| Author | Message | ||
     Frederick R. Phelan Jr. (contemplation) New member Username: contemplation Post Number: 1 Registered: 03-2004 |
Hi, We are doing a flow problem with two diffusing species. At the outlet, we want to calculate the measure D = SUM[i=1,N](c_i - c_avg)^2/N, where the sum is computed for every node across the boundary (a kind of a variance). Here, c_avg is a defined scalar value, and the boundary is just a straight 1-D line. Is there anyway to do this internally in the flexpde script without exporting the boundary values to a text file and manipulating the data myself. The problem is time dependent. Thanks. | ||
| Robert G. Nelson (rgnelson) Moderator Username: rgnelson Post Number: 116 Registered: 06-2003 |
Do you mean the c_i to indicate a value of C at node i? Or are these separate components, comprising N different variables? FlexPDE does not allow you direct access to the stored mesh, because it wants to be free to refine or merge it, compress and restructure it at will. You can, however, form integrals, since the focus of FlexPDE is on the mathematical character of your problem, and not the implementation details. If you name a boundary segment or feature, you can integrate anything you want on that segment. See "integral" in the Help Index. | ||
| Frederick R. Phelan Jr. (contemplation) New member Username: contemplation Post Number: 2 Registered: 03-2004 |
Sorry this was not clear ... yes, by c_i I meant the value of c at boundary node i. I guess I thought that there was a way to form an array of the boundary values, and then use it in the sum. How do I do a boundary integral over only a small portion of the boundary? The outlet is just two point that is part of an overall region. Thanks. | ||
| Robert G. Nelson (rgnelson) Moderator Username: rgnelson Post Number: 118 Registered: 06-2003 |
You can overlay a FEATURE on an existing boundary (or part of an existing boundary) and give it a name. Then you can integrate on it. It is wise, though not mandatory, to include the endpoints of the Feature in the trace of the original boundary. Backstrom does this kind of overlay, for example, in "Backstrom_Books | Fields_of_Physics | b_Electricity | Elax4.pde". | ||
| Frederick R. Phelan Jr. (contemplation) Junior Member Username: contemplation Post Number: 3 Registered: 03-2004 |
I am not following this reference ... is this part of the samples provided with version 4? I have version 3. There does not appear to be any feature examples in 3 but I'll give it a shot. Thanks. | ||
| Robert G. Nelson (rgnelson) Moderator Username: rgnelson Post Number: 120 Registered: 06-2003 |
The referenced problem is in the "Backstrom_Books" folder in the FlexPDE installation directory. This folder has been part of the FlexPDE distribution since version 1.0. |