[Gmsh] ... electric field lines ...
Christophe Geuzaine
cag32 at case.edu
Tue Oct 10 01:17:18 CEST 2006
mkoch at gvtc.com wrote:
> OK,
>
> so, what I suggested below seems to work OK.
>
> The problem is, Plugin(StreamLines) seems to allow to start the field
> lines on a rectangular grid only. That makes the plot look relatively
> ugly, unless the grid is very fine, but then it takes a long time to
> calculate.
>
> Instead, I think what would be needed is an arbitrary definition of
> starting points, such as on irregular electrode or ground surfaces. I
> realize that might be hard to implement, especially when trying to go
> through the simplified Plugin user interface.
>
> On the other hand, for GetDP, surfaces must usually be defined, and
> thus it may be possible in GMsh to somehow "recall" these surfaces and
> thus their geometry points?
That sounds like a good idea: we could maybe specify a geometrical
entity--and the plugin would extract either the geometrical points or
the points from the mesh to start the plugin. Or we could use another
view as the input...
>
> Regards,
>
> Matt Koch
>
> ----- Message from mkoch at gvtc.com ---------
> Date: Fri, 6 Oct 2006 10:10:37 -0500
> From: mkoch at gvtc.com
> Reply-To: mkoch at gvtc.com
> Subject: Re: [Gmsh] ... electric field lines ...
> To: mkoch at gvtc.com
> Cc: Christophe Geuzaine <cag32 at case.edu>, mattkoch at scitex.us,
> gmsh at geuz.org
>
>
>> Hi All,
>>
>> I just looked into StreamLines.cpp, and a I am not even going to
>> pretend I understand what goes on in there. However, in GetDP
>> PostProcessing, could one not define a new vector field as F/|F|,
>> rather than F itself? And then indeed the StreamLines Plugin should
>> apply, as long as one does not interpret time in there as literal time,
>> but rather as some sort of independent space parameter?
>>
>> My concern is, that upon perusing StreamLines.cpp, I did not see any
>> obvious reference to an ODE solver, such as the one from GSL. Instead,
>> I see on lines 289 through 294 and below a reference to something that
>> looks like some sort of homemade Runge-Kutta algorithm? What am I
>> missing?
>>
>> Thanks,
>>
>> Matt Koch
>>
>> ----- Message from mkoch at gvtc.com ---------
>> Date: Fri, 6 Oct 2006 09:20:41 -0500
>> From: mkoch at gvtc.com
>> Reply-To: mkoch at gvtc.com
>> Subject: Re: [Gmsh] ... electric field lines ...
>> To: Christophe Geuzaine <cag32 at case.edu>
>> Cc: mattkoch at scitex.us, gmsh at geuz.org
>>
>>
>>> Hi All,
>>>
>>> I think the Plugin(StreamLines) is different from what we would need
>>> for a Plugin(FieldLines), because of the field normalization:
>>>
>>> StreamLines:
>>> dx/dt = vx(x,y,z)
>>> dy/dt = vy(x,y,z)
>>> dz/dt = vz(x,y,z)
>>>
>>> FieldLines:
>>> dx/ds = Fx(x,y,z)/|F(x,y,z)|
>>> dy/ds = Fy(x,y,z)/|F(x,y,z)|
>>> dz/ds = Fz(x,y,z)/|F(x,y,z)|
>>>
>>> Nevertheless, it should be possible to copy the StreamLines plugin to a
>>> FieldLines plugin and add this normalization to it. I'll take a look at
>>> the .CPP file later on today. However, I hope that most of the stuff in
>>> there is in pure C, as I am virtually illiterate in C++.
>>>
>>> Regards,
>>>
>>> Matt Koch
>>>
>>>
>>> ----- Message from cag32 at case.edu ---------
>>> Date: Thu, 05 Oct 2006 18:57:50 -0400
>>> From: Christophe Geuzaine <cag32 at case.edu>
>>> Reply-To: Christophe Geuzaine <cag32 at case.edu>
>>> Subject: Re: [Gmsh] ... electric field lines ...
>>> To: mattkoch at scitex.us
>>> Cc: gmsh at geuz.org
>>>
>>>
>>>> Matt Koch wrote:
>>>>> Hi All,
>>>>>
>>>>> this seems to be a simple matter of solving the following
>>>>> equations for F = (Fx,Fy,Fz) as the vector (yeah right, NOTHING
>>>>> is EVER simple):
>>>>>
>>>>> dx/ds = Fx/|F|
>>>>> dy/ds = Fy/|F|
>>>>> dz/ds = Fz/|F|
>>>>>
>>>>> with |F| = sqrt(Fx^2 + Fy^2 + Fz^2)
>>>>>
>>>>> Even a dumb Runge-Kutta approach could probably do. I might could give
>>>> Isn't this pretty much what we do in Plugin(StreamLines)? There we
>>>> solve dX(t)/dt = V, with X(0) chosen as a bunch of points in space and
>>>> V(x,y,z) interpolated from the vector view.
>>>>
>>>>> it a try, but I'd need to know how to write plugins (how to
>>>>> programmatically access fields calculated by GetDP, how to
>>>>> programmatically draw in GMsh, and such), and perhaps get some
>>>>> feedback from y'all on how long it might take to write a
>>>>> "typical" plugin? Would some sort of Runge-Kutta driver or
>>>>> other ODE solver be accessible to a plugin, or would that have
>>>>> to be developed from scratch, or pulled in from GSL, for example?
>>>> Have a look at Plugin/StreamLines.cpp in the Gmsh source code: you'll
>>>> see that it's actually pretty simple to write a plugin.
>>>>
>>>>
>>>>
>>>>> Thanks,
>>>>>
>>>>> Matt Koch
>>>>>
>>>>>
>>>>> Christophe Geuzaine wrote:
>>>>>
>>>>>> Matt Koch wrote:
>>>>>>
>>>>>>> Hello there!
>>>>>>>
>>>>>>> what a wonderful program GMsh is! It takes a little while to
>>>>>>> get used to its GUI, but once you get the hang of it, it is
>>>>>>> extremely useful and intuitive! However, one thing I have not
>>>>>>> been able to figure out yet is how to make electric field lines
>>>>>>> from an electric field vector solution. I looked into the
>>>>>>> StreamLines PlugIn, but that seems to only work off of a
>>>>>>> velocity field. Any thoughts?
>>>>>>
>>>>>> Maybe this could be a good idea for a new plugin?
>>>>>>
>>>>>>
>>>>>>> Thanks,
>>>>>>>
>>>>>>> Matt Koch
>>>>>>> mattkoch at scitex.us
>>>>>>> www.scitex.us
>>>>>>> _______________________________________________
>>>>>>> gmsh mailing list
>>>>>>> gmsh at geuz.org
>>>>>>> http://www.geuz.org/mailman/listinfo/gmsh
>>>>>>>
>>>>>>
>>>>
>>>> --
>>>> Christophe Geuzaine
>>>> Assistant Professor, Case Western Reserve University, Mathematics
>>>> http://www.case.edu/artsci/math/geuzaine
>>>
>>> ----- End message from cag32 at case.edu -----
>>
>> ----- End message from mkoch at gvtc.com -----
>
>
> ----- End message from mkoch at gvtc.com -----
>
>
>
>
> _______________________________________________
> gmsh mailing list
> gmsh at geuz.org
> http://www.geuz.org/mailman/listinfo/gmsh
>
--
Christophe Geuzaine
Assistant Professor, Case Western Reserve University, Mathematics
http://www.case.edu/artsci/math/geuzaine