLOCATABLE ::  u_int       !< 
+    REAL(wp), DIMENSION(:,:,:), ALLOCATABLE ::  u_int_1_l   !< 
+    REAL(wp), DIMENSION(:,:,:), ALLOCATABLE ::  v_int       !< 
+    REAL(wp), DIMENSION(:,:,:), ALLOCATABLE ::  v_int_1_l   !< 
+    REAL(wp), DIMENSION(:,:,:), ALLOCATABLE ::  w_int       !< 
+    REAL(wp), DIMENSION(:,:,:), ALLOCATABLE ::  w_int_1_l   !< 
+    
+!
+!-  rotor tendencies on the segments 
+    REAL(wp), DIMENSION(:), ALLOCATABLE :: thrust_seg   !< 
+    REAL(wp), DIMENSION(:), ALLOCATABLE :: torque_seg_y !< 
+    REAL(wp), DIMENSION(:), ALLOCATABLE :: torque_seg_z !<    
+
+!
+!-  rotor tendencies on the rings
+    REAL(wp), DIMENSION(:,:), ALLOCATABLE ::  thrust_ring       !< 
+    REAL(wp), DIMENSION(:,:), ALLOCATABLE ::  torque_ring_y     !< 
+    REAL(wp), DIMENSION(:,:), ALLOCATABLE ::  torque_ring_z     !<
+    
+!
+!-  rotor tendencies on rotor grids for all turbines
+    REAL(wp), DIMENSION(:,:,:), ALLOCATABLE ::  thrust      !<
+    REAL(wp), DIMENSION(:,:,:), ALLOCATABLE ::  torque_y    !< 
+    REAL(wp), DIMENSION(:,:,:), ALLOCATABLE ::  torque_z    !< 
+
+!
+!-  rotor tendencies on coordinate grid
+    REAL(wp), DIMENSION(:,:,:), ALLOCATABLE ::  rot_tend_x  !< 
+    REAL(wp), DIMENSION(:,:,:), ALLOCATABLE ::  rot_tend_y  !< 
+    REAL(wp), DIMENSION(:,:,:), ALLOCATABLE ::  rot_tend_z  !< 
+!    
+!-  variables for the rotation of the rotor coordinates        
+    REAL(wp), DIMENSION(1:100,1:3,1:3) ::  rot_coord_trans  !< matrix for rotation of rotor coordinates
+    
+    REAL(wp), DIMENSION(1:3) ::  rot_eigen_rad   !< 
+    REAL(wp), DIMENSION(1:3) ::  rot_eigen_azi   !< 
+    REAL(wp), DIMENSION(1:3) ::  rot_eigen_nor   !< 
+    REAL(wp), DIMENSION(1:3) ::  re              !< 
+    REAL(wp), DIMENSION(1:3) ::  rea             !< 
+    REAL(wp), DIMENSION(1:3) ::  ren             !< 
+    REAL(wp), DIMENSION(1:3) ::  rote            !< 
+    REAL(wp), DIMENSION(1:3) ::  rota            !< 
+    REAL(wp), DIMENSION(1:3) ::  rotn            !< 
+
+!
+!-- Fixed variables for the speed controller
+
+    LOGICAL  ::  start_up = .TRUE.   !< 
+    
+    REAL(wp) ::  Fcorner             !< corner freq for the controller low pass filter
+    REAL(wp) ::  min_reg25           !< min region 2.5
+    REAL(wp) ::  om_rate             !< rotor speed change
+    REAL(wp) ::  slope15             !< slope in region 1.5
+    REAL(wp) ::  slope25             !< slope in region 2.5
+    REAL(wp) ::  trq_rate            !< torque change
+    REAL(wp) ::  vs_sysp             !< 
+    REAL(wp) ::  lp_coeff            !< coeff for the controller low pass filter 
+    
+    REAL(wp), DIMENSION(:), ALLOCATABLE :: omega_gen_old   !< last gen. speed
+    REAL(wp), DIMENSION(:), ALLOCATABLE :: omega_gen_f     !< filtered gen. sp
+    REAL(wp), DIMENSION(:), ALLOCATABLE :: omega_gen_f_old !< last filt. gen. sp
+    REAL(wp), DIMENSION(:), ALLOCATABLE :: torque_gen      !< generator torque
+    REAL(wp), DIMENSION(:), ALLOCATABLE :: torque_gen_old  !< last gen. torque
+
+    REAL(wp), DIMENSION(100) :: omega_rot_l = 0.0_wp !< local rot speed [rad/s]
+!
+!-- Fixed variables for the yaw controller
+
+    REAL(wp), DIMENSION(:)  , ALLOCATABLE ::  yawdir           !< direction to yaw
+    REAL(wp), DIMENSION(:)  , ALLOCATABLE ::  phi_yaw_l        !< local (cpu) yaw angle
+    REAL(wp), DIMENSION(:)  , ALLOCATABLE ::  wd30_l           !< local (cpu) long running avg of the wd
+    REAL(wp), DIMENSION(:)  , ALLOCATABLE ::  wd2_l            !< local (cpu) short running avg of the wd
+    REAL(wp), DIMENSION(:)  , ALLOCATABLE ::  wdir             !< wind direction at hub
+    REAL(wp), DIMENSION(:)  , ALLOCATABLE ::  u_inflow         !< wind speed at hub
+    REAL(wp), DIMENSION(:)  , ALLOCATABLE ::  wdir_l           !< 
+    REAL(wp), DIMENSION(:)  , ALLOCATABLE ::  u_inflow_l       !<
+    REAL(wp), DIMENSION(:,:), ALLOCATABLE ::  wd30             !<
+    REAL(wp), DIMENSION(:,:), ALLOCATABLE ::  wd2              !<
+    LOGICAL,  DIMENSION(1:100)            ::  doyaw = .FALSE.  !<
+    INTEGER(iwp)                          ::  WDLON            !<
+    INTEGER(iwp)                          ::  WDSHO            !<
+
+
+    SAVE
+
+
+    INTERFACE wtm_parin
+       MODULE PROCEDURE wtm_parin
+    END INTERFACE wtm_parin
+    
+    INTERFACE wtm_check_parameters
+       MODULE PROCEDURE wtm_check_parameters
+    END INTERFACE wtm_check_parameters
+        
+    INTERFACE wtm_init_arrays
+       MODULE PROCEDURE wtm_init_arrays
+    END INTERFACE wtm_init_arrays
+
+    INTERFACE wtm_init
+       MODULE PROCEDURE wtm_init
+    END INTERFACE wtm_init
+    
+    INTERFACE wtm_read_blade_tables
+       MODULE PROCEDURE wtm_read_blade_tables
+    END INTERFACE wtm_read_blade_tables
+           
+    INTERFACE wtm_forces
+       MODULE PROCEDURE wtm_forces
+       MODULE PROCEDURE wtm_yawcontrol
+    END INTERFACE wtm_forces
+    
+    INTERFACE wtm_rotate_rotor
+       MODULE PROCEDURE wtm_rotate_rotor
+    END INTERFACE wtm_rotate_rotor
+    
+    INTERFACE wtm_speed_control
+       MODULE PROCEDURE wtm_init_speed_control
+       MODULE PROCEDURE wtm_speed_control
+    END INTERFACE wtm_speed_control
+
+    INTERFACE wtm_tendencies
+       MODULE PROCEDURE wtm_tendencies
+       MODULE PROCEDURE wtm_tendencies_ij
+    END INTERFACE wtm_tendencies
+    
+    
+    PUBLIC wtm_check_parameters, wtm_forces, wtm_init, wtm_init_arrays,        &
+           wtm_parin, wtm_tendencies, wtm_tendencies_ij, wind_turbine 
+
+ CONTAINS
+
+
+!------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> Parin for &wind_turbine_par for wind turbine model
+!------------------------------------------------------------------------------!
+    SUBROUTINE wtm_parin
+
+
+       IMPLICIT NONE
+       
+       INTEGER(iwp) ::  ierrn       !<
+
+       CHARACTER (LEN=80) ::  line  !< dummy string that contains the current line of the parameter file 
+
+       NAMELIST /wind_turbine_par/   air_dens, dtow, gear_eff, gear_ratio,     &
+                                  gen_eff, inertia_gen, inertia_rot, max_miss, &
+                                  max_torque_gen, max_trq_rate, min_miss,      &
+                                  min_reg15, min_reg2, nairfoils, nturbines,   &
+                                  omega_rot, phi_yaw, pitch_add, pitch_control,&
+                                  rated_genspeed, rated_power, rcx, rcy, rcz,  &
+                                  rnac, rr, segment_length, segment_width,     &
+                                  slope2, speed_control, tilt, time_turbine_on,&
+                                  turb_cd_nacelle, turb_cd_tower,              &
+                                  yaw_control, yaw_speed
+
+!
+!--    Try to find wind turbine model package
+       REWIND ( 11 )
+       line = ' '
+       DO  WHILE ( INDEX( line, '&wind_turbine_par' ) == 0 )
+          READ ( 11, '(A)', END=10 )  line
+       ENDDO
+       BACKSPACE ( 11 )
+
+!
+!--    Read user-defined namelist
+       READ ( 11, wind_turbine_par, IOSTAT=ierrn )
+       
+       IF ( ierrn < 0 )  THEN
+          message_string = 'errors in \$wind_turbine_par'
+          CALL message( 'wtm_parin', 'PA0???', 1, 2, 0, 6, 0 )
+       ENDIF
+       
+!
+!--    Set flag that indicates that the wind turbine model is switched on
+       wind_turbine = .TRUE.
+
+ 10    CONTINUE   ! TBD Change from continue, mit ierrn machen
+
+
+    END SUBROUTINE wtm_parin
+
+    SUBROUTINE wtm_check_parameters
+
+    
+       IMPLICIT NONE
+    
+       IF ( ( .NOT.speed_control ) .AND. pitch_control )  THEN
+          message_string = 'pitch_control = .TRUE. requires '//                &
+                           'speed_control = .TRUE.'
+          CALL message( 'wtm_check_parameters', 'PA0???', 1, 2, 0, 6, 0 )
+       ENDIF
+       
+       IF ( ANY( omega_rot(1:nturbines) <= 0.0 ) )  THEN
+          message_string = 'omega_rot <= 0.0, Please set omega_rot to '     // &
+                           'a value larger than zero'
+          CALL message( 'wtm_check_parameters', 'PA0???', 1, 2, 0, 6, 0 )
+       ENDIF
+       
+       
+       IF ( ANY( rcx(1:nturbines) == 9999999.9_wp ) .OR.                       &
+            ANY( rcy(1:nturbines) == 9999999.9_wp ) .OR.                       &
+            ANY( rcz(1:nturbines) == 9999999.9_wp ) )  THEN
+          
+          message_string = 'rcx, rcy, rcz '                                 // &
+                           'have to be given for each turbine.'          
+          CALL message( 'wtm_check_parameters', 'PA0???', 1, 2, 0, 6, 0 )          
+          
+       ENDIF
+
+ 
+    END SUBROUTINE wtm_check_parameters 
+    
+                                        
+!------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> Allocate wind turbine model arrays
+!------------------------------------------------------------------------------!
+    SUBROUTINE wtm_init_arrays
+
+
+       IMPLICIT NONE
+
+       REAL(wp) ::  delta_r_factor   !< 
+       REAL(wp) ::  delta_r_init     !< 
+
+!
+!--    To be able to allocate arrays with dimension of rotor rings and segments,
+!--    the maximum possible numbers of rings and segments have to be calculated:
+
+       ALLOCATE( nrings(1:nturbines) )
+       ALLOCATE( delta_r(1:nturbines) )
+
+       nrings(:)  = 0
+       delta_r(:) = 0.0_wp
+
+!
+!--    Thickness (radial) of each ring and length (tangential) of each segment:
+       delta_r_factor = segment_width
+       delta_t_factor = segment_length
+       delta_r_init   = delta_r_factor * MIN( dx, dy, dz)
+       delta_t        = delta_t_factor * MIN( dx, dy, dz)
+
+       DO inot = 1, nturbines
+!
+!--       Determine number of rings:
+          nrings(inot) = NINT( rr(inot) / delta_r_init )
+
+          delta_r(inot) = rr(inot) / nrings(inot)
+
+       ENDDO
+
+       nrings_max = MAXVAL(nrings)
+
+       ALLOCATE( nsegs(1:nrings_max,1:nturbines) )
+       ALLOCATE( nsegs_total(1:nturbines) )
+
+       nsegs(:,:)     = 0
+       nsegs_total(:) = 0
+
+
+       DO inot = 1, nturbines
+          DO ring = 1, nrings(inot)
+!
+!--          Determine number of segments for each ring:
+             nsegs(ring,inot) = MAX( 8, CEILING( delta_r_factor * pi *         &
+                                                 ( 2.0_wp * ring - 1.0_wp ) /  &
+                                                 delta_t_factor ) )
+          ENDDO
+!
+!--       Total sum of all rotor segments:
+          nsegs_total(inot) = SUM( nsegs(:,inot) )
+
+       ENDDO
+
+!
