Index

Fn & vs imposed along boundary

Ver: 0
 

DESCRIPTION

For flow problems, entering this menu allows the user to specify mixed essential/natural boundary conditions for the momentum equation. The default values of fn and vs are both zero. A non-vanishing value can be selected for the normal component of the force in any geometry. A non-zero tangential velocity component can be imposed for for 2-D and 2-1/2-D flows. However, only vanishing tangential velocity components can be specified for 3-D flows.

The normal vector at a boundary is assumed to point out of the flow domain.

For the specified component of the boudnary condition, the current value is recalled, and the possibility of modifying it is given (when available).

  OPTIONS
 
-1
 Upper level menu
1
 Constant
The current component is constant on the corresponding boundary line or face
2
 Linear function of coordinates
A linear dependence upon the current space coordinates can be selected
NOTES With vanishing parameters, this boundary conditions applies to outflow conditions for generalized Newtonian flows.

The user should be aware of the system of units, if dimensional values are used.

The units for fn and vs are :
 
Parameter
Mass
Length
Time
Temperature
    fn
1
-1
-2
-
    vs
-
1
-1
-

EXAMPLES For the Poiseuile flow of an inelastic liquid, a normal force (pressure) can be specified instead of a flow rate. In particular, the user should select:
1. vanishing vs along the inlet boundary,
2. a non-vanishing fn (a pressure) along the inlet boundary
Such a boundary condition is the dual counterpart to the inflow boundary condition.   SEE ALSO