GetDP

[Christophe Geuzaine]

Samuel Kvasnica wrote:
> 
> Hi Christophe,
> 
> After few more hours I spent with getDP I have (stupid) questions again:
> 
> Is getDP bound someway to SI units or are units given just by constants used in .pro files ?

No constant is predefined in GetDP (except PI), so everything must be
given in .pro files.

> Are coordinates used in .geo files in mm or meters ? 

Well, it depends on the problem you define later... If you define a
problem in GetDP with SI units, then the mesh in GMSH is in meters.

> Is there some command to rescale the whole drawing ?

No, but I keep this in mind for the future.

> 
> I tried to compute Br and Bz components of magnectic field on a line in 5mm distance
> from magnetron using the OnLine type for postoperation. Results seem to be correct,
> but not very smoothly - rather hairy (at ~2000) mesh nodes. I tried to incrrease the node
> density and got better results (at ~15000) nodes, but I could still imagine better graph.
> Could you give me an advice how to reach more continuous results ?

You could use higher order interpolation, e.g. by adding new basis
functions to the nodal basis functions used in your problem. For
example, the following line could be added in the function space (this
defines hierachical basis functions associated with edges):

{ Name se2 ; NameOfCoef ae2 ; Function HBF_PerpendicularEdge_2E ; 
  Support Domain_Mag ; Entity EdgesOf[ All ] ; }

Constraints should of course also be defined on these functions.


> When I tried to increase node density again (~25000), the solution seemed to diverge and

You should probably adapt the solving technique by editing the
SOLVER.PAR file (e.g. invrease de number on non-zero elements kept in
the ILU factorization which serve as a preconditioner to the krylov
accelerator).

> This one was better. Anyway, awk seems to be the optimal processing tool in this case.

Yes, I agree. BTW, I would like to have suggestions to produce some
simple post processing formats. How do you think data should be
presented in the default format? A bit like with the 'gnuplot2' option?
Or should the numbers be more strongly formatted (e.g. with the same
number of digits)? Or...?


> And the main problem is, gmsh renders the data also when it is not needed, e.g. when you drag another
> window
> over gmsh and back and gmsh gets repaint message from X server. It should save rendered data into pixmap
> and update

Yes, I'll think about that...

> Particulary I meant some solver for Navier-Stokes equations. I was just asking because colleague sitting
> next to me is interrested in CFD and likes getDP. I've noticed there's software called TOCHNOG from
> university of Twente dedicated to CFD. Is there such a big difference in numerical methods used for CFD
> and electromagnetics that software packages usually support only one of these ?
> 

The methods have similarities, but the way to solve accurately a
convection-diffusion equation requires some king of upwinding in the
spatial discretization scheme (i.e. some non-centered scheme like SUPG,
taking the flow direction into account). Nothing is done for these kinds
of methods in GetDP for the moment.


> And the last one:  Is there a trivial way to display magnetic field line by giving coordinates of 1 point?
> 

???

-- 
Christophe Geuzaine

Tel: +32-(0)4-366.37.10    mailto:Christophe.Geuzaine at ulg.ac.be
Fax: +32-(0)4-366.29.10    http://www.montefiore.ulg.ac.be/~geuzaine/