[aspect-devel] Dynamic Topography vs Topography

[Rene Gassmoeller]

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
> *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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>
>
>
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