| Author | Message | ||
     Jaspreet (ftjin) Member Username: ftjin Post Number: 14 Registered: 02-2006 |
I wish to implement a time variable BC which says that at any time t, the head does not exceed 0 m. Is it possible to do the same in FlexPDE? If so, how? | ||
| Robert G. Nelson (rgnelson) Moderator Username: rgnelson Post Number: 587 Registered: 06-2003 |
The Natural Boundary Condition describes some kind of generalized flux (depending on how you write your equations). In a diffusion system written as div(flux)=source, the Natural BC is the outward normal component of the flux of the system variable. If you define a boundary flux that opposes values of the variable greater than some maximum, you will have built a penalty system that enforces the clamp. For example: Natural(head) = IF(head > 0) THEN Large*head^2 ELSE 0 If you make Large too large, you will drive the timestep to tiny values. If you make it too small, you will get serious excursions of Head above zero. Find a compromise that satisfies you. You will also need a reasonably dense mesh along the boundary, in order to resolve the position of the transition. |