[Getdp] ... Formulation question ...

[mkoch at gvtc.com]

Hi Bernhard,

thanks for your support. I think I do exactly as you said in my  
Constraint{}. I use the following line:

{Region VlmPlt;Type Init;Value X[];}

If I am not too mistaken, in 2D, this should generate a plane that  
inclines linearly along the x-axis, and the "solution" actually bears  
that out. Also:

d/dt(Phi) - v * Grad(Phi) = 0

works perfectly fine, even though the solution becomes very jagged at  
the edges after a while, but:

d/dt(Phi) - s * Norm(Grad(Phi)) = 0

does not seem to advance in time. And the Galerkin term containing the  
velocity vector v vs. the one containing the speed scalar s is  
literally the only difference between the two! Well that, and using  
Dof{d Phi} in the velocity term and {d Phi} in the speed term.

Therefore, I believe this has something to do with the usage or  
non-usage of "Dof". I think Olivier Castany is checking out my files,  
so we'll see what he might find.

Best Regards,

Matt Koch



----- Message from Bernhard.Kubicek at arsenal.ac.at ---------
     Date: Thu, 8 Mar 2007 10:04:35 +0100
     From: Kubicek Bernhard <Bernhard.Kubicek at arsenal.ac.at>
Reply-To: Kubicek Bernhard <Bernhard.Kubicek at arsenal.ac.at>
  Subject: Re: [Getdp] ... Formulation question ...
       To: mkoch at gvtc.com, getdp at geuz.org


> Hello!
> Maybe the reason is in your formula:
> d/dt(Phi)= Spd| grad phi|
> if phi is initialized with zero, it will always be zero (apart from   
> assigned boundary conditions).
> Maybe you can initalize phi with something usefull,e.g. using a   
> coordinate dependent function in the constraint as value. Watch out   
> for the difference betweeen "assign" and "init" constraints.
> Another possibility, would be to calculate an initial solution for   
> phi by its own formulation, and then use a chained resolution to   
> transfer this initial field to your already existing transient   
> solution.
> nice greetings,
>  bernhard
>
>
> -----Ursprüngliche Nachricht-----
> Von: getdp-bounces at geuz.org [mailto:getdp-bounces at geuz.org] Im   
> Auftrag von mkoch at gvtc.com
> Gesendet: Mittwoch, 7. März 2007 18:33
> An: getdp at geuz.org
> Betreff: Re: [Getdp] ... Formulation question ...
>
>
> Hello Olivier,
>
> so I tried exactly what you suggested below (I think). And I tried it
> with the TimeLoopTheta scheme set to 0.0, 0.5 and 1.0. In all cases,
> GetDP no longer complains about any errors, which is nice. BUT, in
> neither case does it appear as if the second Galerkin term is anything
> but zero. I am certain that Spd[] is not zero, so I suspect Norm[{d
> Phi}] somehow remains zero?
>
> I even tried Sqrt[{d Phi}*{d Phi}] instead of Norm[{d Phi}], but that
> does not work either. How is that possible? In the general heat
> conduction equation posted on the Wiki, there is a radiation term, and
> it uses something equivalent to {Phi}^4, and that seems to work
> (although, it also uses source and boundary terms, which are absent
> from my equations).
>
> How come {Phi}^4 turns into something non-zero after a while, but
> Norm[{d Phi}] seemingly does not? I mean, I even know that Phi is
> initialized to something that does not create a zero Norm[{d Phi}].
> So, from the start, Norm[{d Phi}] should be noon-zero and thus drive
> Dt[Dof{Phi},{Phi}] to something other than zero for the other time
> steps as well!? Instead, I get a solution that is equivalent to
> d/dt(Phi) = 0, rather than the desired d/dt(Phi) + Spd*Norm(Grad(Phi))
> = 0.
>
> Any thoughts?
>
> Regards,
>
> Matt
>
> ----- Message from castany at quatramaran.ens.fr ---------
>      Date: Sun, 4 Mar 2007 21:37:55 +0100
>      From: Olivier Castany <castany at quatramaran.ens.fr>
> Reply-To: Olivier Castany <castany at quatramaran.ens.fr>
>   Subject: Re: [Getdp] ... Formulation question ...
>        To: getdp at geuz.org
>
>
>> Hello,
>>
>> now that you give a more precise desciption of your problem, I
>> understand that you want to solve a dynamic equation.
>>
>> I can only be of little help since I do not understand the part b) of
>> the algorithm you want to program.
>>
>> I can just say that it is possible to program the equation :
>>
>>> a) d/dt(Phi) + Spd*Norm(Grad(Phi)) = 0
>>
>> the formulation would be :
>>
>> Galerkin { Dt [ Dof{Phi} , {Phi} ] ; ... }
>> Galerkin { [ Spd[] * Norm[{d Phi}]  , {Phi} ] ; ... }
>>
>> and the resolution with "TimeLoopTheta" will be an explicit Euler
>> algorithm.
>>
>> As I don't really understand your algorithm with b), I can't say if it
>> is possible to do it with GetDP. My feeling is that it is not
>> currently possible without modifying the program.
>>
>> Regards,
>>
>> O.C.
>>
>> PS : if you manage to do something nice with the level set equations,
>> maybe you can post it later or put it on the wiki ?
>> _______________________________________________
>> getdp mailing list
>> getdp at geuz.org
>> http://www.geuz.org/mailman/listinfo/getdp
>>
>
>
> ----- End message from castany at quatramaran.ens.fr -----
>
>
>
>
>
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----- End message from Bernhard.Kubicek at arsenal.ac.at -----