The normal and tangential force condition is similar to the normal and tangential
velocity condition described in Normal and Tangential Velocity Condition. This condition
is typically used for exit sections of free surface problems. The normal and tangential
directions are defined as described in Normal and Tangential Velocity Condition, and
and 
are surface force densities expressed, for
example, in Pa. A traction force on the boundary section produces a positive
. A counterclockwise tangential force produces a positive value of
(in 2D). In 3D, due to orientation conventions (as is the case for the
tangential velocity component), it is difficult to assign a nonzero value for
. If the tangential force in a 3D problem is nonzero, you should use
the global force condition (described in Global Force Condition)
instead.
Important: For viscoelastic simulations, you should not impose a zero normal force at the
inlet or outlet of the computational domain where a shear flow is expected. Due to
normal stresses, 
will, in general, not be zero when the shear rate is nonzero.
Special viscoelastic outflow conditions (described in Outflow Condition) are provided for this purpose. Note that it
is, in general, perfectly valid to impose a zero normal force at the exit of a free
surface if no traction applies. In this case, the fully developed velocity profile
corresponds to a plug flow and viscoelasticity does not generate normal stresses.
To define the normal and tangential force on a boundary section, select the Normal and tangential forces imposed (fn, fs) menu item in the list of boundary condition choices.
Normal and tangential forces imposed (fn, fs)
Then specify 
as a Constant, a Linear function of
coordinates, or a Map from CSV (Excel) file. When
you select Upper level menu after specifying 
, Ansys Polydata will bring you to the menu where you can specify
in the same manner.