+!--    Maximum number of segments per ring:
+       nsegs_max = MAXVAL(nsegs)
+
+!!
+!!--    TODO: Folgendes im Header ausgeben!
+!       IF ( myid == 0 )  THEN
+!          PRINT*, 'nrings(1) = ', nrings(1)
+!          PRINT*, '--------------------------------------------------'
+!          PRINT*, 'nsegs(:,1) = ', nsegs(:,1)
+!          PRINT*, '--------------------------------------------------'
+!          PRINT*, 'nrings_max = ', nrings_max
+!          PRINT*, 'nsegs_max = ', nsegs_max
+!          PRINT*, 'nsegs_total(1) = ', nsegs_total(1)
+!       ENDIF
+
+
+!
+!--    Allocate 1D arrays (dimension = number of turbines)
+       ALLOCATE( i_hub(1:nturbines) )
+       ALLOCATE( i_smear(1:nturbines) )
+       ALLOCATE( j_hub(1:nturbines) )
+       ALLOCATE( j_smear(1:nturbines) )
+       ALLOCATE( k_hub(1:nturbines) )
+       ALLOCATE( k_smear(1:nturbines) )
+       ALLOCATE( torque_total(1:nturbines) )
+       ALLOCATE( thrust_rotor(1:nturbines) )
+
+!
+!--    Allocation of the 1D arrays for speed pitch_control
+       ALLOCATE( omega_gen(1:nturbines) )
+       ALLOCATE( omega_gen_old(1:nturbines) )
+       ALLOCATE( omega_gen_f(1:nturbines) )
+       ALLOCATE( omega_gen_f_old(1:nturbines) )
+       ALLOCATE( pitch_add_old(1:nturbines) )
+       ALLOCATE( torque_gen(1:nturbines) )
+       ALLOCATE( torque_gen_old(1:nturbines) )
+
+!
+!--    Allocation of the 1D arrays for yaw control
+       ALLOCATE( yawdir(1:nturbines) )
+       ALLOCATE( u_inflow(1:nturbines) )
+       ALLOCATE( wdir(1:nturbines) )
+       ALLOCATE( u_inflow_l(1:nturbines) )
+       ALLOCATE( wdir_l(1:nturbines) )
+       ALLOCATE( phi_yaw_l(1:nturbines) )
+       
+!
+!--    Allocate 1D arrays (dimension = number of rotor segments)
+       ALLOCATE( alpha_attack(1:nsegs_max) )
+       ALLOCATE( chord(1:nsegs_max) )
+       ALLOCATE( phi_rel(1:nsegs_max) )
+       ALLOCATE( thrust_seg(1:nsegs_max) )
+       ALLOCATE( torque_seg_y(1:nsegs_max) )
+       ALLOCATE( torque_seg_z(1:nsegs_max) )
+       ALLOCATE( turb_cd(1:nsegs_max) )
+       ALLOCATE( turb_cl(1:nsegs_max) )
+       ALLOCATE( vrel(1:nsegs_max) )
+       ALLOCATE( vtheta(1:nsegs_max) )
+
+!
+!--    Allocate 2D arrays (dimension = number of rotor rings and segments)
+       ALLOCATE( rbx(1:nrings_max,1:nsegs_max) )
+       ALLOCATE( rby(1:nrings_max,1:nsegs_max) )
+       ALLOCATE( rbz(1:nrings_max,1:nsegs_max) )
+       ALLOCATE( thrust_ring(1:nrings_max,1:nsegs_max) )
+       ALLOCATE( torque_ring_y(1:nrings_max,1:nsegs_max) )
+       ALLOCATE( torque_ring_z(1:nrings_max,1:nsegs_max) )
+
+!
+!--    Allocate additional 2D arrays
+       ALLOCATE( rotx(1:nturbines,1:3) )
+       ALLOCATE( roty(1:nturbines,1:3) )
+       ALLOCATE( rotz(1:nturbines,1:3) )
+
+!
+!--    Allocate 3D arrays (dimension = number of grid points)
+       ALLOCATE( nac_cd_surf(nzb:nzt+1,nysg:nyng,nxlg:nxrg) )
+       ALLOCATE( rot_tend_x(nzb:nzt+1,nysg:nyng,nxlg:nxrg) )
+       ALLOCATE( rot_tend_y(nzb:nzt+1,nysg:nyng,nxlg:nxrg) )
+       ALLOCATE( rot_tend_z(nzb:nzt+1,nysg:nyng,nxlg:nxrg) )
+       ALLOCATE( thrust(nzb:nzt+1,nysg:nyng,nxlg:nxrg) )
+       ALLOCATE( torque_y(nzb:nzt+1,nysg:nyng,nxlg:nxrg) )
+       ALLOCATE( torque_z(nzb:nzt+1,nysg:nyng,nxlg:nxrg) )
+       ALLOCATE( tow_cd_surf(nzb:nzt+1,nysg:nyng,nxlg:nxrg) )
+
+!
+!--    Allocate additional 3D arrays
+       ALLOCATE( u_int(1:nturbines,1:nrings_max,1:nsegs_max) )
+       ALLOCATE( u_int_1_l(1:nturbines,1:nrings_max,1:nsegs_max) )
+       ALLOCATE( v_int(1:nturbines,1:nrings_max,1:nsegs_max) )
+       ALLOCATE( v_int_1_l(1:nturbines,1:nrings_max,1:nsegs_max) )
+       ALLOCATE( w_int(1:nturbines,1:nrings_max,1:nsegs_max) )
+       ALLOCATE( w_int_1_l(1:nturbines,1:nrings_max,1:nsegs_max) )
+
+!
+!--    All of the arrays are initialized with a value of zero:
+       i_hub(:)                 = 0
+       i_smear(:)               = 0
+       j_hub(:)                 = 0
+       j_smear(:)               = 0
+       k_hub(:)                 = 0
+       k_smear(:)               = 0
+       
+       torque_total(:)          = 0.0_wp
+       thrust_rotor(:)          = 0.0_wp
+
+       omega_gen(:)             = 0.0_wp
+       omega_gen_old(:)         = 0.0_wp
+       omega_gen_f(:)           = 0.0_wp
+       omega_gen_f_old(:)       = 0.0_wp
+       pitch_add_old(:)         = 0.0_wp
+       torque_gen(:)            = 0.0_wp
+       torque_gen_old(:)        = 0.0_wp
+       
+       yawdir(:)                = 0.0_wp
+       wdir(:)                  = 0.0_wp
+       u_inflow(:)              = 0.0_wp
+
+!
+!--    Allocate 1D arrays (dimension = number of rotor segments)
+       alpha_attack(:)          = 0.0_wp
+       chord(:)                 = 0.0_wp
+       phi_rel(:)               = 0.0_wp
+       thrust_seg(:)            = 0.0_wp
+       torque_seg_y(:)          = 0.0_wp
+       torque_seg_z(:)          = 0.0_wp
+       turb_cd(:)               = 0.0_wp
+       turb_cl(:)               = 0.0_wp
+       vrel(:)                  = 0.0_wp
+       vtheta(:)                = 0.0_wp
+
+       rbx(:,:)                 = 0.0_wp
+       rby(:,:)                 = 0.0_wp
+       rbz(:,:)                 = 0.0_wp
+       thrust_ring(:,:)         = 0.0_wp
+       torque_ring_y(:,:)       = 0.0_wp
+       torque_ring_z(:,:)       = 0.0_wp
+
+       rotx(:,:)                = 0.0_wp
+       roty(:,:)                = 0.0_wp
+       rotz(:,:)                = 0.0_wp
+       turb_cl_tab(:,:)         = 0.0_wp
+       turb_cd_tab(:,:)         = 0.0_wp
+
+       nac_cd_surf(:,:,:)       = 0.0_wp
+       rot_tend_x(:,:,:)        = 0.0_wp
+       rot_tend_y(:,:,:)        = 0.0_wp
+       rot_tend_z(:,:,:)        = 0.0_wp
+       thrust(:,:,:)            = 0.0_wp
+       torque_y(:,:,:)          = 0.0_wp
+       torque_z(:,:,:)          = 0.0_wp
+       tow_cd_surf(:,:,:)       = 0.0_wp
+
+       u_int(:,:,:)             = 0.0_wp
+       u_int_1_l(:,:,:)         = 0.0_wp
+       v_int(:,:,:)             = 0.0_wp
+       v_int_1_l(:,:,:)         = 0.0_wp
+       w_int(:,:,:)             = 0.0_wp
+       w_int_1_l(:,:,:)         = 0.0_wp
+
+
+    END SUBROUTINE wtm_init_arrays
+
+
+!------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> Initialization of the wind turbine model
+!------------------------------------------------------------------------------!
+    SUBROUTINE wtm_init
+
+    
+       IMPLICIT NONE
+
+       INTEGER(iwp) ::  i  !< running index
+       INTEGER(iwp) ::  j  !< running index
+       INTEGER(iwp) ::  k  !< running index
+       
+!
+!--    Help variables for the smearing function       
+       REAL(wp) ::  eps_kernel       !<       
+       
+!
+!--    Help variables for calculation of the tower drag       
+       INTEGER(iwp) ::  tower_n      !<
+       INTEGER(iwp) ::  tower_s      !<
+!
+!--    Help variables for the calulaction of the nacelle drag
+       INTEGER(iwp) ::  i_ip         !<
+       INTEGER(iwp) ::  i_ipg        !<
+       
+       REAL(wp) ::  yvalue               
+       REAL(wp) ::  dy_int           !< 
+       REAL(wp) ::  dz_int           !<
+       
+       REAL(wp), DIMENSION(:,:), ALLOCATABLE :: circle_points  !<
+              
+       INTEGER(iwp), DIMENSION(:), ALLOCATABLE :: index_nacb       !< 
+       INTEGER(iwp), DIMENSION(:), ALLOCATABLE :: index_nacl       !< 
+       INTEGER(iwp), DIMENSION(:), ALLOCATABLE :: index_nacr       !< 
+       INTEGER(iwp), DIMENSION(:), ALLOCATABLE :: index_nact       !< 
+       
+       ALLOCATE( index_nacb(1:nturbines) )
+       ALLOCATE( index_nacl(1:nturbines) )
+       ALLOCATE( index_nacr(1:nturbines) )
+       ALLOCATE( index_nact(1:nturbines) )
+
+
+       IF ( speed_control)  THEN
+       
+          CALL wtm_speed_control
+
+       ENDIF
+
+!
+!------------------------------------------------------------------------------!
+!--    Calculation of parameters for the regularization kernel
+!--    (smearing of the forces)
+!------------------------------------------------------------------------------!
+!
+!--    In the following, some of the required parameters for the smearing will
+!--    be calculated:
+
+!--    The kernel is set equal to twice the grid spacing which has turned out to
+!--    be a reasonable value (see e.g. Troldborg et al. (2013), Wind Energy,
+!--    DOI: 10.1002/we.1608):
+       eps_kernel = 2.0_wp * dx
+!
+!--    The zero point (eps_min) of the polynomial function must be the following
+!--    if the integral of the polynomial function (for values < eps_min) shall
+!--    be equal to the integral of the Gaussian function used before:
+       eps_min = ( 105.0_wp / 32.0_wp )**( 1.0_wp / 3.0_wp ) *                 &
+                 pi**( 1.0_wp / 6.0_wp ) * eps_kernel
+!
+!--    Square of eps_min:
+       eps_min2 = eps_min**2
+!
+!--    Parameters in the polynomial function:
+       pol_a = 1.0_wp / eps_min**4
+       pol_b = 2.0_wp / eps_min**2
+!
+!--    Normalization factor which is the inverse of the integral of the smearing
+!--    function:
+       eps_factor = 105.0_wp / ( 32.0_wp * pi * eps_min**3 )
+       
+!--    Change tilt angle to rad:
+       tilt = tilt * pi / 180.0_wp
+      
+!
+!--    Change yaw angle to rad:
+       phi_yaw(:) = phi_yaw(:) * pi / 180.0_wp
+
+
+       DO inot = 1, nturbines
+!
+!--       Rotate the rotor coordinates in case yaw and tilt are defined
+          CALL wtm_rotate_rotor( inot )
+          
+!
+!--       Determine the indices of the hub height
+          i_hub(inot) = INT(   rcx(inot)                 / dx )
+          j_hub(inot) = INT( ( rcy(inot) + 0.5_wp * dy ) / dy )
+          k_hub(inot) = INT( ( rcz(inot) + 0.5_wp * dz ) / dz )
+
+!
+!--       Determining the area to which the smearing of the forces is applied.
+!--       As smearing now is effectively applied only for distances smaller than
+!--       eps_min, the smearing area can be further limited and regarded as a
+!--       function of eps_min:
+          i_smear(inot) = CEILING( ( rr(inot) + eps_min ) / dx )
+          j_smear(inot) = CEILING( ( rr(inot) + eps_min ) / dy )
+          k_smear(inot) = CEILING( ( rr(inot) + eps_min ) / dz )
+       
+       ENDDO
+
+!
+!------------------------------------------------------------------------------!
