[aspect-devel] Dynamic Topography vs Topography

[Payman Janbakhsh]

Hi Rene
That would be something I myself need for my research. so I would be glad to start working on it with the team's help and guidance, given the time frame and it being my first try at creating a plug-in .
I'll contact you via research gate to get more details .

Cheers

Payman


Sent from my Samsung Galaxy smartphone.


-------- Original message --------
From: Rene Gassmoeller <rene.gassmoeller at mailbox.org>
Date: 2016-11-09 9:37 PM (GMT-05:00)
To: aspect-devel at geodynamics.org
Subject: Re: [aspect-devel] Dynamic Topography vs Topography


Hi Payman,

surprisingly (also to me) ASPECT currently does not have a postprocessor that outputs a map of the topography of a deformed mesh. The closest thing is the visualization/depth postprocessor that will output the depth of every point of the domain. However, the `depth()` function of the geometry model is bounded to (0,maximal_depth), so it will not output positive topography correctly. If you would be willing to spend some time helping create a postprocessor for topography that would certainly be a useful addition. Let us know if you would have the time and willingness to do so, we could then discuss the details of the implementation (always easier to discuss that first, before writing something and then reworking it many times).

Depending on your intended purpose you would either need to create a general postprocessor that outputs the topography into a separate file (as for example postprocess/heat_flux_map), or a visualization postprocessor that adds another field to the .vtu output of the solution (as for example postprocess/visualization/depth). However, there might be some challenges to make it work for arbitrary model geometries.

Let me know what you think about that,

Rene


On 11/09/2016 06:40 AM, Payman Janbakhsh wrote:
Thanks Rene, sorry for late reply
It was my misunderstanding that for a free surface I can use the generated dynamic topography text files and see the surface evolution across my model domain at any given time step.
Is there an implemented option for it currently ?  (for a free surface).
Not the Topography postprocessor since it gives the max(min)  vs time(run time) ,
   Looking for a measure of surface mesh elevation(from its initial datum or a mean) vs X lateral dimension, at any given time step.
Thanks

payman
From: Aspect-devel [mailto:aspect-devel-bounces at geodynamics.org] On Behalf Of Rene Gassmoeller
Sent: November 7, 2016 2:58 PM
To: aspect-devel at geodynamics.org<mailto:aspect-devel at geodynamics.org>
Subject: Re: [aspect-devel] Dynamic Topography vs Topography


Hi Payman,

I guess the short answer is: They do different things. The topography postprocessor measures the actual deformation of the mesh (i.e. you will only see significant values, if you use a deforming mesh / free surface). The dynamic topography however is calculated as: How much topography would be here, if the pressure were to be balanced by overlying topography (for a longer explanation including formulas take a look at the postprocessor description in the manual or the source code).

So as long as you do not use a free surface, the values of the 'topography' postprocessor will be close to zero (there might be a tiny value). And if you use a free surface the 'dynamic topography' postprocessor will likely no longer calculate anything useful (because the pressure is already compensated by building a topography).

Hope that helps,

Best,

Rene

On 11/06/2016 01:58 PM, Payman Janbakhsh wrote:
Hi
When running a model, postprocessor outputs min and max topography at the end of each time step. In my case shows  values around + - 1.5m  (early steps).
Then when using dynamic topography postprocessor to plot dynamic topography vs X, with or without the option of Subtract mean of topography, my plot  shows values between -150m to 200m in some areas and zero(in the case of subtracted mean)  for the rest of the x dimension.
Why is there a discrepancy between Topography min/max  and dynamic topography at the same time step? Shouldn't the topography min/max reflect the min /max on my dynamic topography plot?

Thank you

Payman




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