[Gmsh] Questions

[Christophe Geuzaine]

Fabrizio Cacchione wrote:
> Dear Christophe,
> thank you for you help.
> I think I'm going to use your program as preprocessor, but it seems to 
> be difficult to use it as post processor.
> The main problem concerns the way gmsh reads the ascii results file.
> In fact, when I perform my analysis, I write something like:
> 
> /Step = 1
> Displacements (Nodal)
> node 1         disp_x disp_y
> ...
> node  n-th    disp_x disp_y
> ...
> ...
> //Step = n
> Displacements (Nodal)
> node 1         disp_x disp_y
> ...
> node  n-th    disp_x disp_y
> /
> /
> 
> /If I'd like to use gmsh (as I would) I should have to reorganize my 
> data in the following form (right?) :
> 
> /Displacements (Nodal)
> node 1         disp_x disp_y  (step 1)
> ..
> //node 1         disp_x disp_y  (step n-th)
> ..
> ..
> node m-th    //disp_x disp_y  (step 1)
> ..
> //node m-th    //disp_x disp_y  (step n-th )
> 
> /So, if there is no chance to change the way gmsh reads the file, I'd be 
> forced to rearrange the whole output file (up 1 Gb)  in order to use 
> gmsh...and it would take a lot of time.
> /
> /I'm looking forward for any suggestion.

Hello Fabrizio - I also often use this kind of data organization. In
that situation I just create one view for each time step: Gmsh can
handle an arbitrary number of views and it can deal with these separate
views as efficiently as with a single multi-step view, so I'm usually
happy with that solution. The only disadvantage is that the total amount
of disk space used is greater (since the node data is repeated for each
time step).

In practice, depending on the size of my data set, I store all the views
in a single file or sometimes create one separate file for each view, 
which I can then load selectively (and thus reduce the memory required 
for the analysis). In any case you can use 'Tools->Options-> 
Post-processing->View links' to apply options to multiple views at once, 
and the up and down arrow keys to loop through (animate) the views 
(instead of the left and right arrow keys for multi-step views).

Also note that if all the views are based on the same grid, Gmsh can
combine the separate views into a multi-time-step view by using the
'View->Combine->Time Steps' menu, or by using the '-combine' command
line option.

Hope this helps,

Christophe


PS: I'm CC:ing the list on this message, as this is a fairly frequently 
asked question.

-- 
Christophe Geuzaine
Applied and Computational Mathematics, Caltech
geuzaine at acm.caltech.edu - http://geuz.org