+!--    Determine the area within each grid cell that overlaps with the area
+!--    of the nacelle and the tower (needed for calculation of the forces)
+!------------------------------------------------------------------------------!
+!
+!--    Note: so far this is only a 2D version, in that the mean flow is
+!--    perpendicular to the rotor area.
+
+!
+!--    Allocation of the array containing information on the intersection points
+!--    between rotor disk and the numerical grid:
+       upper_end = ( ny + 1 ) * 10000 
+
+       ALLOCATE( circle_points(1:2,1:upper_end) )
+       
+       circle_points(:,:) = 0.0_wp
+
+       
+       DO inot = 1, nturbines                     ! loop over number of turbines
+!
+!--       Determine the grid index (u-grid) that corresponds to the location of
+!--       the rotor center (reduces the amount of calculations in the case that
+!--       the mean flow is perpendicular to the rotor area):
+          i = i_hub(inot)
+
+!
+!--       Determine the left and the right edge of the nacelle (corresponding
+!--       grid point indices):
+          index_nacl(inot) = INT( ( rcy(inot) - rnac(inot) + 0.5_wp * dy ) / dy )
+          index_nacr(inot) = INT( ( rcy(inot) + rnac(inot) + 0.5_wp * dy ) / dy )
+!
+!--       Determine the bottom and the top edge of the nacelle (corresponding
+!--       grid point indices).The grid point index has to be increased by 1, as
+!--       the first level for the u-component (index 0) is situated below the
+!--       surface. All points between z=0 and z=dz/s would already be contained
+!--       in grid box 1.
+          index_nacb(inot) = INT( ( rcz(inot) - rnac(inot) ) / dz ) + 1
+          index_nact(inot) = INT( ( rcz(inot) + rnac(inot) ) / dz ) + 1
+
+!
+!--       Determine the indices of the grid boxes containing the left and 
+!--       the right boundaries of the tower:
+          tower_n = ( rcy(inot) + 0.5_wp * dtow(inot) - 0.5_wp * dy ) / dy
+          tower_s = ( rcy(inot) - 0.5_wp * dtow(inot) - 0.5_wp * dy ) / dy
+
+!
+!--       Determine the fraction of the grid box area overlapping with the tower
+!--       area and multiply it with the drag of the tower:
+          IF ( ( nxlg <= i )  .AND.  ( nxrg >= i ) )  THEN
+
+             DO  j = nys, nyn
+!
+!--             Loop from south to north boundary of tower
+                IF ( ( j >= tower_s )  .AND.  ( j <= tower_n ) )  THEN
+
+                   DO  k = nzb, nzt
+
+                      IF ( k == k_hub(inot) )  THEN
+                         IF ( tower_n - tower_s >= 1 )  THEN
+!
+!--                      leftmost and rightmost grid box:
+                            IF ( j == tower_s )  THEN
+                               tow_cd_surf(k,j,i) = ( rcz(inot) -              &
+                                    ( k_hub(inot) * dz - 0.5_wp * dz ) )  *    & ! extension in z-direction
+                                  ( ( tower_s + 1.0_wp + 0.5_wp ) * dy    -    &
+                                    ( rcy(inot) - 0.5_wp * dtow(inot) ) ) *    & ! extension in y-direction
+                                  turb_cd_tower(inot)
+                            ELSEIF ( j == tower_n )  THEN
+                               tow_cd_surf(k,j,i) = ( rcz(inot)            -   &
+                                    ( k_hub(inot) * dz - 0.5_wp * dz ) )  *    & ! extension in z-direction
+                                  ( ( rcy(inot) + 0.5_wp * dtow(inot) )   -    &
+                                    ( tower_n + 0.5_wp ) * dy )           *    & ! extension in y-direction
+                                  turb_cd_tower(inot)
+!
+!--                         grid boxes inbetween
+!--                         (where tow_cd_surf = grid box area):
+                            ELSE
+                               tow_cd_surf(k,j,i) = ( rcz(inot) -              &
+                                    ( k_hub(inot) * dz - 0.5_wp * dz ) )  *    &
+                                    dy * turb_cd_tower(inot)
+                            ENDIF
+!
+!--                      tower lies completely within one grid box:
+                         ELSE
+                            tow_cd_surf(k,j,i) = ( rcz(inot)                 - &
+                                       ( k_hub(inot) * dz - 0.5_wp * dz ) ) *  &
+                                       dtow(inot) * turb_cd_tower(inot)
+                         ENDIF
+!
+!--                  In case that k is smaller than k_hub the following actions
+!--                  are carried out:
+                      ELSEIF ( k < k_hub(inot) )  THEN
+                      
+                         IF ( ( tower_n - tower_s ) >= 1 )  THEN
+!
+!--                         leftmost and rightmost grid box:
+                            IF ( j == tower_s )  THEN                         
+                               tow_cd_surf(k,j,i) = dz * (                     &
+                                      ( tower_s + 1 + 0.5_wp ) * dy         -  &
+                                      ( rcy(inot) - 0.5_wp * dtow(inot) )      &
+                                                        ) * turb_cd_tower(inot)
+                            ELSEIF ( j == tower_n )  THEN
+                               tow_cd_surf(k,j,i) = dz * (                     &
+                                      ( rcy(inot) + 0.5_wp * dtow(inot) )   -  &
+                                      ( tower_n + 0.5_wp ) * dy                &
+                                                         ) * turb_cd_tower(inot)
+!
+!--                         grid boxes inbetween
+!--                         (where tow_cd_surf = grid box area):
+                            ELSE
+                               tow_cd_surf(k,j,i) = dz * dy * turb_cd_tower(inot)
+                            ENDIF
+!
+!--                         tower lies completely within one grid box:
+                         ELSE
+                            tow_cd_surf(k,j,i) = dz * dtow(inot) *             &
+                                                turb_cd_tower(inot)
+                         ENDIF ! end if larger than grid box
+
+                      ENDIF    ! end if k == k_hub
+
+                   ENDDO       ! end loop over k
+
+                ENDIF          ! end if inside north and south boundary of tower
+
+             ENDDO             ! end loop over j
+
+          ENDIF                ! end if hub inside domain + ghostpoints
+       
+          
+          CALL exchange_horiz( tow_cd_surf, nbgp )
+
+!
+!--       Calculation of the nacelle area
+!--       CAUTION: Currently disabled due to segmentation faults on the FLOW HPC
+!--                cluster (Oldenburg)
+!!
+!!--       Tabulate the points on the circle that are required in the following for
+!!--       the calculation of the Riemann integral (node points; they are called
+!!--       circle_points in the following):
+!
+!          dy_int = dy / 10000.0_wp
+!
+!          DO  i_ip = 1, upper_end
+!             yvalue   = dy_int * ( i_ip - 0.5_wp ) + 0.5_wp * dy           !<--- segmentation fault
+!             sqrt_arg = rnac(inot)**2 - ( yvalue - rcy(inot) )**2          !<--- segmentation fault
+!             IF ( sqrt_arg >= 0.0_wp )  THEN
+!!
+!!--             bottom intersection point
+!                circle_points(1,i_ip) = rcz(inot) - SQRT( sqrt_arg )
+!!
+!!--             top intersection point
+!                circle_points(2,i_ip) = rcz(inot) + SQRT( sqrt_arg )       !<--- segmentation fault
+!             ELSE
+!                circle_points(:,i_ip) = -111111                            !<--- segmentation fault
+!             ENDIF
+!          ENDDO
+!
+!
+!          DO  j = nys, nyn
+!!
+!!--          In case that the grid box is located completely outside the nacelle
+!!--          (y) it can automatically be stated that there is no overlap between
+!!--          the grid box and the nacelle and consequently we can set
+!!--          nac_cd_surf(:,j,i) = 0.0:
+!             IF ( ( j >= index_nacl(inot) )  .AND.  ( j <= index_nacr(inot) ) )  THEN
+!                DO  k = nzb+1, nzt
+!!
+!!--                In case that the grid box is located completely outside the
+!!--                nacelle (z) it can automatically be stated that there is no
+!!--                overlap between the grid box and the nacelle and consequently
+!!--                we can set nac_cd_surf(k,j,i) = 0.0:
+!                   IF ( ( k >= index_nacb(inot) )  .OR.                           &
+!                        ( k <= index_nact(inot) ) )  THEN
+!!
+!!--                   For all other cases Riemann integrals are calculated.
+!!--                   Here, the points on the circle that have been determined
+!!--                   above are used in order to calculate the overlap between the
+!!--                   gridbox and the nacelle area (area approached by 10000
+!!--                   rectangulars dz_int * dy_int):
+!                      DO  i_ipg = 1, 10000
+!                         dz_int = dz
+!                         i_ip = j * 10000 + i_ipg
+!!
+!!--                      Determine the vertical extension dz_int of the circle
+!!--                      within the current grid box:
+!                         IF ( ( circle_points(2,i_ip) < zw(k) ) .AND.          &  !<--- segmentation fault
+!                              ( circle_points(2,i_ip) >= zw(k-1) ) ) THEN
+!                            dz_int = dz_int -                                  &  !<--- segmentation fault
+!                                     ( zw(k) - circle_points(2,i_ip) )
+!                         ENDIF
+!                         IF ( ( circle_points(1,i_ip) <= zw(k) ) .AND.         &  !<--- segmentation fault
+!                              ( circle_points(1,i_ip) > zw(k-1) ) ) THEN
+!                            dz_int = dz_int -                                  &
+!                                     ( circle_points(1,i_ip) - zw(k-1) )
+!                         ENDIF
+!                         IF ( zw(k-1) > circle_points(2,i_ip) ) THEN
+!                            dz_int = 0.0_wp
+!                         ENDIF
+!                         IF ( zw(k) < circle_points(1,i_ip) ) THEN
+!                            dz_int = 0.0_wp                      
+!                         ENDIF 
+!                         IF ( ( nxlg <= i ) .AND. ( nxrg >= i ) ) THEN
+!                            nac_cd_surf(k,j,i) = nac_cd_surf(k,j,i) +        &  !<--- segmentation fault
+!                                                  dy_int * dz_int * turb_cd_nacelle(inot)
+!                         ENDIF   
+!                      ENDDO
+!                   ENDIF
+!                ENDDO
+!             ENDIF
+! 
+!          ENDDO
+!        
+!          CALL exchange_horiz( nac_cd_surf, nbgp )                                !<---  segmentation fault
+
+       ENDDO   ! end of loop over turbines
+
+       tow_cd_surf   = tow_cd_surf   / ( dx * dy * dz )      ! Normalize tower drag
+       nac_cd_surf = nac_cd_surf / ( dx * dy * dz )      ! Normalize nacelle drag
+
+       CALL wtm_read_blade_tables
+ 
+    END SUBROUTINE wtm_init
+
+
+!------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> Read in layout of the rotor blade , the lift and drag tables
+!> and the distribution of lift and drag tables along the blade
+!------------------------------------------------------------------------------!
+!
+    SUBROUTINE wtm_read_blade_tables
+
+
+       IMPLICIT NONE
+
+       INTEGER(iwp) ::  ii   !< running index
+       INTEGER(iwp) ::  jj   !< running index
+    
+       INTEGER(iwp) ::  ierrn       !<
+    
+       CHARACTER(200) :: chmess     !< Read in string 
+
+       INTEGER(iwp) ::  dlen        !< no. rows of local table 
+       INTEGER(iwp) ::  dlenbl      !< no. rows of cd, cl table
+       INTEGER(iwp) ::  ialpha      !< table position of current alpha value
+       INTEGER(iwp) ::  iialpha     !< 
+       INTEGER(iwp) ::  iir         !< 
+       INTEGER(iwp) ::  radres      !< radial resolution
+       INTEGER(iwp) ::  t1          !< no. of airfoil
+       INTEGER(iwp) ::  t2          !< no. of airfoil
+       INTEGER(iwp) ::  trow        !< 
+       INTEGER(iwp) ::  dlenbl_int  !< no. rows of interpolated cd, cl tables
+    
+       REAL(wp) :: alpha_attack_i   !<
+       REAL(wp) :: weight_a         !< 
+       REAL(wp) :: weight_b         !< 
+
+       INTEGER(iwp), DIMENSION(:), ALLOCATABLE :: ttoint1    !<
+       INTEGER(iwp), DIMENSION(:), ALLOCATABLE :: ttoint2    !<
+    
+       REAL(wp), DIMENSION(:), ALLOCATABLE :: turb_cd_sel1   !< 
+       REAL(wp), DIMENSION(:), ALLOCATABLE :: turb_cd_sel2   !<
+       REAL(wp), DIMENSION(:), ALLOCATABLE :: turb_cl_sel1   !< 
+       REAL(wp), DIMENSION(:), ALLOCATABLE :: turb_cl_sel2   !<
+       REAL(wp), DIMENSION(:), ALLOCATABLE :: read_cl_cd     !< read in var array
+              
+       REAL(wp), DIMENSION(:), ALLOCATABLE    :: alpha_attack_tab   !< 
+       REAL(wp), DIMENSION(:), ALLOCATABLE    :: trad1              !< 
+       REAL(wp), DIMENSION(:), ALLOCATABLE    :: trad2              !<          
+       REAL(wp), DIMENSION(:,:), ALLOCATABLE  :: turb_cd_table      !<
+       REAL(wp), DIMENSION(:,:), ALLOCATABLE  :: turb_cl_table      !<
+                                          
+       ALLOCATE ( read_cl_cd(1:2*nairfoils+1) )
+
+!
