|
[Sponsors] |
February 16, 2008, 22:55 |
post processing dam break problem
|
#1 |
Guest
Posts: n/a
|
Hi, im currently working on a problem of solving the dam break problem using the VOF method on CFX. I have managed to generate the models however when post processing my models apear as blocks instead of smooth surfaces. At first I thought this was due to the way i defined the simulations however if i put a plane through the middle at any point in the model the flows are smooth. Any ideas any one. thanks again Chris
|
|
February 17, 2008, 06:12 |
Re: post processing dam break problem
|
#2 |
Guest
Posts: n/a
|
Hi,
How are you displaying the surface? Usually you use an isosurface set at a volume fraction of 0.5 Glenn Horrocks |
|
February 17, 2008, 06:23 |
Re: post processing dam break problem
|
#3 |
Guest
Posts: n/a
|
Hi Glen, yeah I am using an isovolume with a volume fraction of 0.5 but still cant think why the simulation is blocky. Do you think it could be a problem with my settings when creating the model? regards Chris
|
|
February 17, 2008, 11:46 |
Re: post processing dam break problem
|
#4 |
Guest
Posts: n/a
|
Use an *isosurface* not an isovolume. Here's the difference:
- The edge of an isovolume is defined by the mesh cell boundaries and is therefore rough even for smooth data. Roughly speaking, a single value is associated with each cell, and so each cell is either completely in or completely out of the isovolume. This makes it look rough. - The surface of an isosurface is defined by interpolating the results from the mesh and solving to find a smooth surface at the required value. This results in a smooth boundary. Try, for example, doing both an isovolume and an isosurface for something like the X or Y coordinates in CFXPost, which of course should be smooth, and you'll se the effect[*] Hope that helps. andy. [*] Unless of course you have a structured mesh where all the cells are aligned to share X or Y coordinate boundaries! In that case try another variable. ;-) |
|
February 17, 2008, 13:35 |
Re: post processing dam break problem
|
#5 |
Guest
Posts: n/a
|
Andy, thanks for that. Just a quick question though, Will the isosurface be a 2D surface and not 3D? cheers Chris
|
|
February 17, 2008, 17:17 |
Re: post processing dam break problem
|
#6 |
Guest
Posts: n/a
|
Hi,
An isosurface, in general is a surface with curvature in 3 dimensions. If you have done a 2D simulation it will have curvature in 2 dimensions and be flat in the 3rd dimension. If you have done a 2D simulation and you want contour lines (the 2D version of isosurfaces), first generate a plane or use a symmetry plane to generate a contour object. Glenn Horrocks |
|
February 18, 2008, 04:58 |
Re: post processing dam break problem
|
#7 |
Guest
Posts: n/a
|
Chris - Yes it will be the 2D surface that encloses the volume described by the condition that defines it...so it will be 'hollow' - but for visualising a free surface after a dam break I think it's what you want.
I think the best thing is for you to just try it and see, rather than me explaining in great detail - it's only a 2 minute job to try it out!! I don't know of any way of getting a smooth isovolume in CFX-Post. I honestly think there isn't one, but if I'm wrong I hope someone more knowledgable will post the details for both of us... Regards, Andy |
|
February 22, 2008, 07:33 |
Re: post processing dam break problem
|
#8 |
Guest
Posts: n/a
|
Andy/Glen thank you so much for your help. The isosurface looks great and when combined with an isovolume I have managed to get a complete model of the Dam Break Problem. Will owe both of you a pint. Chris
|
|
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
[OpenFOAM] Tracking Volume Surface dam break problem | sega | ParaView | 4 | July 14, 2009 09:41 |
post processing problem | Charles | FLUENT | 2 | June 2, 2008 04:12 |
Dam break problem | sega | OpenFOAM Running, Solving & CFD | 3 | April 20, 2008 11:03 |
Post Processing in FEM | Abhijit Tilak | Main CFD Forum | 0 | April 26, 2004 12:59 |
Dam break // wet bed | Mehdi BEN ELHADJ | Main CFD Forum | 4 | August 24, 2000 08:39 |