===== Namelist "External_Force" =====
This data set is used to define an external force that steers the flow. Otherwise, it can be omitted.

===== Full data set of the namelist =====

    &External_Force  Force_Option_I_Direction= 0           , Force_Option_J_Direction= 0         , Force_Option_K_Direction= 0 ,
                     Force_Reference_Value_I_Direction= 0.0, Force_Reference_Value_J_Direction= 0, Force_Reference_Value_K_Direction= 0.0 /

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===== Definition of the data set =====
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==== Force_Option_I_Direction ====
   * Type : Integer value
   * This option selects the type of force on the I-component of the force vector.
     * 0 : the force component is zero
     * 1 : the force component is constant 
     * 2 : the force component is time dependent and depends on the mass flowrate (special case used for the simulation of a channel flow with periodical boundary conditions).
     * 3 : the force component is time dependent and depends on both mass flowrate and wall friction (special case used for the simulation of a channel flow with periodical boundary conditions).
   * Default value = 0
==== Force_Option_J_Direction ====
   * Type : Integer value
   * This option selects the type of force on the J-component of the force vector (see above).
   * Default value = 0
==== Force_Option_K_Direction ====
   * Type : Integer value
   * This option selects the type of force on the J-component of the force vector (see above).
   * Default value = 0
==== Force_Reference_Value_I_Direction ====
   * Type : Real value
   * Reference value of the force component along the I-direction.
   * Default value = 0.0
==== Force_Reference_Value_J_Direction ====
   * Type : Real value
   * Reference value of the force component along the J-direction.
   * Default value = 0.0
==== Force_Reference_Value_K_Direction ====
   * Type : Real value
   * Reference value of the force component along the K-direction.
   * Default value = 0.0