+!--    Read in the distribution of lift and drag tables along the blade, the
+!--    layout of the rotor blade and the lift and drag tables:
+
+       OPEN ( 201, FILE='WTM_DATA', STATUS='OLD', FORM='FORMATTED', IOSTAT=ierrn )
+
+       IF ( ierrn /= 0 )  THEN
+          message_string = 'file WTM_DATA does not exist'
+          CALL message( 'wtm_init', 'PA0???', 1, 2, 0, 6, 0 )
+       ENDIF
+!
+!--    Read distribution table:
+
+       dlen = 0
+
+       READ ( 201, '(3/)' )
+
+       rloop3: DO
+          READ ( 201, *, IOSTAT=ierrn ) chmess
+          IF ( ierrn < 0  .OR.  chmess == '#'  .OR.  chmess == '')  EXIT rloop3
+          dlen = dlen + 1
+       ENDDO rloop3
+
+       ALLOCATE( trad1(1:dlen), trad2(1:dlen), ttoint1(1:dlen), ttoint2(1:dlen))
+
+       DO jj = 1,dlen+1
+          BACKSPACE ( 201, IOSTAT=ierrn )
+       ENDDO
+
+       DO jj = 1,dlen
+          READ ( 201, * ) trad1(jj), trad2(jj), ttoint1(jj), ttoint2(jj)
+       ENDDO
+
+!
+!--    Read layout table:
+
+       dlen = 0 
+
+       READ ( 201, '(3/)')
+
+       rloop1: DO
+          READ ( 201, *, IOSTAT=ierrn ) chmess
+          IF ( ierrn < 0  .OR.  chmess == '#'  .OR.  chmess == '')  EXIT rloop1
+          dlen = dlen + 1
+       ENDDO rloop1
+
+       ALLOCATE( lrd(1:dlen), ard(1:dlen), crd(1:dlen) )
+       DO jj = 1, dlen+1
+          BACKSPACE ( 201, IOSTAT=ierrn )
+       ENDDO             
+       DO jj = 1, dlen
+          READ ( 201, * ) lrd(jj), ard(jj), crd(jj) 
+       ENDDO
+
+!
+!--    Read tables (turb_cl(alpha),turb_cd(alpha) for the different profiles:
+
+       dlen = 0
+
+       READ ( 201, '(3/)' )
+
+       rloop2: DO
+          READ ( 201, *, IOSTAT=ierrn ) chmess
+          IF ( ierrn < 0  .OR.  chmess == '#'  .OR.  chmess == '')  EXIT rloop2
+          dlen = dlen + 1
+       ENDDO rloop2 
+
+       ALLOCATE( alpha_attack_tab(1:dlen), turb_cl_table(1:dlen,1:nairfoils),  &
+                 turb_cd_table(1:dlen,1:nairfoils) )
+
+       DO jj = 1,dlen+1
+          BACKSPACE ( 201, IOSTAT=ierrn )
+       ENDDO 
+
+       DO jj = 1,dlen
+          READ ( 201, * ) read_cl_cd
+          alpha_attack_tab(jj) = read_cl_cd(1)
+          DO ii= 1, nairfoils
+             turb_cl_table(jj,ii) = read_cl_cd(ii*2)
+             turb_cd_table(jj,ii) = read_cl_cd(ii*2+1)
+          ENDDO
+
+       ENDDO
+
+       dlenbl = dlen 
+
+       CLOSE ( 201 )
+
+!
+!--    For each possible radial position (resolution: 0.1 m --> 630 values) and
+!--    each possible angle of attack (resolution: 0.01 degrees --> 36000 values!)
+!--    determine the lift and drag coefficient by interpolating between the
+!--    tabulated values of each table (interpolate to current angle of attack)
+!--    and between the tables (interpolate to current radial position):
+
+       ALLOCATE( turb_cl_sel1(0:dlenbl) )  
+       ALLOCATE( turb_cl_sel2(0:dlenbl) )  
+       ALLOCATE( turb_cd_sel1(0:dlenbl) )
+       ALLOCATE( turb_cd_sel2(0:dlenbl) )
+
+       radres     = INT( rr(1) * 10.0_wp ) + 1_iwp
+       dlenbl_int = INT( 360.0_wp / accu_cl_cd_tab ) + 1_iwp
+
+
+       ALLOCATE( turb_cl_tab(0:dlenbl_int,1:radres) )
+       ALLOCATE( turb_cd_tab(0:dlenbl_int,1:radres) )
+
+
+       DO iir = 1, radres ! loop over radius
+
+          DO iialpha = 1, dlenbl_int  ! loop over angles
+
+             cur_r = ( iir - 1_iwp ) * 0.1_wp             
+             alpha_attack_i = -180.0_wp + REAL( iialpha-1 ) * accu_cl_cd_tab
+             ialpha = 1
+
+             DO WHILE ( alpha_attack_i > alpha_attack_tab(ialpha) )
+                ialpha = ialpha + 1
+             ENDDO
+!
+!--          Find position in table
+             lct = MINLOC( ABS( trad1 - cur_r ) )
+!                lct(1) = lct(1)
+
+             IF ( ( trad1(lct(1)) - cur_r ) .GT. 0.0 )  THEN
+                lct(1) = lct(1) - 1
+             ENDIF
+
+             trow = lct(1)
+!
+!--          Calculate weights for interpolation
+             weight_a = ( trad2(trow) - cur_r ) / ( trad2(trow) - trad1(trow) )
+             weight_b = ( cur_r - trad1(trow) ) / ( trad2(trow) - trad1(trow) )
+             t1 = ttoint1(trow)
+             t2 = ttoint2(trow)
+
+             IF ( t1 .EQ. t2 ) THEN  ! if both are the same, the weights are NaN
+                weight_a = 0.5_wp    ! then do interpolate in between same twice
+                weight_b = 0.5_wp    ! using 0.5 as weight
+             ENDIF
+
+             IF ( t1 == 0 .AND. t2 == 0 ) THEN
+                turb_cd_sel1 = 0.0_wp
+                turb_cd_sel2 = 0.0_wp
+                turb_cl_sel1 = 0.0_wp
+                turb_cl_sel2 = 0.0_wp
+             ELSE
+                turb_cd_sel1 = turb_cd_table(:,t1)
+                turb_cd_sel2 = turb_cd_table(:,t2)
+                turb_cl_sel1 = turb_cl_table(:,t1)
+                turb_cl_sel2 = turb_cl_table(:,t2)
+             ENDIF
+
+!
+!--          Interpolation of lift and drag coefficiencts on fine grid of radius 
+!--          segments and angles of attack
+
+             turb_cl_tab(iialpha,iir) = ( alpha_attack_tab(ialpha) -           &
+                                          alpha_attack_i ) /                   &
+                                        ( alpha_attack_tab(ialpha) -           &
+                                          alpha_attack_tab(ialpha-1) ) *       &
+                                        ( weight_a * turb_cl_sel1(ialpha-1) +  &
+                                          weight_b * turb_cl_sel2(ialpha-1) ) +&
+                                        ( alpha_attack_i             -         &
+                                          alpha_attack_tab(ialpha-1) ) /       &
+                                        ( alpha_attack_tab(ialpha) -           &
+                                          alpha_attack_tab(ialpha-1) ) *       &
+                                        ( weight_a * turb_cl_sel1(ialpha) +    &
+                                          weight_b * turb_cl_sel2(ialpha) )
+             turb_cd_tab(iialpha,iir) = ( alpha_attack_tab(ialpha) -           &
+                                          alpha_attack_i ) /                   &
+                                        ( alpha_attack_tab(ialpha) -           &
+                                          alpha_attack_tab(ialpha-1) ) *       &
+                                        ( weight_a * turb_cd_sel1(ialpha-1) +  &
+                                          weight_b * turb_cd_sel2(ialpha-1) ) +&
+                                        ( alpha_attack_i             -         &
+                                          alpha_attack_tab(ialpha-1) ) /       &
+                                        ( alpha_attack_tab(ialpha) -           &
+                                          alpha_attack_tab(ialpha-1) ) *       &
+                                        ( weight_a * turb_cd_sel1(ialpha) +    &
+                                          weight_b * turb_cd_sel2(ialpha) )
+   
+          ENDDO   ! end loop over angles of attack
+
+       ENDDO   ! end loop over radius
+    
+    END SUBROUTINE wtm_read_blade_tables
+
+
+!------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> The projection matrix for the coordinate system of therotor disc in respect
+!> to the yaw and tilt angle of the rotor is calculated
+!------------------------------------------------------------------------------!
+    SUBROUTINE wtm_rotate_rotor( inot )
+
+
+       IMPLICIT NONE
+
+       INTEGER(iwp) :: inot
+!
+!--    Calculation of the rotation matrix for the application of the tilt to
+!--    the rotors
+       rot_eigen_rad(1) = SIN( phi_yaw(inot) )    ! x-component of the radial eigenvector
+       rot_eigen_rad(2) = COS( phi_yaw(inot) )    ! y-component of the radial eigenvector 
+       rot_eigen_rad(3) = 0.0_wp                  ! z-component of the radial eigenvector
+
+       rot_eigen_azi(1) = 0.0_wp                  ! x-component of the azimuth eigenvector
+       rot_eigen_azi(2) = 0.0_wp                  ! y-component of the azimuth eigenvector
+       rot_eigen_azi(3) = 1.0_wp                  ! z-component of the azimuth eigenvector
+
+       rot_eigen_nor(1) =  COS( phi_yaw(inot) )   ! x-component of the normal eigenvector
+       rot_eigen_nor(2) = -SIN( phi_yaw(inot) )   ! y-component of the normal eigenvector
+       rot_eigen_nor(3) = 0.0_wp                  ! z-component of the normal eigenvector
+    
+!
+!--    Calculation of the coordinate transformation matrix to apply a tilt to
+!--    the rotor. If tilt = 0, rot_coord_trans is a unit matrix.
+
+       rot_coord_trans(inot,1,1) = rot_eigen_rad(1)**2                   *     &
+                                   ( 1.0_wp - COS( tilt ) ) + COS( tilt ) 
+       rot_coord_trans(inot,1,2) = rot_eigen_rad(1) * rot_eigen_rad(2)   *     &
+                                   ( 1.0_wp - COS( tilt ) )              -     &
+                                   rot_eigen_rad(3) * SIN( tilt )
+       rot_coord_trans(inot,1,3) = rot_eigen_rad(1) * rot_eigen_rad(3)   *     &
+                                   ( 1.0_wp - COS( tilt ) )              +     &
+                                   rot_eigen_rad(2) * SIN( tilt )
+       rot_coord_trans(inot,2,1) = rot_eigen_rad(2) * rot_eigen_rad(1)   *     &
+                                   ( 1.0_wp - COS( tilt ) )              +     &
+                                   rot_eigen_rad(3) * SIN( tilt )
+       rot_coord_trans(inot,2,2) = rot_eigen_rad(2)**2                   *     &
+                                   ( 1.0_wp - COS( tilt ) ) + COS( tilt ) 
+       rot_coord_trans(inot,2,3) = rot_eigen_rad(2) * rot_eigen_rad(3)   *     &
+                                   ( 1.0_wp - COS( tilt ) )              -     &
+                                   rot_eigen_rad(1) * SIN( tilt )
+       rot_coord_trans(inot,3,1) = rot_eigen_rad(3) * rot_eigen_rad(1)   *     &
+                                   ( 1.0_wp - COS( tilt ) )              -     &
+                                   rot_eigen_rad(2) * SIN( tilt )
+       rot_coord_trans(inot,3,2) = rot_eigen_rad(3) * rot_eigen_rad(2)   *     &
+                                   ( 1.0_wp - COS( tilt ) )              +     &
+                                   rot_eigen_rad(1) * SIN( tilt )
+       rot_coord_trans(inot,3,3) = rot_eigen_rad(3)**2                   *     &
+                                   ( 1.0_wp - COS( tilt ) ) + COS( tilt )
+
+!
+!--    Vectors for the Transformation of forces from the rotor's spheric
+!--    coordinate system to the cartesian coordinate system
+       rotx(inot,:) = MATMUL( rot_coord_trans(inot,:,:), rot_eigen_nor )
+       roty(inot,:) = MATMUL( rot_coord_trans(inot,:,:), rot_eigen_rad )
+       rotz(inot,:) = MATMUL( rot_coord_trans(inot,:,:), rot_eigen_azi )
+    
+    END SUBROUTINE wtm_rotate_rotor
+
+
+!------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> Calculation of the forces generated by the wind turbine
+!------------------------------------------------------------------------------!
+    SUBROUTINE wtm_forces
+
+
+       IMPLICIT NONE
+
+       CHARACTER (LEN=2) ::  turbine_id
+
+       INTEGER(iwp) ::  i, j, k          !< loop indices
+       INTEGER(iwp) ::  inot             !< turbine loop index (turbine id)
+       INTEGER(iwp) ::  iialpha, iir     !<
+       INTEGER(iwp) ::  rseg, rseg_int   !<
+       INTEGER(iwp) ::  ring, ring_int   !<
+       INTEGER(iwp) ::  ii, jj, kk       !<
+    
+       REAL(wp)     ::  sin_rot, cos_rot   !<
+       REAL(wp)     ::  sin_yaw, cos_yaw   !<
+       
+       REAL(wp) ::  aa, bb, cc, dd  !< interpolation distances
+       REAL(wp) ::  gg              !< interpolation volume var  
+       
+       REAL(wp) ::  dist_u_3d, dist_v_3d, dist_w_3d  !< smearing distances
+
+       
+!
+!      Variables for pitch control
+       REAL(wp)     ::  torque_max=0.0_wp
+       LOGICAL      ::  pitch_sw=.FALSE.
+
+       INTEGER(iwp), DIMENSION(1) :: lct=0
+       REAL(wp), DIMENSION(1)     :: rad_d=0.0_wp
+
+
+       CALL cpu_log( log_point_s(61), 'wtm_forces', 'start' )
+
+
+       IF ( simulated_time >= time_turbine_on ) THEN
+
+!
+!--       Set forces to zero for each new time step:
+          thrust(:,:,:)         = 0.0_wp
+          torque_y(:,:,:)       = 0.0_wp
+          torque_z(:,:,:)       = 0.0_wp
+          torque_total(:)       = 0.0_wp
+          rot_tend_x(:,:,:)     = 0.0_wp
+          rot_tend_y(:,:,:)     = 0.0_wp
+          rot_tend_z(:,:,:)     = 0.0_wp
+          thrust_rotor(:)       = 0.0_wp
+!
+!--       Loop over number of turbines:
+          DO inot = 1, nturbines
+
+             cos_yaw = COS(phi_yaw(inot))
+             sin_yaw = SIN(phi_yaw(inot))
+!
+!--          Loop over rings of each turbine:
+             DO ring = 1, nrings(inot)
+
+                thrust_seg(:)   = 0.0_wp
+                torque_seg_y(:) = 0.0_wp
+                torque_seg_z(:) = 0.0_wp
+!
+!--             Determine distance between each ring (center) and the hub:
+                cur_r = (ring - 0.5_wp) * delta_r(inot)
+
+!
+!--             Loop over segments of each ring of each turbine:
+                DO rseg = 1, nsegs(ring,inot)
+!
+!--                !-----------------------------------------------------------!
+!--                !-- Determine coordinates of the ring segments            --!
+!--                !-----------------------------------------------------------!
+!
+!--                Determine angle of ring segment towards zero degree angle of
+!--                rotor system (at zero degree rotor direction vectors aligned
+!--                with y-axis):
+                   phi_rotor = rseg * 2.0_wp * pi / nsegs(ring,inot)
+                   cos_rot   = COS( phi_rotor )
+                   sin_rot   = SIN( phi_rotor )
+
+!--                Now the direction vectors can be determined with respect to
+!--                the yaw and tilt angle:
+                   re(1) = cos_rot * sin_yaw
+                   re(2) = cos_rot * cos_yaw    
+                   re(3) = sin_rot
+
+                   rote = MATMUL( rot_coord_trans(inot,:,:), re )
+!
+!--                Coordinates of the single segments (center points):
+                   rbx(ring,rseg) = rcx(inot) + cur_r * rote(1)
+                   rby(ring,rseg) = rcy(inot) + cur_r * rote(2)
+                   rbz(ring,rseg) = rcz(inot) + cur_r * rote(3)
+
+!--                !-----------------------------------------------------------!
+!--                !-- Interpolation of the velocity components from the     --!
+!--                !-- cartesian grid point to the coordinates of each ring  --!
+!--                !-- segment (follows a method used in the particle model) --!
+!--                !-----------------------------------------------------------!
+
+                   u_int(inot,ring,rseg)     = 0.0_wp
+                   u_int_1_l(inot,ring,rseg) = 0.0_wp
+
+                   v_int(inot,ring,rseg)     = 0.0_wp
+                   v_int_1_l(inot,ring,rseg) = 0.0_wp
+
+                   w_int(inot,ring,rseg)     = 0.0_wp
+                   w_int_1_l(inot,ring,rseg) = 0.0_wp
+
+!
+!--                Interpolation of the u-component:
+
+                   ii =   rbx(ring,rseg) * ddx
+                   jj = ( rby(ring,rseg) - 0.5_wp * dy ) * ddy
+                   kk = ( rbz(ring,rseg) - 0.5_wp * dz ) / dz
+!
+!--                Interpolate only if all required information is available on
+!--                the current PE:
+                   IF ( ( ii >= nxl )  .AND.  ( ii <= nxr ) )  THEN
+                      IF ( ( jj >= nys )  .AND.  ( jj <= nyn ) )  THEN
+
+                         aa = ( ( ii + 1          ) * dx - rbx(ring,rseg) ) *  &
+                              ( ( jj + 1 + 0.5_wp ) * dy - rby(ring,rseg) )
+                         bb = ( rbx(ring,rseg) - ii * dx )                  *  &
+                              ( ( jj + 1 + 0.5_wp ) * dy - rby(ring,rseg) )
+                         cc = ( ( ii+1            ) * dx - rbx(ring,rseg) ) *  &
+                              ( rby(ring,rseg) - ( jj + 0.5_wp ) * dy )
+                         dd = ( rbx(ring,rseg) -              ii * dx )     *  &
+                              ( rby(ring,rseg) - ( jj + 0.5_wp ) * dy ) 
+                         gg = dx * dy
+
+                         u_int_l = ( aa * u(kk,jj,ii)     +                    &
+                                     bb * u(kk,jj,ii+1)   +                    &
+                                     cc * u(kk,jj+1,ii)   +                    &
+                                     dd * u(kk,jj+1,ii+1)                      &
+                                   ) / gg
+
+                         u_int_u = ( aa * u(kk+1,jj,ii)     +                  &
+                                     bb * u(kk+1,jj,ii+1)   +                  &
+                                     cc * u(kk+1,jj+1,ii)   +                  &
+                                     dd * u(kk+1,jj+1,ii+1)                    &
+                                   ) / gg
+
+                         u_int_1_l(inot,ring,rseg) = u_int_l          +        &
+                                     ( rbz(ring,rseg) - zu(kk) ) / dz *        &
+                                     ( u_int_u - u_int_l )
+
+                      ELSE 
+                         u_int_1_l(inot,ring,rseg) = 0.0_wp
+                      ENDIF
+                   ELSE
+                      u_int_1_l(inot,ring,rseg) = 0.0_wp
+                   ENDIF
+
+
+!
+!--                Interpolation of the v-component:
+                   ii = ( rbx(ring,rseg) - 0.5_wp * dx ) * ddx
+                   jj =   rby(ring,rseg)                 * ddy
+                   kk = ( rbz(ring,rseg) + 0.5_wp * dz ) / dz 
+!
+!--                Interpolate only if all required information is available on
+!--                the current PE:
+                   IF ( ( ii >= nxl )  .AND.  ( ii <= nxr ) )  THEN
+                      IF ( ( jj >= nys )  .AND.  ( jj <= nyn ) )  THEN
+
+                         aa = ( ( ii + 1 + 0.5_wp ) * dx - rbx(ring,rseg) ) *  &
+                              ( ( jj + 1 )          * dy - rby(ring,rseg) )
+                         bb = ( rbx(ring,rseg)     - ( ii + 0.5_wp ) * dx ) *  &
+                              ( ( jj + 1 ) * dy          - rby(ring,rseg) )
+                         cc = ( ( ii + 1 + 0.5_wp ) * dx - rbx(ring,rseg) ) *  &
+                              ( rby(ring,rseg)           -        jj * dy )
+                         dd = ( rbx(ring,rseg)     - ( ii + 0.5_wp ) * dx ) *  &
+                              ( rby(ring,rseg)           -        jj * dy )
+                         gg = dx * dy
+
+                         v_int_l = ( aa * v(kk,jj,ii)     +                    &
+                                     bb * v(kk,jj,ii+1)   +                    &
+                                     cc * v(kk,jj+1,ii)   +                    &
+                                     dd * v(kk,jj+1,ii+1)                      &
+                                   ) / gg
+
+                         v_int_u = ( aa * v(kk+1,jj,ii)     +                  &
+                                     bb * v(kk+1,jj,ii+1)   +                  &
+                                     cc * v(kk+1,jj+1,ii)   +                  &
+                                     dd * v(kk+1,jj+1,ii+1)                    &
+                                  ) / gg
+
+                         v_int_1_l(inot,ring,rseg) = v_int_l +                 &
+                                     ( rbz(ring,rseg) - zu(kk) ) / dz *        &
+                                     ( v_int_u - v_int_l )
+
+                      ELSE
+                         v_int_1_l(inot,ring,rseg) = 0.0_wp
+                      ENDIF
+                   ELSE
+                      v_int_1_l(inot,ring,rseg) = 0.0_wp
+                   ENDIF
+
+
+!
+!--                Interpolation of the w-component:
+                   ii = ( rbx(ring,rseg) - 0.5_wp * dx ) * ddx
+                   jj = ( rby(ring,rseg) - 0.5_wp * dy ) * ddy
+                   kk =   rbz(ring,rseg)                 / dz
+!
+!--                Interpolate only if all required information is available on
+!--                the current PE:
+                   IF ( ( ii >= nxl )  .AND.  ( ii <= nxr ) )  THEN
+                      IF ( ( jj >= nys )  .AND.  ( jj <= nyn ) )  THEN
+
+                         aa = ( ( ii + 1 + 0.5_wp ) * dx - rbx(ring,rseg) ) *  &
+                              ( ( jj + 1 + 0.5_wp ) * dy - rby(ring,rseg) )
+                         bb = ( rbx(ring,rseg)     - ( ii + 0.5_wp ) * dx ) *  &
+                              ( ( jj + 1 + 0.5_wp ) * dy - rby(ring,rseg) )
+                         cc = ( ( ii + 1 + 0.5_wp ) * dx - rbx(ring,rseg) ) *  &
+                              ( rby(ring,rseg)     - ( jj + 0.5_wp ) * dy )
+                         dd = ( rbx(ring,rseg)     - ( ii + 0.5_wp ) * dx ) *  &
+                              ( rby(ring,rseg)     - ( jj + 0.5_wp ) * dy )
+                         gg = dx * dy
+
+                         w_int_l = ( aa * w(kk,jj,ii)     +                    &
+                                     bb * w(kk,jj,ii+1)   +                    &
+                                     cc * w(kk,jj+1,ii)   +                    &
+                                     dd * w(kk,jj+1,ii+1)                      &
+                                   ) / gg
+
+                         w_int_u = ( aa * w(kk+1,jj,ii)     +                  &
+                                     bb * w(kk+1,jj,ii+1)   +                  &
+                                     cc * w(kk+1,jj+1,ii)   +                  &
+                                     dd * w(kk+1,jj+1,ii+1)                    &
+                                    ) / gg
+
+                         w_int_1_l(inot,ring,rseg) = w_int_l +                 &
+                                     ( rbz(ring,rseg) - zw(kk) ) / dz *        &
+                                     ( w_int_u - w_int_l )
+                      ELSE
+                         w_int_1_l(inot,ring,rseg) = 0.0_wp
+                      ENDIF
+                   ELSE
+                      w_int_1_l(inot,ring,rseg) = 0.0_wp
+                   ENDIF
+
+                ENDDO
+             ENDDO
+
+          ENDDO
+
+!
+!--       Exchange between PEs (information required on each PE):
+#if defined( __parallel )
+          CALL MPI_ALLREDUCE( u_int_1_l, u_int, nturbines * MAXVAL(nrings) *   &
+                              MAXVAL(nsegs), MPI_REAL, MPI_SUM, comm2d, ierr )
+          CALL MPI_ALLREDUCE( v_int_1_l, v_int, nturbines * MAXVAL(nrings) *   &
+                              MAXVAL(nsegs), MPI_REAL, MPI_SUM, comm2d, ierr )
+          CALL MPI_ALLREDUCE( w_int_1_l, w_int, nturbines * MAXVAL(nrings) *   &
+                              MAXVAL(nsegs), MPI_REAL, MPI_SUM, comm2d, ierr )
+#else
+          u_int = u_int_1_l
+          v_int = v_int_1_l
+          w_int = w_int_1_l
+#endif
+
+
+!
+!--       Loop over number of turbines:
+
+          DO inot = 1, nturbines
+pit_loop: DO
+
+             IF ( pitch_sw )  THEN
+                torque_total(inot) = 0.0_wp
+                thrust_rotor(inot) = 0.0_wp
+                pitch_add(inot)    = pitch_add(inot) + 0.25_wp
+!                 IF ( myid == 0 ) PRINT*, 'Pitch', inot, pitch_add(inot)
+             ELSE
+                cos_yaw = COS(phi_yaw(inot))
+                sin_yaw = SIN(phi_yaw(inot))
+                IF ( pitch_control )  THEN
+                   pitch_add(inot) = MAX(pitch_add_old(inot) - pitch_rate *    &
+                                         dt_3d , 0.0_wp )
+                ENDIF
+             ENDIF
+
+!
+!--          Loop over rings of each turbine:
+             DO ring = 1, nrings(inot)
+!
+!--             Determine distance between each ring (center) and the hub:
+                cur_r = (ring - 0.5_wp) * delta_r(inot)
+!
+!--             Loop over segments of each ring of each turbine:
+                DO rseg = 1, nsegs(ring,inot)
+!
+!--                Determine angle of ring segment towards zero degree angle of
+!--                rotor system (at zero degree rotor direction vectors aligned
+!--                with y-axis):
+                   phi_rotor = rseg * 2.0_wp * pi / nsegs(ring,inot)
+                   cos_rot   = COS(phi_rotor)
+                   sin_rot   = SIN(phi_rotor)
+!
+!--                Now the direction vectors can be determined with respect to
+!--                the yaw and tilt angle:
+                   re(1) = cos_rot * sin_yaw
+                   re(2) = cos_rot * cos_yaw
+                   re(3) = sin_rot
+
+!                  The current unit vector in azimuthal direction:                         
+                   rea(1) = - sin_rot * sin_yaw
+                   rea(2) = - sin_rot * cos_yaw
+                   rea(3) =   cos_rot
+
+!
+!--                To respect the yawing angle for the calculations of
+!--                velocities and forces the unit vectors perpendicular to the
+!--                rotor area in direction of the positive yaw angle are defined:
+                   ren(1) =   cos_yaw
+                   ren(2) = - sin_yaw
+                   ren(3) = 0.0_wp
+!
+!--                Multiplication with the coordinate transformation matrix
+!--                gives the final unit vector with consideration of the rotor
+!--                tilt:
+                   rote = MATMUL( rot_coord_trans(inot,:,:), re )
+                   rota = MATMUL( rot_coord_trans(inot,:,:), rea )
+                   rotn = MATMUL( rot_coord_trans(inot,:,:), ren )
+!
+!--                Coordinates of the single segments (center points):
+                   rbx(ring,rseg) = rcx(inot) + cur_r * rote(1)
+
+                   rby(ring,rseg) = rcy(inot) + cur_r * rote(2)
+
+                   rbz(ring,rseg) = rcz(inot) + cur_r * rote(3)
+
+!
+!--                !-----------------------------------------------------------!
+!--                !-- Calculation of various angles and relative velocities --!
+!--                !-----------------------------------------------------------!
+!
+!--                In the following the 3D-velocity field is projected its
+!--                components perpedicular and parallel to the rotor area
+!--                The calculation of forces will be done in the rotor-
+!--                coordinates y' and z.
+!--                The yaw angle will be reintroduced when the force is applied
+!--                on the hydrodynamic equations
+!
+!--                Projection of the xy-velocities relative to the rotor area
+!
+!--                Velocity perpendicular to the rotor area:
+                   u_rot = u_int(inot,ring,rseg)*rotn(1) +                     &
+                   v_int(inot,ring,rseg)*rotn(2) +                             &
+                   w_int(inot,ring,rseg)*rotn(3)
+!
+!--                Projection of the 3D-velocity vector in the azimuthal
+!--                direction:
+                   vtheta(rseg) = rota(1) * u_int(inot,ring,rseg) +            & 
+                                  rota(2) * v_int(inot,ring,rseg) +            &
+                                  rota(3) * w_int(inot,ring,rseg)
+!
+!--                Determination of the angle phi_rel between the rotor plane
+!--                and the direction of the flow relative to the rotor:
+
+                   phi_rel(rseg) = ATAN( u_rot /                               &
+                                         ( omega_rot(inot) * cur_r -           &
+                                           vtheta(rseg) ) )
+
+!
+!--                Interpolation of the local pitch angle from tabulated values
+!--                to the current radial position:
+
+                   lct=minloc(ABS(cur_r-lrd))
+                   rad_d=cur_r-lrd(lct)
+                   
+                   IF (cur_r == 0.0_wp) THEN
+                      alpha_attack(rseg) = 0.0_wp
+                   ELSE IF (cur_r >= lrd(size(ard))) THEN
+                      alpha_attack(rseg) = ( ard(size(ard)) +                  &
+                                             ard(size(ard)-1) ) / 2.0_wp
+                   ELSE 
+                      alpha_attack(rseg) = ( ard(lct(1)) *  &
+                                             ( ( lrd(lct(1)+1) - cur_r ) /     &
+                                               ( lrd(lct(1)+1) - lrd(lct(1)) ) &
+                                             ) ) + ( ard(lct(1)+1) *           &
+                                             ( ( cur_r - lrd(lct(1)) ) /       &
+                                               ( lrd(lct(1)+1) - lrd(lct(1)) ) ) )
+                   ENDIF
+
+!
+!--                In Fortran radian instead of degree is used as unit for all
+!--                angles. Therefore, a transformation from angles given in
+!--                degree to angles given in radian is necessary here:
+                   alpha_attack(rseg) = alpha_attack(rseg) *                   &
+                                        ( (2.0_wp*pi) / 360.0_wp )
+!
+!--                Substraction of the local pitch angle to obtain the local
+!--                angle of attack:
+                   alpha_attack(rseg) = phi_rel(rseg) - alpha_attack(rseg)
+!
+!--                Preliminary transformation back from angles given in radian
+!--                to angles given in degree:
+                   alpha_attack(rseg) = alpha_attack(rseg) *                   &
+                                        ( 360.0_wp / (2.0_wp*pi) )
+!
+!--                Correct with collective pitch angle:
+                   alpha_attack = alpha_attack + pitch_add(inot)
+
+!
+!--                Determination of the magnitude of the flow velocity relative
+!--                to the rotor:
+                   vrel(rseg) = SQRT( u_rot**2 +                               &
+                                      ( omega_rot(inot) * cur_r -              &
+                                        vtheta(rseg) )**2 )
+
+!
+!--                !-----------------------------------------------------------!
+!--                !-- Interpolation of chord as well as lift and drag       --!
+!--                !-- coefficients from tabulated values                    --!
+!--                !-----------------------------------------------------------!
+
+!
+!--                Interpolation of the chord_length from tabulated values to
+!--                the current radial position:
+
+                   IF (cur_r == 0.0_wp) THEN
+                      chord(rseg) = 0.0_wp
+                   ELSE IF (cur_r >= lrd(size(crd))) THEN
+                      chord(rseg) = (crd(size(crd)) + ard(size(crd)-1)) / 2.0_wp
+                   ELSE 
+                      chord(rseg) = ( crd(lct(1)) *                            &
+                            ( ( lrd(lct(1)+1) - cur_r ) /                      &
+                              ( lrd(lct(1)+1) - lrd(lct(1)) ) ) ) +            &
+                            ( crd(lct(1)+1) *                                  &
+                            ( ( cur_r-lrd(lct(1)) ) /                          &
+                              ( lrd(lct(1)+1) - lrd(lct(1)) ) ) )
+                   ENDIF
+
+!
+!--                Determine index of current angle of attack, needed for
+!--                finding the appropriate interpolated values of the lift and
+!--                drag coefficients (-180.0 degrees = 0, +180.0 degrees = 36000,
+!--                so one index every 0.01 degrees):
+                   iialpha = CEILING( ( alpha_attack(rseg) + 180.0_wp )        &
+                                      * ( 1.0_wp / accu_cl_cd_tab ) )
+!
+!--                Determine index of current radial position, needed for
+!--                finding the appropriate interpolated values of the lift and
+!--                drag coefficients (one index every 0.1 m):
+                   iir = CEILING( cur_r * 10.0_wp )
+!
+!--                Read in interpolated values of the lift and drag coefficients
+!--                for the current radial position and angle of attack:
+                   turb_cl(rseg) = turb_cl_tab(iialpha,iir)
+                   turb_cd(rseg) = turb_cd_tab(iialpha,iir)
+
+!
+!--                Final transformation back from angles given in degree to
+!--                angles given in radian:
+                   alpha_attack(rseg) = alpha_attack(rseg) *                   &
+                                        ( (2.0_wp*pi) / 360.0_wp )
+
+!
+!--                !-----------------------------------------------------!
+!--                !-- Calculation of the forces                       --!
+!--                !-----------------------------------------------------!
+
+!
+!--                Calculate the pre_factor for the thrust and torque forces:
+
+                   pre_factor = 0.5_wp * (vrel(rseg)**2) * 3.0_wp *  &
+                                chord(rseg) * delta_r(inot) / nsegs(ring,inot)
+
+!
+!--                Calculate the thrust force (x-component of the total force)
+!--                for each ring segment:
+                   thrust_seg(rseg) = pre_factor *                             &
+                                      ( turb_cl(rseg) * COS(phi_rel(rseg)) +   &
+                                        turb_cd(rseg) * SIN(phi_rel(rseg)) )
+
+!
+!--                Determination of the second of the additional forces acting
+!--                on the flow in the azimuthal direction: force vector as basis
+!--                for torque (torque itself would be the vector product of the
+!--                radius vector and the force vector):
+                   torque_seg = pre_factor *                                   &
+                                ( turb_cl(rseg) * SIN(phi_rel(rseg)) -         &
+                                  turb_cd(rseg) * COS(phi_rel(rseg)) )
+!
+!--                Decomposition of the force vector into two parts:
+!--                One acting along the y-direction and one acting along the
+!--                z-direction of the rotor coordinate system:
+
+                   torque_seg_y(rseg) = -torque_seg * sin_rot
+                   torque_seg_z(rseg) =  torque_seg * cos_rot
+
+!
+!--                Add the segment thrust to the thrust of the whole rotor
+                   thrust_rotor(inot) = thrust_rotor(inot) +                   &
+                                        thrust_seg(rseg)                   
+                   
+
+                   torque_total(inot) = torque_total(inot) + (torque_seg * cur_r)
+
+                ENDDO   !-- end of loop over ring segments
+
+!
+!--             Restore the forces into arrays containing all the segments of
+!--             each ring:
+                thrust_ring(ring,:)   = thrust_seg(:)
+                torque_ring_y(ring,:) = torque_seg_y(:)
+                torque_ring_z(ring,:) = torque_seg_z(:)
+
+
+             ENDDO   !-- end of loop over rings
+
+
+             CALL cpu_log( log_point_s(62), 'wtm_controller', 'start' )
+
+             
+             IF ( speed_control )  THEN
+!
+!--             Calculation of the current generator speed for rotor speed control
+             
+!                                     
+!--             The acceleration of the rotor speed is calculated from 
+!--             the force balance of the accelerating torque
+!--             and the torque of the rotating rotor and generator
+                om_rate = ( torque_total(inot) * air_dens * gear_eff -         &
+                            gear_ratio * torque_gen_old(inot) ) /              &
+                          ( inertia_rot +                                      & 
+                            gear_ratio * gear_ratio * inertia_gen ) * dt_3d
+
+!
+!--             The generator speed is given by the product of gear gear_ratio
+!--             and rotor speed
+                omega_gen(inot) = gear_ratio * ( omega_rot(inot) + om_rate )     
+             
+             ENDIF
+             
+             IF ( pitch_control )  THEN
+
+!
+!--             If the current generator speed is above rated, the pitch is not
+!--             saturated and the change from the last time step is within the 
+!--             maximum pitch rate, then the pitch loop is repeated with a pitch
+!--             gain
+                IF ( (  omega_gen(inot)  > rated_genspeed   )  .AND.           &
+                     ( pitch_add(inot) < 25.0_wp ) .AND.                       &
+                     ( pitch_add(inot) < pitch_add_old(inot) +                 & 
+                       pitch_rate * dt_3d  ) ) THEN 
+                   pitch_sw = .TRUE.
+!
+!--                Go back to beginning of pit_loop                   
+                   CYCLE pit_loop
+                ENDIF
+                
+!
+!--             The current pitch is saved for the next time step
+                pitch_add_old(inot) = pitch_add(inot)
+                pitch_sw = .FALSE.
+             ENDIF
+             EXIT pit_loop             
+          ENDDO pit_loop ! Recursive pitch control loop
+
+
+!
+!--          Call the rotor speed controller
+             
+             IF ( speed_control )  THEN
+!
+!--             Find processor at i_hub, j_hub             
+                IF ( ( nxl <= i_hub(inot) )  .AND.  ( nxr >= i_hub(inot) ) )   &
+                   THEN
+                   IF ( ( nys <= j_hub(inot) )  .AND.  ( nyn >= j_hub(inot) ) )&
+                      THEN
+                      CALL wtm_speed_control( inot )
+                   ENDIF
+                ENDIF
+                               
+             ENDIF
+
+
+             CALL cpu_log( log_point_s(62), 'wtm_controller', 'stop' )
+
+             CALL cpu_log( log_point_s(63), 'wtm_smearing', 'start' )
+
+
+!--          !-----------------------------------------------------------------!
+!--          !--                  Regularization kernel                      --!
+!--          !-- Smearing of the forces and interpolation to cartesian grid  --!
+!--          !-----------------------------------------------------------------!
+!
+!--          The aerodynamic blade forces need to be distributed smoothly on
+!--          several mesh points in order to avoid singular behaviour
+!
+!--          Summation over sum of weighted forces. The weighting factor
+!--          (calculated in user_init) includes information on the distance
+!--          between the center of the grid cell and the rotor segment under
+!--          consideration
+!
+!--          To save computing time, apply smearing only for the relevant part
+!--          of the model domain:
+!
+!--
+!--          Calculation of the boundaries:
+             i_smear(inot) = CEILING( ( rr(inot) * ABS( roty(inot,1) ) +       &
+                                        eps_min ) / dx )
+             j_smear(inot) = CEILING( ( rr(inot) * ABS( roty(inot,2) ) +       &
+                                        eps_min ) / dy )
+
+             DO i = MAX( nxl, i_hub(inot) - i_smear(inot) ),                   &
+                    MIN( nxr, i_hub(inot) + i_smear(inot) )
+                DO j = MAX( nys, j_hub(inot) - j_smear(inot) ),                &
+                        MIN( nyn, j_hub(inot) + j_smear(inot) )
+                   DO k = MAX( nzb_u_inner(j,i)+1, k_hub(inot) - k_smear(inot) ), &
+                                k_hub(inot) + k_smear(inot)
+                      DO ring = 1, nrings(inot)
+                         DO rseg = 1, nsegs(ring,inot)
+!
+!--                         Determine the square of the distance between the
+!--                         current grid point and each rotor area segment:
+                            dist_u_3d = ( i * dx               - rbx(ring,rseg) )**2 + &
+                                        ( j * dy + 0.5_wp * dy - rby(ring,rseg) )**2 + &
+                                        ( k * dz - 0.5_wp * dz - rbz(ring,rseg) )**2
+                            dist_v_3d = ( i * dx + 0.5_wp * dx - rbx(ring,rseg) )**2 + &
+                                        ( j * dy               - rby(ring,rseg) )**2 + &
+                                        ( k * dz - 0.5_wp * dz - rbz(ring,rseg) )**2
+                            dist_w_3d = ( i * dx + 0.5_wp * dx - rbx(ring,rseg) )**2 + &
+                                        ( j * dy + 0.5_wp * dy - rby(ring,rseg) )**2 + &
+                                        ( k * dz               - rbz(ring,rseg) )**2
+
+!
+!--                         3D-smearing of the forces with a polynomial function
+!--                         (much faster than the old Gaussian function), using
+!--                         some parameters that have been calculated in user_init.
+!--                         The function is only similar to Gaussian function for
+!--                         squared distances <= eps_min2:
+                            IF ( dist_u_3d <= eps_min2 ) THEN
+                            thrust(k,j,i) = thrust(k,j,i) +                    &
+                                            thrust_ring(ring,rseg) *           &
+                                            ( ( pol_a * dist_u_3d - pol_b ) *  & 
+                                             dist_u_3d + 1.0_wp ) * eps_factor
+                            ENDIF
+                            IF ( dist_v_3d <= eps_min2 ) THEN
+                            torque_y(k,j,i) = torque_y(k,j,i) +                &
+                                              torque_ring_y(ring,rseg) *       &
+                                              ( ( pol_a * dist_v_3d - pol_b ) *&
+                                               dist_v_3d + 1.0_wp ) * eps_factor
+                            ENDIF
+                            IF ( dist_w_3d <= eps_min2 ) THEN
+                            torque_z(k,j,i) = torque_z(k,j,i) +                &
+                                              torque_ring_z(ring,rseg) *       &
+                                              ( ( pol_a * dist_w_3d - pol_b ) *&
+                                               dist_w_3d + 1.0_wp ) * eps_factor
+                            ENDIF
+
+                         ENDDO  ! End of loop over rseg
+                      ENDDO     ! End of loop over ring
+              
+!
+!--                   Rotation of force components:
+                      rot_tend_x(k,j,i) = rot_tend_x(k,j,i) +                  &
+                                      thrust(k,j,i)*rotx(inot,1) +             &
+                                      torque_y(k,j,i)*roty(inot,1) +           &
+                                      torque_z(k,j,i)*rotz(inot,1)
+                                
+                      rot_tend_y(k,j,i) = rot_tend_y(k,j,i) +                  &
+                                      thrust(k,j,i)*rotx(inot,2) +             &
+                                      torque_y(k,j,i)*roty(inot,2) +           &
+                                      torque_z(k,j,i)*rotz(inot,2)
+                                
+                      rot_tend_z(k,j,i) = rot_tend_z(k,j,i) +                  &
+                                      thrust(k,j,i)*rotx(inot,3) +             &
+                                      torque_y(k,j,i)*roty(inot,3) +           &
+                                      torque_z(k,j,i)*rotz(inot,3)                               
+
+                   ENDDO        ! End of loop over k
+                ENDDO           ! End of loop over j
+             ENDDO              ! End of loop over i
+
+             CALL cpu_log( log_point_s(63), 'wtm_smearing', 'stop' )          
+                   
+          ENDDO                  !-- end of loop over turbines
+
+                
+          IF ( yaw_control )  THEN
+!
+!--          Allocate arrays for yaw control at first call
+!--          Can't be allocated before dt_3d is set
+             IF ( start_up )  THEN
+                WDLON = NINT( 30.0_wp / dt_3d )  ! 30s running mean array
+                ALLOCATE( wd30(1:nturbines,1:WDLON) )
+                wd30 = 999.0_wp                  ! Set to dummy value
+                ALLOCATE( wd30_l(1:WDLON) )
+                
+                WDSHO = NINT( 2.0_wp / dt_3d )   ! 2s running mean array
+                ALLOCATE( wd2(1:nturbines,1:WDSHO) )
+                wd2 = 999.0_wp                   ! Set to dummy value
+                ALLOCATE( wd2_l(1:WDSHO) )
+                start_up = .FALSE.
+             ENDIF          
+
+!
+!--          Calculate the inflow wind speed 
+!--
+!--          Loop over number of turbines:
+             DO inot = 1, nturbines
+!
+!--             Find processor at i_hub, j_hub             
+                IF ( ( nxl <= i_hub(inot) )  .AND.  ( nxr >= i_hub(inot) ) )   &
+                   THEN
+                   IF ( ( nys <= j_hub(inot) )  .AND.  ( nyn >= j_hub(inot) ) )&
+                      THEN
+
+                      u_inflow_l(inot) = u(k_hub(inot),j_hub(inot),i_hub(inot))
+
+                      wdir_l(inot) = -1.0_wp * ATAN2(                          &
+                         0.5_wp * ( v(k_hub(inot),j_hub(inot),i_hub(inot)+1) + &
+                                    v(k_hub(inot),j_hub(inot),i_hub(inot)) ) , &
+                         0.5_wp * ( u(k_hub(inot),j_hub(inot)+1,i_hub(inot)) + &
+                                    u(k_hub(inot),j_hub(inot),i_hub(inot)) ) )
+
+                      CALL wtm_yawcontrol( inot )
+
+                      phi_yaw_l(inot) = phi_yaw(inot)
+
+                   ENDIF
+                ENDIF
+                   
+             ENDDO                                 !-- end of loop over turbines
+
+!
+!--          Transfer of information to the other cpus            
+             CALL MPI_ALLREDUCE( u_inflow_l, u_inflow, nturbines, MPI_REAL,    &
+                                 MPI_SUM, comm2d, ierr )
+             CALL MPI_ALLREDUCE( wdir_l, wdir, nturbines, MPI_REAL, MPI_SUM,   &
+                                 comm2d, ierr )
+             CALL MPI_ALLREDUCE( phi_yaw_l, phi_yaw, nturbines, MPI_REAL,      &
+                                 MPI_SUM, comm2d, ierr )
+             
+             DO inot = 1, nturbines
+!             
+!--             Update rotor orientation                
+                CALL wtm_rotate_rotor( inot )
+
+             ENDDO ! End of loop over turbines
+                           
+          END IF 
+          
+          IF ( speed_control )  THEN
+!
+!--          Transfer of information to the other cpus
+!              CALL MPI_ALLREDUCE( omega_gen, omega_gen_old, nturbines,        &
+!                                  MPI_REAL,MPI_SUM, comm2d, ierr )
+             CALL MPI_ALLREDUCE( torque_gen, torque_gen_old, nturbines,        &
+                                 MPI_REAL, MPI_SUM, comm2d, ierr )
+             CALL MPI_ALLREDUCE( omega_rot_l, omega_rot, nturbines,            &
+                                 MPI_REAL, MPI_SUM, comm2d, ierr )
+             CALL MPI_ALLREDUCE( omega_gen_f, omega_gen_f_old, nturbines,      &
+                                 MPI_REAL, MPI_SUM, comm2d, ierr )
+            
+          ENDIF
+
+          DO inot = 1, nturbines
+
+             IF ( myid == 0 ) THEN
+                IF ( openfile_turb_mod(400+inot)%opened )  THEN
+                   WRITE ( 400+inot, 106 ) simulated_time, omega_rot(inot),    &
+                             omega_gen(inot), torque_gen_old(inot),            &
+                             torque_total(inot), pitch_add(inot),              &
+                             torque_gen_old(inot)*omega_gen(inot)*gen_eff,     &
+                             torque_total(inot)*omega_rot(inot)*air_dens,      &
+                             thrust_rotor(inot),                               & 
+                             wdir(inot)*180.0_wp/pi,                           &
+                             (phi_yaw(inot))*180.0_wp/pi                   
+                             
+                ELSE
+
+                   WRITE ( turbine_id,'(I2.2)')  inot
+                   OPEN ( 400+inot, FILE=( 'TURBINE_PARAMETERS'//turbine_id ), &
+                                            FORM='FORMATTED' )
+                   WRITE ( 400+inot, 105 ) inot
+                   WRITE ( 400+inot, 106 ) simulated_time, omega_rot(inot),    &
+                             omega_gen(inot), torque_gen_old(inot),            &
+                             torque_total(inot), pitch_add(inot),              &
+                             torque_gen_old(inot)*omega_gen(inot)*gen_eff,     &
+                             torque_total(inot)*omega_rot(inot)*air_dens,      &
+                             thrust_rotor(inot),                               & 
+                             wdir(inot)*180.0_wp/pi,                           &                   
+                             (phi_yaw(inot))*180.0_wp/pi
+                ENDIF
+             ENDIF
+
+!--          Set open flag
+             openfile_turb_mod(400+inot)%opened = .TRUE.
+          ENDDO                                    !-- end of loop over turbines
+
+       ENDIF
+
+       CALL cpu_log( log_point_s(61), 'wtm_forces', 'stop' )
+       
+!
+!--    Formats
+       105 FORMAT ('Turbine control data for turbine ',I2,1X,':'/ &
+              &'----------------------------------------'/ &
+              &'   Time   RSpeed  GSpeed  ', &
+               'GenTorque  AeroTorque  Pitch  Power(Gen)  Power(Rot)  ',       &
+               'RotThrust  WDirection  YawOrient')
+
+       106 FORMAT (F9.3,2X,F7.3,2X,F7.2,2X,F9.1,3X,F9.1,1X,F6.2,2X,F10.1,2X,   &
+                   F10.1,1X,F9.1,2X,F7.2,1X,F7.2)
+
+
+    END SUBROUTINE wtm_forces
+
+    
+!------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> Yaw controller for the wind turbine model
+!------------------------------------------------------------------------------!
+    SUBROUTINE wtm_yawcontrol( inot )
+    
+       USE constants
+       USE kinds
+                
+       IMPLICIT NONE
+      
+       INTEGER(iwp)             :: inot
+       INTEGER(iwp)             :: i_wd_30
+       REAL(wp)                 :: missal
+
+       i_wd_30 = 0_iwp
+
+!  
+!--    The yaw controller computes a 30s running mean of the wind direction.
+!--    If the difference between turbine alignment and wind direction exceeds
+!--    5Â°, the turbine is yawed. The mechanism stops as soon as the 2s-running
+!--    mean of the missalignment is smaller than 0.5Â°.
+!--    Attention: If the timestep during the simulation changes significantly
+!--    the lengths of the running means change and it does not correspond to
+!--    30s/2s anymore.
+!--    ! Needs to be modified for these situations !
+!--    For wind from the east, the averaging of the wind direction could cause
+!--    problems and the yaw controller is probably flawed. -> Routine for
+!--    averaging needs to be improved!
+!
+!--    Check if turbine is not yawing
+       IF ( .NOT. doyaw(inot) )  THEN
+!
+!--       Write current wind direction into array
+          wd30_l    = wd30(inot,:)
+          wd30_l    = CSHIFT( wd30_l, SHIFT=-1 )
+          wd30_l(1) = wdir(inot)
+!
+!--       Check if array is full ( no more dummies )
+          IF ( .NOT. ANY( wd30_l == 999.) ) THEN 
+
+             missal = SUM( wd30_l ) / SIZE( wd30_l ) - phi_yaw(inot)
+!
+!--          Check if turbine is missaligned by more than max_miss
+             IF ( ABS( missal ) > max_miss )  THEN
+!
+!--             Check in which direction to yaw          
+                yawdir(inot) = SIGN( 1.0_wp, missal )
+!
+!--             Start yawing of turbine
+                phi_yaw(inot) = phi_yaw(inot) + yawdir(inot) * yaw_speed * dt_3d
+                doyaw(inot) = .TRUE.
+                wd30_l = 999.  ! fill with dummies again
+             ENDIF
+          ENDIF
+         
+          wd30(inot,:) = wd30_l
+
+!      
+!--    If turbine is already yawing:
+!--    Initialize 2 s running mean and yaw until the missalignment is smaller
+!--    than min_miss
+
+       ELSE
+!
+!--       Initialize 2 s running mean
+          wd2_l = wd2(inot,:)
+          wd2_l = CSHIFT( wd2_l, SHIFT = -1 )
+          wd2_l(1) = wdir(inot)
+!      
+!--       Check if array is full ( no more dummies )
+          IF ( .NOT. ANY( wd2_l == 999.0_wp ) ) THEN
+!
+!--          Calculate missalignment of turbine        
+             missal = SUM( wd2_l - phi_yaw(inot) ) / SIZE( wd2_l )
+!
+!--          Check if missalignment is still larger than 0.5 degree and if the
+!--          yaw direction is still right
+             IF ( ( ABS( missal ) > min_miss )  .AND.                          &
+                  ( yawdir(inot) == SIGN( 1.0_wp, missal ) ) )  THEN
+!
+!--             Continue yawing        
+                phi_yaw(inot) = phi_yaw(inot) + yawdir(inot) * yaw_speed * dt_3d
+             ELSE
+!
+!--             Stop yawing        
+                doyaw(inot) = .FALSE.
+                wd2_l = 999.0_wp ! fill with dummies again
+             ENDIF
+          ELSE
+!
+!--          Continue yawing
+             phi_yaw(inot) = phi_yaw(inot) + yawdir(inot) * yaw_speed * dt_3d
+          ENDIF
+      
+          wd2(inot,:) = wd2_l
+            
+       ENDIF
+     
+    END SUBROUTINE wtm_yawcontrol 
+
+
+!------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> Initialization of the speed control
+!------------------------------------------------------------------------------!
+    SUBROUTINE wtm_init_speed_control
+
+
+       IMPLICIT NONE
+
+!
+!--    If speed control is set, remaining variables and control_parameters for 
+!--    the control algorithm are calculated
+!
+!--    Calculate slope constant for region 15
+       slope15   = ( slope2 * min_reg2 * min_reg2 ) / ( min_reg2 - min_reg15 )
+!
+!--    Calculate upper limit of slipage region
+       vs_sysp   = rated_genspeed / 1.1_wp
+!
+!--    Calculate slope of slipage region
+       slope25   = ( rated_power / rated_genspeed ) /                          &
+                   ( rated_genspeed - vs_sysp )
+!
+!--    Calculate lower limit of slipage region
+       min_reg25 = ( slope25 - SQRT( slope25 * ( slope25 - 4.0_wp *            &
+                                                 slope2 * vs_sysp ) ) ) /      &
+                   ( 2.0_wp * slope2 )
+!
+!--    Frequency for the simple low pass filter
+       Fcorner   = 0.25_wp
+! 
+!--    At the first timestep the torque is set to its maximum to prevent
+!--    an overspeeding of the rotor
+       torque_gen_old(:) = max_torque_gen  
+     
+    END SUBROUTINE wtm_init_speed_control
+
+
+!------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> Simple controller for the regulation of the rotor speed
+!------------------------------------------------------------------------------!
+    SUBROUTINE wtm_speed_control( inot )
+
+
+       IMPLICIT NONE
+
+       INTEGER(iwp)             :: inot
+       
+         
+
+!
+!--    The controller is based on the fortran script from Jonkman 
+!--    et al. 2009 "Definition of a 5 MW Reference Wind Turbine for
+!--    offshore system developement"
+
+!
+!--    The generator speed is filtered by a low pass filter 
+!--    for the control of the generator torque       
+       lp_coeff = EXP( -2.0_wp * 3.14_wp * dt_3d * Fcorner )
+       omega_gen_f(inot) = ( 1.0_wp - lp_coeff ) * omega_gen(inot) + lp_coeff *&
+                           omega_gen_f_old(inot)
+
+       IF ( omega_gen_f(inot) <= min_reg15 )  THEN
+!                        
+!--       Region 1: Generator torque is set to zero to accelerate the rotor:
+          torque_gen(inot) = 0
+       
+       ELSEIF ( omega_gen_f(inot) <= min_reg2 )  THEN
+!                        
+!--       Region 1.5: Generator torque is increasing linearly with rotor speed:
+          torque_gen(inot) = slope15 * ( omega_gen_f(inot) - min_reg15 )
+                         
+       ELSEIF ( omega_gen_f(inot) <= min_reg25 )  THEN
+!
+!--       Region 2: Generator torque is increased by the square of the generator
+!--                 speed to keep the TSR optimal:
+          torque_gen(inot) = slope2 * omega_gen_f(inot) * omega_gen_f(inot)
+       
+       ELSEIF ( omega_gen_f(inot) < rated_genspeed )  THEN
+!                        
+!--       Region 2.5: Slipage region between 2 and 3:
+          torque_gen(inot) = slope25 * ( omega_gen_f(inot) - vs_sysp )
+       
+       ELSE
+!                        
+!--       Region 3: Generator torque is antiproportional to the rotor speed to
+!--                 keep the power constant:
+          torque_gen(inot) = rated_power / omega_gen_f(inot)
+       
+       ENDIF
+!                        
+!--    Calculate torque rate and confine with a max
+       trq_rate = ( torque_gen(inot) - torque_gen_old(inot) ) / dt_3d
+       trq_rate = MIN( MAX( trq_rate, -1.0_wp * max_trq_rate ), max_trq_rate )
+!                        
+!--    Calculate new gen torque and confine with max torque                         
+       torque_gen(inot) = torque_gen_old(inot) + trq_rate * dt_3d
+       torque_gen(inot) = MIN( torque_gen(inot), max_torque_gen )                                             
+!
+!--    Overwrite values for next timestep                        
+       omega_rot_l(inot) = omega_gen(inot) / gear_ratio
+
+    
+    END SUBROUTINE wtm_speed_control    
+
+
+!------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> Application of the additional forces generated by the wind turbine on the 
+!> flow components (tendency terms)
+!> Call for all grid points
+!------------------------------------------------------------------------------!
+    SUBROUTINE wtm_tendencies( component )
+
+    
+       IMPLICIT NONE
+
+       INTEGER(iwp) ::  component   !< prognostic variable (u,v,w)
+       INTEGER(iwp) ::  i           !< running index
+       INTEGER(iwp) ::  j           !< running index
+       INTEGER(iwp) ::  k           !< running index
+
+
+       SELECT CASE ( component )
+
+       CASE ( 1 )
+!
+!--       Apply the x-component of the force to the u-component of the flow:
+          IF ( simulated_time >= time_turbine_on )  THEN
+             DO  i = nxlg, nxrg
+                DO  j = nysg, nyng
+                   DO  k = nzb_u_inner(j,i)+1, k_hub(1) + k_smear(1)
+!
+!--                   Calculate the thrust generated by the nacelle and the tower
+                      tend_nac_x = 0.5_wp * nac_cd_surf(k,j,i) *               &
+                                         SIGN( u(k,j,i)**2 , u(k,j,i) )     
+                      tend_tow_x   = 0.5_wp * tow_cd_surf(k,j,i) *             &
+                                         SIGN( u(k,j,i)**2 , u(k,j,i) ) 
+                                                   
+                      tend(k,j,i) = tend(k,j,i) - rot_tend_x(k,j,i)            &
+                                  - tend_nac_x - tend_tow_x
+                   ENDDO
+                ENDDO
+             ENDDO
+          ENDIF
+
+       CASE ( 2 )
+!
+!--       Apply the y-component of the force to the v-component of the flow:
+          IF ( simulated_time >= time_turbine_on )  THEN
+             DO  i = nxlg, nxrg
+                DO  j = nysg, nyng
+                   DO  k = nzb_v_inner(j,i)+1, k_hub(1) + k_smear(1)
+                      tend_nac_y = 0.5_wp * nac_cd_surf(k,j,i) *               &
+                                         SIGN( v(k,j,i)**2 , v(k,j,i) )     
+                      tend_tow_y   = 0.5_wp * tow_cd_surf(k,j,i) *             &
+                                         SIGN( v(k,j,i)**2 , v(k,j,i) )                      
+                      tend(k,j,i) = tend(k,j,i) - rot_tend_y(k,j,i)            &
+                                  - tend_nac_y - tend_tow_y
+                   ENDDO
+                ENDDO
+             ENDDO
+          ENDIF
+
+       CASE ( 3 )
+!
+!--       Apply the z-component of the force to the w-component of the flow:
+          IF ( simulated_time >= time_turbine_on )  THEN
+             DO  i = nxlg, nxrg
+                DO  j = nysg, nyng
+                   DO  k = nzb_w_inner(j,i)+1,  k_hub(1) + k_smear(1)
+                      tend(k,j,i) = tend(k,j,i) - rot_tend_z(k,j,i)
+                   ENDDO
+                ENDDO
+             ENDDO
+          ENDIF
+
+
+       CASE DEFAULT
+
+          WRITE( message_string, * ) 'unknown prognostic variable: ', component
+          CALL message( 'wtm_tendencies', 'PA04??', 1, 2, 0, 6, 0 ) 
+
+       END SELECT
+
+
+    END SUBROUTINE wtm_tendencies
+
+
+!------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> Application of the additional forces generated by the wind turbine on the 
+!> flow components (tendency terms)
+!> Call for grid point i,j
+!------------------------------------------------------------------------------!
+    SUBROUTINE wtm_tendencies_ij( i, j, component )
+
+
+       IMPLICIT NONE
+
+       INTEGER(iwp) ::  component   !< prognostic variable (u,v,w)
+       INTEGER(iwp) ::  i           !< running index
+       INTEGER(iwp) ::  j           !< running index
+       INTEGER(iwp) ::  k           !< running index
+
+       SELECT CASE ( component )
+
+       CASE ( 1 )
+!
+!--       Apply the x-component of the force to the u-component of the flow:
+          IF ( simulated_time >= time_turbine_on )  THEN
+
+             DO  k = nzb_u_inner(j,i)+1,  k_hub(1) + k_smear(1)
+!
+!--             Calculate the thrust generated by the nacelle and the tower 
+                tend_nac_x = 0.5_wp * nac_cd_surf(k,j,i) *                     &
+                                   SIGN( u(k,j,i)**2 , u(k,j,i) )     
+                tend_tow_x   = 0.5_wp * tow_cd_surf(k,j,i) *                   &
+                                   SIGN( u(k,j,i)**2 , u(k,j,i) ) 
+                tend(k,j,i) = tend(k,j,i) - rot_tend_x(k,j,i)                  &
+                            - tend_nac_x - tend_tow_x
+             ENDDO
+          ENDIF
+
+       CASE ( 2 )
+!
+!--       Apply the y-component of the force to the v-component of the flow:
+          IF ( simulated_time >= time_turbine_on )  THEN
+             DO  k = nzb_v_inner(j,i)+1,  k_hub(1) + k_smear(1)
+                tend_nac_y = 0.5_wp * nac_cd_surf(k,j,i) *                     &
+                                   SIGN( v(k,j,i)**2 , v(k,j,i) )     
+                tend_tow_y   = 0.5_wp * tow_cd_surf(k,j,i) *                   &
+                                   SIGN( v(k,j,i)**2 , v(k,j,i) )                      
+                tend(k,j,i) = tend(k,j,i) - rot_tend_y(k,j,i)                  &
+                            - tend_nac_y - tend_tow_y
+             ENDDO
+          ENDIF
+
+       CASE ( 3 )
+!
+!--       Apply the z-component of the force to the w-component of the flow:
+          IF ( simulated_time >= time_turbine_on )  THEN
+             DO  k = nzb_w_inner(j,i)+1,  k_hub(1) + k_smear(1)
+                tend(k,j,i) = tend(k,j,i) - rot_tend_z(k,j,i)
+             ENDDO
+          ENDIF
+
+
+       CASE DEFAULT
+
+          WRITE( message_string, * ) 'unknown prognostic variable: ', component
+          CALL message( 'wtm_tendencies', 'PA04??', 1, 2, 0, 6, 0 ) 
+
+       END SELECT
+
+
+    END SUBROUTINE wtm_tendencies_ij
+
+ END MODULE wind_turbine_model_mod
